Abstract
M.Sc. (Chemistry)
Water purification technologies based on membranes are prone to fouling by natural organic matter (NOM) and other biological species in water. This leads to the short lifespan of the membranes and high demand in energy than normal due to high pressure needed to pump water across the fouled membrane. In a quest to address these challenges, polyethersulfone (PES) and polyvinylidene flouride (PVDF) membranes supported on 3 different types of non-woven fabrics NWF1(polyester), NWF2 (polyphenylene sulphide) and NWF3( thicker polyester) were fabricated using the phase inversion method. This enabled the modification the active top layer of PES and PVDF thin film while maintaining the high mechanical strength offered by the NWFs. FTIR spectroscopy, sessile drop contact angle measurements, thermo-gravimetric analysis (TGA), scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to study the membranes. The membrane flux and rejection were studied using the cross-flow membrane unit. The contact angle results revealed that the hydrophilicity of PES and PVDF membranes increased as the polyvinyl pyrrolidone (PVP) concentration was increased. TGA revealed that the PES and PVDF membranes were thermally stable up to 580ºC and 530ºC respectively. The cross-sectional SEM revealed that membrane pores become enlarged when PVP has been added. AFM showed that membrane roughness improved when PVP was added. A rejection of 98% humic acid was obtained for PES membranes supported on NWF1, compared to 94 % and 96 % for membranes supported on NWF2 and NWF3 respectively. The highest rejection of humic acid (HA) recorded for PVDF membranes supported on NWF1 was found to be 97 % compared to the 95% for membranes supported on NWF2 and NWF3 fabrics respectively. PES membranes supported on NWF2 exhibited low but best As(III) metal ions rejections whilst PVDF membranes supported on NWF3 exhibited low but best rejections for Cr(III) metal ions.