Anodic performance of microbial electrolysis cells in response to ammonia nitrogen

In this study, the authors investigated how various total ammonia nitrogen (TAN) concentrations (128–1231 mg nitrogen/l) in the substrate medium affect the anodic performance of dual-chamber microbial electrolysis cells (MECs) with an anion-exchange membrane (AEM) and a cation-exchange membrane (CEM). The current densities and midpoint potentials of the bioanode in the AEM-MEC were independent of TAN concentration changes. In comparison, current densities in the CEM-MEC considerably dropped at a high TAN concentration of 1231 mg nitrogen/l, and the midpoint potential of the bioanode became increasingly positive, indicating that the anode biofilm was negatively affected by a high TAN concentration. Comparison of pH and TAN concentration changes in the anolyte in the CEM-MEC suggests that high levels of TAN did not directly influence anode-respiring bacteria (ARB) metabolism; accumulation of protons was the primary reason for the deterioration of anodic performance. However, the patterns of changes in chemical oxygen demand (COD) removal efficiencies and coulombic efficiencies in response to increased TAN concentrations were quite similar in the two MECs. The COD removal efficiencies also decreased at elevated TAN concentrations, while coulombic efficiencies increased, suggesting that non-ARB activity was reduced in both MECs.