Regeneration of activated carbon air-cathodes by half-wave rectified alternating fields in microbial fuel cells

The activated carbon air-cathode is promising but usually be rapidly contaminated in wastewater due to the salt accumulation and biofilm formation on the catalysis layers in microbial fuel cells (MFCs). For the first time, the half-wave rectified alternating fields (AC+) was demonstrated as a novel, efficient and energy-saving way to remove ions from porous surface and regenerate this cathode. 1.2 V AC+ treatment recovered the power generation by 50% and 43% in 12 h when the cathodes were operated in MFCs for 20 and 30 d, comparing to 12–15% recoveries of direct current (DC) treatment, but the energy needed of AC+ was only 1/4 of DC. Pores in the catalyst layer were substantially cleaned after AC+ treatment, leading to a 43% increase in cathodic oxygen diffusion coefficient. Bacteria attached to the cathode were simultaneously inactivated (65 ± 1% dead). The biofilm on cathodes was expanded from 34 ± 1 to 51 ± 1 µm by salts released from the catalyst layer. These findings provide a novel energy-saving technology to prolong the performance of activated carbon air-cathodes in MFCs, which can be also used to remove ions and biofouling from the porous surface.