Enhanced properties of bio-pellet fuel from sawdust via low-temperature wet torrefaction with varying acetic acid concentrations

Sawdust, a lignocellulosic by-product of the wood processing industry, is abundantly available in tropical regions. Its low energy content, heterogeneity, and bulk density limit its use as a fuel. This study explores wet torrefaction as a pre-treatment to enhance sawdust pellet fuel properties. Sawdust was hydrothermally treated at 110 °C–130 °C, with some samples processed in acetic acid solutions (1.3, 1.8, and 2.3 M) and others in distilled water for 80 min. The resulting hydrochar was mixed with 5 wt% starch binder and pelletized, then dried for 3–5 days. Samples were characterized under bomb calorimetry, proximate, thermogravimetry, and differential thermal analyses, along with hydrophobicity and combustion tests. Higher torrefaction temperatures and acetic acid concentrations improved calorific value and reduced ash content. The best-performing sample, treated with 2.3 M acetic acid at 130 °C, achieved 4745 kcal/kg and 1.97% ash. Wet torrefaction effectively enhances bio-pellet fuel, offering a cleaner alternative to coal. The novelty of this study lies in the systematic evaluation of wet torrefaction parameters at relatively low temperatures with varying acid concentrations, providing new insights into optimizing biomass pretreatment for cleaner and more sustainable solid fuel production.