Development of an Investment Decision Tool for Biogas Production from Biowaste in Mediterranean Islands

Biomethane is the Renewable Energy Source (RES) derived from the purification of biogas produced from Anaerobic Digestion (AD) process using biomass. Biomethane can be injected into the natural gas grid, thereby contributing towards satisfying the energy demands of society. The aim of this work is to test an investment decision tool for assessing the financial feasibility of an AD plant using biowaste for producing biogas and, then, biomethane, as well as digestate and, then, compost. The first Sicilian AD plant aimed at producing biomethane was built in the province of Caltanissetta in 2021.The innovative Enersi Sicilia plant treats 56,000 t of Organic Fraction of Municipal Solid Waste (OFMSW) per year to generate 499.22 Sm3h−1 of biomethane. This plant yields a yearly total of 4,168,483 Sm3 of biomethane, thereby replacing 8,450 t of oil equivalent and avoiding the emission of 6,126 t of fossil CO2 into the atmosphere. The solid fraction of digestate is recovered and processed into compost, that corresponds to approximately 25–30% of the original feed in biomass weight. This compost is classified as a “mixed composted soil conditioner”, that can be used in agriculture, within Circular Bioeconomy (CBE). The financial feasibility of AD plant case study was assessed through Cost-Benefit Analysis (CBA), by assuming a reference period of 20 years, both with and without the financial subsidy provided by the Italian government to those who market biofuels, i.e. certificate of introduction in consumption. The reliability and robustness of CBA results were verified through the Sensitivity Analysis (SA). Even without the subsidy, the AD plant proved to be a good financial investment, without taking into consideration all its social and environmental benefits. The financial feasibility of the investment would be preserved up to an 8.21% yearly increase of the operational costs. The production and use of biomethane and other renewable gases in existing infrastructures would allow EU to achieve the climate objectives of Paris Agreement, i.e. to save e 140 billion a year by 2050. The interest of the growing market in biomethane mobility demonstrates the great potential of alternative uses of this gas.