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 (NO) 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 N m d respectively. The NO emissions and nitrate nitrogen (NO-N) concentration both peaked at a TN value of approximately 100 mg N L. NO emissions had a positive correlation with NO-N concentration (p < 0.001). This correlation suggests that the effect of TN loading on NO emissions may be related to NO-N in aquatic environment. Significant correlation was observed between NO emission and the gene abundance of NO 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 NO emissions when designing constructed wetlands.