Removal performance and changes in the microbial communities of SBRs under aerobic and anoxic conditions with trace tetracycline pressure.

The reactor performance and microbial community composition of sequencing batch reactor (SBR) under aerobic and anoxic conditions were investigated in this study. The experimental results showed high chemical oxygen demand (COD) removal efficiency. The tetracycline (TC) removal efficiencies were not obviously affected by aerobic and anoxic conditions, and were 64-97 and 60-87%, respectively. Aerobic condition was observed to be more suitable for decreasing tetracycline-resistant bacteria (TRB) than anoxic condition in synthetic and real wastewater. Denaturing gradient gel electrophoresis (DGGE) and clone library analysis revealed that Chlorobaculumthiosulfatiphilum was the dominant species in the tested SBR systems. TC significantly influenced the relative numbers of TRB- and TC-resistant genes, and the microbial community diversity changed with the addition of 250 μg L(-1) of TC. The genes of tetA and tetC, tetM and tetS, tetA and tetM, tetS and tetA showed significant correlation with each other (P < 0.05).