Ultrafiltration Membrane Fouling Research Articles

Membrane fouling behaviors in membrane Fenton process without acid-base agents controlled by current density for nanofiltration concentrate treatment

Effective generation of H+ and OH− in the Fenton by electrodes is crucial for addressing the impact of acidity and alkalinity on the environment. In this study, electrolysis was coupled with membrane Fenton for nanofiltration concentrate treatment and membrane fouling behaviors were investigated. The effects of current density and dosage (H2O2 and Fe2+ ) were studied. According to the Box-Behnken design results, both current density and the dosages of H2O2 and Fe2+ positively influenced the removal of organic pollutants, with the former showing the most significant effect. Hydroxyl radical (•OH) oxidized the organic pollutants into intermediates, realizing a removal efficiency of 74.50 %. The anode oxidation and Fenton process effectively degraded fluorescent components, particularly humic acid-like substances. Ammonia nitrogen was degraded by active chlorine produced at the anode, with an average removal rate of 51.36 %. Additionally, an increase in current density enhanced ion exchange membrane fouling. Chemical composition analysis suggested that the membrane was primarily covered with hydroxide crystal substances. The ultrafiltration (UF) membrane analysis indicated that cake layer formation was responsible for the trans-membrane pressure (TMP) increase, and cake-complete was the primary mechanism contributing to UF membrane fouling. The membrane Fenton process without acid-base agents exhibits significant potential for contaminants removal from nanofiltration concentrate and is advantageous for cleaning membrane fouling.

Understanding the fouling characteristics in ultrafiltration membrane for marine algae-laden seawater pretreatment: Focus on the role of algal extracellular organic matter

The increasing frequency and extent of harmful algal blooms (HABs) due to global warming and environmental pollution pose significant challenges to the ultrafiltration (UF)-seawater reverse osmosis (SWRO) desalination process. The UF process is a dominant pretreatment method to reduce HAB fouling potential in subsequent SWRO processes. Herein, we systematically evaluate the UF membrane fouling characteristics at different growth phases of HAB algae in terms of reversible/irreversible fouling and pinpoint the fouling mechanisms on UF membranes in the real seawater matrix. We employed Prorocentrum donghaiense as a model marine HAB specie to characterize algal derivatives, including extracellular organic matter (EOM) and granule particles. LC-OCD, MFIs, 3D-EEM, and GPC were used to analyze algae-derived matters. Results from the multiple fouling model revealed that algal solution in both stationary and decline phases exhibit severe membrane fouling, characterized by rapid cake layer formation, swift flux decline, and high membrane resistance. Soluble EOM (S-EOM) was the primary contributor to membrane fouling, linked to its elevated concentrations of dissolved organic matters, polysaccharides, proteins, and humic substances, which are predominantly hydrophobic. Additionally, granule particles mitigated organic membrane fouling, as evidenced by the smaller permeate volume required for S-EOM cake layer formation (<5 mL), resulting in a faster initial flux decline. These results revealed a shift in released organic matter from protein-centric to humic substance-centric during the transition from exponential growth to the decline phase, with correlation analysis further underscoring the substantial contribution of humic substances to membrane resistance. This research highlights the distinct UF membrane fouling characteristics at different marine algal growth stages, offering theoretical support for predicting and managing HABs.

Ultraviolet/dielectric barrier discharge enhanced ultrafiltration for treating natural water: Performance, mechanism and iodinated disinfection by-product fate

This study employed ultraviolet (UV)/ dielectric barrier discharge (DBD) pre-treatment to mitigate ultrafiltration membrane fouling and enhance the purification efficiency of natural surface water. Moreover, as an emerging contaminant, the iodinated disinfection by-products’ fate and degradation performance were discussed. The investigation revealed that the generation of numerous active species (⋅OH, ⋅O2−, 1O2, etc) under high input voltage and low pH conditions were advantageous for augmenting membrane flux, with sodium sulfate electrolyte playing a role in promoting the formation of selective sulfate radicals. Fluorescence excitation-emission matrix spectroscopy indicated that the UV/DBD system at 5.5 kV can effectively degrade proteins and humic substances in surface water, leading to an enhancement in water quality. With the assistance of UV radiation, macromolecular organic matter underwent extensive decomposition into smaller molecules, thus creating an ideal environment for controlling membrane fouling in the UV/DBD system. Additionally, it was identified the intermediate products and degradation pathways during iopamidol degradation by UV/DBD. It also affirmed the minimal risk of disinfection by-product generation with this strategy. The study provides a viable and efficient pre-treatment approach for mitigating membrane fouling and purifying water.

Contribution of specific extracellular organic matter on membrane fouling in ultrafiltration and coagulation-ultrafiltration of algae-laden water

This study explores the specific impact of bound and dissolved extracellular organic matter (bEOM and dEOM), and their collective influence with algal cells on membrane fouling during ultrafiltration (UF) and coagulation-UF of algae-laden water. By characterizing the organic properties and adsorptive behaviors of bEOM and dEOM, and analyzing their subsequent impacts, we clarify their roles and contributions to membrane fouling. Our analyses revealed that bEOM, characterized by its higher molecular weight (MW) and hydrophobic nature, contains more protein-like substances compared to dEOM. Quartz Crystal Microbalance with Dissipation (QCM-D) analysis highlights significant differences in their adsorption behaviors, with bEOM demonstrating greater adhesion and higher adsorptive fouling potential. Despite bEOM's lower concentration relative to dEOM, at a ratio of 0.12–1, their contributions to irreversible membrane resistance are nearly identical, at 30.7% and 30.9% respectively, in the UF of algae-laden water. Coagulation pretreatment effectively reduces bEOM's fouling potential by forming larger flocs, thus minimizing its contact with the membrane. In terms of irreversible membrane resistance, the contributions are 6.5% from cells, 24.8% from bEOM, and 68.6% from dEOM. The presence of dEOM complicates coagulation efficiency due to its low MW components and high hydrophilicity. Using the Hermia model, atomic force microscopy (AFM), and scanning electron microscopy (SEM), we demonstrated how bEOM and dEOM modify membrane fouling mechanisms, particularly by influencing cake layer formation. These insights emphasize the distinct and significant contributions of bEOM and dEOM to membrane fouling, necessitating targeted strategies for their management to enhance the efficiency and sustainability of UF systems in water treatment facilities.

Control ultrafiltration membrane fouling in Chlorella-laden water treatment by integrated heat-activated peroxydisulfate pre-oxidation and coagulation treatment

The membrane fouling induced by algal extracellular organic matter (EOM) remain a bottleneck in restricting ultrafiltration (UF) application during harmful algal-water treatment. In current study, the application of heat-activated peroxydisulfate (PMS) and coagulation (Aluminum chlorohydrate, PACI) on membrane fouling behavior during Chlorella-laden water treatment was investigated. The membrane fouling mechanism was analyzed using the extended Derjaguin-Landau-Verwey-Over-beek (XDLVO) theory. The results revealed that separated heat-activated PMS could enhance the filtration flux of EOM at high PMS does >0.2 mM, whereas the membrane fouling was further alleviated by combined heat-activated PMS (0.2–1.0 mM) and PACI (20 mg/L) treatment, especially at low PMS dose. Combined heat-activated PMS and PACI pretreatment could effectively increase the adhesive repulsion between membrane and foulants and reduce the cohesion free energies between organic foulants than those by separated heat-activated PMS treatment, making the initial filtration flux reduced and the cake layer looser. Moreover, the organic foulants of proteins, polysaccharides, and humic-like organics were removed. Cake formation was the major fouling mechanism when EOM was treated with/without separated heat-activated PMS treatment, whereas the membrane fouling mechanism was changed from cake layer formation to pore blocking after combined heat-activated PMS and PACI treatment. Overall, this research provided a feasible method in membrane fouling control during Chlorella -laden water treatment.

Effect of In Situ Aeration on Ultrafiltration Membrane Fouling Control in Treating Seasonal High-Turbidity Surface Water

Effect of In Situ Aeration on Ultrafiltration Membrane Fouling Control in Treating Seasonal High-Turbidity Surface Water

Sustainable control of organic-inorganic combined fouling of electroactive ultrafiltration membrane during electrocatalytic-driven self-cleaning process: Mechanism and implications

Organic-inorganic combined fouling of membrane is a tough problem that restrained its application in water treatment, which was insufficient and non-sustainable to be alleviated by conventional chemical cleaning. Herein, a facile and sustainable control strategy was developed to mitigate biopolymer-Ca2+ combined fouling for an electroactive metal-organic framework ultrafiltration membrane. Bovine serum albumin (BSA) and sodium alginate (SA) were selected as model biopolymer. The results showed BSA and SA fouling both accelerated with increasing Ca2+ concentration (0–1.0 mM) via calcium bridging action and hydraulic cleaning was insufficient to restore flux (flux recovery < 7 %). By comparison, flux can be fully recovered by applying electricity to all combined fouling, suggesting membrane presented outstanding self-cleaning performance. According to the free radical quenching test and physicochemical property of biopolymer, fouling control mechanism was revealed because in-situ electro-generated OH and O2− free radicals caused decomplexation of biopolymer and Ca2+, and then degraded biopolymer into smaller and less hydrophobic fragments that repulsed membrane. Extended Derjaguin–Landau–Verwey–Overbeek theory further unveiled the foulants-membrane interaction shifted from attraction to repulsion after self-cleaning. This strategy has the advantages of low chemical cleaning reagents and energy consumption, which may provide the guidance for sustainable control of organic-inorganic combined membrane fouling.

Co-activation of peroxymonosulfate activation with sunlight and tailored catalytic MnFe2O4/MWCNTs membrane to mitigate membrane fouling caused by NOM and synergistic oxidation mechanism analysis

Membrane fouling has been a major factor hindering the development of ultrafiltration membranes. Herein, a novel in situ oxidation system was constructed via introducing MnFe2O4/MWCNTs into polyvinylidene fluoride (PVDF) membranes, utilizing sunlight to synergistically activate persulfate (PMS) to mitigate ultrafiltration membrane fouling. The mechanism of mitigating membrane fouling in MnFe2O4/MWCNTs-PVDF ultrafiltration membranes was systematically explored under four system (single filtration, single sunlight irradiation, single PMS oxidation and sunlight co-activated PMS). The MnFe2O4/MWCNTs-PVDF membranes exhibited different fouling characteristics under the four systems, with the sunlight and MnFe2O4/MWCNTs membrane co-activated PMS filtration system showing the highest humic acid (HA) removal efficiency of 90.2 %, as well as the lowest Rr (0.2108 × 1012m−1) and Rir (0.4525 × 1012m−1). To further evaluate the practicality and effectiveness of the sunlight-MnFe2O4/MWCNTs-PMS system, the secondary effluent was selected to verify the treatment effect on natural organic matter (NOM) of actual water. By observing the microscopic morphology of the fouled membrane surface, it was evident that, compared with the other three filtration systems, the filter cake layer on the MnFe2O4/MWCNTs membrane surface of the sunlight co-activated PMS system was obviously reduced, and the structure of the cake layer was more loose. It can be concluded that the principle behind the synergistically activated system to alleviate the membrane fouling was to accelerate the mineralization rate of HA molecules, oxidize the HA into a smaller particle size that can pass through the membrane pores. The main reactive oxygen species and HA degradation mechanism in the synergistic activation system were further elucidated by electron paramagnetic resonance (EPR) analysis and density functional theory calculations (DFT). The results indicated that the degradation of HA by the synergistically activated PMS system involved a combination of free radicals (·O2−、SO4·− and ·OH) and non-free radicals (1O2). Overall, the in-situ oxidation system provided an alternative way to alleviate ultrafiltration membrane fouling.

Comparison of chlorine and peroxymonosulfate in enhancing vacuum ultraviolet for treating secondary effluent to mitigate ultrafiltration membrane fouling

Herein, sodium hypochlorite (NaClO) and peroxomonosulfate (PMS) were systematically compared in enhancing vacuum ultraviolet (VUV) oxidation for alleviating ultrafiltration membrane fouling of effluent organic matter. Results indicated that VUV/NaClO pre-treatment exhibited significantly better performance than VUV/PMS, with the irreversible fouling resistance reduced by 64 %. Simultaneously, 96 % of fluorescent substances were removed by VUV/NaClO, and an apparent decrease in surface deposits was observed, with membrane pores exposed and clearly visible. The calculation results through the extended Derjaguin-Landau-Verwey-Overbeek theory indicated that the enhanced hydrophilicity of pollutants reduced the tendency of pollutants to adhere to the membrane surface, leading to the weakening of membrane fouling degree. In the VUV/PMS process, HO• and SO4•– were detected with steady-state concentrations of 8.55 × 10-14 and 1.53 × 10-13 M. By contrast, the VUV/NaClO system generated HO•, Cl•, ClO•, and Cl2•– with steady-state concentrations of 1.15 × 10-13, 8.79 × 10-14, 7.30 × 10-13 and 1.50 × 10-13 M. In conclusion, VUV/NaClO pre-treatment demonstrated high efficiency and significant potential in improving water quality and decreasing membrane fouling in secondary effluent treatment.

Dynamic evolution of ultrafiltration membrane fouling affected by S(IV)–Fe(II)-activated permanganate pretreatment during a long-term operation

ABSTRACT The S(IV)–Fe(II)/PM pretreatment has demonstrated preliminary potential as an effective ultrafiltration (UF) pretreatment technology. However, a comprehensive understanding of its impact on UF membrane fouling control and the dynamic evolution of membrane fouling during prolonged operation is still lacking. In this study, a relatively prolonged fouling experiment was conducted. Results revealed that the S(IV)–Fe(II)/PM pretreatment exhibited superior performance over Al(III) coagulation pretreatment in mitigating the transmembrane pressure difference and addressing both reversible and irreversible membrane fouling. The application of a cluster analysis method to classify membrane fouling evolution stages further confirmed that S(IV)–Fe(II)/PM pretreatment effectively decelerated the rate of membrane fouling evolution. The surface cake layer of UF membranes pretreated with S(IV)–Fe(II)/PM exhibited greater looseness and smoothness. It also showed better results than Al(III) coagulation pretreatment in reducing the accumulation of organic foulants, controlling the Si content and reducing the total microorganisms and live microorganisms in the UF feed water. Variance Partitioning Analysis indicated that the combined contribution of organic, inorganic, and biological foulants was the most significant for UF membranes after S(IV)–Fe(II)/PM pretreatment (50.4%) and UF membranes after Al(III) coagulation pretreatment (70.2%). These findings underscore the efficacy of S(IV)–Fe(II)/PM pretreatment in controlling UF membrane fouling under prolonged operation.

The molecular weight-fouling matrix: A novel dissection of polysaccharide interactions in ultrafiltration processes

Polysaccharides, recognized as critical organic pollutants, exhibit fouling tendencies intricately tied to molecular weight (MW). While extensive discussions have focused on the MW of polysaccharides, a comprehensive understanding of its direct impact on membrane fouling remains elusive. In this study, dextran with different MWs acted as model pollutants, revealing the intricate relationship between polysaccharide MW and fouling behavior. Data on specific flux and filtration resistance indicated an initial decline and subsequent increase in fouling with increased MW. Noteworthily, polysaccharides with an intermediate MW of 40 kDa exhibited the least fouling. Advanced analytical methods indicated the source of the reduced fouling to pronounced intermolecular repulsions and crucial molecular configuration shifts. While the lower MW variants resisted membrane adhesion, their higher MW counterparts fostered dense filter cake layer development, causing serious membrane fouling. By describing the nuanced roles of MW on ultrafiltration membrane fouling, this investigation not only deepens insights into the nexus between organic foulant MW and fouling, but also illuminates pathways for innovative strategies in mitigating polysaccharide-induced fouling in ultrafiltration water treatment processes.

Effect of Long-Term Sodium Hypochlorite Cleaning on Silicon Carbide Ultrafiltration Membranes Prepared via Low-Pressure Chemical Vapor Deposition.

Sodium hypochlorite (NaClO) is widely used for the chemical cleaning of fouled ultrafiltration (UF) membranes. Various studies performed on polymeric membranes demonstrate that long-term (>100 h) exposure to NaClO deteriorates the physicochemical properties of the membranes, leading to reduced performance and service life. However, the effect of NaClO cleaning on ceramic membranes, particularly the number of cleaning cycles they can undergo to alleviate irreversible fouling, remains poorly understood. Silicon carbide (SiC) membranes have garnered widespread attention for water and wastewater treatment, but their chemical stability in NaClO has not been studied. Low-pressure chemical vapor deposition (LP-CVD) provides a simple and economical route to prepare/modify ceramic membranes. As such, LP-CVD facilitates the preparation of SiC membranes: (a) in a single step; and (b) at much lower temperatures (700-900 °C) in comparison with sol-gel methods (ca. 2000 °C). In this work, SiC ultrafiltration (UF) membranes were prepared via LP-CVD at two different deposition temperatures and pressures. Subsequently, their chemical stability in NaClO was investigated over 200 h of aging. Afterward, the properties and performance of as-prepared SiC UF membranes were evaluated before and after aging to determine the optimal deposition conditions. Our results indicate that the SiC UF membrane prepared via LP-CVD at 860 °C and 100 mTorr exhibited excellent resistance to NaClO aging, while the membrane prepared at 750 °C and 600 mTorr significantly deteriorated. These findings not only highlight a novel preparation route for SiC membranes in a single step via LP-CVD, but also provide new insights about the careful selection of LP-CVD conditions for SiC membranes to ensure their long-term performance and robustness under harsh chemical cleaning conditions.

Variation in organic matter characteristics and mitigation of ultrafiltration membrane fouling by chlorine and UV/chlorine pre-oxidation in secondary effluent treatment

Membrane fouling caused by effluent organic matter (EfOM) limits its further application in wastewater reuse. In this study, the effect of UV/chlorine pretreatment on membrane fouling was investigated in treating secondary effluent by ultrafiltration (UF) process. The relation between organic matter changes and fouling alleviation after UV/chlorine pretreatment was also studied according to the molecular weight (MW) changes in various resin fractions derived from EfOM. Results showed that UV/chlorine pretreatment effectively alleviated irreversible fouling, whereas chlorine pre-oxidation primarily mitigated reversible fouling. UV/chlorine pre-oxidation reduced 18% of reversible membrane fouling and 38% of irreversible membrane fouling at a chlorine dosage of 8 mg/L, indicating better performance in membrane fouling mitigation than chlorine pre-oxidation. UV/chlorine pre-oxidation also decreased dissolved organic matter in the UF permeate. The hydrophobic acidic (HPO-A) fraction caused dominant membrane fouling, while the hydrophilic (HPI) fraction contained most of high MW organic matter. Pre-oxidation changed the polarity of organic matter in the HPO-A fraction and decomposed the organics of high MW in the HPI fraction, which alleviated membrane fouling. These results showed that UV/chlorine pre-oxidation was a prospective pretreatment process prior to UF in wastewater reclamation.

Continuation of a cleaning process: Application of MNBs-coagulation process to mitigate ultrafiltration membrane fouling

The MNBs-coagulation process as a novel and cleaning enhanced coagulation process has been demonstrated to enhance the removal efficiency of hydrophilic organics. In this study, while continuing the concept of cleaning production, the MNBs-coagulation process was first applied to the ultrafiltration process and was expected to alleviate the ultrafiltration membrane fouling. This study investigated the effect of the involvement of MNBs in coagulation-ultrafiltration process (the MC-UF process) on the fouling behaviour of ultrafiltration membrane based on the calculation of membrane resistance distribution and the fitting of membrane fouling model. In addition, the NOM removal efficiency, floc characteristics analysis and membrane hydrophilicity analysis were used to illustrate the mechanism of mitigating ultrafiltration mebrane fouling by the MC-UF process. The experimental results showed that the involvement of MNBs in the coagulation-ultrafiltration process was able to reduce the irreversible fouling and TMP by 43.1 % and 41.6 % respectively. This phenomenon could be attributed to the involvement of MNBs in the coagulation process to improve the removal efficiency of hydrophilic organics and to enhance the characteristics of flocs, thus reducing the possibility of hydrophilic organics and broken flocs entering and blocking the membrane pores. In addition, the FT-IR spectral changes before and after the floc breakage were analyzed by 2D-COS technique in this study, and it was found for the first time that the participation of MNBs in the coagulation process could change the sequence of functional group transformation within the floc, and promote the generation of hydrogen bonds between flocs by hindering the generation of hydroxyl groups (-OH), and improve the shear resistance and regrowth capacity of flocs while reducing the possibility of broken flocs entering and blocking membrane pores. In summary, the MC-UF process proposed in this study can significantly mitigate ultrafiltration membrane fouling while meeting cleaning production, providing theoretical support for the application of the process to practical engineering.

Synergistic roles of oxidation and self-aggregation in efficient ultrafiltration membrane fouling alleviation using a flow-through Sb-SnO2 anode during wastewater reclamation

The application of ultrafiltration (UF) in wastewater reclamation alleviates the demand for limited water supplies. However, the membrane fouling caused by the effluent organic matter (EfOM) becomes a major obstacle for UF application. In this study, a pre-oxidation strategy for UF using a Sb-SnO2 (ATO) anode in flow-through mode was proposed with the hopes to improve the performance of UF during wastewater reclamation. The results indicated that this flow-through ATO (FA) anode significantly outperformed a boron-doped diamond (BDD) anode in terms of EfOM degradation and membrane fouling control. It is noteworthy that apart from oxidation, the self-aggregation behavior of foulants was also involved in the mechanisms of membrane fouling mitigation. On the one hand, FA pre-oxidation relieved the burden of membrane fouling by decomposing the macromolecular EfOM into small molecular organic matter, and even mineralizing it. The effective destruction of unsaturated EfOM by FA pre-oxidation made a remarkable contribution to fouling mitigation due to the strong correlation between the total fouling index and UV254. On the other hand, the surface morphology of membrane and interface properties of foulants revealed the self-aggregation behavior of foulants. FA pre-oxidation made the foulants aggregate spontaneously and reduced the potential of forming a dense cake layer on the membrane surface, which was conductive for water permeation. Overall, FA pre-oxidation proved to be a feasible and chemical-free option for UF pretreatment to simultaneously produce high-quality reused water and alleviate membrane fouling during wastewater reclamation.

High performance photodegradation resistant PVA@TiO2/carboxyl-PES self-healing reactive ultrafiltration membrane

The occurrence of ultrafiltration (UF) membrane fouling frequently hampers the sustainable advancement of UF technology. Reactive self-cleaning UF membranes can effectively alleviate the problem of membrane fouling. Nevertheless, the self-cleaning process may accelerate membrane aging. Addressing these concerns, we present an innovative design concept for composite self-healing materials based on self-cleaning UF membranes. To begin, TiO2 nanoparticles were incorporated into the polymer molecular structure via molecular design, resulting in the synthesis of TiO2/carboxyl-polyether sulfone (PES) hybrid materials. Subsequently, the nonsolvent-induced phase inversion technique was employed to prepare a novel of UF membrane. Lastly, a polyvinyl alcohol (PVA) hydrogel coating was applied to the hybrid UF membrane surface to create PVA@TiO2/carboxyl-PES self-healing reactive UF membranes. By establishing a covalent bond, the TiO2 nanoparticles were effectively and uniformly dispersed within the UF membrane, leading to exceptional self-cleaning properties. Furthermore, the water-absorbing and swelling properties of PVA hydrogel, along with its capacity to form hydrogen bonds with water molecules, resulted in UF membranes with improved hydrophilicity and active self-healing abilities. The results demonstrated that the water contact angle of PVA@5%TiO2/carboxyl-PES UF membrane was 43.1°. Following a 1-h exposure to simulated solar exposure, the water flux recovery ratio increased from 48.16% to 81.03%. Moreover, even after undergoing five cycles of 12-h simulated sunlight exposure, the UF membranes exhibited a consistent retention rate of over 97%, thus fully demonstrating their exceptional self-cleaning, antifouling, and self-healing capabilities. We anticipate that the self-healing reactive UF membrane system will serve as a pioneering and comprehensive solution for the self-cleaning antifouling challenges encountered in UF membranes while also effectively mitigating the aging effects of reactive UF membranes.

Applying S(IV)-Fe(II) binary activation of permanganate as ultrafiltration pretreatment for fouling mitigation: Performance, influencing factors, and mechanism

The widespread implementation of ultrafiltration (UF) technology, which has gained popularity for drinking water treatment, has been impeded by rising operational costs and shortened membrane lifespans resulting from membrane fouling. Here, an integrated pretreatment technique combining oxidation, adsorption, and coagulation was developed using the S(IV)–Fe(II) binary activated permanganate (PM) system, S(IV)–Fe(II)/PM. The efficacy of S(IV)–Fe(II)/PM pretreatment in mitigating UF membrane fouling was investigated for various raw water sources, including lakes, rivers, and seawater. The operational parameters of S(IV)–Fe(II)/PM pretreatment were optimized, and the underlying mechanisms for fouling alleviation were explored. Relative to conventional pretreatment methods, S(IV)–Fe(II)/PM pretreatment reduced reversible fouling-induced resistance by 13%–92% and irreversible fouling-induced resistance by 11%–86%. The S(IV)–Fe(II)/PM system exhibited optimal mitigation of membrane fouling at a PM:S(IV):Fe(II) dosage ratio of 2:3:3, with Grapid × Trapid = 45948, Gslow × Tslow = 12480, and a settling time of 30 min (where G is the velocity gradient and T is contact time). The effectiveness of S(IV)–Fe(II)/PM pretreatment in controlling UF membrane fouling can be attributed to the following mechanisms: 1) modification of feed water quality in terms of organic compound characteristics and concentration, colloidal particle quantity and size distribution, and microbial activity and quantity; and 2) adjustment of the membrane surface deposition environment, resulting in reduced polysaccharide and protein content, particle size distribution range, and biomass, as well as alterations in physicochemical properties such as hydrophilicity and interfacial free energy. This study highlights the efficacy of S(IV)–Fe(II)/PM pretreatment in ensuring high-quality UF effluent while effectively reducing membrane fouling, especially its potential for alleviating irreversible membrane fouling.

Electro-separation of chitooligosaccharides with specific degrees of polymerization using electrodialysis ultrafiltration

Biological activities of chitooligosaccharides (COSs) are related to their purity and intrinsic structure. However, a wide range of size distribution and degree of polymerization (DP) of COS make it challenging for their meticulous biological research and applications. This research investigated the protonation behavior and the separation mechanism of individual COSs molecules at semi-pilot scale using an electrodialysis-ultrafiltration membrane. Results indicated that COSs were protonated to varying degrees in the pH ranges of 3.28 to 7.95 with a pKa value stand nearly at 6.44. A semi pilot scale investigation of operational parameters successfully separated a fraction with degree of polymerization (DP) ≤ 4 (>93% of total COS migrated) at flow velocity 6.79 cm/s and electric potential of 9 V/cm with highest DP 3 (>36% of the fraction) in 60 min. Additionally, few other fractions (DP ≤ 3 and DP ≤ 5) were efficiently separated from the industrial sample at different processing times. Moreover, the selective conditions also prevent the fouling of ultrafiltration membrane. Conclusively, the inadequate or too high applied electric potential and solution flow velocities have significant influence on migration of target molecules.

Moderate pre-photocatalysis-enhanced coagulation alleviates ultrafiltration membrane fouling of algae-laden water

Moderate chemical pre-oxidation of coagulation to remove algae without breakage of the algae cells and release of algal organic matter has been well reported, while little was known about moderate pre-photocatalysis followed by coagulation on the ultrafiltration performance and membrane fouling control during algae-laden water treatment. Herein, three pretreatment methods (photocatalysis, coagulation and moderate pre-photocatalysis-enhanced coagulation (PC)) were investigated to reduce membrane fouling during ultrafiltration of algae-laden water. Moderate photocatalysis by a composite of Bi2O3-TiO2/PAC (Bi-doped TiO2 nano-composites supported by powdered activated carbon) not only avoided algae cell breakage and controlled the release of intracellular organic matter, but also halved the aluminum sulphate (AS) coagulant dosage, since Bi2O3-TiO2/PAC acted as both a photocatalyst and flocculation core. Under optimal conditions (1.2 g/L Bi2O3-TiO2/PAC irradiated under visible light for 20 min and 0.1 mM AS), the removal of OD680, DOC and UV254 were 83.8 %, 60.3 % and 77.3 % respectively. Moderate photocatalysis degraded medium and high molecular weight organics (biopolymers, humic substances and building blocks) to low MW acidic and neutral organics, resulting in effective removals of humic substances and microbial metabolites typically present in algal-derived pollutant. Following PC pre-treatment with ultrafiltration, 87.5 % increase in the final specific flux, 96.1 % reduction in irreversible resistance, and a change in the fouling mechanism from cake layer blockage to intermediate blockage. In addition, the zeta potential was reduced and the interaction force between pollutant-pollutant/membrane became a repulsive force. This work demonstrates the potential benefits of moderate pre-photocatalysis-enhanced coagulation to remove algal contaminants and mitigate ultrafiltration membrane fouling.

Evaluation of diffusion coefficients as surrogate indicators for electrostatic repulsion in ultrafiltration membrane fouling

Impacted by the electrostatic repulsion between ultrafiltration (UF) membranes and natural organic matter (NOM), organic fouling precipitates significant operational difficulties in water treatment facilities. This study investigated the applicability of diffusion coefficients as surrogate indicators to evaluate the electrostatic repulsive forces between NOMs and UF membrane surfaces. We utilized three distinct types of NOMs and three different UF membranes, each possessing different charge characteristics. Notably, we found that the reduction in diffusion coefficients was markedly pronounced when membranes rich in ionizable functional groups with strong negative charges were involved, indicating heightened electrostatic repulsion. To confirm the reliability of diffusion coefficient reduction as a surrogate indicator of the electrostatic repulsive force, a comprehensive membrane fouling test was conducted. The results revealed a strong correlation between the two parameters, enhancing our understanding of the intricate dynamics of membrane fouling (R2 = 0.9744–0.9907). Thus, this study proposes the concept of utilizing the reduction in the diffusion coefficient as a surrogate indicator to represent the electrostatic repulsive force between NOMs and the UF membrane surface. This innovative approach contributes to enables proactive and predictive assessments of membrane performance, fostering a shift toward proactive maintenance and enhances the operational efficiency of water treatment facilities.