Dry Anaerobic Digestion of Food Industry by-Products and Bioenergy Recovery: A Perspective to Promote the Circular Economy Transition

Anaerobic digestion (AD) can be a suitable alternative for agro-industrial by-products energy recovery, contributing to reducing environmental side effects caused by incorrect disposal of these materials. In this study, dry AD reactors were started-up with acai seeds, brewer's spent grains (BSG), and poultry feathers, all solid by-products generated from the food industry. The results demonstrated that during 22 days of dry AD, the BSG reactor presented the best operational performance, as follows: (i) highest solids biodegradation (up to 70%); (ii) accumulated biogas volume (up to 10 L); (iii) methane composition (57.49%); and (iv) methane yield (39.51 L CH₄kg^-1 total volatile solids). The biogas combustion in a combined heat and power engine could locally generate electric (0.101 MWh ton^-1 BSG) and thermal energy (455.21 MJ ton^-1 BSG), which could be used to self-supply the industrial facility, avoiding greenhouse gas emissions (0.03 ton CO_2eq ton^-1 BSG) from the traditional energy sources. Based on the experimental dataset, the dry AD of agro-industrial by-products can be a promising approach to produce methane-rich biogas, being mainly of interest for the beer industry, as an alternative for energy recovery in a circular economy concept.