[Effect of Cu²⁺ on Denitrification Using NO₂^- as an Electron Acceptor]

The short-cut biological nitrogen removal process has been widely used in industrial wastewater treatment, and denitrification is a crucial step for removing nitrogen on which the effect of Cu²⁺, a common heavy metal ion in wastewater, has not been studied. In this study, sludge with good short-range biological nitrogen removal characteristics in an A/O reactor was selected to investigate the short-term and long-term effects of Cu²⁺ on denitrification using NO₂^- as an electron acceptor. The results showed that Cu²⁺ had a significant inhibitory effect on denitrification process using NO₂^- as an electron acceptor, and the semi-inhibitory concentration EC₅₀ of sludge activity was 4.79 mg·L^-1. In the long-term experiment, the concentration of Cu²⁺ was gradually increased. When the concentration of Cu²⁺ was 0.5 mg·L^-1and 1 mg·L^-1, the denitrification activity of the sludge could be restored to the original level after acclimation. When the concentration of Cu²⁺ was increased to 3 mg·L^-1, the denitrification performance was destroyed and difficult to recover, at which point the NO₂^--N removal rate was reduced to less than 10% and the denitrification system was severely inhibited. However, there was some recovery of sludge denitrification capacity after the addition of Cu²⁺ had been stopped for 14 days. At the same time, during the long-term effect of Cu²⁺, the EPS content increased, which played an important role in protecting the microorganism against Cu²⁺ toxicity, and increased the sludge particle size and, as a result, sludge sedimentation.