Commercial NF Membranes Research Articles

The performance of nanofiltration membranes in seawater and desalination brine applications: Saudi Water Authority experience

The process of dual brine concentration employs an NF-RO-MBC configuration as its fundamental setup. Understanding the ion rejection capabilities of NF in seawater is crucial within this framework. Testing of fourteen commercial NF membranes using Jubail seawater revealed variations in ion rejection capabilities. Twelve membranes operated at a consistent feed pressure of 17.7 bar. The results categorized membranes based on their TDS rejection into high (≥ 45 %), medium (25–45 %), and low (< 25 %) rejection membranes. When concentrating the NF-treated SWRO brine, NF membranes can be utilized in the MBC system. Eight commercial NF membranes were evaluated with SWRO brine, where Na and Cl constituted over 96 % of the TDS. The investigation assessed the concentration performance and secured solid quantity in the reject relative to the feed by applying pressures of up to 40 bar for the conventional NF membranes and up to 65 bar for the newly introduced HPNF membranes. Among these membranes, two conventional and two HPNF membranes exhibited promise for concentrating SWRO brine. In addition, the ion rejection performance of five commercial NF membranes on SWRO brine was examined for a potential RO-NF-MBC configuration, suggesting suitable NF membranes for SWRO brine separation. Lastly, the ion rejection performance was studied in a multistage NF system with varying feed compositions at each stage and compared with projected performance. The accumulated NF membrane performance database will be utilized to optimize the overall membrane system configuration for seawater and brine separation and concentration.

GO and surfactant assisted regulation of polyamide nanofiltration membranes for improved separation performance

Fabricating nanofiltration membranes with high water permeance and selectivity by tailoring the structure and morphology is crucial to efficient water purification. In this work, the fabrication of thin film nanocomposite (TFN) nanofiltration membranes by combining two methods, the surfactant-assembly interfacial polymerization (SARIP) and the addition of graphene oxide (GO) or ionic liquid functionalized graphene oxide (GO-IL) for the preparation of the selective PA layer on a novel porous substrate is reported. For the preparation of the porous substrate, mechanically robust, aromatic polyethers containing polar pyridine units (PDSPP) were chosen targeting to improved hydrophilicity and thus enhanced water permeability. The anionic sodium dodecyl sulfate (SDS) surfactant was used to regulate the interfacial polymerization thereby enabling the formation of dense PA layers with high cross-linking degree and consequently high salt rejections. On the other hand, the addition of GO/GO-IL nanosheets could impart hydrophilicity and antifouling properties. The novel porous PDSPP substrate was selected for the fabrication of TFN membranes due to its improved water permeability and superior salt rejection and increased hydrophilicity compared to commercial PSf substrate. The detailed study of the fabricated TFN membranes by ATR-FT-IR, SEM, AFM, XPS, contact angle measurements revealed the formation of polyamide selective layers with rougher surfaces, increased hydrophilicity and high cross-linking degrees (from 44 % to 94 %), resulted from the synergistic effect of SDS and GO incorporation. Moreover, the prepared TFN membranes exhibited high salt rejections while maintaining a moderate water permeability. In particular, the membrane containing the neat GO (TFNGO50) displayed excellent Na2SO4 and MgSO4 rejections (98.8 % and 99.5 %, respectively) while the NaCl rejection was 47.0 % and a water permeability value of 4.2 L m-2h−1 bar−1. The divalent salt rejections were among the highest values reported in the literature in comparison with commercial NF membranes and TFN membranes containing GO/functionalized GO. When GO-IL nanosheets were embedded in the PA layer, the water permeability was slightly improved while the salt rejections were significantly reduced compared to TFNGO50. Lastly, the incorporation of GO enhanced the anti-fouling properties of the prepared membranes due to increased hydrophilicity of the PA surface.

Supramolecular chemistry assisted construction of ultra-permselective polyamide nanofilm with asymmetric structure for ion sieving

Highly-permselective NF membranes are critical to energy-efficient ionic separation. Herein, an ultra-permselective polyamide (PA) nanofilm with asymmetric two-layered structure is achieved by supramolecular chemistry modulated interfacial polymerization (IP) process. Such nearly-40-nm asymmetric PA nanofilm consists of a PA dense layer with nanoscale homogeneity and a polydopamine-β-cyclodextrin (PDA-β-CD) porous layer induced by mussel-inspired surface chemistry, with crosslinking. Experimental characterizations reveal that the exceptionally-hydrophilic and highly-porous PDA-β-CD coating imparts the spatial enrichment and temporal retardation of amine monomers via H-bonding and host-guest interactions, conducing to form the diffusion-difference-enabled striped PA nanofilm with nanoscale ordered structures and enhanced cross-linking degree. Meanwhile, the PDA-β-CD porous coating not only can finely tune the microstructure of PA nanofilm, but also highly prefers for surmounting funnel effect and shortening water transport path. As a result, the resultant asymmetric PA nanofilm attains a noticeable water permeance of 38.59 ± 2.42 L m−2 h−1 bar−1, competitive retention of Na2SO4 (99.4 ± 0.2 %) and unprecedented Cl−/SO42− selectivity of 202.1, far outperforming the state-of-the-art commercial and lab-made NF membranes. Moreover, it evinces an outstanding ion-sieving performance under the high-salinity solutions, suggesting that our approach for tuning microstructure enables the development of ultra-permeability and excellent selectivity for application in brine refinement and salt reclamation.

Thin-film nanocomposite membranes for efficient removal of emerging pharmaceutical organic contaminants from water

Membranes are receiving significant attention to remove emerging organic micropollutants (OMPs) from wastewater and natural water sources. Herein, we report the facile preparation of a novel thin-film nanocomposite (TFN) membrane with high permeability and efficient removal of OMPs. ZnO nanoparticles were first synthesized using the co-precipitation method and functionalized with N1-(3-Trimethoxysilylpropyl)diethylenetriamine to make the surface rich with amine groups and then synthesized nanomaterials were covalently cross-linked into the active layer during the interfacial polymerization (IP) process. The performance of the membranes containing the cross-linked ZnO was significantly better than the non-cross-linked ZnO NPs containing membranes. Adding multiple hydrophilic groups and entities on the surface significantly decreased the contact angle (from ∼60° to 20°). SEM images confirmed the uniform presence and homogeneous distribution of the functionalized NPs throughout the entire membrane surface. Zeta potential measurements showed the modified membranes have a lower negative charge than the pristine membranes. Filtration studies revealed a significant increase in permeability ascribed to the creation of nanochannels in the membrane's active layer. The modified membranes outperformed commercial NF membranes in removing four common OMPs with rejection efficiencies of ∼30%, 64%, 60%, and 70% for Sulfamethoxazole, Amitriptyline, Omeprazole, and Loperamide HCl, respectively. The higher removal efficiency was attributed to the weakened hydrophobic interactions due to the presence of hydrophilic moieties and a stronger size exclusion effect. Moreover, the modified membranes showed high resistance to bacterial adhesion in static conditions.

Role of competitive effect in the separation mechanism of matrine and oxymatrine using commercial NF membranes

Sophora flavescens contains two alkaloids, matrine (MT) and oxymatrine (OMT), which have similar structures but distinct functions and require separation. The present study employed four nanofiltration membranes, namely NT101, NT103, NF270, and NF90, in order to explore the rejection mechanisms of MT and OMT. The behavior of single-component and binary mixtures was assessed during nanofiltration at different pH values. To systematically compare the intermolecular interactions between different alkaloids and the membranes, molecular dynamics simulations (MDS) were conducted. The results indicated that rejection by NT101 and NF270 was primarily influenced by electrostatic and hydrophobic effects. Owing to their relatively smaller pore size, rejections for NF90 and NT103 remained consistently high under the sieving effect. In addition, binary aqueous solutions consisting of MT and OMT can be separated by NT101 (separation factor of 5.46 after secondary filtration), probably because alkaloids compete for adsorption on the membrane. MDS demonstrated that the presence of MT increased the distance and weakened the interaction between OMT and the membrane, increasing OMT rejection. This study provides insightful guidance for the effective application of membrane technology in the separation of natural products.

Dealcoholization of Unfiltered and Filtered Lager Beer by Hollow Fiber Polyelectrolyte Multilayer Nanofiltration Membranes-The Effect of Ion Rejection.

Membrane-based beverage dealcoholization is a successful process for producing low- and non-alcoholic beer and represents a fast-growing industry. Polyamide NF and RO membranes are commonly applied for this process. Polyelectrolyte multilayer (PEM) NF membranes are emerging as industrially relevant species, and their unique properties (usually hollow fiber geometry, high and tunable selectivity, low fouling) underlines the importance of testing them in the food industry as well. To test PEM NF membranes for beer dealcoholization at a small pilot scale, we dealcoholized filtered and unfiltered lager beer with the tightest available commercial polyelectrolyte multilayer NF membrane (NX Filtration dNF40), which has a MWCO = 400 Da, which is quite high for these purposes. Dealcoholization is possible with a reasonable flux (10 L/m2h) at low pressures (5-8.6 bar) with a real extract loss of 15-18% and an alcohol passage of ~100%. Inorganic salt passage is high (which is typical for PEM NF membranes), which greatly affected beer flavor. During the dealcoholization process, the membrane underwent changes which substantially increased its salt rejection values (MgSO4 passage decreased fourfold) while permeance loss was minimal (less than 10%). According to our sensory evaluation, the process yielded an acceptable tasting beer which could be greatly enhanced by the addition of the lost salts and glycerol.

Positively charged modification of commercial nanofiltration membrane to enhance the separation of mono−/divalent cation

AbstractThe separation efficiency of mono−/divalent cations by a commercial nanofiltration membrane can be enhanced by increasing the surface positive charge. In this study, a novel surface grafting method was suggested, including activation with 2‐chloro‐1‐methyliodopyridine (CMPI), and sequent graft polyethylene‐imine (PEI) and 2,3‐epoxypropyltrimethylammonium chloride (EPTAC). Less flux reduction (&lt;30%) and higher separation factor of Mg2+/Na+ (8.03–9.77) was achieved with the modified membrane under the grafting condition of 0.05 wt% CMPI, 2 wt% PEI, and 1 wt% EPTAC. The modified membranes had higher surface positive charge, hydrophilicity and cross‐linking degree. During the 32‐h filtration of a mixed salt solution, the modified membranes showed larger permeance (&gt;11 L m−2 h−1 bar−1) and higher ion selectivity than the pristine membrane, with separation factors of Mg2+/Na+ and Mg2+/Li+ ranging 36.3–46.2 for the modified membranes. The modified membranes also have higher antifouling properties and are more stable at higher pH condition. The results demonstrate a facile and scalable surface modification method to improve the cation selectivity of commercial NF membranes, which shows great potential in the application of mono−/divalent ion separation.

Ceramic nanofiltration membranes for efficient fouling mitigation through periodic electrolysis

Ceramic membranes are gaining importance in several mainstream membrane applications. Their high chemical and thermal resistance stability make them ideal candidates for oil/water separation, dye rejections, in dairy production, catalyst recovery and in treating a variety of wastewater effluents. Although ceramic microfiltration and ultrafiltration membranes are a predominant research area, there is still limited research on ceramic nanofiltration membranes, especially on controlling its fouling propensity. High flux values in such membranes can cause rapid fouling which lead to a compromise in membrane performance. In this work, we have modified commercial ceramic TiO2 NF membrane by coating it with titanium through an e-beam deposition process. Coating with titanium did not bring about any change in the inherent membrane properties such as its thermal resistance, structure and hydrophilicity. The superhydrophilic membrane showed good electrical conductivity, which enabled us to test the membrane for its self-cleaning ability through periodic electrolysis. Sodium alginate, yeast, humic acid and their mixtures were used as model foulants. A cross-flow filtration setup was used where the membrane acted as a cathode and a potential of 2–4.5 V was applied periodically depending upon the type of foulant. Without membrane cleaning, a sharp decline in flux to even till 10 % of its original value was noticed during some filtration tests. However, a high flux recovery from 88 to 98 % was achieved when the membrane was subjected to intermittent cleaning. The Ti-coated NF ceramic membrane showed efficient surface cleaning. The generation of hydrogen bubbles helped in sweeping away the cake layer formed as a result of concentration polarization. These electro-ceramic NF membranes allow us to address critical problems associated with such pressure driven processes where biofouling is a major problem.

Ultrathin-film composite (uTFC) membranes based on amorphous perfluoropolymers for liquid separations

Thin-film composite membranes based on ∼100 nm cross-linked polyamides (PAs) are state-of-the-art membranes for liquid separations such as desalination. However, the PA layer shows poor antifouling properties and instability in chlorine solutions. Herein, we show for the first time that glassy amorphous perfluoropolymers (PFPs, such as Teflon AF and Hyflon AD) can be fabricated into ultrathin film composite (uTFC) membranes with a selective layer of <20 nm for desalination. Increasing the polymer concentration in the coating solutions from 0.05 mass% to 0.3 mass% increases the selective layer thickness from 9 to 25 nm. When Teflon AF2400 was fabricated into 16-nm selective layers on various porous supports, the water permeance decreases from 0.37 LMH/bar for PES10k to 0.07 LMH/bar for PES1k, and the Na2SO4 rejection increases from 86.6% to 95.2%. While the water permeance is lower than the commercial PA-based NF membranes, the rejection in these PFP-based membranes is comparable. The effect of the porous support on the water permeance can be ascribed to the geometric restriction and satisfactorily described using an empirical model. Interestingly, the membranes also exhibit good Na+/Li+ separation performance and stable performance for organic solvent nanofiltration, showcasing the versatility of the PFP-based uTFC membranes for various liquid separations.

In-situ radical graft modification of NF270 to improve membrane separation: Effects of water salinity and fouling types

This study used the concentration–polarization method to perform the radical-graft-modification of a commercial NF membrane (NF270) for enhancing membrane separation performance and mitigating membrane fouling. Influencing factors including different background water salinity and fouling types were systematically evaluated using humic acid (HA) and sodium alginate (SA) for simulating organic and biological fouling, respectively. Increasing water salinity caused decreasing permeate flux as well as the rejection of salt and pharmaceuticals and personal care products (PPCPs) of the pristine and grafted membranes, especially at high electrical conductivity (EC) = 10,000 μs cm−1. In comparison with the clean pristine membrane, the grafted membrane exhibited 19%–26% higher NaCl rejection and 3%–48% higher PPCP rejection, and remained relatively stable permeate flux, especially at low and medium EC (500–5,000 μs cm−1). Compared with the fouled pristine membranes, the fouled grafted membranes at EC=250–10,000 μs cm−1 exhibited 1%–30% and 1%–12% higher PPCP rejection with HA and SA fouling, respectively, especially for TRI and CBZ with high hydrophobicity. The grafted layer displayed a synergistic effect on membrane separation by adding an additional barrier along with enhancing the electrostatic repulsion between the solutes and membrane surface. The mitigation of HA and SA fouling was confirmed using scanning electron microscopy with fewer deposits and smoother surface on the grafted membrane surface. In sum, the results evidenced successful achievement and application of the in-situ radical graft modification technology to improve salt and PPCP rejection as well as mitigate organic and biological fouling with different water salinity.

Modification of polyamide nanofiltration membrane with ultra-high multivalent cations rejections and mono-/divalent cation selectivity

Due to their inherent negatively charged surface and large intra-membrane pore, the typical polyamide nanofiltration membranes possess the inferior retentions against Ca2+/Mg2+ and undesired mono-/divalent cation selectivity. Here, a novel dual-functional acyl chloride monomer comprising two protected amino groups, 3,5-bis-(sulfinylamino)benzoyl chloride (AB2), is designed and used as organic phase additive that enables simultaneous regulation of the surface charge and pore structure of polyamide (PA) selective layer. Both structure characterizations and simulations confirm that AB2 additive significantly reduces surface negative charges, surface carboxyl density, surface roughness, thickness and mean pore size of the- separation layer, which sharpens pore size distribution, strengthens electrostatic repulsion to cations and enhances water molecule transport. As a result, the optimal PIP-TMC/AB2 membrane shows the remarkably improved CaCl2/MgCl2 rejections (above 99.0%) and mono-/divalent cation selectivity, together with a preferable permeate flux (135.3 ± 3.12 LMH), surpassing most commercial and advanced NF membranes. Moreover, its multivalent cations removal capability and Mg2+/Li+ separation performance retain outstanding in highly concentrated feed solution, suggesting it has enormous potential for water softening and lithium recovery from brine.

Membrane Filtration Opportunities for the Treatment of Black Liquor in the Paper and Pulp Industry

Black liquor is a highly alkaline liquid by-product of the kraft pulping process, rich in organic molecules (hemicelluloses, lignin, and organic acids) and inorganic pulping chemicals such as sodium salts and sulphur-containing compounds. The release of this wastewater without further treatment could have serious environmental and financial implications. Therefore, a costly treatment process is used nowadays. Nanofiltration has been studied in the last few years as a promising alternative to recycle the cooking chemicals required for the separation of lignin and cellulose, but the development of pH-stable membranes with the potential to operate at industrial scales is fundamental in order to make this possible. In this study, the filtration performance of two in-house made membranes is evaluated and compared with a commercial NF membrane to determine the viability of their use for the treatment of black liquor. For this purpose, filtration experiments with simulated black liquor were performed. We identified that Membrane A has the higher potential for this application due to its competitive permeate flux (ca. 24 L m−2 h−1 at a trans-membrane pressure of 21.5 bar), and high rejection of organic components and salts from the cooking liquor (on average, 92.50% for the TOC, 84.10% for the CO32−, 88.70% for the sulphates, 73.21% for the Na+, and 99.99% for the Mg2+).

Tuning the excess charge and inverting the salt rejection hierarchy of polyelectrolyte multilayer membranes

Polyelectrolyte multilayers (PEMs) coated on porous membrane supports have shown versatile opportunities for tailoring the resulting membrane characteristics. PDADMAC/PSS multilayers used as a separation layer deliver outstanding NF properties in terms of selectivities and permeances, as well as stability. Charge overcompensation of PDADMAC limits the possibilities of tuning the charge distribution in the PEM. We present a new membrane preparation methodology combining low ionic strength in the polycation and high ionic strength in the polyanion coating solutions, resulting in a PEM build-up with excess negative fixed charges. In contrast to PEMs build from only either low or high ionic strength in the PE coating solutions, this asymmetric approach results in a significant higher adsorption of PSS than PDADMAC for the PEMs, as proved by QCM measurements. The high negative excess charge of the new PEM hollow fiber membranes (PEMMs) leads to Na2SO4 rejections of above 99%. More specifically, the salt rejection hierarchy is inverted, having higher rejections for the monovalent NaCl than for MgCl2. PEMMs with a high amount of negative excess charges are especially promising for anion rejection applications such as phosphate removal from effluents. The achieved high rejections for mono- and divalent phosphate ions and simultaneously high fluxes can compete and even outperform commercial NF membranes. Combining asymmetric low and high ionic strength in the PE coating solutions is therefore an effective way to control the net excess charge and its related salt rejection hierarchy.

Monovalent/Divalent salts separation via thin film nanocomposite nanofiltration membrane containing aminated TiO2 nanoparticles

Nanofiltration is widely used in separation of ions with different sizes and charges. However, thin-film composite nanofiltration membrane is hard to reach satisfied selectivity for monovalent ions from divalent ions. In this study, polyamide thin film nanocomposite (TFN) nanofiltration membranes were prepared via interfacial polymerization of piperazine and trimesoyl chloride on a PES substrate by incorporation of aminated titanium dioxide (APTES-TiO2). Surface morphology, roughness of the TFN membranes with varied concentration of aminated TiO2 were tested by SEM, AFM and Zeta analysis. The results showed membrane containing 0.3(w/v%) amino-modified titanium dioxide with ion-selective properties had greatly improved pure water flux while the Na2SO4 rejection keeps at a relative high level (>95%). For the separation of single salt solution, 0.3(w/v%) TFN has a higher rejection for sodium chloride (23.2%) and sodium sulfate (99.7%). For monovalent/divalent mixed salt solution has a separation factor of 477.89 in terms of chloride ion (Cl−) and sulfate (SO42−) in the mixed solution with a salt concentration ratio of 1:19, which was higher than that of the conventional commercial NF membranes, such as Desal-DL, NF 270. This method provides the possibility of recovering concentrated brine and industrial separation of monovalent and divalent ions.

Effect of (TiO2: ZnO) ratio on the anti-fouling properties of bio-inspired nanofiltration membranes

Membrane fouling and biofouling, which arises from the nonspecific interaction between the membrane surface and foulants, significantly impedes the efficient application of membrane technology. The addition of nanoparticles could have an impact on the properties of membranes used for nanofiltration. Nanoparticles can provide various functionalities to a membrane but, there are very few studies of the effect of mixing catalysts in PDA-modified membranes. In this study, polydopamine has been used to firmly bind a combination of nanoparticles on thin film composite (TFC) membranes. Two simple methods (a one-step and a two-step method) to assemble a multifunctional (TiO2, ZnO) layer of nanoparticles onto a commercial NF membrane as support have been evaluated by applying fast deposition of polydopamine (PDA). The membrane performance was evaluated based on the relative flux decline.Results show that the modification methods did not compromise the rejection of MgSO4, combined with an increase ∼15% in the rejection of NaCl. A 25% increase in the hydrophilicity of the modified membranes compared to pristine membrane was evidenced. In addition, the two-step modification method has antimicrobial activity for an ultralow load of 0.03 wt% ZnO nanoparticles; the antimicrobial activity increased when the membrane had a combination of TiO2:ZnO nanoparticles at 1:2 and 2:1 ratios using Bacillus Subtilis as model bacteria. The photocatalytic activity of the nanoparticles layer was demonstrated through the removal of methylene blue from a solution contacting the membrane when exposed to solar radiation.

Membrane selection for the Gold mining pressure-oxidation process (POX) effluent reclamation using integrated UF-NF-RO processes

Abstract The UF-NF-RO integrated route has emerged as a reclamation alternative for mine effluent from the pressure-oxidation processing (POX), producing concentrate metals stream, recover acid and water for reuse. Despite the route potentiality, it is still necessary to seek for more chemically stable membranes to increase the process sustainability, particularly because the membranes are exposed to aggressive conditions (acid effluent) and a high rejection is desired. Thus, in this study, commercial NF membranes (NF90, NF270, MPF34, DK, and Duracid) and RO membranes (BW30, LP, TFC-HR, XN45, and SG) were evaluated in terms of key performance parameters, such as permeate flux, metals rejection, acid recovery, fouling potential, maximum permeate recovery (RR), and chemical stability. The DK and SG, as NF and RO membranes respectively, showed the highest potential for POX effluent treatment application. In the NF process, an average concentration factor of 2 was observed for metals concentration retentate at 50 % permeate RR. For metals, particularly for cobalt, nickel, and copper, this concentration was favorable to subsequent recovery processes. The RO generated a retentate with sulfuric acid 2.5 times more concentrated and low impurity content (0.00058 g L−1) and 40 % RR was chosen for the process considering the permeate quality, which can be used as reuse water. Besides that, the amount of lime demanded for neutralization in the proposed route is approximately 41 % lower compared to regular process. The results showed that for the designing system the membrane selection is a critical part, mainly due the effluent characteristics.

Reclamation of aqueous solution synthetically polluted with endocrine disturbing chemicals by commercial NF membrane

The target of this study is the removal of Di butyl phthalate, Bisphenol – A and Paracetamol as endocrine disrupting chemicals from aqueous solution using NF99 as a commercial nanofiltration membrane at different operating parameters of pressures (10, 20 and 30 bar), pH (3-11) and different EDCs concentrations using % TOC removal as indicator for the efficiency of the understudied membrane. It was found that the % TOC rejection of Paracetamol was the highest (86 %) at pH 10. The endocrine disrupting chemicals rejection was detected to be increased with the increase of operating pressure till 20 bar. The impactt of pH on %TOC removal of EDCs was altered depending on the pka of each compound. Moreover, the anti-fouling property of NF 99 membrane has been investigated by evaluating the membrane rejection and flux using humic acid as a common natural organic matter. The experimental design was estimated by MINITAB software and the results was analyzed by the factorial analysis which suggest that the pH is the most significant factor affecting the removal process.

DiaNanofiltration-based process for effective separation of Li+ from the high Mg2+/Li+ ratio aqueous solution

Lithium separation from salt lake brines with a high concentration of magnesium is challenging. In this work, separation efficiencies for Li+ and Mg2+ with three commercial NF membranes (NF-270, Desal-5DL, and Desal-5DK) were systematically investigated by DiaNanofiltration method. Experimental results showed that DiaNanofiltration was an effective technique to separate Li+ and reduce the high Mg2+/Li+ ratio from ternary salt solutions of LiCl and MgCl2. The solution-diffusion transport model was also used to calculate the real retention of Li+ and Mg2+, which predicted good agreement with the experimental results of the diafiltration process based on steric hindrance and the Donnan exclusion mechanism. NF270 membrane exhibited high permeation to Li+, about 90% for the ternary solution of LiCl + MgCl2 + H2O at a flux of 21.33 L·m−2·h−1. The real Mg2+ retention was attained around 96% with DK membrane, which was higher as compared to NF270 due to the steric hindrance effect. Moreover, the Mg2+/Li+ ratio was also reduced from 30 to 1.7 in the single-stage DiaNanofiltration process.

Fabrication and Properties of Nanofiltration Membranes Assembled with Chitosan on Poly(Ether Sulfone) Membranes Surface-Functionalized with Acyl Chloride Groups

Composite membranes with a cross-linked chitosan active layer (CS-membrane) on a poly(ether sulfone) (PES) support layer surface-functionalized with acyl chloride groups were fabricated as nanofilters. The support layers composed of PES and PES functionalized with amine groups (PES-Am) were surface-functionalized with acyl chloride groups (membrane-COCl). The membrane-COCl reacted further with amine groups in chitosan to form CS-membrane. The CS-membrane exhibited increased salt removal rates, antibacterial activity, and a decrease in water flux with increasing PES-Am content up to 20 wt % in the support layer. The CS-membrane formed on the support layers containing 20 wt % PES-Am and a commercial NF membrane showed almost the same MgSO₄ rejection (97.5%), whereas the former had about 1.4 times higher water flux than the latter. Consequently, NF membranes having better water flux, fouling resistance, and antibacterial activity than commercial NF membrane were fabricated without reducing salt rejection by assembling a cross-linked chitosan layer on a PES support layer surface-functionalized with acyl chloride groups.

Thin film composite nanofiltration membrane for lactic acid production in membrane bioreactor

In this work the thin film composite nanofiltration (TFC-NF) membrane was fabricated for lactic acid separation in membrane bioreactor. The morphological study was carried out with scanning electron microscopy (SEM) and atomic force microscopy (AFM). The SEM and AFM studies indicated that using interfacial polymerization causes a rough and dense film to be formed on the polyethersulfone (PES) support membrane. The permeate flux and separation properties of the membrane was investigated at 25 °C and trans membrane pressure (TMP) of 5 bar and was compared with 3 commercial NF membranes. The high lactose and low lactic acid rejection of 80% and 19% was obtained with TFC NF membrane. The membrane was used to produce lactic acid from whey lactose in membrane bioreactor (MBR). Continuous lactic acid production has two stages of Integration of fermentation and membrane separation which were assessed and compared to the conventional bioreactor performance (CBR). In order to produce lactic acid from whey, the Lactobacillus bulgaricus (ATCC 8001) was used in the process. The maximal productivity of 6.1 gL−1 h−1 was obtained at the dilution rate of 0.24 h−1, while the value obtained in the CBR was 3.4 gL−1 h−1 at the same dilution rate. The maximum concentration of lactic acid was obtained at the dilution rate of 0.04 h−1 in both MBR and CBR with values of 38.2 and 22.5 gL−1.