Simultaneous enhancement of nitrogen removal and nitrous oxide reduction by a saturated biochar-based intermittent aeration vertical flow constructed wetland: Effects of influent strength

The effective nitrogen removal in constructed wetlands (CWs) is still a challenge for treating various low carbon wastewaters. In this study, two types of vertical flow (VF) CWs equipped with intermittent aeration-non biochar and intermittent aeration-biochar were introduced to comparatively evaluate the nitrogen removal performances and transmission under different influent strengths of low C/N wastewaters. The results showed that biochar-aerated VFCWs achieved higher removal efficiencies for organic matter (95-97%), NH4+-N (63-98%) and TN (63-82%) under various influent strengths when comparing with non-biochar-aerated VFCWs. Simultaneously, lower N2O emissions (271-884 mu gm(-2) h(-1)) were also obtained in biochar-aerated VFCWs. However, nitrogen removal decreased with the increasing influent strength in both types of VFCWs, which suggested that weak denitrification would restrict nitrogen removal under low influent strengths, while high influent strengths resulted in low nitrification in VFCWs. The results demonstrated that the combination of biochar and aeration in VFCWs could be an alternative strategy for prompting nitrogen removal and reducing N2O emissions, especially for treating low C/N wastewaters with low and middle strengths.