Intensified nitrogen transformation in intermittently aerated constructed wetlands: Removal pathways and microbial response mechanism

Abstract

Nitrogen (N) removal processing in vertical flow constructed wetlands (VFCWs) with different designs often varies greatly. Here, a long term VFCWs study for domestic wastewater treatment was carried out to investigate the impact of intermittent aeration and three construction-waste media (common gravel, red brick and fly-ash brick) on N loss, N retention and microbial community. The total nitrogen (TN) removal was significantly higher in aerated VFCWs (91.31%–93.91%) compared with non-aerated VFCWs (12.22%–53.92%), with the highest removal rate in system VI filled with fly-ash brick. Nitrification/denitrification was the main N sink in aerated VFCWs accounting for 36.79%–55.44%, while media storage (8.47%–48.64%) dominated in non-aerated systems because of nitrification limitation. <16% of the TN removal was uptake by plants, and N2O emission contributed about 0.08%–0.39%. Microbial study found that functional bacteria increased with intermittently aeration. The analysis revealed the crucial influence of oxygen supply and media on N transformations in VFCWs.