Mitigating cathode biofouling in membrane-less MFCs using CuO-doped activated carbon: a comparative study of batch and continuous modes

A membrane-less microbial fuel cell system was developed and evaluated using CuO-incorporated activated carbon (CuO/AC) cathodes designed for dual functionality: enhanced oxygen reduction reaction activity and antibacterial performance. CuO/AC composites were synthesized via wet impregnation followed by thermal treatment, and the 10wt% CuO/AC formulation demonstrated the best performance. The optimized cathode achieved a maximum power density of ~ 1.25 W/m² and a peak current density of ~ 5.2 A/m², significantly outperforming pristine AC and AC-CNTs cathodes. Long-term stability tests showed that the 10wt% CuO/AC cathode maintained an open cell potential around 0.85-1.0 V in batch mode for over 40 days, while AC-CNTs cathodes exhibited lower open cell potential and severe performance degradation due to biofouling. Microscopic analysis confirmed heavy biofilm and microbial colony formation on AC-CNTs cathode, whereas the CuO-containing cathode surface remained clean and free from microbial colonization. Moreover, MFCs operated in continuous mode demonstrated superior operational stability and higher COD removal efficiency (~ 85.3%) compared to batch mode (~ 76.0%), despite slightly lower OCP and initial power densities. These findings highlight the synergistic role of CuO in enhancing cathodic performance and biofouling resistance, while also demonstrating the industrial relevance of continuous mode operation for stable and efficient wastewater treatment coupled with energy recovery.