Study Of Composite Nanofiltration Membrane Preparation And Membrane Separation Technology Integration

A large amount of non-biodegradable wastewater is generated every day, in textile,paper, carpet, leather, plastics and printing industries. The wastewater discharged intothe environment would cause undesirable damage to the ecosystem. Hence, it isdesired to effectively remove non-biodegradable molecules from wastewater beforedischarge.First, Orange G dye was efficiently removed from aqueous solution byultrafiltration （UF） membrane separation enhanced with activated carbon adsorption.The powdered activated carbon （PAC） was deposited onto the UF membrane surface,forming an intact filter cake. The enhanced UF process simultaneously exploited thehigh adsorption ability of PAC toward dye molecules and the high water permeationflux of porous membrane. Typically, the dye rejection ratio increased from43.6%forthe single UF without adsorption to nearly100%for the enhanced UF process. Theinfluencing factors on the dye removal were investigated. The results indicated thatwith sufficient PAC incorporation, the formation of intact PAC filtration cake led tonearly complete rejection for the dye under optimized dye concentration and operationpressure, without sacrificing the permeation flux of the filtration process.Next, four kinds of thin-film composite （TFC） nanofiltration （NF） membranes werefabricated on the polyethersulfone ultrafiltration substrate through interfacialpolymerization. Four monomers of diethylenetriamine （DETA）, triethylenetetramine（TETA）, tetraethylenepentamine （TEPA）, piperazidine （PIP） were dissolved inaqueous phase, and the trimesoylchloride （TMC） monomer was dissolved inn-heptane solution. The morphology of the four TFC nanofiltration membranes wasobserved by a field emission scanning electron microscopy （FESEM） measurement.The surface charges of nanofiltration membranes were probed by Zeta-potentialmeasurement, and the surface wetting property was detected by water contact angle.Based on the90%rejection of Orange G solution, the permeability of the fourcomposite membranes was evaluated to make a comparation by a series filtrationexperiments. All the experiment results showed that aqueous monomer solubility inorganic solution would impact the separation performance of the compositemembranes, that was the higher solubility endowed larger porosity to the membranesurface. Accordingly, the PIP/TMC composite membrane exhibited betterpermeability with pure water flux,66L/（m2hMPa）, permeation flux decline,2.5%, and permeation flux recovery,97.7%under the90%rejection for orange G solution.Then, based on salting out effect, CaCl₂was added in TEPA aqueous solution toenhance the solubility of TEPA in n-heptane and react with TMC to prepare theTEPA/TMC composite NF membrane. The surface morphology, contact angle weremeasured and compared with the control membrane. And the permeability ofTEPA/TMC composite membranes with addition of CaCl₂was also evaluated. It wasfound that the addition of CaCl₂would increase the TEPA solubility in n-heptane bysalting out effect, and then increase the porosity and permeability of the TEPA/TMCcomposite NF membrane. The pure water flux of TEPA/TMC composite membranewith the1wt%CaCl₂addition was about32.6L/（m2h） compared with18.2L/（m2h）of the control membrane. The existence of CaCl₂was in the form of complex withTEPA molecules, enhancing the inoxidability and mechanical stability of thecomposite TEPA/TMC membrane, which could be demonstrated by XPS and FT-IRmeasurements. The TEPA/TMC composite membrane also showed stimuli-responsiveproperty which could be attributed to the complex structure permitting the bond openand connection.Finally, NF was utilized to treat high-concentration of Orange G solution withMicro-Electrolysis technique as the pre-treatment. The influence of pH, temperature,operation time and Orange G solution concentration on the separation efficiency ofMicro-Electrolysis was evaluated. It was found that the suitable operation conditionwas pH value,4, operation time,60min, temperature,60oC. The total efficacy of thecombination of nanofiltration and micro-electrolysis was very efficient, and showedpractical application potential.