Improved chromium (VI) reduction performance by bacteria in a biogenic palladium nanoparticle enhanced microbial fuel cell

Highlights: • GAC average particle size was optimized to improve Cr(VI)-reducing MFC performance. • The synthesized Bio-PdNPs were successfully implemented in modifying GAC. • GAC modified with Bio-PdNPs successfully improved Cr(VI)-reducing MFC performance. -- Abstract: Hexavalent chromium (Cr(VI)) is discharged from several anthropogenic activities that make use or produce Cr(VI) leading to environmental pollution. In this study, we explore an environmentally friendly process for the treatment of Cr(VI) with a codeposition of zero-valent palladium on the anode electrode of a microbial fuel cell (MFC). The MFC featured a granular activated carbon (GAC) anode modified with biogenic palladium nanoparticles (Bio-PdNPs). Temperature, pH, and initial Cr(VI) concentration were first optimized to 38 °C, pH 4, and 100 mg L⁻¹ Cr(VI), respectively. Thereafter, the GAC average particle size was successfully optimized to 0.6–1.1 mm which was shown to promote the highest cell attachment. GAC below this size range had minimal cell attachment. The results from the study also showed that the GAC can be successfully modified using Bio-PdNPs to improve the performance of Cr(VI)-reducing MFC with Bio-PdNPs loading of 6 mg Bio-PdNPs g⁻¹ GAC resulting in peak output potential difference of 393.1 mV, maximum power density of 1965.4 mW m⁻³, and complete removal of 100 mg L⁻¹ Cr(VI) in 25 h.