Different treatments of six selected Mediterranean agro-industrial by-products, i.e., citrus pulp, olive pomace cattle and poultry manure, whey and silage, were investigated through LCA application with the aim of analysing their environmental sustainability, in terms of “level of greenness”. In detail, an AD-based treatment system composed of four biogas plants fed by a mix of the selected agro-industrial by-products (scenario 1) was compared with the conventional treatment of those feedstocks (scenario 2), i.e., land application, biowaste composting, olive pomace treatment, and feeding treatment. The results clearly demonstrated that the AD-based treatment system is the most environmentally sustainable solution, since the environmental damages associated with the investigated scenarios are equal to 11.08 μpt and 598.44 μpt, for scenario 1 and scenario 2, respectively. These results confirmed that, as reported in the literature, anaerobic digestion of agro-industrial feedstocks is considered to be a “green” solution with high saving potential with respect to greenhouse gas (GHG) emissions, and plays a relevant role in renewable energy production by valorising agro-industrial by-products, by contributing to closing of organic matter cycles within a circular economy perspective. The results achieved in this study could represent a guideline to improve sustainability of energy generation by AD-based systems. In fact, since the results were obtained by means of real-world modelled scenarios, they could be extended to other AD-based systems analogous to that analysed in this study for developing and supporting sustainable economy concepts and energy-food-waste nexus approaches.

Anaerobic digestion (AD) has the potential to catalyse the shift from a linear to a circular economy. However, effective treatment and management of both solid (DSF) and liquid (DLF) digestate fraction treatment and management require adopting sustainable technologies to recover valuable by-products like energy, biofuels, biochar, and nutrients. This study reviews state-of-the-art advanced technologies for DSF and DLF treatment and valorisation, using life cycle assessment (LCA) and techno-economic analysis (TEA) in integrated digestate management (IDM). Key findings highlight these technologies' potential in mitigating environmental impacts from digestate management, but there's a need to improve process efficiency, especially at larger scales. Future research should prioritize cost-effective and eco-friendly IDM technologies. This review emphasizes how LCA and TEA can guide decision-making and promote sustainable agricultural practices. Ultimately, sustainable IDM technologies can boost resource recovery and advance circular economy principles, enhancing the environmental and economic sustainability of AD processes.

The global shift towards using biomass for biofuels and chemicals is accelerating due to increasing environmental concerns and geopolitical strategies. This study investigates a biorefinery model using citrus-processing-waste, specifically citrus pulp, to produce high-value products for various industries, including cosmetics, pharmaceuticals, flavours, fragrances, and food packaging. In Italy, particularly Sicily region, citrus processing generates significant amounts of waste, often improperly disposed of, contributing to environmental problems. Researchers have demonstrated that citrus waste can yield commercially valuable compounds. This study specifically focuses on orange peel waste (OPW), which constitutes about half of the fruit's weight, aiming to extract pectin and limonene through a combined process. The extraction process was carried out on a laboratory scale, and its sustainability was evaluated using a life cycle assessment (LCA) with SimaPro 8.1 software and the Impact 2002 + method. The functional unit adopted for this study is 300 g of OPW, obtained after the pre-treatment phase, from which 0.14 g of limonene and 8.22 g of pectin were extracted. The LCA results revealed that pectin extraction has a significantly higher environmental impact compared to limonene extraction, primarily due to the use of ethanol as a solvent, followed by electricity consumption. To mitigate this impact, the LCA assessed alternative, more sustainable solvents, resulting in a 73.4% reduction in the environmental footprint of the pectin extraction process. These findings underscore the critical role of LCA, even at the laboratory scale, in identifying environmental hotspots and providing insights for improving and optimizing processes for potential industrial-scale applications.