Techno-Economic Assessment of Anaerobic Digestion for Olive Oil Industry Effluents in Greece

Olive mill wastes are some of the most important waste streams in Mediterranean countries, such as Greece, and their uncontrolled disposal without treatment imposes serious environmental impacts. In the last few decades, the European Union has defined the framework for a sustainable circular economy, aiming for viable waste treatment solutions. Under this scope, anaerobic digestion could be a remarkable solution for efficiently reducing waste organic matter and producing green energy, at the same time. In this study, the economic sustainability of an anaerobic digestion unit for olive mill effluents was assessed. It was found that a centralized treatment plant that can process liquid olive mill effluents during the olive harvesting season and other agro-industrial by-products (such as fruit and vegetable waste) for the rest of the year could be a viable solution, with waste capacities of 780 m3OMW d−1 and 245 kgFVW d−1. The internal rate of return was estimated at 6%, the net present value was estimated to be EUR 2 million, while the payback period was calculated to be 12 years. Furthermore, through the sensitivity analysis, the selling price of the electricity produced and the productivity of the waste processed in the plant alongside the olive mill wastewater were identified as the main factors affecting the viability of the process. The findings of this study can be applied in the development of a biomass-processing facility, taking into consideration the economic feasibility and the processing of challenging-to-treat wastes to generate green energy.