Studies On Preparation And Performance Of Polyamide Hollow Fiber Composite Forward Osmosis Membrane

Forward osmosis membrane has been greatly developed in recent years. In this paper, the studies were focused on preparation and characterization of the hollow fiber composite membrane. The composite FO membranes were prepared by interfacial polymerization with a thin-film polyamide layer on the porous substrates. The factors affecting the formation of the thin-film layer were studied. Different test conditions were employed to study their effect on the performance of FO membrane. The membrane module used in domestic sewage treatment with different concentrations was studied to evaluate the further application of FO membranes. Furthermore, the fouling of FO membrane in presence of humic acid in the feed solution was investigated to explore the property of anti-fouling of the composite FO membrane.In order to improve the performance of membranes, a series of experiments were conducted to investigate the influence of interfacial polymerization conditions, including concentration of reactants and reaction time, which can affect the degree of the polymerization and finally the performance of the thin-film layer. The optimal condition of interfacial polymerization was1.5%(w/w) m-phenylenediamine in water,0.1%(m/v) trimesoyl chloride in hexane and with60seconds reaction time at room temperature. When concentration of trimesoyl chloride remained unchanged, m-phenylenediamine concentration increased from0.5%to2.5%. When the concentration of m-phenylenediamine increased, water flux dropped while reverse salt flux decreased at first and then increased. But the salt rejection remained above98%although it varied with different concentrations of m-phenylenediamine. When m-phenylenediamine concentration is low, the polyamide active layer is too thin to generate high salt rejection. While the concentration is high, the polyamide active layer became uneven and too thick. When m-phenylenediamine solution concentration was1.5%(w/w), the polyamide active layer was dense and uniform and suitable for application. But when polysulfone hollow fiber membrane was employed as support membrane, the performance of polyamide composite membrane was poor and the salt rejection rate was only about90%, which is not suitable for practical application.The test conditions in the FO process including the membrane orientation, draw solution concentration had been studied, which can affect the performance of the FO membranes through putting effect on the internal concentrated polarization (ICP). Membrane orientation had certain effect on water flux. In PRO mode, the water flux was higher, and the reverse solute fluxes was lower. The concentration of draw solution had a closely matter with water flux and the reverse solute flux. With the increase of concentration of draw solution, osmosis driving force increased, so water flux increased, but Reverse salt flux increases too. Reverse solute diffusion phenomenon in the forward osmosis process was studied. The results indicated that different draw solutes make membrane performance different. Use the same concentration of sodium chloride, potassium chloride, sodium sulfate, potassium sulfate as draw solution, results show that with increasing ionic radius, the water flux decreased, Reverse salt flux decreases, indicates that the better salt reject rate. For relatively larger ions, since the charge is more dispersed,hydration shell is held with a weaker electric field in comparison to smaller ions with stronger electrical fields. As a result, the larger of the ion, the less effect it will have in ordering the water molecules around it. The ionic radius greater than the sodium ion, so the formation of potassium ions in the hydrated ra dius less than the radius of hydration of the sodium ions (K+as0.26, Na+as0.34), potassium hy drated ions easier penetration through the membrane, potassium chloride reverse salt flux amount is higher than the reverse salt flux of sodium chloride.This paper discussed the composite membrane for sewage treatment, It was also found that, the effect of concentrated internal concentration polarization in PRO mode less than diluted internal concentration polarization in FO mode on the water flux, but ammonia, nitrite and phosphate reject in the wastewater are not good as FO mode. With the increase in the speed of the peristaltic pump, the water flux increased, but the increase is not obvious, graduall the nutrients in the wastewater through permeable membrane, the results show that the nutrients rejection in yielding water will also dropped. The anti-fouling of FO membrane was investigated in presence of humic acid and the performance of FO membrane was found decrease little in the course of the entire pollution. there was little membrane fouling, and after cleaning, flux was recovered mostly. this result also shows that fouling in FO are almost fully reversible by water rinsing, possibly attributable to the less compact fouling layer due to the low hydraulic pressure applied, visible contamination of the infiltration process lighter pollutants is simply attached to the surface of the composite membrane, suggesting that chemical cleaning may be avoided.