Membrane Fouling Propensity Research Articles

Impact of PCLNPG Nanopolymeric Additive on the Surface and Structural Properties of PPSU Ultrafiltration Membranes for Enhanced Protein Rejection

This research explored the use of a partially cross-linked graft copolymer (PCLNPG) as an innovative nanopolymer pore-forming agent to enhance polyphenylsulfone (PPSU) membranes for protein separation applications. The study systematically examined the impact of incorporating PCLNPG at varying concentrations on the morphological and surface properties of PPSU membranes. A thorough characterization of the resulting PPSU-PCLNPG membranes was performed, focusing on changes in morphology, water affinity, porosity, pore size, and pore size distribution. The experimental findings demonstrated that the use of PCLNPG led to a significantly more porous structure, as confirmed by SEM analysis, with notable increases in porosity and pore size (nearly double). Additionally, the hydrophilicity of the PPSU membrane was remarkably enhanced. Performance evaluations revealed a substantial improvement in pure water flux, with the flux nearly tripling. The BSA retention was directly correlated with the concentration of the PCLNPG pore former for a loading range of 0.25–0.75 wt.%. The incorporation of PCLNPG also reduced the membrane fouling propensity by reducing both cake layer resistance (Rc) and pore plugging resistance (Rp). These results underscore the potential of PCLNPG-PPSU membranes for wastewater reclamation and nutrient recovery applications.

Molecular weight insight into critical component contributing to reverse osmosis membrane fouling in wastewater reclamation

Molecular weight (MW) of organics was one of the important factors influencing membrane fouling propensity. This study identified critical foulants of reverse osmosis (RO) membranes in reclaimed water by MW fractionation. MW > 10 kDa component was identified as the critical fouling contributor (CFC) in secondary effluent (SE), which accounted for only 13 ± 5% of dissolved organic carbon (DOC) but contributed to 86 ± 11% of flux decline. Throughout 12-month monitoring, SE and MW > 10 kDa component showed a similar fouling variation tendency: apparently higher fouling potential in winter and lower in summer, while MW < 10 kDa component presented minor fouling changes. Morphology of membrane fouled by CFC characterized a smooth and thick foulant layer on membrane surface. CFC was mainly composed of proteins and polysaccharides, and a protein-polysaccharide-protein “sandwich” fouling layer structure was preferentially formed on membrane surface. extended Derjaguin–Landau-Verwey–Overbeek (xDLVO) analysis demonstrated that strong attractive interactions between CFC and membrane surface dominated the fouling process. Furthermore, computational fluid dynamics (CFD) simulation revealed strong filtration resistance of CFC, confirming its significant fouling potential. Dual effects including attractive interactions and advantageous ridge-and-valley surface appearance accounted for the significant fouling propensity of MW > 10 kDa component and glean valuable insights into RO fouling mechanisms of reclaimed water in practical application.

Revealing the contradiction between DLVO/XDLVO theory and membrane fouling propensity for oil-in-water emulsion separation

Oil fouling is the crucial issue for the separation of oil-in-water emulsion by membrane technology. The latest research found that the membrane fouling rate was opposite to the widely used theoretical prediction by Derjaguin-Landau-Verwey-Overbeek (DLVO) or extended DLVO (XDLVO) theory. To interpret the contradiction, the molecular dynamics was adopted to explore the molecular behavior of oil and emulsifier (Tween 80) at membrane interface with the assistance of DLVO/XDLVO theory and membrane fouling models. The decreased flux attenuation and fitting of fouling models proved that the existence of Tween 80 effectively alleviated membrane fouling. Conversely, DLVO/XDLVO theory predicted that the membrane fouling should be exacerbated with the increase of Tween 80 concentration in O/W emulsion. This contradiction originated from the different interaction energy between oil/Tween 80 molecules and polyether sulfone (PES) membrane. The favorable free energy of Tween 80 was resulted from the sulfuryl groups in PES and hydrogen bonds (O-H…O) formation further strengthened the interaction. Therefore, Tween 80 could preferentially adsorb on membrane surface and form an isolation layer by demulsification and steric hindrance and resist the aggregation of oil, which effectively alleviated membrane fouling. This study provided a new insight in the interpretation of interaction in O/W emulsion.

Multifunctional photocatalytic membrane distillation for treatment of hypersaline produced water using hydrophobically modified tubular ceramic membranes

Produced water (PW) is the subsurface water brought to the surface during oil and gas production. PW is primarily disposed of by deep well injection, but it can be treated for beneficial use applications. However, efficient technologies for treating hypersaline PW with complex water chemistry are limited. This study developed an innovative, multifunctional photocatalytic membrane distillation (PMD) technology using hydrophobically modified tubular ceramic membranes coated with TiO2 nanoparticles as photocatalysts for treating unconventional PW. The effects of membrane modifications were characterized in terms of membrane morphology, pore size, chemical functionality, zeta potential, hydrophobicity, liquid entry pressure, water production, permeate water quality, and membrane fouling and scaling propensity. The desalination performance of the PMD technology was demonstrated using unconventional PW with total dissolved solids concentrations of 135,000 mg/L and 175,000 mg/L, and NH3-N concentrations of 1551 mg/L and 613 mg/L, respectively. The novel PMD concept provides a promising technology for hypersaline PW treatment, and TiO2 coating significantly reduced membrane fouling and scaling, improved distillate quality, and maintained stable permeate flux. The photocatalyst activation by ultraviolet-light emitting diodes (UV-LED) light further increased the permeate flux and enhanced the total organic carbon removal from 82.0% (without UV-LED) to 89.7% (with UV-LED). UV-LED irradiation did not affect ammonia and metals removal in PMD, reaching 99.4% and > 99.99% removal, respectively.

Effects of solid retention time and exposure mode to electric current on Remazol Brilliant Violet removal in an electro-membrane bioreactor.

The performance of an electrochemically assisted anoxic-oxic membrane bioreactor (A/O-eMBR) was assessed as an alternative for azo dye (Remazol Brilhant Violet (RBV)) removal from simulated textile wastewater. The A/O-eMBR was operated under three experimental conditions (runs I, II, and III), in which different solids retention time (SRT) (45 and 20 d) and exposure mode to electric current (6'ON/30'OFF and 6'ON/12'OFF) were assessed. The reactor exhibited excellent decolorization performance for all runs, with average dye removal efficiency ranging from 94.3 to 98.2%. Activity batch assays showed that the dye removal rate (DRR) decreased from 16.8 to 10.2mg RBV L-1h-1 when the SRT was reduced from 45 to 20 d, likely attributed to the lower biomass content under lower sludge age. At the electric current exposure mode of 6' ON/12'OFF, a more substantial decrease of DRR to 1.5mg RBV L-1h-1 was noticed, suggesting a possible inhibitory effect on dye removal via biodegradation. By reducing the SRT to 20 d, a worse mixed liquor filterability condition was observed, with a membrane fouling rate (MFR) of 0.979kPa d-1. In contrast, using the electric current exposure mode of 6'ON/12'OFF resulted in lower membrane fouling propensity, with an MFR of 0.333kPa d-1. A more attractive cost-benefit ratio for dye removal was obtained using the exposure mode of 6'ON/30'OFF, for which the energy demand was estimated at 21.9-22.6 kWh kg dye-1 removed, almost two times lower than that observed for the mode of 6'ON/12'OFF.

A new insight into the low membrane fouling tendency of liquid-liquid hollow fiber membrane contactor capturing ammonia from human urine

To unravel the low membrane fouling tendency and underlying membrane fouling mechanism of liquid-liquid hollow fiber membrane contactor (LL-HFMC) capturing ammonia from human urine, the ammonia flux decline trend, membrane fouling propensity, foulant-membrane thermodynamic interaction energy and microscale force analysis at different feed urine pH were comprehensively investigated. The 21-d continuous experiments showed that the ammonia flux decline trend and membrane fouling propensity significantly strengthened with the decrease of feed urine pH. The calculated foulant-membrane thermodynamic interaction energy decreased with the decreasing feed urine pH and agreed with the ammonia flux decline trend and membrane fouling propensity. The microscale force analysis showed that the absence of hydrodynamic water permeate drag force resulted in the foulant located at long distance from the membrane were difficult to approach the membrane surface, thus considerably alleviating membrane fouling. Additionally, the vital thermodynamic attractive force near the membrane surface increased with the decrease of feed urine pH, which made the membrane fouling further relieved at high pH condition. Therefore, the absence of water permeate drag force and operating at high pH condition minimized the membrane fouling during the LL-HFMC ammonia capture process. The obtained results provide a new insight into the low membrane tendency mechanism of LL-HFMC.

Does Surface Roughness Necessarily Increase the Fouling Propensity of Polyamide Reverse Osmosis Membranes by Humic Acid?

Surface roughness has crucial influence on the fouling propensity of thin film composite (TFC) polyamide reverse osmosis (RO) membranes. A common wisdom is that rougher membranes tend to experience more severe fouling. In this study, we compared the fouling behaviors of a smooth polyamide membrane (RO-s) and a nanovoid-containing rough polyamide membrane (RO-r). Contrary to the traditional belief, we observed more severe fouling for RO-s, which can be ascribed to its uneven flux distribution caused by the "funnel effect". Additional tracer filtration tests using gold nanoparticles revealed a more patchlike particle deposition pattern, confirming the adverse impact of "funnel effect" on membrane water transport. In contrast, the experimentally observed lower fouling propensity of the nanovoid-containing rough membrane can be explained by: (1) the weakened "funnel effect" thanks to the presence of nanovoids, which can regulate the water transport pathway through the membrane and (2) the decreased average localized flux over the membrane surface due to the increased effective filtration area for the nanovoid-induced roughness features. The current study provides fundamental insights into the critical role of surface roughness in membrane fouling, which may have important implications for the future development of high-performance antifouling membranes.

Facile engineering of PES ultrafiltration membranes using polyoxometalates for enhanced filtration and antifouling performance

The pursuit of augmented membrane separation performance is mainly proceeded by breaking the permeability-selectivity trade-off and ameliorating the membrane fouling propensity. Here, we report the usage of phosphomolybdic acid (PMo12) as a functional additive to fabricate poly (ether sulfone) (PES) based composite ultrafiltration membranes via a non-solvent induced phase separation process. In contrast to the control PES membrane, the introduction of PMo12 endowed the composite membranes with increased surface pore density, porosity and selective layer thickness as well as the enhanced hydrophilicity and charge property through altering the phase inversion rate, thereby resulting in a significantly increased filtration performance. Specifically, the optimized composite membrane presented a water flux of 572.67 ± 21.73 L·m−2·h−1 and a bovine serum albumin rejection of 99.31 ± 0.22 %, which are ca. 340 % and 0.7 % higher than those of the control PES membrane, respectively. Importantly, the composite membrane also displayed enhanced anti-organic and anti-biofouling properties with the assistance of the introduced PMo12. This work provides an efficient pathway to simultaneously enhance the filtration and antifouling performance toward the further advancement of UF membrane for water purification.

Porous substrate affects fouling propensity of thin-film composite nanofiltration membranes

Fouling is a critical consideration for the design of thin-film composite (TFC) nanofiltration membranes. Traditional wisdom believes that fouling propensity is primarily dictated by membrane surface properties while porous substrates play little role (on the basis on the latter have no effect on the foulant-membrane interaction). Nevertheless, porous substrates can regulate the water transport pathways, resulting in uneven water flux distribution over the membrane surface. For the first time, we experimentally investigated the micro-scale water flux distribution for nanofiltration membranes with different substrate porosities and the impact of such flux distribution pattern on fouling. With gold nanoparticles as tracers, we demonstrated more evenly distributed water flux at increasing substrate porosity. This was found to effectively alleviate membrane fouling by eliminating localized hot spots of high flux. Furthermore, higher substrate porosity also effectively enhanced the membrane water permeance due to the optimized water transport pathways. Our study reveals the fundamental relationship between the micro-scale transport behavior and the membrane fouling propensity, which provides a firm basis for the rational design of TFC membranes toward better separation performance.

In situ PEGylation of polyamide network of thin film composite membrane by inter-polymer H-bond complex formation

Fouling propensity of membranes is a bottleneck problem. PEGylation is an effective approach to improve the antifouling property of a polyamide (PA) thin film composite (TFC) membrane. However, reactive PEG involves in the covalent network formation with PA leading to the increase of network pore size and lowers the rejection efficiency of the membranes. Post-surface modification by reactive PEG leads to lowering of permeates flux. End-functional (reactive) PEG samples are costly and prepared by multi-step process. Herein, the high pKa value of the fraction of –COOH groups of PA network is utilized for the formation of stable complex with PEG. Addition of linear PEG into the aqueous solution of m-phenylenediamine during interfacial polymerization leads to grafting of polyamide network by PEG through the formation of interpolymer H-bond complex of ether oxygen of PEG and –COOH groups of cross-linked PA network. PEG in the PA network increases the hydrophilicity, permeate flux, rejection efficacy and antifouling property of the membranes. The PEG chains remain stable in the PA network in the pH window of acidic to ≤8 as confirmed by the ATR-IR, wetting behavior, model spectroscopic experiments and X-Ray photoelectron spectroscopy. A PEGylated membrane prepared by the in situ addition of PEG (molecular weight 2000 g mol−1, 1% w v−1) into the MPD solution shows 20–30% higher permeate water flux, superior salt rejection efficiency and fouling resistant property than that of a pristine membrane. This approach is simple, cost-effective and easy to implicate.

The effect of different static biocarriers on process performance, membrane fouling and microbial community in submerged membrane bioreactor treating municipal wastewater under high and low carbon/nitrogen ratios

This study investigated the impact of two different static biocarriers (polyvinyl chloride (PVC) and polyurethane (PU)) addition in MBR for process performance, membrane fouling and microbial community treating municipal wastewater under high and low carbon/nitrogen (C/N) ratios. The results indicated that PU biocarrier addition could help to accumulate the bacteria for nitrification and denitrification (Tauera, Amaricoccus and Nitrospira in the mixed liquor and Solitalea and Sphingobacteriales_unclassified on the biocarrier), which slightly enhanced the total nitrogen removal especially under a low influent C/N ratio of 6.7. Additionally, the PU biocarrier addition can also alter the bulk sludge characteristics with lower soluble microbial products (SMP) concentration, lower SMP protein to carbohydrates ratio and bigger particle size, leading to lower membrane fouling propensity even under a low influent C/N ratio. PU biocarrier addition also reduced the relative abundance of extracellular polymer substances (EPS) secretion-related bacteria (Sphingobacterials_unclassified and Ohtaekwangia) and mitigated the membrane fouling propensity. However, this is not the case with PVC biocarrier addition, which might be due to the physical properties of the static biocarrier since PU has higher porosity, specific surface area and less negative surface zeta potential than PVC. Importantly, the static biocarrier addition can improve the nitrogen removal especially under a low influent C/N ratio and facilitate the membrane fouling control, but it depends on the physical characteristics of the biocarriers.

Two-dimensional nanoporous and lamellar membranes for water purification: Reality or a myth?

• Progress in 2D nanoporous and lamellar membranes is critically reviewed. • Sub-nanoporous membranes can achieve high water permeance and rejection. • Lamellar membranes provide effective rejection of dye molecules at high water flux. • Enhanced ion rejection by lamellar membranes requires 2D material functionalisation. • Research is required on scalability, stability, fouling and pore size engineering. Wastewater contains only ∼ 1% impurities that are required to be separated precisely for water recycling and reuse applications, particularly in water scare regions. Membrane-based separation has been recognised as an environmentally-friendly and energy-efficient process for effective pollutant removal and clean water production. To further improve the selectivity and water flux of membranes, two-dimensional (2D) materials, such as graphene and those exhibiting graphene-like properties, have been intensively studied for nanoporous and lamellar membrane fabrication in the last decade. Herein, we critically review the progress in 2D membranes for water purification and uniquely discuss the performance governing factors and research gaps from the standpoint of environmental and material chemists, which are critical to realize 2D membrane commercialization. The major points of this review are: (1) among the six types of reviewed 2D membranes, graphene, graphene oxide and reduced graphene oxide membrane have been predominantly studied for water treatment. (2) atomically thin nanoporous membranes with a defined pore size can achieve excellent water permeance and selectivity but large-scale fabrication of nanoporous membranes with uniform shape and size of nanopores remains a challenge. (3) salt separation performance of the pressurized lamellar membranes may not be comparable to commercial nanofiltration membranes. (4) functionalization or crosslinking of 2D materials is inevitable to stabilize 2D membrane pore structure and/or improve molecule separation. (5) membranes fabricated using emerging 2D materials such as born nitride and MXene appear to show better stability than graphene oxide membranes. (6) several aspects, particularly membrane stability, long-term performance, and membrane fouling propensity need attention to realize commercial application of 2D membranes in water treatment.

Jellyfish swarm impair the pretreatment efficiency and membrane performance of seawater reverse osmosis desalination

Circumstantial evidence has suggested that jellyfish swarms impair the operation of seawater reverse osmosis desalination facilities. However, only limited information is currently available on the pretreatment efficiency of jellyfish and their effects on reverse osmosis (RO) membrane performance. Here, we have comprehensively tested the pretreatment efficiency of a dual-media gravity filter and cartridge micro-filtration following the addition of jellyfish into the feedwater. Concurrently, the fouling propensity and performance of the RO membranes were examined. We show that jellyfish demise resulted in seawater eutrophication that triggered a significant increase in bacterial biomass (∼50-fold), activity (∼7-fold), and release of transparent exopolymer particles (∼5-fold), peaking three days after the addition of jellyfish into the feedwater. In parallel, a significant reduction in permeate water flux was recorded (∼10%) while trans-membrane pressure sharply increased (15%), reaching the operation pressure limit of our system (75 bar) after five days. At the conclusion of the experiments, the membrane surface was heavily covered by large chunks of organic-rich material and multilayered biofilms. Our results provide a holistic view on the operational challenges of seawater reverse osmosis (SWRO) desalination triggered by jellyfish swarms in coastal areas. Following the above, it can be inferred that freshwater production will likely be halted three days after drawing the jellyfish into the pretreatment system. Outcomes from these results may lead to the development of science-based operational protocols to cope with growing occurrence of jellyfish swarms around the intake of SWRO desalination facilities worldwide.

Dealcoholization of kiwi wine by forward osmosis: Evaluation of membrane fouling propensity and product quality

Forward osmosis (FO) was used to dealcoholize kiwi wine (KW). The effect of dealcoholization on the physiochemical characteristics of KW, and on the CTA-FO membrane, was determined for three draw solutions (DSs) frequently used in FO, i.e., MgCl2, NaCl, and KCl. The highest water flux (11.1 L/m2h) and lowest alcohol content (0.45 v/v) were observed for MgCl2 DS. Fourier transform-infrared spectroscopy established that the three DSs did not significantly change the functional groups of the membrane surface. Scanning electron microscopy and atomic force microscopy confirmed that the least contaminated membrane was that used for MgCl2 DS dealcoholization. Furthermore, MgCl2 DS dealcoholized KW contained the greatest variety (n = 23) and highest content of volatile organic compounds (2735.36 μg/mL), and the highest phenolic content (91.59 μg/mL); it also displayed the highest antioxidant activity. The experimental results confirmed the suitability of FO for the dealcoholization of KW.

Surface charge control of poly(methyl methacrylate-co-dimethyl aminoethyl methacrylate)-based membrane for improved fouling resistance

• P(MMA-co-DMAEMA) was synthesized and blended with polysulfone UF membrane. • Blend PSF-PMD membrane was quaternized to increase surface positive charge. • Membrane was grafted with 2-carboxyethyl acrylate for surface neutralization. • Neutralization resulted in comprehensive anti-fouling smooth membrane surface. • Surface charge control is simple and effective to mitigate membrane fouling. In this study, a new poly(methyl methacrylate-co-dimethyl aminoethyl methacrylate) (P(MMA-co-DMAEMA))-based membrane was fabricated and modified to control surface charge in order to improve fouling resistance. The positively-charged P(MMA-co-DMAEMA) copolymer was first synthesized from the free radical polymerization of methyl methacrylate (MMA) and dimethylamino-2-ethyl methacrylate (DMAEMA). The copolymer was blended with polysulfone and cast into a membrane via nonsolvent-induced phase separation. The membrane was then quaternized using iodomethane and neutralized by grafting 2-carboxylethyl acrylate via UV irradiation. The membrane surface charge, composition, morphology, hydrophilicity, and anti-fouling properties were evaluated. Surface charge control of the membrane resulted in outstanding antibacterial activity and fouling resistance against model protein foulants. While the incorporation of P(MMA-co-DMAEMA) in the membrane and its quaternization greatly improved the surface hydrophilicity of the membrane and endowed positive surface charge as well. Neutralization of the blend membrane endowed a smooth and electroneutral surface layer on the membrane surface, which led to not only excellent anti-bacterial activity and comprehensive resistance against charged foulants, but also high flux retention after simple membrane washing. Dynamic filtration using protein and bacterial foulants revealed the ability of the membrane with almost zero net surface charge to regulate fouling even in practical filtration applications. The results in this study exhibit a simple and effective method for mitigation of membrane fouling propensity for practical application.

Athermal concentration of apple juice by forward osmosis: Process performance and membrane fouling propensity

The athermal concentration as green and sustainable technique is desired for fruit juice concentration to improve product quality and decrease the energy consumption. The emerging forward osmosis (FO) process was employed for apple juice concentration at ambient operational conditions in order to preserve juice nutrition and flavor. The parameters of FO process (membrane property, crossflow velocity of feed solution (FS), type of draw solutes, and concentration of draw solution (DS)) were detailedly investigated for the effects on water flux, membrane fouling control and membrane cleaning. The content of total soluble solids (TSS) in the apple juice was increased from 11°Brix to 60°Brix. The acidity and total phenols were both increased by 4.07-fold and 4.92-fold, respectively. The apple juice can be concentrated up to about 5.45-fold according to TSS by a single stage FO process after 48 h. The membrane fouling mechanism was investigated by the flux change with and without the pectin. Furthermore, different methods of membrane cleaning were further assessed to recover the water flux. Hydraulic flushing could efficiently recover the flux up to 95.2%. The optimization of the FO process parameters could further facilitate FO process for athermal concentration of apple juice, which may have great potentials for the practical applications in the food processing.

Elucidating the intensifying effect of introducing influent to an anaerobic side-stream reactor on sludge reduction of the coupled membrane bioreactors

Three anoxic/oxic membrane bioreactors (AO-MBRs) coupled with the anaerobic side-stream reactor (ASSR) with different influent flow distribution ratios (IFDRs) were assessed to elucidate how IFDR in the ASSR affected pollutants removal, sludge reduction, membrane fouling, and potential co-occurrence network of microorganisms. When the IFDR in the ASSR was increased from 0% (ASSR0-MBR), to 25% (ASSR25-MBR) and 75% (ASSR75-MBR), chemical oxygen demand removal was enhanced and nutrient removal was comparable. Compared to ASSR0-MBR, ASSR25- and ASSR75-MBR further improved the sludge reduction by 7.6% and 10.9%, respectively. ASSR25-MBR followed cake-complete model due to the weak membrane surface scouring and high concentration of extracellular polymeric substances, while ASSR0- and ASSR75-MBR fitted cake-standard model. The increased IFDR in the ASSR boosted the relative abundance of hydrolytic and slow-growing bacteria. The co-occurrence networks of sludge reduction, nutrient removal and membrane fouling propensity indicated that the symbiotic relationships were dominant.

Fouling propensity in reverse electrodialysis operated with hypersaline brine

The impact of fouling on the performance of Reverse Electrodialysis operated with highly concentrated brine is a poorly investigated area. In this work, the fouling propensity and stability of Ion Exchange Membranes (IEMs), developed by Fujifilm Manufacturing Europe BV (The Netherlands), is investigated under the condition of seawater and brine. The fouling propensity of the IEMs was depicted by the determination of the Gibbs energy barrier of based-on the Classical Nucleation along with the Theoretical modeling of heterogeneous nucleation as a function of electrochemical (contact angle, permittivity, charge density) and morphological (roughness) membrane properties validated by CaCO3 precipitation. Results indicate that Cation Exchange Membranes (CEM) are more susceptible to the scaling due to the reduced energy barrier of heterogeneous nucleation. FTIR-ATR analysis on six months-aged membranes samples indicated a partial modification in the chemical structure of Anion Exchange Membranes (AEM) induced by the organic fouling associated with humic substances. The tensile tests demonstrated substantial mechanical stability of IEMs. Lab-scale RED tests operated with artificial brine over 30 days showed a significant increase in pressure drop through feed channels due to significant colloidal fouling along with a 23% reduction of maximum gross power density with consequent decrease of net power density.

Mechanism of pre-ozonation in control of protein fouling of ultrafiltration membranes: Synergistic effect between ozone oxidation and aeration

Pre-ozonation is often used before ultrafiltration (UF) to control membrane fouling, usually by supplying ozone into water or wastewater via aeration. However, the role of aeration in pre-ozonation for mitigation of membrane fouling has not been well elucidated. Hence, in this study, bovine serum albumin (BSA) was used as a protein-type foulant in experiments on the outcomes and underlying mechanisms of pre-ozonation. The change in the membrane fouling behavior, the transformation of BSA, and the fouling-layer properties were investigated after pre-ozonation with and without aeration. The results showed that the membrane fouling notably declined after pre-ozonation, which mainly attributed to the synergistic effect between ozone oxidation and aeration. Ozone oxidation unfolded the BSA molecules and exposed their hydrophobic groups, and these unfolded BSA aggregated and adhered to the surface of the microbubbles produced by aeration. This induced BSA foaming and aggregation in the ozonated suspension. With pre-ozonation for a short contact time of 5 min, small BSA aggregates in water were retained on the UF membrane surface to form a highly porous deposition layer with a low filtration resistance. With pre-ozonation for a contact time of 10 min or longer, BSA foaming led to the formation of large aggregates that were efficiently removed from water in the ozone reactor, which greatly reduced the foulant loading of the water and its subsequent membrane fouling rate. In contrast, when quantitative and quiescent ozonation was performed without aeration, ozone oxidation alone worsened the membrane fouling propensity of the BSA solution.

Facile development of comprehensively fouling-resistant reduced polyketone-based thin film composite forward osmosis membrane for treatment of oily wastewater

Forward osmosis (FO) has proven to be a suitable process for treatment of problematic oily wastewater, due to its relatively higher water recovery rate and lower energy requirement, as opposed to pressure-driven membrane processes. Despite the lower membrane fouling propensity during FO operation, the development of comprehensively fouling-resistant membranes is further desired in FO as a suitable oily wastewater treatment process. In this current work, reduced aliphatic polyketone (rPK)-based thin film composite (TFC) membranes were developed. Reduction conditions using NaBH4 were tested, and the suitability of reduction was evaluated with membrane morphology, water wettability, and resistance to oil. The resultant rPK-TFC membrane, whose substrate was reduced with 0.5% (w/w) NaBH4 for 10 min, exhibited 37.8 L m−2 h−1 water flux in PRO mode. Using a foulant solution containing 1% (v/v) soybean oil, and 100 ppm humic acid, sodium alginate, and bovine serum albumin, the resultant rPK-TFC membrane maintained an outstanding 95% average flux recovery ratio, while the pristine PK-TFC membrane achieved an average flux recovery ratio of 67%. The results indicate that reduction of aliphatic polyketone is a facile method to develop membranes with outstanding water permeability and fouling resistance.