Performance of thermophilic semi-dry anaerobic digestion process changing the feed biodegradability.

The study concerns the application of the semi-dry single phase thermophilic anaerobic digestion process to the organic fraction of municipal solid waste. The experiments were carried out using 3 m3 and 1 m3 CSTR pilot scale reactors. The process performance in terms of biogas yields, digester stability and kinetic aspects was studied, considering a progressive increase in the feed biodegradability, in order to evaluate the process behaviour changing from an undifferentiated collection of waste to a separate collection. This was carried out using blends of two different kinds of substrates: mechanically sorted organic fraction of municipal solid wastes (MS-OFMSW) and source sorted organic fraction of municipal solid wastes (SS-OFMSW). The study shows that OLR up to 6 kg TVS/m3d can be applicable for the medium selected fraction (TVS/TS < or = 0.7), while for the MS-OFMSW alone this limit can be doubled. The results obtained with SS-OFMSW alone suggest the use of the double phase process to give more stable conditions.