Food waste biogas residue-derived composite biochar for effective Cu2+ removal by capacitive deionization

Capacitor deionization (CDI) technology has potential applications in heavy metal removal with low operating cost, environmental friendliness, and comprehensive benefits for water remediation. In this work, using food waste biogas residue as the carbon source, food waste biogas residue composite biochar with rich pore structure was prepared by adding tobacco stalk and KOH activation as the CDI electrode material, and Cu 2+ was taken as target pollutant for heavy metal removal studies. The pore volume of food waste biogas residue composite biochar with activation temperature at 600 ℃ was 2 times larger than that of food waste biogas residue and tobacco stalk biochar. The influence of temperature on structure, composition, electrochemical performance of biochar was further systematically investigated. Food waste biogas residue composite biochar with activation temperature at 800 ℃ (ABTC800) exhibited much larger specific surface area (2044.58 m 2 /g), abundant porous structure (1.29 cm 3 /g), and higher specific capacitance. The removal capacity of ABTC800 electrode can be up to 171.26 mg/g at 3 h in 50 mg/L Cu 2+ solution at a voltage of 0.8 V. Weak acidity is more favorable for Cu 2+ adsorption. ABTC800 had an excellent adsorption capacity towards Cu 2+ . In addition, characterizations revealed that Cu 2+ removal mainly relied on electrostatic adsorption, surface complexation, precipitation, and reduction during the whole process. This study proposed a promising strategy of biogas residue reuse for heavy metal removal.