Elucidation of anaerobic phenol degradation mechanisms and novel bulking phenomenon in a mesophilic anaerobic sludge blanket reactor in long-term operation

In this study, to evaluate the performance of an upflow anaerobic sludge blanket (UASB) reactor for the treatment of phenol wastewater with high-organic loading, a long-term operation was conducted for 2,747 days by varying the organic loading rate, phenol concentration, and operating temperature. During the reactor operation, a novel type of bulking phenomenon was observed in the UASB reactor, and the reactor performance was significantly decreased. Therefore, to elucidate the mechanisms of phenol degradation and bulking, microbiome analyses based on the 16S rRNA gene amplicon and shotgun metagenomic sequencing were performed.