Evaluation of Enhanced Treatment of Tannery Wastewater Containing Chromium and Cadmium by Mesoporous Alkali–Activated Biochar from Ficus religiosa leaves

The present study investigates the adsorption potential of mesoporous biochar derived from Ficus religiosa leaves for removing chromium (Cr) and cadmium (Cd) from aqueous solution and tannery wastewater. The biochar was synthesised through pyrolysis at 600°C followed by alkali activation. Characterisation techniques, including FTIR, XRD, SEM-EDX, and BET analysis, confirmed the mesoporous structure and presence of functional groups on the biochar surface. The effects of pH, adsorbent dosage, starting metal concentration, contact time, and temperature on the removal of Cr(VI) and Cd(II) have been investigated by batch adsorption experiments. Optimal removal efficiencies of 94% for Cr(VI) and 97% for Cd(II) were achieved at pH 5, adsorbent dosage of 6 g, and contact time of 420 minutes. Adsorption equilibrium data fitted well with the Freundlich isotherm model, indicating multilayer adsorption, while kinetic studies revealed that the adsorption process followed pseudo-second-order kinetics. The biochar showed very high C max values of 406.43 mg/g and 295.16 mg/g for chromium and cadmium, respectively. Thermodynamic parameters suggested the adsorption was spontaneous and exothermic. The biochar also exhibited significant antibacterial and antifungal activities, enhancing its potential for wastewater treatment. Desorption studies using EDTA demonstrated good regeneration capacity over three adsorption-desorption cycles. The biochar was further applied to treat real tannery effluent, effectively reducing physicochemical parameters and heavy metal concentrations. These findings highlight the promising application of Ficus religiosa biochar as an eco-friendly and efficient adsorbent for heavy metal remediation in industrial wastewater.