Irreversible Fouling Research Articles

Designing anti(-bio)fouling membranes with synergistic grafting of quaternized and zwitterionic polymers through surface initiated atom transfer radical polymerization

Membrane-based filtration technologies have significant potential to address the global problem of freshwater scarcity. However, fouling, caused by nonspecific adsorption of foulants and microbiological growth during filtration, remains a considerable concern. To address this, a rational surface design method comprising bifunctional coating with both defensive and attacking techniques has been devised, which can successfully decrease fouling and biofouling. To generate a bifunctional membrane, a single-step surface-initiated atom-transfer radical polymerization (SI-ATRP) of monomers with zwitterionic and quaternized imidazolium moieties was done on a polydopamine (PDA) primed polyvinylidene fluoride (PVDF) membrane. The PDA layer’s catechol functionalities provided abundant anchoring sites, allowing the grafting of a dense polymer layer on the membrane. The addition of active zwitterionic and quaternized imidazolium moieties in the grafted polymer chains resulted in very low fouling and microbiological species death. Extensive antifouling studies revealed that the functionalized membranes have excellent flux recovery (>93%), low irreversible fouling (<8.5%), and long-term filtration stability. This surface functionalization strategy based on a bifunctional unit represents a significant advancement in fouling mitigation by minimizing membrane-foulant interactions and killing adhered bacteria, with the potential to significantly broaden the range of membrane-based filtration applications and contribute to more efficient and sustainable water purification processes.

Acrylonitrile-Acrylic Acid Copolymer Ultrafiltration Membranes for Selective Asphaltene Removal from Crude Oil.

In this study, ultrafiltration membranes were developed via a nonsolvent-induced phase separation method for the removal of asphaltenes from crude oil. Polyacrylonitrile (PAN) and acrylonitrile copolymers with acrylic acid were used as membrane materials. Copolymerizing acrylonitrile with acrylic acid resulted in an improvement in the fouling resistance of the membranes. The addition of 10% of acrylic acid to the polymer chain decreases the water contact angle from 71° to 43°, reducing both the total fouling and irreversible fouling compared to membranes made from a PAN homopolymer. The obtained membranes with a pore size of 32-55 nm demonstrated a pure toluene permeance of 84.8-130.4 L/(m2·h·bar) and asphaltene rejection from oil/toluene solutions (100 g/L) of 33-95%. An analysis of the asphaltene rejection values revealed that the addition of acrylic acid increases the rejection values in comparison to PAN membranes with the same pore size. Our results suggest that the acrylonitrile-acrylic acid copolymer ultrafiltration membranes have promising potential for the efficient removal of asphaltenes from crude oil.

Activation of peroxymonosulfate with biochar-supported CuO (CuO@BC) for natural organic matter removal and membrane fouling control

To achieve excellent activation efficiency of peroxymonosulfate (PMS), this work prepared a biochar-supported CuO (CuO@BC) catalyst, and the CuO@BC/PMS system was proposed to remove the organic matter in natural surface water and reduce the fouling of ultrafiltration membrane. The successful synthesis of CuO@BC was demonstrated through characterization of its microscopic morphology and chemical composition by various techniques. The prepared heterogeneous catalyst showed a strong catalytic effect on PMS, which significantly removed natural organic matter through the production of active substances (•OH, SO4•−, O2•− and 1O2) from water. With respective degradation rates of 39.4% and 59.4%, the concentrations of DOC and UV254 dropped to 1.702 mg/L and 0.026 cm−1, respectively. Additionally, the CuO@BC/PMS oxidation displayed potent oxidation capabilities for contaminants and fluorescent organics with various molecular weights. The system effectively decreased the amount of organic matter that caused reversible and irreversible fouling of polyethersulfone membranes in natural water by 85.8% and 56.3%, respectively. The main fouling mechanisms changed as well, with standard and complete blocking dominating the entire filtration process. The results demonstrated the capacity of the CuO@BC/PMS system to remove contaminants in natural water and mitigate membrane fouling.

Performance evaluation of polyethersulfone membranes modified with poly (acrylic acid‐co‐N‐vinyl pyrrolidone) grafted mesoporous carbon nitride for effective removal of cadmium(II) from wastewater

AbstractIndustrial pollutants in water streams, such as heavy metals, are among the most important issues for ecosystem and human health. Membrane filtration is an appealing technique for the removal of these contaminants from wastewater. In this study, composite ultrafiltration polyethersulfone (PES) membranes were fabricated by implementing poly (acrylic acid‐co‐N‐vinyl pyrrolidone) grafted mesoporous carbon nitride (MCN) nanoparticles to improve the performance of membranes. Polymer grafted MCN was synthesized through (3‐methacryloxypropyl)trimethoxysilane and (3‐Aminopropyl)triethoxysilane treatment and subsequent in situ radical polymerization on MCN. Modified membranes exhibited significantly improved hydrophilicity; the contact angle decreased from 66° for the PES membrane to 36° for the modified membranes. In addition, the morphology, surface roughness, thermal stability, and mechanical stability of membranes were studied. The results revealed that the pure water flux of membranes was improved from 82.6 to 329. 8 L/m2 h by increasing the nano‐additive content. Moreover, the membranes showed a maximum rejection of 92.3% for Cd2+ metal ions. Studying the fouling resistance of membranes showed a significant increase in fouling ratio recovery from 42.77% to 87.64%. It was also found that the irreversible fouling values were remarkably reduced because of the higher hydrophilicity of fabricated composite membranes.

Insights into the control mechanism of different coagulation pretreatment on ultrafiltration membrane fouling for oily wastewater treatment

Oily wastewater treatment is necessary to reduce environmental pollution. Herein, a coagulation-ultrafiltration integrated process was used to remove emulsified oil. AlCl3, FeCl3, polyaluminum chloride (PAC), polyferric chloride (PFC), and polydimethyl diallyl ammonium chloride (PDMDAAC) were used in coagulation process. It was found that PAC was more effective than AlCl3 and Fe based coagulants in treating oil/water emulsions. Flocs formed in PAC+PDMDAAC, PDMDAAC+PAC, and PAC-PDMDAAC coagulation systems had different size, resistance, structure, and recovery ability, which was due to the changes in the dominant coagulation mechanism. The flocs formed by PAC-PDMDAAC composite coagulant were large and loose, indicating that bridging action and entrapment dominated the removal of oil droplets. PAC-PDMDAAC was efficient in reducing irreversible membrane fouling, while the PAC+PDMDAAC dual coagulation system performed well in controlling reversible fouling. The PDMDAAC+PAC system had a large adsorption resistance and a small cake layer resistance. The PAC-PDMDAAC system had a large polarization resistance. The different membrane resistance distribution was closely related to the discrepancy in coagulation behaviors. Therefore, the enhancement in coagulation performance is the key factor to alleviate membrane fouling. This study will provide theoretical guidance for the treatment of actual oily wastewater.

Role of Titanium Dioxide-Immobilized PES Beads in a Combined Water Treatment System of Tubular Alumina Microfiltration and PES Beads.

The membrane process has a limit to the decay of various pollutants in water. To improve the problem, the roles of backwashing media and titanium dioxide (TiO2) photocatalyst-immobilized-polyethersulfone (PES) beads' concentration were investigated in a combined system of tubular alumina MF and the PES beads for advanced drinking water treatment. The space between the outside of the MF membrane and the module inside was filled with the PES beads. UV at a wavelength of 352 nm was irradiated from outside of the acryl module. A quantity of humic acid and kaolin was dissolved in distilled water for synthetic water. Water or air intermittent backwashing was performed outside to inside. The membrane fouling resistance after 3 h process (Rf,180) was minimum at 30 g/L of the PES beads for water backwashing, and at 40 g/L for air backwashing when increasing the PES beads from 0 to 50 g/L. The irreversible membrane fouling resistance after physical cleaning (Rif) was at the bottom at 5 g/L of the PES beads for water backwashing, which was 3.43 times higher than minimal at 40 g/L of the PES beads for air backwashing. The treatment effectiveness of turbidity increased when increasing the PES beads' concentration from 0 to 50 g/L; however, it reached a maximum at 98.1% at 40 g/L and 99.2% at 50 g/L for water and air backwashing, respectively. The treatment effectiveness of UV254 absorbance, which was dissolved organic matter (DOM), increased dramatically when increasing the PES beads; however, it reached a peak of 83.0% at 40 g/L and 86.0% at 50 g/L for water and air backwashing, respectively. Finally, the best PES beads' concentration was 20~30 g/L to minimize the membrane fouling; however, it was 50 g/L to remove pollutants effectively. The water backwashing was better than the air at treating DOM; however, the air backwashing was more effective than the water at removing turbid matter and reducing membrane fouling.

Mercapto functionalized–natural zeolites/PVDF mixed matrix membrane for enhanced removal of methylene blue

Azo dye-containing wastewater is one of the most critical contaminants due to modern industrial activities, especially in the textile industry. Membrane technology has been the most prominent separation technique to alleviate these pollutants with less energy input and less raw material utilization. In this sense, zeolite-based mixed matrix membranes have offered increased filtration performance as they combine the favorable properties of polymeric membranes, molecular sieving, and the negative charge properties of zeolites. The crucial challenge is the compatibility of the inorganic filler and the polymer matrix to boost flux and rejection; otherwise, both will be dramatically compensated. Herein, low-cost natural zeolites were functionalized using mercapto silane ((3-mercaptopropyl) trimethoxysilane) agent and incorporated into porous polyvinylidene fluoride (PVDF). The resulting mixed matrix membranes showed significantly higher rejection (97.01%) and flux (37.14 L m−2h−1) compared to those of pristine PVDF membrane (rejection and flux of 82.78% and 24.05 L m−2h−1, respectively). These positive results are due to the compatibility between the mercapto-functionalized natural zeolites and PVDF matrix. In the absence of mercapto groups, the rejection could be enhanced, but the permeability decreased. In addition, the antifouling properties of the mercapto functionalized–natural zeolites/PVDF mixed matrix membrane is desirable, as indicated by the higher flux recovery ratio and lower reversible and irreversible fouling.

Role of Membrane-Solute Affinity Interactions in Carbamazepine Rejection and Resistance to Organic Fouling by Nano-Engineered UF/PES Membranes.

In this study, polyethersulfone (PES) ultrafiltration (UF) membranes were modified with GO, Ag, ZnO, Ag-GO and ZnO-GO nanoparticles to improve carbamazepine removal and fouling prevention by making membrane surfaces more hydrophilic. The fabricated membranes were characterized for surface and cross-sectional morphology, surface roughness and zeta potential, as well as hydrophilicity, functional groups, surface tension parameters and water permeability Thereafter, the membranes were evaluated for their efficiency in removing MgSO4 and carbamazepine as well as antifouling properties. To understand the role of affinity interactions in rejection and fouling, membrane-solute adhesion energies (∆Gslm) were quantified based on the Lifshitz-van der Waals/acid-base method. Unlike previous studies, which have generalized fouling prevention to be due to improvements in hydrophilicity upon adding nanoparticles, this work further explored the role of surface tension components on rejection and fouling prevention. The addition of nanoparticles improved membrane hydrophilicity (77-62°), water permeability (11.9-17.7 Lm-2 h-1 bar-1), mechanical strength (3.46-4.11 N/mm2), carbamazepine rejection (30-85%) and fouling prevention (60-23% flux decline). Rejection and antifouling properties increased as ∆Gslm became more repulsive (i.e., less negative). Membrane modification reduced irreversible fouling, and the fouled membranes were cleaned by flushing with water. Fouling related more to membrane electron donor components (γ-), while the roles of electron acceptor (γ+) and Lifshitz-van der Waals components (γLW) were less important. This work provides more insights into the role of affinity interactions in rejection and fouling and how rejection and fouling mechanisms change with nanoparticle addition.

Efficient removal of dyes by light‐responsive graphene oxide‐blended polyethersulfone nanofiltration membranes

AbstractOne of the popular, low‐cost, efficient, and environmentally friendly methods for separating pollutants and water purification are membrane‐based processes. In this study, nanofiltration membranes were modified using the photo‐responsive graphene oxide‐spiropyran (GO‐SP) nanosheets as novel additive. Graphene oxide was employed to improve permeability, antifouling, and mechanical properties of the membranes. Spiropyran was added due to the increase in the self‐cleaning properties of the PES membranes. First, spiropyran (SP) as a photochromic compound was chemically immobilized onto the graphene oxide (GO) surface. Different examinations such as ultraviolet–visible (UV–Vis) spectroscopy, energy‐dispersive X‐ray spectroscopy (EDS), field emission scanning electron microscopy (FE‐SEM), and atomic force microscopy (AFM) were used to check the effective grafting of spiropyran. Then, nanofiltration membranes containing polyethersulfone (PES) and GO‐SP additive with different weight percentages (0.15, 0.25, 0.5, and 0.75 wt.%) were prepared. Membranes comprising 0.5 wt.% GO‐SP exhibited the best surface properties, and at concentrations above 0.5 wt.%, aggregation of GO‐SP additive occurred on the surface of the membrane. The Young modulus increased from 45.11 MPa for pure PES membrane to 82.63 MPa for PES/GO‐SP‐0.75. The flux of pure water, rejection of bovine serum albumin (BSA) protein, and separation of anionic dyes including Congo Red (CR) and Coomassie Brilliant Blue (CBB) were measured to show the filtration performance of the fabricated membranes. It was observed that the addition of 0.5 wt.% GO‐SP increased the flux of pure water of the PES‐based membrane from 2.97 to 14.6 L/m2 h. All prepared membranes rejected more than 94% of CBB and CR dyes. The addition of GO‐SP also developed the performance of the membranes against fouling. In addition, the effects of UV light on membrane fouling, dye rejection, and contact angle were investigated. According to the results, irradiation of GO‐SP with UV light decreased the contact angle and increased the flux of pure water. In the presence of UV light, the membrane containing 0.5 wt.% GO‐SP exhibited 58.74% reversible fouling, 8.30% irreversible fouling, and 93% flux recovery ratio, indicating its better performance than the pure membrane.

Membrane bioreactor assisted volatile fatty acids production from agro-industrial residues for ruminant feed application

Volatile fatty acids (VFAs) supplementation in ruminants’ diet as a source of energy and chemical precursors and their effect on animal’s physiology and well-being has long been of scientific interest. Production of VFAs through anaerobic digestion of agro-industrial residues not only creates value but also presents an alternative sustainable approach for ruminant feed supplementation. Therefore, this study aimed to investigate the bioconversion of agro-industrial residues produced in large quantities such as apple pomace (AP), thin stillage (Ts), and potato protein liquor (PPL) to VFAs, fully complying to regulations set for ruminant feed supplement production. In this regard, batch acidogenic fermentation assays (pH 6–10) and semi-continuous immersed membrane bioreactor (iMBR) were applied. In batch assays, at pH 10 the co-digestion of Ts and PPL produced the highest VFAs concentration (14.2 g/L), indicating a yield of 0.85 g CODVFAs/g volatile solids (VS)added. The optimum batch condition was then applied in the iMBR for in situ fermentation and recovery of VFAs at different organic loading rates (OLR). With increasing the OLR to 3.7 gVS/L.day, the highest VFAs concentration of 28.6 g/L (1,2 g CODVFAs /gVSadded) was achieved. Successful long-term (114 days) membrane filtration was conducted in a media with a maximum of 40 g/L of total solids (TS), facing irreversible membrane fouling in the final stages. Acidogenic fermentation using an iMBR has the potential to play an important role in the future of feed additive provision through the biorefining of agro-industrial wastes via the carboxylate platform, given the role of VFAs production from organic residues.

Ultrasonic-mediated electrochemical design of graphene/polyacrylonitrile conductive membrane for antifouling and electrofiltration

Electrofiltration using conductive membranes can effectively alleviate membrane fouling. However, poor dispersion and aggregation in water severely constrain the ability of graphene (Gr) to synthesize conductive membranes. Herein, the water-dispersible Gr with high conductivity is tailored by ultrasonic-assisted electrochemical exfoliation and loaded onto the polyacrylonitrile (PAN) membrane by classical vacuum filtering in layers. The customization at 6 V voltage, 40 W ultrasonic power, and 23.87 g/m2 mass loading endows an optimal improvement in membrane pore structure, permeability, mechanical behavior, and electrochemical properties. The graphene/polyacrylonitrile (Gr/PAN) conductive membrane exhibits a high conductivity of 6.43 S/cm and a water flux of 450.19 L m-2h−1. The membrane shows remarkable antifouling capabilities by achieving a 99.8% rejection rate, 89.74% flow rate recovery, and only 10.26% irreversible fouling using yeast as a pollutant model. The normalized flux of the membrane can stay high at 0.41 after electrofiltration for 120 min, outperforming other conductive membranes in comparison. Cyclic electrofiltration of the developed membrane exhibits a 53.85% higher normalized flux than when no electric field is present, demonstrating its potential for long-lasting antifouling under electric fields. This study offered a novel strategy for the straightforward construction of highly functional graphene-based conductive membranes utilized in electrofiltration.

Membrane fouling during nutrient recovery from digestate using electrodialysis: Impacts of the molecular size of dissolved organic matter

Electrodialysis (ED) has shown application potential in nutrient recovery from digestate thanks to the frequent electrode reversal practice that can clean the ion-exchange membranes regularly. However, the fouling caused by dissolved organic matter (DOM) is still a challenge to the long-term operation of ion-exchange membranes in ED, and the mechanism of this fouling has not been well studied regarding these compounds’ molecular size. Taking pig manure digestate as an example, this study utilized an ultrafiltration-ED design to fractionate the DOM into many different ranges of molecular size and then assessed the molecule size-specific DOM-fouling to ED membranes. The results showed that the fouling to the anion-exchange membrane (AM) was significantly influenced by molecular size, while the cation-exchange membrane was antifouling over full molecular size ranges. The DOM with a molecular size of smaller than 10 kDa, accounting for 9.1% of the total DOM in digestate, was found to mainly cause AM deterioration. In particular, the DOM smaller than 1 kDa migrated into the interior of AM, thus increasing the membrane resistance by 25.7% and decreasing the ion exchange capacity by 3.5%. The DOM with molecular size in the range of 1–10 kDa caused the fouling in the zone of 0–100 μm depth from the membrane surface. Meanwhile, the DOM with molecular size larger than 10 kDa did not cause obvious irreversible fouling. For instance, the DOM being larger than 0.1 μm, accounting for 75.2% of the total organic matter in the digestate, did not cause irreversible membrane fouling. These results indicate that attentions should be paid to the fouling caused by DOM with small molecular size of less than 10 kDa.

New insights into membrane fouling in coagulation-ultrafiltration by cake characteristics analysis: A case study with PACl-Al13 and PACl

Membrane fouling is a bottleneck issue that hindered the further application of ultrafiltration technology. To alleviate membrane fouling, coagulation-ultrafiltration (C-UF) process using polyaluminum chloride (PACl) and PACl-Al13 with high proportion of Al13O4(OH)247+ as coagulants, respectively, were investigated at various pH conditions. Results indicated that an increase in solution pH contributed to larger floc size and looser floc structure for both PACl and PACl-Al13. It was conducive to the formation of more porous cake, as evidenced by mean pore area and pore area distribution of cake, leading to lower reversible fouling. Furthermore, humic acid (HA) removal presented a trend of first increasing and then decreasing with the increase of pH. The optimal HA removal was achieved at pH 6 regardless of coagulant type, suggesting that the slightest irreversible fouling should be occurred at this point. Interestingly, the irreversible fouling with PACl coagulant achieved a minimum value at pH 9, while the minimal irreversible fouling with PACl-Al13 was observed at pH 6. We speculated that the cake formed by PACl could further intercept HA prior to UF process at alkaline pH. Furthermore, compared with PACl, PACl-Al13 had a stronger charge neutralization ability, thus contributing to more compact floc structure and higher HA removal at various pH conditions. By UF fractionation measurement, higher HA removal for PACl-Al13 was due to higher removal of HA with molecular weight less than 50 kDa.

Superior performance of catalytic ozonation on molecular-level transformation of effluent organic matter and self-cleaning property in catalytic ozonation membrane reactor

Catalytic ozonation membrane reactor (COMR) is one of the most promising technologies for municipal wastewater reclamation. Herein, we evaluated superior performance of catalytic ozonation in COMR through filtration of effluent organic matter (EfOM) using the origin and three catalytic membranes. We found that filtration primarily contributed to rejection of protein-like fluorescence enriched in relatively high-oxygen compounds (O/C >0.4) with high molecular weight and catalytic ozonation further removed humic-like materials and highly unsaturated, aromatic and reduced compounds (O/C<0.4; H/C<1.3), demonstrating complementary function of catalytic ozonation and filtration. The superior performance of catalytic ozonation than ozonation is reflected in higher removal of medium molecular weighted humic-like materials and S-containing compounds, enhancing the mineralization and reaction extent of EfOM. Additionally, catalytic ozonation exhibited strong self-cleaning property and eliminated irreversible membrane fouling. Our findings provide molecular-level insights into the reaction mechanism governing the COMR towards municipal wastewater reclamation.

Fabrication of Ultrafiltration Membranes from PAN Composites with Hydrophilic Particles for Separation of Heavy Oil Components

In this work, membranes were obtained from PAN with the addition of particles of graphene oxide (GO), PAN pyrolyzed under the influence of IR radiation (IR-PAN-a) and nanodiamonds (ND). The pore structure of the obtained membranes was studied. It has been shown that the addition of particles slightly reduces the average pore size of the membranes from 17 to 12–15 nm, which leads to a decrease in the membranes water permeance from 158 to 80.9–119.9 kg/m2 h bar. At the same time, the addition of particles led to hydrophilization of the surface—the water contact angle decreased from 65° to 48°–55°, which contributed to an increase in the flow of oil solutions in toluene by 2–3 times compared to the PAN membrane. At the same time, the addition of GO and IR-PAN-a contributed to a significant increase in the irreversible membrane fouling. On the other hand, the addition of nanodiamonds not only reduced the overall membrane fouling and increased the permeability of the separation mixture from 4.93 to 8.47 kg/m2 h bar, but also made it possible to recover more than 96% of the pure toluene flux. The membranes rejection with the addition of ND in the filtration of oil solutions in toluene 10 g/L was 85–89%.

Iron oxide doped ceramic membranes for combined organic – Inorganic colloidal fouling mitigation

Membrane fouling by the combined effect of organic – inorganic substances is a major hurdle toward the wide application of ultrafiltration processes. In this work, ceramic membranes were modified with low loading of in situ generated iron oxide nanoparticles to alleviate this fouling. Humic acid and/or silica nanoparticle dispersion were used as model foulants. The combined stream induced prompt initial flux decline and greater fouling extent to the pristine membrane, independent of silica content. On the other hand, the modified membranes displayed significantly enhanced antifouling characteristics. Compared to as-received membranes, modified membranes displayed up to 60% lower permeate flux decline at the end of fouling cycle. Moreover, still compared to as-received membranes, the irreversible fouling decreased by 22%, and the organic removal increased by up to 2 times, particularly for the larger pore size membranes. The adhesion interaction energies between the different membrane – foulant systems, based on the extended DLVO theory, successfully predicted the fouling behavior for the modified membranes in terms of reversibility. The results of this study provide an insight into organic – inorganic fouling mechanisms and suggest protocols for effective, inexpensive membrane modification techniques for fouling mitigation.

Irreversible membrane fouling caused by free TEP: Mitigation performance and mechanism of the integrated MIEX/UF process

Free transparent exopolymer particles (TEP) are an important type of TEP. Researchers have recognized the significant contribution of free TEP to irreversible membrane fouling when treating algae-laden water. Constructing a reasonable process to effectively decelerate membrane fouling caused by free TEP is necessary for the ultrafiltration of algae-laden water. Our experiments indicate that the integrated process of magnetic anion exchange resin (MIEX)/ultrafiltration (UF) can effectively impede the irreversible membrane fouling caused by free TEP. Compared with independent UF, after multi-cycle filtration, the growth rate of hydraulically and chemically irreversible fouling decreased by 40 % and 21 %, respectively, during the MIEX/UF process. The interfacial forces between free TEP and polyvinylidene fluoride (PVDF)/MIEX were determined using atomic force microscopy, and the results showed that the interfacial force of MIEX–free TEP was 4.3-fold higher than that of PVDF–free TEP. Although the adsorption of free TEP by MIEX partly reduced membrane fouling during the MIEX/UF process, the MIEX dynamic layer contributed the most to the alleviation of irreversible membrane fouling during MIEX/UF. Our experimental results provide a more feasible process design for effectively controlling the TEP-induced irreversible membrane fouling.

Role of visible light photocatalysis in alleviation and mechanism transformation of ultrafiltration membrane fouling caused by natural organic matter

In this study, a novel composite based on bismuth oxide, reduced graphene oxide and titanium dioxide (labeled as BRGT) was utilized for visible light photocatalysis to mitigate ultrafiltration membrane fouling caused by natural organic matter (NOM). The results show that the coexistence of NOM and the BRGT composite (without photocatalysis) did not aggravate membrane fouling, and the membrane preferentially retained a high molecular weight, hydrophobic component of NOM that formed a dense cake layer with BRGT composite. As the photocatalysis time increased, the extent of membrane fouling was alleviated. The maximum specific flux recovered from 0.21 to 0.73 at 60 min, and the hydraulic reversible and irreversible resistances ere 1.15 × 1010 and 4.23 × 1010 m−1, respectively. The reduction of NOM in the feed water, especially the removal of UV254, played a significant role in the alleviation of membrane fouling. Additionally, the changes in the properties of NOM, including the reduction of fluorescent humic and protein/polyphenol components corresponding to reversible and irreversible fouling, respectively, the photo-degradation of high molecular weight NOM into low molecular weight NOM (such as low molecular weight-acids), and the conversion of hydrophobic fractions into hydrophilic fractions, contributed to the mitigation of membrane fouling. We also found a strong negative correlation between the roughness of the cake layer and irreversible fouling. Overall, the changes in the properties of NOM in feed water can hinder or even inhibit the formation of the cake layer, and the use of visible light photocatalysis of the BRGT composite has great potential to alleviate ultrafiltration membrane fouling caused by natural organic matter.

Reverse osmosis pretreatment by a fluidized magnetic ion exchange resin for application in a power plant: Pilot-scale and high-rate operations and foulant characterization

Biofouling is one of the most serious problems in reverse osmosis (RO) operations. Here, we operated a pilot-scale MIEX® system with a high-rate configuration as a pretreatment for an RO system in a water purification plant. The goal was to investigate the RO foulants obtained with and without pretreatment by MIEX®. The MIEX® resin (10 to 300 mL/L) removed dissolved organic matter (DOM) within 5 min. A pilot-scale fluidized reactor with 100 mL/L of MIEX® removed 35.6%, 49.4%, and 56.2% of dissolved organic carbon (DOC) for effective resin doses of 0.03, 0.06, and 0.12 mL/L, respectively. Unknown screening analysis by Orbitrap mass spectrometry revealed that the MIEX® pretreatment decreased or removed 165–363 DOM features with carbon, hydrogen, and oxygen (CHO features) and 145–220 CHO features with N heteroatoms (CHON features) with effective resin doses of 0.03–0.12 mL/L. Moreover, fluorescence EEM revealed the preferential removal of terrestrial DOM, resulting in over half of the protein-like substances remaining in the RO feed. MIEX® selectively removed highly oxygenated DOM features within a short contact time, while condensed aromatic structures and lignin-like compounds were removed after 30 min. Increasing the MIEX® dose resulted in the additional removal of DOM features with less oxygenated characters and longer alkyl chains. The RO system with and without MIEX® pretreatment was similarly fouled by protein-like substances and CHON features; however, the MIEX® pretreatment decreased CHO features and terrestrial DOM foulants. The MIEX® pretreatment decreased organic and irreversible fouling and doubled the RO system lifetime, resulting in lower chemical cleaning and pressure requirements for an identical permeate volume.

Integration of antibacterial and photocatalysis onto polyethersulfone membrane for fouling mitigation and contaminant degradation

Biofouling is a significant constraint in the development of membrane filtration technology. In this study, Ag nanoparticles (AgNPs) were synthesized homogeneously in situ on the polyethersulfone (PES) membrane surface, and titanium dioxide (TiO2) photocatalytic agent was subsequently coated through the functional polydopamine intermediate layer. The Ag-TiO2-PDA/PES membrane presented enhanced hydrophilicity, attractive antibacterial ability, and photocatalytic performance. The AgNPs modification achieved 96% bacterial inactivation by using the E.coli DH5α as the model microorganism, and TiO2 provided a photocatalytic degradation ability to the membrane. The improved flux recovery of the Ag-TiO2-PDA/PES membrane, which was approximately 95% in the third cyclical filtration, revealed the efficient antifouling ability through AgNPs and TiO2 modification. The Ag-TiO2-PDA/PES membrane inhibited biofouling in dynamic filtration by AgNPs and degraded the irreversible fouling by TiO2 during the cleaning procedure. The combined modification of the PES membrane by AgNPs and TiO2 exhibited a synergistic effect on the improvement of antifouling properties. This study provides a multifunctional membrane design strategy by combining antibacterial and photocatalysis to improve membrane fouling resistance.