Heavy Metal Pollution in Water Supplies: Removal and Recovery
Abstract
Heavy metal contamination in drinking water represents one of the most critical environmental and public health challenges worldwide, affecting an estimated 200 million people annually. This review evaluates the evolution and current state of heavy-metal separation technologies, focusing on lead, copper, and cadmium as key contaminants of concern. Conventional treatment methods, such as coagulation and filtration, achieve 50–90% removal for metals like Pb²⁺, Hg²⁺, and Cr³⁺ under optimal conditions but perform poorly for Cd²⁺, Ni²⁺, and Zn²⁺. Emerging strategies including adsorption, electrochemical separation, photoreduction, and bioremediation, offer enhanced selectivity and efficiency under specific conditions. Adsorption using nanostructured carbons and zeolites achieves lead removal efficiencies exceeding 95%, while permeable reactive barriers report maximum adsorption capacities up to 476 mg/g. Electrocoagulation can achieve 96–99% Pb²⁺ removal at current densities of 5–10 mA/cm² and pH 5, whereas electrodialysis achieves ~75% Pb²⁺ removal under pilot-scale conditions (5 mg/L initial concentration, 0.6 V per cell pair, 4-hour batch time). Bioremediation of Cu²⁺ using bacteria, fungi, and algae achieves 63–85% removal in batch studies, while cadmium photoreduction using bismuth/sulphur co-dopedcarbon quantum dots reaches up to 94% removal at pH 8, 10 mg/L initial concentration, and 120 minutes contact time. Despite technological progress, achieving sub-µg/L metal concentrations under complex water chemistries continues to challenge current methods. Economic feasibility, secondary waste generation, and system resilience under dynamic contamination events remain major barriers. Future research must prioritise integrated, adaptive separation systems that couple advanced materials with digital optimisation, balancing performance with sustainability and energy efficiency. Such cross-disciplinary innovation is essential to ensure universal access to safe drinking water in the face of accelerating industrialisation, population growth, and climate uncertainty.
