Impacts of Cu(II) on the kinetics of nitrogen removal during the wastewater treatment process

• Cu2+ inhibited nitrifying bacteria more significantly than denitrifying bacteria.
• Denitrifying bacteria were more sensitive than nitrifying bacteria to Cu(II).
• Cu(II) inhibited the SNUR and final removal efficiencies of nitrogen bio-removal.

The effects of Cu(II) on the substrate removal kinetics, including the COD, NH+4-N, and NO−x–N removal, were investigated by batch assays. Results showed that Cu(II) loading concentration of 10 mg/L significantly inhibited both the organic substrate removal efficiency and its specific removal rate, and the inhibitory rate was higher in the nitrification process than in the denitrification process. The removal efficiency and the specific uptake rate of NH+4-N would be significantly inhibited by the Cu(II) loading concentration of 10 mg/L. As for the denitrificantion process, the feeding concentration of Cu(II) no more than 20 mg/L posed no significant inhibitory effect on the final removal efficiencies of NOx−-N, however, 5 mg/L Cu(II) addition would inhibit the specific nitrogen oxides uptake rate by 32.43%. The same Cu(II) loading concentrations caused much higher inhibitory rate to the specific uptake rate of the NH+4-N than to that of the NOx−-N. Additionally, the relationships between the Cu(II) loading concentrations and their inhibitory rates to the specific removal rate of COD, NH+4-N, and NOx−-N could all be well described by regression equations.