Microbial fuel cells (MFCs) can have high pollutant removal efficiencies and generate electricity; however, the use of selective membranes represents a considerable expense. In this investigation, the performance of a membraneless MFC was evaluated at different hydraulic retention times (HRTs) of 12, 24, 36, and 48 h. The chemical oxygen demand removal efficiencies (CODREs) were 93.5, 90.9, 87.3, and 85.4%, and the biochemical oxygen demand (BODRE) values were 94.5, 91.5, 88.9, and 85.5 at HRTs of 48, 36, 24, and 12 h, respectively. Lower concentrations of solids (suspended solids and total dissolved solids), total nitrogen, phosphorus, fats and oils, and microbiological contamination (helminth eggs and fecal coliforms) were detected when operating the system at a 48 h HRT. At an HRT of 12 h, no decrease in electrical conductivity was detected, whereas at 48 h, it decreased by 19.6%. The oxidation–reduction potential and OCV increased at longer HRTs. The microorganisms detected at the anode were Achromobacter denitrificans, Achromobacter anxifer, and Pseudomonas aeruginosa. The 48 h HRT improved the chemical, physical, and microbiological quality of the municipal wastewater, favoring voltage generation.

Microbial fuel cells (MFCs) are an emerging technology that converts the chemical energy stored in organic substrates into electrical energy using microorganisms as catalysts. However, their performance is often limited by the anode design and architecture. To address this, conductive anodes with well-defined pore sizes were manufactured via 3D printing and evaluated for electrical energy generation and wastewater treatment in microbial fuel cells. The maximum power density, coulombic efficiency, and accumulated biomass observed were 14.94 mW/m², 4.87 ± 0.56%, and 0.186 ± 0.025 g, respectively, for the anode with a 2.3 mm pore size. The maximum chemical oxygen demand (COD) removal efficiency was 86.98 ± 1.89% for the anode with a pore size of 1.6 mm. However, this difference was minimal and not significant compared to the anode with a 2.3 mm pore size, which achieved 85.77 ± 2.31%. Additionally, the lowest internal resistance observed was 1246.44 Ω, corresponding to the MFC equipped with the anode with a pore size of 2.3 mm. Taken together, these results indicate that, when using 3D-printed anodes with controlled architectures, an intermediate pore size, neither too large nor too small, provides an adequate balance between electrochemical performance and efficient wastewater treatment in microbial fuel cells.