Decreasing hydraulic retention time of anaerobic membrane bioreactor: Effect on core genera and microbial contaminants removal

A pilot -scale (35 L) anaerobic membrane bioreactor (AnMBR) treating municipal wastewater was operated under decreasing hydraulic retention times (HRT) of 12 h, 10 h and 8 h, and evaluated for its performance and removal of bacterial cells. There was an increased variability in COD and bacterial cells removal when HRT was 8 h, and a positive net growth rate of potential pathogen -containing genera Mycobacterium sp. was reported when AnMBR was operated at HRT of 8 h. Specifically, metagenomic assembled genomes of opportunistic pathogenic Mycobacterium franklinii were reconstructed uniquely in the 8 h HRT effluent. In contrast, co -occurrence network results showed when the HRT was 10 h, the microbial interactions were higher and bacterial syntrophs and methanogens had a more prevalent role in the microbial network. Our findings suggest that an optimal HRT (10 h) is required to achieve stable AnMBR performance and removal of microbial contaminants from untreated municipal wastewater, and can facilitate proper sizing of AnMBR.