Influence of methane enrichment by aeration of recirculated supernatant onmicrobial activities during anaerobic digestion

A methane enrichment process (MEP) was evaluated that involved air purging of recycled digester contents to strip CO2 and increase biogas methane cont ent. The objective of this work was to determine if the aeration resulted i n oxygen inhibition of microbial activities involved in anaerobic digestion of municipal solid waste. To assess the degree of biological perturbation associated with the MEP, the reactor effluent was sampled twice while the M EP was operating and twice while it was not operating. Analyses were run on composite samples (representing several different sample ports of the non- mixed reactor) and samples of digester effluent entering and leaving the ME P process. The analyses included volatile organic acids (VOA), effluent sol ids content, dehydrogenase activity, specific methanogenic activities (SMA) , and enzyme-linked immunosorbent assay (ELISA) for methanogenic, sulfate-r educing, and cellulolytic bacterial species. Methane enrichment in these ex periments occurred with the methane content of the biogas exceeding 90%. Th ere were no effects of the MEP on effluent VOA concentration. The MEP had n o effect on volatile solids (VS) levels of composite samples representing t he non-mixed digester contents, however, VS was reduced in effluent passing through the MEP. Although MEP had an inhibitory effect on anaerobic popula tions leaving the MEP process, no inhibitory effects were observed in measu rements of microbial activities in digester samples, including specific met hane production rate, dehydrogenase, and numbers of specific organisms esti mated using ELISA techniques. (C) 1999 Published by Elsevier Science Ltd. A ll rights reserved.