Salt Rejection Of Membranes Research Articles

Leveraging calcium-NOM complexation phenomenon as RO fouling mitigation strategy during treatment of lake water

Organic fouling during reverse osmosis (RO) is exacerbated by the presence of calcium up to a limit where extremely high calcium concentration results in lesser fouling due to formation of large organic-calcium aggregates with lower cake resistance. Therefore, this work leveraged on this phenomenon and used calcium chloride as coagulant (at varying concentration) to reduce membrane fouling while enhancing NOM removal. Membrane cleaning efficiency through calcium-EDTA chelation which disintegrates the fouling layers was explored. RO fouling was performed with sodium alginate solutions and lake water. The fouled membranes were soaked in 0.1 ​mM EDTA (1 ​h) and backwashed with water to remove the fouling layer. Alginate fouling was worsened (45–85 ​%) by increase in calcium concentration up to 5 ​mM but lessened at > 5 ​mM calcium concentration (35–15 ​%). Similar observations were made when filtering lake water, except that lesser fouling was observed at calcium concentrations greater than 15 ​mM. Membrane soaking in EDTA enhanced cleaning efficiency leading to over 90 ​% flux recovery for both alginate and late water. However, prolonged membrane exposure to 10 ​mM calcium resulted in slight decline in membrane salt rejection (<2 ​% change) and tensile stress (1.3–1.1 ​N/mm2), while the membrane flux increased (<3 ​% change). Finally, NOM removal improved with calcium addition (up to 90 ​%) – key in reducing potential formation of disinfection by-products due to addition of disinfection agents. The proposed use of calcium as a common coagulant/chelating agent for fouling mitigation/remediation during advanced membrane filtration has a potential for wider application and commercialization.

Evaluating and predicting surfactant-induced hydrophilization of pore channels in membrane distillation

Membrane distillation (MD) processes are susceptible to membrane pore wetting, which compromises the membrane's salt rejection efficiency and deteriorates the quality of the distillate. However, current understanding of the dynamics of membrane wetting remains incomplete, and the conventional indicators used to detect post-wetting, such as conductivity and distillate flux, have limitations.We develop a theoretical model for the wetting front (l) to elucidate the adsorption of surfactant molecules and their role in the hydrophilization of commercial polyvinylidene fluoride (PVDF) membranes under various sodium dodecyl sulfate (SDS) concentrations and different membrane pore sizes. Subsequently, we utilize an in-situ impedance-based monitoring technique to quantitatively track the progression of wetting and validate our model's ability to accurately describe the relationship between the wetting front and the square root of time (l=Kt) to obtain the wetting progression coefficient K within the first 30 min of the slow wetting stage.Hence, K, through the combination of impedance measurement and modelling, offers the advancement of wetting until the critical wetting front is reached. This critical wetting front, located at the half point of the membrane thickness, signifies the occurrence of partial wetting, alerting the need for membrane cleaning to mitigate full wetting before it occurs. Additionally, the potential for membrane recoverability can be assessed by examining the variation of K after cleaning, thereby facilitating the evaluation of the effectiveness of different membrane cleaning strategies. The theoretical model and applicable parameters presented in this study contribute to the understanding and quantification of mechanisms slow wetting in surfactant-induced scenarios and provide a promising method for determining the appropriate membrane for the desired feed and the optimal membrane cleaning strategy for extending the lifespan of membranes.

Enhanced water permeability of hollow fiber composite reverse osmosis membrane using porous α-cellulose/polysulfone hollow fiber membrane as the substrate

The hollow fiber composite (HFC) reverse osmosis (RO) membrane with a special self-supporting structure has attracted a great deal of attention in the fields of separation and purification. However, low permeability is an urgent problem restricting its wide application. A porous polysulfone (PSF) hollow fiber support membrane was fabricated through the dry–wet spinning technique and hydrophilic α-cellulose © powder was incorporated in the PSF membrane matrix to improve the membrane’s water permeability. The HFC RO membrane was prepared via the interfacial polymerization process on the inner surface of the C/PSF support membrane. The membrane morphology and surface hydrophilicity were evaluated through scanning electron microscopy observation and dynamic water contact angle (WCA) measurement. The effects of α-cellulose incorporation on the separation performance of PSF hollow fiber membranes and HFC RO membranes were investigated. The results showed that the surface hydrophilicity and water permeability of the PSF membrane were significantly improved after the introduction of α-cellulose. The WCA of the modified PSF support membrane decreased from 84.6° for the neat PSF membrane to 70.25°, and the pure water flux can reach a maximum value of 102.1 L/(m2 · h) (0.1 Mpa), which was 1.3 times that of the pristine membrane. The HFC RO membrane using the hydrophilic modified PSF membrane as the substrate exhibited an enhanced water flux of 15.6 L/(m2 · h) and, meanwhile, the membrane salt rejection remained above 97.6% (1.0 wt% NaCl aqueous solution, 0.7 Mpa). The HFC RO membrane showed extremely high rejection rates (99%) for different dyes (congo red and methylene blue). No obvious performance deterioration was observed for the HFC RO membrane during continuous vacuum membrane distillation (VMD) experiments for 60 h.

Cellulose acetate/polyvinylidene fluoride based mixed matrix membranes impregnated with UiO-66 nano-MOF for reverse osmosis desalination

Reverse osmosis (RO) is considered a lifesaver technology to conquer the current catastrophic water shortage situation. However, reaching a competitive RO membrane is a challenging issue. Therefore, this study investigated the optimum polymeric blending ratio between cellulose acetate (CA) and polyvinylidene fluoride (PVDF) to have a new blended polymeric membrane named cellulose acetate polyvinyl (CAPV-X), where X is the PVDF concentration %, with enhanced properties. The optimum prepared CA/PVDF blended membrane was selected for further enhancement with nano sized metal organic framework (UiO-66 MOF). Selection was made depending on each membrane salt rejection. A membrane characterization was performed based on Fourier transform infrared (FTIR), X-ray diffractometer (XRD), scanning electron microscope, thermal gravimetric analysis, and contact angle. FTIR and XRD data confirmed the successful preparation of the blended polymeric membranes CAPV-5, CAPV-7 and CAPV-10. Further, they proved UiO-66 nanofiller impregnation in the hybrid CA/PVDF/UiO-66 membrane (CPU). The addition of PVDF and nano-MOF had a slight positive effect on the membrane thermal stability. The contact angle increased with increasing the PVDF concentration and decreased once more with the impregnation of UiO-66. The RO membrane performance revealed that the optimum CA/PVDF ratio was found to be 93/7% with around 80% salt rejection and a permeate water flux of 4 L/m2 h. CPU composite membrane was then fabricated to enhance salt rejection and permeate water flux. The testing data indicated that salt rejection and permeate water flux increased over blended CAPV-7 membrane by almost 12% and 42%, respectively. Overall, CPU hybrid membrane could be used for water desalination with a good salt rejection of 90.2% and a permeate water flux of 5.7 L/m2 h.Graphical abstract

Amino-embedded carbon quantum dots incorporated thin-film nanocomposite membrane for desalination by pervaporation

This study provides an in-depth investigation on the incorporation of carbon quantum dots (CQDs) in fabricating novel thin-film nanocomposite (TFN) membranes to address the high demand for highly water-permeable pervaporation (PV) membranes for desalination processes, especially for treating high-salinity water, brine, or wastewater. CQDs have emerged as a green nanofiller for improving membrane performance owing to its excellent biocompatibility, non-toxicity, uniform dispersion, and rich functional groups. Herein, we synthesize amino-embedded carbon quantum dots (ACQDs) via a simple one-pot hydrothermal method and employ them in interfacial polymerization to fabricate the ACQD-TFN membrane. Benefiting from the incorporation of ACQDs, the optimized ACQD-TFN membrane exhibited an enhanced water flux of 23.2 kg·m−2·h−1 at 70 °C during the treatment of a 10 wt% NaCl solution, which was 44% higher performance than that of the unmodified thin-film composite membrane. The ACQD-TFN membrane's salt rejection remained at 99.9% even after 96,000 ppm·h chlorine exposure, exhibiting excellent chlorine resistance. Also, the ACQD-TFN membrane's regular surface microstructure and increased hydrophilicity endowed good anti-fouling property, and its flux recovery rate reached 91% after 5 fouling-cleaning cycles. This work provides a feasible strategy for fabricating highly permeable, chlorine-resistant, and anti-fouling PV membranes for desalination applications.

Synergetic influence of F-MWCNTS on polyvinylpyrrolidone sodium alginate composite membrane for reverse osmosis

In this study, novel composite membrane of functionalized multi-walled carbon nanotubes (F-MWCNTs) polyvinyl pyrrolidine (PVP) and sodium alginate (Na-Alg) with unique characteristics were synthesized for the application of reverse osmosis (RO) desalination. The MWCNTs in different amounts were systematically and uniformly dispersed in PVP/Na-Alg polymer matrix during the synthesis of membranes by dissolution casting method. The effect of F-MWCNTs content in the performance of the composite membrane was investigated for RO desalination process compared to PVP/Na-Alg blended membrane. The spectral studies were carried out by Fourier transform infrared spectroscopy (chemical bonding) and scanning electron microscopy (surface morphology). The thermogravimetric analysis (TGA) of membranes also recommended that composite membrane with the highest content of F-MWCNT has more excellent thermal stability compared to PVP/Na-Alg blended membrane and other modified membrane samples. The most striking experimental results show that the incorporation of F-MWCNTs improved the general RO performance of the composite membranes. The modified composite membrane surface became rough as compared to the PVP/Na-Alg blend membrane surface. The PVP/Na-Alg blended membrane shows a maximum permeation flux of 5.5 L/m2h and high-water content. This experimental analysis also presented that tethered F-MWCNTs/PVP/Na-Alg polymer matrix membrane, with stronger F-MWCNTs/polymer matrix interactions, enhanced the composite membrane's salt rejection performance by 85.4% for the highest content of F-MWCNTs. Therefore, it can be concluded that all the membrane samples presented excellent capacity to resist the growth of gram-negative E. coli bacteria.

Controlling the inner surface pore and spherulite structures of PVDF hollow fiber membranes in thermally induced phase separation using triple-orifice spinneret for membrane distillation

In this study, we controlled the inner surface structures of polyvinylidene fluoride (PVDF) hollow fiber membranes via a thermally induced phase separation process using a triple-orifice spinneret for direct-contact membrane distillation (DCMD). The coextrusion of propylene carbonate (PC) through the outermost channel of the spinneret led to porous outer surfaces with similar pore sizes and spherulitic structures for all the PVDF hollow fiber membranes. In the innermost channel, the extrusion of solvents having different compatibilities with PVDF and the diluent (PC) as the bore liquids controlled the inner surface pore sizes and spherulite structures, and the effects of these inner surface structures on the DCMD performance were investigated in detail. Increasing the compatibility of the bore liquids toward the diluent led to an increase in the inner surface pore size because of the formation of loose, isolated spherulites, which remarkably enhanced the water vapor permeability from 4 to 8.3 L m−2 h−1, while reducing the membrane hydrophobicity, liquid entry pressure, and salt rejection. When increasing the bore liquid compatibility with the polymer, the surface pore size decreased because of the tight spherulite contact, enhancing membrane salt rejection and wetting resistance. Given the significance of bore liquid compatibility with the diluent and the polymer in controlling the inner surface structures, a useful guideline is presented for selecting the appropriate bore liquids to prepare hollow fiber membranes with the desired inner surface structures for high MD performance.

Design of nanofiltration (NF) hollow fiber membranes made from functionalized bore fluids containing polyethyleneimine (PEI) for heavy metal removal

Effective methods are still lacking for large-scale production of thin-film composite (TFC) hollow fiber membranes made from interfacial polymerization. It is the bottleneck limiting the scale-up of TFC nanofiltration (NF) hollow fiber membranes for wastewater treatments. This study fills the niche in NF hollow fiber production by simplifying the interfacial polymerization process while maintaining the membrane's salt rejection. By blending sulfonated polysulfone (SPSf) in the polyethersulfone (PES) dope solution and using polyethyleneimine (PEI) in the bore fluid for hollow fiber production, amine groups are actively introduced onto membranes. The amine groups can be further modified with various molecules, for instance, poly(acrylic acid) (PAA), glutaraldehyde (GA) and 1,3,5-benzebetricarbonyl chloride (TMC), resulting in precisely designed membranes suitable for heavy metal removal. The best membrane formed in this study has a small mean effective pore size (μp) of 0.57 nm, a molecular weight cut-off (MWCO) of 157 Da and a good pure water permeability (PWP) of 5.14 LMH/bar. It also has over 90% rejections of heavy metal ions, such as Ni2+, Zn2+ and Cu2+. The membrane displays good performance stability in a continuous 96-h operation and in acid washes. The study may provide useful insights in designing TFC NF hollow fiber membranes that are suitable for large-scale production.

Experimental and statistical investigation on fabrication and performance evaluation of structurally tailored PAN nanofiltration membranes for produced water treatment

The present study aims at investigating the effects of multiple fabrication and design parameters on the performance of nanofiltration (NF) membranes. By employing the Plackett-Burman design method, obtained results demonstrate that citric acid (0–1.5 wt.%), TiO2 (0–1 wt.%), and solvent evaporation time (1–3 min) are the top dominant factors affecting the pure water flux (PWF) of NF membranes. Also, the effects of the dominant factors and their corresponding interactions are statistically assessed through RSM technique by employing a quadratic model. Based on the ANOVA results the proposed models for the PWF and CaSO4 rejection responses are statistically significant. The calculated optimum values for citric acid, TiO2, and solvent evaporation time are 0.87 wt.%, 0.98 wt.%, and 1.34 min respectively. It is shown that by increasing the concentration of TiO2 both PWF and rejection of membrane enhanced from 108.8–131.5 (lit.m−2.h-1) and from 73.5–83 % respectively. Furthermore, an increment in citric acid concentration leads to the promotion of the surface hydrophilicity and salt rejection of membranes. From the morphological point of view, increasing the TiO2 concentration leads to formation of membranes with more porous sublayers while longer solvent evaporation times results in the formation of membranes with smaller macrovoids.

Analysis of temperature effects on the specific energy consumption in reverse osmosis desalination processes

Specific Energy Consumption (SEC) is key parameter involved in optimizing design and operation of RO-desalination plants, used for treating various feed-waters. This study deals with feed-water temperature Tf effects on the performance of a typical RO unit (operating in constant recovery mode), that includes an energy recovery device (ERD), focusing on SEC for brackish and sea-water desalination. Account is taken of temperature-effects on physico-chemical water-properties and membrane performance-parameters, that enable reliable determination of itemized contributions to SEC; the latter include energy losses in mechanical devices (pumps and ERD) and in the RO process, mainly due to species separation and fluid-friction through membranes and narrow flow-channels. In general, within a Tf range ~15 to 40 °C, increased feed-water temperature results in SEC reduction in desalinating low salinity waters. However, for high salinities as in sea-water, the significantly increasing osmotic pressure (with Tf) tends to neutralize other positive effects, thus leading to a minimum SEC at ~30 °C for typical membrane-module parameter-values. Furthermore, increased Tf in desalination of both low- and high-salinity waters tends to negatively impact on membrane salt rejection and scaling, which should be considered in optimization studies. The methodology adopted in this work would be useful in such studies.

Functionalized nanoporous graphene membrane for water desalination; Effect of feed salinity on permeability and salt rejection, a molecular dynamics study

Feed water composition are sometimes instable and thus affecting the desalination processes. The effect of feed water salinity on permeability and salt rejection of graphene-based desalination membranes as novel desalination material, was investigated using molecular dynamics simulation to examine the performance of the membrane and permeate water quality. Hydroxylated (OH) pore was tested with pore diameter of 7.4 Å. Three feed water salinity of 33.4 (sea water), 50.1, 66.8, and 83.5 g/L was studied. The result indicated that best water permeability was observed for 33.4 g/L of water salinity while salt rejection of this membrane was lowest for this salinity. Concentration polarization graphs were obtained for desalination process indicating a concentrated area before the membrane as salty as more than 1000 g/L of while the highest off-membrane salinity reached to utmost 2 g/L. Density map plots for water molecules near the nanopores clearly displayed the orientation of water molecules as function of time and coordinate which proves that higher salinity causes lower congestion of water molecules near the pore as result of hydration effects or decreased water permeability as a result of a considerable drop in water entropy. This observation was approved by radial distribution graphs of water molecules around Na and Cl ions that displayed higher bounding at higher salinity. The effect of hydrated ions on water transport and salt rejection revealed the importance of the finely manipulating the feed composition.

The rejection of mono- and di-valent ions from aquatic environment by MWNT/chitosan buckypaper composite membranes: Influences of chitosan concentrations

Owing to the scarcity of proper drinking water is an urgent problem, MWNT/Chitosan membrane is greeting to reject mono- and di-valent ions from water. MWNT/Chitosan membrane was fabricated through the dispersion of Multi-walled carbon nanotubes (MWNTs) in an aqueous solution containing different concentrations of chitosan. The influence of solution concentration on membrane salt rejection properties, as well as contact angle, electrical conductivity, water permeability, mechanical properties, zeta potential, surface area and internal pores morphologies has been investigated. The resulting buckypaper demonstrate that the contact angle (91° ± 4° to 124° ± 3°), electrical conductivity (17 ± 1 to 83 ± 3 S/cm), water permeability (0.59 ± 0.04 to 5.73 ± 0.3 L/m2 h bar), surface area and internal pores morphologies of the buckypaper membranes were decreased by increasing the concentration of chitosan. While, the mechanical properties (tensile strengths varied between 35 ± 2 and 75 ± 3 MPa) and zeta potential of these buckypaper membranes were found to increase with increasing the amounts of chitosan. A buckypaper fabricated from MWNTs and a high concentration of chitosan (0.4% w/v) showed a higher rejection efficiency for these salts, possibly due to their smaller internal pore volumes and lower specific surface area.

Performance Enhancement of Reverse Osmosis (RO) Membrane Using Nanocomposite Materials

Many attempts were made to enhance the performance of reverse osmosis (RO) membranes in the desalination process. Using ion exchange (IX) bed before RO process and modifying the structure of RO membranes are some of these attempts. Thin film nanocomposite (TFN) membrane is the novel type of RO membranes which is the best in nanofiltration applications. TFN membranes have many new advantages due to the change of their structure in comparison with traditional membranes. In this study the performance of a TFN membrane was compared with that of standard thin film composite (TFC) spiral wound water desalination RO membrane for filtration of IX produced water. The results from the filtration process showed that the flux and water permeability of TFN are 1.55 and 1.56 times that of TFC for feed water with 2050 ppm NaCl concentration with nearly unchanged level of the membrane salt rejection, which will reduce the filtrated water cost.

Interlayer-free Membran Silika Pektin untuk Pervaporasi Air Rawa Asin

Wetland in South Kalimantan is one of surface water sources to provide clean water. However, seawater intrusion has spread into the wetland aquifer and reduce the quality of water. Silica-pectin membrane is a promising technology for desalination. The membranes were tested for desalination by pervaporation at room temperature (~25 °C). During pervaporation process, the water contacts to membrane and the separation is started to occurs as vapour phase by maintaining vacuum pressure (~1 bar). The permeate was collected in the cold trap after condensed using nitrogen liquid. The purpose of this research was to investigate the performance of interlayer-free silica pectin membrane for wetland saline water. Experimental results shows the fluxes of membrane are 0.35 and 0.19 kg.m-2 h-1 ( pectin 0%wt); 0.23 and 0.16 kg.m-2 h-1 (pectin 0.1%wt); 0.58 and 3.63 kg.m-2 h-1 (pectin 0.5%wt); 3.40 and 0.12 kg.m-2 h-1 (pectin 2.5%wt) calcined at 300 and 400 °C, respectively. Natural organic matter (NOM) and salt concentration in wetland saline water can reduce the fluxes up to (~98%). Nevertheless, overall salt rejection of membranes achieved &gt;99%. It was found that low calcination gives better performance at high pectin concentration. While pectin concentration was limited at high calcination.

A New Approach to Provide High Water Permeable Polyethersulfone based Nanofiltration Membrane by Air Plasma Treatment

In this study, polyethersulfone based nanofiltration membranes were modified by air plasma generated through dielectric barrier discharge to increase the membrane hydrophilicity aiming to improve the separation and antifouling characteristics. The effect of plasma time on the physico-chemical and separation properties of membrane was investigated. The PES nanofiltration membranes were fabricated by the solution casting technique associated with phase inversion method. The FTIR spectra showed formation of imine and amine functional groups on the membrane surface. The water contact angle decreased form 58 ° to 31 ° by plasma treatment which produces more hydrophilic surface. SEM and SOM images demonstrated that the surface morphology was changed due to ions collision with membrane surface bombardment. AFM results indicated that membrane roughness was initially enhanced by plasma treatment up to 1 minute, and then decreased again by a further increase of treatment time. Membrane water flux increased from 10.05 (L/m2.h) to 35.17 (L/m2.h) remarkably by plasma treatment up to 1 minute and then decreased again at longer treatment times. An opposite trend was observed for the salt rejection of membranes. The water flux was enhanced ~270% for the modified membrane at 2 min plasma treatment whereas rejection declined less than 18%.

In situ modification of polyamide reverse osmosis membrane module for improved fouling resistance

In situ improvement of fouling resistance of the state-of-the-art polyamide reverse osmosis membrane module on the basis of the fouling characteristic of the fluid to be treated is of great practical significance. In this work, in situ modification was performed with the spiral wound polyamide reverse osmosis membrane module for improved fouling resistance to specific foulant. Small molecular monomers of amidosulfonic acid (ASA), diethanolamine (DEA) and piperazine (PIP) were grafted onto the surface of the flat-sheet polyamide-based thin-film composite membrane within the module separately through 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC)-activated amidation of carboxyl groups. The results of fouling experiments indicated that the fouling resistance of the polyamide reverse osmosis membrane module to the model foulants of bovine serum protein (BSA), sodium alginate (SA) and dodecyl trimethyl ammonium bromide (DTAB) could be effectively improved through grafting monomers ASA, DEA and PIP, respectively, showing significant reduction in declines of membrane flux to aqueous BSA, SA and DTAB solutions by 47.2%, 41.3% and 34.4%. The changes of membrane surface hydrophilicity and negative charge were in charge of the improved antifouling property. The in-situ modification was also found to slightly enhance membrane salt rejection and have nearly no influence on membrane water flux.

Titanium dioxide nanoribbons/multi-walled carbon nanotube nanocomposite blended polyethersulfone membrane for brackish water desalination

A series of titanium dioxide nanoribbons (TNRs)/multi-walled carbon nanotubes (MWCNTs)/polyethersulfone (PES) blend membranes with different proportions of TNRs/MWCNTs were synthesized via phase inversion method. The nanocomposite (TNRs/MWCNTs) prepared by hydrothermal method followed by chemical vapor deposition (CVD). Energy dispersive X-ray (EDX) analyses and X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) used for characterizing the nanocomposite. The characterization revealed that the nanocomposite consists of a single phase of TiO2-B and multi-walled carbon nanotubes. The mass ratio of TNRs/MWCNTs is 1:1. The morphology of TiO2-B is a nanoribbons structure with porous pits on its surface. Multi-walled carbon nanotubes (MWCNTs) grow on these nanoribbons and form a network structure-like. The influence of nanocomposite incorporation on the morphology, porosity, contact angle, mechanical properties, and performance of the prepared membranes was investigated as a function of pure water flux and salt rejection %. The hydrophilicity is increased by increasing the nanocomposite content whereas the contact angle and porosity decreased. The SEM images showed that the spongy-like structure of bare-PES is changed by incorporation of TNRs/MWCNTs to a macro-void structure. The nanocomposite reinforces and enhances the mechanical properties of the synthesized membranes. The tensile strength increased from 45.7 to 96.6 kg/cm2 by blending 0.5 wt% TNRs/MWCNTs. Also, the incorporation of TNRs/MWCNTs increases the ac electrical properties of the membrane regarding the conductivity (σ), dielectric constant (έ) and dielectric loss (ε″). The membrane performance was tested using synthetic solution with a salinity of 2000, 5000, 7000, and 20,000 mg/l NaCl. The test is carried out at low-pressure reverse osmosis system (LPRO). The highest average salt rejection of membranes was 99.54%, 99.84%, 98.53%, and 94.06%, respectively with the addition of 0.5% of TNRs/MWCNTs, while the average salt rejection was 61.63%, 50.9%, 41.7%, and 75% using bare-PES. The anti-fouling nature and dye removal for all membranes were tested. The flux recovery ratio (FRR) with (PES/0.5 wt% of TNRs/MWCNTs) membrane reach 89% while the bare-PES showed 58%. In addition, the modified membranes showed high removal of 50 mg/l Congo red dye. (PES/0.5 wt% of TNRs/MWCNTs) rejected 98.1% of the dye while the bare-PES rejected 68.14%. The 0.5 wt% of TNRs/MWCNTs embedded to PES considered the best composite content.

Enhancing Properties and Performance of Cellulose Acetate/Polyethylene Glycol (CA/PEG) Membrane with the addition of Titanium Dioxide (TiO2) by Using Surface Coating Method

In this study, cellulose acetate/polyethylene glycol (CA/PEG) membrane with composition 80/20 was prepared by phase inversion method. Titanium dioxide with different number has been added by using surface coating. Hydrophilicity, morphology, flux permeate and salt rejection of membranes has been studied. The hydrophilicity is determined by Fourier-Transformed Infra-Red (FTIR) spectra and contact angle analysis. Surface and fractured morphology are identified by using Scanning Electron Microscopy (SEM). The experiment results show that hydrophilicity of CA/PEG membrane increases with the addition and the increasing of TiO2 contents. However, with further increasing of TiO2, hydrophilicity of CPT membrane decreases. The optimum membrane is CA/PEG/TiO2 80/20/1,25 g/L solvent (CPT 3) with flux permeate of 111,82 L.m-2h-1 and salt rejection of 48,30%.

Surface modification of thin film composite reverse osmosis membrane by glycerol assisted oxidation with sodium hypochlorite

Need for improvement in water flux of thin film composite (TFC) RO membrane has been appreciated by researchers world over and surface modification approach is found promising to achieve higher water flux and solute rejection. Thin film composite RO membrane was exposed to 2000mg/l sodium hypochlorite solution with varying concentrations of glycerol ranging from 1 to 10%. It was found that there was a drop in concentration of sodium hypochlorite after the addition of glycerol because of a new compound resulted from the oxidation of glycerol with sodium hypochlorite. The water flux of the membrane treated with 1% glycerol with 2000mg/l sodium hypochlorite for 1h was about 22% more and salt rejection was 1.36% greater than that of only sodium hypochlorite treated membrane for the same concentration and time. There was an increase in salt rejection of membrane with increase in concentration of glycerol from 1% to 5%, however, increasing glycerol concentration further up to 10%, the salt rejection declined. The water flux was found declining from 1% glycerol solution to 10% glycerol solution. The membrane samples were characterized to understand the change in chemical structure and morphology of the membrane.

Experimental study on the effect of polysaccharides on incipient membrane scaling during desalination

Experimental results are reported on the effect of polysaccharides in the early stage of membrane scaling. Sodium alginate at small concentration (2 and 10mg/L) was employed as typical polysaccharide. Synthetic solutions, characterized by small bulk supersaturation ratio S in calcium sulfate (S~1.4), were filtered through a desalination membrane in dead-end cells under agitation. Three types of tests were performed; i.e. membrane scaling in absence of alginates (as reference), combined fouling-scaling (i.e. scaling in presence of alginates) and scaling tests after a fouling layer was formed on the membrane. Examination of various deposits by Scanning Electron Microscopy (SEM) and determination of calcium on membrane deposits and in filtered solids (from retentate and feed-fluid samples) provide useful insights including clear evidence that alginates tend to inhibit CaSO4 crystallization, likely due to calcium binding with carboxylates of alginate macromolecules and formation of gel deposits. The inhibition effect, manifested in the reduced deposit-mass density on membranes and crystallization–rate, as well as in crystal-shape modification, is stronger at the higher alginate concentration. Similarly, incipient membrane scaling, pretreated with alginate foulant solution, appears to be significantly inhibited compared to clean membranes. Under the conditions tested, membrane salt rejection was unaffected.