Adsorption of contaminants on hydrochar derived from biomass via hydrothermal carbonization

Abstract

In this study, fermented grain (FG) and sewage sludge (SS) were hydrothermally carbonized (HTC) to produce hydrochars (HCs). The obtained HCs were then chemically modified (MHCs) by impregnation. The chemical composition and morphological properties of the resulting HCs and MHCs were analyzed and compared using CHS, SEM-EDS, XRF, TGA, BET, and FTIR techniques. Their contaminant removal performance was evaluated in aqueous solution for nutrients (NH₄⁺–N and PO₄³⁻–P) and metal ions (Cr(III), Cr(VI), Cu(II), Pb(II) and Zn(II)) at a fixed dose of 10 g/L as well as in gaseous environments (cyclohexane, acetone, toluene) at fixed initial concentrations. Cr(III) equilibrium adsorption data were evaluated at different initial concentrations up to 200 mg/L. After modification, MHCs showed improved adsorption of nutrients (up to 44.3% removal) as well as cationic heavy metals (removal rates over 98.8%), while the adsorption of anionic forms derived from Cr(VI) decreased. The maximum adsorption capacities of trivalent chromium for HC_FG, MHC_FG, HC_SS, and MHC_SS were 0.32, 18.87, 7.47, and 18.93 mg/g, respectively. Among the tested HCs, toluene obtained the greatest adsorption capacity up to 2.74 mg/g, followed by acetone and cyclohexane. These findings reveal that chemical modification is a suitable strategy to develop enhanced adsorbents derived from waste.