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Cooperative Extension Lewis County
Final Report June 2010 (updated)
Feasibility Study of Anaerobic Digestion and Biogas Utilization Options for the Proposed Lewis County Community Digester
www.manuremanagement.cornell.edu
Feasibility Study of Anaerobic Digestion and Biogas Utilization Options for the Proposed Lewis County Community Digester
By:
Curt Gooch, P.E.1, Senior Extension Associate
Jennifer Pronto1, Research Support Specialist
Brent Gloy, Ph.D2, Professor
Norm Scott, Ph.D1, Professor
Steve McGlynn1, Research Support Specialist
Christopher Bentley1, Undergraduate Student
1Biological and Environmental Engineering Department
2Department of Applied Economics and Management
334 Riley-Robb Hall
Cornell University
Ithaca, New York 14853
June 11, 2010
Updated June 30, 2010
Foreword
The Feasibility Study of Anaerobic Digestion and Biogas Utilization Options for the Proposed Lewis
County Community Digester project is not a feasibility study in its strictest definition, but rather an
assessment of the farm and non-farm biomass resources available in and around the village of Lowville,
an investigation into the available options for co-digesting them (various combinations of materials and
site locations), an estimation of the biogas that could be produced by the various scenarios, the resulting
energy produced, and net energy available for use, and an economic profitability assessment for each of
the options investigated. The scope of work for this project was somewhat dynamic as adjustments
were continually made based on progress of evaluating the information at hand. This report was
written to provide the findings and recommendations of the feasibility study to the client, the Lowville
Digester Workgroup, and also to serve as an educational tool for the stakeholders of this and future
proposed centralized anaerobic digester projects.
The proposed Lewis County Community Digester project exemplifies the full potential of a centralized
anaerobic digester. Manure and, waste biomass materials (processing byproducts from multiple
sources), are mixed together and heated to produce biogas; a locally generated, clean burning,
renewable energy. Waste biomass is generated daily by food processing plants and restaurants, public
facilities and institutions such as schools and hospitals, and at private residences. Co-digesting manure
and these materials reduces the burden on landfills and reduces greenhouse gas (GHG) emissions. The
U.S. dairy industry has formally committed to reducing its GHG emissions by 25% by 2020 and this
project is an example of how this can be effectively accomplished, from a technical/applied perspective.
In fact, the Lewis County Community Digester project demonstrates the vision behind “Dairyville 2020”
– the Innovation Center for U.S. Dairy’s Dairy Power Initiative flagship project. The major shortcomings
at this point are high capital costs and less than required energy purchase prices needed to make such
systems economically feasible.
Acknowledgements This document is the culmination of a team effort by the authors and many others who provided their
assistance and support. The authors wish to acknowledge and thank the following individuals/groups
for their contributions:
Senator Joseph Griffo, 47th District in New York State, for funding this project and for his continued
interest.
The dairy farmers of Lewis County who completed the farm surveys.
Representatives for the non-farm biomass suppliers who completed the non-farm surveys.
Drs. Dave C. Ludington and Michael B. Timmons, Professor Emeritus and Professor, respectively, of
Biological and Environmental Engineering at Cornell University for their efforts in reviewing drafts of the
feasibility study and for their constructive inputs and suggestions.
Members of the Lowville Digester Workgroup for their confidence in the Cornell team to provide a
feasibility study that would contain unbiased information and for their teamwork and collaboration
while the feasibility study was being conducted.
Ms. Christine Ashdown (Cornell Office of Sponsored Programs) for her timely efforts in developing the
contract for this project and for her continued support to funded project opportunities pursued by
members of the Cornell PRO-DAIRY program.
Ms. Michele Ledoux (Cornell Cooperative Extension – Lewis County) for her trust in the Cornell team
and for her work in securing the funding and performing contract administration tasks that resulted in a
workable means to performing this work.
Ms. Norma McDonald (North American Sales Manager, Organic Waste Systems, Inc.) for providing key
information on energy crop digesters suitable for U.S. applications needed to perform the annual
economic profitability analysis for the energy crop digester scenarios investigated.
Mr. Todd Vernon (Senior Sales Manager, GE Energy – Jenbacher) for providing key information on the
Jenbacher engine-generator sets needed to perform the annual economic profitability analysis.
Mr. Frans Vokey (Cornell Cooperative Extension – Lewis County) for his overall leadership of the
Lowville Digester Workgroup and Cornell collaboration, and for all of his efforts in planning and running
project meetings.
Mary Beth Anderson (community resident) for her assistance in collecting samples from non-farm
biomass suppliers and for work on distributing and collecting non-farm biomass surveys.
Mike Durant (Soil and Water Conservation District) for designing the project map.
Table of Contents
Foreword
Acknowledgements
Table of Contents
Table of Figures
Table of Tables
Abbreviations and Acronyms
Executive Summary p. 1
Introduction p. 15
Chapter 1. Basics of Centralized Dairy Manure-based Anaerobic Digestion, Biogas Utilization, and Nutrient Recovery Systems
p. 23
Chapter 2. Literature Review of Centralized AD Projects p. 39
Chapter 3. Farm and Community Biomass Survey p. 49
Chapter 4. Biomass Sample Collection and Analysis p. 61
Chapter 5. Biomass Transportation p. 71
Chapter 6. Preliminary Investigation of Five AD Scenarios p. 77
Chapter 7. Final AD Scenario Selection and Details p. 93
Chapter 8. Next Steps and Recommendations p. 115
References p. 117
Appendix
A. Glossary of terms p. 121
B. Farm-based Survey p. 127
C. Non Farm-Based Survey p. 131
D. Substrate Sampling Report p. 133
E. Biochemical Methane Potential; Laboratory Procedure p. 137
F. Projected Farm Survey Responses p. 139
Table of Figures Page Figure 1. New York State map showing location of project-site ................................................................. 16 Figure 2. Typical CAD system process flow diagram ................................................................................... 23 Figure 3. A CAD in Jutland, Denmark .......................................................................................................... 24 Figure 4. Danish above-grade complete mix vertical digesters in background .......................................... 29 Figure 5. Thermal to electric conversion efficiency of six NYS on-farm engine-generator sets. (Source: Gooch, Pronto, Ludington, Unpublished, 2010) ......................................................................................... 32 Figure 6. Basic process flow diagram for advanced biogas clean-up for biomethane production. ........... 34 Figure 7. Advanced digestate treatment to segregate and concentrate nitrogen, phosphorus, and potassium. ................................................................................................................................................... 38 Figure 8. Landfill tipping fees ($/ton) by region of the U.S. (Repa, 2005) .................................................. 47 Figure 9. Landfill tipping fees ($/ton), developed from Figure 8 (Repa, 2005). ......................................... 47 Figure 10. Lowville regional map with collaborating dairy farms superimposed along concentric circles of various radii centered on downtown Lowville............................................................................................ 54 Figure 11. Quantity (millions lbs/yr.) of substrates (wet weight). ............................................................. 57 Figure 12. Biochemical Methane Potential (BMP) data (cumulative biogas yield) for substrate 4. ........... 62 Figure 13. Graphical representation of biochemical methane potentials for all substrates tested. .......... 63 Figure 14. Estimated annual minimum, maximum, and average methane production by substrate. ....... 66 Figure 15. Estimated aggregated annual minimum, maximum, and average methane production of non-farm biomass substrates and manure. ....................................................................................................... 66 Figure 16. Nutrient concentrations for pre- and post-digestion conditions for N, P, K.............................. 70 Figure 17. Diagram of estimating a break-even tipping fee for non-farm biomass substrate suppliers. ... 75 Figure 18. CAD Site 1 for Scenario Nos. 1 and 2. ........................................................................................ 78 Figure 19. Remote AD Site 2 for Scenario Nos. 3, 3a, and 3b. .................................................................... 79 Figure 20. Remote AD Site 3 for Scenario Nos. 3, 3a, and 3b. .................................................................... 80 Figure 21. Process flow diagram for Scenario No. 1 using the average annual total volume of the seven non-farm biomass substrates. .................................................................................................................... 81 Figure 22. Process flow diagram for Scenario No. 2 using the average annual total volume of the three non-farm biomass substrates. .................................................................................................................... 83 Figure 23. Process flow diagrams for Scenario No. 3 using the average annual total volume of the three non-farm biomass substrates for Site 2 and Site 3. All manure and digestate are trucked. ..................... 85 Figure 24. Process flow diagram for Scenario No. 3a using the average annual total volume of three non-farm biomass substrates for Site 2 and Site 3. Manure and digestate are pumped and trucked. ............ 87 Figure 25. Process flow diagram for Scenario No. 3b using the average annual total volume of three non-farm biomass substrates for Site 2 and Site 3. ........................................................................................... 89 Figure 26. Final Scenario No. 2 process flow diagram. ............................................................................... 94 Figure 27. Energy crop anaerobic digester process flow diagram. ............................................................. 94 Figure 28. Comparison of the volume of manure sent to the CAD and volume of CAD effluent received, by farm. ....................................................................................................................................................... 96 Figure 29. Comparison of the volume of manure sent to the CAD and volume of CAD effluent received, by farm, taking into account each farm's nutrient balance situation....................................................... 112 Figure 30. Image of residential food waste sample collected. ................................................................. 134 Figure 31. Meat and butcher waste from substrate number 4. ............................................................... 135
Table of Tables Page Table 1. Typical fuel-to-power efficiency values (adapted and updated from Wright, 2001). .................. 33 Table 2. St.Albans/Swanton, VT project statistics ...................................................................................... 39 Table 3. LREC project statistics ................................................................................................................... 41 Table 4. Dane County, WI (Waunakee cluster) project statistics ............................................................... 42 Table 5. Cornell project statistics ................................................................................................................ 43 Table 6. York, NY project statistics .............................................................................................................. 43 Table 7. Salem, NY project statistics ........................................................................................................... 44 Table 8. Perry, NY project statistics ............................................................................................................ 45 Table 9. Port of Tillamook project statistics................................................................................................ 46 Table 10. Summary of current (2009) farm survey data ............................................................................. 51 Table 11. Summary of nutrient balance information as provided in farm surveys ................................... 53 Table 12. Summary of non-farm biomass survey results............................................................................ 56 Table 13. Select Lewis County crop farm data ............................................................................................ 58 Table 14. BMP analysis results for all substrates tested ............................................................................. 63 Table 15. Biogas production potential of non-farm biomass substrates and manure ............................... 65 Table 16. Potential biogas production of available energy crop acreage ................................................... 65 Table 17. CES lab results for each non-farm biomass substrate: nutrients ................................................ 67 Table 18. CES lab results for each non-farm biomass substrate: solids...................................................... 67 Table 19. Estimated annual mass of nitrogen series for raw AD feedstock .............................................. 68 Table 20. Estimated annual mass of phosphorus and potassium series for raw AD feedstock ................ 68 Table 21. Predicted annual mass of nitrogen for post-digested AD feedstock ......................................... 69 Table 22. Predicted annual mass of phosphorus and potassium for post-digested AD feedstock ........... 70 Table 23. Capital and annual cost estimates for a project-owned trucking fleet ....................................... 72 Table 24. Contracted trucking fleet example schedule .............................................................................. 73 Table 25. Scenario No. 3a means of manure and digestate transport ....................................................... 87 Table 26. Comparison of the five AD scenarios .......................................................................................... 91 Table 27. Scenario No. 2 participating farms and associated manure generation ..................................... 94 Table 28. Scenario No. 2 feedstock volumes .............................................................................................. 97 Table 29. Potential methane and biogas production volumes for each feedstock in Scenario No. 2 CAD 98 Table 30. Capital costs ($) for Scenario No. 2 CAD system, engine-generator set, and biogas clean-up
system, and totals for two different energy sale options ............................................................... 101 Table 31. Annualized capital costs ($) for the Scenario No. 2 CAD system based on minimum, maximum,
and average biogas production quantities...................................................................................... 102 Table 32. Scenario No. 2 CAD, annual operating and maintenance expenses ($) .................................... 103 Table 33. Scenario No. 2 CAD, total annual costs ($) ................................................................................ 103 Table 34. Scenario No. 2 CAD net annual economic profitability ($) 2,3 for various biomethane sale prices
and biogas production volumes (no tipping fees received) ............................................................ 104 Table 35. Scenario No. 2 CAD net annual economic profitability ($) 2,3 for various electrical energy sale
prices and biogas production volumes (no tipping fees received) ................................................. 104 Table 36. Scenario No. 2 CAD net annual economic profitability ($) 2,3 for various biomethane sale prices
and biogas production volumes, including current tipping fee paid by substrate supplier #8 ...... 105 Table 37. Scenario No. 2 CAD net annual economic profitability ($) 2,3 for various electrical energy sale
prices and biogas production volumes, including current tipping fee paid by substrate supplier #8 ......................................................................................................................................................... 105
Table 38. Scenario No. 2 CAD net annual economic profitability ($)2 for various biomethane sale prices and tipping fee revenues ................................................................................................................ 106
Table 39. Scenario No. 2 CAD, net annual economic profitability ($)2 for various electrical energy sale prices and tipping fee revenues ...................................................................................................... 106
Table 40. Annualized capital costs ($) for energy crop digester system .................................................. 108 Table 41. Net annual economic profitability ($) for various electricity prices and feedstock costs ......... 109 Table 42. Capital cost estimate for construction of on-farm short-term manure storage per farm ........ 111 Table 43. Scenario No. 2 CAD nitrogen series annual masses by feedstock source and totals ................ 111 Table 44. Scenario No. 2 CAD phosphorus and potassium series masses by feedstock source and totals
......................................................................................................................................................... 111 Table 45. Farm survey responses based on projections for two years ..................................................... 139 Table 46. Farm survey responses based on five year projections ............................................................ 140
Abbreviations and Acronyms AD Anaerobic digestion BMP (1) Best Management Practice BMP (2) Biochemical Methane Potential Btu British thermal unit (mmBtu = 1 x 106 Btu), (TBtu = 1 x 1012 Btu) CAD Centralized anaerobic digester CAFO Concentrated Animal Feeding Operation cfm Cubic feet per minute CCE-LC Cornell Cooperative Extension of Lewis Count CIP Clean-in place wastewater CMMP Cornell Manure Management Program CNMP Comprehensive Nutrient Management Plan CBM Compressed biomethane CH4 Methane CHP Combined heat and power CNG Compressed natural gas CO2 Carbon dioxide COD Chemical oxygen demand Decatherm = 1 million Btu ESP Electrical service provider FOG Fats, oils, and greases ft3 Cubic foot gal US gallon (3.8 liters) GE General Electric Company GHG Greenhouse gas GWh Giga-Watt hours GWP Global Warming Potential gpm Gallons per minute H2 Hydrogen H2S Hydrogen sulfide HRT Hydraulic retention time kg Kilogram kW Kilowatt kWh Kilowatt-hour L Liter LCE Lactating cow equivalent LWWTP Lowville Wastewater Treatment Plant Lb(s) US pound LNG Liquefied natural gas m3 Cubic meter mmscf Million standard cubic feet MW Megawatt MWh Mega-Watt hours N2 Nitrogen N2O Nitrous oxide NH3 Ammonia
NPK Nitrogen, phosphorus and potassium content of fertilizer/organic matter NRCS Natural Resources Conservation Service NYS New York State OLR Organic loading rate O&M Operations and maintenance PPA Power Purchase Agreement REC Renewable energy credit RNG Renewable natural gas STP Standard Temperature and Pressure TSS Total suspended solids SCFM Standard cubic feet per minute (adjusted for temperature and pressure) SLDM Sand-Laden Dairy Manure SLS Solid-liquid separator SPDES State Pollutant Discharge Elimination System VFA Volatile fatty acids VS Volatile solids VSS Volatile suspended solids yd3 Cubic yard
1
Executive Summary
The region surrounding Lowville, New York has multiple existing large scale renewable energy systems,
including wind and hydro-power. In the spirit of broadening the area’s renewable energy systems,
members of the Lowville Digester Work Group (comprised of representatives from Cornell Cooperative
Extension of Lewis County (CCE-LC), Kraft® Foods, Lewis County Economic Development Office,
residents, dairy farmer representatives, Lewis County Farm Bureau, and the Soil and Water Conservation
District) desire to develop a locally-owned and operated biomass-based renewable energy system. The
energy produced would stay local and the system would provide direct benefits to Lewis County
farmers, businesses, and residents. This desire prompted an investigation of anaerobic digestion
technology and its application in a centralized anaerobic digester (CAD) system that would use both
farm and non-farm biomass feedstock sources as input materials.
The Lowville Digester Work Group, in June of 2009, commissioned Cornell University (Ithaca, New York)
to conduct this feasibility study through funding provided by Senator Joseph Griffo of the 47th District in
New York State. Cornell worked closely with the Lowville Digester Work Group to develop the feasibility
study scope of work and key parts of its implementation.
The scope of the feasibility study consisted of multiple biomass related components including: resource
assessments, sampling and laboratory analyses (biochemical methane potential and nutrient
concentration investigation), methane production estimations and trucking analyses. The scope of work
also included biogas to energy conversion quantifications, digester site option investigations, and
economic profitability analyses. The major findings pertinent to each of these areas investigated are
provided below; the report contains additional information and details.
Biomass Resource Assessment
Many potential sources of farm and non-farm biomass in and around Lowville were initially identified by
members of CCE-LC. Project specific surveys, one for use in assessing the dairy farms and one for
assessing the non-farm biomass sources, were developed by Cornell University and CCE-LC. Identified
farms were surveyed by members of CCE-LC while non-farm biomass sources were surveyed by the
Lewis County Economic Development office.
2
The farm survey results revealed that there are 25 dairy farms (herd size ranges from 62 to 787 cows)
within an 18-mile radius of downtown Lowville with a total of 5,327 lactating cow equivalents (LCEs). All
of these farms have long-term manure storages (6-month or longer), and use organic bedding material
to bed their cow stalls. Five of the farms reported they have excess organic nutrients (nitrogen,
phosphorus, and potassium), while nine farms indicated that they are nutrient deficient, and 11 are in
balance. An opportunity exists for this project to help farms better manage their nutrients and lessen
the need to purchase commercial fertilizers. The survey responses also showed that the number of LCEs
would increase by approximately 675 cows over two years, and then by 150 more cows after five years.
It should be noted that the actual change in cow numbers in the future (increase or decrease) will be
driven primarily by dairy farm profitability.
The non-farm survey results revealed there are 11 potential sources of biomass (local food processors,
food vendors and residents were surveyed) in the local area that could be aggregated and co-digested
with manure. The minimum estimated useable quantity of substrates from the six non-farm biomass
sources with the highest volumes, was 110 million lbs/year, and the maximum quantity of useable
substrate was 160 million lbs/year. Two of the potential sources (whey mixed with CIP water and post-
digested sludge) provide the bulk (largest volume) of the non-farm biomass available for digestion.
Initial survey results prompted investigation into additional sources of biomass for co-digestion to
further increase potential biogas production. This included manure from sand-bedded dairy farms,
which was ruled not to be an option at this time due to the small farm sizes and comparatively large
capital equipment cost to effectively separate bedding sand from manure. Potential biomass sources
from Fort Drum, a nearby United States Army base, Reed Canary grass from fallow ground along the
Black and Beaver Rivers, and sludge from the Lowville Wastewater Treatment plant (LWWTP) were also
considered and investigated but due to availability, harvesting, and handling issues, all were deemed not
feasible for inclusion at this time, and therefore were not included in further analysis.
Energy crops (corn silage and haylage) fed directly to an energy crop digester were also considered. Two
farms, one north of Lowville and the other south of Lowville, that are currently solely cash crop farms
were included, but kept separate, in the overall analysis.
3
Biomass Sampling and Laboratory Analysis
Based on the information available from the 10 completed non-farm biomass surveys1, the decision was
made to obtain samples from five of the 10 potential feedstock sources, with one source having two
different materials analyzed, for a total of six potential feedstock materials analyzed. These included
waste grease, meat processing by-products, mixed food scraps, post-digested sludge, and diluted whey.
Sub-samples of the collected materials were analyzed in triplicate at the Cornell Agricultural Waste
Management Laboratory to quantify the biogas and methane (CH4) produced by these materials, on a
unit basis. As expected, the laboratory results showed that the waste grease material produced the
highest unit yield (363 L CH4/kg raw substrate2) and the diluted whey the least (2 L CH4/kg raw
substrate2). Sub-samples were also analyzed at an EPA certified laboratory, to quantify their nutrient
composition.
Biogas and methane production estimates for dairy manure were obtained from previous work
conducted at the Cornell Agricultural Waste Management Laboratory where several manure samples
had previously been obtained from commercial New York State dairy farms and analyzed using the same
procedure (Labatut and Scott, 2008).
Methane Production Estimation
The methane (CH4) production for dairy manure and each identified non-farm biomass substrate was
estimated by multiplying the methane production (on a unit mass basis) by the annual estimated
biomass quantity provided in each of the completed surveys. Using this approach, the estimated
minimum annual methane production was 10 thousand ft3 CH4/yr for waste grease (due to its
comparative low quantity available) and the maximum was 157 million ft3 CH4/year for manure (due to
the comparatively high quantity available).
Energy crop methane production estimates were developed using typical yields (wet tons/acre) for corn,
grass, and alfalfa silage for Lewis County, applied to the cropland currently farmed by the two
potentially collaborating cash crop farmers (2,000 and 400 acres). Total biomass yields were multiplied
by unit methane yields for each crop; overall, the estimated annual methane yield from the energy crop
digester was 97 million ft3 CH4/year.
1 Substrate supplier #11 was not initially surveyed; it was discovered subsequent to the conclusion of the survey period. 2 Expressed on a wet weight basis
4
Energy Potential Quantification
Assuming that manure from 15 selected farms3 and the three non-farm biomass substrates with the
highest volumes are co-digested, and using the average estimated gross and parasitic electrical energy
values, the resulting potential net electrical energy available from the CAD facility would be
approximately 8,880 MWh/year. Assuming a typical residence uses 7,250-kWh/year, approximately
1,225 homes could be powered by the CAD facility. If all net energy available were used for biomethane
sale, the CAD facility would be capable of producing 80,800 million Btu’s, which would have a residential
value (at a price of $13.81/1,000 ft3 natural gas) of $1,115,900.
Trucking Analysis
The proposed project would encompass facilitating the transport of raw manure to the centralized
anaerobic digester (CAD) facility (30 million gallons per year), and CAD effluent (42-48 million gallons per
year), back to the collaborating farms at no cost to the collaborating farms. The CAD effluent is a higher
volume than the manure proportion of the influent due to the inclusion of non-farm biomass substrates
at the CAD facility, which would be transported to the CAD by each substrate supplier at their cost. Two
options for the transport of manure and CAD effluent were analyzed; initiating a project-owned trucking
fleet, or contracting with an existing trucking company. A 6,000-gallon manure tanker truck was
assumed for all trucking-related analyses.
The analysis of a project-owned trucking fleet, with an estimated initial capital cost of $1.5 million and
estimated annual expenses of more than $420,000, was deemed not economically feasible at this time.
Contracting with an existing trucking company is the recommended option to pursue in order to simplify
the overall CAD facility start-up by lessening the capital cost and reducing the risks. Although this option
entails higher annual costs, (estimated to be $1.3 million dollars in total annual expense), the project-
run fleet is a possibility to pursue at any time following project start-up.
3 These 15 farms referred to are the selected farms under Scenario No. 2
5
Digester Site/Configuration Scenarios Investigated
Five different digester site/configuration scenarios were initially analyzed and presented, along with
other interim project findings, to the Lowville Digester Work Group at a December 2009 meeting. The
five scenarios explored were:
Scenario No. 1: Co-digest manure from all (25 farms) dairy farms surveyed, and seven (out
of 11 total) non-farm biomass substrates at a central location adjacent to the LWWTP.
This option makes use of all manure and most non-farm biomass substrates discovered by
the completed surveys.
Scenario No. 2: Co-digest manure from 14 dairy farms, and three non-farm biomass
substrates at a central location adjacent to the LWWTP. This option was explored to
reduce trucking costs by reducing the number of collaborating farms.
Scenario No. 3: Co-digest manure from only 12 dairy farms, and one non-farm biomass
substrate at one of two remote sites, and co-digest manure from four dairy farms and two
non-farm biomass substrates at a second remote site. This option was explored to
determine the impacts of having multiple, smaller, regional digesters to further reduce
trucking costs.
Scenario No. 3a: Identical to Scenario No. 3, except that 33% of the manure would be
piped to each remote digester site, and the remainder would be trucked. This option was
also pursued to determine impacts on trucking costs.
Scenario No. 3b: Identical to Scenario No. 3, but includes 400 acres of energy crops
digested at one remote site and 2,000 acres of energy crops digested at the second
remote site. This option was explored to investigate the impacts of including an energy
crop digester on overall biogas production and profitability.
The Lowville Digester Work Group chose Scenario No. 2 CAD, as described above, for complete
investigation at the December, 2009 meeting, and it was decided that one additional farm would be
included in the scenario before performing an economic profitability analysis.
6
The remainder of the Executive Summary provides details and the results of a complete analysis
performed for the Scenario No. 2 CAD, and since the Lowville Work Group also requested a detailed
analysis of an energy crop digester co-located with the Scenario No. 2 CAD manure and non-farm
biomass digester, this information is also provided below.
Scenario No. 2 CAD System Overview
The estimated annual average volume of non-farm biomass substrates available for co-digestion by
three local suppliers was 16 million gallons per year (range 13 to 19 million gallons per year) and the
manure volume available from the 15 targeted collaborating farms was 30 million gallons per year.
Therefore, the CAD should be sized to handle at least on average 122,400 gallons of influent per day.
Using a digester hydraulic retention time of 22.54 days, the digester treatment volume needed was
calculated to be 2.8 million gallons. A digester configuration of one or multiple tanks can be used to
accomplish this overall size requirement. The average estimated capital cost for a complete mix digester
system of this size was $5.89 million (range $4.73 to $7.14 million).
The annual cost to transport manure to the CAD site (adjacent to the existing LWWTP) and digester
effluent back to the collaborating farms was estimated to be on average $1.12 million annually (range
$1.07 million to $ 1.17 million). It was assumed that the trucking cost for the non-farm biomass material
to the CAD site would be paid by the substrate suppliers, as is currently the case.
The average estimated gross volume of biogas produced was 188 million ft3/year (range 140 million to
237 million ft3/year). Using a biogas methane concentration of 60%, the annual estimated volume of
methane produced was 113 million ft3/year (range 84 million to 142 million ft3/year).
4 22.5 days is the average of 20 and 25 days, which are common retention times for similarly sized systems
7
Two of the most commonly implemented biogas utilization options were investigated:
1) Use biogas to fuel a reciprocating engine-generator set5
2) Sell cleaned biogas as renewable natural gas, biomethane, by first removing
impurities (carbon dioxide, hydrogen sulfide, and moisture) using pressure-swing
adsorption gas clean-up technology6.
For option 1, it was assumed that thermal energy harvested from the engine-generator set would be
used to meet all of the digester heating requirements (warming the CAD influent to target operating
temperature and then maintaining it); field experience has shown that this is an appropriate assumption
to make. For option 2, it was assumed that 20 percent of the biogas produced by the digester would be
needed to meet this demand; this assumption needs to be confirmed, based on information about the
design of each digester system considered, specifically, how well the vessel is insulated and the
exposure it has to winter wind and temperature. The overall estimated annual parasitic heating
requirement was 20,200 million Btu’s per year (range 15,000 to 25,500 million Btu’s per year). Using the
average estimated parasitic heating requirement, the annual cost to provide this heat ranged from
$81,000 to $282,000 per year for a natural gas purchase price range of $4 to $14 per decatherm,
respectively.
For parasitic electrical requirements, for both biogas utilization options, the average estimated parasitic
electrical energy requirement of the CAD system was determined the same way. Calculations were
performed using data from vendor information obtained for other similar sized systems to determine
the electrical energy requirement per gallon of influent material; the results were that the average
electrical energy requirement was found to be 0.0313 kWh per gallon of influent7 (range 0.0121 to
0.0505 kWh per gallon of influent). Applying these energy values to the CAD system, the estimated
average annual parasitic electrical energy requirement was 1,400,000 kWh per year (range 540,000 to
2,257,000 kWh per year). Using the average estimated parasitic energy requirement, the estimated
annual cost to provide this energy ranged from $112,000 to $252,000 for an electrical energy purchase
price range of $0.08 to $0.18 per kWh, respectively.
5 Other, less commonly used methods exist for converting biogas to electrical energy (e.g. microturbines) 6 Other methods are available for scrubbing biogas to make biomethane (e.g. membrane separation, regenerative amine wash)
7 Influent is defined as the biomass on the in-flow side of a treatment, storage, or transfer device
8
Nutrient Management Implications
Assuming the non-farm biomass imported for co-digestion supplies excess nutrients to the post-
digestion product that would be available for sale to area crop farms, the project could potentially
receive $226,000/year in total revenue. Of the $226,000/year, $86,000/year would be derived from the
sale of nitrogen, $121,000/year would be derived from the sale of phosphorus, and $19,000/year would
be derived from the sale of potassium.
Economic Profitability Analysis- Scenario No. 2 CAD
A net annual economic profitability analysis was performed for the Scenario No. 2 CAD to determine if
this scenario was economically viable considering the options of: 1) selling electrical energy at a price
range of $0.08 to $0.18 per kWh, or 2) selling biomethane (cleaned biogas) at a price range of $4 to $14
per decatherm. For both of these options, separate net annual economic profitability analyses were
performed, which included a tipping fee equal to the tipping fee being paid by one of the three non-
farm biomass suppliers whose substrate was selected for co-digestion (the other two tipping fees were
not provided by the completed surveys).
For all of the analyses, the cost of capital (discount rate) used was 5%, the economic life of the digester
was 20 years, and the replacement cycle of the engine-generator set was 10 years. Trucking costs to
haul manure to the CAD site and effluent to collaborating farms was included as an annual cost. Other
annual costs included operation and maintenance of (1) the CAD system (based on data obtained from
vendor quotes for other similar systems), (2) the engine-generator set ($0.018 per kWh) and (3) the
biogas clean up system.
The results of the net annual economic analysis showed that for all energy sale options investigated it
was more costly to own and operate the system each year, than the system would receive in revenue
annually. In other words, no option was found to be economically profitable.
Based on these results, a final net annual economic profitability analysis was conducted to determine
the tipping fees needed for the two energy sale options investigated to result in a Scenario No. 2 CAD
financially break-even situation. For the option of selling electrical energy at a price ranging from $0.08
to $0.18 per kWh, the break-even tipping fee range was determined to be $21 to $9 per ton,
9
respectively. For the option of selling biomethane at a price range of $4 to $14 per decatherm, the
break-even tipping fee range was determined to be $29 to $16 per ton, respectively.
The calculated break-even tipping fee ranges were substantially below the average tipping fee of over
$70 per ton currently charged by landfills for the northeastern U.S., but somewhat higher than the
calculated tipping fee currently being paid by the non-farm biomass supplier considered for this
project with the most biomass available annually.
Energy Crop AD System Overview
The proposed Lowville energy crop digester is an anaerobic digester designed to process high solids
energy crop materials (corn silage and/or haylage). Such digesters are widely used in Germany and
other European countries and produce about eight times the biogas as digesters fed manure only
(Effenberger, 2006).
Silage corn and grass hay would be harvested and ensiled as if they were going to be fed to dairy cattle.
Sufficient quantities would be stored to enable the energy crop digester feed hopper (usually a walking
floor bin) to be filled once-a-day, year round, normally with a pay loader. Several times per day, the
control system would automatically transfer a portion of the feedstock into the digester; screw
conveyors (augers) are normally used due to the high solids content of corn silage and haylage.
The energy crop digester economic analysis performed for this feasibility study used “in-the-bunk” silage
prices ranging from $30 to $55/ton, meaning that the costs to grow and harvest the crops and ensile
and store them are covered by the purchase price.
In addition to the energy crop feedstock, a small portion of manure is also normally added to the energy
crop digester, about 10 percent by weight, to help stabilize digester pH and to provide some dilution
water to lessen the power required to provide in-vessel mixing.
Energy crop digester effluent, laden with organic nutrients, is the consistency of digested manure. For
this feasibility study, it is assumed the effluent would be stored on-site for a short period of time and
periodically trucked to the energy crop source farms for longer-term storage and for subsequent use as
fertilizer to grow the next rotation of energy crops. Some of the surplus nutrients from the Lowville CAD
10
system could also be trucked to the collaborating farms to meet the overall fertilizer requirements for
the crops grown on those farms.
Economic Profitability Analysis - Energy Crop AD System
The same net annual economic profitability analysis was performed for the energy crop AD system. For
this analysis, the only energy sale option investigated was the sale of electrical energy8, using a sale price
range of $0.08 to $0.18 per kWh with varying feedstock (fermented corn silage and haylage) prices
between $30 and $55 per wet ton.
Again, the cost of capital (discount rate) used was 5 percent, the economic life of the digester was 20
years, and the replacement cycle of the engine-generator set was 10 years. Trucking costs to haul
digester effluent to collaborating farms was included as an annual cost, as it would be paid by the
project. Other annual costs included operation and maintenance of: (1) the CAD system (based on data
obtained from industry vendors), (2) the engine-generator set ($0.018 per kWh) and (3) biogas clean up
system.
The results of the net annual economic analysis showed that for all digester feedstock and energy sale
price options investigated it was more costly to own and operate the system each year than the
system would receive in revenues annually. This is the same result that was found for the Scenario No.
2 CAD options investigated.
Recommendations and Future Work
The recommendation for a CAD system is based on conducting thorough and complete technical and
economic feasibility analyses, as well as the vision of the Lowville Digester Work Group. Based on this,
the recommendation is to further investigate one centrally-located complete mix AD, sited adjacent to
the LWWTP that would co-digest manure from 15 targeted collaborating dairy farms and targeted non-
farm biomass substrates (currently the following three substrates: whey, post-digested sludge, and
glycerin) that are by-products generated nearby.
8 Biogas clean-up to biomethane was not investigated, since economic profitability analysis results for the Scenario No. 2 CAD showed little difference in the bottom line when compared to electrical energy sales.
11
The future net annual economic profitability behind this recommendation is encouraging, given that, (1)
the calculated tipping fee needed for the system to break-even is well below the average tipping fee
charged in the northeastern U.S. and many predict regulations will be instituted in the near future
restricting the land-filling of organic matter, (2) future regulations aimed at reducing the impact of fossil-
fuel derived energy (specifically GHG emissions and climate change) would likely positively impact
renewable energy projects, (3) energy produced from such projects would have less price volatility than
fossil fuel-based energy products, and (4) the annual economic profitability will improve with reductions
in capital cost by receiving grants and/or premium payments for renewable energy.
If future efforts are put forth to further investigate one CAD, it is recommended that the two major
areas provided below be addressed in the order presented below and that the bullet items under each
be included.
A. Address Economic Barriers to Project Implementation
Identify other potential sources of non-farm biomass that are currently being land-
filled or otherwise disposed of that could be received by the CAD with a tipping fee
paid by the supplier.
Continue the education and outreach efforts concerning this project and the goals and
objectives of local community members, targeted at collaborating and non-
collaborating dairy farmers and non-farm biomass substrate suppliers to develop
project support targeted towards securing public funding.
Secure grant funding or subsidies that could help offset the capital cost of the CAD
and/or supplement the revenue(s) received for system outputs (raw biogas,
electricity, biomethane, and/or organic nutrients).
Validate the trucking analysis and farm biomass pick-up options determined under
this effort.
Investigate the willingness of non-farm biomass suppliers to enter into reasonable
long-term contracts , with a negotiated tipping fee.
Investigate the willingness of the end user(s) of the net energy produced by the CAD
facility to enter into reasonable long-term contracts.
Explore the potential for selling raw biogas to a local end user.
12
Investigate the possibility of the sale of CAD surplus heat combined with woody
biomass heat to local industry or the community (district heating).
B. Advanced Project Due Diligence
Perform more complete laboratory testing of the targeted substrates mixed
proportionally with manure to better solidify the quantity of biogas that would be
produced by the system.
Perform a value engineering/economic analysis that includes looking at the digester
treatment volume vs. biogas production potential.
Conduct an in-depth site and environmental impact assessment for the targeted
construction site.
Investigate the legal issues for various digester ownership options.
Determine the permit(s) that will be required by the New York State Department of
Environmental Conversation (NYSDEC)9.
Conduct an in-depth investigation into the site improvements that will be required at
each farm in order to participate in the project, and develop an associated budget.
Investigate contracting with an existing trucking company to provide transportation of
farm biomass.
Assess renewable energy credits (RECs) and carbon credits as applied to centralized
digesters.
Conduct a net energy analysis for the proposed system.
Develop a request for proposals (RFP) package to be distributed to AD system
designers.
Validate the economic profitability analysis using the results of the proposed RFP.
Continue investigation into future opportunities, such as manure nutrient extraction
equipment and resulting product marketing opportunities for organic nitrogen,
phosphorus, and potassium.
Continue assessment of alternative biogas market opportunities such as the sale of
biomethane as a vehicle fuel.
9 There are currently no operating dairy manure-based CAD systems in NYS, and an initial inquiry made by Cornell to NYSDEC on
behalf of this project revealed that NYSDEC is not readily prepared to state what permit(s) is/are needed.
13
Nomenclature
Effort was made to make terminology throughout this report consistent to allow for a more clear
understanding of the information presented. Please refer to this list as necessary.
Centralized Anaerobic Digester (CAD) facility The term used to describe the proposed manure and substrate co-digestion AD system, and all of the integrated components.
Energy crops Field crops grown specifically as a feedstock source for an energy crop AD system
Feedstock Describes the entire influent to the CAD
Lewis County Community AD project The name of the proposed project
Lowville Digester Work Group The local volunteer group of decision-making stakeholders on behalf of the project
Manure
Effluent from a dairy housing barn made up of cow urine and feces, bedding, and other minor components such as gravel, undigested feed, and/or milking system gray water.
Methane production potential Quantification of a biomass substrate to produce methane
Non-farm biomass substrates Organic by-product material from local processors of farm products; otherwise referred to as food waste
Non-farm biomass substrate suppliers
Local food processors and vendors who have, upon initial survey, shown interest in supplying organic material for co-digestion; otherwise known as food waste sources
14
15
Introduction
The proposed Lewis County community anaerobic digester (AD) project (see Figure 1) was initiated in
early 2008. Cornell University was contracted to perform a feasibility study of the proposed project in
May 2009, with a targeted completion of December 2009. Three interim project meetings were held by
the Cornell team to present interim project findings and assess progress in October and December, 2009
and March, 2010. After some changes in scope of the project, the final feasibility report was completed
in May 2010.
Lowville goals and objectives
Interest in a community AD from several Lewis County, NY constituents grew from the initial set of goals
developed from multiple community viewpoints. The Lowville Digester Work Group was formed from a
group of local stakeholders interested in determining the application of anaerobic digestion technology
to meet the goals set forth, and to oversee development of the proposed project. The following are the
initial project goals developed by the Lowville Digester Work Group (committee document, 2008):
Goals for the community:
Encourage continued economic growth
Lessen the negative impact of farms on county residents (e.g., farm-based odor)
Reduce the environmental footprint
Goals for the region’s dairy industry:
Provide greater flexibility in manure handling and nutrient management that results in an
economic advantage versus today
Reduce odor associated with manure storage and land application
Allow a greater number of animals per unit of land area with less environmental risk
Goals for local industry:
Gain access to sustainable energy at lower (versus today) cost.
16
Figure 1. New York State map showing location of project-site
Scope of Work
The following questions were posed in the scope of work document developed prior to the beginning of
the feasibility study, and used throughout the study by Cornell University and the Lowville Digester
Work Group to guide the project.
Biomass
1) What is the annual on-farm (manure) and Village of Lowville non-farm biomass potentially
available for anaerobic digestion, by source?
2) How much biomass can be secured, by source?
3) How many farms are currently prepared (on an infrastructure basis) to store raw manure
short- term and digester effluent long-term?
4) What infrastructure upgrades are needed for those farms not currently prepared to store
raw manure short-term and/or digester effluent long-term?
Biomass/biogas transportation
5) What options exist for transporting manure from the farms to the digester location(s) and
digestate back to the farms and what is the estimated cost associated with this?
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6) What options exist for transporting non-farm biomass to the digester location(s) and what
is the estimated cost associated with this?
7) What are the results of an economic sensitivity analysis on biomass transportation cost?
8) What is the feasibility of transporting biogas or biomethane (processed biogas) to a
utilization site?
Anaerobic digestion
9) What are the AD technology options available?
10) Which option is best suited for the application?
11) What are the estimated capital and operating and maintenance costs associated with the
AD and associated equipment?
12) Is it best to truck all biomass destined for digestion to one site or to have an array of
digesters strategically located within the county?
Biogas/energy conversion
13) How much biogas can potentially be produced with the secured biomass?
14) Is biogas clean-up required and if so what option is best?
15) How much energy can be extracted from the biogas?
16) What are the results of a sensitivity analysis performed on the sale price for the energy?
Nutrients
17) What is the expected nutrient value of the manure once digested (tons total-N, ammonia-
N, total-P, ortho-P, and potassium)?
18) What is the anticipated increase in digester effluent volume and nutrient composition
with the importation of securable non-farm biomass sources?
Impacts on the community
19) How many truck loads of manure will be transported to the digester site(s) per day?
20) What labor force is anticipated to operate the overall facility?
18
Economics
21) What is the estimated total annual cost for various digester/biogas utilization scenarios?
Designated responsibilities
In addition to the questions set forth in the scope of work, the same document designated which tasks
each group involved in the project would be responsible for. It was decided that the Cornell Manure
Management Program Team (CMMPT) would provide leadership and overall project coordination to
facilitate the completion of the feasibility study. CMMPT developed and maintained a project schedule
identifying specific tasks, responsible parties and targeted completion dates. Specific responsibilities are
outlined below.
CMMPT
o Deliverables: CMMPT will complete and provide the following items to Cornell
Cooperative Extension of Lewis County:
Initial Findings (written report and oral presentation)
Interim Report (written report and oral presentation)
Final Report (written report and oral presentation)
o The work tasks and components of the feasibility study include:
Gather information from existing centrally located community ADs or
completed feasibility studies that are relevant.
Develop a survey for completion by select dairy farms within Lewis County
Develop a survey to all potential substrate suppliers within Lewis County
Aggregate and analyze results of the above surveys
Perform all calculations required to answer the questions outlined above
Prepare all reports and make oral presentations
Lewis County Cornell Cooperative Extension (CCE)
o Identify farms within a specified radius of possible digester site(s)
o Implement the farm survey and provide reports/summaries to CMMPT
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o Organize project meetings
Lewis County Soil and Water Conservation District (SWCD)
o Using data provided by the Cornell Cooperative Extension, create a map identifying all
potential participating dairy farms within the selected radius of the Village of Lowville
Wastewater Treatment Plant (LWWTP) and other potential digester sites. Incorporate
information on road infrastructure into map so that feasible transportation routes can
be considered.
o Using data provided by the Cornell Cooperative Extension, create a map identifying all
potential substrate suppliers within the selected radii of the LWWTP and other
potential digester sites.
Village of Lowville
o Implement a survey to quantify all potential non-farm biomass substrates within Lewis
County
o Provide completed surveys and results to CMMPT for analysis and use
Lowville Digester Work Group
o Assist with the identification of potential sites for the proposed central AD
o Assist in identifying potential buyers of final products
o Inform community about the project and generate support
Project approach
Cornell University, in agreeing to perform the feasibility study for the Lewis County community AD,
responded to the Lowville Digester Work Group’s request with the following plan of action:
Develop a plan of necessary work to be accomplished on the local level
Aggregate and analyze results of local work
Calculate total quantity and characteristics of digester inputs
o Farm
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o Kraft
o Other
Assist local creation of a map of cooperating farms and other biomass sources
Calculate costs and feasibility of farm-based biomass transportation
Measure biogas producing potential of assumed substrate inputs and calculate projected
biogas production
Review biogas clean up options
o Cost
o Scale
o Availability
Determine the best use of biogas produced
o Generation of electricity
Cost of interconnection
Sale to grid or private
o Sale of cleaned biogas
Sale to Kraft
Sale to community
Sale of energy back to farms
Used to power vehicles/farm trucks
o Market price of each option
o Cost of implementing each option
Analyze all final products from digester and determine marketability
o Solids
Bio-security issues
21
o Heat
o Electricity
o Nutrient-laden liquid effluent
o Compost
o Other
o Determine revenue from each potential sale
Devise a strategy to return organic material/nutrients to farms
o Solids and/or liquids
o Transportation
o Delivery infrastructure feasibility on a farm level
Overall cost benefit analysis for project
Formulate questions for Lewis working group before proceeding, based on initial findings
Incorporate new visions to final recommendation
Develop a mid-study interim report
Develop a final feasibility study report
22
23
Chapter 1. Basics of Centralized Dairy Manure-Based Anaerobic Digestion, Biogas Utilization, and Nutrient Recovery Systems A centralized dairy manure-based anaerobic digestion and biogas utilization system is one where dairy
manure, the system’s stable feedstock, is aggregated from multiple farms, blended together, and co-
digested in a heated vessel for 15 to sometimes more than 30 days. In many cases, non-farm biomass
substrates such as food processing and bio-fuel processing by-products, organic industrial wastes, and
culled and leftover human foods are co-digested with dairy manure. Digestate (digester effluent) is
generally stored short-term on-site at the centralized facility, and then transported back to source farms
for storage until it is used to replenish cropland with nutrients (nitrogen (N), phosphorus (P), and
potassium (K)) and organic matter. Digestate can be further treated, as described later in this chapter,
to achieve various undigested fiber recovery and nutrient conservation and management goals and
objectives. A typical process flow diagram for a centralized digestion system is shown in Figure 2.
Figure 2. Typical CAD system process flow diagram
Centralized digesters are best located where they are strategically placed to minimize transportation of
manure and non-farm biomass substrates and to maximize output energy and digestate utilization. CAD
24
can effectively improve fertilization of cropland by returning CAD effluent to a strategically located site
at the farm, for ease of use in spreading on cropland.
Centralized digestion systems are common-place in Denmark and other European countries; a
centralized digester in Jutland, Denmark is shown in Figure 3.
Figure 3. A CAD in Jutland, Denmark
Overall, centralized digestion of manure provides the opportunity for economies of scale to come into
play that generally cannot happen on individual farms. The capital and operating costs per unit of
influent treated (i.e., cents per gallon) is generally less in larger systems than smaller systems. Another
reason centralized digestion is given due consideration is that it is likely to have the size needed to
justify and pay for a full-time crew to operate the facility. Further, centralized digestion provides the
opportunity for more efficient use of organic nutrients by the collaborating farmers. Digestate can be
sampled more frequently than on-farm, thus better quantifying the nutrients sent back to each
collaborating farm. Also, anaerobic digestion provides a steady and consistent material that is well
suited for secondary or tertiary treatments that can include enhanced nutrient management by
farmers.
25
A common concern with centralized anaerobic systems is biosecurity (disease control). Commingling
of source farm manure and non-farm biomasses is part of the centralized digestion model that
cannot be avoided. Farmers can be especially concerned about biosecurity since manure that may
contain infectious disease causing organisms can be brought onto their farms. However, the risk of
this is lessened when manure is digested; further risk reductions occur when influent or digestate is
pasteurized before being returned to the farm.
Additional information about dairy manure-based centralized digestion systems is provided in this
chapter with the goal of preparing the reader for the following chapters where the work and feasibility
study findings are presented. More in-depth information about on-farm and centralized anaerobic
digestion can be obtained by reviewing the references cited herein.
Centralized digester feedstock materials
Centralized digesters are generally fed two or more of the three different types of biomass materials.
The three types are categorized based on availability, specifically those that are:
Continuously available such as manure, certain food processing wastes like whey, etc.
or at least almost continuously (e.g. some slaughterhouse waste sources)
Seasonally available such as grape puree, onion tops, carrot skins, etc.
Available year-round but not consistently such as processed foods that have exceeded
their shelf life
Manure
For most centralized digestion systems, manure is the stable feedstock material. Not only is it
continuously produced by dairy cattle, it also provides a key role in co-digestion with other, more
biologically convertible materials as it moderates pH due to its buffering capacity.
The average U.S. dairy cow produces 150 lbs. of raw manure per day that contains 20 lbs. of total
solids (TS), 17 lbs. of volatile solids (VS), 1 lb. of (N), 0.17 lbs. of (P), and 0.23 lbs. of (K) per day while
a dry cow and a replacement (heifer) produces measurably less (ASABE, 2005). A portion of the
manure VS are biologically converted to biogas. Digestion of raw manure from a dairy cow produces
on average, 80 ft3 biogas per cow-day (Ludington, 2008).
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Non-farm biomass sources
Any biomass can be digested. Digestion of various biomass materials is largely a function of materials
handling (conveying material from storage into a digester), biodegradability, maintaining a balanced
state within the digester vessel, and economics. Many of the suppliers of non-farm biomass substrates
available for anaerobic digestion currently pay significant tipping fees to the local landfill authority in
order to dispose of their unwanted processing by-products.
In New York State, many farmers are interested in mixing non-farm biomass substrates with manure
due to:
1. The increased biogas production potential the mixture produces
2. The associated tipping fees for allowing substrate suppliers to unload their by-product
on the farm.
Non-farm biomass can have lower solids content than raw manure, so when combined with manure
the resulting mixture needs to be mixed within the digester to keep the solids in suspension.
Some materials, like fats, oils, and greases readily break down in an AD while others like corn silage take
much longer to fully do so. Many non-farm biomass substrates have the potential to produce several
orders of magnitude of biogas per unit of influent mass compared to manure. An example of biogas
production from co-digesting manure with food wastes is between 368 and 560 ft3 biogas per cow-
day, as found on one New York State dairy farm (Gooch et al., 2007).
Like manure, non-farm biomass generally contains measurable levels of nutrients (N, P, and K) that
must be considered when assessing the impact centralized digestion will have on a collaborating
farm’s ability to comply with their Comprehensive Nutrient Management Plan (CNMP).
A centralized anaerobic digester (CAD) that looks to co-digest measurable volumes of non-farm
biomass substrates needs to have reasonable assurance that these are available and securable by
long-term contract or are able to be replaced with alternate biomass sources. This is important
because the capital cost of the centralized digester will be directly affected by the volume of non-
farm biomass sources digested and the associated biogas production potential.
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Anaerobic Digestion
Direct environmental benefits of an anaerobic digestion system include conservation and phase
transformation of manure nutrients (N), (P), and (K) during digestion resulting in an effluent rich in
organic, crop available-nutrients needed to grow feed for livestock and people alike. Since the digestion
process significantly reduces odors associated with untreated biomass stored long-term, digestate can
more effectively be used to fertilize crops. This reduces the need to purchase synthetic fertilizers that
require large amounts of fossil fuels to produce, thus reducing the greenhouse gas (GHG) emissions
associated with crop production. Improvements in water quality are also associated with less use of
synthetic fertilizers.
Anaerobic digesters can be thought of as an extension of a cow’s stomach. Both rely on operative
microbes that flourish in the absence of oxygen to transform foodstuff into useable energy. Operative
microbes are most successful at doing this when they are consistently fed a diet that meets their
nutritional needs and the digester temperature and pH are maintained at target values.
The anaerobic digestion process overall involves three groups of anaerobic microbes. First, hydrolytic
bacteria initiate a process called hydrolysis. These bacteria use extra cellular enzymes to convert
organic insoluble fibrous material into soluble material; however, inorganic solids and hard-to-digest
organic material are not able to be converted.
Next, acid forming bacteria convert the soluble carbohydrates, fats, and proteins to short-chained
organic acids. The acids produced in step two become the food source for the methanogens, which
produce methane gas in the third step.
Various methanogenic species grow in different temperature regimes.
1. Psychrophilic methanogens grow in the lowest of the temperature ranges, less than 68°F.
Methanogens in this range grow slowest and produce the least biogas per unit of time.
Covered lagoon systems, especially those in northern climates, will be in this range much
of the year (Wright, 2001).
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2. Mesophilic methanogens grow in an optimum temperature of about 100°F which is the
most common operational temperature for digesters in the U.S.
3. Thermophilic methanogens grow in an optimum temperature of about 130°F. The higher
operating temperature increases the rate of biomass degradation, increases pathogen
reduction, and allows for shorter retention times thus reducing the capital cost of the
digester vessel.
Digester Types
In the U.S. there are basically three different types of anaerobic digestion systems used today to process
dairy manure. They are: plug-flow, complete mix, and covered lagoon. Of these three, a complete mix
system is the system of choice for use in a centralized digester because the likelihood of co-digestion of
dairy manure with non-farm biomasses is very high. (Digester influent concentrations less than 10
percent total solids are common when co-digesting manure with most food processing by-products
and require mixing to minimize solids settling.)
Complete mix digesters can be either horizontal flow or vertical flow systems. Each is briefly discussed
below.
Complete Mix Digester, Horizontal Flow System
Horizontal-mix digesters incorporate agitation systems in digester vessels. The mixing system is
mainly utilized in scenarios that have influent total solid concentrations greater than 12 percent (not
common with dairy manure-based systems) or less than 10 percent.
Complete Mix Digester, Vertical System
Vertical mixed digester tanks can be either below-grade (atypical) or above-grade (typical) as shown
in Figure 4. Cast-in-place concrete, welded steel, bolted stainless steel, and bolted glass-lined steel
panels are all used to construct vertical tanks.
The mixing process is achieved by various methods, depending on the preference of the system
designer and the overall goals of the system. In one method, an external electrical motor (about 10-
20-Hp) turns a vertical shaft, concentric with the digester tank, which has several large paddles
29
attached. The shaft speed is about 20 RPMs. This system is common for solid top tanks.
Another method uses submersed impeller agitators each driven by either an electrical motor or a
centrally located hydraulic motor. These systems have a much higher blade speed, perhaps 1,750
RPMs, and can be used with both flexible top and solid top applications. One clear advantage of the
first method is the electrical motor is easy to service and replace.
Vertical tanks are insulated during the construction process to reduce the maintenance heating
requirement (heat to maintain digester operating temperature). Significant heat can be lost from
vertical tank digesters if they are not properly insulated. Applicable insulation options are to spray
the tank with foam insulation or to use rigid board insulation attached to the tank and then covered
with metal cladding.
Figure 4. Danish above-grade complete mix vertical digesters in background
Biogas
Anaerobic digestion produces a continuous supply of biogas in quantities sufficient to not only power
the digestion plant but also to utilize the excess in various ways. Producing electricity and/or thermal
30
heat from biogas results in a net reduction of greenhouse gases (GHG). Anaerobic digestion of dairy
manure also mitigates methane emissions otherwise caused by traditional manure handling and storage
practices.
Production of biogas is dependent mainly on the digester hydraulic retention time (HRT), digester
operating temperature, and the biochemical energy potential of the influent. Higher biomass
conversion efficiencies by thermophilic (~135°F) methanogens allow for shorter hydraulic retention
times and consequently reduced capital costs as compared to mesophilic (~100°F) systems. Biochemical
energy of an influent material is most accurately evaluated by conducting long-term (6-month) bench-
top reactor tests (Angenent, 2009) but is generally estimated by measuring the VS content in the
influent. Biochemical methane trials can also be conducted in the laboratory to estimate the biogas
production potential of a biomass sample. Jewell (2007) reported that an appropriate estimation of the
methane (CH4) production is to use a value of 0.5 L CH4/gram of VS degraded. If the dry biogas is 60
percent CH4 this is equivalent to 13.4 ft3 biogas/lb. of VS degraded.
Composition and energy value
On-farm digester monitoring has shown that biogas is comprised mainly of ~60% methane and ~40%
carbon dioxide (CO2), with trace levels of 0.2 to 0.4 percent hydrogen sulfide (H2S). Even though H2S
concentrations are low, biogas is highly corrosive and prudence is needed to avoid pre-mature biogas
transport and utilization equipment failures.
Pure (dry) methane has a low heating value of 896 Btu/ft3 (at standard temperature and pressure: 68°F
and 1 atm) (Marks, 1978). Since biogas is only ~60% methane, its heating value is ~40% lower or about
540 Btu/ft3. Raw biogas is considered to be saturated with water vapor.
Utilization: fuel source for engine-generator sets
Using biogas as an energy source to fuel on-site engine-generator set(s) is the most common use of
biogas today. Large engines that had been adopted for landfill biogas years ago are now widely
available for use at centralized digestion sites. Most are spark-ignited systems with a few compression
ignited systems that also use about 10 percent diesel fuel concurrently as a fuel source.
31
Overall, these “low Btu or dirty gas” engines work well with the exception of difficulties arising from
hydrogen sulfide (H2S). Hydrogen sulfide is very corrosive at low temperatures since it converts to
sulfuric acid. To date, most on-farm biogas-fired engines combat the corrosiveness by running the
engine nearly continuously (keeps the temperature high) and changing oil more frequently than for
cleaner fuel source scenarios.
Recently, some U.S. farmers have implemented methods to reduce H2S concentrations from biogas prior
to utilization. Methods include chemical reaction and biological reduction systems. Scrubbers are
mainstream equipment on European digester systems.
Overall, there are two basic types of generators:
1. Induction generators run off the signal from the utility and are used to allow parallel hook
up with the utility. Induction generators cannot be used as a source of on-farm backup
power since the system needs the signal from the utility line to operate properly.
2. Synchronous generators could be run independently of the utility but matching the
utilities power signal would be very difficult so these types of generators would be used if
the system were not connected to the utility grid.
Most generator systems manufactured today have controls that will allow the engine-generator set to
synchronize with the utility’s electrical frequency and still operate in island mode when there is a
disruption of the grid power. These systems can be set up to “black start” if desired.
Thermal-to-electrical conversion efficiencies for biogas-fired internal combustion engine-generator sets
are less than desirable, but are about the same as other fuels. On-farm digester monitoring has shown
that the conversion efficiency ranged from 22 to 28 percent, as shown in Figure 5.
The electricity production depends on the amount and quality of gas as well as the efficiency of the
engine-generator. Typically, 33-38 kWh/day will be produced per 1,000 ft3/day of biogas produced
(Koelsch et al., undated and EPA, 1997). Some engine-generator set manufacturers show biogas-to-
electrical energy conversion efficiencies as high as 42% in their advertisement literature. As with all
32
large capital purchases, careful evaluation of those systems is needed to ensure they are economically
feasible.
As already mentioned, engine water jacket heat, and sometimes exhaust heat as well, is harvested and
used as the primary means to heat the digester. In the winter, most if not all of this harvested heat is
needed, while in the summer a good portion of it is dumped to the ambient via forced-air/water heat
exchanger.
Figure 5. Thermal to electric conversion efficiency of six NYS on-farm engine-generator sets.
(Source: Gooch, Pronto, Ludington, Unpublished, 2010)
Utilization: fuel source for microturbines
Two New York State dairy farms have microturbines in operation to power generators to produce
electricity. The main interest in microturbines is the premise that they require less maintenance on a
daily basis and also on a long-term basis, and most recently that they potentially produce less exhaust
emissions. Biogas pressure needs to be increased from typical digester pressure values to about 60 psi
before being injected into a microturbine. Corrosion-resistant small-scale compressors are available to
compress raw biogas to this pressure thus lessening the need for an H2S scrubber.
The typical fuel-to-power efficiencies of various biogas utilization options are shown in Table 1. These
efficiency figures do not account for increases due to the use of co-generated heat.
33
Table 1. Typical fuel-to-power efficiency values (adapted and updated from Wright, 2001).
Prime Mover Type Efficiency
Spark ignition engine 18-42%
Compression ignition
engine (Diesel)
30-35% above 1 MW
25-30% below 1 MW
Gas turbine 18-40% above 10 MW
Microturbine 25-35% below 1 MW
One source states the operation and maintenance cost of $0.015 per kWh are estimated for engine-
generators (EPA, 1997). On-going engine-generator set service contracts are offered by one company
that sells them for $0.015 to $0.02 per kWh produced depending on the pre-existing maintenance
performed on the set and presence of an H2S scrubber.
Utilization: fuel source for boilers
On-farm biogas utilization by a boiler is the second most popular use of the energy. Natural gas boilers
can be modified to use biogas as a fuel source. The main modification involves increasing the pipe
delivery size and orifices in the burners to accommodate the lower density fuel. Decreasing the
concentration of H2S in the biogas can extend the life of the boiler equipment. Boilers are mainly used
to provide primary or secondary heating of the digester and in some cases also to provide domestic
heating of farm offices and lounge areas. One farm used boiler heat to heat a calf barn, but this use is
limited.
Utilization: fuel source for other uses
Raw biogas can also be used as a fuel source for drying equipment such as grain dryers, separated
manure solids dryers, evaporators, etc. Other possible uses fall under the category of those needing
fully cleaned (scrubbed) biogas, commonly known as “biomethane”. These possible uses include any
that currently use natural gas (almost pure methane) and as a vehicle fuel. There are two primary
methods to process biogas into biomethane. They are: 1) chemical and, 2) physical removal of
impurities (CO2, H2S, and water vapor). Details of these processes are beyond the scope of this report
but the general flow process diagram is shown in Figure 6.
34
Figure 6. Basic process flow diagram for advanced biogas clean-up for biomethane production.
Advanced Centralized Digester Information
Specific information on a CAD system is presented below.
System electrical demand
Modern CADs require electrical energy to operate with the highest electrical demand normally
associated with the pumps and agitation equipment. The electrical energy used to operate a system
is known as parasitic electrical energy. With all centralized digester systems it is important to
implement a design that is energy efficient. Electrical energy efficiency can be expressed in various
ways including as a function of the: 1) influent volume (annual kWh/annual influent), 2) vessel
treatment volume (annual kWh/tank size), and 3) energy production (kWh consumed/kWh
produced). All systems that are not electrically efficient result in reduced sale of electrical power
and/or increased purchase of electrical energy from the utility.
System thermal (heat) demand
Anaerobic digesters require a controlled heating system for operation. There are two different heat
demands in most systems; they are: 1) differential heat, and 2) maintenance heat. Differential heat is
the heat needed to raise the influent temperature to digester target operating temperature and
35
represents by far the largest heating requirement of the system. Maintenance heat is needed in
most, but not all systems, to maintain digester contents at target operating temperature.
When an engine-generator set is used to convert biogas to electricity, the heat of combustion is
harvested from the engine and used to heat the digester. In this scenario, the heating efficiency of
the digester heating system is less important than if heat is provided by a biogas-fired boiler. Under
the later scenario, a primary goal of the digester system is normally to sell raw or processed biogas
and thus the need exists to minimize the parasitic heating requirement. Installations where heat
sales are important can utilize digester effluent/influent heat exchangers can be used to minimize the
parasitic heating requirement by preheating digester influent.
Biosecurity/disease control
Dairy manure is known to contain various pathogens that survive outside the cow. Not all cows on all
farms have the same contagious pathogens. The centralized digestion model involves commingled
digested manure and non-farm feedstock(s) being returned to the source farms resulting in justified
biosecurity concerns.
The hydraulic retention time (HRT) of complete mix digesters varies at the microscopic level from
manure particle to manure particle. Some manure particles will remain in the digester for greater
than the theoretical HRT while some will short-circuit due to the agitation process and exit sooner.
Data collected from one New York State dairy farm that co-digested dairy manure with several non-
farm biomass sources using a complete mix digester showed that the average reduction of the
commonly measured fecal coliform (an indicator organism) and Mycobacterium paratuberculosis
(Johne’s disease) was 98.4 and 94.8 percent, respectively (Wright et al., 2003).
In Denmark, mixing of non-farm biomass materials with manure is common practice and when this is
done, the Danish government requires the food waste/manure mixture to be pasteurized (70°C for
one hour) prior to being land applied in order for the farm to be in compliance with standard manure
application laws. Observation has shown that pasteurization normally occurs at the centralized
digester site, prior to digestion.
36
Operational considerations
Experience has shown that well-designed centralized digesters can be operated successfully for long
uninterrupted periods of time continuously (24 hours per day, seven days per week, and 365 days per
year) when adequate management and maintenance is provided. Centralized digesters are complex and
involve:
Physical systems including containment vessels and influent /effluent pits
Mechanical systems including pumps, agitators, and sensors
Biological systems including methanogens
The daily success of such a system is deeply rooted in personnel who take “ownership” in the system
and are provided the resources needed to make it successful.
General operational challenges for a CAD system include:
Changes in influent composition; Adding variable qualities or quantities of influent can
allow the acid-forming bacteria to out-produce the methanogens. Acidic conditions can
then develop, compromising the stable environment and production of methanogens.
Foaming; Foaming can occur when rising biogas bubbles do not pop when reaching the
manure/biogas headspace interface in the AD. Foaming can be a major issue when
feedstock composition or feeding rates change, most notably on farms when new corn
silage and/or haylage is fed to cows. Excessive foaming can plug the biogas outlet or enter
the biogas line and gum up pressure regulators or other equipment.
Temperature; Maintaining the temperature of the AD is critical to ensure efficient,
operative microbes and consequently consistent quantity and quality (composition) of
biogas. Attention to design of the digester heating system is important to the success of
the overall system.
Frozen manure; Slushy or frozen manure is common in much of the winter in New York
State. Tremendous energy (about 144 Btu’s/lb) is needed to thaw frozen manure and
then to increase the temperature from 32°F to digester operating temperature (~68
Btu’s/lb manure for a mesophilic digester operating at 100°F). In fact, the requirement
37
can be so high that there is not enough heat to bring the manure up to operating
temperature. With lowered temperatures, biogas production decreases, resulting in even
less heat being available. In a CAD system, frozen manure should not pose any problems,
since the manure must be able to be picked up and transported from the farms to the
CAD, within one day.
Control systems; Automatic controls are essential for continuous performance of a
centralized digester system. Proper control equipment selection will allow the system to
be monitored remotely thus providing the opportunity for employees to have a rotating
schedule of weekends off and being “on call”. The digester should have a preventative
maintenance schedule that includes monitoring equipment that creates input data for the
automated control system.
Safety; Centralized digester employees and managers need to be properly trained for the
safety hazards present in the system. There are safety issues of asphyxiation, fire, and
explosion associated with the production of biogas. Methane can explode when mixed
with air in concentrations of 5 to 15% and a fire hazard exists when there are leaks
present in biogas containment materials. Dangerous levels of ammonia and hydrogen
sulfide may also be present. The same hazards associated with large engines and
electrical generation equipment are also present in these systems.
Digestate nutrient recovery
As previously mentioned, anaerobic digestion provides excellent pre-treatment for subsequent
processes to separate and concentrate N, P and K as shown in Figure 7. A centralized anaerobic digester
system can provide more economies of scale thus presenting increased opportunity to do this over
individual farm-based anaerobic digesters.
Separating nutrients into concentrated materials can provide farmers more flexibility in selecting
nutrients that are needed for specific crops and soil conditions. This will further the environmental
benefit of the project by providing such fertilizers in a form that the farmer can more efficiently apply to
cropland and result in higher crop utilization and less environmental impact. Higher application
efficiencies can be obtained by way of 1) reduced trips to the field, thus decreasing the time required to
38
apply organic fertilizer to cropland, and 2) increased timeliness of application resulting in reduced
nutrient loss to the environment.
Figure 7. Advanced digestate treatment to segregate and concentrate nitrogen, phosphorus, and potassium.
Technologies originally developed for treating municipal wastewater are readily available for
removing excessive phosphorous from manure (and a manure- non-farm biomass blend), but the
economics of the implementation of such systems on-farm are not well established.
39
Chapter 2. Literature Review of Centralized AD Projects
A literature review was conducted to assess and identify centralized (AD) feasibility studies for projects
of similar scope as the proposed Lewis County project. There are a number of existing studies that have
been performed to assess the feasibility of large-scale AD projects; a synopsis of the eight most relevant
reports is presented below. The values presented in this chapter for energy production, cow numbers,
and economics, among others, were taken directly from the feasibility reports and were not verified by
those reviewing them. Some of the values taken from these studies do not follow the logic used to
develop these same values throughout the remainder of this report.
St. Albans/Swanton, Vermont Cooperative Dairy Manure Management Project
The St. Albans/Swanton, Vermont area has a high concentration of dairy farms, and was also the site of
Vermont’s Northwest State Correctional Facility. These key considerations, in addition to environmental
concerns such as a need to improve manure-based odors and reduce nutrient run-off (namely
phosphorous reduction) prompted an investigation into the feasibility of a centralized anaerobic
digestion system (Bennett, 2003). This project has not yet been initiated; the results of the feasibility
study have been circulated for additional input. Basic statistics determined in the feasibility study are
included in Table 2.
Table 2. St. Albans/Swanton, VT project statistics
Proposed input material quantity 226,0001 tons dairy manure/year
Proposed number of farms involved 26 farms
Proposed number of cows involved 10,200 cows
Estimated electrical energy production 2,000 kWh/day
Estimated capital cost $6,000,000 ($581/cow)
Expected cash flow + $0.71/ton of manure 1this number, taken directly from the report calculates to 121 lbs manure/cow-day, and a value of 150 lbs/cow-
day was used for this work done in this feasibility report
This project was initially proposed with a specific end user identified. The nearby Northwest State
Correctional Facility housing 250 inmates, consumed 1.28 million kWh/year of electricity at a cost of
$122,000 per year, and used nearly 11.55 billion ft3 of natural gas per year. The report states:
“At first glance, the transportation cost exceeds the value of the electricity produced by the
digester. Only when all the benefits and revenues are compared to the expenses can this project
be fully appreciated. Then, the large environmental and public impacts are added to the
electricity, heat, and by-products to make this a compelling project.”
40
The project feasibility study considered four general designs:
One central digester
Three mini-central digesters (each serving between 2,000 to 5,000 cows)
Several local cooperative digesters (for farms with over 300 animal units10)
Individual farm digesters
The report advocated one central digester for “best economies of scale and knowledge sharing”, and
because it best fit the needs of the end user in terms of energy usage. Transportation costs were
paramount in making this assessment. The report stated that: “reaching additional farms would involve
dramatic increases in mileage with minimal increases in electricity generated; transportation is a major
on-going expense.” Project trucking requirements estimated nine truck drivers, 6-10 facility personnel,
and 2-3 administrators for a total of 17-22 new jobs created by the project (Bennett, 2003).
Lane Renewable Energy Complex
The Lane Renewable Energy Complex (LREC) was a municipal biogas plant and centralized AD facility
proposed in light of environmental and economic concerns in the Eugene and Springfield, Oregon areas
(Weisman, 2008). The LREC was proposed to be “The United States’ first Kyoto-compliant municipal
biogas power plant and public transportation refueling facility.” In addition to biogas, the AD facility was
proposed to provide organic fertilizer for 200,000 acres throughout Lane County and Oregon. The LREC
project has not yet been implemented; adequate funding is currently being sought.
Pollution in the Willamette River and high fertilizer prices were key concerns to be addressed through
the reduction of runoff from un-incorporated manure. In addition, electricity and a nutrient-laden
fertilizer are claimed to be produced by the AD facility. Basic statistics determined in the feasibility
study are included in Table 3.
10
An ‘animal unit equivalent’ or ‘animal unit’ is generally defined as 1,000 pounds of live animal weight. Note: this is an out of date method of expressing animal equivalents; for dairy applications, expressing parameters on a lactating cow basis is appropriate.
41
Table 3. LREC project statistics
Proposed input material quantity 400 tons1 of agricultural waste, food waste (commercial and residential), and municipal wastewater
Estimated gross biogas production 5.5 million ft3 biogas/year
Estimated electrical energy production 8,300 kWh/day
Estimated capital cost $256,000,000
Projected O&M costs $8,400,000/year
Projected annual net revenue $19,500,000 1No units of time provided in report, i.e. tons/year
The proposed biogas plant would consist of 15 two-stage, 1 million-gallon mesophilic digesters with
slurry recirculation. Biogas would be scrubbed to reduce hydrogen sulfide (H2S) and siloxanes (siloxanes
may originate from municipal sources) before being sent by a blower to five Caterpillar 3520 engine-
generator sets, each with a generating capacity of 1,660-kW, or to a vehicle fuel upgrading system.
The proposed project was planned to be a collaboration between: Lane County, EPA, U.S. Economic
Development Administration, USDA, Oregon Department of Energy, Lane Transit District,
ENERGYneering Solutions Inc., Swedish Biogas International, Union Pacific, Lane Community College,
and the Biogas Institute of the Ministry of Agriculture in Chengdu, Sichuan, People’s Republic of China.
It was anticipated the facility would take 24 months to come online, and it was estimated the project
would create 125 high-quality, full-time positions and 400 construction jobs (Weisman, 2008). The
proposed site for the LREC has several important advantages: it is publicly owned, zoned industrial,
located near a natural gas transmission pipeline, and has an existing 5.5 mile sewage pipeline for
wastewater transfer. The project anticipated receiving $65 million in state and federal grants for the
project.
Dane County, Wisconsin Community Manure Facilities Plan
The feasibility study for the Dane County, Wisconsin project examined two clusters of farms in
Waunakee and Middleton, Wisconsin. Within these clusters, two options were considered: anaerobic
digestion and combustion. The County decided to move forward with plans for the anaerobic digestion
option for the Waunakee cluster (Strand, 2008). Basic statistics determined in the feasibility study for
the Waunakee cluster approach are included in Table 4.
42
Table 4. Dane County, WI (Waunakee cluster) project statistics
Proposed input material quantity 152,000 gallons per day
Proposed number of farms involved 5
Proposed number of cows involved 6,000 animal units
Estimated electrical energy production 9,700 kWh/day
Estimated capital cost1 $6,400,000
Projected O&M costs1 $1,000,000
Estimated GHG reduction 19,800 TCO2e/year 1
Based on the lowest levels of phosphorus removal
The Waunakee cluster included five farms with a total of approximately 6,000 animal units. The farms
were located within approximately one-half mile of each other, with additional farms located nearby.
The main goals of the study were “to strengthen the livestock industry in the county and to protect
water quality as related to manure management.” The scope of the study included a survey of area
farms, identification and selection of farms to be used in the analyses as well as a selection of
management alternatives to be studied, technical and economic analyses of these alternatives, and
discussions of financing methods, non-monetary evaluation, and potential business structures of the
proposed project.
In March 2009, Wisconsin Governor Jim Doyle announced that he would allocate $6.6 million to the
Waunakee area digester and a second digester in Middleton. This is in addition to the $1.2 million
already allocated in the 2009 County budget for construction costs associated with the project.
Additional federal money is currently being sought.
Cornell University’s Proposed Anaerobic Digester
The feasibility study examining an AD facility at Cornell University was completed as part of an
undergraduate class research project examining sustainable development on the Cornell University
campus in Ithaca, New York. This study considered two options for biogas use: introduction to a natural
gas pipeline or use of the biogas to power a hydrogen fuel cell. The report advocates the more
expensive fuel cell option over a natural gas pipeline, for its environmental benefits as well as its
educational opportunities on the Cornell University campus (Casey et al., 2007). “While this project may
represent only a small reduction in Cornell’s actual carbon emissions it provides an important early step
on the long and difficult journey to carbon neutrality,” the report states. Basic project statistics
determined in the feasibility study are included in Table 5.
43
Table 5. Cornell project statistics
Proposed input material quantity 6,300 tons organic waste/year, including veterinary school manure, greenhouse wastes, and dining hall food waste.
Estimated biogas production 1.45 x 107 ft3 biogas/year
Estimated capital cost $5,500,000 (over 20 years)
Cornell University hired Stearns & Wheler GHD to further develop the findings of the report, and the
firm has published their feasibility study findings in, Cornell University Renewable Bioenergy Initiative
(CURBI) Feasibility Study.
Evaluation of Anaerobic Digestion Options for Groups of Dairy Farms in Upstate New York
This feasibility study assessed the potential viability of constructing a CAD in York, New York in
Livingston County, to serve several small farms in the region. The suggested measures of the study were
never implemented, the reason(s) is not known. Basic project statistics determined in the feasibility
study are included in Table 6.
Table 6. York, NY project statistics
Proposed input material quantity 164,000 tons manure/year
Proposed number of farms involved 16 farms
Proposed number of cows involved 4,700
Estimated electricity production 650 kWh/day
Estimated capital cost $1,550,000
Projected O&M costs $317,000/year
Projected annual revenue $235,000/year
While several potential project sizes were examined, the projections above consider 4,700 cows
supplying manure to the CAD, since this resulted in the lowest estimated transportation costs. Break-
even benefit at 4,700 cows was $150/cow, derived from the sale of post-digestion products. Since the
value of these products per cow ranged from $200 - $400, revenue was estimated to be $50/cow,
assuming the conservative $200 value per cow ($235,000/year profit in 1997) (Jewell et al., 1997).
Effects of economies of scale were examined in this report. “As the dairy size decreased to 600 milk
cows, the net cost of managing manure increased to over $200 per cow per year (net cost or value
equals fertilizer value less the cost of land application),” the report states. The study recommended
construction of a 4,000 - 6,000 - cow facility as a first step in the York, NY area. Initially, stabilized waste
would be returned to farms. The report advocated for efforts that would reclaim other by-products,
such as fiber, in a cost-effective manner. The report projected a total annual value of the recovered
44
fiber for bedding to be $50 - $200/cow-year (Jewell et al., 1997).
Feasibility Study of a Central Anaerobic Digester for Ten Dairy Farms in Salem, NY
A Salem-based dairy farmer group contracted with Stearns & Wheler, LLC, and Dr. Stanley A. Weeks to
conduct a feasibility study for constructing a centralized AD to cost-effectively treat manure from 10
dairy farms in Washington County New York (Bothi and Aldrich, 2005). Basic project statistics
determined in the feasibility study are included in Table 7.
Table 7. Salem, NY project statistics
Proposed input material quantity 113,000 tons dairy manure/year
Proposed number of farms involved 10 farms
Proposed number of cows involved 3,700 cows
Estimated electricity production 6,600 kWh/day
Estimated capital cost $2,105,000
Projected O&M costs $1,043,000/year
The study considered three design options:
1. Pre-treatment with solid-liquid separation, digestion and separated solids composting
2. Option one with the addition of a centrifuge process to remove additional solids and
nutrients prior to digestion
3. Solid-liquid separation and digestion with no on-site composting
The report recommended option number three, since the per-cow costs were lowest for this option.
Construction of a centralized AD was deemed not economically feasible at the time the report was
written. Trucking costs were a significant component of the total annual cost for all scenarios. Within
each alternative, several options for material transport were examined. The costs of trucking manure
for these scenarios ranged from $384,000/year for one-way trucking (given that the effluent was
pumped off-site to 6-month storage) to $604,000/year for raw manure trucking and effluent trucking
(given 5 days on-site storage) (Bothi and Aldrich, 2005). Furthermore, the potential energy generation
was beyond the electrical needs of the target end-user. Finding a use for the excess power generated
could improve the economic feasibility of this project.
45
Feasibility Study of Anaerobic Digestion Options for Perry, New York
The New York State Energy Research and Development Authority (NYSERDA) provided partial funding
for a feasibility study to assess anaerobic digestion potential among four of the larger neighboring dairy
operations in the Town of Perry, Wyoming County, NY. Wyoming County is the largest milk-producing
county in New York State. The four CAFOs involved in the study cited odor reduction as their primary
goal in pursuing an alternative manure management system (CCE, 2002). Basic project statistics
determined in the feasibility study are presented in Table 8.
Table 8. Perry, NY project statistics
Proposed input material quantity 90,400 gallons dairy manure/day
Proposed number of farms involved 4 farms
Proposed number of cows involved 3,804 lactating cow equivalents
Estimated biogas production 323,500 ft3 biogas/day
Estimated electricity production 519 kW
Estimated capital cost $1,187,000
Projected annual revenue $91,490
The study examined four options: (1) one centralized digester shared by all farms, (2) one digester
shared by two nearby farms, (3) one digester on each farm with collaboration in other ways, such as
through collaborative marketing or joint composting, and (4) collaboration to recruit an independent
business to provide digestion services for farms. The project statistics presented in Table 8 represent
the centralized digestion option considered. The economic analysis for this option was the least
feasible, due to logistical concerns, low energy benefits, and high transportation costs. The report noted
that if electricity could be sold back to the grid as a premium, the economics of the study would change
significantly. The option considering one digester installed on each farm was found to be the most
economically and logistically feasible option at the time of the study. Two digesters were constructed in
2006, one at Sunny Knoll Farm and one at Emerling Dairy (CCE, 2002), and remain operational today.
Feasibility Study for a Port of Tillamook County Dairy Waste Treatment and Methane
Generation Facility
This report was assembled for the Tillamook Methane Energy and Agricultural Development Policy
Committee. In light of the Tillamook Creamery’s capacity to double its cheese production, local dairies
sought to improve manure waste management. Pathogens, water quality issues, and public health
issues resulting from mostly nitrogen-based pollution were cited as important motivators for a
46
reassessment of manure management practices (Edgar, 1991). Basic project statistics are provided in
Table 9.
Table 9. Port of Tillamook project statistics
Proposed input material quantity 57-128 tons dairy manure solids/day
Proposed number of farms involved 191 dairies
Proposed number of cows involved 25,996 cow-units
Estimated electricity production 123,600 kWh/day; 5.15 MW
Estimated capital cost $1,300,532— $5,739, 674
Projected annual O&M $25,558— $1,233,186
Projected annual revenue $52,300
Initial inquiries into accepting sludge from waste treatment plants at both the City of Tillamook and the
Tillamook Creamery found that regulatory complications outweighed the marginal production benefit of
this added waste stream. The report considered several scenarios with varying degrees of three key
variables: percent total solids of the raw waste being hauled (10% or 13%), the extent of manure
collection (50%, 100%), and the percent of the total number of cows’ manure collected (15%, 25%, 50%,
100%, 200%). The report also considered varying scenarios involving one, two, or three digesters.
Ultimately, the best case for net cost was two plants (Edgar, 1991). The facility was ultimately built and
is in operation under the direction of George DeVore at the time of this writing. In 2007, it seemed the
project had transitioned to using heat produced by the system to dry solids and then to sell organic
material (Scott, 2010).
Economic Feasibility Study for a Centralized Digestion System
A web-based model was developed to be used in performing an economic sensitivity analysis for
centralized anaerobic digester projects (Minchoff, 2006). The model found that tipping fees were a
crucial component of overall CAD economic viability. Average landfill tipping fees ($/ton) for
different regions in the United States are presented in Figure 8, and the data is also presented
graphically in Figure 9. As of the last survey, the Northeast had the highest tipping fees when
compared with the rest of the country, at $70.53/ton (Repa, 2005).
47
Figure 8. Landfill tipping fees ($/ton) by region of the U.S. (Repa, 2005)
Figure 9. Landfill tipping fees ($/ton), developed from Figure 8 (Repa, 2005).
Summary
The centralized digester feasibility studies reviewed were mostly initiated due to local concern over
improved manure management, odor reduction, and/or improved nutrient management. For the
studies that involved co-digestion of dairy manure with non-farm biomass substrates, the amount of
energy produced was higher per dollar of capital investment. While many of the studies were not
deemed economically feasible or were otherwise not implemented, several mentioned that valuation of
environmental benefits could potentially improve the economic outlook for some projects, depending
48
on initial goals of the project. Of the feasibility studies reviewed here to look at the practice and
economics of centralized digestion, the common findings of these feasibility studies were:
Economics: Many of the proposed systems were not found to be economically feasible
at the time the studies were conducted. Manure trucking costs were a prohibitively
large component of the estimated annual operating cost. However, the approaches
taken to analyze transportation expenses generally did not include a line item for
tipping fees received by the digester from non-farm biomass suppliers. Several studies
also found the need to develop a valuation system for benefits that are not readily
perceived, i.e., odor reduction or water quality improvement. Many centralized
digester projects take advantage of additional biomass, beyond manure, for co-
digestion which greatly enhances energy production and can usually generate a tipping
fee for the project. Most of the projects described in this chapter were never pursued,
as many sought grant funding to cover capital costs.
Energy production: Most projects reviewed here planned to generate electricity for
sale to, in most cases, one end user/buyer.
Odor: Concern was expressed about the potential for significant odor emissions from
trucking raw manure to the centralized digester site, and the potential of on-site odors
from the centralized digestion facility. Experience has shown that odors associated
with influent materials stored short-term can be mitigated with systems that collect the
off-gases and process them in a bio-filter. Odor reduction was one of the most
common reasons for pursuing centralized AD.
Biosecurity concerns: There is no way to prevent the commingling of sourced manure
and centralized digester effluent needs to be returned to the source farms. Here it is
important to point out that research has shown that anaerobic digestion of dairy
manure significantly reduces viable populations of two tested pathogens that are a
concern for cattle and humans (Wright et al., 2003).
49
Chapter 3. Farm and Community Biomass Survey
The Lowville community AD project was conceived through discussions about what could be done locally
to preserve and preferably to increase the strength of the agriculture industry in Lewis County. A
community manure treatment and processing center was proposed, including an AD centrally located in
Lowville, New York with the goal of providing benefits to three key groups in Lewis County: dairy
farmers, local industry, and residents.
In order to accurately assess the needs of these key groups and to determine the feasibility of meeting
those needs, two surveys were developed by Cornell University’s Manure Management Program and
Cornell Cooperative Extension of Lewis County (CCE-LC).
The dairy farm manure and non-farm biomass surveys served three purposes:
1. Determine the useable quantity, availability, and general composition of existing
biomass (waste) streams
2. Assess the willingness to cooperate among local farmers and businesses
3. Make contacts and compile data for future community involvement
The first survey, distributed by CCE-LC, was a survey of dairy farms that: (1) fell within a 20-mile radius of
Lowville, (2) did not use sand bedding, and (3) had long-term storage. The presence of a long-term
storage at each farm was a key item that was used to select collaborating farms, as farms with a long-
term storage could participate in the project with little additional capital expense.
CCE-LC representatives administered the dairy farm-based surveys by mail in fall 2008. To improve the
response rate, the farm-based surveys were administered again face-to-face in Spring/Summer 2009.
The second survey was a non-farm biomass survey distributed to select local businesses by the Village of
Lowville. Officials from the village of Lowville administered the non-farm surveys in-person in
Spring/Summer 2009. A blank copy of each survey is provided in Appendix B and C.
50
Dairy farm survey
While it was ultimately decided that those farmers who took the time to fill out a survey could be
considered interested or supportive simply because of their decision to participate in the survey, most
of the farmers responded to the “perspective questions” with caution. “If it benefits me,” was a
common reply of the respondents' willingness to provide the proposed CAD project with their manure.
Delivery of nutrient-laden effluent back to each participating farm will likely prove to be an important
determinant of the project’s ultimate success with the farmers. Overall, willingness to cooperate is
heavily dependent on perceived benefits to the farmer.
A summary of the data obtained through the farm survey is shown in Table 10. Information regarding
each farm’s existing manure storage(s), road access, and bedding type(s) is included. Storage, access,
and bedding are all farm characteristics needed to help determine the degree to which a dairy farm
would be able to participate in a community digester project.
51
Table 10. Summary of current (2009) farm survey data
Farm ID number
Distance from
center of Lowville (miles)
Number of
mature cows
Number of
heifers
Lactating cow equivalents (LCE) (total
solids basis)1
Days of short-term
storage available
Months of long-
term storage
available
Bedding type
1* 2 200 150 262 3-4 6 Bedded
pack/shavings
2 6 0 150 62 1 6 Chopped
hay/shavings
3 6 66 10 70 1-3 5 chopped hay
4 7 105 75 136 0 7 chopped hay
5 7 420 40 436 0 2 mattresses, hay
shavings
6* 7 85 70 114 1-3 6 chopped hay
7* 8 150 100 191 1 6 mattresses,
sawdust
8 8 80 80 113 0 6 chopped hay
9 8 620 407 787 2 4 sand, chopped
hay
10 9 145 115 192 1-3 6 chopped hay
11 9 190 160 256 0 6 Sawdust
12* 9 195 160 261 1-3 5 sand, sawdust
13 9 155 150 217 1 6 chopped hay
14* 9 175 80 208 0 5 flat hay
15 10 70 30 82 0 6 Hay
16 10 62 62 87 0 4 chopped hay
17 11 80 70 109 3 12 chopped hay
(sawdust)
18* 11 500 150 562 2 24 dust hay
19 11 400 430 576 0 10 Sawdust
20 12 54 36 69 0 6 chopped hay
21 13 91 60 116 0 6 mattresses, hay
22 13 91 60 116 0 6 chopped hay
23 15 130 35 144 0 6 Sawdust
24 15 85 10 89 0 6 Sawdust
25 18 50 60 75 0 16 Hay
SUM 4,199 2,750 5,327 Farms with an asterisk (*) next to their ID number have either gravel, stone, or paved road access. No asterisk indicates the presence of a dirt road. All farms in the table have on-farm long-term storage. 1LCE values were not provided on the surveys, but were calculated using survey data.
52
Using information provided in the American Society of Agricultural and Biological Engineering (ASABE)
Practices Standard (ASABE, 2005) along with information from the farm surveys, estimates were made
of the daily mass of manure production and composition by farm.
In order to account for the fact that dry cows and heifers produce less manure and volatile solids per
day than lactating cows, the manure quantity and composition produced by each animal management
group is expressed on a lactating cow equivalent (LCE) basis. ASABE Standards (ASABE, 2005) were used
to establish the baseline manure and total solids production for each management group and
adjustments were made for the dry cow and heifer management groups in such a way that their manure
production and total solids were expressed on a lactating cow equivalent basis.
The survey inquired not only about the present situation of each farm, but also requested answers to
each of the questions based on projections of two years (2011) and five years (2014). Based on
responses from the 25 farms that completed the survey, the number of LCEs is projected to increase by
675 cows over two years, and 150 more after five years. When considering a project such as a CAD with
a significant project life (in this case 20 years), it is important to consider the availability of all feedstocks
on a long-term basis. The overall dairy population in Lewis County is expected to increase over the next
two to five years (Vokey, 2010). The survey results based on two and five year projections are provided
in Appendix F.
The survey also asked farms to describe their nutrient balance situation; the responses regarding
nutrient balance are provided in Table 11. The responses showed that nine farms lack the three key
nutrients (N, P, and K), eleven farms have a balanced nutrient situation, and five farms have excess of at
least one of the three key nutrients. Farms with a lack of nutrients, for example, would likely be more
interested in the nutrient-laden effluent produced as a by-product of anaerobic digestion. Select survey
results from the 25 dairy farms who responded to the survey are superimposed on a map of Lewis
County, NY and shown in Figure 10.
53
Table 11. Summary of nutrient balance information as provided in farm surveys
Farm ID number Nitrogen (N) Phosphorus (P) Potassium (K)
1 lack lack lack
2 lack lack lack
3 lack lack lack
4 lack lack lack
5 balanced balanced balanced
6 lack lack lack
7 excess excess excess
8 excess excess excess
9 balanced balanced balanced
10 lack lack lack
11 excess excess excess
12 balanced balanced balanced
13 lack lack lack
14 lack lack lack
15 balanced balanced balanced
16 balanced balanced balanced
17 balanced balanced balanced
18 lack lack lack
19 excess excess excess
20 balanced balanced balanced
21 balanced excess balanced
22 balanced balanced balanced
23 balanced balanced balanced
24 excess excess excess
25 balanced balanced balanced
54
Figure 10. Lowville regional map with collaborating dairy farms superimposed along concentric circles of various radii centered on downtown Lowville.
55
Non-Farm Survey
The non-farm biomass survey asked businesses what type and how much of each waste stream they had
available, and what they currently pay to dispose of it. Also asked in the survey, was how much
contamination (non-biodegradable materials, i.e., plastic forks or aluminum foil) might be found in each
waste stream, which is important to consider when aggregating non-farm biomass for co-digestion.
Eleven local food processors and businesses responded to the survey; however only a few were found to
have a measurable supply of food waste. Results from all eleven respondents are shown in Table 12,
with sources italicized to indicate they were later sampled for laboratory analysis.
A graphical representation of the annual quantity available from select non-farm biomass substrates,
manure from the 25 dairy farms, and manure from the 15 farms selected for the final scenario, is shown
in Figure 11. It is apparent from the figure that the quantity of most of the non-farm biomass substrates
is insignificant when compared to the quantity of manure available. The two non-farm biomass
substrates with the most meaningful quantities are substrates 8 and 10.
56
Table 12. Summary of non-farm biomass survey results
Non-farm biomass
ID Biomass Description Quantity
Estimated annual quantity available (lbs/year)
Approximate disposal costs
($/year) Minimum Maximum
1 mixed food, milk,
napkins, paper plates, straws
3 yd3/day,
September-June 1,009,000 1,009,000 5,000
2 mixed food, liquid, paper
plates
40 gallons pre-consumer/day,
225 gallons post-consumer/day
790,000 806,000 19,400
3 mixed food, oil, grease 25 lbs/day 9,100 9,100 4,100
4 meat, fat, guts 800 - 2,000 lbs/week December-October
17,000 72,000 N/A
5A mixed food
1-5 gallons pre-consumer/day,
5-10 gallons post-consumer/day
13,200 37,500
4,200
5B waste grease 8 gallons/week 2,200 3,750
6 flowers, stems, petals 50 lbs/week, more in December, February,
May 2,400 2,700 N/A
7 mixed food 3 gallons/week, more in
Summer 1,000 1,250 N/A
8
whey/water 28,800 to 36,000
gallons/day 62,400,000 109,500,000 251,000
Clean in Place (CIP) Wastewater
14,400 gallons/week 4,400,000 6,200,000 26,000
9
oil 5 gallons/week 2,000 2,000
2,300 vegetables 2 gallons/week 800 800
meat 1 gallons/week 400 400
mixed product 5 gallons/week 2,000 2,000
10 post-digested sludge 5,037,261
gallons/year 41,900,000 41,900,000 N/A
111 glycerin
150 gallons/day, 5 days/week
339,000 409,000 N/A
Totals 110,000,000 160,000,000 $312,000
Italicized sources denote samples tested for biochemical methane potentials 1The source for non-farm biomass substrate 11 was discovered further along in the project and the information in the table was
provided directly by the substrate supplier
57
Additional biomass sources
The lower than expected quantity of manure discovered in the completed dairy farm surveys, prompted
investigation of additional sources of biomass for co-digestion, in order to increase the gas producing
potential of the AD system. Co-digestion with additional non-farm biomass substrates provides more
benefits to project economics than additional dairy manure. The other biomass sources investigated are
outlined below. Currently, non-farm surveys have been distributed to other local businesses in an
attempt to supplement the currently low available quantities of non-farm biomass substrates.
Sand-bedded and daily-spread dairy farms
The Lowville Digester Work Group inquired about the inclusion of sand-bedded farms in the area, as
potential candidates to increase manure available for digestion. However, for almost all of the farms in
the region of the proposed CAD project, the economies of scale are not present to allow for sand-
manure separation systems to be economically feasible, and for those that it does, sand-manure
separator effluent is too dilute to warrant transporting to a CAD site.
Several relatively small farms within a 15-mile radius of the proposed digester site in downtown Lowville
were not included since they currently practice daily manure spreading and do not currently have
manure storage capabilities.
Figure 11. Quantity (millions lbs/yr.) of substrates (wet weight).
58
Residential food waste
Residential food waste was considered as a potential non-farm biomass substrate, but serious
investigation was postponed in light of the lack of technologies to make this option feasible. Feasibility
of the large-scale collection of residential organic waste would need to be assessed independently, as it
is outside the scope of this project.
Fort Drum
Fort Drum, a large military base north of Lowville, NY is a potential source of organic substrates that was
investigated; however, a phone conversation with a Fort Drum official revealed that they intend to
develop their own waste management system to handle food waste from their centralized dining
facilities.
Energy crops
The availability of growing energy crops for inclusion to the CAD system was also investigated. Lewis
County has few strictly crop farms; those that do exist total approximately 2,400 acres (Lawrence, 2009).
Details about the two farms surveyed are included in Table 13.
Table 13. Select Lewis County crop farm data
Crop farm Farm acreage Crops grown Location relative to central Lowville
A 2,000 1,000 acres corn 500 acres grass 500 acres alfalfa
15 miles north
B 400 150 acres corn
50 acres soybeans1 200 acres alfalfa/grass
12 miles south
1Not considered as an energy crop for this study; the 50 acres of soybeans were added to the acreage of corn, for estimates associated with this study.
Lowville Wastewater Treatment Plant
The Lowville Wastewater Treatment Plant (LWWTP) was suggested as a potential site for the Lewis
County community AD system; therefore, output solids from the LWWTP were investigated as a possible
organic waste input for the CAD facility. The plant has two aerobic lagoons, one with 23 million gallons
of capacity and the second with 21 million gallons of capacity. The average influent to the LWWTP is 1.1
million gallons per day (gpd), but can be as high as 5 million gpd during high precipitation events (Tabolt,
2009). Lagoon number one was drained in 1998, and 2,860 tons of sludge was removed. The plant
59
manager estimated the sludge removal process would take place approximately every 26 years.
According to previous sludge sample analysis, the sludge contains high concentrations of heavy metals
such as lead (Tabolt, 2009). Due to the intermittent availability, heavy metal concentration, and
unknown impact on the AD process, the solids from the LWWTP were not considered to be feasible for
inclusion to the AD facility.
Fallow Ground
Finally, the possibility of digesting several hundred acres of reed canary grass that grows along the Black
and Beaver Rivers in Lewis County was considered. Historically, this acreage has been harvested for
bedding hay, however, difficulties that prevent utilizing this land base on a reliable basis include:
flooding, debris, fragmented ownership, accessibility, timeliness of harvesting and logistics (Lawrence,
2009). For these reasons, this option was ultimately not included in final biomass source estimates.
60
61
Chapter 4. Biomass Sample Collection and Analysis
In this chapter, the collection and analysis of the non-farm biomass samples is described in detail. After
these samples were collected, they were used in analyses to determine their biochemical methane
potential (BMP). In addition to the BMP analysis, sub samples were sent to a laboratory in Syracuse, NY
for nutrient analysis. The results from both analyses are presented, as well as the implications of the
laboratory results. Laboratory test results from BMP analysis were translated to total volume of biogas
that can be expected to be produced by digesting each of the feedstocks available on an individual basis.
These values are important in assessing energy production capabilities and digester vessel sizing
estimates. Also, nutrient implications are presented based on the laboratory nutrient results. Values
such as the annual mass of nutrients returning to collaborating farms are important for nutrient
management and therefore overall digester facility design.
Sample collection
In order to quantify the methane production potential of available non-farm biomass substrates,
samples were collected from the substrate suppliers on July 15, 2009. Six select non-farm biomass
substrates (2, 4, 5A, 5B, 8, and 10) with the highest available volumes, based on survey results, were
chosen to perform biochemical methane potential (BMP) tests. Samples were stored in 1L plastic screw-
top containers, and placed on ice until refrigerated. All efforts were made to obtain a representative
sample under normal operating conditions. A full substrate sampling report is available in Appendix D.
Laboratory Biochemical Methane Potential test (BMP trials)
Six select non-farm biomass substrates from five sources11 were analyzed for biochemical methane
potential (BMP) at Cornell University’s Agricultural Waste Management Laboratory. All samples
collected were analyzed in triplicate for 30 days, with the exception of substrate 4, which was analyzed
with six replicates, due to the high variability of the substrate sample, resulting in seven individual BMP
trials conducted, as listed below. A synopsis of the laboratory procedures for conducting the BMP trials
are provided in Appendix E developed from Labatut and Scott (2008).
11
Substrates 5A and 5B are from the same source
62
Substrate 2
Substrate 4 (six replicates)
Substrate 5A
Substrate 5B
Substrate 8
Substrate 10
Results
An example of the biogas production data from a 30-day BMP assay depicting biogas yield for substrate
4 is shown in Figure 12. The results from the BMP trials are shown in Table 14 in liters of CH4 per kg of
raw substrate for each of the non-farm biomass substrates, and also represented graphically in Figure
13. The minimum and maximum values are one standard deviation below and above the mean,
respectively. The same information (L CH4/kg substrate) was found for manure from “Experimental and
Predicted Methane Yields from the Anaerobic Co-Digestion of Animal Manure with Complex Organic
Substrates” (Labatut and Scott, 2008).
Figure 12. Biochemical Methane Potential (BMP) data (cumulative biogas yield) for substrate 4.
1only four of six replicates shown; other two replicates contained outlying data points.
63
Table 14. Cornell University Agricultural and Waste Management Laboratory BMP analysis results (2009) for all substrates tested
Non-farm biomass substrate ID
Non-farm biomass substrate description
Yield (L CH4/kg raw substrate)
Minimum Maximum Average
5B Waste grease 258 468 363
4 Meat, fat, guts 149 177 163
5A Mixed food scraps 110 118 114
2 Mixed food scraps, liquid 78 85 81
Raw manure1 Dairy farm manure 20 33 27
10 Post-digested sludge 5 10 7
8 Diluted whey and CIP 2 3 2 1Data from Labatut and Scott, 2008
As can be expected, the grease and meat substrates have the highest methane producing potential.
Pre- and post-consumer food scrap wastes were the second highest producers. As observed through
many manure sampling analyses, the biogas producing potential of manure is expected to be low as
compared with many organic substrates. The whey sample was very dilute, which accounts for the low
methane yields, and the post-digested sludge has already undergone a digestion process, which
accounts for the low methane yields from that substrate.
Figure 13. Graphical representation of biochemical methane potentials for all substrates tested. 1Data from Labatut and Scott, 2008.
After the BMP trials concluded at day 30, two of the substrates showed indications that biogas
production could continue – substrates 2 and 5B. The number of days that CH4 was produced by each
substrate is listed below. Although it is unlikely that a community digester would have a hydraulic
1
64
retention time of more than 30 days, it is worth noting the additional biogas producing capabilities of
certain non-farm biomass substrates.
Substrate 8: 28 days CH4 production complete
Substrate 5A: 30 days CH4 production complete
Substrate 5B: CH4 production could continue past 30 days
Substrate 2: CH4 production could continue past 30 days
Substrate 4: 28 days CH4 production complete
Substrate 10: 22 days CH4 production complete
It should be noted that co-digestion of certain organic substrates with manure has the potential to
create a synergistic effect on biogas production; therefore, simply adding the biogas producing potential
of raw manure and each substrate may underestimate potential total biogas production. However,
there can also be antagonistic effects of non-farm biomass substrates as well, due to inhibitory
characteristics that might disrupt the function of the methanogens, responsible for methane production.
Therefore, minimum, maximum, and average values are presented to show a potential range of biogas
producing capabilities. More in-depth laboratory analyses, such as co-digestion studies using bench-
scale reactors, are necessary to determine the expected behavior of each substrate in an operational
CAD.
Glycerin
Non-farm biomass substrate 11 – glycerin – was discovered after the BMP trials had already been
performed. Therefore, the methane potential of glycerin was calculated using theoretical values and
the following values from Lopez (2009): 1,010 g COD/kg substrate, 292 ml CH4/g COD removed, and 85%
biodegradability of glycerin.
Biogas production estimates
The potential quantity and availability of each of the AD feedstocks along with laboratory analyses were
used to calculate the potential total annual biogas production volume. The results of this analysis,
including minimum and maximum values for biogas production, are shown in Table 15.
The results presented in Table 15 for the biogas production projections of each non-farm biomass
substrate, is shown graphically in Figure 14. Non-farm biomass substrates 8 and 10, although low in
65
methane yields, are high in available quantity and therefore result in the highest overall biogas
production potential on an annual basis for the non-farm substrates. The aggregated minimum,
maximum, and average annual biogas production potential for these seven non-farm biomass substrates
and for manure from 25 farms are shown in Figure 15. It is apparent from
Figure 15 that the impact of the non-farm biomass substrates on overall biogas production is very small
in relation to manure, not due to methane yields per unit of influent, but due to the sheer volume
available.
Table 15. Biogas production potential of non-farm biomass substrates and manure
Methane production potential
(million ft3/year)
Feedstock source ID Minimum Maximum Average
2 0.99 1.10 1.04
4 0.04 0.20 0.12
5A 0.02 0.07 0.05
5B 0.01 0.03 0.02
8 1.86 4.77 3.15
10 3.42 6.60 5.01
11 1.36 2.89 2.13
Raw manure 94 156 125
Energy crops
A total of 2,400 acres of energy crops, including alfalfa, grass hay, and silage corn, are estimated to be
available for use in co-digesting with manure for the proposed Lewis County community AD system. A
summary of the biogas production information is presented in Table 16. Unit biogas yields were
provided by Norma McDonald at Organic Waste System, Inc.
Table 16. Potential biogas production of available energy crop acreage
Tons per year Unit biogas yield1
(scf/ton as fed) Annual biogas production
(million ft3/year)
Corn 22,200 5,550 128
Alfalfa and grass 5,400 5,780 30 1Source: McDonald (2010)
66
Figure 14. Estimated annual minimum, maximum, and average methane production by substrate.
Figure 15. Estimated aggregated annual minimum, maximum, and average methane production of non-farm biomass substrates and manure.
67
Laboratory nutrient testing
Sub samples of the six substrates analyzed for co-digestion were sent to the Certified Environmental
Services Laboratory (CES), an EPA certified lab, in Syracuse, NY for nutrient analysis. The laboratory
results are shown in Table 17 and Table 18.
Table 17. CES laboratory results for each non-farm biomass substrate: nutrients
Non-farm biomass substrate ID
Constituent
TKN1 (mg/kg)
NH3-N1
(mg/kg) Organic N1
(mg/kg) TP1
(mg/kg) OP1
(mg/kg) K1
(mg/kg)
2 5,024 496 4,528 571 181 1,234
4 20,493 8,551 11,941 975 979 2,200
5A 14,394 1,200 13,194 1,295 375 2,334
5B 4,122 291 3,831 393 117 1,096
8 195 28 179 187 78 143
10 3,931 796 3,235 1,971 83 593 1TKN: Total Kjeldhal Nitrogen, NH3-N: Ammonia, Organic N: by subtraction (TKN-NH3-N), TP: Total Phosphorus, OP:
Ortho Phosphorus, K: Potassium
Table 18. CES laboratory results for each non-farm biomass substrate: solids
Non-farm biomass substrate ID Constituent
TS1
(%)
TVS1
(%) pH1 VAAA1
(mg/kg)
COD1
(mg/kg)
2 16 15 4.05 1,602 201,192
4 25 22 6.95 13,317 382,992
5A 35 31 4.29 2,075 385,416
5B 97 92 6.00 653 187,860
8 0.51 0.35 5.22 98 3,636
10 6 4 7.83 359 44,844 1TS: Total Solids, TVS: Total Volatile Solids, VAAA: Volatile acids as acetic acid, COD: Chemical oxygen
demand
Glycerin
Since this non-farm biomass substrate was not identified until after the testing phase of the project was
completed, the total annual mass of N, P, and K imported to the CAD site from this material was
estimated by using nutrient concentration data from an un-publishable source. Since glycerin products
vary widely depending upon source and purity, further analysis of the glycerin product specific to this
project is recommended. Nutrient concentrations for the three key nutrients, N, P, and K in glycerin
used in this analysis were: 100, 1, and 0 pounds per 8,000 gallons glycerin, respectively.
68
Manure
Manure nutrient concentrations were estimated using ASABE standard manure production values, as
provided in Chapter 1. The mass of the three key nutrients, N, P, and K in manure are: 0.99, 0.17, and
0.23 pounds per cow per day, respectively (ASABE, 2005).
Nutrient implications
The estimated minimum and maximum quantities available (Table 12) and the laboratory data for each
non-farm biomass substrate were used to determine the total mass of each nutrient parameter in the
raw non-farm biomass substrates on an annual basis. The total number of LCEs available from the 25
farm surveys received was used in conjunction with the standard values for nutrient concentrations in
manure. The resulting mass of nutrients from both manure and non-farm biomass sources, on a pre-
digestion basis, are provided in Table 19 for the N series, and Table 20 for the P and K series.
Table 19. Estimated annual mass of nitrogen series for raw AD feedstock
Non-farm biomass substrate
Raw Substrate TKN (lbs/year)
Raw Substrate Ammonia-N (lbs/year)
Raw Substrate Organic Nitrogen (lbs/year)
Minimum Maximum Minimum Maximum Minimum Maximum
2 3,980 4,050 390 400 3,580 3,650
4 350 1,480 150 620 200 860
5A 190 540 16 45 170 500
5B 10 15 1 10 15
8 13,050 22,600 1,870 3,240 11,980 20,740
10 165,100 33,430 135,920
11 490 - -
Raw manure1
1,925,000 - - 1manure from 25 farms
Table 20. Estimated annual mass of phosphorus and potassium series for raw AD feedstock
Non-farm biomass substrate
Raw Substrate Total Phosphorus (lbs/year)
Raw Substrate Ortho Phosphorus (lbs/year)
Raw Substrate Potassium (lbs/year)
Minimum Maximum Minimum Maximum Minimum Maximum
2 450 460 140 150 980 1,000
4 20 70 17 70 40 160
5A 20 50 5 14 30 90
5B 1 0 2 5
8 12,540 21,700 5,220 9,040 9,590 16,600
10 82,790 3,470 24,930
11 5 - 0
Raw manure1
330,500 - 447,160 1manure from 25 farms
69
Since the values shown in Table 19 and Table 20 are for raw non-farm biomass substrates, estimates
must be used to quantify the post-digestion concentration of the same nutrients; these values are
shown for the nitrogen series in Table 21 and for the phosphorus and potassium series in Table 22. The
values for post-digested nutrient concentrations were estimated using a percent change value for each
nutrient parameter from previous manure and substrate sampling and monitoring of five digester
systems including one co-digestion system (Gooch et al., 2007). Results indicate that on average,
ammonia-N increases in concentration by 23.4%, organic nitrogen decreases in concentration by 15.9%
and ortho-phosphorus increases in concentration by 14.4% (Gooch et al., 2007). It is assumed that the
mass of total nitrogen, total phosphorus and potassium do not change as a result of the anaerobic
digestion process. A comparison of pre- and post-digestion nutrient concentrations is shown in Figure
16 for the N, P, and K nutrient series for the non-farm biomass substrates. As can be observed there is
no change in the concentration of the major forms of these nutrients, however, for ammonia-N, organic
nitrogen, and ortho-phosphorus, there is a slight increase in concentration due to the digestion process.
Table 21. Predicted annual mass of nitrogen series for post-digested AD feedstock
Non-farm biomass substrate
Post Digestion TKN (lbs/year)
Post Digestion Ammonia-N (lbs/year)
Post Digestion Organic-N (lbs/year)
Minimum Maximum Minimum Maximum Minimum Maximum
2 3,980 4,050 480 490 4,150 4,230
4 350 1,480 180 760 230 1,000
5A 190 540 20 60 200 570
5B 10 15 1 10 15
8 13,050 22,590 2,310 4,000 13,880 24,020
10 165,140 41,240 157,460
11 490 - -
Raw manure1
1,924,730 - - 1manure from 25 farms
70
Table 22. Predicted annual mass of phosphorus series and potassium for post-digested AD feedstock
Non-farm biomass substrate
Post Digestion Total Phosphorus (lbs/year)
Post Digestion Ortho Phosphorus (lbs/year)
Post Digestion Potassium (lbs/year)
Minimum Maximum Minimum Maximum Minimum Maximum
2 450 460 160 170 980 1,000
4 20 70 20 80 40 160
5A 20 50 10 20 30 90
5B 1 0 2 5
8 12,540 21,700 5,970 10,340 9,590 16,610
10 82,790 3,970 24,930
11 5 - 0
Raw manure1
330,510 - 447,160
1manure from 25 farms
Figure 16. Nutrient concentrations for pre- and post-digestion conditions for N, P, K.
71
Chapter 5. Biomass Transportation The literature search performed for existing centralized digester feasibility studies (see Chapter 1)
revealed that transportation costs are usually the largest operating cost component of a CAD. The
approach used in these studies to determine the overall transportation costs were 1) unit cost per gallon
and 2) unit cost per gallon-mile.
For the purposes of this feasibility study, transportation of material to and from each participating farm
and the CAD facility was explored in two different ways, through the use of a project-owned and
operated trucking fleet, and by contracting with an existing trucking company. Each option was
investigated for the proposed Lewis County CAD facility feasibility study and is discussed below. Overall,
it was determined that the best option would be to contract with an existing trucking company.
Transportation costs were based on a methodology that used the estimated time required to pump and
to load or unload a 6,000-gallon truck with a 500 gallon per minute (gpm) truck-mounted pump. The
comparison of trucking options presented is based on participation of all 25 dairy farms who responded
to the survey, however, regardless of which final digestion scenario is chosen, the final determination
remains the same, that it is less costly to contract with an existing trucking company for the proposed
project.
Whether choosing a contracted or an owned trucking fleet, the process and assumptions that are made
for transporting manure from the farms and CAD effluent back, are the same. Manure is picked up from
the short-term storage at each farm, and transported to the CAD facility, at a cost to the project; this
service would be of no cost to the farms. Non-farm biomass substrates incorporated for co-digestion
are not transported through the same means as manure from farms. It is assumed that the substrate
suppliers would continue to be responsible for trucking their waste and paying a tipping fee to the
project. Effluent from the CAD facility would be trucked by the project back to the participating farms,
and deposited in a long-term storage at each farm. The return trucking volumes would consist of both
the manure and non-farm biomass substrates delivered by the substrate suppliers. There is the
possibility to further explore delivery of CAD effluent to satellite storages for each farm, where the
effluent would be delivered to a location more central to the farm’s cropping activities.
72
Owned Trucking Fleet
The first option regarding material transportation to and from participating farms is to create an in-
house trucking division to be owned and operated by the project. In order to handle the manure from
participating dairy farms, it was determined that six 6,000-gallon truck-mounted tanker trucks would be
needed with a 500 gpm truck-mounted pump, with a capital cost of $165,000 per truck (Mack Trucks,
2009), for a total initial cost of $990,000. In addition, it would cost approximately $450,000 (estimated
at $30/ft2) to construct a 15,000 ft2 building to house a maintenance shop, clerical support, employee
amenities (locker and break rooms), and $75,000 (estimated at $5/ft2) for start-up equipment, tools and
computers.
Necessary staff includes six drivers, one clerical person, and one maintenance person for a total of eight
project-related jobs that would be created. Annual labor expenses for the in-house fleet drivers were
calculated using a draft schedule for collection and delivery to/from each farm and the proposed CAD
facility located in downtown Lowville. Costs for fuel, truck maintenance, parts, utilities, insurance and
general overhead are also included in the annual operating cost estimate, which is shown in Table 23.
Table 23. Capital and annual cost estimates for a project-owned trucking fleet
Capital cost ($) Annual Cost ($)
One 6,000 gallon truck 165,000 8,500
6 trucks 990,000 51,000
Fuel cost 19,500
Maintenance Building 450,000 12,000
Equipment/Furnishings 75,000
Driver salary 45,000
6 drivers 270,000
Administrative salary (1) 30,000
Maintenance person salary (1) 40,000
Total $1,515,000 $422,500
In summary, the capital cost estimate for the project-owned trucking fleet scenario is $1,515,000 and
annual operating costs are estimated to be $422,500.
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Contracted Trucking Fleet
The second option regarding material transport to and from participating farms is to enter into a
contract with a private waste hauler. Shue Trucking based in Port Leyden, NY was contacted to obtain
cost estimates and to provide technical feasibility information. Shue provided a quote of $82 per hour
for a driver and truck with all required accessories. The annual cost projections were based upon a
6,000-gallon truck with a 500 gpm truck-mounted pump. Projected total annual volumes of manure and
non-farm biomass substrates were utilized to determine the number of trips required per year to service
all 25 participating farms. The same loading and unloading time requirements were used as for the
project-owned fleet calculations in determining the necessary annual trucking time. An example used to
calculate costs for the contracted fleet scenario is shown in Table 24.
Table 24. Contracted trucking fleet example schedule
Farm ID
Distance from
digester (miles)
Volume manure
to digester (gal/day)
Volume influent
to digester annually
(gal/year)
No. of trips from farm to
digester annually
miles influent trucked annually
Hours per trip
Hours per year
Cost ($/hour)
Annual cost to
transport influent
1
to AD ($/year)
1 2 4,710 1,804,680 300 600 0.75 230 $82 $18,500
2 6 1,110 424,430 70 420 1 70 $82 $5,800
5 7 7,860 3,011,710 500 3,510 1 500 $82 $41,160
7 8 3,440 1,318,140 220 1,760 0.75 170 $82 $13,510 1Only influent trucking costs represented in this table
In summary, there is no trucking-related capital costs associated with the contracted trucking fleet
scenario. The estimated annual operating cost based on 25 farms for the contracted fleet scenario is
$1,260,000 if using the minimum volume of manure and non-farm biomass substrates available (110
million lbs/year). The estimated annual operating cost based on 25 farms for the contracted fleet
scenario is $1,350,000 if using the maximum volume of manure and non-farm biomass substrates
available (160 million lbs/year).
Manure and Digestate Trucking
The location of the 25 collaborating farms can be revisited in Figure 10. When developing scenarios with
a reduced number of farms, the criteria used was whether those farms produced at least 3,000 gallons
of manure per day. It was assumed that a mass of 3,000 gallons of manure stored for one day in the
winter would not be likely to freeze, whereas a smaller amount might, as indicated by several of the
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farm-based surveys. Collaborating farms would not be charged a transportation fee for trucking
material between their farm and the digester; this cost would be covered by revenue (tipping fee)
received from non-farm biomass disposed of at the digester site.
It is important to note that a 5% increase in the calculated volume of manure associated with each farm
was assumed, to account for washwater and other biomass co-mingled with manure at the farm prior to
project pick-up. Also, the assumption was made that there is a 3% reduction of overall influent volume
due to the digestion process, and that effluent from the CAD would consist of digested manure and non-
farm biomass substrates. Assuming less than a 3% reduction would result in higher trucking costs. The
CAD effluent would be a higher volume than the manure initially trucked to the CAD facility, and each
participating farm would receive a weighted amount of this additional volume as digester effluent. The
resulting aggregated volume would be trucked back to participating farms.
Non-farm Biomass Substrate Trucking
It is assumed that substrate suppliers would provide transportation of their biomass by-products from
their business location to the AD facility at their expense. This is a safe assumption to make since the
substrate suppliers currently have to pay trucking costs to transport their organic by-products to a
disposal site. Tipping fees, needed to cover manure transportation expenses, are intended to be
charged to substrate suppliers only, and not to participating farms, as can be seen in Figure 17.
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Figure 17. Diagram of estimating a break-even tipping fee for non-farm biomass substrate suppliers.
76
77
Chapter 6. Preliminary Investigation of Five AD Scenarios One apparent reason for many proposed CAD facilities not being implemented is the cost to transport
manure and digestate between collaborating farms and the CAD site. Therefore, the following five
scenarios were developed based on the survey data from the initial feasibility investigation with specific
emphasis on transportation costs, biogas production, and biogas utilization options. The information
contained in this chapter was presented as an interim report to the Lowville Digester Work Group at a
December 2009 meeting.
Scenario No. 1: co-digest manure from 25 dairy farms (see Figure 10), and seven non-farm
biomass substrates (2, 4, 5A, 5B, 8, 10, 11) at a central location (Site 1) adjacent to the
Lowville wastewater treatment plant (see Figure 18)
Scenario No. 2: co-digest manure from 14 dairy farms, and three non-farm biomass
substrates (8, 10, 11) at a central location (Site 1) adjacent to the Lowville wastewater
treatment plant (see Figure 18)
Scenario No. 3: co-digest manure from 12 dairy farms, and one non-farm biomass
substrate (8) at Site 2 (see Figure 19), and co-digest manure from four dairy farms and two
non-farm biomass substrates (10, 11) at Site 3 (see Figure 20)
Scenario No. 3a: identical to Scenario No. 3, except that at Site 2 manure from five of the
12 farms would be piped to the digester site, and at Site 3 manure from two of the four
farms would be piped to the digester site
Scenario No. 3b: same as Scenario No. 3 with 400 acres of energy crops digested at Site 2
and 2,000 acres of energy crops digested at Site 3
Each scenario and the investigation results were the core of an interim project report presented to the
Lowville Digester Work Group on December 18th, 2009 (details in the remainder of this chapter). As a
result of that presentation, the Lowville Digester Workgroup decided that Scenario No. 2 should be
more fully investigated and the results of that complete investigation are detailed in Chapter 7.
78
The remainder of this Chapter provides baseline information used in evaluating all five scenarios,
additional details about each scenario analyzed, and analysis results (transportation cost, biogas
production, and biogas utilization options) used in part to select one scenario to perform a full economic
evaluation. The corresponding process flow diagram(s) for each scenario includes average feedstock
and effluent volumes, trucking cost, biogas production, electricity and heat generation that represent
the average of the minimum and maximum values.
Figure 18. CAD Site 1 for Scenario Nos. 1 and 2.
Proposed CAD site
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Figure 19. Remote AD Site 2 for Scenario Nos. 3, 3a, and 3b.
Proposed CAD site
80
Figure 20. Remote AD Site 3 for Scenario Nos. 3, 3a, and 3b.
Background for All Scenarios
In each scenario, biogas produced could be used as:
A thermal heat source to fuel a boiler to produce hot water
A fuel source for an engine-generator set to produce electrical power
A renewable alternative to natural gas after being scrubbed
For the centralized scenarios (Scenario Nos. 1 and 2), biogas that has been processed by gas-clean up
equipment could also potentially be injected into a natural gas pipeline as biomethane. Any of the
resulting forms of energy could be sold to one or more buyers; however, for the de-centralized regional
digesters scenarios, sale of energy to one main buyer may not be practical. Biogas production volumes
were determined at STP (0°C and 1 atm), and heat content was calculated using the lower heating value
of methane at STP which is 896 Btu/ft3 and a concentration of 60% CH4 (Marks, 1978).
Proposed CAD site
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Scenario No. 1
Scenario No. 1 consists of one CAD system located at Site 1, adjacent to the Lowville Wastewater
Treatment Plant (LWWTP) in downtown Lowville, as shown in Figure 18. Manure from 25 nearby dairy
farms would be trucked by the project from each farm to the proposed Lewis County community CAD
facility (See Table 10 for details of the 25 farms). Seven non-farm biomass substrates with the highest
volumes (2, 4, 5A, 5B, 8, 10, 11) out of the 11 non-farm biomass sources initially surveyed would be co-
digested. Figure 21 shows a simplified process flow diagram for Scenario No. 1.
Figure 21. Process flow diagram for Scenario No. 1 using the average annual total volume of the seven non-farm biomass substrates.
The following are additional project values determined according to the details of Scenario No. 1:
Average annual mass of non-farm biomass substrates: 134 million lbs/year (16 million gallons/year)
o Minimum: 110 million lbs/year (13 million gallons/year)
o Maximum: 160 million lbs/year (19 million gallons/year)
Average annual total AD feedstock mass: 440 million lbs/year (53 million gallons/year)
o Minimum: 416 million lbs/year (50 million gallons/year)
o Maximum: 465 million lbs/year (56 million gallons/year)
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Average annual manure influent and CAD effluent transportation costs: $1,305,000
o Minimum: $1,260,000
o Maximum: $1,350,000
Average annual volume biogas produced: 228 million ft3/year
o Minimum: 170 million ft3/year
o Maximum: 287 million ft3/year
Average annual volume methane produced: 137 million ft3/year
o Minimum: 102 million ft3/year
o Maximum: 172 million ft3/year
Substrate tipping fee needed: $0.08 per gallon
Scenario No. 2
Scenario No. 2 consists of a centralized digester located at Site 1, as in Scenario No. 1, however with
select farms and select non-farm biomass substrates. Instead of the 25 dairy farms, Scenario No. 2
would involve digesting manure from 14 surveyed dairy farms, chosen for those farms’ ability to
produce at least 3,000 gallons of manure per day. The three non-farm biomass substrates with the
highest volumes (8, 10, 11), out of the 11 sources initially surveyed, would be co-digested with the
manure. Figure 22 shows a process flow diagram for Scenario No. 2. For complete details on the final
Scenario No. 2, please also see Chapter 7.
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Figure 22. Process flow diagram for Scenario No. 2 using the average annual total volume of the three non-farm biomass substrates.
The following are additional project values determined according to the details of Scenario No. 2:
Average annual mass of non-farm biomass substrates: 134 million lbs/year (16 million gallons/year)
o Minimum: 109 million lbs/year (13 million gallons/year)
o Maximum: 158 million lbs/year (19 million gallons/year)
Average annual total AD feedstock mass: 372 million lbs/year (45 million gallons/year)
o Minimum: 348 million lbs/year (42 million gallons/year)
o Maximum: 397 million lbs/year (48 million gallons/year)
Average annual manure influent and CAD effluent transportation costs: $1,120,000
o Minimum: $1,070,000
o Maximum: $1,170,000
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Average annual volume biogas produced: 188 million ft3/year
o Minimum: 140 million ft3/year
o Maximum: 237 million ft3/year
Average annual volume methane produced: 113 million ft3/year
o Minimum: 84 million ft3/year
o Maximum: 142 million ft3/year
A substrate tipping fee needed: $0.07 per gallon
Scenario No. 3
Scenario No. 3 consists of two decentralized regional digesters, one located north of Lowville (Site 2) and
one located south of Lowville (Site 3). Site 2 would digest manure trucked by the project from 12 of the
25 dairy farms, chosen for their proximity to AD Site 2. Site 3 would digest manure trucked by the
project from four of the 25 dairy farms chosen for their proximity to AD Site 3. Site 2 would co-digest
substrate number 8, the highest volume non-farm biomass substrate that is closest to AD Site 2. Site 3
would co-digest substrate numbers 10 and 11, the highest volumes of non-farm biomass substrates, in
proximity to AD Site 3. A simplified process flow diagram for Scenario No. 3 is shown in Figure 23.
85
Figure 23. Process flow diagrams for Scenario No. 3 using the average annual total volume of the three non-farm biomass substrates for Site 2 and Site 3. All manure and digestate are trucked. The following are additional project values determined according to the details of Scenario No. 3:
Minimum annual mass of non-farm biomass substrates for both sites: 109 million lbs/year (13 million
gallons/year)
o Site 2: 67 million lbs/year (8 million gallons/year)
o Site 3: 42 million lbs/year (5 million gallons/year)
Maximum annual mass of non-farm biomass substrates for both sites: 158 million lbs/year (19 million
gallons/year)
o Site 2: 116 million lbs/year (14 million gallons/year)
o Site 3: 42 million lbs/year (5 million gallons/year)
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Minimum annual manure influent and CAD effluent transportation costs for both sites: $684,000/year
o Site 2: $477,000/year
o Site 3: $207,000/year
Maximum annual manure influent and CAD effluent transportation costs for both sites: $740,000/year
o Site 2: $533,000/year
o Site 3: $207,000/year
Average annual volume biogas produced for both sites: 191 million ft3/year
o Site 2: 125 million ft3/year
o Site 3: 66 million ft3/year
Average annual volume methane produced for both sites: 114 million ft3/year
o Site 2: 75 million ft3/year
o Site 3: 39 million ft3/year
Average substrate tipping fee needed:
o Site 2: $0.05 per gallon
o Site 3: $0.04 per gallon
Scenario No. 3a
All aspects of Scenario No. 3a are identical to Scenario No. 3, except that Scenario No. 3a utilizes
a combination of pumping and trucking manure and digestate to/from collaborating farms and
the remote digester sites. Certain farms appear near enough to the proposed remote AD sites
to logically envision that manure may be piped, with the hopes that overall transportation cost
would be lessened by pumping approximately 33% of the total available manure. Table 25
shows which farms would potentially pipe and truck manure according to Scenario No. 3a.
Figure 24 shows a process flow diagram for Scenario No. 3a.
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Table 25. Scenario No. 3a means of manure and digestate transport
Remote Site 2 (Northern site) Remote Site 3 (Southern site)
Farm ID lbs/day 3a. Transport Farm ID lbs/day 3a. Transport
5 65,460 Trucked 4 20,363 Trucked
6 17,055 Trucked 9 118,031 Trucked
7 28,650 Piped 10 28,823 Piped
8 16,920 Piped 11 38,340 Piped
12 39,090 Piped 205,556
13 32,475 Piped
14 31,170 Piped
17 16,305 Trucked
18 84,225 Trucked
19 86,445 Trucked
21 17,340 Trucked
23 21,653 Trucked
456,788
Figure 24. Process flow diagram for Scenario No. 3a using the average annual total volume of three non-farm biomass substrates for Site 2 and Site 3. Manure and digestate are pumped and trucked.
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The following are additional project values determined according to the details of Scenario No. 3a, a
hybrid scenario of manure both piped and trucked from 16 farms to two regional digesters in different
locations.
Minimum annual manure influent and CAD effluent transportation costs for both sites: $539,000/year
o Site 2: $375,000/year
o Site 3: $164,000/year
Maximum annual manure influent and CAD effluent transportation costs for both sites: $599,000/year
o Site 2: $435,000/year
o Site 3: $164,000/year
A substrate tipping fee needed:
o Site 2: $0.04 per gallon
o Site 3: $0.03 per gallon
The costs associated with piping manure and digester effluent between selected farms, shown in Table
25, were not calculated prior to the Dec. 18, 2009 project meeting, and based on the selection by the
Lowville Digester Workgroup to focus on Scenario No. 2, no effort was subsequently made to finish out
the preliminary investigation of this option.
Scenario No. 3b
Scenario No. 3b was developed to examine the effect of including a separate energy crop digester at
each of the two regional digester sites. The same dairy farms and non-farm biomass substrates would
be used to provide material to each of the decentralized regional AD locations as was outlined in
Scenario No. 3. Field crops from crop farm A would be ensiled and digested at Site 2, while field crops
from crop farm B would be digested at Site 3. There would be two digester systems at each de-
centralized site. Figure 25 shows a simplified flow diagram for Scenario No. 3b, with some details
removed for clarity; these details are provided in bullet form following the figure.
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Figure 25. Process flow diagram for Scenario No. 3b using the average annual total volume of three non-farm biomass substrates for Site 2 and Site 3. The following are additional project values determined according to the details of Scenario No. 3b; all
other substrate volumes are identical to Scenario No. 3:
Average annual volume of effluent for Site 2: 35 million gallons/year
o Manure/substrate AD: 31 million gallons/year
o Energy crop AD: 4 million gallons/year
Average annual volume of effluent for Site 3: 15 million gallons/year
o Manure/substrate AD: 14 million gallons/year
o Energy crop AD: 1 million gallons/year
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Minimum annual manure influent and CAD effluent transportation costs for both sites: $704,000/year
o Site 2: $491,000/year
o Site 3: $213,000/year
Maximum annual manure influent and CAD effluent transportation costs for both sites: $759,000/year
o Site 2: $546,000/year
o Site 3: $213,000/year
A substrate tipping fee needed:
o Site 2: $0.05 per gallon
o Site 3: $0.04 per gallon
A summary of the initial investigation of the five scenarios is provided in Table 26. As was mentioned at
the beginning of this chapter, the Lowville Digester Work Group selected Scenario No. 2 to perform
additional investigation and a complete economic analysis. The two main reasons that Scenario No. 2
was selected by the Workgroup were, it provided:
1. Increased opportunities for energy utilization produced by the CAD system, and
2. Increased opportunities for post-digestion treatment of effluent that would benefit
collaborating farms.
There is less risk involved with a centralized AD option as opposed to the de-centralized regional
digesters described in Scenario No. 3, since the project could likely still proceed even if a few of the
farms decided at some point to discontinue participating. Scenario No. 2 would allow for energy
capture from one system, which could be sold to one main buyer. Also, if it is discovered that nutrient
concentrations in the effluent stream need to be adjusted, this scenario allows there to be one point
where this could be done. The Work Group requested that an energy crop digester, located at Site 1 be
included in the full analysis.
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Table 26. Comparison of the five AD scenarios
Scenario No.
No. of feedstock sources
Average AD feedstock mass
(million lbs/year)
Average volume biogas
produced (million
ft3/year)
Average raw manure and CAD effluent
transportation costs
Tipping fee
needed ($/gallon)
1 25 farms,
7 non-farm biomass substrates
440 228 $1,303,000 $0.08
2 14 farms,
3 non-farm biomass substrates
372 188 $1,120,000 $0.07
3
Site 2: 12 farms, 1 non-farm biomass substrate
Site 3: 4 farms, 2 non-
farm biomass substrates
375 191 $684,000 $0.05
3a Same as Scenario
No. 3 375 191 $599,0001 $0.04
3b
Site 2: 12 farms, 1 non-farm biomass substrate,
crop farm A
Site 3: 4 farms, 2 non-
farm biomass substrates, crop farm B
420 344 $732,000 $0.05
1Does not include cost to pump manure and digestate.
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93
Chapter 7. Final AD Scenario Selection Analysis and Results
Overview
As mentioned in the previous chapter, the Lowville Digester Work Group decided during the December,
2009 interim report meeting that Scenario No. 2 was the best scenario of those initially developed and
investigated based on the initial goals they had outlined at the onset of the project (see Introduction)
and the findings developed to date for presentation at that meeting.
Scenario No. 2 as described in the previous chapter was slightly altered to include one additional farm
for the final analysis (15 total farms). During the December meeting, the Lowville Digester Work Group
also requested an analysis of an energy crop digester (co-located at the same site but as a separate
system, due to AD design specifications based on material handling requirements) be performed to
determine the increase in biogas available from the facility. Both the Scenario No. 2 manure/non-farm
biomass CAD and the energy crop digester analysis are based on two separate systems co-located at Site
1, adjacent to the LWWTP.
Scenario No. 2 manure/non-farm biomass CAD is based on manure from the 15 identified
collaborating dairy farms (listed by farm ID in Table 27) and 3 non-farm biomass
substrates with the highest volumes available (8, 10, and 11) out of the 11 surveyed. The
15 farms were chosen for their ability to produce at least 3,000 gallons of manure per day
(justification in Chapter 5). A process flow diagram for Scenario No. 2 is shown in Figure
26.
The energy crop digester is based on two crop farms (A, B) that would supply corn silage
and grass and alfalfa to the site and ensile it for use in constantly feeding the energy crop
digester. A process flow diagram for the energy crop digester is shown in Figure 27.
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Figure 26. Final Scenario No. 2 process flow diagram.
Figure 27. Energy crop anaerobic digester process flow diagram.
Table 27. Scenario No. 2 participating farms and associated manure generation
Farm ID LCEs lbs/day
1 262 39,225
2 62 9,225
5 436 65,460
7 191 28,650
9 787 118,031
10 192 28,823
11 256 38,340
12 261 39,090
13 217 32,475
14 208 31,170
16 87 13,113
18 562 84,225
19 576 86,445
21 116 17,340
23 144 21,653
4,355 653,264
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Transportation
The Lowville CAD project includes transporting manure from collaborating dairy farms to the CAD site
and digestate back to the farms. Non-farm biomass substrates would be trucked to the CAD facility at
the supplier’s expense. The initial transportation assessment for the project centered on whether to
contract with an existing trucking company, or to initiate a trucking division as part of the overall
centralized AD project (details in Chapter 5). It was determined that initially contracting with an existing
trucking company would be more cost effective to the project and provide lower financial risk. At some
point after project start-up, when the economic implications of the project are clear, it will be prudent
to re-evaluate the option of a project-owned trucking fleet to transport material between the farms and
the Scenario No. 2 CAD site.
Based on contracting with an existing fleet, the trucking costs were estimated based on transporting
manure from the dairy farms to the CAD site, and effluent back to participating dairy farms. The
estimated annual trucking costs for Scenario No. 2 manure/non-farm biomass CAD are between
$1,100,000 (minimum substrate assumed) and $1,200,000 (maximum substrate assumed).
As explained in Chapter 5, each dairy farm would receive a higher volume of CAD effluent as compared
with the manure volume provided, as determined by using a weighted basis calculation for each farm;
this is shown in Figure 28.
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Figure 28. Comparison of the volume of manure sent to the CAD and volume of CAD effluent received, by farm.
It is important to consider the impacts of additional traffic a project of this magnitude would have on
the community. For the manure and non-farm biomass CAD, there would be an estimated 13,000 loads
per year brought by the 6,000-gallon manure tankers; this amounts to approximately 35 loads per day
transported through town. It is not known at this time the specific impacts to certain routes, or
upgrades that would be necessary to local infrastructure, i.e., bridges.
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Anaerobic Digestion
The feedstock volumes for Scenario No. 2 are shown in Table 28. Under Scenario No. 2 manure/non-
farm biomass CAD, there are three non-farm biomass substrates that would be co-digested with manure
from 15 collaborating farms. The mass of feedstock available for inclusion to the proposed energy crop
digester was proposed to be co-digested with a portion of the manure (10% of that in the manure/non-
farm biomass CAD), and is also presented in Table 28. Minimum and maximum potential substrate
volumes for all feedstocks were quantified in order to develop a range in quantities available.
Table 28. Scenario No. 2 feedstock volumes
1Based on varying specific gravities, since the purity of the glycerin substrate is unknown
Table 29 contains the minimum, maximum and average values for the potential methane and biogas
production for each individual feedstock, as well as for the total substrate quantity, in the Scenario No. 2
manure/non-farm biomass CAD. The CAD in this scenario is projected to produce on average, 113
million ft3 of methane annually with a thermal value of 101,000 million Btu’s.
Potential quantity
(gal/day) Potential quantity
(lbs/day) Availability (days/year)
Potential quantity available
(million lbs/year)
Feedstock source
Min Max Min Max Min Max Min Max Ave
8 31,000 38,000 257,000 317,000 260 365 66.8 115.7 91.2
10 13,800 13,800 115,000 115,000 365 365 42 42 42
11 150 150 1,300 1,6001 260 260 0.34 0.41 0.37
Subtotal 110 160 135
crop farm A 100,000
100,000 365 365 37 37 37
crop farm B 20,000 20,000 365 365 7.4 7.4 7.4
Subtotal 44.4 44.4 44.4
100% Manure 78,000 78,000 653,000 653,000 365 365 238 238 238
Total 392 441 416
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Table 29. Potential methane and biogas production volumes for each feedstock in Scenario No. 2 CAD
Feedstock source
Minimum methane (million ft
3/year)
Maximum methane (million ft
3/year)
Average methane (million ft
3/year)
Minimum biogas
(million ft
3/year)
Maximum biogas
(million ft
3/year)
Average biogas
(million ft
3/year)
8 1.9 4.8 3.3 3.1 8 5.5
10 3.4 6.6 5 5.7 11 8.4
11 1.4 2.9 2.1 2.3 4.8 3.5
Total substrate 6.7 14.3 10.4 11.1 23.8 17.2
Raw manure 77.1 127.8 102.4 128.5 212.9 170.7
Total 83.8 142 112.7 139.6 236.7 187.9
CAD facility sizing
The Scenario No. 2 manure/non-farm biomass CAD was sized based on providing a 22.5 day12 hydraulic
retention time to co-digest the aggregate daily manure volume from the 15 collaborating farms and the
average daily volume of the three non-farm biomass substrates. It was assumed all manure and
substrates generated at each source would be made available for co-digestion.
Ideally, the system would include a separate influent holding tank for each substrate. A heated
substrate holding tank would be needed if any fats, oils or greases (FOG) were secured in the future for
co-digestion. The size of the substrate holding tank(s) needs to be determined based on each supplier’s
need for disposal of biomass.
The energy crop digester sizing estimates were based on:
1. Farm data for the two identified energy crop farms
2. Average yields for corn, alfalfa and grass hay for the types of farms provided by the
Lewis County Field Crops Educator (Lawrence, 2009)
3. Energy crop digester specifics from a representative of Organic Waste Systems, Inc.
(McDonald, 2010), a company that is currently engaged in the energy crop digester
business.
12
22.5 days is the average of 20 and 25 days, which are the most common retention times for similarly sized systems
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Economics
An economic analysis was conducted to estimate the annual profitability of the Scenario No. 2
manure/non-farm biomass CAD system using data developed by this study and other available
information needed to perform the calculations. The economic analysis considered the costs and
revenues that would be generated by the system. The major cost categories include capital costs,
operating and maintenance costs, and feedstock transportation. The capital costs were converted to
annual economic costs using an annual equivalent cost approach (includes economic depreciation),
using Equation (1).
Equation (1): AEC = PV/ ( 1/r – 1/(r*(1+r)^n) )
With AEC = annual economic cost PV = present value (initial capital investment) r = interest rate
n = time (years) This approach uses discounted cash flow principles to annualize the up-front investment costs. After
annualizing these costs, a series of annual budgets for the system were developed by estimating the
annual income and expenses associated with the project. The analysis did not consider any potential
grants or direct subsidies; these would have the impact of improving the economic results. Similarly, the
analysis did not include items such as insurance or tax implications.
As previously stated, the Scenario No. 2 manure/non-farm biomass CAD and the energy crop digester
system were analyzed independently, since they are mutually exclusive digester systems. The biogas
produced by the two systems could be combined immediately after production to gain economies of
scale for pre-utilization/utilization equipment, but our analysis was not performed with this assumption.
The economic analysis of each system is presented below, starting with the Scenario No. 2 CAD system.
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Scenario No. 2 Manure/Non-Farm Biomass CAD
Capital costs
The capital costs for the three main components of the Scenario No. 2 CAD system are shown in Table
30; these costs were determined by multiplying values for project specific items by a unit cost for each
of the items. The unit costs for the digester system were based on analyses of competitive proposals
received between 2007 and 2009 for previous digester system projects of a similar size and adjusted for
inflation. The unit cost used was $1.84 (minimum), $2.43 (maximum), and $2.14 (average) per gallon of
digester treatment volume. The capital cost for the Scenario No. 2 CAD system is also based on a HRT of
22.5 days13.
The engine-generator set capital cost is based on a unit cost of $800/kW for all GE Jenbacher engine-
generator sets (Vernon, 2010). The size of the engine was determined based on projected quantity and
quality of biogas produced and the nearest sized engine-generator set available14 that best matched the
projections. Other manufacturers of engine-generator sets that are also well-suited for biogas plant
applications exist and data for their systems could also be used in the analysis. The capital costs for the
engine-generator sets shown in Table 30 are for minimum, maximum, and average projected biogas
production volumes.
The capital cost for a biogas clean-up system (hydrogen sulfide and carbon dioxide removal) to produce
pipeline quality biogas (biomethane) was provided by a vendor representative for Guild Associates, Inc.
(Mitariten, 2009) for their Molecular Gate® technology SPEC plant that we understand is appropriate for
all ranges of projected biogas productions for this CAD project, at $796,000.
13
22.5 days is the average of 20 and 25 days, which are the most common retention times for similarly sized systems 14
The theoretical size of the engine-generator set needed was compared with that commercially available, which was not an exact match
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Table 30. Capital costs ($) for Scenario No. 2 CAD system, engine-generator set, and biogas clean-up system, and total cost for two different energy sale options
CAD system Engine-generator
set Biogas clean–up
system
Total Cost: biomethane sale
option1
Total Cost: electricity sale
option2
Minimum 4,730,000 678,000A 796,000 5,526,000 5,408,000
Maximum 7,140,000 1,146,000B 796,000 7,936,000 8,285,000
Average 5,887,000 905,000C 796,000 6,683,000 6,792000
1Assumes total biogas production used in production and sale of biomethane; no electricity sale
2Assumes total biogas production used to generate electricity; no biomethane sale
AFor a 848-kW GE Jenbacher Type 3 engine-generator set
BFor a 1,432-kW GE Jenbacher Type 6 engine-generator set
CFor a 1,131-kW GE Jenbacher Type 4 engine-generator set
The estimated total capital costs of the Lowville CAD system ranged from $4.7 million to $7.1 million.
Annualized capital costs
The total capital investment was converted to an annual equivalent capital investment based upon the
total investment required, the cost of capital invested in the project, and the expected life of the
equipment. The cost of capital was estimated at 5 percent. The cost of capital reflects the opportunity
cost for funds invested in the project. The approach used in this analysis was to treat the discount rate
as a “real” discount rate. In other words, this discount rate does not include the impact of inflation. As
a result, no-inflation factors were applied to the future cash flows. Consistent with the request of the
Lowville Digester Work Group, the 5% cost of capital is relatively low. Increases to the discount rate
would have the impact of increasing the annual economic capital costs of the project. There are two
large capital investments associated with the project, one for the digester itself and one for either the
electrical generation equipment or the biogas clean-up equipment.
The estimated life of the digester system was assumed to be 20 years, and the estimated life of the
engine-generator set and biogas clean-up system were assumed to be 10 years, meaning the set was
replaced on a 10-year replacement cycle and for this analysis the set was replaced at the same price as it
was when the first purchase was made. In other words, the real costs of the generator are expected to
remain the same. The analysis did not inflate cash flows associated with income and expenses. This
approach is consistent with using a relatively low discount rate (5%) that is meant to reflect the real cost
of capital. A future analysis could incorporate inflation expenses into the replacement of the electrical
generation equipment. Similarly, a future analysis could shorten or lengthen the replacement cycle for
the electric generation equipment. In general, lengthening the replacement cycle will improve the
profitability of the system and shortening the cycle will decrease the profitability.
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The annualized capital costs for the Scenario No. 2 CAD system are shown in Table 31. Energy sales via
electricity and biomethane were considered for the three scenarios of minimum, maximum, and
average biogas production quantities. The total annual capital costs for the entire system necessary for
each energy sale option are shown in the two furthest right columns of Table 31. The costs of the
electrical generation equipment are annualized based upon a 10-year replacement cycle. The annual
total capital costs for the system under electrical energy generation range from $468,000 to $721,000.
The total annual capital costs for the system under biomethane production range from $483,000 to
$676,000.
Table 31. Annualized capital costs (ACC) in dollars for the Scenario No. 2 CAD system based on minimum, maximum, and average biogas production quantities.
CAD
system Engine-Generator
set Gas Clean-Up
system
Total ACC: biomethane sale option
1
Total ACC: electricity sale
option2
Minimum 380,000 88,000A 103,000 483,000 468,000
Maximum 573,000 148,000B 103,000 676,000 721,000
Average 472,000 117,000C 103,000 575,000 589,000
1Assumes total biogas production used in production and sale of biomethane; no electricity sale
2Assumes total biogas production used to generate electricity; no biomethane sale
AFor a 848-kW GE Jenbacher Type 3 engine-generator set
BFor a 1,432-kW GE Jenbacher Type 6 engine-generator set
CFor a 1,131-kW GE Jenbacher Type 4 engine-generator set
Annual operating and maintenance costs
Estimates for the annual operating and maintenance (O&M) costs were calculated for the Scenario No. 2
CAD, the engine-generator set, and the biogas clean-up system and the results are shown in Table 32.
The O&M costs for the engine-generator set were estimated using 1.7¢/kWh of energy produced for a
GE Jenbacher unit (Vernon, 2010). The O&M costs for the gas clean-up system were estimated
assuming 5% of capital expenses for annual maintenance and repair costs. The average total O&M costs
assuming biomethane production and sale were estimated at $227,000, and assuming electricity
production and sale, were estimated at $348,000.
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Table 32. Scenario No. 2 CAD, annual operating and maintenance expenses ($)
O&M Digester O&M Generator Biogas Clean-Up Total: biomethane
sale option1
Total: electricity sale option
2
Minimum 87,000 120,000A 40,000 126,000 207,000
Maximum 301,000 203,000B 40,000 341,000 503,000
Average 188,000 160,000C 40,000 227,000 348,000
1Assumes the net biogas production (20% of total for parasitic heating) used in production and sale of biomethane; no
electricity sale 2Assumes total biogas production used to generate electricity; no biomethane sale
AFor a 848-kW GE Jenbacher Type 3 engine-generator set
BFor a 1,432-kW GE Jenbacher Type 6 engine-generator set
CFor a 1,131-kW GE Jenbacher Type 4 engine-generator set
Total annual cost
The total annual cost, based on total annualized capital costs and annual O&M costs, are shown in Table
33. The average total annual costs assuming biomethane production and sale were estimated at
$803,000, and assuming electricity production and sale, were estimated at $937,000.
Table 33. Scenario No. 2 CAD, total annual costs ($) for options of selling biomethane and electricity
Digester system
Engine-Generator set
Biogas Clean-Up system
Total: biomethane sale
option1
Total: electricity
sale option2
Minimum 466,000 208,000A 143,000 609,000 674,000
Maximum 874,000 351,000B 143,000 1,016,740 1,225,000
Average 656,000 277,000C 143,000 803,000 937,000
1Assumes the net biogas production (20% of total for parasitic heating) used in production and sale of biomethane; no
electricity sale 2Assumes total biogas production used to generate electricity; no biomethane sale
AFor a 848-kW GE Jenbacher Type 3 engine-generator set
BFor a 1,432-kW GE Jenbacher Type 6 engine-generator set
CFor a 1,131-kW GE Jenbacher Type 4 engine-generator set
Net economic profitability
The total annual costs (annual capital costs plus annual O&M costs) were compared to the estimated
revenues that could be generated by the Scenario No. 2 CAD system, and are presented for varying
biogas production volumes and revenues for biomethane sale in Table 34 and for electric power sale in
Table 35. The values in both tables indicate the annual economic gain or loss (when the numbers are in
parenthesis) associated with the system. For the option of biomethane sale, the analysis assumes that
20% of the energy generated by the system will be used to meet the parasitic heat needs of the Scenario
No. 2 CAD.
These results indicate that there is no reasonable gas or electricity price at which currently projected
biogas production volumes would allow for the revenue needed to meet capital and O&M costs. The
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annual profitability of the system is highly negative under even the most optimistic energy price
scenarios. This includes the sale of biomethane associated with non-farm biomass co-digested with
manure; it was assumed that the substrate suppliers would cover costs associated with non-farm
biomass transportation from the business to the CAD facility. It is important to note that these are
annual economic costs. In other words, operating the digester with electricity production and sale at
$0.10 per kWh and average gas production would result in an annual economic loss of nearly $1.3
million dollars.
Table 34. Scenario No. 2 CAD net annual economic profitability ($) 2,3,4 for various biomethane sale prices and biogas production volumes (no tipping fees received)
Biomethane sale1 price
($/Decatherm) 4 6 8 10 12 14
Low Biogas Production (1,971,000) (1,861,000) (1,752,000) (1,642,000) (1,532,000) (1,423,000)
High Biogas Production (1,819,000) (1,605,000) (1,391,000) (1,177,000) (963,000) (749,000)
Average Biogas Production (1,906,000) (1,745,000) (1,583,000) (1,421,000) (1,260,00) (1,098,000) 1Assumes net biogas production (20% of total for parasitic heating) used for biomethane sale; no electricity sale
2Assumes average capital and O&M cost estimates
3Includes manure and CAD effluent transportation costs
4Does not include pipeline injection costs
Table 35. Scenario No. 2 CAD net annual economic profitability ($) 2,3,4,5 for various electrical energy sale prices and biogas production volumes (no tipping fees received)
Electric sale1 price
($/kWh) 0.08 0.10 0.12 0.14 0.16 0.18
Low Gas Production (1,620,000) (1,507,000) (1,394,000) (1,281,00) (1,167,000) (1,054,000)
High Gas Production (1,231,000) (1,021,000) (811,000) (600,000) (390,000) (179,000)
Average Gas Production (1,431,000) (1,271,000) (1,111,000) (951,000) (791,000) (630,000) 1Assumes total biogas production used to generate electricity; no biomethane sale
2Assumes average capital and O&M cost estimates
3Includes manure and CAD effluent transportation costs
4Does not include interconnection costs
5 Assumes no revenue from the sale of engine-generator set surplus thermal energy
The above results show that the Scenario No. 2 CAD is not economically viable for either energy sale
option, even with the most optimistic energy sale prices.
When tipping fees currently paid are included, the economic profitability overall becomes less negative;
this is shown in Table 36 and 37. For this analysis, an annual tipping fee of $277,000 ($6/ton)15 was
used, which represents the annual cost for non-farm biomass substrate supplier #8 to dispose of their
by-products. The other two non-farm substrate providers whose by-products were included in this
analysis did not provide the current tipping fees they pay to dispose of their processing by-products.
15
An updated value provided in May 2010 to correct a wrong value shown in the non-farm biomass survey
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Table 36. Scenario No. 2 CAD net annual economic profitability ($) 2,3,4 for various biomethane sale prices and biogas production volumes, including current tipping fee paid by substrate supplier #8
Biomethane sale1 price
($/Decatherm) 4 6 8 10 12 14
Low Gas Production (1,694,000) (1,585,000) (1,475,000) (1,365,000) (1,256,000) (1,146,000)
High Gas Production (1,542,000) (1,328,000) (1,114,000) (900,000) (686,000) (472,000)
Average Gas Production (1,630,000) (1,468,000) (1,306,000) (1,145,000) (983,000) (821,000) 1Assumes total biogas production used for biomethane sale; no electricity sale
2Assumes average annual capital and average O&M cost estimates
3Includes manure and CAD effluent transportation average cost and tipping fee paid to project
4Does not include pipeline injection costs
Table 37. Scenario No. 2 CAD net annual economic profitability ($) 2,3,4,5 for various electrical energy sale prices and biogas production volumes, including current tipping fee paid by substrate supplier #8
Electric sale1 price ($/kWh) 0.08 0.10 0.12 0.14 0.16 0.18
Low Gas Production (1,343,000) (1,230,000) (1,117,000) (1,004,000) (891,000) (778,000)
High Gas Production (955,000) (744,000) (534,000) (323,000) (113,000) 97,000
Average Gas Production (1,155,000) (995,000 (834,000) (674,000) (514,000) (354,000) 1Assumes total biogas production used to generate electricity; no biomethane sale
2Assumes average capital and O&M cost estimates
3Includes manure and CAD effluent transportation costs and tipping fee paid to project
4Does not include interconnection costs
5 Assumes no revenue from the sale of engine-generator set surplus thermal energy
Since the economic profitability of the Scenario No. 2 CAD remained negative even when including the
tipping fee paid by non-farm biomass substrate supplier #8, and realizing the other two suppliers also
already pay a tipping fee to dispose of their by-products, we determined the tipping fees needed to
result in a break-even economic profitability for both energy sales options. The results of these analyses
are shown in Table 38 and 39.
The tipping fee revenue (column 1) represents the range in aggregated annual tipping fees received and
the correlating fee in ($/ton). The price per ton was determined by dividing the tipping fee received
(column 1) by the average total mass of all non-farm biomass received from substrates 8, 10, and 11. If
biogas prices received were $10 per decatherm, the net annual tipping fee revenues required to make
the project break-even would be $1,421,000 per year, at $21/ton. If electrical energy prices received
were $0.14 per kWh, the net annual tipping fee revenues required to make the project break-even
would be $951,000 per year.
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Table 38. Scenario No. 2 CAD net annual economic profitability ($)2,3 for various biomethane sale prices and tipping fees charged for non-farm biomass substrates
Biomethane sale1 price ($/decatherm)
Tipping Fee 4 6 8 10 12 14
($/year) ($/ton)
0 0 (1,906,000) (1,745,000) (1,583,000) (1,421,000) (1,260,000) (1,098,000)
200,000 3 (1,706,000) (1,545,000) (1,383,000) (1,221,000) (1,060,000) (898,000)
400,000 6 (1,506,000) (1,345,000) (1,183,000) (1,021,000) (860,000) (698,000)
600,000 9 (1,306,000) (1,145,000) (983,000) (821,000) (660,000) (498000)
800,000 12 (1,106,00) (945,000) (783,000) (621,000) (460,000) (298,000)
1,000,000 15 (906,000) (745,000) (583,000) (421,000) (260,000) (98,000)
Breakeven ($/year)
1,906,000 1,745,000 1,583,000 1,421,000 1,260,000 1,098,000
Breakeven
($/ton) 29 26 24 21 19 16
1Assumes total biogas production used for thermal energy sale; no electricity sale
2Assumes average capital and O&M cost estimates
3Assumes no revenue from the sale of engine-generator set surplus thermal energy
Table 39. Scenario No. 2 CAD, net annual economic profitability ($)2,3 for various electrical energy sale prices and tipping fees charged for non-farm biomass substrates
Electric sale1 price ($/kWh)
Tipping Fee 0.08 0.10 0.12 0.14 0.16 0.18
($/year) ($/ton)
0 0 (1,432,000) (1,271,000) (1,111,000) (951,000) (791,000) (630,000)
200,000 3 (1,232,000) (1,071,000) (911,000) (751,000) (591,000) (430,000)
400,000 5 (1,032,000) (871,000) (711,000) (551,000) (391,000) (230,000)
600,000 8 (832,000) (671,000) (511,000) (351,000) (191,000) (30,000)
800,000 11 (632,000) (471,000) (311,000) (151,000) 9,000 169,700
1,000,000 13 (432,000) (271,000) (111,000) 49,000 209,000 369,700
Breakeven ($/year)
1,432,000 1,271,000 1,111,000 951,000 $791,000 630,299
Breakeven
($/ton) 21 19 17 14 12 9
1Assumes total biogas production used to generate electricity; no thermal energy sale
2Assumes average capital and O&M cost estimates
3Assumes no revenue from the sale of engine-generator set surplus thermal energy
The above shows that the Scenario No. 2 CAD can be economically viable when a moderate tipping fee
is charged to the suppliers of the non-farm biomass that is significantly less than that charged by the
local landfill, which was reported to be approximately $60/ton by the Lowville Digester Work Group but
more than the calculated tipping fee being paid by non-farm biomass substrate supplier #8. It appears
that a tipping fee range of $17 to $24/ton is needed to break-even, depending on the energy sale option
chosen.
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Energy Crop AD System The Lowville energy crop digester would be an anaerobic digester designed to process high solids energy
crop materials (corn silage and or haylage). Such digesters are widely used in Germany and other
European countries and produce about eight times the biogas as digesters fed manure only
(Effenberger, 2006).
Silage corn and grass hay would be harvested and ensiled as if they were going to be fed to dairy cattle.
Sufficient quantities would be stored to enable the energy crop digester feed hopper (usually a walking
floor bin) to be filled once-a-day, year round, normally with a pay loader. Several times per day, the
control system would automatically transfer a portion of the feedstock into the digester; screw
conveyors (augers) are normally used due to the high solids content of corn silage and haylage. The
energy crop digester economic analysis performed for this feasibility study used “in-the-bunk” silage
prices ranging from $30 to $55/ton, meaning that the costs to grow the crops and harvest and ensile
them are covered by the purchase price.
In addition to the energy crop feedstock, a small portion of manure is also normally added to the energy
crop digester, about 10 percent by mass, to help stabilize digester pH and to provide some dilution
water to lessen the effort required to provide in-vessel mixing.
Energy crop digester effluent, rich in organic nutrients, is the consistency of digested manure. For this
feasibility study, it is assumed the effluent would be stored on-site for a short period of time and
periodically trucked to the energy crop source farms for longer-term storage and for subsequent use as
fertilizer to grow the next rotation of energy crops. Some of the surplus nutrients from the Lowville CAD
system could also be trucked to the source farms to meet the overall fertilizer requirements for the
crops grown on those farms.
Capital Costs
The total capital cost of the energy crop digester was estimated to be $4.5 million dollars. This price was
developed using the same fashion as the capital cost of the Lowville CAD system was determined; unit
price information calculated from data provided by a company involved in energy crop digesters,
Organic Waste Systems, Inc. (McDonald, 2010), was used in conjunction with project specific
information.
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The estimated total capital cost for the GE Jenbacher Type 4 engine-generator set that most closely
matches (1,131 kW) the biogas available to fuel the set is $904,800. For this option, the biogas clean-up
to biomethane was not investigated, since economic profitability analysis results for the Scenario 2 CAD
showed little difference in the bottom line when comparing biomethane sale vs. electrical energy sale.
Annualized capital costs
Using the same procedure and assumptions for determining the annualized capital costs for the Scenario
No. 2 CAD system, the annual capital cost for the energy crop digester and engine-generator set is
$361,000 and $117,000, respectively for a total annual capital cost of $478,000.
Annual operating and maintenance costs
The annual operating and maintenance (O&M) costs were calculated using the same procedure and the
assumptions for the Scenario No. 2 CAD system, with one notable difference being that the energy crop
digester O&M costs were based on the recommendation to use 2.5% of the capital cost of the system
(McDonald, 2010). The energy crop digester and engine-generator set annual O&M costs are $113,000
and $123,000, respectively, for a total annual O&M cost of $236,000.
Digester feedstock cost
The energy crop digester feedstock cost is an important item to consider since it is a major cost of the
system and will have the biggest impact of all costs on profitability. This cost will likely annually be
reflective of the cost to supply corn silage and haylage to dairy cows. Based on farm data and average
crop yields for the area, 27,600 tons of crops would be ensiled at Site 1 and the energy crop digester
project would purchase corn silage and haylage “out of the bunker”. The annual estimated cost for
feedstock is shown in Table 40 for a unit price range of $30 to $55/wet ton.
Table 40. Annualized capital costs ($) for energy crop digester system
Feedstock Unit Cost ($/wet ton) out of a
bunker on-site 30 35 40 45 50 55
Annual Feedstock Cost ($) 828,000 966,000 1,104,000 1,242,000 1,380,000 1,518,000
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Net economic profitability
The net annual economic profitability for the energy crop digester is presented in Table 41 for the
situation only producing electricity for sale, over a range of feedstock and electricity sale prices. The
economic profitability was determined by subtracting the following values from the total average
electricity production: total annual capital costs, total O&M costs, the lowest potential feedstock costs,
and the cost to transport energy crop digester effluent back to collaborating crop farms.
Table 41. Net annual economic profitability ($) for various electricity prices and feedstock costs
Electric sale price
($/kWh) 0.08 0.10 0.12 0.14 0.16 0.18
Energy Crop Digester
Feedstock Unit Cost ($/wet
ton)
30 (967,000) (807,000) (646,000) (486,000) (326,000) (165,000)
35 (1,105,000) (945,000) (784,000) (624,000) (464,000) (304,000)
40 (1,243,000) (1,083,000) (922,000) (762,000) (602,000) (442,000)
45 (1,381,000) (1,221,000) (1,060,000) (900,000) (740,000) (580,000)
50 (1,519,000) (1,359,000) (1,198,000) (1,038,000) (878,000) (718,000)
55 (1,656,000) (1,497,000) (1,336,000) (1,176,000) (1,016,000) (856,000)
The net annual economic profitability is negative for all combinations of feedstock purchase price and
electrical energy sale price considered, meaning that the energy crop digester system would cost more
to own than the value of the annual revenue received. Therefore, consideration of an energy crop
digester is not recommended at this time.
110
Farm Impacts
Capital improvements
In order to successfully implement the Scenario No. 2 CAD system, some of the targeted collaborating
farms will need to make on-farm modifications. Based on the farm survey results (Table 10) seven of
the 15 collaborating dairy farms (Nos. 5, 11, 14, 16, 19, 21, and 23) would need to construct short-term
manure storages in order to hold at least 6,000-gallons of manure to be collected by the 6,000-gallon
manure tanker truck with an on-board pumping system. A short-term manure storage was defined by
the project as a storage with the ability to hold one to three day’s worth of manure generated by that
farm. Constructing a manure storage larger than 6,000-gallons will give a farmer the flexibility to store
manure for additional time, should there be a reason that the manure cannot be picked up from the
farm.
A manure bypass system will also need to be included to be used when the manure tanker truck cannot
access the farm manure storage site; this is unlikely to happen often, but could arise as an issue due to
poor road conditions. The ideal manure bypass system would include a pump capable of pumping
manure not only directly to the farm’s long-term manure storage, but also into the manure tanker for
times when its on-board pumping system may fail and also into the farm’s manure spreader.
Other farm improvements may include access roads and utility upgrades; these are all site specific and
the capital cost associated with them will vary from farm to farm.
The estimated capital cost to construct a 10,000-gallon short-term manure storage with bypass pump is
shown in Table 42. The storage construction cost is based on poured-in-place concrete construction;
the walls are 10” thick and the floor is 6” thick, as recommended by the local Soil and Water
Conservation District office (Durant, 2008). Costs include a manure storage gravel access pad for more
reliable access to the 6,000-gallon manure tanker truck upon collection. These specifications would
require about 40 yd3 of concrete, at a price of $86/yd3 (Durant, 2008). The access pad is assumed to be
6” thick concrete (NRCS, 2008). A centrifugal pump is specified for use as the bypass pump, with an
estimated cost of $16,000 (NRCS, 2008).
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Table 42. Capital cost estimate per farm for construction of a 10,000-gallon on-farm short-term manure storage
Total cost of concrete $3,450
Labor $6,900
Gravel $900
Excavation/site prep $1,500
Pump in short-term storage $16,000
Electrical service/upgrade $2,000
Access road $3,500
Total $34,250
Nutrients
Chapter 4 contains the results of the laboratory nutrient concentration testing of the non-farm biomass
substrates. The raw manure nutrient values shown in Table 43 represent the 15 collaborating farms for
Scenario No. 2. Total post-digestion nutrient mass of nitrogen, phosphorus and potassium series are
provided in Table 43 and Table 44.
Table 43. Scenario No. 2 CAD estimated post-digestion nitrogen series and total annual masses by feedstock source
Digestate source
Post Digestion TKN (lbs/year)
Post Digestion Ammonia-N (lbs/year)
Post Digestion Organic-N (lbs/year)
Minimum Maximum Minimum Maximum Minimum Maximum
8 17,420 25,230 3,090 4,470 18,520 26,830
10 165,140 165,140 41,240 157,460
11 490 - -
Manure 1,573,710 - -
Total 1,756,760 1,764,570 44,330 45,710 175,980 184,290
Table 44. Scenario No. 2 CAD estimated post-digestion phosphorus and potassium series and total masses by feedstock source
Digestate source
Post Digestion Total Phosphorus (lbs/year)
Post Digestion Ortho Phosphorus (lbs/year)
Post Digestion Potassium (lbs/year)
Minimum Maximum Minimum Maximum Minimum Maximum
8 16,730 24,240 7,970 11,540 12,800 18,540
10 82,790 3,970 24,930
11 5 - 0
Manure 270,230 - 365,610
Total 369,755 377,265 11,940 15,510 403,340 409,080
The land base used to grow the crops for the proposed energy crop digester could be used to receive
the nutrients contained in CAD effluent. Discussions between the Lowville Digester Work Group and
owners of area crop farms have shown the willingness of some crop farmers to receive digested effluent
at their farms to replace some or all of the commercial fertilizers currently used. One of the initial goals
112
of the project was to improve the nutrient balance situation in the region; re-distributing nutrients from
farms with excess to farms that are deficient would significantly advance this goal.
Similar to Figure 28, a comparison of the volume of manure provided to the CAD by each farm and the
volume of digested effluent the farm in turn would receive back is shown in Figure 29; however, in this
case, each farm’s individual nutrient balance situation is taken into account. The farms that have either
a balanced or excess nutrient situation would receive an amount of CAD effluent equivalent to the
amount of manure they provide to the CAD project, contrary to the increased amount of effluent they
would receive in the weighted scenario, shown in Figure 28. Assuming farms receive effluent in this
manner, there would be an estimated 11 million gallons/year of excess CAD effluent available for sale to
area crop farms.
Figure 29. Comparison of the volume of manure sent to the CAD and volume of CAD effluent received, by farm, taking into account each farm's nutrient balance situation.
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Assuming the non-farm biomass imported for co-digestion supplies excess nutrients to the post-
digestion product that would be available for sale to area crop farms, the project could potentially
receive $226,000/year in total revenue. Of the $226,000/year, $86,000/year would be derived from the
sale of nitrogen, $121,000/year would be derived from the sale of phosphorus, and $19,000/year would
be derived from the sale of potassium16.
16
Based on fertilizer sale prices for N,P,and K of $0.46/lb, $0.51/lb, and $0.40/lb, respectively.
114
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Chapter 8. Future Work and Recommendations
The recommendation for a CAD system is based on conducting thorough and complete technical and
economic feasibility analyses, as well as the vision of the Lowville Digester Work Group. Based on this,
the recommendation is to further investigate one centrally-located complete mix AD, sited adjacent to
the LWWTP that would co-digest manure from 15 targeted collaborating dairy farms and targeted non-
farm biomass substrates (currently the following three substrates: whey, post-digested sludge, and
glycerin) that are by-products generated nearby.
The future net annual economic profitability behind this recommendation is encouraging, given that, (1)
the calculated tipping fee needed for the system to break-even is well below the average tipping fee
charged in the northeastern U.S. and many predict regulations will be instituted in the near future
restricting the land-filling of organic matter, (2) future regulations aimed at reducing the impact of fossil-
fuel derived energy (specifically GHG emissions and climate change) would likely positively impact
renewable energy projects, and (3) the annual economic profitability will improve with reductions in
capital cost by receiving grants and/or premium payments for renewable energy.
If future efforts are put forth to further investigate one CAD, it is recommended that the two major
areas provided below be addressed in the order presented and that the bullet items under each be
included.
A. Address Economic Barriers to Project Implementation
Identify other potential sources of non-farm biomass that are currently being land-
filled or otherwise disposed of that could be received by the CAD with a tipping fee
paid by the supplier
Continue the education and outreach efforts concerning this project and the goals and
objectives of local community members, targeted at collaborating and non-
collaborating dairy farmers and non-farm biomass substrate suppliers to develop
project support targeted towards securing public funding.
Secure grant funding or subsidies that could help offset the capital cost of the CAD
and/or supplement the revenue(s) received for system outputs (raw biogas,
electricity, biomethane, and/or organic nutrients)
116
Investigate the willingness of non-farm biomass suppliers to enter into reasonable
long-term contracts , with a negotiated tipping fee
Investigate the willingness of the end user(s) of the net energy produced by the CAD
facility to enter into reasonable long-term contracts
B. Advanced Project Due Diligence
Perform more complete laboratory testing of the targeted substrates mixed
proportionally with manure to better solidify the quantity of biogas that would be
produced by the system
Conduct an in-depth site and environmental impact assessment for the targeted
construction site
Investigate the legal issues for various digester ownership options
Determine the permit(s) that will be required by the New York State Department of
Environmental Conversation (NYSDEC)17
Conduct an in-depth investigation into the site improvements that will be required at
each farm in order to participate in the project, and develop an associated budget
Validate the trucking analysis and farm biomass pick-up options
Investigate contracting with an existing trucking company to provide transportation of
farm biomass
Develop a request for proposals (RFP) package to be distributed to AD system
designers
Validate the economic profitability analysis using the results of the proposed RFP
Continue investigation into future opportunities, such as manure nutrient extraction
equipment and resulting product marketing opportunities for organic nitrogen,
phosphorus, and potassium
Continue reassessment of market opportunities such as the sale of biomethane as a
vehicle fuel.
17
There are currently no operating dairy manure-based CAD systems in NYS, and an initial inquiry made by Cornell to NYSDEC on behalf of this project revealed that NYSDEC is not readily prepared to state what permit(s) is/are needed.
117
References
Angenent, Lars. 2009. Associate Professor of Biological and Environmental Engineering, Cornell University. Personal Communication.
American Society of Agricultural and Biological Engineering (ASABE) Standards, 52nd ed. 2005. ASAE
D384.2 Manure Production and Characteristics. ASABE, Joseph, Michigan. Bennett, S. 2003. Feasibility Report of a Cooperative Dairy Manure Management Project in St.
Albans/Swanton, VT.
Bothi, K.I. and B.S. Aldrich. Fact sheet: Feasibility Study of a Central Anaerobic Digester for Ten Dairy
Farms in Salem, NY. www.manuremanagement.cornell.edu 2005.
Casey, J., L. Gerson, A. Smith, N.R. Scott, and L. Albright. 2007. Cornell’s Proposed Anaerobic Digester. Cornell Cooperative Extension (CCE) of Wyoming County. 2002. Feasibility Study of Anaerobic Digestion
Options for Perry, New York. Web address: http://counties.cce.cornell.edu/wyoming/agriculture/programs/anaerobic_digestion/files/FeasabilityStudyFinalReport.doc
Durant, Mike. Natural Resources Conservation Service (NRCS). 2008. Draft engineering drawings for on-
farm manure storage.
Edgar, Thom G., and Andrew G. Hashimoto. 1991. Feasibility Study for a Tillamook County Dairy Waste Treatment and Methane Generation Facility. Department of Bioresource Engineering, Oregon State University.
Effenberger, Mathias. 2006. Dipl. – Ing. M.Sc. Mathias Effenberger. Bavarian State Research Center for Agriculture (LfL) Institute of Agricultural Engineering and Animal Husbandry.
Energy Information Administration (a), 2009. How much electricity does a typical American home use? Website: www.tonto.eia.doe.gov/ask/electricity_faqs.asp#electricity_use_home
Energy Information Administration (b), 2009. Natural gas navigator
Website: http://tonto.eia.doe.gov/dnav/ng/ng_sum_top.asp United States Environmental Protection Agency (USEPA). 1997. A Manual for Developing Biogas Systems
at Commercial Farms in the United States. EPA-430-B-97-015. Gooch, C.A., S.F. Inglis, and P.E. Wright. 2007. Biogas Distributed Generation Systems Evaluation and
Technology Transfer Project – Interim Report. Prepared for: The New York State Energy Research and Development Authority. NYSERDA Project No. 6597. Albany, New York.
118
Gooch, C.A., and J.L. Pronto. 2009. Unpublished graph; Data from NYSERDA Project Nos. 6597 and 9446, Digester Assessment following the protocol developed by Association of State Energy Research and Technology Transfer Institutions.
Jewell, W.J. 2007. Professor Emeritus of Biological and Environmental Engineering, Cornell University.
Personal Communication. Jewell, W.J., et al. 1997. Evaluation of Anaerobic Digestion Options for Groups of Dairy Farms in Upstate
New York. Prepared for: USDA-NRCS. Koelsch, R.K., E.E. Fabian, R.W. Guest, J.K. Campbell. Undated. Anaerobic Digesters for Dairy Farms.
Agricultural and Biological Engineering Extension Bulletin 458. Cornell University, Ithaca, NY 14853.
Labatut, R.A. and N.R. Scott. 2008. Experimental and Predicted Methane Yields from the Anaerobic Co-
digestion of Animal Manure with Complex Organic Substrates. ASABE Paper No. 08-5087. Lawrence, Joe. 2009. Field crop extension educator, Cornell Cooperative Extension of Lewis County.
Personal Communication. Lewis County Digester Work Group. 2008. A Partnership of the Supply Chain with Benefits to the
Community and the Dairy Industry. Committee working document. Lopez, J.A., et al. 2009. Anaerobic digestion of glycerol derived from biodiesel manufacturing.
Bioresource Technology 100 (2009) 5609-5615. Ludington, D.C. and S.A. Weeks. 2008. The Characterization of Sulfur Flows in Farm Digesters at Eight
Farms. Mack Trucks, Canada. 2009. Personal communication. . Marks, L.S. 1978. Mechanical Engineers’ Handbook, 4th Edition. McGraw-Hill Book Company, Inc.
McDonald, Norma. 2010 North American Sales Manager, Organic Waste Systems, Inc. Personal Communication.
Minchoff, CJ, and Kifle G. Gebremedhin. 2006. Economic Feasibility Study for a Centralized Digestion System. Proceedings of the 2006 ASABE Annual International Meeting. Portland, Oregon, July 9-12. American Society of Agricultural and Biological Engineers, St. Joseph, Michigan. Paper No. 064198.
Mitariten, Michael. Senior Engineer. Guild Associates, Inc. 2009. Personal Communication.
Public Interest Energy Research. 2006. Glossary of energy terms. Website: www.pierminigrid.org/glossary.html
119
Repa, Edward W. 2005. NSWMA’s 2005 Tip Fee Survey. National Solid Wastes Management Association Research Bulletin 05-3.
Roka, F.M., R.M. Muchovej, and T.A. Obreza. 2001. Assessing Economic Value of Biosolids. Florida
Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Scott, Norm. 2010. Personal Communication. Strand Associated, Inc. 2008. Community Manure Management Facilities Plan, Dane County, WI. Tabolt, Mark. Lowville Wastewater Treatment Plant Manager. Personal communication. December 15,
2009. Weisman, W. 2008. Lane Renewable Energy Complex, Lane County, Oregon. Vernon, Todd. 2010. Senior Sales Manager, GE Energy - Jenbacher
Vokey, Frans. Cornell Cooperative Extension, Lewis County. Personal communication. 2010. Wright, P.E. 2001. Overview of Anaerobic Digestion Systems for Dairy Farms. Proceedings of Dairy
Manure Systems, Equipment and Technology Conference; Rochester, New York, March 20-22. NRAES-143. Natural Resource, Agriculture, and Engineering Service. Cornell University, Ithaca, New York.
Wright, P.E., Inglis, S.F, Stehman, S.M, and J. Bonhotal. 2003. Reduction of Selected Pathogens in Anaerobic Digestion. Proceedings of the Ninth International Symposium, Animal, Agricultural and Food Processing Wastes IX. Raleigh, North Carolina, Oct. 12-15. American Society of Agricultural and Biological Engineers, St. Joseph, Michigan.
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121
Appendix A. Glossary for New York State Manure-Based Anaerobic Digestion18 Anaerobic bacteria
Microorganisms that live and reproduce in an environment containing no “free” or dissolved oxygen.
Anaerobic digester
A vessel and associated heating and gas collection systems designed specifically to contain biomass undergoing digestion and its associated microbially produced biogas. Conditions provided by the digester include: an oxygen-free environment, a constant temperature, and sufficient biomass retention time.
Anaerobic digestion
A biological process in which microbes break down organic material while producing biogas as a by-product.
Anaerobic lagoon
A holding pond for livestock manure that is designed to anaerobically stabilize manure, and may be designed to capture biogas with the use of an impermeable, floating cover.
Annual capital cost The equivalent annual capital cost converts the total capital costs into an annual charge. The
equivalent annual capital cost is calculated according to the formula EAC= pv/(1/r - 1/(r*(1+r)^n)) where “pv” is the present value or total capital investment in today's dollars, r is the discount rate, and n is the life of the capital investment.
Barn effluent
Material exiting a barn structure, generally consisting of animal excrement (urine and feces) and used bedding material, and may contain milking center washwater.
Biogas
For the purposes of this document, the raw and un-cleaned gas produced by an AD, consisting of mainly methane CH4 (~60%), carbon dioxide CO2 (~40%), water vapor, and hydrogen sulfide.
British Thermal Unit (Btu)
The English System standard measure of heat energy. It takes one Btu to raise the temperature of one pound of water by one degree Fahrenheit at sea level.
18
Reference: (Public, 2006)
122
Capital cost A one-time fixed cost incurred on the purchase of buildings and equipment. A digester’s capital cost includes the purchase of land the system is on, permitting and legal costs, the equipment needed to run the digester, cost of digester construction, the cost of financing, and the cost of commissioning the digester prior to steady-state operation of the digester.
Centralized digester
An anaerobic vessel which uses feedstocks from several farms and/or other biomass sources, within a relatively proximate distance to the digester location.
Co-generation
The sequential use of energy for the production of electrical and useful thermal energy. The sequence can be thermal use followed by power production or the reverse, subject to the following standards: (a) At least 5% of the co-generation project’s total annual energy output shall be in the form of useful thermal energy. (b) Where useful thermal energy follows power production, the useful annual power output plus one-half the useful annual thermal energy output equals not less than 42.5% of any natural gas and oil energy input.
Combined Heat and Power (CHP)
The sequential or simultaneous generation of two different forms of useful energy – mechanical and thermal – from a single primary energy source in a single, integrated system. CHP systems usually consist of a prime mover, a generator, a heat recovery system, and electrical interconnections configured into an integrated whole.
Complete mix digester An anaerobic vessel that is mixed with one or more mixing techniques. Dewater
To drain or remove water from an enclosure. Dewater also means draining or removing water from sludge to increase the solids concentration.
Digestate
Effluent; Material remaining after the anaerobic digestion of a biodegradable feedstock. Digestate is produced both by acidogensis and methanogenesis, and each has different characteristics.
Discount rate The interest rate used in discounting future cash flows. Distributed generation
A distributed generation system involves small amounts of generation located on a utility’s distribution system for the purpose of meeting local (substation level) peak loads.
Distribution system (electric utility)
The substations, transformers and lines that convey electricity from high-power transmission lines to consumers.
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Effluent Digestate; Material exiting the AD vessel. Emission
The release or discharge of a substance into the environment; generally refers to the release of gases or particulates into the air.
End-use sectors The residential, commercial, transportation and industrial sectors of the economy. Engine-Generator set
The combination of an internal combustion engine and a generator to produce electricity; may be single or dual fueled depending on the location and set up.
Flare A device used to safely combust surplus or unused biogas. Greenhouse Gas (GHG)
A gas, such as carbon dioxide or methane, which contributes to a warming action in the atmosphere.
Grid
The electric utility companies’ transmission and distribution system that links power plants to customers through high power transmission line service; high voltage primary service for industrial applications; medium voltage primary service for commercial and industrial applications; and secondary service for commercial and residential customers. Grid can also refer to the layout of gas distribution system of a city or town.
Hydraulic retention time (HRT)
The length of time material remains in the AD. Hydrogen sulfide (H2S)
A toxic, colorless gas that has an offensive odor of rotten eggs. Hydrogen sulfide has serious negative implications for the wear of gas handling equipment for an anaerobic digester system.
Hydrolysis
A biological decomposition process involved in the anaerobic digestion of organic material. Influent Biomass on the in-flow side of a treatment, storage, or transfer device. Installed capacity The total capacity of electrical generation devices in a power station or system. Kilowatt-hour (kWh)
The most commonly used unit of measure of the amount of electric power consumed over time. The stand-alone unit indicates one kilowatt of electricity supplied for one hour.
124
Lagoon In wastewater treatment or livestock facilities, a shallow pond used to store wastewater where biological activity decomposes the waste.
Lost capital The portion of a capital investment that cannot be recovered after the investment is made, usually used to express the immediate loss in value of a purchased or constructed item.
Main tier
Distributed renewable energy systems where the electrical power produced is not used on-site but rather transported to the grid for use elsewhere. Wind generation generally falls into this category.
Manure
The combination of urine and feces. Methane (CH4)
A flammable, explosive, colorless, odorless, gas. Methane is the major constituent of natural gas, and also usually makes up the largest concentration of biogas produced in an anaerobic digester.
Methanogens
Active in phase 3 of the digestion process, acids (mainly acetic and propionic acids) produced in phase 2 are converted into biogas by methane-forming bacteria.
Microturbine
A small combustion turbine with a power output ranging from 25- to 500-kW. Microturbines are composed of a compressor, combustor, turbine, alternator, recuperator, and generator.
Net generation
Gross generation minus the energy consumed at the generation site for use in maintaining energy needs (heat or electric).
Net Present Value (NPV)
The present value of an investment’s future net cash flow minus the initial investment. Generally, if the NPV of an investment is positive, the investment should be made.
Operation and Maintenance (O&M) costs
Operating expenses are associated with running a facility. Maintenance expenses are the portion of expenses consisting of labor, materials, and other direct and indirect expenses incurred for preserving the operating efficiency or physical condition of a facility.
Plug-flow digester
A design for an anaerobic digester in which the material enters at one end and is theoretically pushed in plugs towards the other end, where the material exits the digester after being digested over the design HRT.
125
Present value The current value of one or more future cash payments, discounted at some appropriate interest rate.
Rate of return
The annual return on an investment, expressed as a percentage of the total amount invested. Siloxane
Any of a class of organic or inorganic chemical compounds of silicon, oxygen, and usually carbon and hydrogen, based on the structural unit R2SiO where R is an alkyl group, usually methyl.
Tipping fees
Monies that are paid to a site that is accepting outside sources of organic material (non-farm biomass).
Ton US short ton equals 2,000 lbs Tonne Metric ton equals 1,000 kg Treatment volume
Inside volume of an anaerobic digester that, under normal operating conditions would be full of material undergoing anaerobic decomposition.
Turbine
A device for converting the flow of a fluid (air, steam, water, or hot gases) into mechanical motion.
Volatile solids
Those solids in water or other liquids that are lost on ignition of the dry solids at 550 degrees Centigrade.
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127
Appendix B. Survey data for Lewis County Anaerobic Digester Feasibility (Farm based survey)
Farm name: ________________________________________
Contact: ___________________________________________
Farm mailing (or street) address: __________________________________________________
Who is your nutritionist? _________________________________________________
Do we need permission to contact your nutritionist? _______________________
Cow population questions
At the present time, what is the:
Number of mature cows: ________________
Number of heifers: __________________
Housing type for both groups: _______________________________________________
Bedding type for both groups: _______________________________________________
2 years from now, what changes do you expect to see in the:
Number of mature cows: ________________
Number of heifers: __________________
Housing type for both groups: _______________________________________________
Bedding type for both groups: _______________________________________________
5 years from now, what changes do you expect to see in the:
Number of mature cows: ________________
Number of heifers: __________________
Housing type for both groups: _______________________________________________
Bedding type for both groups: _______________________________________________
Do you have off-site heifer manure? ________________
If yes, what is the:
Address: __________________________________________________
Population of heifers providing manure: __________________
Age span of off-farm heifers: _____________________________________
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Manure composition questions
Is milking center wastewater or other extra water included in the manure? _________________
Estimated amount of extra water: ________________ (gallons/day)
If water is added, is it possibly to separate it from the manure flow? (Y/N) ____________
Does the farm use Rumensin® for any of the cows (lactating or heifer)? ____________________
Does the farm use copper sulfate for foot-baths? ___________________________________
Is there a copy of a recent (< 2 years) manure analysis available? ________________________
Do you have an excess OR a lack of manure nutrients on your farm? ______________________
How much of each of the following do you have in excess, OR are lacking:
N ________________ (lbs/year)
P________________ (lbs/year)
K ________________ (lbs/year)
Manure handling and storage questions
Manure Storage
Size (circle units)
Animal groups
Wastewater included?
Describe access
(paved, dirt road, etc.)
How is manure transferred?
(pumps, gravity, etc.)
How often is this storage spread on
fields?
How many acres is it
spread on?
1 Gal/cu ft Yes/No
2 Gal/cu ft Yes/No
3 Gal/cu ft Yes/No
4 Gal/cu ft Yes/No
5 Gal/cu ft Yes/No
What is the approximate acreage of: (1) Corn: _____ (2) Grass hay: _____ (3) Alfalfa: _____
(4) Other: _____
Is there short-term (1-3 days) storage available? ________________________________
Is there long-term storage available? _____________________________________
If yes, how many months storage does it provide? _______________________
Describe the access to both short-term and long-term storages; is it directly off a paved road? If possible,
please provide a rough map describing the layout. _____________________________
______________________________________________________________________________
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Where, if any, are the existing pumps located in the manure handling system? _______________
______________________________________________________________________________
Is dealing with frozen manure an issue at your farm? ___________________________________
Does your farm have significant waste feed to dispose of (ex. Feed refusal, spoiled forage, etc.)?
_____________________________________________________________________________
Perspective questions
What concerns would you have in spreading manure that you receive back from a common central
anaerobic digester system? __________________________________________________
______________________________________________________________________________
Would you be willing to pay for necessary features or additions that are necessary for the
removal/delivery of manure and digested material (this includes storage facilities, pumps, etc.)?
______________________________________________________________________________
Would you be interested in discussing the formation of a cooperative to run and manage this centralized
digester?
______________________________________________________________________________
Thank you, for taking the time to complete this survey! Feel free to add any additional comments,
concerns or questions in the space below.
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Appendix C. Survey data for Lewis County Anaerobic Digester Feasibility (Non-farm based survey)
Company name: ________________________________________
Industry type: _____________________
Contact: ___________________________________________
Mailing address: _____________________________________________________
Give a description of the type of organic material you would be disposing of:
_____________________________________________________________________________________
___________________________________________________________
Organic waste item
Solid or Liquid?
Fat, oil, or protein?
Pre-consumer or post-
consumer?
Quantity or volume?
Frequency of removal?
Frequency of accumulation (seasonality)1
1This means, do you only produce this waste at a certain time of year?
Do you have any lab analysis of the organic material you would be disposing of? And could this be made
available? _______________________________________________
Do you currently have a method to dispose of the organic material your business produces? (Y/N)
___________________
Do you pay someone to provide this service? (Y/N) ___________________________
What is the approximate cost of this disposal? ________________________________
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What is the setup of the storage facility for the organic material produced by your business? Please
describe any pits, tanks, pumps, or other equipment used in conveying the organic material to disposal.
_____________________________________________
________________________________________________________________________
What are your feelings/concerns about providing this organic material to a common central anaerobic
digester system? ____________________________________________
________________________________________________________________________
Thank you, for taking the time to complete this survey! Feel free to add any additional comments,
concerns or questions in the space below.
133
Appendix D. Substrate Sampling Report
This report details the process of collecting samples of non-farm biomass substrates from substrate
suppliers in Lewis County.
Residential food waste
A local volunteer for the Lowville digester project provided food waste samples from her home which
consisted of residential food waste, chopped with a knife and mixed using a food processor, as shown in
Figure 30. There are considerable logistical problems with obtaining a representative sample of
residential food waste, which varies considerably in content and volume throughout the year and from
home to home.
Meat and butcher’s waste
Samples of meat, fat and guts were collected from a local butcher. The offal was deposited in eight oil
drums and included blood, intestines, hides, livers, fat and other assorted butcher wastes, as shown in
Figure 31. To obtain a representative sample, some blood was pooled into a container along with slices
of liver, intestine and fat that had been manually mixed using a power drill. Since the waste was not
uniform throughout the barrels, the sample incorporated elements from several of the barrels. The
owner of the establishment noted that during deer season (October-December), deer bones would be
the sole by-product from the butchering plant.
Dilute whey
A sample of diluted whey and CIP waste water was collected from a dairy processing plant. Employees
explained that waste whey was disposed of every day while CIP wastewater, was disposed of about
every three days. Thus, a representative sample was taken by mixing three parts whey to one part CIP
wastewater. It should be noted that the substrate supplier already pumps this waste to a location to be
trucked off-site; therefore, no additional infrastructure would likely be necessary for collection and
inclusion to the proposed digester project.
134
Grocery store scraps
A local grocery chain was unable to provide a food waste sample, since the portion of their usable food
waste is deposited into a catch-all dumpster that accumulates a high degree of contamination, such as
plastic, metal and other indigestible refuse. Produce waste is currently piped through the local sewer
system to the wastewater treatment plant after being sent through a garbage disposal. Collaboration
between the bakery, produce, and meat departments within the grocery store need to improve in order
to coordinate a large scale waste separation process in the future.
Post-consumer scraps
Samples were taken from multiple local restaurants all of which contributed samples of mixed pre- and
post-consumer food waste in addition to samples of fryer grease. For the purpose of the biological
methane potential (BMP) trials, food and grease wastes from two of the restaurants were combined in
proportion to what they normally produce. Similar waste streams were provided by two local
institutions that were comprised entirely of post-consumer scraps. One institution separated waste into
solid and liquid portions – these were re-mixed for the purpose of sampling and analysis.
Florist shop waste
Finally, a sample was taken from a local florist consisting of refuse flower stems, flowers, petals, and
other plant matter.
Figure 30. Image of residential food waste sample collected.
135
Figure 31. Meat and butcher waste from substrate number 4.
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Appendix E. Biochemical Methane Potential Laboratory Procedure
320-mL bottles are used in the trials, and contain 200 mL of substrate, inoculum, and nutrient medium. Inoculum is an active anaerobic mixed culture media obtained from an operating bench scale AD reactor. The nutrient medium is added for the purpose of providing the necessary nutrients and trace elements for the microorganism to thrive.
Bottles with only inoculum were used in the set up as controls, to account for the background methane produced in the bottles by the inoculum.
Bottles containing only water were also used in the set up as controls, to correct for internal pressure variations due to external temperature and atmospheric pressure fluctuations.
Prior to incubation, bottles were gassed-out with a mixture of 70% N2 and 30% CO2 and sealed immediately.
Sealed bottles were placed in a mesophilic (37±1°C) incubator containing a shaker to constantly agitate the bottles during the trials.
The biogas production within the bottles was determined by pressure transducers attached to a hypodermic needle inserted through the septa of each bottle.
Pressure measurements were performed continuously over a period of 30 days using a data acquisition (DAQ) system connected to a computer. As pressure built-up in the bottles, it was periodically released by way of a valve in the top of the bottles. The instances of these pressure release events can be seen in Figure 12 by the presence of the small dips across the lines on the graph.
Pressure data recorded by the DAQ system were converted to volume of biogas at a standard temperature and pressure (STP) according to the ideal law of gases (PV = nRT). STP is defined as 1°C and 1atm.
Temperature inside the incubator was also continuously monitored through the DAQ with a thermocouple placed inside a control bottle containing water.
Methane and carbon dioxide content in the biogas was determined by a gas chromatograph (GC) and the methane yield was subsequently calculated.
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139
Appendix F. Projected farm survey responses Table 45. Farm survey responses based on projections for two years
Farm ID number
Number of
mature cows
Number of
heifers
Lactating cow equivalents (LCE) (total solids basis)
1* 200 150 262
2 0 150 62
3 66 10 70
4 105 75 136
5 620 80 653
6* 85 70 114
7* 195 195 275
8 80 80 113
9 688 448 872
10 145 115 192
11 190 160 256
12* 195 160 261
13 155 150 217
14* 175 80 208
15 85 35 99
16 75 70 104
17 80 70 109
18* 600 0 600
19 550 430 726
20 54 36 69
21 91 60 116
22 91 60 116
23 150 40 166
24 85 10 89
25 80 100 121
SUM 4,840 2,834 6,002
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Table 46. Farm survey responses based on five year projections
Farm ID number
Number of
mature cows
Number of
heifers
Lactating cow equivalents (LCE) (total solids basis)
1* 200 150 262
2 0 150 62
3 66 10 70
4 105 75 136
5 620 80 653
6* 85 70 114
7* 195 195 275
8 80 80 113
9 688 448 872
10 145 115 192
11 190 160 256
12* 195 160 261
13 155 150 217
14* 175 80 208
15 85 35 99
16 62 62 87
17 80 70 109
18* 500 150 562
19 750 430 926
20 54 36 69
21 91 60 116
22 91 60 116
23 150 40 166
24 85 10 93
25 50 60 121
SUM 4,897 2,936 6,151