Treatment of Ammonium-Nitrogen–Contaminated Groundwater by Tidal Flow Constructed Wetlands Using Different Substrates: Evaluation of Performance and Microbial Nitrogen Removal Pathways

As a significant oxygen intensified configuration, tidal flow constructed wetlands (TFCWs) are effective for the treatment of water and wastewater rich in NH4+-N. The TFCWs filled with four substrates (gravel, granular active carbon, volcanic rock, and zeolite) were used to treat synthetic groundwater containing NH4+-N. The results showed that higher ammonium removal was achieved in TFCW filled with zeolite (89.20 ± 3.09%) and granular active carbon (53.70 ± 8.91%). The highest accumulation of nitrate was obtained in TFCW filled with volcanic rock, whereas the lowest was obtained in TFCW filled with granular active carbon. The quantitative polymerase chain reactions (qPCR) and high-throughput sequencing of bacterial 16S rRNA pyrosequencing were applied to reveal the involved microbial N removal pathways. The abundance of amoA gene of Nitrospira and anammox gene of unclassified Planctomycetaceae suggested anammox could play a key role in NH4+-N removal in the absence of organic carbon in the simulated groundwater. Besides, the results of adsorption isotherms showed that substrate adsorption coupled with anaerobic ammonium oxidation (anammox) were the major reason for the robust NH4+-N removal performance in TFCW filled with zeolite.