Solid State Anaerobic Digestion to Energy for the organic fraction of MSW: real case experimental analysis

A correct management of the MSW Organic Fraction represent, together with the recycling and recovering of other waste fractions, one of the main activities to be pursued for achieving an environmentally sound waste management system. Generally the most exploited treatments for the Organic Fraction are the biological one, allowing the production of stabilized matter or high quality compost, depending on the quality of the inlet substances. In some cases biological treatment can also allow energy recovery by the exploitation of anaerobic digestion. Usually, the most diffused technology for anaerobic digestion process, as the wet and the semi-dry, require an high organic fraction humidity content, more than 80%. This high humidity content is generally due to some plant automatization needs, for allowing the adoption of continuously feed and continuously stirred reactors, and for trying to increase the process efficiency. Unfortunately these solution have a relevant drawback, represented mainly by the huge amount of liquid phase discharged per unit of Solid Substances treated in the plant. Infact, in some countries, like Italy, the rules about the disposal of such liquid phase, even if arising from waste selected organic fraction treatments, are very stringent, making as consequence the exploitation of wet and semi -dry anaerobic digestion costly and complicated. For this reason, the possibility of exploiting low humidity process anaerobic digestion, with very low leachate production, can be an interesting answer to the aforementioned problems. Among these last treatments, the Solid State Anaerobic Digestion of the waste organic fraction, seems to have suitable feature for being exploited in different waste management systems, as for other biodegradable substances treatment, allowing also an high energy recovery rate. This anaerobic digestion is generally conduct with humidity values lower than 70%, and so with organic fraction at the solid instead of liquid state. Despite some automatization limitation, consisting mainly in the exploitation of batch anaerobic reactors, the leachate production is very narrowed, reducing significantly all the treatment disposal costs and problems. Furthermore, the anaerobic process can be followed by an aerobic one, leading to the production, when possible, of high quality compost, with the possibility of achieving both an energy than material recovery for the Organic Fraction. Anyway, depending on the Organic Fraction features, some Solid State Anaerobic Digestion operating parameters have to be investigated for process optimization needs. In this paper the performance arising from the exploitation of the Solid State Anaerobic Digestion, for the organic fraction arising form the differentiate collection of an existing Italian MSW management system, have been preliminary analysed by the aid of an experimental apparatus. The preliminary results have also been exploited for performing an economical analysis related to the possibility of the realization of a real scale SSAD plant, able to satisfy the analysed waste management system needs.