Ultrafiltration Membrane Fouling Research Articles

Oxidation and coagulation/adsorption dual effects of ferrate (VI) pretreatment on organics removal and membrane fouling alleviation in UF process during secondary effluent treatment

Ultrafiltration (UF) has been widely used in water and advanced sewage treatment. Unfortunately, membrane fouling is still the main obstacle to further improvement in the system. Fe (III) salt, a type of traditional coagulant, is often applied to mitigate UF membrane fouling. However, low molecule organic weight cannot be effectively removed, thus the water quality after single coagulation treatment does not effectively meet the standard of subsequent water reuse during secondary effluent treatment. Recently, it has been found that potassium ferrate (Fe (VI)) has multiple functions of oxidation, sterilization and coagulation, with other studies proving its good performance in organics removal and membrane fouling mitigation. However, the respective contributions of oxidation and coagulation/adsorption have not yet been fully understood. The oxidation and coagulation/adsorption effects of Fe (VI) during membrane fouling mitigation were investigated here. The oxidation effect of Fe (VI) was the main reason for organics with the MW of 8–20 kDa removal, and its coagulation/adsorption mainly accounted for the smaller amounts of molecular organics removed. The oxidation of Fe (VI) was the main method for overcoming membrane fouling in the initial filtration; it largely alleviated the standard blockage. The formation of a cake layer transformed the main membrane fouling alleviation mechanism from oxidation to coagulation/adsorption and further removed smaller amounts of molecule organics with the increase of filtration cycles and Fe (VI) dosages. The main fouling mechanism altered from standard blocking and cake filtration to only cake filtration after Fe (VI) treatment. Overall, the mechanism of the oxidation and coagulation/adsorption of Fe (VI) were differentiated, and would provide a reference for future Fe (VI) pretreatment in UF membrane fouling control during water and wastewater treatments.

Effect of adsorption and coagulation pretreatment sequence on ultrafiltration membrane fouling: Process study and targeted prediction

A novel combined pretreatment strategy, where the hydrophobicity of feedwater is reduced and the morphology of flocs is optimized by varying the sequence of powdered activated carbon (PAC) adsorption and coagulation, is applied to alleviate membrane fouling. To explore the effects of pretreatment sequence and the role of PAC on the membrane fouling, the combined pretreatments of adsorption followed by coagulation (A-C) and coagulation followed by adsorption (C-A) are investigated with various PAC dosages (10, 20, and 50 mg/L). The results reveal that since PAC directly participates in the growth of flocs as the core during A-C pretreatment, the A-C pretreatment is more conducive than the C-A pretreatment to form flocs with a larger size, higher strength, and smaller fractal dimension. Thus, the flocs can accumulate into a porous cake layer to improve the membrane permeability and fouling reversibility. Moreover, the irreversible fouling is highly linearly correlated SUVA values in the early ultrafiltration cycles (R2SUVA = 0.9536) and with the floc strength in the late cycles (R2Strength = 0.9348–0.9763). This finding can be used to make a targeted diagnosis of irreversible fouling in different cycles, providing valuable guidance for prolonging the service life of ultrafiltration membranes.

Investigation of membrane fouling and mechanism induced by extracellular organic matter during long-term exposure to pharmaceuticals and personal care products

This study investigated ultrafiltration membrane fouling by extracellular organic matter (EOM) and the mechanism operating during long-term exposure to pharmaceuticals and personal care products. The results indicated that carbamazepine and diclofenac in algal-laden water altered the filtration flux and membrane fouling by EOM. Exposure to low-concentration carbamazepine (0.25 μg/L) improved the filtration flux and the total (Rtot) and reversible fouling resistance (Rc), whereas the filtration flux and Rtot and Rc were reduced when EOM was used during long-term exposure to high carbamazepine concentrations (>1 μg/L). Both Rtot and Rc were increased when algae were exposed to 0.25 μg/L diclofenac, whereas the filtration flux and Rtot and Rc were alleviated when algae were exposed to >1 μg/L diclofenac. Moreover, carbamazepine and diclofenac (0.25 μg/L − 1000 μg/L) in water enhanced the irreversible fouling resistance (Rb) when ultrafiltration was used to treat algal-laden waters. The mechanism indicated that membrane fouling induced by standard blocking was transformed to complete blocking when EOM was exposed to high levels of carbamazepine (>0.25 μg/L) in the initial filtration process, whereas cake layer formation played an important role during the later filtration process; with low carbamazepine levels (0.25 μg/L), standard blocking of EOM was dominant during the entire filtration process. The membrane fouling mechanism also changed when algal-laden waters were exposed to diclofenac, the membrane fouling was transformed from complete blocking to standard blocking when DFC was present in the initial filtration process, whereas cake layer formation exerted an important role during the late filtration process. This research provides important information on the long-term risks caused by pharmaceutical and personal care products and potential threats to membrane treatment.

Effect of vacuum ultraviolet/ozone pretreatment on alleviation of ultrafiltration membrane fouling caused by algal extracellular and intracellular organic matter

Algal blooms in source water can cause algal organic matter (AOM)-related membrane fouling in drinking water treatment. Herein, the effects of vacuum ultraviolet/ozone (VUV/O3) pretreatment on alleviating ultrafiltration membrane fouling caused by AOM, including extracellular organic matter (EOM) and intracellular organic matter (IOM), were investigated systematically. Compared to its sub-processes (UV/O3, O3, VUV, and UV), VUV/O3 pretreatment showed the best performance on AOM removal and membrane fouling mitigation. After VUV/O3 pretreatment, the DOC of EOM and IOM in feed decreased by 51.1% and 26.7%, respectively, and fluorescence components and UV254 of EOM and IOM in feed decreased obviously. Hence, the final specific fluxes of the membranes increased significantly under the impacts of VUV/O3, and VUV/O3 achieved 89.5% and 97.2% mitigation of reversible fouling caused by EOM and IOM, respectively. VUV/O3 pretreatment also reduced the foulants on membrane surface and surface roughness. Moreover, under the effects of reactive oxygen species oxidation, VUV photolysis, and direct O3 oxidation, VUV/O3 decreased organic load and changed the molecular weight distribution, hydrophilicity, and interaction-free energy of AOM, thus mitigating membrane fouling. Furthermore, the effects of O3 dosage and molecular weight cut-off of ultrafiltration membrane on membrane fouling mitigation by VUV/O3 were also investigated. All results highlighted that VUV/O3 pretreatment had huge potential in mitigating AOM-induced membrane fouling.

Defective MOFs-based electrocatalytic self-cleaning membrane for wastewater reclamation: Enhanced antibiotics removal, membrane fouling control and mechanisms

In order to resolve the poor antibiotics rejection and serious fouling of ultrafiltration (UF) membrane during municipal wastewater reclamation, a novel anodic membrane (defective UiO-66 (D-UiO-66)/Graphite/Polyvinylidene fluoride (PVDF)) with high pure water flux (596.1 L•h − 1•m − 2•bar−1) was fabricated by incorporating defective zirconium based metal-organic framework (D-UiO-66) and conductive graphite particles into PVDF matrix and applied in the coupling of electro-oxidation and membrane filtration process. Compared to the other anodic membranes (i.e., Graphite/PVDF and UiO-66/Graphite/PVDF), D-UiO-66/Graphite/PVDF possesses superior anti-fouling and self-cleaning abilities (flux recovery=100%, model foulant: bovine serum albumin) in both intermittent and continuous supply of electric field under current density of 0.01 mA/cm2; moreover, efficient antibiotics (tetracycline, norfloxacin, tylosin and sulfamethoxazole) removal (> 96.6%) and bactericidal efficiency against E. coli and S. aureus (100%) were achieved simultaneously without the addition of chemical reagents due to the higher electrocatalytic activity of anodic membrane for oxidation of pollutants by •OH and •O2– free radicals. Three degradation pathways of antibiotics were proposed and the self-cleaning mechanism of membrane was dominated by the synergy of the partial mineralization and the reduced fouling potential of foulants after oxidation as revealed by the increase in hydrophilicity, and decrease in negative charge and molecular weight. The fabricated membrane also presents excellent electrochemical stability, separation and self-cleaning performance for treatment of municipal secondary effluent during long-term filtration with low electric energy consumption, which is promising in wastewater reclamation.

Granular activated carbon (GAC) fixed bed adsorption combined with ultrafiltration for shale gas wastewater internal reuse

Membrane processes are widely applied in shale gas flowback and produced water (SGFPW) reuse. However, particulate matters and organic matters aggravate membrane fouling, which is one of the major restrictions on SGFPW reuse. The present study proposed fixed bed adsorption using granular activated carbon (GAC) combined with ultrafiltration (UF) for the first time to investigate the treatment performance and membrane fouling mechanism. The adsorption of GAC for SGFPW was best described by the Temkin isotherm model and the pseudo-second-order kinetic model. GAC fixed bed pretreatment with different empty bed contact times (EBCT) (30, 60 and 90 min) showed the significant removal rate for dissolved organic carbon (DOC) and turbidity, which was 34.7%–42.4% and 98.1%–98.9%, respectively. According to characterization of UF membrane fouling layer, particulate matters and organic matters caused major part of membrane fouling. After being treated by GAC fixed bed, total fouling index (TFI) and hydraulic irreversible fouling index (HIFI) respectively decreased by more than 32.5% and 18.3% respectively, showing the mitigation effect of GAC fixed bed on membrane fouling. According to the XDLVO theory, GAC fixed bed also mitigated membrane fouling by reducing the hydrophobic interactions between the foulants and the UF membrane. The integrated GAC fixed bed-UF process produced high-quality effluents that met the water quality standards of SGFPW internal reuse, which was an effective technology of the SGFPW reuse.

Application of Cyclized Polyacrylonitrile for Ultrafiltration Membrane Fouling Mitigation.

In this study, novel composites were produced by blending partially cyclized polyacrylonitrile (cPAN) and poly(amide-imide) (PAI) in N-methylpyrrolidone in order to fabricate asymmetric membranes via phase inversion method. The compatibility of PAI and cPAN through possible intermolecular interaction was examined by quantum chemical calculations. The composite membranes were characterized by FTIR, SEM, contact angle measurements, etc. A considerable reduction in the contact angles of water and ethylene glycol (EG) was observed after adding cPAN to the PAI membrane, which is evidence of improved membrane hydrophilicity. Membrane transport properties were investigated in ultrafiltration tests by measuring the pure water flux, rejection of proteins, and flux recovery ratio (FRR). The best properties were found for the membrane containing 5 wt% cPAN; an increase in BSA rejection and a remarkable increase in FRR were observed, which can be explained by the hydrophilization of the membrane surface provided by the presence of cPAN.

Potassium ferrate combined with ultrafiltration for treating secondary effluent: Efficient removal of antibiotic resistance genes and membrane fouling alleviation

Antibiotic resistance genes (ARGs) are considered as emerging environmental contaminants, which should be controlled by wastewater treatment plants to prevent their discharge into the environment. However, conventional treatment techniques generally fail to successfully reduce ARGs, and the release of cell-free ARGs was underestimated. In this study, potassium ferrate (Fe(VI)) pretreatment combined with ultrafiltration (UF) process was developed to remove both cell-associated and cell-free ARGs in real secondary effluent, compared to ferric chloride (Fe(III)) and poly-aluminum chloride (PACl) pretreatment processes. It was found that total ARGs especially cell-free ARGs were effectively removed by Fe(VI) oxidation. However, due to the poor settleability of the negatively charged particles formed by Fe(VI) in the secondary effluent, the removal of cell-associated ARGs was less compared to Fe(III) and PACl pretreatments. The combination of Fe(VI) and UF removed the most ARGs (3.26 - 5.01 logs) due to the efficient removal of cell-free ARGs by Fe(VI) (> 2.15 logs) and co-interception of both cell-associated ARGs and Fe(VI) formed particles of the UF. High-throughput sequencing revealed that Fe(VI) decreased the viability and relative abundances of the potential ARGs hosts. Fe(VI)-UF exhibited the best performance on humic-like fluorescent organic matters removal, as well as the least phytotoxicity in the effluent. Moreover, membrane fouling was remarkably alleviated by Fe(VI) pretreatment because (1) Fe(VI) removed macromolecules such as protein-like and polysaccharide-like substances which would block the membrane pores, (2) Fe(VI) improved the hydrophilicity of foulants and reduced the hydrophobic adsorption between foulants and membrane. In short, Fe(VI)-UF is a promising technology to efficiently remove ARGs (especially cell-free ARGs) and alleviate UF membrane fouling in wastewater reclamation.

Oxidation-biotreatment-membrane combined process for external reuse of shale gas wastewater

The external reuse of shale gas wastewater (SGW) is inevitable and challenging from the long-term perspective of the shale gas industry. Among the numerous reuse methods of SGW, pretreatment-membrane combined processes are regarded as a suitable and effective method. In this work, an integrated oxidation-biologically active filtration (BAF)-ultrafiltration (UF)-reverse osmosis (RO) process is firstly proposed for the external reuse of SGW. The results indicated that pre-oxidation, especially O3 pre-oxidation, can effectively improve the efficiency of removing organic matter in the subsequent BAF process, despite the variable feed chemistry and salinity (1.2%-2.3%). Herein, after ozonation, the removal rate of dissolved organic carbon in the BAF system was increased by 1.1–1.3 times. Meanwhile, oxidation-BAF, especially O3-BAF, can also significantly reduce UF membrane fouling (7%-60%) in the subsequent UF system compared with that of the alone BAF system. The principal mechanism of UF membrane fouling mitigation was that oxidation-BAF increased the cohesion energy between foulants and foulants and the adhesion energy between foulants and the UF membrane, making it more difficult for foulants to adsorb on or deposit on the membrane pores and membrane surface. In addition, the effluent of the integrated process can meet the water quality standards for SGW external reuse. Therefore, the O3-BAF-UF-RO process proposed here has broad engineering application potential for desalination, removal of organic pollutants, and realization of safe reuse of SGW.

Characterization of coagulant-induced ultrafiltration membrane fouling by multi-spectral fusion: DOM properties and model prediction based on machine learning

This study used the ultraviolet-visible (UV–vis), synchronous fluorescence, and excitation-emission matrix (EEM) spectroscopy coupled with zeta potential and particle size to explore the dissolved organic matter (DOM) solutions properties with the addition of two kinds of coagulants, including aluminum chloride and ferric chloride, in humic solutions and surface water. The results of zeta potential and particle size showed the size of aggregates became larger with the addition of coagulant. The binding sequence of coagulant to DOM was followed from aromatic amino acids to fulvic-like and humic-likes fractions. The results of the unified membrane fouling index (UMFI) were showed negatively correlated with the concentrations of coagulant due to the cake layers formed by aggregates being looser and more permeable. Among all the 12 spectral parameters, slope radio (SR) and specific fluorescence intensities (SFI) had the most significant correlation to UMFI. The multi-spectral fusion for predicting UMFI was established via multiple linear regressions and the backpropagation neural network (BPNN) by using the parameters with both SR and SFI with good accuracy and robustness. Sensitivity analyses results showed that SFI was more sensitive than SR in solutions with high protein-like substances, while SR was more sensitive than SFI with high humic-like substances.

Oxidation-enhanced ferric coagulation for alleviating ultrafiltration membrane fouling by algal organic matter: A comparison of moderate and strong oxidation

Ultrafiltration is increasingly used in fields of water treatment and bio-energy for algae removal and algae harvest, respectively, but membrane fouling caused by extracellular organic matter is still a challenge. In this work, oxidation-enhanced ferric coagulation was assessed for alleviating membrane fouling by extracellular organic matter with Fe(II)/permanganate and Fe(II)/persulfate compared. Characterization of extracellular organic matter was performed before and after pretreatments to evaluate changes in molecular-weight distribution and hydrophilicity. Moreover, filtration tests were carried out to explore performance and mechanisms of fouling control by the enhanced ferric coagulation. The results indicated that both Fe(II)/permanganate and Fe(II)/persulfate could improve rejection of extracellular organic matter by 20%–40%, in particularly for humic-like acid and protein-like substances. Fe(II)/persulfate outperformed Fe(II)/permanganate in alleviating the flux reduction by extracellular organic matter. Simultaneous oxidation and coagulation, which were associated with in situ formed sulfate radicals and Fe(III), respectively, were the principal mechanism for fouling control. The enhanced ferric coagulation only slightly improved the fouling reversibility, and iron and manganese oxides deposited in the external cake layer rather than inside the membrane. Fe(II)/permanganate did not significantly changes pattern of fouling development, whereas Fe(II)/persulfate induced a shift of fouling mechanisms from dual pore blocking and cake filtration to single intermediate blocking. Overall, the strong oxidation (Fe(II)/persulfate) was more beneficial to the control of membrane fouling by extracellular organic matter than the moderate oxidation (Fe(II)/permanganate).

Pre-depositing versus mixing powdered activated carbons for gravity-driven membrane systems during treated domestic wastewater filtration: Permeability stabilization and removal performance

Pre-deposition of powdered activated carbons (PACs) is an effective method to improve the permeate quality of gravity-driven membrane (GDM) system but always with a limited or even negative effect on its fouling behavior. PAC dosing strategies play dominant roles on the fouling of microfiltration and ultrafiltration membranes under constant flux mode, owing to the alteration of PAC-membrane interactions. Hence, how to further increase the membrane flux in the PAC-GDM system needs more investigation. In this study, the effects of PACs on the fouling by treated domestic wastewater were evaluated during GDM filtration using three different PAC dosing strategies: pre-depositing PACs onto membrane surfaces, and mixing PACs with bulk feeds in reactors totally before filtration and mixing PACs with bulk feeds in reactors periodically during filtration. PACs in three dosing modes all improved the removal of organics, but showed conflict effects on the fouling. Unlike mixed PACs increasing the final flux by more than two times than that obtained in the control system, pre-deposited PACs showed a dramatically negative effect on the flux development with a final value decreased by 75.0%. As demonstrated by the scanning electron microscopy images of biofilm structures and the contents of dissolved organic carbon and adenosine triphosphate in reactors, pre-deposited PAC layer aggravated the accumulation of organics and microorganisms with the formation of a stratified and compact structure, which hindered their back-transport to the bulk water. However, mixed PACs induced the formation of a uniform and porous biofilm, which favored the retained organics and microorganisms migrating back into concentrated waters, especially for pre-mixed PACs. This study links PAC dosing strategies, physical structures of biofilms and spatial distributions of organics and microorganisms, with practical relevance for the hydraulic performance of GDM systems, hopefully leading to a wider application of PAC-GDM systems in wastewater treatment.

Alleviating the membrane fouling potential of the denitrification filter effluent by regulating the COD/N ratio and carbon source in the process of wastewater reclamation

• Higher COD/N ratio in DNF operation led to more aggravated membrane fouling. • Fouling of DNF effluent: glucose > methanol > ethanol > sodium acetate-fed HOA and HON fractions in DNF effluent dominated subsequent UF membrane fouling. • DNF operation could alleviate UF fouling by regulating external carbon addition. • DNF-UF process should be optimized as an integrated system rather than separate units. The process of denitrification filter (DNF) followed by ultrafiltration (UF) has been widely applied for wastewater reclamation in China. The performance of DNF could have significant influences on subsequent UF membrane fouling. In this study, different chemical oxygen demand to nitrogen (COD/N) ratios and carbon sources in DNF were investigated under pilot scale, with the secondary effluent of a wastewater reclamation plant as DNF influent, to explore the impacts of DNF operation on UF membrane fouling. DNF effluent with the increased COD/N ratios from 2.9 to 6.8 rendered more aggravated membrane fouling performance, suggesting that increase of carbon source dosage could significantly increase the fouling potential of DNF effluent. In terms of four commonly-used carbon sources, the fouling potential was higher in the order of glucose > methanol > ethanol > sodium acetate-fed DNF effluent. According to the resin fractionation and fluorescence spectroscopy analysis, water samples with higher membrane fouling potential contained a larger proportion of hydrophobic components. Extended Derjaguin Landau Verwey Overbeek (XDLVO) analysis revealed fouling mechanism that hydrophobic acids (HOA) and hydrophobic neutrals (HON) exhibited both notably attractive interaction with virgin membranes and a strong tendency to aggregate on the already fouled membranes. Compared with the other fractions, HOA and HON presented significantly stronger interaction energy, demonstrating that HOA and HON dominated the membrane fouling process. Therefore, the contents of HOA and HON fractions in DNF effluent could be effectively regulated by optimizing external carbon addition, thus alleviating the subsequent UF fouling. The DNF-UF process should be considered and optimized as an integrated system rather than independent units, and appropriate external carbon addition should be regulated to achieve an optimal process from the perspective of the whole wastewater reclamation plant.

Effects of electroflocculation/oxidation pretreatment on the fouling characteristics of ultrafiltration membranes.

In order to reduce the membrane pollution of ultrafiltration caused by natural organic matter and improve the treatment efficiency, electroflocculation/oxidation is used as the premembrane treatment method. The membrane specific flux attenuation characteristics was compared and analyzed under the conditions of direct ultrafiltration and electroflocculation/oxidation-ultrafiltration. Combined with the analysis of the reversibility of membrane fouling, the mechanism of electroflocculation/oxidation pretreatment to alleviate ultrafiltration membrane fouling was evaluated, and the membrane pore clogging model was used to fit the fouling law. The results show that, in the continuously fed filtration experiment, the electroflocculation/oxidation process involved in the pretreatment and the direct ultrafiltration membrane filtration decreased the ultrafiltration membrane flux to 79.1% and 28.5%, respectively. The reversible resistance generated by ultrafiltration and electroflocculation/oxidation-ultrafiltration processes accounted for 37.70% and 62.26% of their total pollution resistance, whereas the irreversible resistance generated accounted for 47.30% and 12.40%, respectively. Meanwhile, the direct correlation between the the flux dropped and complete clogging became less than that of the ultrafiltration process. The pretreatment significantly strengthened irreversible fouling resistance of the membrane pores. The membrane permeation flux was significantly increased after the electroflocculation/oxidation pretreatment.

Enhancing compatibility and hydrophilicity of polysulfone/poly (ethylene-co-vinyl alcohol) copolymer blend ultrafiltration membranes using polyethylene glycol as hydrophilic additive and compatibilizer

Hydrophilic poly (ethylene-co-vinyl alcohol) (EVOH) was blended with hydrophobic polysulfone (PSF) in the presence of polyethylene glycol (PEG) (20 kDa), which acted as a hydrophilic additive and compatibilizer, to fabricate ultrafiltration (UF) membranes with high porosity and antifouling properties. The polymer blend containing 10 wt% EVOH was selected for optimization using PEG (0 to 24 wt%). After a detailed study, it was concluded that 20 wt% of PEG content was optimal for mixing with PSF/EVOH to increase miscibility. The membranes were characterized using differential scanning calorimetry (DSC) analysis, contact angle, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The effectiveness of PEG as a compatibilizer was observed via no phase separation occurred when the solution was allowed to stand at room temperature for four weeks. It was further confirmed by the appearance of a single Tm peak in DSC. In addition, molecular dynamic simulations illustrated that the PSF/EVOH 90/10 wt% blend had a radial distribution of g(r) = 3.29 Å, and g(r) = 2.69 Å in the presence of PEG, indicating better miscibility in the presence of PEG. Pure water permeance of blend membrane (85/15 wt%) reached 316 L.m-2h−1 bar−1, 54% greater than the pristine membrane. Simultaneously, bovine serum albumin (BSA) rejection of up to 97% and permeance recovery ratio of 87% were observed for the PSF/EVOH 90/10 wt% blend membrane, showing improved hydrophilicity and antifouling properties. These findings identify a potential modifier for fabricating low fouling UF membranes for wastewater treatment by blending with EVOH and PEG.

Mitigation of organic fouling of ultrafiltration membrane by high-temperature crayfish shell biochar: Performance and mechanisms

The paper applied crayfish shell (CFS) biochar to the mitigation of ultrafiltration (UF) membrane fouling induced by humic acid (HA) and sodium alginate (SA). Results indicated that the high adsorption capacity of CFS800 to HA made it effective in alleviating the irreversible membrane fouling induced by HA, and the cross-linking reaction between the hydroxyl calcium components on CFS800 and SA reduced the reversible membrane fouling induced by SA rapidly. Further analysis showed that the “hydrogel flocs” generated by the cross-linking reaction would accumulate on the surface of the substrate membrane and form an amorphous hydrogel layer to intercept the subsequent foulant and purify the water quality further. Meanwhile, the mitigation performance of CFS800 was twice more than that of commercial powder activated carbon (PAC), and the dosage was the main factor affecting its practical application performance and thus could be considered as a promising material in alleviating membrane fouling induced by HA and SA. More importantly, the findings of the present study gave a new sight towards the application of biochar.

An efficient system of aerogel adsorbent combined with membranes for reuse of shale gas wastewater

The internal reuse of shale gas flowback and produced water (SGFPW) can ease the pressure on treatment and management costs and freshwater supply. Internal reuse of SGFPW based on membrane treatments is faced with major challenges of the divalent ion and organic pollutant removal as well as membrane fouling control. To solve these problems, a green and efficient adsorbent of porous biochar aerogel (PBA) was combined with ultrafiltration (UF)-nanofiltration (NF) for SGFPW internal reuse in this study. The removal performance of dissolved organic carbon (DOC, >85.9%) and divalent ions (>70.6%) for three SGFPW showed feasibility of PBA-UF-NF process for internal reuse. Three-dimensional excitation-emission matrix (3D EEM) fluorescence spectrum, organic fractionation and the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory were used to identify the organic composition of SGFPW and analyze membrane fouling. PBA tended to adsorb hydrophobic fraction and alleviated UF membrane fouling caused by attractive hydrophobicity. NF membrane fouling was mitigated due to the increased polar repulsion as well as the decreased synergistic fouling between organics and divalent cations through the reduction of DOC by PBA. PBA-UF-NF process had good performance on organic pollutant and divalent ion removal with decreasing membrane fouling, presenting potential to treat SGFPW onsite for internal reuse.

Alleviation of Ultrafiltration Membrane Fouling by ClO2 Pre-Oxidation: Fouling Mechanism and Interface Characteristics.

In order to alleviate membrane fouling and improve removal efficiency, a series of pretreatment technologies were applied to the ultrafiltration process. In this study, ClO2 was used as a pre-oxidation strategy for the ultrafiltration (UF) process. Humic acid (HA), sodium alginate (SA), and bovine serum albumin (BSA) were used as three typical organic model foulants, and the mixture of the three substances was used as a representation of simulated natural water. The dosages of ClO2 were 0.5, 1, 2, 4, and 8 mg/L, with 90 min pre-oxidation. The results showed that ClO2 pre-oxidation at low doses (1–2 mg/L) could alleviate the membrane flux decline caused by humus, polysaccharides, and simulated natural water, but had a limited alleviating effect on the irreversible resistance of the membrane. The interfacial free energy analysis showed that the interaction force between the membrane and the simulated natural water was also repulsive after the pre-oxidation, indicating that ClO2 pre-oxidation was an effective way to alleviate cake layer fouling by reducing the interaction between the foulant and the membrane. In addition, ClO2 oxidation activated the hidden functional groups in the raw water, resulting in an increase in the fluorescence value of humic analogs, but had a good removal effect on the fluorescence intensity of BSA. Furthermore, the membrane fouling fitting model showed that ClO2, at a low dose (1 mg/L), could change the mechanism of membrane fouling induced by simulated natural water from standard blocking and cake layer blocking to critical blocking. Overall, ClO2 pre-oxidation was an efficient pretreatment strategy for UF membrane fouling alleviation, especially for the fouling control of HA and SA at low dosages.

Hybrid PSf/TNT-SO3H Ultrafiltration Membrane Fouling by Sodium Alginate: Effect of Permeation Flux on Fouling Resistance and Desalination Efficiency

The development of low fouling UF membranes with boosting water flux for implementations in water purifications is critical. Organic foulants and ionic strength are the main characteristics of surface water which affect the membrane performance for water generation and seawater desalination. Low fouling hybrid ultrafiltration membranes were fabricated from a combination of sulfonic acid functionalized titanium nanotubes (TNTs-SO3H) and polysulfone (PSf) by the nonsolvent-induced phase separation approach. The membrane fouling was explored utilizing a polysaccharide sodium alginate (SA) as a hydrophilic nature organic matter, and the impact of Na+ and Ca2+ ions on alginate membrane fouling were also addressed. The results showed that the membranes’ water permeability and natural organic matter fouling resistances were affected by the proportion of TNTs-SO3H in the membranes. The inclusion of TNTs-SO3H improves the water penetration fluxes (Jw1) and surface hydrophilicity of the manufactured membranes. In the UF of sodium alginate solution, the produced membrane comprising 5% TNTs-SO3H exhibits a higher penetration flux and rejection value than the other membranes. The introduction of Na+ and Ca2+ ions to the SA solution reduces the membrane fouling. Furthermore, the adsorption investigation of sodium alginate solutions at [Formula: see text] was lowered as the amount of TNTs-SO3H was increased. After ultrafiltration, the fouled membrane containing 5% TNTs-SO3H is readily removed, and recurrent antifouling experiments indicate a consistent and maximum filtration efficiency.

Effects of Fe(Ii)-Activated Persulfate/Sodium Percarbonate (Ps/Spc) Pretreatment on Ultrafiltration Membrane Fouling Control and Mechanisms

Effects of Fe(Ii)-Activated Persulfate/Sodium Percarbonate (Ps/Spc) Pretreatment on Ultrafiltration Membrane Fouling Control and Mechanisms