Methanogenic community shift in anaerobic batch digesters treating swine wastewater

Abstract

Qualitative and quantitative molecular analysis techniques were used to determine associations between differences in methanogenic microbial communities and the efficiency of batch anaerobic digesters. Two bioreactors were initially seeded with anaerobic sludge originating from a local municipal wastewater treatment plant and then supplemented with swine wastewater. Differences were observed in the total amount of methane produced in the two bioreactors (7.9L/L, and 4.5L/L, respectively). To explain these differences, efforts were taken to characterize the microbial populations present using a PCR-based DGGE analysis with methanogenic primer and probe sets. The groups Methanomicrobiales (MMB), Methanobacteriales (MBT), and Methanosarcinales (MSL) were detected, but Methanococcales (MCC) was not detected. Following this qualitative assay, real-time PCR was used to investigate quantitative differences in the populations of these methanogenic orders. MMB was found to be the dominant order present and its abundance patterns were different in the two digesters. The population profiles of the other methanogenic groups also differed. Through redundancy analysis, correlations between the concentrations of the different microbes and chemical properties such as volatile fatty acids were calculated. Correlations between MBT and MSL populations and chemical properties were found to be consistent in both digesters, however, differences were observed in the correlations between MMB and propionate. These results suggest that interactions between populations of MMB and other methanogens affected the final methane yield, despite MMB remaining the dominant group overall. The exact details of why changes in the MMB community caused different profiles of methane production could not be ascertained. However, this research provides evidence that microbial behavior is important for regulating the performance of anaerobic processes.