Nitrous oxide emission depending on the type of electron acceptor by a denitrifying phosphorus removal sludge

Denitrifying polyphosphate accumulating organisms (DNPAOs) are very promising for simultaneous nitrogen and phosphorus removal. While during denitrification, emission of a greenhouse gas, nitrous oxide (N₂O), may occur. In this study, DNPAOs were enriched in a lab-scale reactor, and N₂O emission was examined under different electron acceptor conditions. During the anoxic phase, with the uptake of phosphorus, denitrification of nitrate nitrogen (NO₃-N) was observed without the accumulation of nitrite nitrogen (NO₂-N). In general, a very low amount of N₂O was produced with nitrate as the electron acceptor, independent of the applied different nitrate concentrations. However, with nitrite as the electron acceptor, a much higher N₂O emission occurred. The N₂O emission factor to the denitrified NO₂-N was 6.2%, 5.3% and 4.9% at the initial NO₂-N concentration of 10, 20 and 40 mg l^-1, respectively. In addition, a much higher N₂O emission occurred with the co-existence of NO₃-N and NO₂-N. The initial organic carbon concentration had no significant effect on N₂O emission with NO₃-N as the electron acceptor. When stored organic carbon by DNPAOs was used as the electron donor, N₂O emission was mainly dependent on the electron acceptor.