Potential of bio-drying for generation of solid recovered fuel from wet organic substrates

Bio-drying is one of the aerobic processes available for waste management. Its aim is the modification of the waste characteristics to increase its Lower Heating Value (LHV). An additional advantage is the easier removal of glass, metals and other inert materials from MSW through a post-selection giving a Solid Recovered Fuel (SRF) as output. In this paper, results of pilot-scale bio-drying, applied to residual MSW (RMSW), to sewage sludge mixed with MSW and to exhausted grape marc alone, are presented in order to understand the potential of bio-drying for wet organic substrates valorisation. In case of RMSW bio-drying, post-selection acts as a second step of energy concentration, giving a result highly depending on the residual MSW food waste (FW) content, that is affected by the strategy and efficiency of selective collection (SC): after 14 days, the increase of LHV resulted +24% in case of FW=50% but only +7% in case of FW=8%. The experimental run of sludge co-bio-drying demonstrated how the final result depends on its moisture and stabilization. In case of exhausted grape marc, the reached LHV (+20% in 14 days) demonstrates that grape marc can be converted in a SRF, having in general low Chlorine and Mercury content.