Closing loops of industrial agro-residues based on a biorefinery approach: extraction of bioactive compounds and bioenergy

An increasing effort has been made to meet the Sustainable Development Goals (SDG), including environmentally sound waste management. Potato and tomato processing industries are responsible for massive waste streams: potato peel (PP) and tomato pomace (TP). This study aims to assess the viability of integrating valorization processes for managing the residues while creating value using the biorefinery approach. The assessment involves the recovery of bioactive compounds (carotenoids, phenolics, and antioxidants) through solid-liquid extraction, followed by biogas production through anaerobic digestion. The operating costs of multiple scenarios, including stand-alone processes and biorefineries, were also calculated to select the most economical route. The diluted ethanolic extraction of pre-treated (dried and milled) PP and TP presented higher total phenolic compounds expressed as gallic acid equivalents -GAE (2.66 mg_GAE/g_sample and 3.29 mg_GAE/g_sample, respectively) than raw PP and TP (1.12 mg_GAE/g_sample and 2.35 mg_GAE/g_sample, respectively). However, higher carotenoid content was obtained from untreated TP (about 1.31 mg_eq-β/g_sample). The methane yield of extracted PP and TP increased by about 100 % and 150 % compared to raw PP and TP, respectively. Thus, the ethanolic extraction of residues significantly improves the anaerobic digestion performance. The operating cost analysis showed that anaerobic digestion was the most economical route, with an operating ratio of 0.6. However, the biorefinery approach remains attractive for residues like TP, which yield high-value extracts, presenting an operating ratio of 0.43. Overall, the biorefinery may be a valuable strategy to create value from residues while managing and contributing to meet SDG 12 (responsible consumption and production).