LAUSR

Abstract Combined impacts of diclofenac (DCF) and divalent copper (Cu2+) on the nitrogen removal, enzyme activity and bacterial community from a sequencing batch reactor were examined. DCF and/or Cu2+ in the influent rendered the decrease of ammonia nitrogen and chemical oxygen demand elimination rates. The combined inhibition impacts of Cu2+ and DCF on ammonia monooxygenase (AMO), nitrite oxidoreductase (NOR), nitrite reductase (NIR) and nitrate reductase (NAR) contents exhibited synergetic, and the AMO and NOR activities reduced levels were lower than NAR and NIR as the mixed Cu2+ and DCF concentration increment. The decreased degrees of AMO activities were higher than NOR at different mixed Cu2+ and DCF concentrations. The contents of reactive oxygen species and lactate dehydrogenase at the mixed Cu2+ and DCF stress were higher than those at the alone Cu2+ and DCF stress, and they increased as the mixed Cu2+ and DCF concentration increase. In extracellular polymeric substances (EPS), the content of protein (PN) was more easily affected by Cu2+ and mixed Cu2+/DCF than polysaccharide (PS), while PN and PS were both sensitive to the stress of DCF. Compared to seeding sludge, the denitrifying bacteria and nitrifying bacteria relative abundance ratio was decreased at the stress of alone Cu2+ and DCF, while the ratio was increased as the mixed Cu2+ and DCF concentration increment.