Insights into the effects of single and combined divalent copper and humic acid on the performance, microbial community and enzymatic activity of activated sludge from sequencing batch reactor.

The performance, microbial community and enzymatic activity of activated sludge from four identical sequencing batch reactors (SBRs) were compared by treating synthetic wastewater under the single and combined divalent copper (Cu) at 20 mg/L and humic acid (HA) at 20 mg/L. Compared with the absence of Cu and HA, the single HA slightly enhanced the oxygen uptake rate (OUR), the nitrification and denitrification rates and the activities of dehydrogenase, nitrifying enzymes and denitrifying enzymes, whereas the single Cu had the opposite results. The combined Cu and HA inhibited the OUR, nitrogen removal rate and enzymatic activity of activated sludge almost the same as the single Cu. The single HA had no obvious effect on the balance between the microbial oxidative stress and antioxidant activity. However, the variations of microbial reactive oxygen species production, peroxidase activity, catalase activity, superoxide dismutase activity, and lactate dehydrogenase release demonstrated that the combined Cu and HA and single Cu produced obvious toxicity to microorganisms in activated sludge. The microbial richness and diversity had some obvious changes under the single and combined Cu and HA. The relative abundances of Nitrosomonas, Nitrospira and some denitrifying genera (e.g. Zoogloea, Dokdonella, Denitratisoma, Flavobacterium and Thermomonas) under the combined Cu and HA were less than those under the single Cu.