Anaerobic Digestion in the Dairy Anaerobic Digestion in the Dairy Industry: Pollution Control Industry: Pollution Control
OpportunitiesOpportunities
Peter CiborowskiPeter CiborowskiMinnesota Pollution Control AgencyMinnesota Pollution Control Agency
Air Innovations ConferenceAir Innovations ConferenceAugust 10, 2004 August 10, 2004
Anaerobic Digestions of Farms Anaerobic Digestions of Farms WastesWastes
1970s energy crisis: Anaerobic digestion as 1970s energy crisis: Anaerobic digestion as an energy sourcean energy source
1980s-1990s: Anaerobic digestion as a 1980s-1990s: Anaerobic digestion as a pollution control measurepollution control measure
2000s: ???2000s: ???
Stages of Anaerobic DigestionStages of Anaerobic Digestion Hydrolysis: Hydrolysis: Liquefaction of complex organic Liquefaction of complex organic
compounds to simpler forms by compounds to simpler forms by hydrolytic hydrolytic bacteria; bacteria; principal endprincipal end products include soluble products include soluble sugars, amino acids, peptides, long-chain fatty sugars, amino acids, peptides, long-chain fatty acids. acids.
Acidogenesis: Acidogenesis: Metabolization of the products Metabolization of the products of hydrolysis by of hydrolysis by Acidogenic bacteria; Acidogenic bacteria; principal principal end products includeend products include s short-chain volatile organic hort-chain volatile organic acids (propionic, butyric, acetic and formic acids (propionic, butyric, acetic and formic acids), COacids), CO22, and H, and H2..
Stages of Anaerobic Digestion Stages of Anaerobic Digestion (cont.)(cont.)
Acetogenesis: Acetogenesis: Reduction of COReduction of CO22 and and catabolization of short-chain fatty acids catabolization of short-chain fatty acids produced during acidogenesis by produced during acidogenesis by ssynthrophic acetogenic and ynthrophic acetogenic and homoacetogenic bacteria; homoacetogenic bacteria; principal end principal end products include acetate, COproducts include acetate, CO22, H, H22..
Methanogenesis: Methanogenesis: Reduction of COReduction of CO22 and and cleaved acetate by cleaved acetate by Methanogens; eMethanogens; end nd products include CHproducts include CH44, CO, CO22,,,, trace Gases. trace Gases.
Anaerobic Digester Types for Dairy Anaerobic Digester Types for Dairy FarmsFarms
Warm Winter ClimatesWarm Winter Climates Covered Anaerobic LagoonCovered Anaerobic Lagoon
Cold/Cool Winter ClimatesCold/Cool Winter Climates Plug Flow DigesterPlug Flow Digester Complete Mix DigesterComplete Mix Digester Slurry-Loop DigesterSlurry-Loop Digester Anaerobic Sequencing Batch Reactor (ASBR)Anaerobic Sequencing Batch Reactor (ASBR)
Operating Parameters for Medium-Operating Parameters for Medium-Rate Farm DigestersRate Farm Digesters
TemperatureTemperature 35-40 C35-40 C pHpH 6.8-7.86.8-7.8 VFAVFA 200-2000 mg/l200-2000 mg/l Organic loading rateOrganic loading rate3-7kg VS/d/m3-7kg VS/d/m33 of of
digester volumedigester volume Retention timeRetention time 15-25 days15-25 days Total solids contentTotal solids content 7-12%7-12%
Digester Size and Cost ParametersDigester Size and Cost Parameters
Needed Digester volume Needed Digester volume 35 ft35 ft33 per cow per cow
500 head example dairy500 head example dairy
Manure ProductionManure Production 30 tons/day30 tons/day Volatile Solids Production Volatile Solids Production 3.5 tons/day3.5 tons/day Digester sizeDigester size 17,500 ft17,500 ft33
CHCH44 output output 13-32 Mcf/day13-32 Mcf/day Capital investmentCapital investment(a)(a) $250,000 ($1995)$250,000 ($1995)
(a)(a) At $500 (%1995) per cow At $500 (%1995) per cow
Environmental Problems Associated Environmental Problems Associated with Dairy Manure Managementwith Dairy Manure Management
Volatile fatty acids productionVolatile fatty acids production HH22S production and emissionS production and emission Ammonia emissionAmmonia emission Ozone and PMOzone and PM2.52.5 precursor emission (e.g., precursor emission (e.g.,
soil NOsoil NOxx emissions) emissions) Methane emissionMethane emission Fine particlesFine particles
Environmental Problems Associated Environmental Problems Associated with Dairy Manure Management with Dairy Manure Management
(cont.)(cont.)
Biological oxygen demand (BOD)Biological oxygen demand (BOD) Manure phosphorus imbalanceManure phosphorus imbalance Water-borne pathogensWater-borne pathogens
Environmental Benefits and Environmental Benefits and Drawbacks of Anaerobic DigestionDrawbacks of Anaerobic Digestion
Environmental AdvantagesEnvironmental Advantages
Reduced biological oxygen demandReduced biological oxygen demand Odor reduction (e.g., VFAs, phenol, mercaptan, Odor reduction (e.g., VFAs, phenol, mercaptan,
HH22S)S) Pathogen destructionPathogen destruction Reduced fly and rodent problemsReduced fly and rodent problems Increased nitrogen availability for crop growthIncreased nitrogen availability for crop growth Improved manure physical qualityImproved manure physical quality
Environmental Benefits and Drawbacks Environmental Benefits and Drawbacks of Anaerobic Digestion (cont.)of Anaerobic Digestion (cont.)
Environmental AdvantagesEnvironmental Advantages
Reduced manure phosphorus imbalanceReduced manure phosphorus imbalance Reduced methane emissionsReduced methane emissions Avoided emissions of fossil COAvoided emissions of fossil CO22 and Hg and Hg
Environmental DrawbacksEnvironmental Drawbacks
Possible increased ammonia volatilizationPossible increased ammonia volatilization SOSOxx emission emission
Measures of Control Potential of Measures of Control Potential of Anaerobic DigestionAnaerobic Digestion
% reduction% reduction
Manure solidsManure solids 20-40%20-40% Manure volatile solidsManure volatile solids 20-45%20-45% Biological oxygen demandBiological oxygen demand 40-75%40-75% Chemical oxygen demandChemical oxygen demand 20-50%20-50% Volatile fatty acidsVolatile fatty acids high high (a)(a)
PathogensPathogens 90%90% MethaneMethane 90%90%(a)(a) 75-95% for digestion of swine manure 75-95% for digestion of swine manure
Energy Production from Anaerobic Energy Production from Anaerobic Digestion of Dairy ManureDigestion of Dairy Manure
ftft33 biogas/cow/day biogas/cow/day 47-9747-97 Biogas energy content (Btu/ftBiogas energy content (Btu/ft33) ) 600-650600-650 kWh (e) /cow/day kWh (e) /cow/day 1.5-3.01.5-3.0 Gal LPG-equiv-avail/cow/day Gal LPG-equiv-avail/cow/day 0.21-0.440.21-0.44
kWhr (e) /animal/year kWhr (e) /animal/year 540-1,117540-1,117 Gal LPG-equivalent-available/yr Gal LPG-equivalent-available/yr 77-16077-160
kW(e)-equivalent animal numbers kW(e)-equivalent animal numbers 8-16 8-16
Energy Production Potential: 500 Energy Production Potential: 500 Cow DairyCow Dairy
Generation capacity: 30 to 60 kW Generation capacity: 30 to 60 kW Annual electrical generation: 270,000 to Annual electrical generation: 270,000 to
559,000 kwh559,000 kwh Gross annual energy production (MMBtu): Gross annual energy production (MMBtu):
10 to 2010 to 20
Sensitive Terms for Economic Sensitive Terms for Economic Analysis of Anaerobic DigestionAnalysis of Anaerobic Digestion
Manure solids contentManure solids content Cost of capitalCost of capital Materials costMaterials cost Value of replacement energyValue of replacement energy Purchase price of excess farm-generated Purchase price of excess farm-generated
electricityelectricity IRR hurdleIRR hurdle
Herd Size Threshold for Economic Herd Size Threshold for Economic Viability of Anaerobic Digestion Viability of Anaerobic Digestion
dairy cowsdairy cows Published literature 1975-2000Published literature 1975-2000 500-800 500-800 2001 estimate for Minnesota 2001 estimate for Minnesota (a)(a)
no policy interventionno policy intervention 650 650 $0.015/kwh production subsidy 350$0.015/kwh production subsidy 350 Best guess, current conditionsBest guess, current conditions 500-600 500-600
(a) Free stall, flush parlor and feed apron and scrape rest, 10% IRR hurdle, $0.07/kwh farm (a) Free stall, flush parlor and feed apron and scrape rest, 10% IRR hurdle, $0.07/kwh farm electric rates, purchase price for excess electricity $0.015-0.04/kwh, no credit for electric rates, purchase price for excess electricity $0.015-0.04/kwh, no credit for pollution control. pollution control.
CaveatsCaveats
Anaerobic digestion works best with new dairies and full integration Anaerobic digestion works best with new dairies and full integration of digester into dairy design (e.g., gravity manure flow, waste heat of digester into dairy design (e.g., gravity manure flow, waste heat use, high manure total solids)use, high manure total solids)
Local conditions are importantLocal conditions are important Accounting for the money-value of time is essential Accounting for the money-value of time is essential
Lesson: Anaerobic digestion is not for everyone. Certainly Lesson: Anaerobic digestion is not for everyone. Certainly anaerobic digestion is not for small producersanaerobic digestion is not for small producers
The economics of anaerobic digestion depend critically about what The economics of anaerobic digestion depend critically about what you assume about the future cost of energy, materials and capital you assume about the future cost of energy, materials and capital and future yields from alternative uses of investment dollars and future yields from alternative uses of investment dollars
Covering Preexisting Anaerobic Covering Preexisting Anaerobic LagoonsLagoons
InexpensiveInexpensive Minimum herd size for economic Minimum herd size for economic
deployment smaller by half that of medium-deployment smaller by half that of medium-rate digestersrate digesters
Where it can be deployed, the optimal use Where it can be deployed, the optimal use of anaerobic digestionof anaerobic digestion
Anaerobic Digestion: Final WordAnaerobic Digestion: Final Word
Anaerobic Digestion: Cross-media pollution Anaerobic Digestion: Cross-media pollution control at a profitcontrol at a profit
Availability of: MPCA, Availability of: MPCA, Anaerobic Digestion Anaerobic Digestion of Livestock Manure for Pollution Control of Livestock Manure for Pollution Control and Energy Production: A Feasibility and Energy Production: A Feasibility AssessmentAssessment, , March 2001, contact MPCA at March 2001, contact MPCA at [email protected]@pca.state.mn.us
