Heterogeneity in microbial fuel cell stacking influences acidogenic metabolism towards bioelectricity generation, fatty acid synthesis and wastewater treatment†

Abstract

This study explores the influence of varied stacking configurations in microbial fuel cells (MFCs) to channel acidogenic metabolism for enhanced bioelectricity generation, value-added chemical synthesis, and wastewater treatment. Five MFC units were operated in series and hybrid configurations, evaluated over nine operational conditions in a gravity-fed, up-flow system with domestic wastewater as the feedstock, spanning a 78 day period. The hybrid stacking configuration promoted an acidogenic metabolic shift, favouring the production of short-chain carboxylic acids, specifically acetic acid (0.23 g L⁻¹) and propionic acid (0.13 g L⁻¹), with efficiencies of 23% and 10.4%, respectively. In contrast, the series stacking configuration proved more effective for bioelectrogenesis with enhanced energy output, achieving four times the power density of the hybrid setup (series: 1.2 W m⁻², 1.27 W h kg⁻¹ COD vs. hybrid: 0.3 W m⁻², 0.35 W h kg⁻¹ COD). Series stacking also delivered a higher coulombic efficiency of 15.6% and a 6% improvement in treatment efficiency compared to that of the hybrid stacking. The open circuit current (OCC) was relatively higher in the series configuration (1.55 mA vs. 0.2 mA in hybrid), indicating improved biocompatibility. Additionally, a power management system (PMS) facilitated temporary energy storage, enabling the illumination of a 1.7 V LED through a supercapacitor without amplifiers. This study demonstrates an approach to sustainable synthesis of value-added products and bioenergy generation by varying the stacking configuration of MFCs.