Tight Ultrafiltration Membranes Research Articles

Characterization of a support-free carbon nanotube-microporous membrane for water and wastewater filtration

Abstract Nonwoven carbon nanotube (CNT) laminates were characterized as support-free membranes for water filtration in terms of structural morphology, water permeability, selectivity and chemical resistance. Nominal pore rating (12–23 nm) estimated by rejection of globular proteins and fluorescence beads fall within the selectivity range of tight ultrafiltration (UF) membranes applied for wastewater treatment. The membranes displayed high permeability (120–400 LMH/bar). High selectivity regardless of high permeability seems to be due to tortuosity and pore structure of the membranes (25–50 μm thickness). The chemical stability of the membranes was tested towards common chemicals used for membrane cleaning (HCl, NaOH, NaClO) but at much severe conditions (24 h exposure at 4–10 fold higher concentrations). High resolution-X-ray photoelectron spectroscopy (XPS) was applied to evaluate chemical resistance. The relative C/O-carbon to oxygen ratio and typical deconvolution curves of C1s lines of the membranes after 24 h exposure depicted no significant changes compared to the reference samples, confirming resistance to chemical oxidation. This combination of features, added to simplicity of fabrication and post-synthesis modification and support-free configuration that enhances chemical stability, offer a worthwhile opportunity of application of these dense-array outer-walled CNT membranes in the UF range, especially at harsh conditions such as wastewater treatment.

Nanofiltration and Tight Ultrafiltration Membranes for the Recovery of Polyphenols from Agro-Food By-Products.

Pressure-driven membrane-based technologies represent a valid approach to reduce the environmental pollution of several agro-food by-products. Recently, in relation to the major interest for natural compounds with biological activities, their use has been also addressed to the recovery, separation and fractionation of phenolic compounds from such by-products. In particular, tight ultrafiltration (UF) and nanolfiltration (NF) membranes have been recognized for their capability to recover phenolic compounds from several types of agro-food by-products. The separation capability of these membranes, as well as their productivity, depends on multiple factors such as membrane material, molecular weight cut-off (MWCO) and operating conditions (e.g., pressure, temperature, feed flow rate, volume reduction factor, etc.). This paper aims at providing a critical overview of the influence of these parameters on the recovery of phenolic compounds from agro-food by-products by using tight UF and NF membranes. The literature data are analyzed and discussed in relation to separation processes, molecule properties, membrane characteristics and other phenomena occurring in the process. Current extraction methodologies of phenolic compounds from raw materials are also introduced in order to drive the implementation of integrated systems for the production of actractive phenolic formulations of potential interest as food antioxidants.

Hydrogel-embedded tight ultrafiltration membrane with superior anti-dye-fouling property for low-pressure driven molecule separation

A hydrogel-embedded tight ultrafiltration membrane composed of sodium polyacrylate-modified polyacrylonitrile with excellent anti-dye-fouling property can effectively separate dyes from salts.

Phase Inversion Directly Induced Tight Ultrafiltration (UF) Hollow Fiber Membranes for Effective Removal of Textile Dyes.

This study has demonstrated the application of tight ultrafiltration (UF) membranes for effective removal of textile dyes from water at a low pressure. Novel UF hollow fiber membranes with well-defined nanopores and surface charges were developed via a single-step spinning process without any post-treatment. The newly developed tight UF hollow fibers not only possess a small mean pore diameter of 1.0-1.3 nm with a molecular weight cutoff (MWCO) of 1000-2000 Da but also have a high pure water permeability (PWP) of 82.5-117.6 L m-2 h-1 bar-1. Through the synergistic effects of size exclusion and charge repulsion, the novel UF hollow fibers can effectively remove various dyes with impressive rejections of 93.2-99.9% at 1 bar. At the same time, more than 92% of inorganic salts (i.e., NaCl and Na2SO4) would permeate through the fibers, reducing the detrimental effects of concentration polarization and providing an attracted avenue for salts reuse. The tight UF hollow fibers also exhibit robust performance in a continuous operation of 170 h or at a high feed recovery of 90%. The fouled fibers can be easily regenerated by backwash of water with a flux recovery of larger than 92%. The newly developed tight UF hollow fiber membranes display huge potential for treating textile wastewater and other impaired effluents because of their great separation performance and simple fabrication process.

Remediation of Solutions Containing Oxyanions of Selenium by Ultrafiltration: Study of Rejection Performances with and without Chitosan Addition

Among the various technical options for removing ionic contaminants from wastewaters, membrane processes and especially their coupling with polymer addition have been proven to provide worthwhile prospects for the removal of metal cations. Nevertheless, their use for the removal of anionic pollutants such as oxyanions has been little studied in the literature. In the present work, the rejection of oxyanions forms of Se(IV) and Se(VI) by tight ultrafiltration membranes was deeply investigated under various experimental conditions. This paper aims at understanding the mechanisms governing oxyanion rejection and determining the potential ways to improve performances. It is first shown that selenium concentration and salt content play a leading role on performances, with high selenium rejection even if pores are noticeably larger than ions. Additionally, results reveal that the pH value also has a tremendous impact on performances due to its influence on both membrane and selenium charges. Finally, chitosan a...

Nanofiltration and Tight Ultrafiltration Membranes for Natural Organic Matter Removal-Contribution of Fouling and Concentration Polarization to Filtration Resistance.

Nanofiltration (NF) and tight ultrafiltration (tight UF) membranes are a viable treatment option for high quality drinking water production from sources with high concentrations of contaminants. To date, there is limited knowledge regarding the contribution of concentration polarization (CP) and fouling to the increase in resistance during filtration of natural organic matter (NOM) with NF and tight UF. Filtration tests were conducted with NF and tight UF membranes with molecular weight cut offs (MWCOs) of 300, 2000 and 8000 Da, and model raw waters containing different constituents of NOM. When filtering model raw waters containing high concentrations of polysaccharides (i.e., higher molecular weight NOM), the increase in resistance was dominated by fouling. When filtering model raw waters containing humic substances (i.e., lower molecular weight NOM), the increase in filtration resistance was dominated by CP. The results indicate that low MWCO membranes are better suited for NOM removal, because most of the NOM in surface waters consist mainly of humic substances, which were only effectively rejected by the lower MWCO membranes. However, when humic substances are effectively rejected, CP can become extensive, leading to a significant increase in filtration resistance by the formation of a cake/gel layer at the membrane surface. For this reason, cross-flow operation, which reduces CP, is recommended.

In situ surface crosslinked tight ultrafiltration membrane prepared by one-step chemical reaction-involved phase inversion process between activated PAEK-COOH and PEI

Carboxylated cardo poly(arylene ether ketone)s (PAEK-COOH) is a thermally stable and hydrophilic membrane fabrication material. Herein, PAEK-COOH was employed as membrane material, being dissolved in N-methyl-2-pyrrolidone (NMP) and 1,4-dioxane (DO) mixed solvent and activated by adding 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) to prepare polymer casting solution. Then the activated polymer film was immersed into polyethylenimine (PEI) aqueous solution that served as coagulation bath for taking the one-step chemical reaction-involved phase inversion process. As illustrated by the SEM images, the fabricated crosslinked tight ultrafiltration membrane had a dense and integrally skinned separation skin layer. Chemical composition and hydrophilicity of membrane surface were studied by ATR-FTIR and water contact angle, respectively. Those results revealed that, via the in situ crosslinking of activated carboxylic acid group and PEI along with the phase inversion process, the PEI molecules had been covalently bonded onto membrane surface and resulted in the increase of membrane hydrophilicity. The optimized membrane had a molecular weight cut off (MWCO) of 12.7kDa and an isoelectric point of 7.4, indicating which is slightly positively charged. The one-step chemical reaction involved phase inversion between reactive macromolecules, i.e., activated PAEK-COOH original polymer film and PEI crosslinker in coagulant, was an efficient and convenient approach for fabrication of highly permeable and selective tight ultrafiltration membranes. Membrane had a dye solution permeability of 80–84Lm−2h−1bar−1 and Congo red (CR) rejection of 99.9% in 100h long-term filtration testing, being capable for dye removal from textile wastewater.

Recovery of humic substances from leachate nanofiltration concentrate by a two-stage process of tight ultrafiltration membrane

Membrane bioreactor (MBR) and nanofiltration (NF) hybrid process has dominated in the treatment of leachate, however, NF concentrate generated from the process remains a challenge to be addressed. Given the high content of humic substances (HS) in NF concentrate, a promising approach by using a two-stage tight ultrafiltration (TUF) process for recovering HS as a water-soluble fertilizer was proposed. The effect of operating factors on membrane flux and rejection of organic matters, and the concentration and desalination performance of this TUF process were investigated on pilot scale. The pressure and temperature posed significant influence on the flux, while slight impact on the rejection of organics, and pH had negligible effect on the flux and the retention of organics. During the concentration and desalting process, the chemical oxygen demand (COD) retention increased slightly from 91% to 94%, and the rejections of divalent and monovalent ions had the respective range of 21–62% and 10–26%, except chloride ion with a negative rejection. The results demonstrated that HS dominated in organics could be effectively separated and refined from inorganic salts. The end concentrate achieved with the two-stage TUF process can meet the requirements of Chinese nation professional standards for water-soluble fertilizers containing HS. This study illustrates the feasibility of recycling HS from NF concentrate.

Tight ultrafiltration membrane: Preparation and characterization of thermally resistant carboxylated cardo poly (arylene ether ketone)s (PAEK-COOH) tight ultrafiltration membrane for dye removal

Cardo poly (arylene ether ketone)s bearing hydrophilic carboxylic acid groups (PAEK-COOH) was successfully synthesized by condensation polymerization of 2-[bis(4-hydroxyphenyl)methyl] benzoic acid and 4,4′-bisfluorodiphenylketone. TGA and DSC analyses demonstrated that the material has an initial decomposition temperature and glass transition temperature of 360°C and 220°C respectively, which revealed the excellent thermal stability of PAEK-COOH. Then PAEK-COOH was employed to fabricate tight ultrafiltration membrane by the nonsolvent induced phase inversion process (NIPS). The water contact angle of the prepared membrane is 61.5°, indicating its good hydrophilicity. The PAEK-COOH tight ultrafiltration membrane possesses a pure water flux of 119.6±2.6Lm−2h−1, dye permeation flux of 100.9±4.3Lm−2h−1 and rejection of 99.8±0.33% for Congo red at dye concentration of 100ppm and operation pressure of 0.4MPa. Membrane has a molecular weight cut off of 9260Da and gives complete penetration of monovalent inorganic salt NaCl but a slight rejection of divalent inorganic salt Na2SO4 (less than 10%). Thus, the membrane could be used in the decolorization of wastewater or fractionation of dye and salt mixture for dye purification. The membrane also exhibits excellent antifouling performance and anti-dye adsorption properties with a flux recovery ratio of 91.5% for BSA and dye adsorption rate below 5.0% for four kinds of studied dyes, respectively.

Tight ultrafiltration membranes for enhanced separation of dyes and Na2SO4 during textile wastewater treatment

Nanofiltration (NF) membranes have been used previously for the recovery of dyes, salts, and water from textile wastewaters with high salinity. However, commercially available NF membranes have a high rejection for divalent salts (i.e., Na2SO4), substantially reducing the salt recovery and membrane flux when treating textile wastewater containing Na2SO4. In this study, a tight ultrafiltration membrane (UH004, Microdyn-Nadir) was proposed to fractionate the dye and Na2SO4 in the textile wastewater. The UH004 membrane with a molecular weight cutoff of 4700Da provided complete passage of monovalent salts, with little rejection of Na2SO4. This significantly increases the filtrate flux that can be achieved with high-salinity wastewater since osmotic pressure and concentration polarization effects are minimized. Furthermore, the retention behavior of four different dyes was evaluated to determine the efficiency of this membrane process. This tight ultrafiltration membrane offered the high retention for direct dyes (i.e., direct red 80, direct red 23, and Congo red) and reactive blue 2. For instance, the UH004 membrane yielded >98.9% rejection for all of the dyes at a pressure of 4bar even in the presence of 60gL−1 Na2SO4. Subsequently, an ultrafiltration-diafiltration process was designed to separate a dye/Na2SO4 aqueous mixture with 98% desalination efficiency and greater than 97% dye recovery after 5 diavolumes. These results clearly demonstrate that tight ultrafiltration membranes can be a stand-alone alternative to NF membranes for the effective fractionation of dye and Na2SO4 in the direct treatment of high-salinity textile wastewater.

The ultrafiltration ceramic membrane used for broth separation in membrane bioreactor

In this work the studies of glycerol fermentation in a bioreactor connected with separation of broth by ultrafiltration process were presented. The study was carried out with broths, which were prepared using Citrobacter freundii bacteria. A tubular tight ultrafiltration ceramic membrane (8kD) was applied and the complete rejection of bacterial and other suspended solids was achieved. The produced permeate was clear, with a turbidity at a level of 0.1NTU. Although a tight ultrafiltration membrane was used, the ions retention was at a low level – below 10%. In a comparison with a classical method of fermentation with broth bleeding, the yield of fermentation was increased by the application of ultrafiltration for treatment of broth from the bioreactor. However, a significant (over 70%) permeate flux decrease was observed due to a fouling, which is an essential limitation in the application of the membrane separation. A periodical module rinsing with 1% NaOH solutions was used for limitation of the fouling influence on a flux decline.

Synthesis, preparation and characterization of UV-cured methacrylated polysulfone-based membranes

A new two-step method involving non-solvent induced phase separation (NIPS) and a UV curing process for the preparation of networked-polysulfone membranes is described. In this approach, first, methacrylated polysulfone macromonomers (PSU-DM)s were prepared by polycondensation followed by end-group esterification. PSU-DMs thin films containing phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (BAPO) photoinitiator cast on glass plates were successively subjected to NIPS and UV curing processes to produce the ultrafiltration membranes. The reverse sequence, i.e. first UV-curing followed by NIPS was also applied. Although different double bond conversions were attained, both procedures essentially yielded structurally analogous membranes which were insoluble in DMF, DMSO, and boiling water. UV-curing behavior, structure, thermo-mechanical and morphological properties of the membranes were investigated. Regardless of the preparation sequences, membranes exhibited pure water permeability in the range of tight ultrafiltration membranes.

Characterization of hydrophilic nanofiltration and ultrafiltration membranes for groundwater treatment as potable water resources

In this work, two hydrophilic nanofiltration (NF) membranes and a tight ultrafiltration (UF) membrane were studied for drinking water production from groundwater resources. Commercial membranes denoted as TS40, TFC-SR3, and GHSP were selected to investigate their performances. It was found that both NF membranes were hydrophilic with contact angle at 28°and 46°, respectively. The tight UF membrane was hydrophobic at contact angle of 68°. In the permeation test, both NF membranes exhibited higher permeability in pure water (4.68 and 3.99 L m−2 h−1 bar−1) than UF membrane (3.15 L m−2 h−1 bar–1). The order of single salt rejection by NF membranes were identified as R (Na2SO4) > R (MgCl2) > R (NaCl), whereas for UF membrane was R (Na2SO4) > R (NaCl) > R (MgCl2). A primary assessment of groundwater treatment for potable water showed that the highlighted components were characterized mainly by color, turbidity, and total dissolved solid (TDS) at 49 PtCo, 14 NTU, and 25 mg/L, respectively. The NF membrane, especially the TFC-SR3, was more efficient at rejecting these components, in quantities of 3 PtCo of color, 0.2 NTU of turbidity, and 10.5 mg/L of TDS, whereas the UF membrane attained 23 PtCo of color, 1.7 NTU of turbidity, and 17.6 mg/L of TDS. In conclusion, the findings on the quality of treated water verified that hydrophilic NF membrane performed well as a promising new technology for groundwater treatment in Malaysia.

Environment-benign preparation of Ag toughening TiO2/Ti tight ultrafiltration membrane via aqueous sol–gel route

A new aqueous sol was synthesized to prepare Ag-doped TiO2/Ti composite tight ultrafiltration (UF) membranes. This sol was prepared based on water (>95 wt%), for which the hydrodynamic size of 8 nm could be obtained by tuning the electrostatic and steric repulsive forces, breaking the limit of the polymeric sol–gel method to prepare tight UF membranes. For the preparation of the sol, high water content can significantly reduce the use of organic solvents and is more environment-benign. Moreover, Ag doping can considerably improve the toughness of the supported membranes to efficiently prevent the TiO2/Ti composite membranes from cracking and overcome the thermal expansion mismatch of ceramic membranes and their metallic supports. The prepared Ag-doped TiO2/Ti composite membranes presented a molecular weight cut-off of 3 kDa with a pure water flux of 24 L m−2 h−1 bar−1 and exhibited good dye removal capabilities. The proposed Ag doping method has considerable potential for the fabrication of integrated hybrid ceramic–metallic composite membranes.

A facile nanoparticle doping sol–gel method for the fabrication of defect-free nanoporous ceramic membranes

Enhanced α-alumina tight ultrafiltration (UF) membranes were fabricated by using a facile nanoparticle doping sol–gel method. The addition of nanoparticles could not only promote the phase transition of alumina from γ to α phase at low temperature, but also play an important role in the defect-patching of substrate during the layer-forming process. The membrane surface was defect-free and smooth. Additionally, a relatively small pore size was observed. The nanoparticle doping sol–gel method showed a good potential for fabricating such integrated UF membranes, which are high performance interlayers for ceramic nanofiltration (NF) membranes.

Multiple MFI measurements for the evaluation of organic fouling in SWRO desalination

A series of MFI (modified fouling index) measurements were performed to evaluate and predict organic fouling potential and mechanism in seawater reverse osmosis (SWRO) desalination, by employing a multiple membrane array system (MMAS) in which microfiltration (MF), loose and tight ultrafiltration (UF) membranes were configured in a consecutive manner to determine the MFIs of particles, colloids, and organics. The results suggested that organic fractions manifested by colloid-MFI should be removed to control organic fouling effectively, as the organic fraction with MW ranging from 30 to 300kDa led to the most severe fouling in RO experiments. The variations in fouling potential according to solution conditions (i.e., pH and Ca2+) were also more accurately evaluated using multiple MFIs than with conventional SDI. This work demonstrated that the current fouling index, relying on a single membrane, could be improved by utilizing multiple membranes with different characteristics (e.g., pore size and hydrophobicity) to assess the fouling behavior of specific organic fractions.

Cellulose nanopapers as tight aqueous ultra-filtration membranes

Recently, we have demonstrated the use of wood-derived nanocellulose papers, herein termed nanopapers, for organic solvent nanofiltration applications. In this study, we extend the use of these nanopapers to tight ultrafiltration (UF) membranes. The feasibility of such nanopaper-based UF membranes intended for use in water purification is shown. Four types of nanocelluloses, namely bacterial cellulose, wood-derived nanocellulose, TEMPO-oxidized cellulose nanofibrils and cellulose nanocrystals, were used as raw materials for the production of these nanopaper-based membranes. The resulting nanopapers exhibit a transmembrane permeance in the range of commercially available tight UF membranes with molecular weight cut-offs ranging from 6 to 25kDa, which depends on the type of nanocellulose used. These molecular weight cut-offs correspond to average pore sizes of a few nanometres. The rejection performance of the nanopapers is on the border of nanofiltration and UF. We demonstrate that the pore size of the nanopapers can be controlled by using different types of nanocellulose fibrils.

Recovery of caustic from mercerizing wastewaters of a denim textile mill

The objective of this study was to evaluate caustic recovery from mercerizing wastewater originating from a denim textile producing plant using membrane technology. For this purpose, ultrafiltration (UF) and nanofiltration (NF) processes were considered. In the first stage, in an attempt to control the possible membrane fouling, pretreatment alternatives of flocculation, centrifugation, and microfiltration were evaluated. These pretreatment application alternatives were unsuccessful as they did not provide considerable color and solids removal. In the second stage, UF and NF processes were tested using a tight UF membrane (GR95PP, Alfalaval) and three NF membranes (NP010 and NP030, Microdyn Nadir, and MPF34, Koch Membranes) to accomplish the caustic recovery without applying any pretreatment. The best performance was obtained with NP010 NF in terms of permeate flux along with color and COD rejections. Then, for this membrane the effects of transmembrane pressure (4.03 and 6.23 bar), cross-flow velocity (from 0.40 to 1.40 m/s), and feed temperature (20 and 40°C) were investigated. Temperature positively affected the permeate flux without significant loss in recovery and rejections. Caustic stream produced had about 98–100% of NaOH in the feed at a concentration of 30–40 g/L and therefore was recyclable after a concentration process.

Membrane treatment of the bleaching plant (EPO) filtrate of a kraft pulp mill

The objective of this study was to evaluate the use of membrane technology to treat oxygen and peroxide-reinforced extraction stage (EPO) filtrate from a kraft pulp mill bleach plant. Three different types of tubular membranes were tested in a pilot plant: (i) tight ultrafiltration (UF); (ii) open UF followed by nanofiltration (UF+NF); and (iii) nanofiltration (NF). According to the separation performance, considering the chemical oxygen demand (COD) and colour removal, permeate flux, operational simplicity and cost, the results indicated that the best option for treatment of (EPO) filtrates was the tight UF membrane. This membrane obtained a COD removal of 79% with a colour reduction of 86%. The effect of (EPO) filtrate UF treatment on the mill effluent treatment plant was evaluated. Compared with the actual mill effluent, the results indicated that if the UF permeate was recycled in the bleaching area, the COD reduction efficiency increased by 7%, the final effluent colour decreased by 8%, the biological sludge production decreased by 18%, and the energy consumption decreased by 40%. In the tertiary treatment plant, the coagulant dosage decreased by 40%, and the tertiary sludge production decreased by 46%.

The impact of EfOM, NOM and cations on phosphate rejection by tight ceramic ultrafiltration

Reverse osmosis (RO) systems for secondary effluent water reuse frequently encounter severe biofouling due to the high nutrient concentration in the RO feed water. Deployment of negatively charged tight ceramic ultrafiltration (UF) may restrict biofouling in RO by phosphate limitation, since the tight ceramic UF can reject dissolved phosphate by electrostatic interactions. However, the organic matter and cations can potentially impact phosphate rejection by tight ceramic UF. In this study, the effects of organic matter and Ca2+ on phosphate rejection by the 3kDa tight ceramic UF membrane were investigated, using synthetic water containing natural organic matter (NOM) and effluent organic matter (EfOM), as well as secondary effluent water. Phosphate rejection was found to be linearly correlated to the zeta potential of the organics in the membrane feed water when the membrane was fouled by NOM. Furthermore, the EfOM-fouled membrane yielded higher phosphate rejection than the membrane fouled by the NOM due to additional adsorption of phosphate by the biopolymers. A preferential phosphate rejection was observed during effluent water filtration by the 3kDa tight ceramic UF membrane.