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Denitrifying activities and nitrous oxide (N2O) emission during denitrification can be affected by copper concentrations. Different denitrifiers were acclimated in sequencing batch reactors with acetate or methanol as the electron donor and nitrate as the electron acceptor. The effect of copper concentrations on the denitrifying activity and N2O emission for the acclimated denitrifiers was examined in batch experiments. Denitrifying activities of the acclimated denitrifiers declined with increasing copper concentrations, and the copper concentration exhibited a higher effect on denitrifiers acclimated with acetate than those acclimated with methanol. Compared with the control without the addition of copper, at the copper concentration of 1 mg/L, the acetate utilization rate reduced by 89% for acetate-acclimated denitrifiers, while the methanol utilization rate only reduced by 15% for methanol-acclimated denitrifiers. Copper also had different effects on N2O emission during denitrification carried out by various types of denitrifiers. For the acetate-acclimated denitrifiers, N2O emission initially increased and then decreased with increasing copper concentrations, while for the methanol-acclimated denitrifiers, N2O emission decreased with increasing copper concentrations.

Nitrous oxide (N 2 O) emission occurs during denitrification, such as in biological wastewater treatments, but few studies have focused on N 2 O emission during denitrification under endogenous conditions. In the present study denitrifiers were acclimated with acetate or methanol as the electron donor, and endogenous denitrification kinetics including denitrification rates and N 2 O emission were examined in batch experiments for the acclimated denitrifiers. Oxidized nitrogen was denitrified slowly during endogenous respiration for denitrifiers acclimated with acetate or methanol, with the denitrification rate of lower than 2 mg/g VSS•h. When the nitrate was used as electron acceptor, a low N 2 O emission ratio (lower than 1%) was obtained, while a high emission ratio (above 10%) was observed with nitrite as electron acceptor for both organic carbon acclimated denitrifiers. More attention should be paid to N 2 O emission during denitrification under endogenous conditions (such as in the settlement tanks) especially for systems with short-cut biological nitrogen removal through nitrite or systems with a high nitrite accumulation.