Co-digestion of Hog Manure with Glycerol to Boost Biogas Production

Oswald Wohlgemut (MSc)July 14, 2008

Farm-scale Anaerobic Digestion

Background

Anaerobic digestion

Lab Research

• Co-digesting hog manure with Glycerol

• Goals– To find optimal glycerol

dosage– To boost biogas and methane

production– To determine nutrient (N,P)

fate through digestion– To gather information to be

used for operating a pilot-scale model

Biodiesel

Glycerol

Why co-digest with glycerol? To find a valuable use for biodiesel waste

To help boost biogas and methane production

Make the process more economical

To reduce GHG emissions

To increase “green energy” in Manitoba

Experimental Setup

4 bench-scale anaerobic digesters (4L) Complete-mix, mesophilic (35ºC), semi-

continuous fed, with gas collection

Experimental Setup

1. Shock Loading Effect – addition of 1%, 2%, 4% pure glycerol (by weight)

2. Comparison Study – comparing 1% pure glycerol to 1% crude glycerol (by weight)

3. Digester Recovery – testing microbial resistance to high COD glycerol loading over time

Feed Characteristics

Hog manure screened and diluted (~1% TS)

pH 7.6Digester Feed COD (g/l) Additional COD

load

Manure (Control) 16.7

Manure + 1% Pure Glycerol 29.7 1.7x

Manure + 2% Pure Glycerol 42.3 2.5x

Manure + 4% Pure Glycerol 72.3 4.3x

Manure + 1% Crude Glycerol 30.1 1.8x

Results

Shock Loading Experiment Control (Manure) ~ 72% CH4

Manure + 1% pure glycerol ~ 64% CH4

Results

Shock Loading Experiment Reactors with 2% and 4% pure glycerol addition

were overloaded with SCOD and did not stabilize

Results

Comparison Experiment Control (Manure) ~ 70% CH4

Manure +1% pure glycerol ~ 63% CH4

Manure + 1% crude glycerol ~ 67% CH4

1.8 X

Results

Digester Recovery Can bacteria recover from overloading? Comparing 2% glycerol loading in

experiment 1 & 3

Experiment 1

Glycerol startGlycerol stop

2.8 X

Experiment 3

Results

Methane Yield and Composition

Substrate m³CH4/kg COD added

% CH4 composition

Control (Manure) 0.239 71

1% pure glycerol + manure

0.257 63

1% crude glycerol + manure

0.245 67

2% pure glycerol + manure

0.244 59

Conclusion

• Biogas and methane production increased with glycerol addition

• A high glycerol shock loading can cause digester failure with a buildup of VFAs

• Bacteria were able to recover and utilize high glycerol COD loading over time

• Methane composition decreases with increasing glycerol addition

• Crude glycerol did not have inhibitory effects

Future Research

Batch experiments with raw manure to determine BMP (Biochemical Methane Potential) of manure with different concentrations of glycerol

Analysis to determine nutrient (P, N) fate through digestion with glycerol

Future Research

Pilot-scale digester in a solar greenhouse

Acknowledgements

Manitoba Agriculture, Food and Rural Initiatives

Dr. Nazim Cicek Dr. Jan Oleszkiewicz My colleagues in the lab

Questions?