Nitrous oxide emissions from pilot scale three-stage constructed wetlands with variable nitrogen loading

Pilot scale three-stage surface flow constructed wetlands (SFCWs) were constructed to study nitrous oxide (N2O) emissions from swine wastewater with different nitrogen levels. The SFCWs had mean total nitrogen (TN) removal efficiencies and removal rates of 84.6-97.1% and 0.6-2.4 g Nm(-2) d(-1) respectively. The N2O emissions and nitrate nitrogen (NO3--N) concentration both peaked at a TN value of approximately 100 mg N L-1. N2O emissions had a positive correlation with NO3--N concentration (p < 0.001). This correlation suggests that the effect of TN loading on N2O emissions may be related to NO3--N in aquatic environment. Significant correlation was observed between N2O emission and the gene abundance of N2O reductase (nosZ; p < 0.05). The general linear model revealed that TN loading affected nosZ gene abundance. These results suggest that pollution loading should be considered to balance nitrogen removal and N2O emissions when designing constructed wetlands.