Hydrochars derived from plant biomass under various conditions: Characterization and potential applications and impacts

• Low temperature hydrochars showed higher yield and surface area.
• Low temperature hydrochars sorbed more methylene blue and lead.
• High temperature hydrochars showed better thermal stability.
• Hydrochars did not significantly affect seed germination rate.
• Two high temperature hydrochars affected root development of seedlings.

Hydrothermally carbonized biomass (hydrochar) has received increased attention recently as a potential agent for contaminant remediation and soil improvement. There is a need to understand how the properties of hydrochar vary with production conditions. In this work, sugarcane bagasse, hickory, and peanut hull were converted into hydrochars at three different temperatures (200 °C, 250 °C, and 300 °C). Basic physicochemical properties of the nine hydrochars were determined and batch aqueous sorption experiments were conducted to measure ability of the hydrochars to sorb methylene blue, lead, and phosphate. The yield, surface area, and pore volume of the hydrochars decreased with increasing conversion temperatures. Among all the hydrochars, the ones made at the lowest temperature (200 °C) were the best for sorption of methylene blue and lead. However, none of the hydrochars were able to remove significant amounts of phosphate from solution. In addition, the hydrochars did not significantly affect seed germination rate, though some did have a significant effect on root development of seedlings. Findings from this work suggest that lower temperature hydrochars may be optimal for contaminant remediation because of their higher sorption ability and absence of negative effect on plants.