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The performance and microbial community changes of an activated sludge sequencing batch reactor were evaluated after exposure to trimethoprim for 51 days. The average chemical oxygen demand, ammonia nitrogen, phosphorus efficiencies were 88.6% ± 0.56%, 90.47% ± 0.29% and 64.25% ± 1.12%, respectively. The protein and polysaccharide contents increased with increasing trimethoprim concentration to protect the cells from the unfavorable conditions. The chemical composition of extracellular polymeric substances increased. For denitrifying bacteria, the read numbers of Pseudomonas , Flavobacterium and Bacillus were both significantly increased from Day 1 to 25 and sharply decreased by Day 50 ( p < 0.05), which is consistent with the tendency of Planctomyces (Anammox). The read number of Paracoccus displayed an increasing trend, whereas Nitrospirales, Nitrospira (nitrite oxidizer) and Nitrosomonadaceae (ammonia oxidizer) were significantly decreased ( p < 0.05). The read number of Rhodocyclaceae (phosphorus oxidizer) was significantly decreased from Day 1 to 25 and sharply increased by Day 50 ( p < 0.05). [ABSTRACT FROM AUTHOR]

An activated sludge sequencing batch reactor (SBR) was fed with synthetic wastewater containing ofloxacin (OFL) for 52 days to study the overall performance of the SBR, the characteristics of extracellular polymeric substances (EPS) and the bacterial community shift. Removal efficiencies of chemical oxygen demand, ammonia nitrogen, phosphorus and OFL were maintained at 90%, 96%, 80% and 65%, respectively. The EPS contents increased with increasing OFL concentration because more EPS was secreted to protect cells from OFL damage. Moreover, the EPS compositions shifted. For denitrifying bacteria, the read number of Pseudomonas and Bacillus sharply decreased initially ( p < 0.05) and increased from Day 25 to Day 50, which agreed with the tendency of Nitrosomonadaceae (ammonia oxidizer), while Paracoccus significantly decreased ( p < 0.05). The read number of Rhodocyclaceae , a phosphorus-accumulating bacterium, increased. Other functional microbes such as Nitrospirales (nitrite oxidizer) and Planctomyces (anammox) sharply decreased under OFL pressure ( p < 0.05). [ABSTRACT FROM AUTHOR]