Biodrying of rejected materials from mechanical separation processes of municipal solid waste for utilization as refuse-derived fuel.

During the municipal solid waste mechanical separation process, the wastes with sizes >50-100 mm, excluding magnetic items and dense materials, are transformed into refuse-derived fuel. The remainder of the two waste streams can be disposed of in landfills, including materials with a size of ≤50 mm (rejected material 1) and heavy materials with a size of >50-100 mm (rejected material 2). The use of rejected materials for refuse-derived fuel (RDF) production in Thailand has not been investigated. This research aimed to convert the rejected materials into RDF using a biodrying process. The results revealed that rejected material 1 contained both plastic and organic waste. It had low moisture content, high volatile solid content, and high heating values (about 2,074.20-2,680.30 kcal/kg) compared to the rejected material 2. It is indicated that the rejected material 1 was a more suitable raw material for RDF production. For studying the effect of continuous aeration rates on the biodrying process for rejected material 1, three experiments were performed using lysimeters and operated at three different aeration rates, 2.27, 2.77, and 3.02 L/min/kg, for 14 days. At the aeration rate of 2.27 L/min/kg, the biodrying process of rejected material 1 had the highest average temperature (45.9-50.76°C) during the thermophilic phase and the highest accumulated temperature integration value (241.05°C). As a result, the moisture, volatile solids, and ash contents could be reduced to 21.67%, 81.21%, and 18.95%, respectively, with a lower heating value of 3,558.12 kcal/kg. However, the ash content from these RDFs exceeded the quality criteria. Therefore, this produced RDF, which was classified as a low-grade RDF. At the three aeration rates, the biodrying process emitted greenhouse gases between 0. 0.0053-0.0295 kg CO2e/kg waste, which was significantly less than the landfill of rejected material.