Addition of biochar and trace elements in the form of industrial FeCl3 to stabilize anaerobic digestion of food waste: dosage optimization and long-term study: Biochar and trace elements (industrial FeCl3) to stabilize anaerobic digestion of food waste

BACKGROUND: Although anaerobic digestion is a promising alternative for the valorization of complex substrates such as food waste, this process is yet to be optimized and options for its stabilization must be developed. This study assessed for the first time if the combined addition of biochar and trace elements in the form of an industrial FeCl₃ solution could serve as a method for stabilizing food waste anaerobic digestion. Both batch and long‐term semi‐continuous reactors were run. RESULTS: Results from batch reactors demonstrated that supplementation of both biochar (10–100 g L⁻¹) and trace elements (FeCl₃; 0.1–0.2 g Fe L⁻¹) favored the digestion kinetics. Their addition improved the maximum methane production rates (from 897 up to 1494 mL day⁻¹) and the average daily methane production rates (from 298 up to 369 mL day⁻¹), related to acetate and propionate consumption, respectively. Continuous reactors confirmed the batch results, with higher methane production rates (up to 1.75 L L⁻¹ day⁻¹) and lower concentrations of acetate and propionate when biochar and trace elements (FeCl₃) were added. CONCLUSION: Addition of biochar and industrial FeCl₃ favored the digestion kinetics, improving volatile fatty acid consumption and methane production rates. These materials appear as an economically‐feasible alternative for stabilizing the valorization of food waste at industrial scale. © 2018 Society of Chemical Industry