Nitrogen removal in response to the varying C/N ratios in subsurface flow constructed wetland microcosms with biochar addition.

Biochar as a substrate has great potential to promote pollutant removal efficiency in subsurface flow constructed wetlands (SSFCWs). However, information about the effect of different influent C/N ratios on treatment efficiency in SSFCWs with biochar is still scarce. In this study, SSFCW microcosms added with and without biochar were performed to investigate comparatively nitrogen removal in response to the domestic wastewater with varying C/N ratios. The results demonstrated that nitrogen removal increased at influent C/N ratios from1 to 3, and then decreased with the rising influent C/N ratios from 3 to 15 in different SSFCWs. Much higher removal efficiencies for COD (92%), NH4+-N (50%), and TN (50%) were obtained in the biochar-added SSFCW especially at the C/N ratio of 3 when comparing to CW without biochar. The higher pollutants removal ability of biochar-added SSFCWs was mainly attributed to the stronger adsorption ability in the porous biochar. However, poor nitrification was observed at various influent C/N ratios in SSFCWs with and without biochar due to lack of enough oxygen. This study supported that the use of biochar could increase the treatment performance in SSFCWs under various influent C/N ratios.