Iron-impregnated spent coffee ground biochar for enhanced degradation of methylene blue during cold plasma application

This study investigates feasibility in the technical convergence of cold plasma and Fe-impregnated biochar to remove slowly-biodegradable methylene blue (MB) as a model contaminant. A problematic biowastes, spent coffee ground, was reused as a renewable source of biochar, and it impregnates Fe to enhance adsorption performance. Results verify that the cold plasma's advanced oxidation coupled with the biochar increases overall MB removal efficiency and accelerates degradation kinetics. Experimental data regression verifies that the impregnated Fe significantly enhances the kinetic constants for total organic carbon (0.019–0.045 min⁻¹) and MB (0.050–0.065 min⁻¹). Also, it was confirmed that Fe-impregnation clearly shortens the periods required for almost complete MB degradation to within 1 h. In addition, the higher Fe was impregnated, the stronger synergistic effects on MB degradation rates was observed. The analyses of nitrate, nitrite, and sulfate supports that the MB could be lower down to detection limit by the suggested combination. These results provide useful information about the synergistic combination of physicochemical processes as a viable option to effectively manage slowly-biodegradable pollutants.