Membrane Fouling Resistance Research Articles

High-performance polyethyleneimine based reverse osmosis membrane fabricated via spin-coating technology

Conventional thin-film composite (TFC) reverse osmosis (RO) membranes prepared by ultrafast and uncontrolled interfacial polymerization (IP) generally have unsatisfactory permeability and high fouling propensity, which distinctly impedes their development and wide application. Controllable thickness and roughness offer an opportunity to optimize the permeability and fouling resistance of RO membranes. In this work, we propose spin-coating assisted multilayer interfacial polymerization (SMIP) as a promising approach to fabricating high-performance RO membranes using polyethyleneimine (PEI) and 1, 3, 5-benzoyl chloride (TMC). SMIP integrates the high efficiency and uniformity of spin-coating technology, the nano-level and individual properties control of multilayer interfacial polymerization, and the simplicity of the IP process. Combining the strong hydrophilicity with low diffusion efficiency and positive charge of PEI, a thin, intrinsically hydrophilic, smoother and almost electro-neutral polyamide (PA) nanofilm was obtained. The optimal RO membrane with a controlled thickness of the selective layer (≈61 nm) has a water permeance of 3.12 L m−2 h−1 bar−1 and an acceptable NaCl rejection of 97.5%, while the strong hydrophilicity, minimal surface roughness and almost neutral surface charge afford it excellent fouling resistance. SMIP technology not only provides a new approach to preparing highly permeable and low-fouling RO membranes using macromolecular monomers, but also has great application potential in other separation membranes due to its precise control of the selective layer.

A comparative evaluation of reverse osmosis membrane performance when combined with anaerobic or aerobic membrane bioreactors for indirect potable reuse applications

The filtration performance and fouling behaviour of reverse osmosis (RO) membranes was investigated for the post-treatment of aerobic (Ae) and anaerobic (An) MBR effluents treating municipal wastewater for potable reuse. Both MBR effluents followed by RO can produce a water quality sufficient for indirect potable water reuse, while fluorescence excitation-emission scan suggests RO can effectively remove disinfection by-products precursors, ensuring the safety for chlorine based reuse water distribution by rejecting the dissolved organic matters in MBR effluents. AnMBR effluent leads to more fouling when compared to the AeMBR effluent with an average membrane fouling resistance of 12.35 × 1013 m−1 and 8.97 × 1013 m−1. Elemental analysis and membrane surface imaging results demonstrate that the foulant deposition sequence is organic and colloidal at first, followed by inorganic substances, while TOC and Ca are the most deposited foulants from both effluents. The unremoved ammonia in the AnMBR effluent may partially go through in the RO permeate and exceed the threshold in Singapore's PUB NEWater standard, while experiencing a significantly higher deposition rate of 13.8 % than the nitrate (0.02 %) from the AeMBR effluent. The findings suggest that the combination of AnMBR with RO offers a more sustainable approach than with the AeMBR but nutrients removal, with the potential of recovery, is recommended before the RO membranes to limit the fouling propensity and achieve a permeate of sufficient quality.

Monitoring of experimental landfill cells with membrane concentrate infiltration: A systematic assessment of leachate quality and treatment performance

The present study investigates the impacts of reverse osmosis concentrate (ROC) infiltration on the leachate quality and treatment performance. Simulated landfill cells were constructed and monitored for 254 days. Integrated leachate samples were treated using a reverse osmosis (RO) system to assess changes in leachate quality on membrane fouling and effluent ecotoxicity. Our findings showed that concentrate infiltration increased the leachate's organic content and recalcitrance. The pollution parameters' median values were higher in leachates drained from cells that operated with ROC recirculation (i.e., 6729 vs 1367 mg L−1 [chemical oxygen demand, COD], 33.39 vs 17.39 cm−1 [absorbance at 254 nm, UV254]; p-value < 0.05). Membrane fouling resistance was 6-fold higher when the RO system was used to treat the methanogenic leachates generated by cells operating at ROC infiltration mode. The ecotoxicological assessment using Vibrio fischeri bacteria indicated that membrane concentrate recirculation increases leachate ecotoxicity and decreases its removal efficiency by RO treatment. The current research provides information to re-examine the recirculation practice of leachate concentrate streams. Recommendations and research prospects are drawn in this context.

A review of seawater desalination with membrane distillation: material development and energy requirements

Abstract The importance of membrane technology development in our daily life cannot be overemphasized. Over the past decades, membrane technology has become very popular in providing potable water for mankind. However, old technologies (such as reverse osmosis and ultrafiltration) which are highly energy intensive are still very common in water treatment industries. In this review, the capability of low energy consumption membrane distillation (MD) technology is reviewed with emphasis on material development and energy requirement. We begin by reviewing the history of the MD process, configurations, module types, membrane materials, material fabrication methods, material properties, material modification techniques, application, and energy requirements. Factors which influence the performance of MD – both design and operating conditions – are then extensively discussed. Furthermore, we report desalination and wastewater treatment as the hottest areas of application where MD has gained significant interest. Membrane hydrophobicity and fouling resistance are identified as pivotal areas where improvement in MD performance is being sought. We then discuss various industries where MD is presently being applied. We conclude by highlighting the energy requirements of MD and identify solar energy as a renewable energy resource which could meet the energy requirement of MD technology. It is hoped that this review paper will foster interest in and provide insights on material development for membrane distillation application.

Dynamic scouring of multifunctional granular material enhances filtration performance in membrane bioreactor: Mechanism and modeling

The granular material (GM) is able to effectively improve the membrane fouling control in membrane bioreactor (MBR) by dynamic scouring, adsorption behavior and enzymatic degradation. However, their roles and effects on the filtration performance of MBR remain unclear. The present work investigated the GM dynamic scouring mechanism, revealed the multifunctional quantitative evaluation, and clarified the filtration performance at various GM operating conditions in MBR. First, the aerobic granular sludge (AGS)-filtration process was still limited by the presence of irreversible membrane fouling, which decreased the filtration performance in MBR (threshold flux [169.5 L m−2 h−1] and (turning point of membrane fouling resistance [1.1 × 1012 m−1]). To solve this problem, the GMs (activated carbon [AC] and laccase immobilized activated carbon [LAC]) was added into the AGS-filtration process to enhance the filtration performance. Above all, based on momentum conservation, the dynamic scouring mathematical model was put forward to elucidate the dynamic scouring mechanism of GM towards the membrane surface. The scouring stress on the membrane surface was proportional to the total mass of GM and offered an additional shear effect for clearly promoting the collision between GM and foulant, and decreasing their deposition on the membrane surface via friction with the membrane. Then, both AC and LAC exhibited a highly desirable adsorption efficiency for foulant removal, whereas the enzymatic degradation of LAC also furtherly straightened this effect. Furthermore, a new contribution quantification model was proposed for evaluating the contribution rates of dynamic scouring (59.1%), adsorption behavior (36.4%) and enzymatic degradation (4.6%) to boost the filtration performance, implying that the dynamic scouring and adsorption behavior brought about the dominated promotion. At the GM of 8 g/L and size of 300–600 μm, AGS-filtration exhibited an optimized performance in term of threshold flux, turning point of membrane fouling resistance and membrane cleaning. The present study offers insights into the mechanism that GM multifunctional scouring enhanced filtration performance in MBR.

Novel negatively-charged amphiphilic copolymers of PVDF-g-PAMPS and PVDF-g-PAA to improve permeability and fouling resistance of PVDF UF membrane

Novel negatively charged polyvinylidene fluoride (PVDF) membranes containing amphiphilic copolymer additives: PVDF-g-2-acrylamido-2-methylpropane sulfonic acid (PVDF-g-PAMPS) and PVDF-g-acrylic acid (PVDF-g-PAA) were synthesized via the phase inversion method. The formation of functional groups and chemical composition of the synthesized amphiphilic copolymers ((PVDF-g-PAMPS) and (PVDF-g-PAA)) were investigated by Fourier transform infrared (FTIR) spectroscopy and 1H nuclear magnetic resonance (1H NMR) spectroscopy. The characterization of the copolymerized blended membranes ((PVDF-g-PAMPS/PVDF) and (PVDF-g-PAA/PVDF)) were investigated by using ATR-FTIR, SEM, AFM, porosity, mean pore radius, water contact angle, zeta potential, and mechanical stability techniques. The membrane hydrophilicity and antifouling performance of the copolymerized membranes were evaluated using the filtration performance. It was found that the negatively charged modified membranes with 10 wt% PVDF-g-PAMPS and 10 wt% PVDF-g-PAA presented a significant pure water flux (181.6 and 336.7 L/m2h, respectively at 0.2 MPa) and an outstanding flux recovery ratio (FRR) (up to 100%) in comparison with the original PVDF (97.5 L/m2h and 74%). Besides, the surface zeta potential of the copolymerized membranes confirmed noteworthy negatively charged in the copolymer surface, which showed better performance of BSA protein and Direct Red 23 dye rejection capability of 100% and more than 99%, respectively. The strong synergetic impacts of hydrogen bonding and the electrostatic repulsion of negatively charged grafted sulfonic and carboxylic groups against protein foulants were ascribed to the increased performance of the copolymerized blended membranes.

Application of g-C3N4/ZnO nanocomposites for fabrication of anti-fouling polymer membranes with dye and protein rejection superiority

Polysulfone (PSf) membranes are privileged for water and wastewater treatment, but because of their hydrophobic nature, they suffer from fouling, which lowers their performance and lifetime. In this work, g-C3N4 and g-C3N4/ZnO nanomaterials were synthesized via a hydrothermal method to modify the PSf membrane for effective dye separation and reduction of organic fouling. Since g-C3N4/ZnO possesses –OH and –NH reactive groups, g-C3N4/ZnO/PSf membrane revealed higher porosity, hydrophilicity, negative surface charge, and lower contact angle. The results of filtration analysis also showed a higher performance for nanomembranes with respect to the neat PSf. Permeability and fouling resistance of neat PSf membrane were well below those of nanocomposite membranes, such that by incorporation of 0.5 wt% g-C3N4/ZnO nanocomposite in PSf they significantly improved to 85.93 L/m2 h bar and 90%, respectively. The rejection rate was also increased for both types of dyes used in this study (99.9% for Reactive green 19 and 85.5% for Reactive Yellow 160). The outcome of this research would suggest the application of graphitic nitride nanomaterials for developing highly efficient polymer membranes.

Zwitterion grafted forward osmosis membranes with superwetting property via atom transfer radical polymerization

AbstractA superwetting forward osmosis membrane was prepared by grafting a zwitterion (2‐methacryloyloxyethyl phosphorylcholine, MPC) onto the polyamide membrane layer via atom transfer radical polymerization (ATRP) to enhance antifouling property. The modification of the hydrophilic layer was confirmed by the characterization including Fourier‐transform infrared spectroscopy (FTIR), X‐ray photoelectron spectroscopy (XPS), and contact angle goniometer. Moreover, membrane antifouling performance was evaluated by dynamic membrane fouling test using bovine‐serum‐albumin (BSA) and sodium alginate (SA). The grafted membranes not only showed high fouling resistance after being exposed to up to 500 ppm SA for 10 h, but also demonstrated excellent water flux recovery with the presence of up to 1000 ppm BSA, which was significantly improved as compared to the unmodified membrane. Robust hydration layer formed by the grafted zwitterion polymer could act as a physical and energy barrier preventing attachment of organic foulants on the membrane surface, thus significantly improving membrane fouling resistance.

Mechanism study on the effect of peracetic acid (PAA), UV/PAA and ultrasonic/PAA oxidation on ultrafiltration performance during algae-laden water treatment

In this work, peracetic acid (PAA), ultraviolet (UV)/PAA and ultrasonic (US)/PAA pre-oxidation were applied to enhance ultrafiltration (UF) performance during algae-laden water treatment. The results showed that 10 mg/L PAA, exhibiting an optimal performance with membrane fouling resistance reduced by 76.26%. Low dosage of UV/PAA can effectively control fouling by enhancing the degradation of dissolved organics. Though more radicals were generated with the increasing dosage of PAA during the UV/PAA process, flux deterioration was occurred when PAA dosage over 10 mg/L, owing to a negative correlation between fouling resistance and algal integrity loss. Compared with UV, US exhibited a worse activation effect on PAA with less reactive radicals produced. Even worse, US can stimulate the stress metabolism of algal cells with slightly integrity loss, which then resulted in an exacerbation of permeate quality. Fouling mechanism analysis revealed that the delay formation of cake layer with membrane fouling alleviation mainly through efficient degradation of macromolecular organics. The investigation of synergistic and individual effect of EOM degradation, algae rupture and IOM release on the filtration performance revealed that EOM degradation was the primary mechanism for fouling control while algae rupture rather than IOM release was crucial for membrane fouling aggravation. This indicates that moderate oxidation, with property of high organic degradation and low cell rupture, was the working principal and objectives for algae-laden water treatment. Additionally, it was found that the ·OH radicals produced during UV/PAA process can efficiently degrade representative odors. In general, pretreatments of PAA and low dosages of UV/PAA showed promising prospects in improving the UF performance of algae-laden water and treating algal secretions.

Effect of Fe(II)-Activated Peroxymonosulfate (PMS) on the Performance of Ultrafiltration (UF) Process for Secondary Effluent Treatment and Reuse

The secondary effluent of the wastewater treatment plant is considered as one of the reused water sources and needs advanced treatment to meet increasingly stringent water treatment standards. Ultrafiltration, as one of the most widely used advanced treatment technologies, is limited due to membrane fouling, and coagulation and pre-oxidation have received extensive attention as pretreatment methods to alleviate membrane fouling. This research proposes a new method of Fe(II)-activated peroxymonosulfate (PMS) coagulation and a pre-oxidation system coupled with ultrafiltration (UF) to treat secondary effluent from sewage plants, separately evaluating the treatment effect under different molar ratios of Fe(II)/PMS. The Fe(II)/PMS decontamination mechanism and membrane fouling control effect were elucidated through pollutant removal efficiency, membrane morphology, membrane flux trend, and membrane fouling resistance distribution. According to the experimental results, the optimal effect of organic matter removal and membrane fouling mitigation was achieved at the Fe(II)/PMS dosage of 60/60 μM/μM (molar ratio 1:1). The efficiency of pretreatment methods in removing organics and fluorescent components and mitigating membrane fouling followed the order of Fe(II)/PMS &gt; Fe(III) &gt; inactivated PMS. Fe(II)/PMS could produce a synergistic effect in a high concentration state (60 μM), relying on the dual effects of coagulation and oxidation to alleviate membrane fouling. Coagulation and pre-oxidation by Fe(II)/PMS significantly reduced the clogging of membrane pores and the proportion of irreversible resistance, effectively controlling membrane fouling and improving effluent quality. SEM images further confirmed its effectiveness, and EPR results unequivocally indicated that its synergistic mechanism was mediated by •OH and SO4•−. The research results can provide ideas for advanced wastewater treatment and secondary effluent reuse.

Graphene-Coated PVDF Membranes: Effects of Multi-Scale Rough Structure on Membrane Distillation Performance.

Graphene-coated membranes for membrane distillation have been fabricated by using a wet-filtration approach. Graphene nanoplatelets have been deposited onto PVDF membrane surfaces. Morphology and physicochemical properties have been explored to evaluate the changes in the surface topography and related effects on the membrane performance in water desalination. The membranes have been tested in membrane distillation plants by using mixtures of sodium chloride and humic acid. The multi-scale rough structure of the surface has been envisaged to amplify the wetting and fouling resistance of the graphene-coated membranes so that a better flux and full salt rejection have been achieved in comparison with pristine PVDF. Total salt rejection and an increase of 77% in flux have been observed for coated membrane with optimized graphene content when worked with NaCl 0.6 M (DCMD, ΔT ≈ 24 °C) over a test period of 6 h. The experimental findings suggest these novel graphene-coated membranes as promising materials to develop functional membranes for high-performing water desalination.

Semi-aromatic polyamide membrane incorporated with yolk-shell mesoporous hybrid nanospheres for ultrahigh permeability and improving comprehensive property

In this report, yolk-shell (YS) organic-inorganic hybrid nanospheres (YSHNs) with radially ordered mesopores were synthesized by a co-assembly strategy using 1,2-bis(triethoxysilyl)ethane and tetraethoxysilane as precursors, and cetyltrimethylammonium bromide as a soft template. Then, Silver nanoparticles (AgNPs) were uniformly embedded in the hollow cavities of the YSHNs. The semi-aromatic polyamide (SAP) based nanocomposite membrane was fabricated using 1,3,5-cyclohexane tricarbonyl chloride as an organic phase, meta-phenylene diamine as an aqueous phase, and the mesoporous YS hybrid nanospheres as nanoadditives by an interfacial polymerization approach. The results show that the YS nanospheres were successfully incorporated into the polyamide (PA) separation layer, and the membrane becomes very hydrophilic. The membrane incorporated with the aminated YS mesoporous nanospheres exhibits ultrahigh pure water permeability (PWP, 9.34 L m−2 h−1 bar−1) and comparable NaCl rejection (96.1%), which is dramatically higher than the membrane with common mesoporous nanospheres. It is because that the hollow cavity of the YS nanosphere further decreases the membrane resistance, and the aminated spherical surface improves the interfacial compatibility between the PA matrix and the YS nanospheres. Furthermore, the flexible YS hybrid structure and the mesoporous core could play an important buffering for avoiding the shell fracture under a high operation pressure. The chlorine resistance of the YS-nanosphere incorporated membrane is significantly improved compared to the pristine SAP membrane in a strong chlorination strength (5500 ppm h, pH = 5). The confined AgNPs in the YS mesostructure endow the membrane with a sustainable antibiofouling property. Moreover, the polylysine modification improves the membrane fouling resistance and performance stability.

A sacrificial protective layer as fouling control strategy for nanofiltration in water treatment

High-performance nanofiltration (NF) membrane with super antifouling capability as well as reusability is highly desired in water treatment. A new antifouling strategy by a coating-decoating-recoating cycle was investigated for effective removal of fouling and restoring the original membrane performance. The functional membrane surface was fabricated by in-situ coating a ‘green’ and biodegradable carboxymethyl chitosan (CMCS) layer as physical barrier. The CMCS layer can be decoated and re-coated by simple procedures. Results showed that (i) the CMCS layer enhanced surface hydrophilicity, surface smoothness and fouling resistance of NF membrane, (ii) both the unfouled and fouled CMCS layer were easily decoated by the strong acid solution, (iii) the CMCS layer was easily re-coated by facile recoating and (iv) the water flux recovery ratio of membrane with coating layer was maintained more than 88.8% during fouling testing by natural organic matter (NOM) after four sequential cycles of coating, decoating and recoating process. The re-coated membrane exhibited stable, improved membrane operational and antifouling performance. The coating-decoating-recoating approach is proven to be low-cost and eco-friendly strategy for NOM fouling control on NF membrane in water treatment applications.

A Polysulfone/Cobalt Metal–Organic Framework Nanocomposite Membrane with Enhanced Water Permeability and Fouling Resistance

Ultrafiltration membranes are widely used in water and wastewater applications. The two most important membrane characteristics that determine the cost-effectiveness of an ultrafiltration membrane process are membrane permeability and fouling resistance. Metal–organic frameworks (MOFs) have been intensively investigated as highly selective sorbents and superior (photo) catalysts. Their potential as membrane modifiers has also received attention recently. In this study, a non-functionalized, water-stable, nanocrystalline mixed ligand octahedral MOF containing carboxylate and amine groups with a cobalt metal center (MOF-Co) was incorporated into polysulfone (PSF) ultrafiltration (UF) membranes at a very low nominal concentration (2 and 4 wt %) using the conventional phase inversion method. The resultant PSF/MOF-Co_4% membrane exhibited water permeability up to 360% higher than of the control PSF membrane without sacrificing the selectivity of the membrane, which had not been previously achieved by an unmodified MOF. In addition, the PSF/MOF-Co_4% membrane showed strong resistance to fouling by natural organic matter (NOM), with 87 and 83% reduction in reversible and irreversible NOM fouling, respectively, compared to the control PSF membrane. This improvement was attributed to the increases in membrane porosity and surface hydrophilicity resulting from the high hydrophilicity of the MOF-Co. The capability of increasing membrane water permeability and fouling resistance without compromising membrane selectivity makes the MOF-Co and potentially other hydrophilic MOFs excellent candidates as membrane additives.

Stable fouling resistance of polyethylene (PE) separator membrane via oxygen plasma plus zwitterion grafting

Low-cost and fouling resistant microfiltration/ultrafiltration membranes for wastewater treatment has been a challenging task when balancing the membrane cost and performance stability. Herein, a low-cost polyethylene (PE) lithium-ion battery separator was explored as a potential solution. To tackle the intrinsic hydrophobic character which incurs severe fouling, a novel cascade process of plasma treatment plus zwitterion grafting was designed: first oxygen plasma to endow oxygen-containing groups for hydrophilicity and supply “grafting sites”, and grafting zwitterion 3-[[3-(trimethoxysilane)-propyl] amino] propane-1-sulfonic acid (TMAPS) for robust fouling resistance. The membranes were analyzed by water contact angle, Fourier-transform Infrared Spectroscopy (FTIR), Energy Dispersive Spectroscopy (EDS), and X-ray Photoelectron Spectroscopy (XPS). Challenged by two typical foulants, e.g., humic acid (HA) and bovine serum albumin (BSA), the zwitterion grafted membrane showed the best antifouling performance. Oxygen plasma treated PE membrane presented a better performance towards HA than to BSA. The Resistance-in-Series model revealed that the plasma-treated membrane showed improvement in reversible resistance but not in irreversible resistance. Migration of hydrophobic PE segment to the surface due to the low glass transition temperature was attributed to the low fouling resistance of the plasma-treated membrane. However, the zwitterion-grafted membrane led to stabilized hydrophilicity and inhibited the hdrophobic-hydrophobic interaction between the membrane and foulant, thus resulting to significantly improved flux recovery and low irreversible fouling rate. This study clarified that oxygen plasma alone is not sufficient to provide sufficient fouling resistance, but grafting with zwitterion provides stable hydrophilicity and fouling resistance.

MXene (Ti3C2Tx)/Cellulose Acetate Mixed-Matrix Membrane Enhances Fouling Resistance and Rejection in the Crossflow Filtration Process

Obstacles in the membrane-based separation field are mainly related to membrane fouling. This study involved the synthesis and utilization of covalently crosslinked MXene/cellulose acetate mixed matrix membranes with MXene at different concentrations (CCAM-0% to CCAM-12%) for water purification applications. The membranes’ water flux, dye, and protein rejection performances were compared using dead-end (DE) and crossflow (CF) filtration. The fabricated membranes, especially CCAM-10%, exhibited high hydrophilicity, good surface roughness, significantly high water flux, high water uptake, and high porosity. A significantly higher flux was observed in CF filtration relative to DE filtration. Moreover, in CF filtration, the CCAM-10% membrane exhibited 96.60% and 99.49% rejection of methyl green (MG) and bovine serum albumin (BSA), respectively, while maintaining a flux recovery ratio of 67.30% and an irreversible fouling ratio at (Rir) of 32.70, indicating good antifouling performance. Hence, this study suggests that covalent modification of cellulose acetate membranes with MXene significantly improves the performance and fouling resistance of membranes for water filtration in CF mode relative to DE mode.

Investigation of fluoride and silica removal from semiconductor wastewaters with a clean coagulation-ultrafiltration process

Fluoride and silica contamination in water is a worldwide issue due to the wastewater discharge from semiconductor industry. Coagulation-ultrafiltration (UF) process is commonly used to treat semiconductor wastewaters, but it requires excessive amounts of coagulant/flocculant. In this study, a clean coagulation-UF process using chemical mechanical polishing (CMP) wastewater as a coagulant to treat fluoride-containing wastewater was firstly proposed. The fluoride-containing wastewater, CMP wastewater, mixed fluoride-containing wastewater and CMP wastewater, and mixed fluoride-containing wastewater and polyaluminium chloride/polyacrylamide were compared to investigate turbidity removal efficiency, fluoride removal efficiency and membrane fouling resistance. The negatively charged SiO2 particles in CMP wastewater were found to be adsorbed on the positively charged CaF2 particles surface through electrostatic interaction. Results indicated that CMP wastewater provided a superior turbidity removal efficiency and a minimal membrane fouling resistance compared to conventional coagulant. After UF filtration, the fluoride concentration and turbidity were 2.09 mg L−1 and 0 NTU, respectively, which met the median fluoride effluent standard. The extended Derjaguin-Landau-Verwey-Overbeek theory showed that increasing molar ratio of SiO2 to CaF2 improved the interfacial free energy between membrane and suspended particles, thus mitigating membrane fouling. This clean design principle and strategy will broaden the sustainability of coagulation-UF process for wastewater treatment.

Liposome-integrated seawater reverse osmosis membrane prepared via facile spray-assisted interfacial polymerization

In this work, we demonstrated the effectiveness of using spray-assisted interfacial polymerization (IP) technique in fabricating liposome-integrated thin film nanocomposite (TFN) membranes for seawater reverse osmosis (SWRO). The liposome loading within the selective polyamide (PA) layer of the TFN membrane can be precisely controlled by manipulating spraying conditions to eliminate the wastage of precious additives compared to the conventional blending method. Spraying the liposomes after applying the aqueous phase of M-phenylenediamine (MPD) could prevent the loss and disruption of liposome distribution over the substrate layer. Upon incorporating 4 mg/m2 of liposomes, the best-performing S4-a membrane is able to achieve 27% higher water permeability than the liposome-free membrane, demonstrating a permeability of 3.24 L/m2·h·bar along with 99.3% NaCl rejection for seawater desalination. Characterization showed that dynamic liposomes had affected the IP process by creating a larger miscible reaction zone for IP, which led to the formation of a rougher PA surface with more nanovoids in the ultra-thin selective layer, thus, contributing to higher effective surface area and less hydraulic resistance for improving water permeability. An additional PVA layer was coated atop the liposome-integrated membrane to effectively improve the membrane stability and fouling resistance, leading to a comparable level of salt rejection with the state-of-the-art commercial membranes in treating real seawater, while water permeability was enhanced by 26–185%. This work presents a readily scalable spray-assisted IP technique to fabricate liposome-integrated SWRO membrane for seawater desalination.

Optimal Water Backwashing Condition in Combined Water Treatment of Alumina Microfiltration and PP Beads.

Membrane fouling is a dominant limit of the membrane separation process. In this research, the optimal water backwashing to solve the membrane fouling problem was investigated in the combined water treatment process of alumina MF and pure polypropylene (PP) beads. Additionally, the influence of membrane shape (tubular or seven channel) was examined, depending on the water backwashing period. The optimal backwashing time (BT) could be 20 s in the combined water treatment process, because of the highest total treated volume (VT) in our BT 6–30 s conditions. The optimal backwashing period (BP) could be 6 min, because of the minimum membrane fouling and the maximum VT in the combined process of tubular alumina MF and PP beads. The resistance of reversible membrane fouling (Rrf) showed a major resistance of total membrane fouling, and that of irreversible membrane fouling (Rif) was a minor one, in the combined process using tubular or seven channel MF. The Rif showed a decreasing trend obviously, as decreasing BT from NBW to 2 min for seven channel MF. It means that the more frequent water backwashing could be more effective to control the membrane fouling, especially irreversible fouling, for seven channel membranes than tubular membranes.

Fouling resistant and performance tunable ultrafiltration membranes via surface graft polymerization induced by atmospheric pressure air plasma

Surface modification of polysulfone (PSf) surface, via acrylic acid (AA) surface graft polymerization, induced by atmospheric pressure Air plasma (Air APP) surface treatment, was explored for imparting UF membrane fouling resistance and tuning its performance. PSf surface activation with Air APP and subsequent tethering of PAA chains resulted in a higher degree of surface hydrophilicity relative to the use of He and He/O2 plasmas. Surface-nano-structed (SNS) PSf membranes with tethered PAA chains were of increased surface hydrophilicity and the polar component of the surface energy by 14% and 556%, respectively, and had a greater negative zeta potential (by 26% at pH >∼6) relative to the native-PSf membrane. Fouling filtration tests with bovine serum albumin (BSA) and sodium alginate demonstrated reduced fouling resistance, relative to the native-PSf membrane. Moreover, complete permeability recovery of the fouled SNS-PAA-PSf membrane was achieved, via simple water backwash, relative to 66%-81% permeability recovery for the native PSf membrane. Tethering the PSf UF surface with PAA chains was also enabled tuning of the membrane molecular weight cutoff (MWCO) and hydraulic permeability. It was shown that starting with the same PSf UF membrane a series of SNS-PAA-PSf membranes can be synthesized whereby performance tuning was achieved over a MWCO range of 5.5–11 kDa and a corresponding permeability range of 12.7–23.5 L·m−2·h−1·bar−1. The present approach of PSf UF membrane surface structuring with tethered PAA chains, employing Air APP for surface activation, was shown to be effective for UF membrane fouling reduction and performance tuning. Thus, the present study results suggest that there is merit in exploring its scalability given the utilization of air as a low cost plasma source gas.