Impact of COD/N ratio on nitrous oxide emission from microcosm wetlands and their performance in removing nitrogen from wastewater

Constructed wetlands (CWs) are considered to be important sources of nitrous oxide (N2O). In order to investigate the effect of influent COD/N ratio on N2O emission and control excess emission from nitrogen removal, free water surface microcosm wetlands were used and fed with different influent. In addition, the transformation of nitrogen was examined for better understanding of the mechanism of N2O production under different operating COD/N ratios. It was found that N2O emission and the performance of microcosm wetlands were significantly affected by COD/N ratio of wastewater influent. Strong relationships exist between N2O production rate and nitrite (r = 0.421, p < 0.01). During denitrification process, DO concentration crucially influences N2O production rate. An optimal influent COD/N ratio was obtained by adjusting external carbon sources for most effective N2O emission control and best performance of the CWs in nitrogen removal from wastewater. It is concluded that under the operating condition of COD/N ratio = 5, total N2O emission is minimum and the microcosm wetland is most effective in wastewater nitrogen removal.