Effects of influent COD/TN ratio on nitrogen removal in integrated constructed wetland–microbial fuel cell systems

Given that the relationship between the influent C/N (generally referred to as COD/TN) ratio and nitrogen removal has not been well understood in integrated constructed wetland–microbial fuel cell (CW-MFC) systems, this study aimed to investigate the effects of COD/TN ratio on nitrogen removal in CW-MFCs. Results showed that the MFC could reduce the dependence of denitrification on organic carbon sources in CWs, and influent COD/TN ratios ≥3 could result in a TN removal of 90.30–91.46% in CW-MFCs. Moreover, the MFC could significantly enhance TN removal by 4.81% to 15.48% when the influent COD/TN ratios decreased from 9.00 to 1.23 in CWs. The lower the influent COD/TN ratio was, the stronger the enhancement of the MFC. There was a significant positive relationship (R2 > 0.99) between the electricity output and influent CODCr concentration (50–360 mg/L) in the CW-MFC.