Single and combined effects of divalent copper and hexavalent chromium on the performance, microbial community and enzymatic activity of sequencing batch reactor

Divalent copper (Cu2+) and hexavalent chromium (Cr6+) are often encountered in industrial wastewater and municipal wastewater, the effect of combined Cu2+ and Cr6+ on biological wastewater treatment systems has cause wide concern. In the present research, the performance, microbial community and enzymatic activity of sequencing batch reactors (SBRs) were compared under the single and combined Cu2+ at 20 mg/L and Cr6+ at 10 mg/L. The chemical oxygen demand (COD) and ammonia nitrogen (NH4+-N) removal efficiencies under the combined Cu2+ and Cr6+ were less than those under the single Cu2+ and Cr6+. The combined Cu2+ and Cr6+ displayed more inhibition effects on the oxygen uptake rate, nitrification rate and denitrification rate of activated sludge than the single Cu2+ and Cr6+. The inhibitory effects of the combined Cu2+ and Cr6+ on the activities of dehydrogenase, ammonia monooxygenase, nitrite oxidoreductase, nitrite reductase and nitrate reductase showed significant increases by comparison with the single Cr6+. However, the combined Cu2+ and Cr6+ had a little more inhibitory effects on the enzymatic activities than the single Cu2+. The microbial richness and diversity displayed some obvious changes under the single and combined Cu2+ and Cr6+ by comparison the absence of Cu2+ and Cr6+. The relative abundances of nitrifying genera (e.g. Nitrosomonas and Nitrospira) under the combined Cu2+ and Cr6+ was less than those under the single Cu2+ and Cr6+. These findings will be helpful to better understand the combined effects of multiple heavy metals on biological wastewater treatment systems. (C) 2020 Elsevier B.V. All rights reserved.