Biosorption-based elimination of hexavalent chromium using Bacillus cereus F4810/72 isolated from tannery effluents

The leather industry of West Bengal continuously discharges chromium-laden effluents, with hexavalent chromium [Cr(VI)] being particularly persistent and toxic. Hexavalent chromium released from tannery effluents poses serious environmental and public health hazards due to its high mobility, solubility, and carcinogenicity. Biosorption offers a sustainable and cost-effective alternative to conventional physicochemical remediation methods. In this study, the biosorption potential of Bacillus cereus F4810/72, a strain previously isolated from tannery wastewater, was systematically evaluated for Cr(VI) removal under varying physicochemical conditions. Batch experiments were conducted to investigate the influence of initial metal concentration (10-1000 µg/mL), contact time (10-100 min), pH (1-9), biomass concentration (1-4 g/L), temperature (10-60 °C), and agitation speed (10-120 rpm) on biosorption efficiency. Maximum Cr(VI) removal (approximately 79-80%) was achieved under optimized conditions: 250 µg/mL initial Cr(VI), 4 g/L biomass, pH 3, 50 °C, 70 min contact time, and 80 rpm agitation. Langmuir and Freundlich isotherm models were applied to elucidate adsorption behavior. Nonlinear Langmuir modeling indicated monolayer adsorption with a maximum capacity (Q_max) of 28.57 mg/g, whereas the Freundlich model (R² = 0.98) suggested adsorption onto a heterogeneous surface. Regeneration studies showed that 2 M HCl and a combined HNO₃-ascorbic acid eluent exhibited superior desorption efficiencies, maintaining high uptake-release performance across three cycles. Overall, B. cereus F4810/72 demonstrates strong Cr(VI) biosorption and regeneration potential, highlighting its viability as a low-cost, eco-friendly biosorbent for chromium-contaminated industrial wastewater systems.