Performance comparison of macromolecular assisted and immobilized low pressure membranes in the removal of toxic metals

Abstract

The removal of toxic heavy metals (Cd, Pb and Hg) from aqueous solution has been attempted in two different modes by using macromolecular assisted and immobilized multilayered modified polyether sulfone membranes (PES). PES membrane was modified with chitosan (CHI) and poly (styrene sulfonate) (PSS) using layer by layer (LbL) method. Humic acid (HA) and cholesterol (CHO) were used for immobilization. SEM and AFM confirmed that the obtained films were rough and highly porous. FTIR analysis confirmed successful immobilization of macromolecules in poly-ion coated membranes. Ellipsometric studies confirmed that the thickness of system increased with immobilization. Thermogravimetric analysis proved that the membranes were thermally stable upto 550 °C. The macromolecule assisted low pressure filtration was carried out by the addition of HA and CHO to the respective spiked metal ion solutions prior to filtration. More than 98% of the heavy metal ions were retained by macromolecules immobilized membranes. For Cd2+ ions, rejection efficiency of 6 bilayered PES membrane achieved ∼90% with HA and CHO immobilized at a concentration of 20 μmol/L and 400 μmol/L respectively. For Pb2+ ions, rejection efficiency attained ∼90% for HA (2 bilayered system) and for CHO (4 bilayered system) immobilized at 15 μmol/L and 400 μmol/L respectively. The rejection efficiency for Hg2+ ions obtained above 95% for both HA and CHO immobilized membranes at 2 bilayer with concentrations 15 μmol/L and 300 μmol/L respectively. The macromolecule assisted filtration also showed very good removal for all metal ions with efficiency above ∼90%. High macromolecule concentration with high number of bilayers has resulted high flux with negligible effect on the retention of heavy metals. Thus, this membrane system provides a very simple, efficient, easy and convenient approach for the removal of toxic metal ions by employing a combination of poly-ion coated polymer membrane with macromolecules.