Performance and mechanism of falling water enhanced tidal flow constructed wetlands (F-TFCW) for rural grey water treatment

Constructed wetlands (CW) are a promising treatment technology for decentralized rural sewage. However, the pollutant removal efficiency of CW is low due to the limitation of DO concentration. In this study, a falling water enhanced tidal flow constructed wetlands (F-TFCW) was constructed to solve the problems of insufficient oxygen supply and low pollutant removal efficiency in CW. In this regard, the effects of falling water reoxygenation, tidal operation, and flood rest ratio (F/R) on the pollutant removal performance of F-TFCW were examined. Also, the pollutant removal mechanism of F-TFCW was revealed through microbial analysis and biochar XPS characterization. The results showed that the COD, NH4+-N, and TP removal rates of F-TFCW were 99.50 ± 0.21%, 87.16 ± 1.76%, and 88.43 ± 1.35%, respectively, when the F/R was 3:1. The falling water inflow and tidal operation significantly improved the reaeration influence of the constructed wetland. The microbial community analysis represented that the dominant bacteria of the F-TFCW could degrade organic compounds or adapt to tidal flow operation. The tidal operation remarkably changed the core microorganisms of the artificial wetland. In the flood phase of F-TFCW, the COD removal relied mainly on aerobic degradation and the biochar adsorption process. In the experimental step, the microbes degraded the organic matter adsorbed by biochar, which enabled a certain degree of biochar regeneration. This paper provided a new idea to enhance the pollutant treatment efficiency for constructed wetlands.