Abstract
In recent years, the increasing market trend of Renewable Energy Sources (RES) in the European Union has been connected with the public subsidies guaranteed to encourage their production. In Italy, the northern regions have played a leading role and contributed deeply to increase the share of RES in the national energy mix. An increase in the number of Anaerobic Digestion (AD) plants fed with agricultural feedstock has been detected, reaching 1800 units in only 20 years. AD is considered as one of the most promising technologies for RES production, especially when wastes are used as feed. In fact, the use of wastes brings to increase the added value and reduces the economic and environmental costs related to the waste treatment as well as the energy purchase. Despite these advantages, the economic subsidy framework has encouraged entrepreneurs to increase the productivity of plants by using dedicated crops as feed, of which maize silage is the most widely used. Since the economic subsidy for bioenergy production has already been reduced, it can be expected its end in the future, thus potentially making the feeding of plants with dedicated crops uneconomic. In particular, subsidies could be essential to guarantee revenues and to cover the feeding supply costs.
This study aims to evaluate the consequences of the potential deletion of the subsidy framework for AD production plants. Consequential life cycle assessment (cLCA) method was implemented in order to evaluate the environmental effects related to: (i) the substitution of dedicated crops in the feeding mix with pig and cow slurry; (ii) the end of plants fed with dedicated crops and the substitution of the related renewable energy production with non-renewable energy in the national energy mix.
Results highlighted that the substitution of cereal silages with an additional share of animal slurry entails an environmental improvement respect to the BASELINE scenario. Considering the displacement of land use towards the cultivation of cereals for feeding, the contraction of import contributes to an improvement of environmental impacts. The higher nitrogen efficiency of the digestate could also reduce the volume of supplemental fertilisers for crops cultivation. Moreover, slurry storage at farm in traditional open tanks causes an increase in Greenhouse Gas Emissions (GHG) due to emissions to the atmosphere. The achieved results support the decision of policy makers to drive the future towards a more sustainable energetic production.
