Utilization of mixed organic-plastic municipal solid waste as renewable solid fuel employing wet torrefaction

The largest obstacles in the utilization of municipal solid waste (MSW) as solid fuel in developing countries such as Indonesia are its high water content, irregular size and shape, and difficulty-to-sort due to the mix of plastic and organic waste. Based on literature study, wet torrefaction could be an appropriate pre-treatment process for mixed MSW because it requires no initial drying and mixed organic-plastic MSW can be processed without initial sorting. In this research, experiments were conducted to investigate the effect of wet torrefaction on increasing the fuel properties of mixed MSW. Based on field survey, the composition of the analyzed sample was: leaf litter (34.67%), food waste (23.33%), vegetable waste (14.33%), fruit waste (11.00%), and non-recycled plastic (16.67%). The experiments were conducted in a 2.5-L stirring reactor temperature variation (150, 175, 200 and 225 °C) with several holding times and solid loads. The result showed that wet torrefaction at a temperature of 200 °C with holding time of 30 min and solid load of 1:2.5 was the optimum condition, producing solid product with uniform physical shape, small particles and homogeneous particle size distribution, HHV of 33.01 MJ/kg and energy yield of 89%. The wet torrefaction process is not only suitable to convert the mixed MSW into renewable high energy density solid fuel, but it can also be used to produce separate organic product that can be used as solid fuel and plastic product that can be prepared for other treatments, such as pyrolysis to produce liquid fuel or recycling.