Desalination and water recovery: control of membrane fouling

Ultrafiltration (UF), Nanofiltration (NF) and Reverse Osmosis (RO) technologies are widely used for the production of safe drinking water, and for the recovery of reusable water from various industrial effluent streams. The most commonly encountered phenomenon in these processes, especially in water recovery application, is membrane fouling, and control of membrane fouling is regarded as a significant challenge. Membranes with charged and hydrophilic surfaces are reported to be less susceptible to fouling and often reversible. UF/RO membranes containing negatively charged and/or neutral hydrophilic functional groups on the surface were prepared by surface modification of suitable membranes. The surface modified 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 9–50 l/m²-h at the operating pressure of 4 kg/cm². The UF membranes were tested for water recovery from reactive dye effluents containing solutes with molecular sizes in the range of 600–1000 Da along with inorganic solutes. Surface-modified RO membranes were utilised for desalination of brackish water.