Microbial community in an anaerobic membrane bioreactor and its performance in treating organic solid waste under controlled and deteriorated conditions

The adoption of anaerobic membrane bioreactors (AnMBRs) for organic solid waste management is important for the recovery of energy and high-quality treated water. However, few studies have focused on AnMBR treatment of high-strength organic solid waste and the microorganisms involved under deteriorated operating conditions. In the present study, a 15-L bench-scale AnMBR was operated using a model slurry of high-strength organic solid waste with the organic loading rate (OLR) increasing from 2.3 g chemical oxygen demand (COD) L-1 day(-1) (represented as a controlled condition) to 11.6 g COD L-1 day(-1) (represented as a deteriorated condition), and microbial community dynamics over 120 days of operation were analyzed. The abundances of methanogens and bacteria that were dominant under the controlled condition decreased as a result of both high organic loading and sludge withdrawal under the deteriorated condition and did not recover thereafter. Instead, numbers of putative volatile fatty acid (VFA)-producing bacterial operational taxonomic units (OTUs) related to the genus Prevotella increased rapidly, reaching a relative abundance of 43.2%, leading to the deterioration of methanogenic AnMBR operation. Considering that the sequences of these OTUs exhibited relatively low sequence identity (91-95%) to those of identified Prevotella species, the results strongly suggest that the accumulation of VFAs by novel VFA-producing bacteria in the digestion sludge promotes the disruption of the methanogen community under deteriorated conditions.