Effect of a microbiota activator on accumulated ammonium and microbial community structure in a pilot-scale membrane bioreactor

Microbiota activators (MAs) have been used to improve the reactor performances of biological wastewater treatment processes. In this study, to remove ammonium (NH4+) accumulated during the pre-operation of a pilot-scale membrane bioreactor (MBR) under high-organic-loading conditions, an MA was added to the MBR system and the resulting changes in reactor performances and microbial communities were monitored for 12 days. The NH4+ concentrations in the sludge and effluent decreased (from 427 to 246 mg/L in the sludge (days 1–9)), and mixed liquor suspended solid increased (from 6,793 to 11,283 mg/L (days 1–12)) after the addition of MA. High-throughput Illumina sequencing of 16S rRNA genes revealed that the microbial community structure changed along with the NH4+ removal resulting from the MA addition. In particular, the relative abundance of an Acidovorax-related operational taxonomic unit (OTU) increased significantly, accounting for approximately 50% of the total microbial population at day 11. In contrast, the ammonia-oxidizing bacteria and archaea showed low abundances (