anaerobic digestion at noblehurst farms, inc.: case … and improve business viability ... a...

Last Updated 3/2009 Case Study AD-5

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Manure Management Program www.manuremanagement.cornell.edu

UUAnaerobic Digestion at Noblehurst Farms, Inc.: Case Study

Dept. of Biological and Environmental Engineering, Cornell University

Jennifer Pronto & Curt Gooch, P.E.

March 2009

Contents:

Farm overview

o General facts

o Why the digester?

Digester System

o System and process description

o System drawing

o Liquids and solids process description

o Heat and electricity generation

Economics

o Initial capital costs

Lessons learned

Previous testing results

Contact information

UUAnaerobic digestion overview

Digester type: Plug-Flow (two parallel cells)

Digester designer Cow Power

Influent Raw Manure, hog processing waste

Stall bedding material Post-digested separated manure solids

Number of cows 1,600 total cows

Rumensin®

usage Yes

Dimensions (WxLxH) 50’x120’x16 (each cell is 25 ft. wide)

Cover material Hard top (Pre-cast and cast-in-place concrete)

Design temperature (°F) 100

Estimated total loading rate (gpd) 30,000

Treatment volume (gallons) 673,246

Estimated hydraulic retention time 23 days

Solid-liquid separator Yes, post-digestion, Vincent (KP-10)

Biogas utilization Caterpillar engine with 130-kW generator

Carbon credits sold/accumulated Yes

Monitoring results available Yes; see page 5

http://www.manuremanagement.cornell.edu/


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UUFarm overview

Noblehurst Farms, Inc., managed by Robert Noble, is located in Livingston County, New

York

The farm has 1,500 lactating dairy cows

The farm raises forage crops on 2,000 acres of crop land

The primary reasons for construction of the anaerobic digester were to address environmental

issues and improve business viability

Digester construction began in the summer of 2001 and the biogas-fired engine-generator set

started producing electricity on January 15, 2003

The digester was sized for future herd expansion in mind

The project was budgeted for $648,830. Obtaining a cost-sharing contract from the New York

State Energy Research and Development Authority (NYSERDA) helped move the project

forward.

UUWhy the digester?

Noblehurst Farms had several reasons for choosing to construct an anaerobic digester.

Environmental concerns were a high priority as the farm is sited in two watersheds that provide

the primary drinking water supply for nearby communities. Traditionally manure was spread

daily on cropland and thus water pollution from manure-borne pathogens and nutrient loading

was a concern. Long-term storage could create greater odor issues in a community that already

had expressed their objection to existing odors from the intensive dairy farming in the area.

As increasing pressure from environmental regulations and the surrounding community

increased, Noblehurst considered a centralized digester for better manure management.

However, when the centralized feasibility study: Evaluation of Anaerobic Digestion Options for

Groups of Dairy Farms in Upstate New York (Jewell et al., 1997) suggested a system containing

only one or two farms to be the best alternative, Noblehurst decided on a single-farm anaerobic

digester. The reasoning for this decision was to better utilize the electricity produced and to

minimize manure transportation costs.

The overall project goals were to construct and operate a cost-effective anaerobic digester

system, which would demonstrate the following benefits:

• Odor reduction

• Pathogen reduction

• Nutrient control

• Reduction of methane emissions

• Reduction in volatile solids introduced into storage tanks/ponds

• Electricity savings and sales

• Heating savings


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Digester System

UUSystem and process description

The digester system includes several subsystems (see Figure 1) including:

Manure collection and transport

Co-mingling with hog processing waste substrate

Anaerobic digestion

Biogas utilization by an engine-generator set

Digester effluent solid-liquid separation

Separated solids handling for use as freestall bedding

Separated liquid handling to long-term storage and field application

The plug-flow digester containment vessel is a rectangular, below-grade cast-in-place concrete

tank (120’ x 50’ x 16’) consisting of two digesters separated by a concrete wall (see Figure 1).

The digester has a flat top made of pre-stressed concrete panels overlaid with cast-in-place

concrete, insulation, and earth. The digester biogas head space is sealed from the inside to

prevent biogas leakage. Fifteen inches of water column pressure was the design pressure

developed within the head space as a result of the hard top. One goal of this system was to

eliminate the need for a blower to compress the biogas before utilization by the engine-generator

set.

With 1,500 milkers onsite, the manure production is estimated to be 30,300 gal/day or

11,055,300 gal/year. The estimated retention time of the digester is about 23 days.

Figure 1. Flow diagram of Noblehurst manure treatment system


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UULiquids and solids process description

Manure is scraped from each freestall barn to a central below-grade channel, where it flows by

gravity to a collection pit (approximately 28,000-gallon capacity) located on the east side of the

barns and adjacent to a short-term concrete manure storage facility that existed before the

anaerobic digestion project. Barn manure and liquid effluent from the screw-press separator is

mixed in this pit to obtain an overall dry matter content of about 10 percent to facilitate pumping

digester influent to the digester influent manifold. The goal was to distribute influent essentially

equally to each of the two parallel digesters on an intermittent basis for 12 hours a day.

A sediment trap with suction pump access was built into each digester to facilitate removal of

accumulated grit and fixed manure solids (those that are not digestible).

Effluent from each digester flows by gravity to a common cast-in-place concrete effluent pit

located below grade. Effluent is pumped to a Vincent screw-press separator located in the 2nd

story of an adjacent three-sided building. Separated solids are stockpiled until needed for

freestall bedding material. All separated solids are used for bedding; there is no excess available

for alternative use. Quality of the separated manure solids was investigated from an

opportunistic pathogen standpoint and reported on at the 2006 National Mastitis Council meeting

(see Gooch et al., 2006). Overall, the post-digested separated solids had relatively low pathogen

concentrations but concentrations rapidly grow exponentially once the bedding has been in the

stalls for 24 hours or longer.

Screw-press separated liquid effluent flows by gravity to the short-term storage located adjacent

to the digester influent pit. As previously mentioned, some of this liquid is used to dilute barn

effluent to about 10 percent dry matter so it can be more easily pumped into the digester. The

reminder of the separated liquid is pumped to a remote earthen long-term storage where it is held

until recycled to the farm’s land base in accordance with their CAFO permit.

Biogas Utilization

UUCombined heat and power generation

The current estimated biogas production is 40,000 ft3

per day. Biogas is collected from both

digesters and used to fire an engine-generator set. The engine is a Caterpillar 3406NA (285-Hp)

and the generator is a Marathon 447 (130-kW). The generator output varies; it has run as high as

100-kW and as low as 60-kW. The engine-generator set has an estimated electricity production

of 788,400 kWh/year based on a 90-kW output.

Engine water jacket water is used to heat digester influent and maintain operating temperature.

Excess heat is dumped to the ambient with a water to air heat exchanger.


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Economics

Items Cost/Benefit *

Capital Costs

Digester

- Digester Construction and Materials

- Cover for digester

Subtotal

$250,000

$60,000

$310,000

Engine-Generator Set

- Engine Generator

- Switching Equipment

- Engine Building

Subtotal

$241,000

$18,000

$43,500

$302,500

Manure Storage $60,000

Solids and Liquids Separation

- Separator

- Separator Building

Subtotal

$26,000

$35,000

$61,000

Others (flare, pumps) $14,200

Total Capital Cost $747,700

Total Capital Cost per cow $680

Total Annual Capital Cost $68,522

Annual Operating Costs

Maintenance, Repairs, Labor, Fuel,

Insurance, etc.

$37,675

Manure Spreading Cost (@ 0.005/gallon) $51,000

Annual Benefits

Electricity Savings and Sales (projected) -$60,000

Heating Fuel Savings (projected) -$6,000

Compost sale (projected sales @ net

$2/cubic yard)

-$11,680

Odor Control (@$9/cow/year) -$9,900

Total Annual Benefits -$77,680

Annual Net Cost Per Cow ($/cow/year) $50 **

Note: * - The operating costs (maintenance and repairs) and revenues are projected numbers as of

November 1, 2003. An updated analysis will be provided with real data once the system is operated for one

year.

** - Manure management without digester and solids separator would cost $50/cow.

Table 1. Initial capital costs for Noblehurst Farms

Lessons Learned Noblehurst Farms reports the following lessons have been learned as a result of constructing and

managing their anaerobic digester.

Before the on-farm system was constructed, a feasibility study was performed to explore the

possibility of partnering with other nearby farms to construct a community-based anaerobic

digester. A major disadvantage was the expense of manure transportation to the community site

and digester effluent transportation back to each farm was a huge cost for the community system

to overcome.


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Digesters with concrete hard tops are very difficult to seal and when the biogas head space is

maintained at a positive pressure, biogas leaks occur. Biogas leaks cause loss of biogas available

for energy conversion and most importantly result in increased farmstead odors. Pressure testing

the biogas containment system before filling the digester with manure is time consuming and

expensive but apparently needed to ensure that the sealant has been properly applied.

Complete engine-generator set and biogas handling skids, appropriately sized and assembled in

factories, provided ease of design and mechanical equipment installation. The systems were

assembled with compatible equipment and controls so on-farm installation was easily

accomplished.

Two side-by-side digesters were constructed to avoid an excessively long single digester and

reasonable spans for the clear-span concrete top are viable design options. Additionally, the twin

digester design makes it possible to shut down and start up each digester independently and

therefore increases management flexibility. Operating experience has shown that it is hard to

divide digester influent equally between the two digesters; an appropriately designed flow meter

along with an automated control device may help solve this problem.

Burying the engine-generator set exhaust pipe and outletting it some distance from the engine

room reduces corrosion of the biogas utilization building and also helps reduce noise near the

building. Internal combustion engines are loud. Additional sound control may be needed on

some sites.

Maintaining digester operating temperature control is important, especially during the winter.

Frozen manure and manure with excessive water is regularly bypassed around the digester.

However, when the digester feed is reduced biogas production drops and less heat is available to

warm influent to temperature and maintain it. Either added external energy is needed to maintain

the digester temperature or the digester would need several months and warmer weather to

recover.

Temperature sensors installed in vessel read 3°F higher than reality. Checking and calibrating the

instrumentation should be an important step in start-up procedures.

Previous Testing Results Noblehurst Farm’s anaerobic digester system, along with six others in New York State, is in the

process of being monitored to determine key performance items such as: manure stabilization,

engine-generator set performance, reduction in greenhouse gas emissions, and economic benefit

to the farm. Five of the seven systems currently being monitored were also monitored in the

past, including Noblehurst Farm’s.

The following data was taken from an interim monitoring report written in 2007; the complete

report is available on line at www.manuremanagement.cornell.edu and can also be obtained by

contacting us directly.


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UUWaste stabilization results

Digester influent and effluent samples were collected monthly from 8/2003 to 4/2005, and

screw-press influent and effluent samples were collected monthly from 10/2004 to 2/2005. The

values in the following table are the average (Avg), standard deviation (St. Dev.), 99 percent

confidence interval (CI) and the number of samples (n) for digester influent, digester No. 1

effluent, digester No. 2 effluent along with the same parameters for the solid-liquid separator

influent, liquid effluent, and solids effluent.

A confidence interval for a mean specifies a range of values within which the unknown

population parameter, in this case the mean, may lie. A negative value for the percent change in

a constituent concentration indicates an increase in the constituent concentration as a result of the

digestion or separation process, while a positive value represents a constituent concentration

reduction. Shaded table cells indicates those values found to be statistically different at the 99

percent CI while those cells not shaded were not found to be statistically different at the 95

percent CI.

Constituent Statistic

Digester

influent

conc.

Digester

cell #1

effluent

Digester

cell #2

effluent

% change

in conc.

Digester

cell #1

% change

in conc.

Digester

cell #2

Solid-

Liquid

separator

influent

conc.

Solid

liquid

separator

liquid

effluent

conc.

Solid-

liquid

separator

solid

effluent

conc.

pH

(Std. units)

Avg. 7.42 7.74 7.75

-- --

7.74 7.83 8.83

St. Dev. 0.39 0.18 0.14 0.13 0.10 0.09

CI 0.17 0.08 0.06 0.06 0.09 0.08

n 21 21 21 20 5 5

TS

(percent)

Avg. 10.4 8.52 8.20

18.1 21.2

8.25 4.90 37.4

St. Dev. 2.29 1.31 1.57 1.21 0.24 2.15

CI 0.98 0.56 0.67 0.53 0.21 1.89

n 21 21 21 20 5 5

TVS

(percent)

Avg. 7.72 6.51 6.26

15.5 18.8

6.28 3.29 33.4

St. Dev. 1.91 1.22 1.39 1.09 0.20 2.04

CI 0.82 0.52 0.60 0.48 0.18 1.79

n 21 21 21 20 5 5

Volatile

acid as

Acetic acid

(mg/kg)

Avg. 2,881 569 589

80.2 79.5

-- -- --

St. Dev. 1,021 270 395 -- -- --

CI 437 115 169 -- -- --

n 21 21 21 -- -- --

COD

(mg/kg)

Avg. 78,586 63,107 63,067

19.7 19.7

61,714 42,440 127,360

St. Dev. 28,638 17,272 17,846 10,221 7,324 78,660

CI 12,248 7,387 7,633 4,479 6,420 68,947

n 21 21 21 20 5 5

DCOD

(mg/l)

Avg. 23,508 20,211 18,168

14.0 22.7

19,242 -- --

St. Dev. 11,021 8,060 5,869 6,653 -- --

CI 4,714 3,447 2,510 2,916 -- --

n 21 21 21 20 -- --

Log10MAP

(cfu/gram)

Avg. 3.6 1.7 2.0

98.7 98.1

1.8 -- --

St. Dev. 0.4 0.4 0.4 0.3 -- --

CI 0.3 0.4 0.4 0.2 -- --

n 11 9 8 11 -- --


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Constituent Statistic

Digester

influent

conc.

Digester

cell #1

effluent

Digester

cell #2

effluent

% change

in conc.

Digester

cell #1

% change

in conc.

Digester

cell #2

Solid-

Liquid

separator

influent

conc.

Solid

liquid

separator

liquid

effluent

conc.

Solid-

liquid

separator

solid

effluent

conc.

Log10F.

Coli.

(mpn/gram)

Avg. 6.0 3.5 3.8

99.5 99.5

3.6 3.3 3.0

St. Dev. 0.6 0.7 0.5 0.5 0.8 0.5

CI 0.3 0.4 0.3 0.2 1.1 0.7

n 19 17 17 19 4 3

TKN

(mg/kg)

Avg. 4,075 4,203 4,001

-3.15 1.81

4,029 3,931 4,444

St. Dev. 974 869 829 776 625 756

CI 416 372 355 340 548 683

n 21 21 21 20 5 5

NH3-N

(mg/kg)

Avg. 1,944 2,516 2,329

-29.4 -19.7

2,414 2,450 2,180

St. Dev. 634 464 515 470 519 599

CI 271 199 220 206 455 525

n 21 21 21 20 5 5

ON

(mg/kg)

Avg. 2,130 1,687 1,672

20.8 21.5

1,616 1,481 2,265

St. Dev. 923 749 681 629 231 723

CI 395 321 291 276 203 634

n 21 21 21 20 5 5

TP

(mg/kg)

Avg. 503 218 514

-3.10 -2.26

508 471 892

St. Dev. 148 102 92 79 50 101

CI 63 44 39 35 44 89

n 21 21 21 20 5 5

OP

(mg/kg)

Avg. 242 310 290

-28.0 -19.7

300 301 563

St. Dev. 80 40 56 44 50 36

CI 34 17 24 19 44 31

n 21 21 21 20 5 5

K

(mg/kg)

Avg. 2,374 2,363 2,499

0.47 -5.26

2,435 2,707 2,241

St. Dev. 422 580 500 500 262 547

CI 239 328 283 295 230 479

n 12 12 21 11 5 5

Cu

(mg/kg)

Avg. 15.7 15.3 20.75

-- --

-- -- --

St. Dev. 6.2 6.15 4.86 -- -- --

CI 6.08 6.03 4.76 -- -- --

n 4 4 4 -- -- --

UUBiogas and energy production results

Energy production and use data was collected between 8/2004 and 5/2005. The average daily

biogas production was divided by the average daily weight of VS consumed by the digester to

compare the digester’s efficiency in production of biogas. The biogas carbon dioxide

concentration was measured using a Bacharach, Inc. FYRITE gas analyzer. The biogas was

tested by the farm or the researchers during farm visits, and the recorded values are shown.

The electrical energy generated, purchased, sold, displaced, and used by each farm is shown in

the table. Displaced energy was the energy sold subtracted from the energy produced. Farm

utilization was calculated by adding the energy displaced and the energy purchased.


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Monthly

metered

biogas

(ft3)

Average

biogas

CO2

content

(%) 1

Monthly energy generated,

purchased, sold, displaced,

and used on-farm (kWh)

Capacity

factor

Energy

(kWh) per

cubic foot of

biogas used

Average 1,472,822 39.0

Generated: 59,642

Purchased: 22,601

Sold: 8,382

Displaced: 51,257

Used on-farm: 73,858

0.560 31.32

Range 415,500

1,995,126

32

40

Generated: 18,267 to 85,893

Purchased: 1,551 to 60,637

Sold: 71 to 22,749

Displaced: 18,196 to 68,330

Used on-farm: 56,374 to 92,966

0.151 to

0.918

33.0 to

45.5

Standard Dev. 475,334 -- -- -- --

Number

samples 14 months 24 10 months

17

months 17 months

Table 3. Energy production and usage according to the results from NYSERDA’s Interim Report

for the “Biogas Distributed Generation Systems Evaluation and Technology Transfer” project. 1Therefore, the estimated CH4 concentration is CO2 + CH4= 10

UUResults from current monitoring project

Digester system monitoring at Noblehurst Farms continues, following the Association of State

Energy Research & Technology Transfer Institutions (ASERTTI) protocol (Martin, 2007),

developed to standardize monitoring and reporting of anaerobic digestion systems.

This case study will be updated to show the results of the continued monitoring along with other

information that becomes available.

Who to Contact

Rob Noble, Managing Partner, Noblehurst Farms, Inc. Phone: 585-584-3122, e-mail:

[email protected]

Curt Gooch, P.E., Dairy Housing and Waste Management Engineer, PRO-DAIRY Program,

Biological and Environmental Engineering, Cornell University, Phone: 607-255-2088, e-

mail: [email protected]

Dave Palmer, Designer, Cow Power Inc., Syracuse, New York. Phone: (315) 457-8250, e-

mail: [email protected]


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References

Martin, J.H., A Protocol for Quantifying and Reporting the Performance of Anaerobic Digestion

Systems for Livestock Manures, 2007.

”Big-5 Interim Report”: See “Biogas Distributed Generation Systems Evaluation And

Technology Transfer - Interim Project Report. April, 2007” Project #: 6597.

http://www.manuremanagement.cornell.edu/HTMLs/Project_Reports.htm

Jewell, W.J., et al., 1997. Evaluation of Anaerobic Digestion Options for Groups of Dairy

Farms in Upstate New York.

Gooch, C.A., J.S. Hogan, N. Glazier, and R. Noble. 2006. Use of post-digested separated

manure solids as freestall bedding: a case study. Written for Presentation at the NMC 2006

Annual Meeting, Tampa, Florida

Acknowledgements The authors would like to thank the New York State Energy Research and Development Authority (NYSERDA) for funding in support of this work. Any opinions, findings, conclusions or recommendations expressed in this publication are those of the authors and do not necessarily reflect the views of NYSERDA or the State of New York, and reflect the best professional judgment of the authors based on information available as of the publication date. Reference to any specific product, service, process, or method does not constitute an implied or expressed recommendation or endorsement of it. Further, Cornell University, NYSERDA and the State of New York make no warranties or representations, expressed or implied, as to the fitness for particular purpose or merchantability of any product, apparatus, or service, or the usefulness, completeness, or accuracy of any processes, methods, or other information contained, described, disclosed, or referred to in this publication. Cornell University, NYSERDA and the State of New York make no representation that the use of any product, apparatus, process, method, or other information will not infringe privately owned rights and will assume no liability for any loss, injury, or damage resulting from, or occurring in connection with, the use of information contained, described, disclosed, or referred to in this publication.

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