Physical Characteristics and Moisture Content of RDF Pellets Produced from Mixed Coarse-Fine Sawdust with Calcium Oxide Addition

Kalimantan’s abundant forestry biomass waste offers strong potential for producing Refuse-Derived Fuel (RDF) pellets, adding economic value while minimizing waste and emissions. This study examines the effects of coarse–fine sawdust ratios and calcium oxide (CaO) addition on the physical and moisture characteristics of RDF pellets made from mixed Kalimantan sawdust. The sawdust mixtures were pelletized using a standard compression method and evaluated for bulk density, moisture content, and proximate composition. Without CaO, initial moisture content reached 26.72%, requiring drying at 100–120 °C for 30 minutes. With 5% CaO, moisture content decreased to 7.42 ± 12.33%, averaging a 10% reduction as drying temperature increased, though still slightly above the 7–12% standard range. Blending coarse and fine sawdust improved pellet compaction, while CaO enhanced moisture removal, resulting in higher net calorific values (4004–4251 kcal kg−1) and greater mechanical durability during storage. The optimal sawdust blend with CaO met RDF physical property requirements, though further drying optimization is recommended. These results demonstrate that controlling particle size and incorporating CaO additives can significantly enhance RDF pellet quality from biomass residues, supporting efficient and sustainable bioenergy production.