Phosphate Recovery by High Flux Low Pressure Multilayer Membranes

Abstract

This work illustrates the potential use of PEI/PSS bilayers assembled via layer by layer (lbl) method on a nylon microfiltration membrane for the recovery of phosphate from water in the presence of chloride under ultrafiltration conditions. A total of nine bilayers were used for the selective recovery of phosphate. Bilayers were constructed from polyelectrolyte solutions of varying ionic strength (0-1 M of NaCl). The selected pH for deposition of PEI (5.9) and the presence of supporting salt in the polyelectrolyte solution is expected to provide membranes with high permeability and high charge density. This particular combination of bilayers yielded high flux membranes that allowed selective removal of H(2)PO(4)(-) in the presence of Cl(-) at low pressure (0.28 bar). The magnitude of negative solute rejection of chloride showed increasing trend with the number of bilayer for a particular salt concentration. Whereas the increase in magnitude with ionic strength is so high (-6.18 to -269.17 at 0.5 M NaCl for 9 bl) that gave the best observed Cl(-)/H(2)PO(4)(-) selectivity (310.23, flux 13.53 m(3)/m(2)-day). To the best of our knowledge, this is the first time a multilayer polyelectrolyte system with such a high selectivity and rejection for H(2)PO(4)(-) is reported. The solution flux decreased with the number of bilayers and ionic strength. The rejection of phosphate was dependent on feed pH, concentration of deposited polyelectrolyte solution, and composition of membrane support.