The suitable biomass carbon source for improving nitrogen removal in surface flow constructed wetland system: Fresh...

Plant biomass can be used as a carbon source to enhance the nitrogen removal effect. Related researches mainly focused on withered biomass, while little on fresh biomass. In this study, batch experiments revealed that the carbon release rate (60.5 mg TOC g^-1) of fresh biomass was significantly higher than that of withered biomass (44.9 mg TOC g^-1), while the nitrogen release rate showed the opposite trend. Compared with withered biomass, fresh biomass could release more sugar and less refractory humic acid, which means higher bioavailability. After adding fresh biomass, TN removal rate increased from 18.65% to 51.59%. The TN removal in the wetland adding withered biomass increased from 13.59% to 42.25%. The biomass addition had a slight impact on the effluent sensory quality in the first two days. After adding fresh biomass and withered biomass, the relative abundance of denitrifying bacteria like Flavobacterium and Pseudomonas in the system significantly increased. In general, fresh biomass was more suitable as a denitrification carbon source for surface flow constructed wetlands.