Development of biochar-based composites electrodes from pyrolysis of coffee silverskin: microbial fuel cells for wastewater treatment

Addressing the need for cost-efficient and environmentally friendly electrode materials for large-scale applications of bioelectrochemical systems, this study implemented the principles of circular economy to produce biochar- and hydroxyapatite/biochar-based conductive cathodes to be employed in clean and green technologies for wastewater treatment. Silverskin, the byproduct of coffee roasting responsible for generating significant waste worldwide, was subjected to a pyrolysis process to produce conductive biochar, then characterized in terms of physico-chemical properties. Biochar-based inks were formulated and employed to produce microporous layers on carbon cloth, finally used as cathodic materials in microbial fuel cells systems. The presence of hydroxyapatite in biochar-based composites was also evaluated with the goal of combining the remediation activity of biochar towards dissolved organic compounds, with that of hydroxyapatite towards inorganic ionic pollutants (such as Cd(II) and Zn(II)). Despite underperforming compared to other more technological and optimized materials, waste-derived biochar and its composite with hydroxyapatite were demonstrated to open novel frontiers in design and architecture of “multi-pollutants targeted” smarter bioelectrochemical systems, where not only microcurrent production, but a broader range of wastewater treatment can be addressed.