Metal ion separation and protein removal from aqueous solutions using modified cellulose acetate membranes: Role of polymeric additives

Metal ion separation from industrial effluents and protein removal from food and bio-related industrial waste streams are gaining increased visibility due to environmental concern and saving valuable materials. In this work, an attempt has been made to remove the valuable proteins and metal ions using modified cellulose acetate (CA) based membranes prepared in the absence and presence of the polymeric additives such as polyvinylpyrrolidone (PVP) and polyethyleneglycol (PEG 600) in various compositions. Studies were carried out to find the rejection and permeate flux of proteins such as bovine serum albumin (BSA), pepsin and trypsin and metal ions such as Cu(II), Zn(II), Co(II), and Cd(II) using polyethyleneimine (PEI) as the chelating ligand. On increasing concentrations of PVP and PEG, the rejection of proteins and metal ions is decreasing while the permeate flux has an increasing trend. These effects are due to the increased pore formation in the CA membranes because of the additives. In general, it was found that CA/PVP blend membranes displayed higher permeate flux and lower rejection compared to CA/PEG blend membranes at all additive concentrations. The extent of separation of proteins was found to be directly proportional to the molecular weight of the protein while the extent of removal of metal ions depends on the affinity of metal ions to PEI to form macromolecular complexes and the stability of the formed complexes.