Oily wastewater is one of the most challenging streams to deal with especially if the oil exists in emulsified form. In this study, electrospinning method was used to prepare nanofiberous polyvinylidene fluoride (PVDF) membranes and study their performance in oil removal. Graphene particles were embedded in the electrospun PVDF membrane to enhance the efficiency of the membranes. The prepared membranes were characterized using a scanning electron microscopy (SEM) to verify the graphene stabilization on the surface of the membrane homogeneously; while FTIR was used to detect the functional groups on the membrane surface. The membrane wettability was assessed by measuring the contact angle. The PVDF and PVDF / Graphene membranes efficiency was tested in separation of emulsified oil from aqueous solutions. The results showed that PVDF-Graphene nanofiber membrane exhibited better performance than the plain PVDF nanofiber membrane with average water flux of 210 and 180 L.m-2.h-1, respectively. Both membranes showed high oil rejection with more than 98%.
Nanofiltration (NF) ceramic membrane have found increasing applications particularly in wastewater and water treatment. In order to estimate and optimize the performance of NF membranes, the membrane should be characterized correctly in terms of their basic parameters such as effective pore radius (rp) and equivalent effective thickness as well as effective surface charge ( ), the effective charge density ( ) and Donnan potential ( ). The impact of electrokinetic (zeta) potential on the membrane surface charge density, effective membrane charge density and Donnan potential at two different concentrations of the reference solutions 0.001, 0.01 M sodium chloride at various pH values from 3 to 9, and effective pore radius (rp) for nominal 0.9 nm ceramic TiO2 NF membrane were evaluated. Experiments were conducted at cross flow (1.0 m/s) using Microelectrophoresis technique for measuring membrane zeta potential, effective pore radius, and Donnan steric pore model (DSPM). The TiO2 membrane isoelectric point (net membrane charge equals zero) was found at pH of 3.7, 3.5 for 0.001 and 0.01 M NaCl respectively. The results showed that the NF membrane zeta potential changes its sign from positive to negative after the isoelectric point. The evaluated effective pore radius was found to be equal to 0.56 nm by using (DSPM) and the membrane equivalent effective thickness equals to (2×10-6 m).
Nanofiltration (NF) and zeta potential are being increasingly used in water, wastewater, and pharmaceutical applications. In this study, the zeta potential behaviors of eight different 0.01 M salts (NaCl, KCl, NaHCO 3 , MgCl 2 , CaCl 2 , Na 2 CO 3 , Na 2 SO 4, and MgSO 4) for 0.9 nm tubular ceramic titanium dioxide NF membrane were measured for the first time using a filtration potential technique by conducting in-situ two electrodes made from a composite material that consisted of pure silver and 4% gauge 21 gold. The measurements were conducted under pH 3-9 at an applied transmembrane pressure (TMP) of 0.25-1.5 bar. Experimental results showed that the membranes of the salts were negatively charged at neutral pH and had an isoelectric point (IEP) of pH 3.4−3.8. Membrane zeta potential results were compared and justified using the electrophoresis method for the same membrane. The powder dispersions of the pulverized membrane in this measuring technique were a suspension at a certain salt concentration. Experimental results from the electrophoresis method agreed with those of the filtration potential method, whose IEP was at pH 3.3−3.5. The rejection experiments of the reference solutions (0.1 and 0.01 M NaCl) were conducted at a constant applied TMP of 12 bar. Rejections results showed that both NaCl concentrations were a function of pH. The low rejections were 17% and 21% at pH 3.8 for 0.01 and 0.001 M NaCl, respectively, and the high rejections were 34.2% and 38% at pH 9. This work also investigated the effects of the measured membrane zeta potential on the ion rejection of the standard solution of NaCl (0.01 and 0.001 M) using a similar pH range.
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