Title : Contaminated sorghum conversion via hydrothermal carbonization: Solid/Liquid products characterization
Abstract:
The safe valorization of heavy metals (HMs)-contaminated biomass from phytoremediation sites is challenging because it necessitates a certain strategy for the safe disposal of the contaminants. Hydrothermal carbonization (HTC) presents a promising thermochemical method to treat HMs-contaminated biomass by converting it into hydrochar, which can then be used as a solid biofuel. This study focuses on producing clean hydrochar (HC) by determining the optimal conditions for transferring HMs from contaminated sorghum (CS) to the liquid phase of HTC, while also characterizing the liquid phase, which may require further treatment. The main parameters studied were HTC temperature (180-200-220-240°C) and exposure time (0.5-2-4 hours). Main results show that the high heating value (HHV) of hydrochars (HC) increases from 20.6 to 25.5 MJ/kg as the reaction temperature rises from 180 to 240°C. Conversely, the yield of HC decreases from 80% to 62% within this temperature range. Combustion parameters (comprehensive combustibility index (CCI), ignition index (Di), flammability index (F)) indicate that HC 200-0.5 is the most suitable hydrochar for solid fuel applications. The HTC liquid phases (LP) have an acidic pH of 3.96±0.08 due to the presence of carboxylic acids, which make up 56-89% of the composition at temperatures between 180 and 240°C. Phytotoxicity evaluation of the HTC liquid phase reveal high toxicity, attributed to the elevated concentrations of phenolic compounds and heavy metals. The study concludes that efficient HMs transfer from CS to the HTC liquid phase can be achieved at a reaction temperature of 200°C with exposure times between 0.5 and 2h. This offers promising potential for upgrading sorghum contaminated with heavy metals into a biofuel that meets international standards.
Keywords:Contaminated sorghum, Heavy metals, Hydrothermal carbonization, Hydrochar, Liquid phase, Parametric study.
