Inhibition effect of Cu(II) on nitrogen removal in anammox-denitrification couple system

Due to the wide application in industries, copper can be detected in some nitrogen-rich wastewater. In this research, short-term and long-term experiments were conducted to explore the effects of Cu(II) on the anammox-denitrification couple system. It concluded that the half inhibition concentration (IC₅₀) of Cu(II) was 35.54 mg/L. The system in reactor could tolerate low concentrations of Cu(II) (≤5 mg/L), while the total nitrogen removal efficiency decreased from 93 % to 33 % under 10 mg/L of Cu(II). After 45 days exposure to Cu(II) (1-10 mg/L), 14.54 mg/g SS copper accumulated in the sludge, which largely inhibited the microbial activity. More extracellular polymeric substances (EPS) were secreted to defend against copper toxicity. Proteobacteria (19.18 %-44.04 %) was the dominant phylum and showed excellent tolerance and adaptability to Cu(II). The dominant anammox bacteria, Candidatus_Brocadia, was slightly enhanced under low concentrations of Cu(II), but was highly inhibited under 10 mg/L of Cu(II). PICRUSt2 results showed that some metabolic activities were suppressed under the exposure of copper while defensive responses were also induced. Metabolic disorders eventually led to the death of some microbes, resulting in unrecoverable deterioration in microbial activity. Overall, this study explores the effect of Cu(II) on the anammox-denitrification process and provides a possible inhibition mechanism.