A circular valorization of fat, oil, grease (FOG): Integrating FOG-derived biosurfactant production and FOG-fed microbial fuel cells

The treatment of lipid-rich wastewater using microbial fuel cells (MFCs) is often limited by the low solubility and bioavailability of hydrophobic substrates such as fat, oil, and grease (FOG). In this study, we present a sustainable and circular strategy wherein biosurfactants (BSFs) are produced from FOG using Bacillus velezensis and used to enhance FOG bioavailability and consequent degradation in MFCs. BSF production (2.3 g/L) was confirmed via foaming, drop collapse, oil displacement, CTAB-methylene blue agar, and emulsification index assays. When used to increase the bioavailability of FOG, the presence of BSFs improved all key MFC performance metrics. Notably, a 5.5-fold increase in maximum power density was observed from 0.08 to 0.44 W/m² when BSFs were added and FOG was used as the sole organic substrate at a 0.27% (v/v) concentration. Current density (1.1 A/m²), COD removal (81.1%), and coulombic efficiency (7.9%) also improved when BSFs were present. The control MFCs operated without BSF showed significant performance deterioration, attributed to poor emulsification, substrate accumulation, and limited availability of substrate. Comparative tests using triolein as a model lipidic substrate highlighted the effectiveness of BSF-assisted FOG degradation.