| The produced oily wastewater is known as one of the main waste streams generated by different industries,such as oil,gas,petrochemical,food,textile,and medicines productions.In the last decade,due to the increase of the produced water volume,the discharge of the wastewater to the environment has become a major problem for the countries all over the world.Different physical,chemical,and biological treatment processes have been introduced and applied for the water purification and separation of organic-inorganic contaminants from the wastewater.However,separation and removal of the suspended oil particles with small size distribution and dissolved contaminants from the waste stream have remained a challenge for the conventional treatment processes.Moreover,many chemical treatments are costly processes and produce hazards byproducts and sludge.Variation of the feed stream concentration and characteristics directly affect the quality of the purified stream.Herein,membrane separation technology,which is independent of feed stream quality,has been introduced as an appropriate and low-cost separation method to refine the waste stream.Different membrane structures based on the polymeric and ceramic materials have been produced and used for wastewater treatment.Compared to the polymeric membranes,the ceramic-based membranes with significant structural stability have got attention for industrial point of view.The ceramic membranes have been commonly fabricated based on the metal-oxide ceramics.Besides,the non-oxide ceramic-based materials such as silicon nitride have been rarely used and investigated as potential material for membranes fabrication.Herein,the hollow fiber silicon nitride membranes were fabricated and optimized to be used for cross-flow microfiltration of oily wastewater.In brief,the thesis reports the morphological adjustment of the silicon nitride hollow fiber membrane for conventional cross-flow filtration,the effect of the filtration operating process on the separation performance of the membranes during oily wastewater filtration and membrane fouling characterization,and membrane modification by hydrophilic silica nanoparticles for efficient oil/water separation.Moreover,the silicon nitride hollow fibers,as a robust structure,were successfully used as the substrate for the fabrication of novel thin film polyamide nanocomposite membranes.The novel nanofiltration membranes were fabricated by incorporation of novel functionalized nanoparticles and two-dimensional graphene oxide based nanohybrids and nanocomposites into the polyamide active layer of the nanofilter membrane.The fabricated nanofilter membranes were successfully used for water desalination and organic solvent nanofiltration.The present thesis is divided into the following sections:1.The first chapter introduces the conventional wastewater treatment processes.We reviewed the main concepts of the membrane separation technology,including the common pressure-driven membrane for water filtration,the materials for membrane fabrication including organic and inorganic substances,the methods for the membrane fabrication,the membranes module configurations,filtration process configuration,and the concepts of concentration polarization and membrane fouling.2.In chapter 2,morphological engineering of silicon nitride(Si3N4)hollow fiber membrane was carried out by considering hydrodynamic viscous fingering phenomena.The influence of the solvent,the air gap,and the rate of internal coagulant on the finger-like/spongy layer thickness ratio,porosity,bending strength,pore size distribution,and water permeation,was thoroughly investigated.Membrane morphology was controlled by optimizing fabrication parameters in order to achieve the desired fiber structure for the final functional application.3.In chapter 3,the effect of trans-membrane pressure(TMP),feed flow rate(FFR),and pH of the feeding emulsion on the separation performance was determined experimentally.Membrane fouling was increased by dissociation of oil droplets during filtration at high applied pressure and feed flow rates.Fouling phenomena were studied based on standard pore blocking model.The pH by affecting the surface charge of the Si3N4 hollow fibers and zeta potential of the feed emulsion has also been introduced as a prominent influential factor on separation efficiency.4.In chapter 4,uniform deposition of SiO2 nanoparticles on the outer surface of the Si3N4 hollow fiber membrane was achieved via the sol-gel method using tetraethylorthosilicate(TEOS)at various concentrations.At highest TEOS concentration in the sol-gel process,the generated SiO2 nanoparticles entirely covered the membrane surface,resulting in the presence of a newly-formed smooth selective filtering layer.It has reduced the surface roughness and increased the surface hydrophilicity of the membrane.These features have considerably enhanced the selectivity of the membranes,especially in the case of submicron contaminants,and suppressed fouling phenomena in oil/water separation process.5.In chapter 5,novel thin film composite(TFC)and nanocomposite(TFN)membranes were fabricated by in-situ interfacial polymerization of m-phenylenediamine aqueous solution and 1,3,5-benzenetricarbonyltrichloride organic solution on polyethersulfone/silicon nitride composite hollow fiber substrate.Amino functionalization of silica nanoparticles(MSNPs)by p-aminophenol improved the compatibility of nanoparticles with polyamide active layer,and decreased the formation of agglomerates during the interfacial polymerization,enabling,therefore,the successful fabrication of high-quality TFN membranes.The hydrophilicity of TFN was significantly improved by incorporating functionalized nanoparticles,which is attributed to the presence of hydrophilic amine groups(-NH2)on the surface of the modified nanoparticles.6.In chapter 6,graphene oxide based nanohybrids decorated with TiO2 nanoparticles(TiO2@rGO)were synthesized and incorporated into the TFN membrane for efficient organic solvent nanofiltration(OSN)with antifouling properties.TiO2@rGO incorporated TFN membranes showed intense permeability increment and antifouling characteristics in comparison with the controlled composite membrane and graphene oxide(GO)incorporated TFN membrane.The GO nanosheets structure favored solvent channeling and TiO2 provided super hydrophilic characteristics,both resulted in a super permeable-hydrophilic OSN membrane with high structural stability and premium antifouling properties.7.In chapter 7,high desalination performance,dyes retention,and antibacterial properties were achieved with a multifunctional thin film nanocomposite(MTFN)membrane,fabricated by the incorporation of a novel nanocomposite structure of reduced graphene oxide@Ti02@Ag(rGO@Ti02@Ag)into the polyamide active layer.The specific characteristics of the graphene-based nanocomposite,synthesized by microwave-assisted irradiation process,favored water channelization and provided super-hydrophilicity and antibacterial properties to the MTFN membranes.The water contact angles confirmed the superb surface hydrophilicity of the MTFN membranes.90%reduction in the number of viable bacteria(E.coli),after 3 h of contact with MTFN membranes,confirmed the superior antibacterial activity of the produced membranes.8.In chapter 8,the conclusions of the dissertation were presented. |
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