Submitted to: Applied Biochemistry and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/23/2009
Publication Date: 3/1/2010
Citation: Ahn, H., Smith, M.C., Ingram, S.K., White, J.W. 2010. Evaluation of biogas production by dry anaerobic digestion of switchgrass-animal manure mixtures. Applied Biochemistry and Biotechnology. 160:965-975.
Interpretive Summary: Performance of anaerobic digestion of animal manure-switchgrass mixture was evaluated under dry (85% moisture content) and thermophilic conditions (55oC). Three different mixtures of animal manure (swine, poultry, and dairy) and switchgrass were digested using batch-operated 1-L reactors. Considering the overall results of anaerobic digestion of animal manure- switch grass mixtures, the swine manure test units maintained well balanced conditions while the dairy and poultry manure test units showed poor performances. The swine manure test units proved to have the high biogas production potential (0.337 L methane/g Volatile solids). Although dairy and poultry manure performed poorly during this study, they may still have high potential as biomass for dry anaerobic digestion if appropriate designs are developed to prevent significant volatile fatty acids accumulation and pH drop. Future research into feasible operational conditions to improve biogas production of dairy and poultry manure is necessary. In addition, a suitable design to minimize the energy required to maintain reactor temperature needs to be developed. The energy required for heating may be reduced by lowering the digestion temperature or by linking the digester to an economical complementary heat source such as a composting system.
Technical Abstract: Anaerobic digestion is a biological method used to convert organic wastes into a stable product for land application without adverse environmental effects. The biogas produced can be used as an alternative renewable energy source. Dry anaerobic digestion (> 15% TS; total solid) has an advantage over wet digestion (<10% TS) because it allows for the use of a smaller volume of reactor and because it reduces wastewater production. In addition, it produces a fertilizer that is easier to transport. Performance of anaerobic digestion of animal manure-switchgrass mixture was evaluated under dry (15% TS) and thermophilic conditions (55oC). Three different mixtures of animal manure (swine, poultry, and dairy) and switchgrass were digested using batch-operated 1-L reactors. The swine manure test units showed 52.9% VS removal during 62 day trial while dairy and poultry manure test units showed 9.3% and 20.2%, respectively. Over the 62 day digestion, the swine manure test units yielded the highest amount of methane 0.337 L CH4 /g VS, while the dairy and poultry manure test units showed very poor methane yield 0.028 L CH4 /g VS and 0.002 L CH4 /g VS, respectively. These results indicate that the swine manure test units has the highest biogas production potential among the three different types of animal manure.