Modular structured network for the management of livestock manure in rural areas

The environmental impacts of livestock breeding, especially pig-farming, is often considered as unbearable for fragile and valuable landscapes and territories. Nevertheless livestock activity is an important resource for many rural areas and manure management systems can play a significant role in reducing the impacts and in contributing to the closing of the meat production chain. The most relevant impact generated by livestock activities is represented by the nutrient content of the waste produced. Traditional centralized and scattered treatment systems usually involve anaerobic digestion processes and even though this technology has many years of testing and is fairly reliable for what concerns the transformation of the organic substrate of the ingestate, it has no interaction with nutrients such as nitrogen and phosphorus. After the enactment of the EU directive 91/676/CEE, the risk represented by nitrogen contamination of water resources has been a primary objective for decision makers, especially those involved in planning and management of rural areas. In Italy this issue has been approached without a reliable referential framework with changing fortunes. In the region of Umbria, Italy, are located two of the oldest centralized pigs manure treatment plants of the nation, but none of them has been able to reduce the environmental impacts of livestock manure. The strategic objective of this research concerns the valorisation of rural land through the identification of a modular structured network of anaerobic digestion and nitrogen removal plants. This network should be able to answer to the rural areas needs of protecting the environment and to give sustainability to livestock activities at the same time. Anaerobic digestion is supposed to be performed at farm scale with simplified mono-stage reactors, in order to contain the installation costs, followed by a desulphuration step. Consequently the produced treated biogas will be send to a combined heat and power (CHP) farm-scale plant. The digestate will then undergo a separation process with the solid fraction being dehydrated for agronomic use. The liquid fraction of the digestate will still be nutrient rich and therefore, according to the regulatory framework, must be treated in order to lower the nitrogen content before its reuse. Nitrogen removal plant are needed to perform this last crucial step and will represent the condensation nuclei of the macro nodes of the projected territorial network. The chosen study area is the catchment basin of lake Trasimeno (Umbria) for its valuable landscape characteristics and its archetypal rural area structure.