Investigation of multiphysics in tubular microbial fuel cells by coupled computational fluid dynamics with multi-order Butler-Volmer reactions

Abstract

Microbial fuel cells (MFCs) are considered as an emerging concept for sustainable wastewater treatment with energy recovery. The anode of an MFC plays a key role in conversion of organic compounds to electricity, and thus understanding the multiphysics within the anodic compartment will be helpful with MFC optimization and scaling-up. In this study, a multi-order Butler–Volmer reaction model was proposed to compute organic consumption and energy recovery. Computational fluid dynamics (CFD) was applied to analyze the hydrodynamics and species transport inside the anodic compartment. By comparing to the experimental data, the reaction order of anodic surface reaction was determined as 6.4. The reaction model gave good agreement with experimental data when the influent sodium acetate was 1.0, 0.5 and 0.3 g L^-1 at anodic hydraulic retention time (HRT) of 10 h, indicating the effectiveness of this multi-order Butler–Volmer reaction model. When the influent sodium acetate was 0.2 g L^-1 or the anodic HRT was 15 h, the model exhibited discrepancies in predicting current generation and effluent chemical oxygen demand (COD) concentration, likely due to the interference of the decayed biomass and the activities of non-electroactive bacteria. The results of this study have demonstrated the viability of coupling CFD with a multi-order reaction model to understand the key operating factors of an MFC.