Microwave-converted insect frass biochar as a high-performance anode for crude glycerol-powered microbial fuel cells

The growing scale of insect farming has led to the generation of large volumes of frass, which is often overlooked despite its potential for resource recovery. In this study, we developed a value-added pathway by converting mealworm frass into electroactive biochar via microwave-assisted pyrolysis (MAP), offering a rapid, energy-efficient alternative to conventional thermal treatment. The resulting biochar, rich in nitrogen and oxygen surface functionalities, was used to fabricate a novel anode for microbial fuel cells (MFCs). Electrochemical analysis revealed that the MAP-derived electrode exhibited excellent charge transfer performance (397.6 Ω) and high capacitance (0.29 F/g), significantly outperforming its conventionally pyrolyzed counterpart. When integrated into an MFC treating crude glycerol—a major by-product of biodiesel refining—the system achieved complete substrate removal (99.85 %) within four days and reached a peak power density of 5678 mW/m², outperforming standard carbon cloth anodes by over 70 %. Microbial profiling further indicated enhanced colonization of electroactive and glycerol-degrading microbes on the frass-based biochar. The enrichment of Firmicutes and Desulfobacterota enhanced the electrochemical activity of MFC1000W and effectively reduced the charge transfer resistance (452.9 Ω). Bacteroides contributed to the growth of various exoelectrogens and accelerated electron transfer. This work not only provides a sustainable route for insect frass valorization, but also demonstrates its functional potential in bioelectrochemical systems for waste-to-energy conversion.