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FROM WASTE TO WORTHANAEROBIC DIGESTION
Becky LarsonAssistant Professor and Extension SpecialistBiological Systems Engineering
November 24, 2015
What is Anaerobic Digestion?• Biological process• Breakdown of organic materials (called feedstocks) • Absence of oxygen (anaerobic conditions)• Produced biogas - methane (CH4) and carbon dioxide (CO2)
Why install a digester?• Energy independence• Reductions in green house gases• Flexibility in manure management • Reduced odors & pathogens• Reduction in other environmental impacts• Potential for additional asset streams (?)
• Bedding• Tipping fees• Environmental credits
• Profits?• What can’t digesters do?
Anaerobic Digestion in the U.S.
USEPA AgSTAR, 2011
Anaerobic Digestion Livestock & Swine Operations
Animals No. of Digesters Operational or in Construction
Methane Emissions
Reductions (metric tons CO2-eq/year)
Shutdown Projects
All Livestock 261 3,480,955 52Swine 39 1,491,718 10
• North Carolina has 10 swine digesters, others are scattered around country
• Operational from as far back as 1985• From 1,200 to 1,200,000 million animals• Completely mixed, covered lagoons, mixed plug flow
designs• Gas use in boilers, electricity, cogeneration, flares
USEPA AgSTAR, 2015
Biogas Opportunities RoadmapVoluntary Actions to Reduce Methane Emissions and Increase Energy Independence
U.S. Department of Agriculture, U.S. Environmental Protection Agency, U.S. Department of Energy
August 2014
Traditional Anaerobic Digestion Process Flow
Slurry
Biogas
SeparatorDigestate
Filtrate (liquid)
Fiber (solid)
Feedstock's
Anaerobic Digestion Feedstocks
Cheese Whey
Swine Manure
Dairy Manure
Cattle Manure
Cucumber Waste
Yard ClippingsMunicipal Organics
Human Waste
Food Processing Waste
Vegetables
Grasses
Characterized by rapid bacterial growth
“Weak link” in the process of producing biogas
Goal?...Avoid inhibition, maintainstabilization!
Stage Three: Acetogenesis
Stage One: Hydrolysis
Stage Two: Acidogenesis
Stage Four: Methanogenesis CO2 reducing
methanogensaceticiastic
methanogens
acetogens(H2
producing)
fermentative bacteria
fermentative bacteria
PROPIONATE, BUTYRATE, etc.
(Short-chain volatile organic acids)
fermentative bacteria
fermentative bacteria
COMPLEX POLYMERS(Proteins, polysaccharides, etc.)
MONOMERS AND OLIGOMERS(Sugars, amino acids, peptides)
acetogens(H2 consuming)
H2 + CO2 ACETATE
CH4, CO2
Source: Syed Hashsham, PhD, lecture notes, Michigan State University
The Biological Process of Producing Biogas
Biogas Yield
Kestutis Navickas. 2007. Bioplin Tehnologija in Okolje,
Anaerobic Digester Completely Mixed and Plug Flow
AD System Types
Covered storage
Covered Lagoon Digester and FlareBaldwin Dairy, Baldwin, WI Covered Lagoon at a Swine Farm
Olivia, MN
Advantages included odor control, low cost, integrated manure storage and minimal operational costsDisadvantage include seasonal biogas production in cold climates and difficulties with sludge removal
Plug flow & mixed plug flow
Plug flow digester and flare Emerald Dairy, Baldwin, WI
Inside a plug flow digester under construction Baldwin Dairy, Baldwin, WI
Advantages include low cost of construction and ease of daily operationDisadvantage include the limited range of feedstock TS concentration
Completely mixed
Complete mix digester Green Valley Dairy, Krakow, WI
Complete mix digester Five Star Dairy, Elk Mound, WI
Inside a completely mixed AD
Slow speed agitator fixed to the digester floor
Inside a complete mix digester under construction Westfalia, Germany
Submersible mix mounted to a mast
Fixed film
Fixed film digester mediaJ.J. Farber Farm, East Jewett, NY
Fixed film digesterROPA, Regensburg, DE
Advantages include low cost of construction and ease of daily operationDisadvantage include the limited range of feedstock TS concentration
Dry Digestion
OshKosh Dry Digester, BIOFerm
Small Scale Digesters
Small Scale Digestion
Ecofys bag digester, ecofys.com
Community DigestersDane County Digester, 2011
Biogas • Biogas Components
• CH4 (50 – 65%)• CO2 (40 – 50%)• H2S (<1%)• Other Trace Elements (?)
• Generator (CHP) – electricity production• Most common (ease of use)• High cost• Requires pretreatment or specially
designed equipment• Compressed Biogas
• High cost of clean-up• Requires design• High revenue
• Biogas Treatment• High cost systems• Multi-phase approach
Digestate
• Must be disposed• Liquid and solid commonly used for fertilizer
• Solids potential for higher value products
• AD results in:• nutrient mineralization• odor reduction• pathogen reduction• antibiotic degradation
Nutrients & Anaerobic Digestion
Wright, et al. 2004. Preliminary Comparison of Five Anaerobic Digestion Systems on Dairy Farms in New York State
0
1000
2000
3000
4000
5000
6000
AA DDI FA ML* NH
TKN Con
centratio
n (m
g/kg)
Facility
TKN
Input
Output
Nutrients & Anaerobic Digestion
0
500
1000
1500
2000
2500
3000
AA DDI FA ML* NHAmmon
ia Con
centratio
n (m
g/kg)
Facility
Ammonia
Input
Output
Wright, et al. 2004. Preliminary Comparison of Five Anaerobic Digestion Systems on Dairy Farms in New York State
Increase of 24%
Ammonia
0
5000
10000
15000
20000
25000
30000
35000
40000
Pre Digestion Post Digestion
Am
mon
ia (m
g/L)
Nutrients & Anaerobic Digestion
Wright, et al. 2004. Preliminary Comparison of Five Anaerobic Digestion Systems on Dairy Farms in New York State
0100200300400500600700800900
AA DDI FA ML* NHTotal Pho
spho
rus Co
ncen
tration
(mg/kg)
Facility
Total Phosphorus
Input
Output
Phosphorus
020406080
100
Liquid %Solid %
N-P-K
Concentration N (g/kg) P2O5 (g/kg) K2O (g/kg)
Manure 50 18 41
Liquid 101 27 75
Solid 15 14 8
Ratio N P2O5 K2O
Manure 3 1 2Liquid 4 1 3
Solid 2 2 1
OdorSwine ManureHansen et al. 2006, Applied Engineering in Agriculture• Slurry concentrations of
malodorous VFA were reduced 79-97% from AD
• Odor concentration above undisturbed slurry store reduced (higher odors after mixing)
• Land application odor reductions:• 17% anaerobic digestion• 50% anaerobic digestion
and solid liquid separation
Orzi et al., 2015, Science of the Total Environment• Odors reduced 98%• P2-P6 are pig slurries• VFA destruction related to measured odor
reductions
Pathogens in manure from a single farm by year and season
Autumn, 2009Spring, 2010
Autumn, 2010Spring, 2011
1
10
100
1000
10000
100000
1000000
10000000
100000000
1E+09
Mean Pathogen
Con
centratio
n (gc/gm
)Bovine Polyomavirus
Farm #1
Farm #3
Farm #4
Farm #5
Farm #6
Farm #7
Farm #8
Antibiotic Degradation
Alvarez et al., 2010, Bioresource Technology• Fate of antibiotics in pig manure in AD• oxytetracycline (OTC) and chlortetracycline (CTC)• Reduction in antibiotics over time, as well as
methane production• Antibiotics adsorbed to solids increasing duration
for destruction
• Many antibiotics to be tested
• Not many studies to date
• May increase intermediates
• Beef manure studies by Arikan(2006, 2007, 2008) found some degradation in initial component, increases in some intermediaries
-60.00
-50.00
-40.00
-30.00
-20.00
-10.00
0.00
10.00
-60
-50
-40
-30
-20
-10
0
10
SLS AD AD+SLS
kg C
O2-
eq to
n-1ex
cret
ed m
anur
e
CO2(f) CO2(b) N2O(f) N2O(b) CH4(f) CH4(b) NET
Global Warming Potential
Ammonia Emissions
0.0
0.3
0.6
0.9
1.2
1.5
1.8
Collection Storage Application
NH3 emissions (AD)kg NH3-eq ton-1 excreted manure
0.0
0.3
0.6
0.9
1.2
1.5
1.8
2.1
Collection Storage Application
NH3 emissions (BC)kg NH3-eq ton-1 excreted manure
Limitations to Adoption• Lack of Awareness of Biogas Benefits.• Unpredictable Biogas Market
Conditions• Lack of Market Maturity. • Lack of Full Valuation• Inconsistencies across Federal, State,
and Local Governments.• Lack of Technical and Applied
Research & DevelopmentBiogas Opportunities RoadmapVoluntary Actions to Reduce Methane Emissions and Increase Energy Independence U.S. Department of Agriculture, U.S. Environmental Protection Agency, U.S. Department of EnergyAugust 2014
• Capital cost• Operating cost• Energy use• Energy value• By-product
Revenue
Thank You!
Becky Larsonralarson2@wisc.edu(608) 890-3171
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