Enhanced bio-decolorization of acid orange 7 and electricity generation in microbial fuel cells with superabsorbent-containing membrane and laccase-based bio-cathode

Abstract

This study investigates the decolorization of the azo dye Acid Orange 7 (AO7) and the simultaneous generation of electricity in air-cathode microbial fuel cells (AC-MFCs) with a fungal bio-cathode. The laccase-producing white-rot fungus Ganoderma lucidum BCRC 36123 that was seeded on wood-chips around the cathode of the AC-MFCs functioned synergistically with an anaerobic microbial consortium in the anode chamber to degrade AO7. Superabsorbent polymer (SAP) was mixed with polyvinyl alcohol (PVA) to form a polymer electrolyte membrane (PEM) that separated the cathode from the anolyte of the AC-MFC to provide high proton transfer rate and water retention capacity, promoting the decolorization of AO7 and electricity generation. The solid-state cultivation of Ganoderma lucidum yielded 17.3 times more laccase than did the liquid-state cultivation of the same fungus. A maximal open-circuit voltage of 699 mV and a 96.7% decolorization of AO7 at 500 mg/L were achieved in AC-MFCs that were equipped with a PEM with an optimal PVA/SAP ratio of 1:2. A maximal power density of 207.74 mW/m2, which was 10–15 times those obtained in similar studies in the literature, was obtained at an AO7 concentration of 500 mg/L. Over 84% of the by-products of AO7 decolorization were further degraded in the AC-MFC during a 30 day test period. This study reveals the feasibility of using both the improved PEM and a white-rot fungus in a solid-state culture on the cathode to increase considerably the pollutant removal efficiency of MFCs and the amount of electricity they generate.