Production of green energy from co-digestion: perspectives for the Province of Cuneo, energetic balance and environmental sustainability

In Italy and many European countries, energy production from biomass is encouraged by strong economic subsidies so that biomass energy plants are getting large diffusion. Nevertheless, it is necessary to define the environmental compatibility taking into account global parameters as well as environmental impacts at regional and local scales coming from new polluting emissions. The environmental balances regarding new energy plants are of primary importance within very polluted areas such as Northern Italy where air quality limits are systematically exceeded, in particular for PM₁₀, NO₂, and ozone. The paper analyzes the renewable energy scenario relating to manure anaerobic digestion and biogas production for the Province of Cuneo, N–W Italy, and the environmental sustainability of the possible choices. The study is focused on energy producibility, heat and power, nitrogen oxides and ammonia emissions, GHG (greenhouse gases) balances dealing also with indirect releases of CH₄ and N₂O, as well as emissions due to energy crops production. The most important conclusion that can be drawn is that the production of renewable energy from anaerobic digestion could cover up to 13 % of the Province electricity consumption, but sustainability in terms of CO₂ emissions can be reached only through an overriding use of agricultural waste products (manure and by-products instead of energy crops) and cogeneration of thermal energy at disposal; the application of the best available techniques to waste gas cleaning, energy recovery, and digestate chemical–physical treatments allows positive emissive balances.