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.