Performance of Low Pressure Nanofiltration Membrane in Forward Osmosis Using Magnesium Chloride As Draw Solute

Forward osmosis (FO) using locally available nanofiltration (NF) membrane and magnesium chloride as draw solution has been carried out for concentration of wastewater. Maximum water flux of 11.8 L m(-2)h(-1) with pure water feed at 55 degrees C using 1 mol L-1 MgCl2 draw solution was observed. Water flux of 7.58 L m(-2)h(-1) was obtained for industrial wastewater feed. Membrane fouling was found to be reversible and > 90 % water flux could be easily recovered by cleaning with deionised water. Specific energy consumption in the FO process was 0.26 kWh m(-3). The membrane could effectively reject feed solutes for synthetic dye wastewater feed, allowing only pure water to pass through. Draw solute recovery and better quality water generation (< 1000 mg L-1 TDS) was achieved by a low pressure nanofiltration process (<= 10 bar). Recovery of MgCl2 by an alternate chemical method is also demonstrated. Morphology of the membrane was analyzed by scanning electron microscopy of the membrane surface and cross-section. Small-angle X-ray scattering (SAXS) investigation of the membrane is attempted to understand micro-phase-separated structures of this membrane. Overall, the coupled FO-NF process could produce good quality pure water from industrial wastewater with a prolonged membrane life.