Effects of ammonium ions from the anolyte within bio-cathode microbial fuel cells on nitrate reduction and current density

•The ammonium in the anolyte was promoted electron movement.•The ammonium in the cathode was detected in the ammonium-free system.•The nitrate removal was superior when ammonium was present in the anode chamber.

This study was to determine the effects of the ammonium ion in the anolyte of the two-chamber bio-cathode MFC, which uses nitrate ions as the final electron acceptor, on the nitrate reduction and the current density. The ammonium nitrogen mass transfer coefficient was 3 × 10−6 cm/s and the diffusivity was 6 × 10−8 cm2/s through Nafion 117 under abiotic conditions, with the circuit disconnected. When the TCBC-MFC was operated at 96.6 ± 11.2 mg/L of SCODcr in the anode chamber and 37.9 ± 2.8 mg/L of nitrate nitrogen in the cathode chamber at an external resistance 100 Ω, the analytical denitrification rate was being 7.89 ± 0.78 g/m3 d in the presence of ammonium ions and 3.07 ± 0.26 g/m3 d in the absence of ammonium ions. The current density was 176.1 ± 31.7 mA/m2 when NH4+-N was present in the anolyte and 28.2 ± 19.4 mA/m2 without NH4+-N. Thus, it was determined that the ammonium ions in the anolyte were promoted electron movement, which increased the denitrification rate to twice that in the ammonium-free system.