High degree of contaminant removal and evolution of microbial community in di fferent electrolysis-integrated constructed wetland systems

The molecular mechanism of contaminant removal in different electrolysis-integrated constructed wetlands (CWs) was explored. Electrolysis (microbial fuel cells (MFC) and direct current (EC))-integrated CWs achieved high removal efficiencies for chemical oxygen demand (COD; 82.18% in MFC-CWs and 81.57% in EC-CWs), total nitrogen (TN; 75.08% in MFC-CWs and 69.19% in EC-CWs) and total phosphorus (TP; 92.56% in MFC-CWs and 92.86%), which was higher than that in CWs. Additionally, MFC-CWs had an average voltage of 384.56 +/- 44.49 mV with the highest power density of 977 mW m(-2). The pollutant removal performance of the MFC-CWs was better than that of the EC-CWs. Microorganisms in electrolysis-integrated CWs, especially in the MFC-CWs, gained higher diversity and richness than those in CWS. However, the effects between MFC and EC for CWs were different. In addition, nitrogen functional genes in electrolysis-integrated CWs were significantly more abundant than those in the CWs, and the electron transfer rate also increased. Combined analyses of microorganisms and functional genes revealed that the main contributors to nitrogen removal were anaerobic ammoxidation, ammonia oxidation, denitrification, and dissimilatory nitrate reduction to ammonium (DNRA) for CWs, anaerobic ammoxidation, ammonia oxidation, denitrification and DNRA for EC-CWs, anaerobic ammoxidation, ammonia oxidation and denitrification for MFC-CWs