Carbon Dioxide-Driven anaerobic digestion with Zero-Valent iron for enhanced biomethanation of food waste

To improve biomethanation in the anaerobic digestion of food waste (FW), carbon dioxide (CO₂) and zero-valent iron (ZVI) were applied, and the impact of varying dosages and injection times was assessed. The conditions of 1 g/L ZVI and 3-min CO₂ injection resulted in significant methane yield improvements, with FW4 reaching a peak of 624.4 mL/gVS at day 18, 44.7 % higher than the control (FW0). Hydrolysis efficiencies for proteins, polysaccharides, and lipids increased by 41 %, 65 %, and 57 %, while acidogenesis efficiencies rose by 48 %, 44 %, and 24 %, respectively. Additionally, CO₂ optimized the microbial community composition, notably increasing Methanobacterium abundance by 25.7 %. Finally, three-dimensional excitation-emission matrix (3D-EEM) fluorescence spectrograms confirmed the degradation of organic compounds, while cyclic and differential pulse voltammetry revealed increased reduction-oxidation activity. These findings underscore a promising strategy to enhance AD processes' stability and methanogenic efficiency by combining CO₂-driven approaches with ZVI.