Experimental characterization of municipal solid waste bio-drying

The bio-mechanical treatment of Municipal Solid Waste (MSW) is adopted in Europe either as a pre-treatment before landfilling or as a pre-treatment before combustion. In this frame, the bio-drying process concerns the aerobic bioconversion applied mainly to MSW residual of selective collection. The aim of this process is the exploitation of the biochemical exothermic reactions for the evaporation of the highest amount of the humidity in the waste, with the lowest consumption of organic carbon. The obtained material can be easily refined to produce Refuse Derived Fuel. The present paper reports original assessments of process parameters characterizing the MSW bio-drying. In particular, outputs of a few pilot scale experimental runs have been elaborated in order to assess the following overall process parameters: m3AIR kg-1 of waste, m3AIR kg-1 of consumed volatile solids, m3AIR kg-1 of initial volatile solids, m3AIR kg-1 of organic fraction in the waste. Additionally, the assessed volatile solid dynamics during the bio-drying process are presented. These data are not generally available in the literature. Concerning the organic fraction contents in the waste suitable for bio-drying, usually its application is in the range of about 30-50%. The reasons are: a) lower values can give limited results in term of Lower Heating Value (LHV) increase of the bio-dried material; b) the application to waste with higher organic fraction content has the limitation of starting with very low LHV affecting the final characteristics of the bio-dried material. In this organic fraction range the air flow-rate is significant: it can vary between 6 and 10 m3/kgMSW, that is similar to the off-gas generable from the incineration of the same waste.