The impact of influent mode on nitrogen removal in horizontal subsurface flow constructed wetlands: A simple analysis of hydraulic efficiency and nutrient distribution

Influent mode in constructed wetlands can cause changes of hydraulic efficiency and carbon source distribution. In this study, impacts of four influent modes on nitrogen removal were studied by hydraulic tracer test and nutrient distribution analysis. NH4+-N, TN and COD were sampled along the reactors in different layers. Results showed that diffusive inflow contributed highest NH4+-N and TN removal reaching 64.3% and 60.9%, respectively. It proved that diffusive inflow achieved higher effective volume ratio and hydraulic efficiency. Moreover, nutrient distribution analysis implied that diffusive inflow enhanced reaeration causing efficient NH4+-N reduction. Compared with other modes, diffusive inflow has also resulted in well-distributed carbon source for denitrification in bottom layer. In addition, ANOVA test analyzed the significance among influent modes indicating that diffusive inflow had obvious effects on enhancing nitrogen removal. The study documented the feasibility of using diffusive inflow to enhance the treatment by improving hydraulic conditions and carbon source distribution in CWs.