Single and combined effect of divalent copper and oxytetracycline on the performance, microbial community and enzymatic activity of sequencing batch reactors

Divalent copper (Cu2+) and oxytetracycline (OTC) are often encountered in industrial wastewater and municipal wastewater, whereas no systematic report has been found in evaluating the impacts of combined Cu2+ and OTC on the performance of bioreactor treatment wastewater. In the present study, the performance, nitrogen removal rate, microbial community and enzymatic activity of sequencing batch reactors (SBRs) were compared under the single and combined 20 mg/L Cu2+ and 5 mg/L OTC. Compared with the absence of Cu2+ and OTC, the COD and NH+4-N removal efficiencies at 5 mg/L OTC was virtually unchanged during the whole operation process, whereas the presence of single Cu2+ and combined Cu2+ and OTC inhibited the COD and NH+4-N removal. The combined Cu2+ and OTC had more inhibitory effects on the oxygen uptake rate, nitrification rate and denitrification rate of activated sludge than the single Cu2+ or OTC. The activities of dehydrogenase, ammonia monooxygenase, nitrite oxidoreductase, nitrite reductase and nitrate reductase were inhibited more by the combined Cu2+ and OTC than the single Cu2+ or OTC. The microbial reactive oxygen species production and lactate dehydrogenase release under the combined Cu2+ and OTC were more than those under the single Cu2+ or OTC under the same operational time. The microbial richness and diversity of SBRs displayed some obvious differences under the single and combined Cu2+ and OTC. These findings will be helpful to better understand the combined effects of heavy metals and antibiotics on biological wastewater treatment systems. (C) 2020 Elsevier B.V. All rights reserved.