Understanding the impact of operational conditions on performance of microbial peroxide producing cells

Microbial peroxide producing cells (MPPCs) are microbial electrochemical cells used to synthesize hydrogen peroxide (H₂O₂) in the cathode chamber. Catholyte hydraulic retention time (HRT), different catholytes and their concentrations, and a ferrochelating stabilizer are varied in a continuous-flow cathode MPPC to evaluate their impacts on performance. Using NaCl catholytes, the MPPC produced as high as 3.1 ± 0.37 g H₂O₂ L⁻¹ at a 4-h HRT with as little as 1.13 W-h g⁻¹ H₂O₂ energy input and with up to 57 g L_cathode⁻¹ d⁻¹ at a 1-h HRT. For these conditions, the H₂O₂ production rate provides more than 3 times the H₂O₂ required for disinfection or micro-pollutant removal while using 5–25% of the power used in conventional H₂O₂ production processes. Attempts to improve H₂O₂-production by adding weak acid buffers or H₂O₂-stabilizing EDTA fail for different reasons. The addition of the ferrochelator EDTA to prevent H₂O₂ auto-decay deteriorates MPPC performance, because EDTA diffuses from the cathode to the anode, inhibiting iron utilization by anode-respiring bacteria. Weak acid buffers failed to reduce cathode concentration overpotentials. Buffering catholytes lowered the H₂O₂ yield due to large pH gradients at the cathode chamber entrance, causing the formation of H₂O instead of H₂O₂ or O₂ re-formation from H₂O₂ auto-decay.