Changes in microbial community structure during anaerobic repeated-batch treatment of cheese-processing wastewater

Abstract

This study investigated changes in microbial community structure, associated with changes in process performance, in an anaerobic bioreactor treating cheese-processing wastewater in repeated-batch mode. During the operation of three batch cycles, the overall reaction rate increased with the increase in starting microbial population size over cycles, indicating a positive effect of biomass accumulation on process performance. Bacterial community structure varied significantly over cycles in the reactor. In contrast, methanogen community structure was maintained almost unchanged (>90% similarity) during the experiment. This indicates that changes in bacterial community structure interestingly had little influence on the formation of methanogen community structure in the reactor. Another notable point is that the reactor methanogen community was greatly dominated by hydrogenotrophic methanogens (up to 90% of the total population), likely suggesting H2-utilizing pathway as the major methanogenesis route in the reactor. This is contrary to the conventional wisdom that aceticlastic methanogens are the main drivers of methanogenesis in anaerobic digesters under normal conditions.