Effect of solids retention time on antibiotics removal performance and microbial communities in an A/O-MBR process

The effect of solids retention time on reactor performance and microbial community composition in anoxic/aerobic membrane bioreactors (A/O-MBR) were investigated in this study. Experimental results showed high removal efficiencies of conventional pollutants. Antibiotics removal efficiencies were obviously affected by SRT changes. Longer SRT (above 30 days) was proved to be suitable operational condition for antibiotics removal. Denaturing gradient gel electrophoresis (DGGE) and clone library analysis revealed that bacteria belong to Betaproteobacteria and Gammaproteobacteria were the dominant species during wastewater treatment and antibiotics removal. SRT significantly influenced the relative numbers of nitrifying bacteria. Removal efficiency of total nitrogen (TN) decreased when SRT was 3 days, because nitrogen loading exceeded the denitrification ability of the reactors. Unlike tet C and tet E genes, sulfa antibiotics resistance gene presented a decreasing tendency with the decrease of SRT, and finally affected sulfa antibiotics removal efficiencies.