There Organic fraction of urban solid waste, commonly Forsu, can be treated with industrial processes of anaerobic digestion from which they are obtained biogas for the production of electrical and thermal energy and by-products such as compost and soil improvers. In this way the Forsu it becomes a resource for cities, the economy and a sustainable environment.
Anaerobic digestion is a degradation process that can use substrates of various types, from crops dedicated to livestock waste, from civilian sludge to food by-products, to Forsu. The latter is among the most interesting sources because it is the most available and because its treatment to produce energy is compost stimulates in parallel the separate waste collection. There are also home biodigesters for the home production of biogas such as the ARTI biodigester used in countries where energy distribution is a problem.
The treatment of Forsu it is certainly a resource for the community, and its effectiveness could increase by limiting its obstacles. One of the main, as was pointed out during the conference on the 'waste resource' organized in Milan by the CNR, is that the transformation of Forsu coming from the waste collection implies a laborious pre-treatment phase in order to eliminate impurities. This means that if all of us did better the selection of the wet in the house, the whole process would work better and would cost less.
In the existing plants for the treatment of organic waste - at the CNR conference there were Austep, Hera Ambiente and Biotec Sistemi - the Forsu urban is pre-treated for a long time to eliminate foreign elements such as plastic, sand, various types of aggregates and glass and then directed to anaerobic digestion which, depending on the industrial process, can be humid (with the addition of water to obtain an organic pulp ) or dry (without adding water).
In both cases the result of the anaerobic digestion of the Forsu is the production of a biogas rich in carbon dioxide and methane with which it is possible to produce electricity and heat that can be destined in a small part to the self-consumption of the treatment plant and for the greater part to the public network. The by-product of the process is a digestate from which, through a subsequent aerobic phase, they can be obtained compost and soil improvers.
The quality of the by-products of anaerobic digestion of Forsu it is another very delicate aspect. The compost obtained in many cases does not have the quality standards of the best traditional soils and is regarded with suspicion by professional growers. On the direct use of digestate as a soil improver to be spread in the fields, there are strong controversies. Even the creation of biogas plants, especially when the source consists of dedicated crops, is opposed in Italy by some farmers and at the center of legal disputes.
The Councilor for the Environment of the Municipality of Milan Pierfrancesco Maran also intervened at the conference on waste as a resource organized by the National Research Council, who spoke of waste collection as a new opportunity for Milan towards EXPO 2015. In Milan, the separate collection of Forsu it began in 2012 and is about to be extended to the whole city after a year.
The Department of Bio-Agri-Food Sciences of the CNR is organizing a master in "Energy and bioproducts from biomass for the sustainable management of production chains". Information on www.master-bioenergia.org.