Co-pelletization of coarse olive pits and food-industry residues for sustainable bioenergy production: physicochemical, environmental, and techno-economic assessment

Abstract

Co-pelletization of agro-industrial residues represents a promising route for decentralized and low-carbon bioenergy production. This study investigates the valorization of a cellulose and glycerin-rich granular residue (RI), generated by the food processing industry during sausage manufacturing and currently landfilled through co-pelletization with coarse olive pits (CA). This strategy addresses the insufficient heating value of the target residue RI for commercial application via mono-pelletization, aiming to convert it into a solid biofuel suitable for industrial biomass boilers while complying with the ISO 17225 specifications. A simplified, low-energy pre-treatment was applied, avoiding fine milling (particle size ≥ 1 mm) and enabling pelletization at high moisture (30–35 %). Four CA/RI blends (10–40 % RI w/w) were evaluated under ISO 17225 standards. The optimal blend (70%CA/30%RI) achieved a higher heating value of 17.6 MJ·kg^-1, bulk density comparable to commercial wood pellets, and mechanical durability exceeding A2-grade thresholds. Combustion tests revealed lower NO_x, SO_x, and VOC emissions relative to Pinus radiata pellets, with slightly higher CO levels attributed to laboratory-scale combustion constraints. Olive pits were selected for their local availability and proven suitability as industrial boiler fuel. Life cycle assessment (LCA) indicated a 35 % lower carbon footprint compared to conventional Pinus radiata pellets. Techno-economic analysis estimated a production cost of 162.4 USD·t⁻¹ with profitability achievable at a 1,800 t·yr⁻¹ scale. These results confirm that simplified co-pelletization of CA and RI is technically feasible, economically viable, and environmentally advantageous, providing a circular bioeconomy pathway for valorizing underutilized food-industry residues.