Eco-Friendly Remediation of Heavy Metal-Contaminated Effluents Using Indigenous Bacterial Biosorbents

Abstract

Heavy metal contamination of aquatic ecosystems poses a serious environmental and public health concern due to the persistence and toxicity of metal ions such as cadmium (Cd²⁺), lead (Pb²⁺), and mercury (Hg²⁺). In the present study, metal-resistant bacteria were isolated from industrial wastewater and evaluated for their potential in multimetal bioremediation. Fourteen bacterial colonies were initially obtained on metal-supplemented media, from which three dominant isolates showing highest tolerance were selected and identified as Bacillus subtilis (HM1), Pseudomonas aeruginosa (HM2), and Enterococcus faecalis (HM3) based on biochemical profiling and Bergey’s Manual classification. Minimum inhibitory concentration analysis indicated significantly higher metal tolerance of HM2 compared to other isolates (p < 0.05). Biosorption experiments demonstrated that pH, temperature, and contact time markedly influenced metal removal. Maximum uptake occurred at pH 7.0, 32 °C, and 48 h. At optimized conditions, HM2 achieved removal efficiencies of 86.4 ± 2.6% for Cd²⁺, 93.2 ± 2.9% for Pb²⁺, and 80.1 ± 2.3% for Hg²⁺. Time-course studies showed rapid uptake within 24 h and equilibrium at 48 h, following pseudo-second-order kinetics with correlation coefficients exceeding 0.98, indicating chemisorption-driven biosorption. A mixed bacterial consortium (HM1+HM2+HM3) exhibited synergistic enhancement, achieving 88.7 ± 2.3% Cd²⁺, 92.4 ± 2.5% Pb²⁺, and 81.2 ± 2.1% Hg²⁺ removal, representing a 6–10% improvement over monocultures (p < 0.01). FTIR analysis revealed characteristic peak shifts from 3420→3385 cm⁻¹ (–OH/–NH), 1655→1622 cm⁻¹ (–COOH), and 1085→1050 cm⁻¹ (–PO₄), confirming involvement of surface functional groups in metal chelation. Application of the consortium to contaminated effluent reduced residual metal concentrations from 100 mg/L to 11.3 ± 0.9 mg/L (Cd²⁺), 7.6 ± 0.8 mg/L (Pb²⁺), and 18.8 ± 1.1 mg/L (Hg²⁺), all below permissible discharge limits. Collectively, the findings establish, that the developed bacterial consortium provides an efficient, eco-friendly, and cost-effective strategy for remediation of multimetal-contaminated wastewater, with strong potential for scale-up in industrial treatment systems.