Insight into the Impact of Millimeter-Pore Size of 3D Bioanodes on Biofilm Behavior and System Performance in Microbial Electrochemical Systems

Microbial electrochemical systems (MESs) can simultaneously treat environmental pollutants and recover electricity, with research aiming to enhance efficiency by employing three-dimensional (3D) porous anodes to boost microbial enrichment. Large millimeter-sized pores are considered advantageous for 3D anode construction, addressing microbial colonization and mass transfer limitations. However, there is a notable gap in understanding the selection and impact of millimeter-level pore sizes on the biofilm behavior and system performance in 3D anode MESs. This study investigated 3D anodes with pore sizes of 1 mm, 3 mm, and 5 mm. Experimental and theoretical analyses show that while millimeter-level pore sizes improve mass transfer, larger pore sizes reduce both the enriched microorganisms and the power density. The anode with a 1 mm pore size performed best (34.9 W/m3), while larger pore sizes performed worse than the nonporous anode, challenging the notion that introducing pore structures necessarily enhances performance. A principle for pore size selection is proposed: ensure mass transfer first and then choose an appropriate pore size to increase the total surface area and optimize microbial enrichment. This study provides a theoretical basis for selecting pore sizes in MES 3D anodes.