Microbial community structure and activity in a compartmentalized, anaerobic bioreactor

The objective of this study was to evaluate staging and its effects on reactor performance in a compartmentalized bioreactor, designated the anaerobic migrating blanket reactor (AMBR). The AMBR was operated by reversing the flow several times per day, which allowed for substantial biomass migration without biomass accumulation in the final compartment. During reactor startup, the structures of the microbial communities in the five compartments were quite similar despite substantial differences in substrate types and concentrations in the different compartments. During the rest of the operational period, biomass migration was reduced by changing operating conditions and, as a result, a larger difference in the structures of the microbial communities developed for the different compartments (biomass staging). For example, after changing operating conditions, rRNA levels for the acetate-utilizing methanogen Methanosaeta concilii were approximately 35 and 10% of the total rRNA in the middle and outside compartments, respectively (before changing operating conditions these levels were approximately 20 and 12% of the total rRNA, respectively). Promoting larger differences in the structures of the microbial communities for the different compartments did not improve reactor performance as lower levels of M. concilii in the outside compartments hindered acetate removal and compromised effluent quality.