The anaerobic and starving treatment eliminates filamentous bulking and recovers biocathode biocatalytic activity with residual organic loading in microbial electrochemical system

The biocathode microbial electrochemical system (MES) was promising for wastewater treatment. However, the residual dissolved organic matter in catholyte caused the excessive proliferation of heterotrophic bacteria and restricted the power output and organic matter removal performance. The periodic anaerobic and starving (AS) treatment was designed and applied to eliminate filamentous bulking and rebuild electrochemical active cathode biofilm. The biocathode filamentous bulking caused rapid current drop and effluent quality deterioration, during which the Sphaerotilus dominated in biofilm. After three-day AS treatment, the current density recovered from 2.4 ± 0.3 to 3.8 ± 0.1 A m⁻³ within 2–4 h with the maximum power density raised from 0.59 ± 0.03 to 1.33 ± 0.06 W m⁻³. The effluent chemical oxygen demand reduced from 115 ± 6 to 32 ± 10 mg L^–1. Compare with biocathode bulking, the biomass adhesion ratio (K_bc) on cathode brushes greatly dropped from 230 ± 29 to 62 ± 12 ug mg⁻¹ after AS treatment, while the biomass specific biocatalytic activity increased by 9 times from 3.2 ± 0.4 to 29.1 ± 4.6 μA mg⁻¹. The oxygen diffusion resistance (R_d) rather than charge transfer resistance (R_ct) mainly restricted cathodic oxygen reduction reaction (ORR) during biocathode bulking. The AS treatment can effectively reduce the R_d from 357.2 ± 20.6 to 151.8 ± 5.5 Ω and decrease the R_ct from 28.6 ± 1.0 to 8.8 ± 0.1 Ω. Therefore, periodic anaerobic and starving treatment effectively regulated the operation of microbial electrochemical systems by maintaining functional cathodic bio-community.