Circular bioenergy from citrus waste: Life cycle evaluation in the Mediterranean context

An effective strategy for enhancing the sustainability of production processes is to adopt a circular economic approach utilising agro-industrial by-products and waste to generate value-added compounds, biofuels, and energy. Citrus processing generates large quantities of orange-peel waste (OPW), and recent research shows that OPW has promising potential for biogas production. Because its availability is restricted to few months of the year for seasonal variations, relying solely on OPW constrains the continuous operation of biogas plants. The inherent volatility of crop yields, coupled with the inhibitory effects of d-Limonene, renders the sole reliance on this substrate a significant risk for anaerobic digestion operations. Within this context, the study aims to analyse the technological feasibility of ensiling OPW to mitigate seasonality, alongside the economic and environmental sustainability of generating electricity from the resulting biogas via anaerobic digestion (AD). This research considers the potential for continuous, year-round use of OPW, both fresh and ensiled. This approach is then compared with two other substrates widely available in the Mediterranean region: two-phase and three-phase olive pomace. Technical feasibility was assessed across all three scenarios. In parallel, the environmental impact was quantified using the Life Cycle Assessment (LCA) methodology, while the financial aspect was estimated through Life Cycle Costing (LCC) at the farm level. The results indicate positive environmental and economic outcomes across all scenarios, findings that are confirmed by sensitivity analyses of these two key dimensions. For example Climate change performance varies across the scenarios, with OPWFE showing the lowest impact (0.316 kg CO2 eq), while OPWTwPP and OPWThPP exhibit higher impacts by 11% and 17%, respectively, relative to this reference scenario. In contrast, economic performance peaks in OPWThPP (IRR = 23%), with OPWTwPP and OPWFE displaying lower profitability, reduced by 9% and 17%, respectively, compared to the most profitable scenario. The conclusions provide valuable insights for promoting business-oriented strategies that aim to pursue a new ecological transition pathway.