Electron-deficient wastewater treatment in membrane-aerated conductive biofilm reactor: Performance and mechanism

[Display omitted] •The effect of the electric field on nosZ was avoided in counter-diffusion biofilm.•The process of NH4+-N to NH2OH can occur both at the cathode and anode.•The abundance of all functional genes related to denitrification in Thauera.•The denitrification process at the cathode is likely to be completed in Thauera. A membrane-aerated conductive biofilm reactor (MA-CBR) was constructed for carbon-limited wastewater treatment and to reduce the stress of the electric field on nitrous oxide reductase (NosZ). Counter-diffusion with an embedded aerobic layer declined the effect of current on NosZ (K00376) for N2O reduction. Other coding genes for denitrification in cathodic membrane aerated biofilms, including K02568, K00368, K15864, K02305, and K04561, were also positively affected by the electric field and significantly accumulate in Thauera. NH4+-N oxidation can occur at the anode and cathode (membrane aeration biofilm). This cathodic synergistic NH4+-N oxidation provided more electrons to be directly utilized by the denitrifying bacteria at the cathode. Compared to the MABR, the total nitrogen removal efficiency of MA-CBR increased by 5.68 mg/L, 11.02 mg/L, and 15.63 mg/L at voltages of 0.25 V, 0.50 V, and 0.75 V, respectively.