Fouling resistant membranes in desalination and water recovery

Abstract

Low molecular weight cut off (MWCO<1000 Da) polyethersulfone nanofiltration membranes and polyamide brackish water thin film composite membranes containing negatively charged and / or neutral hydrophilic functional group on the surface were prepared by surface modification of the membranes by in situ redox polymerization of acrylate monomers. The NF membranes have been used for treatment of dye effluent solution whereas the composite membranes were tested for brackish water desalination without adopting chemical pretreatment protocol to assess their fouling resistance nature. The NF membranes exhibited separations of 68-85% for Na₂SO₄, 19-31% for MgSO₄, 10-26% for NaCl and 2-12% for CaCl₂ with water permeation rates of 10-50 l/m² h at the operating pressure of 4 kg / cm² for 2000 ppm feed solution. The NF membranes were tested for water recovery from reactive dye effluents containing solutes sizes in the range of 600-1000 Da along with salt solution and were found to reject the dyes >99%. The permeation rate of high flux membranes reduces gradually with time and reaches to about half of the original flux after 3 h of permeation. The original water fluxes have been recovered by simple water washing of the membranes. Surface modified RO composite membranes (flat coupons as well as 4' modules) have shown good fouling resistant properties for brackish water desalination.