Continuous-series microbial fuel cell for tofu liquid waste: effects of catholyte and inoculum

This study investigates a continuous-series microbial fuel cell (MFC) with 50% recycle for simultaneous tofu wastewater treatment and bioelectricity generation. A five-stack horizontal reactor was operated with three substrate–inoculum configurations (substrate only; substrate + Sidoarjo mud; substrate + Sidoarjo mud + Bacillus subtilis ) and oxidizing catholytes (K 2 S 2 O 8 and KMnO 4 at 10–50 mM). System performance was evaluated using high-frequency monitoring (voltage, current, pH, temperature) and conventional wastewater parameters (biochemical oxygen demand /BOD, chemical oxygen demand /COD, protein degradation). The mixed inoculum (mud + B. subtilis ) combined with 50 mM K 2 S 2 O 8 produced the best overall performance, achieving the highest organic removal (79.01% BOD removal, 86.67% COD removal, and 81.7% protein degradation) and highest electricity generation (4.378 mW/m 2 power density) in 15 Days. Extended operation (45 days) confirmed improved stability and sustained treatment efficiency over time (95.22% BOD removal, 92.60% COD removal, and 79.38% protein degradation, 15.808 mW/m 2 total power density). The results demonstrate the potential of combining inoculum synergy, catholyte selection, and continuous-series reactor design to enhance the performance of MFCs for high-strength, protein-rich industrial wastewater. • Five-stack continuous MFC with 50% recycle and 1-s IoT monitoring. • 50 mM K 2 S 2 O 8 catholyte (PS50) outperformed KMnO4 in the cathode. • Sidoarjo mud + Bacillus subtilis sped protein breakdown and bioelectricity. • 45-day removals: BOD 95.22% and COD 92.60% on tofu wastewater. • Total power 1.58×10ˆ7 mW/m 2 ; energy 1.135×10ˆ11 kJ/m 2 at 45 days.