Effects of high ammonia loading and in-situ short-cut nitrification in low carbon‑nitrogen ratio wastewater treatment by biocathode microbial electrochemical system

The microbial electrochemical system (MES) has great advantages in wastewater treatment for rapid chemical oxygen demand (COD) removal and low sludge yield rate. Herein, biocathode MES was proposed to remove COD from high-ammonia wastewater with low carbon‑nitrogen ratio and regulate the nitrogen forms in effluent for ANAMMOX process. The biocathode was more sensitive to ammonia nitrogen (NH4+-N) than anode and determined the power generation of MES. With COD of 500–550 mg L−1 in influent, increasing NH4+-N from 50 to 150 mg L−1 improved maximum power output (Pmax) from 3.0 ± 0.2 to 3.4 ± 0.1 W m−3, which was then reduced with further increase of NH4+-N from 300 to 600 mg L−1. However, for the cathodic reductive current, the negative effects of ammonia only revealed with NH4+-N ≥ 450 mg L−1. The cathodic equilibrium potential drop determined the power degradation, because the increased reductive compounds (NH4+ and COD) in catholyte. The high NH4+-N reduced the abundance of denitrifiers, exoelectrogens and organic-degrading bacteria on electrodes, while that of nitrogen-fixing bacteria increased. External alkalinity addition achieved in-situ short-cut nitrification and nitrite accumulation. With comparable NH4+ and NO2−, limited NO3− and low COD, the biocathode MES effluent was then suitable for subsequence ANAMMOX process.