Effect of blending olive leaves and olive mill wastewater on the potential biogas production

The growing production of olive oil, particularly in Mediterranean regions, generates large volumes of by-products such as olive mill wastewater (OMWW) and olive leaves, which pose environmental management challenges but also present opportunities for resource recovery. This study aims to assess the technical feasibility of co-digesting OMWW with olive leaves to enhance methane production and improve the sustainability of olive oil processing residues. To achieve this objective, Biochemical Methane Potential (BMP) assays were conducted to evaluate and compare the anaerobic mono-digestion of olive mill wastewater (OMWW), designated as feedstock mixture 1 (FM1), with its co-digestion supplemented with 4 % (w/w, TS basis) olive leaves, referred to as feedstock mixture 2 (FM2). The experimental setup involved monitoring key indicators such as biogas yield, methane concentration, and process stability to evaluate performance. The tests revealed that FM1 achieved a higher total biogas yield (192.80 Nm 3 /t), while FM2 resulted in a higher methane concentration (52.60 %), indicating improved biogas quality and energy potential. Both digestion setups demonstrated stable performance throughout the trials. These findings suggest that co-digestion of OMWW with olive leaves can enhance methane content and offer a viable route for valorizing olive mill residues. Future research should aim to optimize co-substrate ratios, ensure long-term process stability, and evaluate the scalability of the approach for industrial applications. • Results indicate that adding 4 % olive leaves to OMWW can enhance biogas production. • Co-digesting olive leaves with OMWW improves biogas quality compared to OMWW alone. • Findings support a circular economy approach for sustainable olive mill practices. • Olive leaves removed during mill cleaning are typically spread over nearby fields. • These results may boost profitability and help reduce olive oil production costs.