Integrated evaluation of carbon fiber brush structure, salt bridge geometry, and kitchen wastewater-derived model substrates for microbial fuel cells

• Substrate type strongly influences MFC voltage output and power density. • Brush anode density affects substrate distribution and voltage stability. • Smaller salt bridges suppress catholyte crossover and improve stability. • Adequate anode coverage of the cathode supports stable MFC operation. • Kitchen wastewater-derived model substrates show feasibility for MFC use. This study addresses two major challenges in microbial fuel cells (MFCs), namely limited operational stability and the need for inexpensive, waste-derived substrates. We hypothesized that optimizing carbon fiber brush structure and agarose salt bridge geometry would improve the stability of Escherichia coli -based MFCs, while kitchen wastewater-derived model substrates could serve as feasible low-cost feedstocks for bioelectricity generation. A dual-chamber MFC system was used to evaluate the effects of brush density, brush size, salt bridge dimensions, and substrate type. The results showed that substrate type primarily governed the achievable open-circuit voltage (OCV) and power output, whereas brush and salt bridge parameters mainly influenced OCV stability. A smaller salt bridge cross-sectional area produced the most stable OCV, indicating that suppression of catholyte crossover into the anode chamber was more important than the associated increase in ionic resistance. The intermediate-density brush anode outperformed both low- and high-density variants, suggesting that adequate void space within the brush is important for substrate distribution and electroactive bacterial colonization. In addition, reduced cathode coverage by the anode shortened the duration of stable OCV. Under the optimized configuration, MFCs supplied with aqueous rice extract and aqueous meat extract achieved maximum power densities of 292.8 and 266.6 mW m -2 , respectively. A key contribution of this study is the combined evaluation of brush structure, salt bridge geometry, and kitchen wastewater-derived model substrates in the same dual-chamber MFC system. These findings provide practical design guidance for improving MFC stability and support the feasibility of low-cost waste-derived substrates for bioelectricity generation.