Fouling Propensity Research Articles

INFLUENCE OF OPERATING CONDITIONS ON THE ULTRAFILTRATION TREATMENT OF BRILLIANT BLUE BATIK DYE

The batik industry produces a large amount of wastewater that degrades water quality. Ultrafiltration (UF) is an efficient and low-pressure filtration method for water treatment, particularly for dye wastewater. This study aims to analyze the efficiency of commercial UF polyethersulfone (PES) membranes in the treatment of brilliant blue batik dye. The effect of operating conditions involving operating pressure (2, 3, 4 bar) and pH (3, 6, and 9) of dye solution at 50 mg/L on membrane performance was evaluated via a crossflow filtration system. Higher dye rejection was obtained at close to neutral pH and higher pressure. On the other hand, the fouling propensity was mainly affected by pressure and the membrane experienced a slower flux decline at lower pressure. This is owing to the synergistic interaction between size sieving and electrostatic repulsion. The optimum membrane performance was achieved at pH 6 and 3 bar. Future studies can work on real dye wastewater produced from the batik industry.

Innovative approach to predict the fouling propensity of orange juice suspended particles through relevant physical characterisation

SummaryThe feasibility of predicting at laboratory‐scale the fouling propensity of orange juice suspended particles based on their physical properties, was investigated. Samples were generated from mixtures of two selected size class of large and fine particles. The particle‐size distribution, rheological and textural properties of these samples were characterised as well as their fouling propensity using permeability test. Qualitative and quantitative statistical analyses revealed significant correlations between specific resistance to filtration (SRF) and hydration velocity (Vh), statistical diameter (D90) and shear strain at flow point (ɣf). Partial Least Square method allowed to discriminate contrasted values of log(SRF) of suspended particles using a simplified model (R2 = 0.79; RMSEC; RMSECV <20% of SRF mean; RPD = 1.6), based on 5 predictor variables (Vh, ɣf, D90, D[4;3] and ). These findings, offer new prospects to guide the choice of pretreatment or specific operating conditions to improve the performance of fruit juices microfiltration.

Effect of biomass retention time on performance and fouling of a stirred membrane photobioreactor

Co-culture of microalgae-activated sludge has the potential to purify wastewater while reduce energy demand from aeration. In this work, a mechanically stirred membrane photobioreactor (stirred-MPBR) was used to evaluate the impact of the biomass retention time (BRT) on the treatment performance and membrane fouling. Results showed that stirred-MPBR was affected by BRT during treating domestic wastewater at a flux of 16.5 L m−2 h−1. The highest productivity was attained at BRT 7d (102 mg L−1 d−1), followed by BRT 10d (86 mg L−1 d−1), BRT 5d (85 mg L−1 d−1), and BRT 3d (83 mg L−1 d−1). Statistical analysis results showed that BRT 7d had a higher COD removal rate than BRT 10d, however, there is no difference in total nitrogen removal rate. The highest TP removal occurred when the biomass operated at BRT as short as 3d. Reduced BRTs caused a change in the microalgae-activated sludge biomass fraction that encouraged nitrification activity while simultaneously contributing to a higher fouling rate. The bound protein concentrations dropped from 31.35 mg L−1 (BRT 10d) to 10.67 mg L−1 (BRT 3d), while soluble polysaccharides increased from 0.99 to 1.82 mg L−1, respectively. The concentrations of extracellular polymeric substance fractions were significantly altered, which decreased the mean floc size and contributed to the escalating fouling propensity. At the optimum BRT of 7d, the stirred-MPBR showed sufficient access to light and nutrients exchange for mutualistic interactions between the microalgae and activated sludge.

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.

High propensity of membrane fouling and the underlying mechanisms in a membrane bioreactor during occurrence of sludge bulking

While sludge bulking often occurring in activated sludge processes generally leads to serious membrane fouling in membrane bioreactors (MBR), the underlying causes are still unclear. In this study, fouling behaviors of a MBR operated at stages of normal and sludge bulking were compared, and the fouling mechanisms of the different behaviors were explored. It was found that, the MBR could be stably operated in normal stage without membrane cleaning for about 60 days, whereas, daily membrane cleaning had to be carried out when operated in sludge bulking stage. The bulking sludge possessed a rather high specific filtration resistance (SFR) of about 1.36×1014 m·kg−1, which is over 5.33 times than that of the normal sludge. A series of characterizations demonstrated that the bulking sludge had rather lower dewaterability, smaller particle size, higher fractal dimension, higher viscosity, abundant filamentous bacteria and different functional groups of extracellular polymer sustains (EPS). It was suggested that microbial community transition was responsible for the occurrence of sludge bulking, further affecting membrane fouling. Based on these characterizations, it was reported that adhesion propensity (indicated by the thermodynamic interaction) of the bulking sludge to the membrane surface is about 3.6 times than that of the normal sludge. It was proposed that, extra force should be provided to offset a chemical potential gap caused by foulant layer structure transition during sludge bulking in order to sustain filtration of the bulking sludge, resulting in extremely high SFR. This study offered deep thermodynamic mechanisms of MBR fouling during occurrence of sludge bulking.

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.

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.

Bacterial surface attachment and fouling assay on polymer and carbon surfaces using Rheinheimera sp. identified using bacteria community analysis of brackish water

Biofouling on surfaces in contact with sea- or brackish water can severely impact the function of devices like reverse osmosis modules. Single species laboratory assays are frequently used to test new low fouling materials. The choice of bacterial strain is guided by the natural population present in the application of interest and decides on the predictive power of the results. In this work, the analysis of the bacterial community present in brackish water from Mashabei Sadeh, Israel was performed and Rheinheimera sp. was detected as a prominent microorganism. A Rheinheimera strain was selected to establish a short-term accumulation assay to probe initial bacterial attachment as well as biofilm growth to determine the biofilm-inhibiting properties of coatings. Both assays were applied to model coatings, and technically relevant polymers including laser-induced graphene. This strategy might be applied to other water sources to better predict the fouling propensity of new coatings.

Revealing the role of supernatant and granular sludge fractions on granular anaerobic membrane bioreactor fouling

In order to design efficient fouling mitigation strategies in granular anaerobic membrane bioreactors (G-AnMBR), foulant characteristics and their role have to be thoroughly investigated. Raw mixed liquor of G-AnMBR was split by sieving into granules and supernatant fractions at 0.125 mm. Then, the fouling potential and reversibility of the different samples (granules, supernatant and raw mixed liquor) were assessed by measuring critical fluxes and through filtration tests. Various hydrodynamic conditions, i.e. gas sparging and recirculation, were applied to evaluate the impact of shear stress on fouling propensity. Results revealed that the supernatant fraction, composed of fine compounds and micro-particles, had a strong fouling potential, whilst the granule fraction led to minor fouling filtration resistance. Three-dimensional excitation emission fluorescence spectroscopy emphasised the prominent role of colloidal proteins in G-AnMBR membrane fouling. During the filtration test of raw mixed liquor, the fouling propensity of the micro-particles was lowered, since the structural cake layer was modified. Gas sparging allowed for the mitigation of cake formation, but excess of shear forces may lead to granule break-up and more irreversible fouling. Liquid recirculation led to a higher filtration resistance, but almost all the membrane permeability was recovered by physical cleaning. A short filtration cycle without gas sparging followed by a short period of relaxation and gas sparging could be a suitable fouling mitigation method. In this way, release of micro-particles from granule break-up could be limited, the cake build-up would be mostly reversible by physical cleaning, and the energy demand of gas sparging would be greatly reduced, thereby improving the energy neutrality of the G-AnMBR biotechnology.

Ceramic nanofiltration membranes for efficient fouling mitigation through periodic electrolysis

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

Aging of polyvinylidene fluoride (PVDF) ultrafiltration membrane due to ozone exposure in water treatment: Evolution of membrane properties and performance

Pre-ozonation is an effective pretreatment tactic for mitigating fouling of ultrafiltration (UF) membrane in water and wastewater treatment, but the compatibility of polymeric UF membranes with residual ozone remains unclear. In this study, effects of long-term ozone exposure on properties and performance of polyvinylidene fluoride (PVDF) UF membrane reinforced by polyethylene terephthalate (PET) layer were systematically investigated. The exposure intensities were designed to simulate ozone exposure at 0.1 mg/L for 0.5–5 years. Chemical composition analysis suggested that the hydrophilic additives, such as possibly polyvinyl pyrrolidone (PVP), was gradually degraded and released from the membrane, whereas the PVDF matrix exhibited fairly good ozone resistance. Ozonation resulted in increase of pore size and decrease of surface hydrophilicity, which can be attributed to oxidation and dislodgement of hydrophilic additives. Accordingly, long-term ozonation led to moderate changes in performance factors, including increase of membrane permeability by 34%, decrease of retention ability by 21.8%, increase of organic fouling propensity. It is worth noting that membrane tensile strength suffered substantial decrease after ozonation, probably due to ozonation of the PET support layer. Overall, it seems that the PVDF functional layer exhibited good ozone resistance, but the PET support layer was the Achilles' heel of the reinforced PVDF membrane for integrating with pre-ozonation.

Organic-inorganic composite ultrafiltration membrane with anti-fouling and catalytic properties by in-situ co-casting for water treatment

Organic-inorganic composite membranes have received much attention for superior water-treatment performance, where manipulating distribution of inorganic nanoparticles in membrane matrix remains a great challenge. Therefore, an in-situ co-casting was developed to modulate distribution of nanoparticles in membrane matrix for preparing multifunctional dual-layer manganese dioxide-polyvinylidene fluoride (MnO2-PVDF) composite ultrafiltration membrane. Results showed MnO2-PVDF membranes possessed apparent bi-layer structure and nanoparticles were distributed uniformly on the surface and upper layer. Such a configuration improved hydrophilicity with a maximum pure water permeance of 1012.97 L/m2·h·bar and displayed excellent mechanical strength. From anti-fouling tests, 7.5 wt% MnO2-PVDF membrane presented the highest flux recovery of 83.2%, and low fouling propensity in either bovine serum albumin (BSA) solution or secondary effluent. The enhanced anti-fouling resulted from less attractive or even repulsive interactions between MnO2-PVDF membranes and foulants. Furthermore, the MnO2-PVDF membrane could accomplish ∼100.0% water flux recovery by a facile peroxymonosulfate (PMS) cleaning, following BSA fouling. Similarly, the catalytic capability of MnO2-PVDF membrane for PMS was evidenced through the removal of various organic pollutants. In long-term operation, the composite membrane displayed excellent stability and low Mn ion leaching. Our results provide a promising route for structural regulation and development of organic-inorganic composite membranes for water treatment.

Effects of pharmaceuticals on the fouling propensity of membrane bioreactor: Case of iodinated X-ray contrast media

Membrane bioreactor (MBR) has shown promising results in the abatement of pharmaceuticals, however, its fouling propensity has continued to put challenges in its wide-scale applicability. The present study is the first study that investigated the MBR fouling behaviour in the presence of iodinated X-ray contrast media (ICM). The study found that ICM aggravated the fouling issue by reducing the filtration cycle by 21 % and enhancing the production of key foulants- extracellular polymeric substances (EPS) and soluble microbial products (SMP). Size exclusion chromatography (SEC) results revealed the presence of a higher molecular weight (MW) organics in the EPS in ICM dosed phase. Also, excitation-emission matrix (EEM) contours of EPS showed that the exposure to ICM seemed to stimulate the secretion of aromatic proteins comprising tryptophan (28.7 %) and tyrosine (22.07 %) compared to the non-ICM dosed phase (25.10 % for tryptophan and 20.39 % for tyrosine). The floc size of the sludge was found to increase to 67.6 ± 10.2 µm from 22.4 ± 4.8 µm in the presence of ICM as a result of increased EPS content. Further, ICM addition resulted in a slight reduction of the sludge microbial activity (∼10 %). ICM also changed the microbial dynamics of the sludge by enriching the abundance of biofilm forming phyla such as Bacteroidetes and TM7. The findings of this study provide fundamental insights into the fouling propensity of MBR in presence of ICM, and highlight that the changes caused in the EPS secretion profile would be responsible for enhanced fouling.

Low-cost recycled end-of-life reverse osmosis membranes for water treatment at the point-of-use

Decentralized systems applied at the point-of-use (POU) could be an alternative for a safe drinking water supply in isolated regions and developing countries. Based on that, it was investigated the recycling of end-of-life reverse osmosis (EoL-RO) household modules as an alternative for groundwater treatment at the POU. The membranes were recycled through chemical oxidation using NaOCl (440,000 ppm h) and were validated in a long-term operation. The systems operated in a dead-end configuration mode without external energy requirements for permeation, only the hydraulic force provided by the water grid. The increase in permeability from 4.5 to 50.4 L/m2h.bar and decrease in salinity rejection from 99.4 to 11.6% suggests that the EoL-RO was effectively converted to ultrafiltration (UF). The recycled membrane still presented a lower resistance to filtration due to its porous characteristics (average pore size 0.04 ± 0.01 μm). In the perspective of POU application, the lower energy requirement for the recycled membranes compared to EoL-RO would represent advantages if compared to reverse osmosis household modules, more energy-demanding filters. Effective water treatment and a low fouling propensity were observed for long-term operation at the POU. The monitoring data demonstrates a steady permeate flux (21.2 ± 0.46 L/m2h) and filtration resistance (6.37 ± 0.16 × 1014 1/m), producing a total permeate volume (3,000 L) comparable with commercial filtration systems and in compliance with the 109 potability standards analyzed. From a broader perspective, the advantages of using recycled membranes could be extended to environmental aspects, preventing the production of waste from spent membranes and focusing on cleaner production of technical processes.

The Effect of Heat Sterilization on Key Filtration Performance Parameters of a Commercial Polymeric (PVDF) Hollow-Fiber Ultrafiltration Membrane.

Membrane processes can be integrated with fermentation for the selective separation of the products from the fermentation broth. Sterilization with saturated steam under pressure is the most widely used method; however, data concerning heat sterilization applicability to polymeric ultrafiltration (UF) membranes are scarcely available. In this study, the effect of the sterilization process on the filtration performance of a commercial polyvinylidene difluoride (PVDF) hollow fiber UF membrane was evaluated. Membrane modules were constructed and sterilized several times in an autoclave. Pure water flux tests were performed, to assess the effect of heat sterilization on the membrane’s pure water permeance. Dextran rejection tests were performed for the characterization of membrane typical pore size and its fouling propensity. Filtration performance was also assessed by conducting filtration tests with real fermentation broth. After repeated sterilization cycles, pure water permeance remained quite constant, varying between approx. 830 and 990 L·m−2·h−1·bar−1, while the molecular weight cut-off (MWCO) was estimated to be in the range of 31.5–98.0 kDa. Regarding fouling behavior, the trans-membrane pressure increase rate was stable and quite low (between 0.5 and 7.0 mbar/min). The results suggest that commercial PVDF UF membranes are a viable alternative to high-cost ceramic UF membranes for fermentation processes that require heat sterilization.

Long term operation performance and membrane fouling mechanisms of anaerobic membrane bioreactor treating waste activated sludge at high solid concentration and high flux

High solid anaerobic membrane bioreactor (HSAnMBR) is widely applied in biomass treatment and energy regeneration, while membrane operation performance and membrane fouling control remain critical issues. In this study, a HSAnMBR was utilized for waste activated sludge (WAS) treatment at organic loading rates of 3.69–3.72 gCOD/L·d and biogas yield was ranged in 0.38–0.39 L/gVSfed with the COD conversion efficiency of 40 %. The membrane operated stably when the average flux was 9.6, 4.5 and 1.2 L/m2/h at mixed liquor total solid of 25, 30 and 40 g/L with a filtration: relaxation of 4:1, 1:1 and 1:2, respectively. The distinctive characteristics of membrane fouling at high solid condition were that the polysaccharides and proteins had high fouling propensity and were the main composition of the foulant layer. Furthermore, phosphorus and magnesium were the predominant causes of inorganic fouling. The minerals precipitated on the membrane and were embedded into membrane pores, contributing to cake layer formation and pore blocking. This research provided a comprehensive analysis of the membrane operation characterization and fouling mechanisms of HSAnMBR, which was expected to push forward HSAnMBR applications to WAS treatment.

Evaluation of structural/performance variation between α-Al2O3 and polyvinylidene fluoride membranes under long-term clean-in-place treatment used for water treatment

The objective of this study was to compare the structural stabilities of alumina (α-Al2O3) and polyvinylidene fluoride (PVDF) membranes against harsh clean in place (CIP) and fouling conditions. Fouling propagation and flux recovery were examined for five CIP cycles by using an acid and an oxidant as cleaning chemicals. Furthermore, variations in the surface characteristics of pristine, fouled, and chemically cleaned α-Al2O3 and PVDF membranes were examined by field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), contact angle measurement, and Fourier transform infrared spectroscopy (FTIR), and the increase in the normalized pressure and variation in rejection efficacy of foulants were evaluated. Additionally, the fouling propensity and reversibility were determined on the basis of fouling indices, the resistance-in-series model, and total fouling analysis. The results showed that the α-Al2O3 membrane was less susceptible to fouling compared with the PVDF membrane and exhibited a less structural deterioration. Moreover, foulant deposition/adsorption on the ceramic membrane was confined to the surface and could be efficiently removed through hydraulic cleaning. Owing to less variation in its hydrophilic nature and electrostatic attraction, the filtration pressure increase was less compared with that for the PVDF membrane. In particular, α-Al2O3 showed 12 % lower residual fouling, a high and stable rejection efficiency, recoverable fouling resistance of 61.17 %–66.07 %, a quantitatively unchanged irreversible fouling resistance, and relative decreases from 25.49 %–16.24 % at the end of the experiment.

PVDF membranes modified with diblock copolymer PEO-b-PMMA as additive: Effects of copolymer and barrier pore size on filtration performance and fouling in a membrane bioreactor

In the present work, filtration performance and fouling behavior of four poly(vinylidene difluoride) (PVDF) membranes with different composition and molecular weight cut-off (MWCO) were investigated in a lab-scale submerged membrane bioreactor (MBR) system, treating real pharmaceutical wastewater. Poly(ethylene oxide)-block-poly(methyl methacrylate) (PEO-b-PMMA) diblock copolymer or FeCl2 or the combination of PEO-b-PMMA and FeCl2 were used as special additives during membrane formation. A 30-day filtration experiment was performed using four membranes in the same aeration tank simultaneously, and filtration performance of the membranes was investigated over the entire filtration period. Fouling parameters were calculated for all membranes and the TMP-step method was used to determine the critical flux of the membranes. Formed cake layers onto the surface of the membranes at the end of each filtration run were collected and extracellular polymeric substances (EPSs), excitation and emission matrix (EEM) fluorescence spectroscopy, and Fourier transform infrared (FTIR) spectroscopy analyses were performed for the cake layers. Collected cake layers after EPSs extraction were dried and their masses were measured to estimate anti-biofilm formation potential of the membranes. Obtained results revealed that incorporation of the PEO-b-PMMA diblock copolymer into the PVDF membrane accompany with FeCl2 salt which tailors the MWCO and prevents the increment of the pore size improves membrane performance and reduces its fouling propensity, in a way that membrane with smaller MWCO containing copolymer revealed lower flux decline, higher critical flux, higher flux recovery ratio (FRR) and lower biofilm mass per area. Moreover, EPS and EEM analyses revealed that membrane surface chemistry has considerable effect on the composition of the cake layers. Finally, chemical oxygen demand (COD) removal efficiency proved that MWCO does not have obvious effect on effluents’ quality. The present study confirms the importance of the surface chemistry and MWCO on fouling behavior of the membranes in the MBR system and reveals that the addition of the PEO-b-PMMA diblock copolymer to the PVDF membrane improves antifouling property of the membrane considerably.

Confining Nano-Fe3O4 in the Superhydrophilic Membrane Skin Layer to Minimize Internal Fouling.

Membrane surface fouling is often reversible as it can be mitigated by enhancing the crossflow shear force. However, membrane internal fouling is often irreversible and thus more challenging. In this study, we developed a new superhydrophilic poly(vinylidene fluoride) (P-PVDF) membrane confined with nano-Fe3O4 in the top skin layer via reverse filtration to reduce internal fouling. The surface of the P-PVDF membrane confined with nano-Fe3O4 had superwetting properties (water contact angle reaching 0° within 1 s), increased roughness (from 182 to 239 nm), and enhanced water affinity. The Fe3O4@P-PVDF membrane surface showed a thicker and enhanced hydration layer, which prevented foulants from approaching membrane surfaces and pores, thereby improving the rejection. For example, when 50 ppm humic acid (HA) solution was used as the feed, the removal efficiency of the Fe3O4@P-PVDF membrane was ∼67%, while the HA removal of the P-PVDF membrane was only ∼20%. The results from the resistance-in-series model showed that nanoconfinement of Fe3O4 in the top skin layer of the membrane allowed foulants to accumulate on the membrane surface (i.e., surface fouling) rather than within the internal pores (i.e., internal fouling). The filtration results under crossflow fouling and cleaning confirmed that the Fe3O4@P-PVDF membrane had higher surface fouling but it was much more reversible and much lower internal fouling compared with the control membrane. Our fouling analysis offers new insights into mass transfer mechanisms of the membrane with a nanoconfinement-enhanced hydration layer. This study provides an effective strategy to develop membranes with low internal fouling propensities.