Study on the performance of accessory microbial fuel cell (MFC) integrated to the constructed wetlands (CWs) for deep wastewater treatment

Deep nitrogen removal is difficult due to inefficient organic carbon sources in tail water from sewage treatment facilities. Microbial fuel cell integrated with constructed wetlands (MFC-CWs) filled with high density polyethylene (HDPE) as the biocarriers were constructed for deep denitrification of tail water, and was compared with MFC and CW. The influences of electrode gap and hydraulic retention time (HRT) on denitrification as well as electricity generation performance were investigated. It was found that appropriate electrode gap extension might enhance chemical oxygen demand (COD) and nitrogen removal, and MFC-CW got the highest electricity generation and nitrogen removal with the electrode gap at 25cm. Extending HRT promoted deep denitrification, resulting in an initial increase followed by a subsequent decrease in power generation performance. The maximum power density of MFC-CW attained 1.95mW/m2 with an HRT of 2 d. It was found that microbial abundances in the upper cathode of the systems were higher, and the growth and metabolisms of microorganisms were enhanced in MFC-CWs. Saccharimonadales and SBR1031 in MFC-CW were the dominant genera, which promoted nitrogen removal. The results provide a reference for the study of synchronous denitrification and electricity generation performance in MFC-CW with HDPE as bio-fillers.