The use of microalgal biomass as a carbon source for nitrate removal in horizontal subsurface flow constructed wetlands

This study explores the feasibility of using microalgae biomass (Chlorella sp.) as a carbon source to increase the denitrification efficiency of horizontal subsurface flow constructed wetlands (HSSF-CWs). The results show that a large amount of organic matter is released in the process of microalgal powder decomposition. After alkali pretreatment, enhancements in the cumulative release amount (from 51.3 mg.L-1 to 106.8 mg.L-1) and stable release rate (from 0.13 mg.L-1.h(-1) to 0.25 mg.L-1.h(-1)) of organic matter were observed. The addition of microalgal powder with alkali pretreatment to HSSF-CWs improved the removal of nitrate (NO3--N) by 27.9% and total nitrogen (TN) by 17.7% compared to that without addition. There were limited side effects influencing the release of COD and TP in the effluent. For the treatment of wastewater with a low C/N ratio, it is feasible to add microalgal biomass as an external carbon source to HSSF-CWs to improve denitrification efficiency.