Batch mesophilic anaerobic digestion of mixtures of lignocellulosic biomasses from Ecuador: influence of inoculum type and thermal pretreatment on methane production and process kinetics

Comprehensive and integral treatment of agricultural wastes is crucial to palliate the environmental impact associated with uncontrolled disposal. However, waste management should be focused on a local perspective. In this study, the anaerobic co-digestion of four lignocellulosic by-products generated in Ecuador (cocoa husks, coconut shells, rice hulls, and sugarcane bagasse) was evaluated. Two different mixture ratios, the impact of thermal pretreatment, and the influence of the inoculum origin were also assessed. Results showed that the anaerobic inoculum collected from a brewery factory showed the highest efficiency. Moreover, thermal pretreatment improved the methane yields (158–160 NLCH4 kg−1VS). However, the highest kinetic constant (1.1 ± 0.1 d−1; first-order kinetic model) and the maximum methane production rate (153 ± 3 NLCH4 kg−1VS d−1; logistic model) were obtained for the untreated mixtures. Finally, the substrate mixture ratio did not influence the anaerobic digestion performance. Therefore, the present study provides preliminary insights into the viability of anaerobic co-digestion as a feasible technology for the valorization of agro-industrial lignocellulosic residues to reduce the effect of seasonal production variations.