Constructed wetland - Microbial fuel cell (CW-MFC) packed with suspended fillers to enhance denitrification with Acorus calamus biomass addition

There is an urgent need to meet strict nitrogen discharge limitation for secondary effluent from wastewater treatment plants, but the nitrogen removal is restricted due to the lack of carbon sources. To address the issues, high -density polyethylene (HDPE) was utilized in the constructed wetland -microbial fuel cell (CW-MFC) for the treatment of low carbon wastewater. Meanwhile, wetland plant biomass was efficiently reclaimed, leading to higher nitrogen removal and bioelectricity generation. CW-MFC with biomass added in the anode attained the maximum total nitrogen (TN) removal of 97.55 % and power density of 2.22 mW/m 2 with hydraulic retention time (HRT) of 2d, which were much better than those in CW, CW-MFC with no biomass and CW-MFC with biomass added in the cathode. Owing to the HDPE fillers and Acorus calamus biomass addition in CW-MFC, more than 88 % chemical oxygen demand (COD) and 70 % TN were removed with HRT of 1.5d. In addition, metabolisms related to glycolysis, cellulose degradation and nitrogen were increased in CW-MFC, contributing to the enrichment of denitrifying, electroactive and heterotrophic nitrification -aerobic denitrification (HN-AD) bacteria. This study verifies the feasibility of application of HDPE as the biocarriers in CW-MFC and provides mechanistic insights for the enhancement of nitrogen removal in low carbon wastewater treatment with plant biomass addition.