The porous membrane works upon sieving mechanism, where the separation and transport properties are dependent upon membrane morphology and porosity. This porosity and pore size are dependent upon membrane materials and formation parameters. Polysulfone (PSF) is one of the widely used membrane material due to its stability properties. Current work is targeted towards optimization of PSF based membranes by varying dope solution concentration and composition with the use of polyethylene glycol (PEG (MW6000)) as porogen in dope solution to enhance the transport rate and selectivity. An increase in PEG rejection with linear decrease in water flux and pore size was observed with the increase in dope solution concentration. Uniform membranes formation without any abnormal pore-size is observed from transport properties. The use of PEG as porogen leads to increased porosity due to leaching of Porogen during the phase inversion, which resulted in enhanced transport rate (85%). Further the formed membranes maintained pore size as seen from bubble point, rejection and pore size analysis. This resulted in maintenance of selectivity. Such increased transport with high selectivity is highly essential when applicability of membranes in industrial processes like process separation and waste treatment are considered. This would lead to large industrial benefits.

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Chromium (Cr) is one of the important materials of metal family with large applications in formation of ferrous alloys viz., steel. Due to its excellent chemical, mechanical and thermal properties it is largely used in mineral, leather tanning, dye, steel, and other alloy industries. Effluents of these industries containing traces of Cr are polluting water bodies and soil in surrounding. It would result in entering in food chain, where it has highly adverse effect on humans, animals, and environment. Hence its recovery from effluent and other streams is highly essential before disposal and exposure to surrounding. The polysulfone (PSF) based membranes were optimized using polyethylene glycol (PEG) as porogen, while ZnO as an additive either treated with or without acid for removal of Cr from water. A reduction in molecular weight of PEG resulted in decrease in water flux indicates reduction in pore size. Further incorporation of ZnO increases the Cr removal. The Cr removal increases further with incorporation of acid treated ZnO. Additionally, HCl treated ZnO showed higher rejection properties, while the effect is not that prominent in HNO3 treated ZnO. This shows the importance of optimization of membrane surface charge for heavy metal removal.

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.