Removal of Heavy Metals from Water: Technological Advances and Today's Lookout Through Membrane Applications

Abstract

Water contamination by heavy metal is a great environmental concern. It leads to many health issues ranging from diarrhoea, vomiting to life-threatening diseases like cancer, lung/kidney damage. This also affects soil biota/plant growth. Metal-ions have a tendency of bio-accumulation, hence pose a major issue upon entry in the food-cycle. Their removal from water is necessary before use for human/agricultural applications. Different methods reported for metal-ion separation are conventional methods viz. chemical-precipitation, ion-exchange, adsorption, coagulation, flocculation, flotation, electrochemical possess good separation efficiency, but the generation of a secondary pollutant, recovery issues restrict their applicability. Hence, there is a need of reliable techno-economical, environment-friendly, sustainable separation, recovery method. Membrane-based methods viz. reverse-osmosis, nano filtration, electrodialysis, ultrafiltration has ability to treat water for heavy metal recovery without chemical contamination. Recovered materials can be recycled/utilized further. Among different membrane-based processes, micellar/polymer enhanced ultrafiltration requires chemical addition and affects purity. Electrodialysis, reverse-osmosis, nanofiltration processes require large energy/operational issues. Hence, simple ultra filtration with membrane modification is preferable as low-energy requirements. This paper discusses details of conventional/advanced methods for heavy metal separation with the fundamental process, parameters, advantages/limitations.