Removal of Chromium and Colorant from Synthetic Dyeing Factory Wastewater by Biochar Derived from Water Hyacinth

Water pollution from dyeing industry effluents, particularly due to chromium and synthetic dyes, poses significant environmental and public health risks. This study evaluated the efficiency of water hyacinth-derived biochar (WHB) for removing trivalent chromium (Cr(III)) and acid blue dye from synthetic wastewater through batch adsorption experiments. WHB was produced via slow pyrolysis in an oil drum at 1,000 °C for 45 min. Characterization using BET, FTIR, and XRF showed a surface area of 122.026 m2/g, total pore volume of 0.1052 cm³/g, predominant hydroxyl groups, and major inorganic components including CaO (73.40% w/w) and K2O (18.40% w/w). WHB achieved 99.95% Cr(III) removal (at 50-mg/L initial concentration) within a 4 h equilibrium time and 79.79% dye removal efficiency (at 100-mg/L initial concentration) within 72 h. Adsorption kinetics followed a pseudo-second-order model, indicating chemical adsorption as the dominant mechanism. Cr(III) reached the equilibrium 18 times faster than the dye, likely due to the dye’s higher molecular weight (416.38 g/mol), which may hinder its diffusion and adsorption onto biochar. Overall, WHB produced at high temperature shows favorable physicochemical properties for the effective removal of Cr(III) and acid blue dye. Utilizing water hyacinth for biochar production supports the circular economy and promotes biomass utilization in wastewater treatment.