Anaerobic Digestion: Biomass to Bioenergy Douglas W. Hamilton, Ph.D., P.E. Associate Professor, Biosystems and Agricultural Engineering Waste Management.

Anaerobic Digestion:Biomass to Bioenergy

Douglas W. Hamilton, Ph.D., P.E.Associate Professor,

Biosystems and Agricultural Engineering

Waste Management Specialist,

Oklahoma Cooperative Extension Service

Anaerobic Digestion of Manure Understanding Basic Processes

Digestion Process

CH4

CO2

H2

NH3

H2S

+

Biogas

Acid Formers

Methane Formers

Liquifiers

Acid Formers

Methanogens

Hydrolizers

Community Needs1. Food

2. Proper pH

3. Sufficient Temperature

4. Sufficient Time to Reproduce

5. Absence of Inhibitory Substances

Community Needs

Proper pH : ~ 6.5 to 7.5

Community Needs

Sufficient Temperature

Psychrophilic (15-25o C)Mesophilic (30-38o C)Thermophilic (50-60o C)

Community Needs

Sufficient time to reproduce

HRT = Volume of Reactor/Flow out

SRT = Solids in Reactor/Solids Leaving

Anaerobic Digestion of Manure Understanding Basic Processes Types of Reactors

Low Rate Reactor

SRT = HRT

High Rate Reactor

SRT > HRT

How much energy?

Anaerobic Digestion of Manure Understanding Basic Processes Types of Reactors Organic Matter of Wastewater and Manure Methane Production Potential Toxic and Inhibitory Materials

Codigestion

Mixing a highly digestible material with a source of microorganisms (manure) to produce a large volume of biogas.

Methane Potential Volatile Solids Content

Combustion

OM + O2 → CO2 + H2O + Ash + Heat

Combustion

OM + O2 → CO2 + H2O + Ash + Heat

TS FS

Combustion

OM + O2 → CO2 + H2O + Ash + Heat

TS FSVS

VS db%

Beef Manure 82

Dairy Manure 84

Wood Shavings 99

Alfalfa Silage 95

Grease 99

Aerobic Catabolism

OM + O2 → CO2 + H2O + Cells + Heat

Aerobic Catabolism

OM + O2 → CO2 + H2O + Cells + Heat

Oxygen Demand

Aerobic Catabolism

OM + O2 → CO2 + H2O + Cells + Heat

Oxygen DemandCODBODu

Methane Potential Volatile Solids Content COD

Anaerobic Catabolism

OM + Heat → CH4 + CO2 + H2O + Cells

Anaerobic Catabolism

OM + Heat → CH4 + CO2 + H2O + Cells

Biogas

Combustion

OM + Heat → CH4 + CO2 + H2O + Cells

CH4 + 2O2 → CO2 + H2O + Heat

Combustion

OM + Heat → CH4 + CO2 + H2O + Cells

CH4 + 2O2 → CO2 + H2O + Heat

Oxygen Demand

Combustion

CH4 +2O2 → CO2 + H2O + Heat

Two moles O2 per mole CH4

Combustion

CH4 +2O2 → CO2 + H2O + Heat

2nOD = nCH4

Combustion

CH4 +2O2 → CO2 + H2O + Heat

PV = nRT

Combustion

CH4 +2O2 → CO2 + H2O + Heat

VCH4 = 2nODRT/P

Ultimate Gas Yield

CH4 +2O2 → CO2 + H2O + Heat

0.38 L CH4 produced per kg OD removed

@ 20oC and 1 atm

VS db%

COD:VS

Beef Manure 82 1.2

Dairy Manure 84 1.2

Wood Shavings 99 0.19

Alfalfa Silage 95 0.70

Grease 99 0.40

Methane Potential Volatile Solids Content COD BMP

BMP Biochemical Methane Potential

www.bioprocess.com

D.P. Chynowethwww.agen.ufl.edu

VS db%

COD:VSCOD

converted to CH4

%

Beef Manure 82 1.2 17

Dairy Manure 84 1.2 55

Wood Shavings 99 0.19 33

Alfalfa Silage 95 0.70 110

Grease 99 0.40 52

D.P. Chynowethwww.agen.ufl.edu

Sp

ecif

ic M

eth

ane

Yie

ld (

L C

H4 g

-1 V

S)

VS db%

COD:VSCOD

converted to CH4

%

Specific Methane

YieldL CH4 g-1 VS

Beef Manure 82 1.2 17 0.084

Dairy Manure 84 1.2 55 0.24

Wood Shavings 99 0.19 33 0.067

Alfalfa Silage 95 0.70 110 0.30

Grease 99 0.40 52 0.81

Community Needs1. Food

2. Proper pH

3. Sufficient Temperature

4. Sufficient Time to Reproduce

5. Absence of Inhibitory Substances

Methane Potential Volatile Solids Content COD BMP ATA

ATA Anaerobic Toxicity Assay

Inhibition (%)

I = (1 - Pt/Pc) X 100

Where:Pc = gas produced 0% inclusionPt = gas produced at test inclusion

ATA Anaerobic Toxicity Assay

Methane Potential Volatile Solids Content COD BMP ATA Pilot Testing

Pilot Scale Testing

Pilot Scale Testing

BoSo θv

1 - K µmθs – 1 + K

VRE =

Chen, Y.R. and A.G. Hashimoto. 1980. Substrate utilization kinetic model for biological treatment processes. Biotech &. Bioeng. 22:2081-2095

Any Questions?