Effects of dissolved oxygen and influent COD/N ratios on nitrogen removal in horizontal subsurface flow constructed wetland

Horizontal subsurface flow constructed wetland (SSF CW) provides good conditions to denitrification but the ability of this system to nitrify NH4+–N is limited. The performance response of SSF CW to simulated wastewater with different COD/N (chemical oxygen demand: TN in influent) ratios was studied during an 8-month period in greenhouse conditions to improve the removal of NH4+–N. In this study, several wetland litters were hydrolyzed to get relevant carbon extracting solution, which was applied to the wetland systems. During the nitrification process, the variation of dissolved oxygen (DO) with COD/N ratios had a significant effect on the removal of NH4+–N. It was found that the total nitrogen (TN) removal efficiency increased with COD/N ratios. Appropriate control of the carbon or nitrogen source concentration and the COD/N ratio in the influent could achieve the optimal nitrogen removal.