Unlocking biomass potential: Improving adsorption in sugarcane mill mud waste via hydrothermal carbonisation

This study explores the hydrothermal carbonisation of mill mud waste from a sugar mill, aiming to demonstrate a cost-effective adsorbent material for organic molecules. The hydrothermal process significantly altered the mill mud, removing inorganic materials and reducing carbon-oxygen bonds, leading to improved adsorptive properties. The hydrothermal carbonisation process transformed the physical structure from multi-layered agglomerates to single-layered discrete carbon forms, as confirmed by electron microscopy and X-ray photoelectron spectroscopy. The adsorption capacity for organic compounds, evaluated through a methylene blue dye assay, increased nearly threefold after carbonisation, reaching 42.7 mg of methylene blue per gram of carbonised mill mud, compared to 15.1 mg per gram of untreated mill mud. Isotherm studies indicated that the carbonised mill mud followed a monolayer adsorption profile, in contrast to the untreated sample. The adsorptivity of imidacloprid, a widely used pesticide in Australian sugarcane farms, was demonstrated, providing practical applications for stockpiled waste mill mud near sugarcane farms and sugar mills. The carbonised mill mud exhibited higher imidacloprid removal efficiency compared to the untreated sample (98.82 % vs 39.39 %) at 5 mg of mill mud per millilitres of solution. Comparisons with activated carbon samples further highlighted the effectiveness of the hydrothermal carbonisation process and the potential mechanisms enhancing the adsorptive capacity of mill mud. These findings suggest that the hydrothermally carbonised mill mud could serve as an effective and economic adsorbent for environmental remediation, such as barriers against pesticide runoff in sugarcane plantations within agricultural regions.