Optimization of coagulation pre-treatment for alleviating ultrafiltration membrane fouling: The role of floc properties on Al species

Removal of Micropollutants in Water Reclamation by Membrane Filtration: Impact of Pretreatments and Adsorption

Organic micropollutants (OMPs) present in water and wastewater are in the spotlight because of their potentially harmful effects even at low concentrations and the difficulties of their elimination in urban wastewater treatment plants (UWWTPs). This study explores the impact of some membrane filtration processes on the removal of a group of 11 OMPs with an eye on the effects of two pretreatments (i.e., coagulation and adsorption onto powdered activated carbon (PAC)) and the adsorption of OMPs onto the membranes on the overall removal. For this purpose, ultrafiltration (UF) and nanofiltration (NF) experiments were conducted with selected OMPs spiked in ultrapure water and secondary effluents from UWWTPs. It was observed that the adsorption of OMPs onto the membranes was influenced by the characteristics of the membranes, as well as the presence of effluent organic matter (EfOM). Since adsorption was the dominant mechanism for the rejection of OMPs by UF membranes, a study of the adsorption equilibrium of the micropollutants using UF membrane pieces as the adsorbent was conducted. The adsorption isotherms for the most hydrophobic OMPs fitted the Langmuir model. The efficiency of coagulation and powdered activated carbon (PAC) adsorption coupled with UF were also investigated. Both pretreatments alleviated membrane fouling and improved the rejection of organic and inorganic matter. The PAC pretreatment significantly improved the removal of OMPs in the combined PAC/UF process. The best options for achieving reclaimed water with satisfactory physicochemical quality, nearly devoid of OMPs and microorganisms, and suitable for diverse reuse purposes are either the NF treatment or the combination of PAC/UF.

Removal behaviors and mechanism of polystyrene microplastics by coagulation/ultrafiltration process: Co-effects of humic acid

Microplastics (MPs) have been detected in drinking water, which could absorb or accumulate humic acid (HA) and threaten the water quality. Coagulation-ultrafiltration (CUF) is a common drinking water treatment technology, but its behavior and mechanism of removing MPs and MPs-HA remain unclear. In this study, the removal mechanism of polystyrene (PS)-MPs coagulated by Al- and Fe-based salts with or without HA was investigated to optimize the CUF process. The results showed that Al-based salt (92.7 %) was better than Fe-based salt (91.2 %) in the removal efficiency of PS or HA, and the optimal coagulants dosage of PS-HA composite system (12 mg·L^-1) was higher than that of the individual PS system (9 mg·L^-1). Moreover, the coagulation mechanism was studied by Fourier transform infrared spectroscope (FTIR) and X-ray photoelectron spectroscopy (XPS). The oxygen group in PS and PS-HA was the main binding site of Al and Fe hydrolysate, and the effects of charge neutralization, adsorption bridging, and sweep flocculation became weaker in turn at the optimal dosage. In addition, the cake layer formed by coagulation and the presence of HA alleviated the irreversible membrane fouling by intercepting flow and re-adsorption. This study guides the improvement of the traditional drinking water treatment process to remove MPs.

Strategies to improve membrane performance in wastewater treatment

Membrane technology has rapidly gained popularity in wastewater treatment due to its cost-effectiveness, environmentally friendly tools, and elevated productivity. Although membrane performance in wastewater treatment has been reviewed in several past studies, the key techniques for improving membrane performance, as well as their challenges, and solutions associated with the membrane process, were not sufficiently highlighted in those studies. Also, very few studies have addressed hybrid techniques to improve membrane performance. The present review aims to fill those gaps and achieve public health benefits through safe water processing. Despite its higher cost, membrane performance can result in a 36% reduction in flux degradation. The issue with fouling has been identified as one of the key challenges of membrane technology. Chemical cleaning is quite effective in removing accumulated foulant. Fouling mitigation techniques have also been shown to have a positive effect on membrane photobioreactors that handle wastewater effluent, resulting in a 50% and 60% reduction in fouling rates for backwash and nitrogen bubble scouring techniques. Membrane hybrid approaches such as hybrid forward-reverse osmosis show promise in removing high concentrations of phosphorus, ammonium, and salt from wastewater. The incorporation of the forward osmosis process can reject 99% of phosphorus and 97% of ammonium, and the reverse osmosis approach can achieve a 99% salt rejection rate. The control strategies for membrane fouling have not been successfully optimized yet and more research is needed to achieve a realistic, long-term direct membrane filtering operation.

Highly efficient Al-Ti gel as a coagulant for surface water treatment: Insights into the hydrolysate transformation and coagulation mechanism

In view of the insufficient coagulation efficiency of traditional inorganic coagulants, a series of Al-Ti gels with different Ti/triethanolamine (TEA), Ti/H₂O, and Ti/Al molar ratios were prepared by sol-gel process in this study. Fourier transform infrared (FTIR) spectra of the Al-Ti gels preliminarily confirmed the interaction between Al and Ti by detecting the appearance of the Al-O-Ti bond. The peak shift of the chemical bonds in X-ray photoelectron spectra (XPS) and the transformation of the hydrolysate species in the Al-Ti gels were analyzed to further explore the interaction mechanism between Al and Ti. It was found that moderate TEA could inhibit the hydrolysis of Ti precursors by taking up the coordination sites of H₂O to form a CO-Ti bond. Density functional theory (DFT) calculation results showed that Ti could be incorporated into the framework of aluminum hydrolysates to form an Al-O-Ti bond, and [Al₂Ti₂(OH)_x(TEA)_y(H₂O)_8-x-y]^14-x was the most possible copolymerization hydrolysate. Based on the above research results, the most efficient Al-Ti gel was selected and applied to the actual lake water treatment. The highest UV₂₅₄ removal efficiency with the addition of Al-Ti gel was > 60%, nearly 25% higher than that of Ti gel. The hydrolysates of Al-Ti gel, such as TiO(OH)_2(am), Al(OH)_3(am), and [Al₂Ti₂(OH)_x(TEA)_y(H₂O)_8-x-y]^14-x, could remove organic matters through the incorporation of charge neutralization, adsorption, complexation, and sweeping effects. These results provide a new idea for studying the interaction mechanism between Al and Ti in composite coagulants, and have theoretical guiding significance to actual water treatment.

Coagulation behavior of polyaluminum-titanium chloride composite coagulant with humic acid: A mechanism analysis

The hydrolysate species of metal-based coagulants and the binding sites of humic acid (HA) are highly dependent on the pH conditions. Exploring the binding sites and modes between coagulant hydrolysates and HA molecules is critical to understanding the coagulation mechanism. In this paper, the binding behavior between HA molecules and the hydrolysates of a polyaluminum-titanium chloride composite coagulant (PATC) was investigated under different pH conditions by semi-quantitative FTIR and XPS. It was found that oligomeric and mesopolymeric hydrolysates were the dominant species under acid conditions, which could complex with the hydroxyl and carboxyl groups of HA by forming COAl/Ti coordinate bonds. However, large amounts of H⁺ could compete with Al³⁺ and weaken the removal efficiency of HA. With the increase of pH, the hydrolysis process of the PATC and the deprotonation of HA were simultaneously underway. Under weakly acid conditions, the complexation of the aluminum hydrolysates with carboxyl groups was improved due to the gradually diminishing competition of H⁺ and the enhanced charge neutralization of the further polymerized hydrolysates. Consequently, the maximum UV₂₅₄ removal by adding PATC was observed at pH 6. Under alkaline conditions, the sweeping effect of amorphous hydroxide dominated the HA removals, which was accompanied by the surface complexation of Al/Ti nuclear with carboxyl groups as well as the hydrogen bonds between hydroxyl and hydroxide. This study provides a new clue for the interaction mechanisms between the hydrolysates of composite coagulants and the dominant functional groups of HA at various pH conditions.

Coagulation-ultrafiltration integrated process for membrane fouling control: Influence of Al species and SUVA values of water

Natural organic matter (NOM) pollution is a great challenge for the ultrafiltration (UF) process owing to the inevitable membrane fouling. In this study, three Al species coagulants (Al_a/Al_b/Al_c) and their composites in combination with Poly dimethyl ammonium chloride (PolyDMDAAC) were used as a pretreatment strategy for the UF process. Then, test waters with different NOM fractions (i.e., humic acid, fulvic acid, protein, and polysaccharide) were prepared to analyze the effects of NOM characteristics on membrane fouling behaviors. The results indicated that compared with Al_b and Al_c, Al_a showed higher removal efficiencies for hydrophobic NOM, aromatic organic matters, and suspended particles, but a limited effect on removing dissolved organic carbon (DOC). Al_a or Al_a-PolyDMDAAC effectively mitigated membrane fouling by removing the hydrophobic NOM in the coagulation process and forming the porous cake layer in the UF process. The test waters with higher specific ultraviolet absorbance (SUVA) resulted in more severe total and reversible membrane fouling but lighter irreversible fouling. After pretreatment by Al_a or Al_a-PolyDMDAAC, water samples with the medium SUVA value exhibited remarkable alleviation of membrane fouling due to the formation of large, compact, and robust flocs, as well as the construction of loose and poriferous cake layer on the membrane surface. Although hydrophilic NOM was challenging to be removed by coagulation, the interception and re-adsorption of porous cake layers contributed to the alleviation of irreversible fouling.

The suitability of titanium salts in coagulation removal of micropollutants and in alleviation of membrane fouling

Coagulation is a conventional method in water treatment. In recent decades, with the rapid development of membrane filtration, the use of coagulation is facing some new challenges. How to minimize the membrane fouling became a leading-edge topic in the study of coagulation. Here, the performances of three types of titanium coagulants were evaluated in terms of both the coagulation removal of toxic micropollutants and the alleviation of membrane fouling. Three oxysalts and two antibiotics were taken as representatives of inorganic and organic micropollutants. As compared with titanium tetrachloride (TiCl₄) and polytitanium chloride (PTC), titanium xerogel (TXC) with a higher polymerization degree showed much better performances in direct coagulation removal of oxysalts and antibiotics and in pre-coagulation for mitigating membrane fouling in both coagulation-sedimentation-ultrafiltration (CSUF) and in-line coagulation-ultrafiltration (CUF) processes. In the CSUF system, the membrane permeate flux with TXC pre-coagulation (89.5%) was much higher than those of TiCl₄ (56.1%) and PTC (57.4%). After a 5 day continuous operation, the transmembrane pressure in the CUF system with TXC coagulation was increased only to 4.9 kPa, while those of PTC and TiCl₄ were 12.2 and 18.5 kPa, respectively. The results here demonstrate that TXC is a promising coagulant for pollutant removal and membrane fouling alleviation, due to the following merits: better floc properties, weaker pH-dependence, and higher resistance to coordination with organic pollutants. The observation shed new lights on the fabrication and application of coagulants in a wide variety of scenarios.

Pre-coagulation with cationic flocculant-composited titanium xerogel coagulant for alleviating subsequent ultrafiltration membrane fouling by algae-related pollutants

In-line coagulation-ultrafiltration is reliable to achieve the safe disposal of algae-laden water with alleviated membrane fouling. Poly(diallyl dimethyl ammonium chloride) (PDADMAC)-composited titanium xerogel (TXC) coagulant (abbreviated as P-T) was reported to possess better resistance to organic matter loads, and its mitigation effect on subsequent ultrafiltration efficiency towards algae-related pollutants was investigated in this study. Results showed that P-T coagulation effectively mitigated membrane fouling over pH 5.0-9.0, whereas TXC only worked better under acidic condition. Acidic environment facilitated algae and organic matter removal by pre-coagulation, thus greatly improving ultrafiltration efficiency. Under neutral and alkaline conditions, PDADMAC portion in P-T enhanced the coagulation removal towards algae and protein constituents, and simultaneously promoted the formation of flocs with unique porous structure, which jointly contributed to its high-efficient alleviation ability. Nevertheless, PDADMAC increased adhesion force between P-T coagulated flocs and membrane surface, thus slightly reducing the recovery rate of membrane flux at pH 5.0. Pearson correlation analyses implied that removing algae cells would prevent reversible fouling-induced flux decline, whereas eliminating organic matter could greatly promote ultrafiltration efficiency via mitigating irreversible fouling. Therefore, elevating removal efficiency of organic matters is still the major objective for ultrafiltration pretreatment technologies and the optimization direction towards TXC-based coagulants.

Insight into the influence of humic acid and sodium alginate fractions on membrane fouling in coagulation-ultrafiltration combined system

Membrane fouling has become the one of main obstacles for the widespread application of membrane technology in water treatment processes. Coagulation as pretreatment is proven to be effective for the alleviation of membrane fouling. In this study, the influence of humic acid (HA)/sodium alginate (SA) fractions in the structure and resistance of cake layer on the membrane surface was investigated. The presence of SA at an appropriate fraction could facilitate the formation of large and loosely branched flocs and thereby form a more permeable cake layer on the membrane surface due to good bridging and charge neutralization abilities of SA molecules. The particle image velocimetry (PIV) technique was employed for monitoring the dynamic formation process of cake layer under different HA/SA fractions. The cake layer with a higher thickness was observed to be rapidly formed on the membrane surface at the presence of SA in water. According to the theoretical analysis, the membrane fouling in coagulation-ultrafiltration (UF) combined system demonstrated to be highly dependent on the size and intra-porosity of flocs. The fractal dimension of flocs might have an impact on the resistance of cake layer through affecting the porosity of aggregated flocs. The SA molecules could be used as the coagulant aid for effective alleviation of membrane fouling and the improvement of filtration performance in a coagulation-UF combined system.

Membrane processes

This literature review provides a review for publications in 2018 and 2019 and includes information membrane processes findings for municipal and industrial applications. This review is a subsection of the annual Water Environment Federation literature review for Treatment Systems section. The following topics are covered in this literature review: industrial wastewater and membrane. Bioreactor (MBR) configuration, membrane fouling, design, reuse, nutrient removal, operation, anaerobic membrane systems, microconstituents removal, membrane technology advances, and modeling. Other sub-sections of the Treatment Systems section that might relate to this literature review include the following: Biological Fixed-Film Systems, Activated Sludge, and Other Aerobic Suspended Culture Processes, Anaerobic Processes, and Water Reclamation and Reuse. This publication might also have related information on membrane processes: Industrial Wastes, Hazardous Wastes, and Fate and Effects of Pollutants.

Algae-Laden Fouling Control by Gravity-Driven Membrane Ultrafiltration with Aluminum Sulfate-Chitosan: The Property of Floc and Cake Layer

Gravity-driven membrane (GDM) ultrafiltration is a promising water treatment method due to its low energy consumption and low maintenance. However, the low stable permeability in algae-laden water treatment is currently limiting its wider application. With the ultimate goal of increasing permeability, the aim of this study was to evaluate the effect of a composite coagulant of aluminum sulfate-chitosan (AS-CS) on the GDM filtration performance. In parallel tests with a single AS coagulant and without pre-coagulation, the analysis of membrane fouling resistance and the membrane fouling mechanism were evaluated. The results indicated that the AS-CS/GDM system can alleviate 23.74% and 58.80% membrane fouling, respectively, compared with AS/GDM and the GDM system. The AS-CS/GDM system can effectively remove humic-like substances having a molecular weight (MW) of 3–100 kDa, resulting in removal of 98.32% of algae cells and removal of 66.25% of dissolved organic carbon; the AS-CS/GDM system thereby improved the concentration of attached biomass on the membrane surface with the stronger biodegradability of organic matters. The application of AS-CS pre-coagulation in the GDM process could enhance the proliferation of microorganisms and the removal of low molecular weight humic-like substances. Therefore, the AS-CS/GDM system is a potentially important approach for algae-laden water treatment.

Polysaccharides derived from Enteromorpha prolifera for the removal of silver nanoparticle-humic acid contaminants by a coagulation-ultrafiltration process

Silver nanoparticles (AgNPs) pose serious health risks to humans as the adsorption between AgNPs and humic acid (HA) makes it difficult to remove them from surface water. To solve this problem, polysaccharides extracted from a marine alga, Enteromorpha prolifera (denoted as Ep), were used to eliminate the AgNP–HA composite contaminant via a coagulation-ultrafiltration (C-UF) process. The structure of Ep, AgNP–HA removal mechanism and membrane fouling were analyzed. The results indicated that the backbone of Ep was composed of (1 → 4)-linked l-rhamnopyranose, (1 → 4)-linked d-xylose and (1 → 4)-linked glucuronic acid. With the charge neutralization of PAC hydrolysates and the bridging-sweep role of Ep, AgNPs could be removed completely by the C-UF process. The coagulation performance and membrane flux were the highest when the PAC and Ep dosages were 2.0 mg L⁻¹ and 0.3 mg L⁻¹, respectively. In addition, when Ep was applied in the C-UF process, the flocs exhibited larger sizes, faster growth rates, better recovery ability and looser structures, which resulted in lower cake resistance and less pore blocking of the UF membrane. Consequently, the membrane flux could be improved by about 25–30% due to the addition of Ep.

Applying Ep as a coagulant aid in C-UF process could simultaneously remove AgNPs and reduce membrane fouling.

PAC-PDMDAAC pretreatment of typical natural organic matter mixtures: Ultrafiltration membrane fouling control and mechanisms

Precoagulation by polyaluminum chloride-poly dimethyl diallyl ammonium chloride (PAC-PDMDAAC) prior to ultrafiltration (UF) was conducted to evaluate the influence of PAC-PDMDAAC on controlling membrane fouling from typical natural organic matter (NOM) mixtures of humic acid (HA), bovine serum albumin (BSA) and sodium alginate (SA). Membrane flux decline and flux recovery after backwashing were investigated to evaluate the membrane fouling. The fouling mechanisms were determined from the floc size, floc structure and membrane resistance. PAC-PDMDAAC effectively alleviated membrane fouling caused by the HA, HA-BSA, HA-SA and HA-BSA-SA mixtures; furthermore, membrane fouling was better mitigated in the HA-SA and HA-BSA-SA mixtures. The untreated HA-SA and HA-BSA-SA mixtures caused much more serious total membrane resistance and fouling due to blocking and adsorption in the membrane pores by particles with sizes similar to those of the pores. The increased membrane flux and decreased irreversible resistance after the PAC-PDMDAAC pretreatment were attributed to the formation of flocs with a large size and small fractal dimension, which mainly formed a cake layer on the membrane surface. However, PAC-PDMDAAC was not particularly effective in reducing the irreversible membrane fouling originating from the HA and HA-BSA mixtures due to the formation of aggregates and pore blocking by microflocs.

Pretreatment of ceramic membrane microfiltration in wastewater reuse: A comparison between ozonation and coagulation

To determine the most efficient pretreatment for ceramic membrane filtration (CMF) of primary clarifier effluent (PE), the effectiveness of ozonation and coagulation was investigated from the viewpoint of both virus removal and mitigation of membrane fouling. Our results showed virus removal by coagulation to be more efficient as a CMF pretreatment, whereas ozonation showed better efficiency when used as a CMF posttreatment. The effect of ozonation and coagulation on ceramic membrane fouling was investigated during short-term operation. With the use of coagulation before CMF (PACl + CMF), irreversible fouling resistance was 0.5 × 10¹¹ m^-1 at a dosage of 150 mg/L of polyaluminum chloride (PACl), which was 10 times lower than when ozonation was used as a pretreatment to CMF (O₃+CMF) (0.7 × 10¹² m^-1 at 50 mg-O₃/L). This result indicates coagulation to be more efficient than ozonation for mitigating ceramic membrane fouling. Based on these results, the process sustainability of PACl + CMF was then investigated during longer-term operation. At a dosage of 150 mg/L of PACl, the PACl + CMF process could be sustainably operated for 120 h without any need for chemically enhanced backwashing, which was twice as long as for PACl dosages of 50 and 100 mg/L. Coagulation is thus a more efficient pretreatment for CMF of PE from the viewpoint of both virus removal and mitigation of ceramic membrane fouling. The hygienic safety of reclaimed water can be further improved if ozonation is used as a CMF posttreatment.

Alleviating membrane fouling of modified polysulfone membrane via coagulation pretreatment/ultrafiltration hybrid process

In this study, ultrafiltration membrane fouling was alleviated by hydrophilic modification and coagulation pretreatment. A polydopamine (PDA) layer was used as a bridge to introduce the nano titanium dioxide (TiO₂) onto the polysulfone (PSf) membranes, forming a hydrophilic modified layer. A relationship model was established between the coagulation efficiencies and floc properties and membrane fouling of the modified PSf membranes during the coagulation/ultrafiltration (C-UF) process. The combination styles of flocculants, poly dimethyldiallylammonium chloride (PDMDAAC) and polyaluminum chloride (PAC) were used in C-UF hybrid process. The characterization results indicated that the hydrophilicity was significantly enhanced in the modified PSf membranes. Scanning electron microscopy (SEM) tests proved that the PDA layer could be tightly bound to TiO₂ by coordination bond onto PSf membrane surface. In the acidic conditions, more TiO₂ nano-particles were adhered on the PDA particles surface as the pH of (NH₄)₂TiF₆ solution was increased, which resulted in higher hydrophilicity of membranes. In addition, the C-UF tests exhibited that the coagulation efficiency was greatly improved in the PAC/PDMDAAC system, and the PSf membrane modified by PDA/TiO₂ in UF tests significantly reduced the membrane fouling, this was partially due to the formation of TiO₂ modified coating with higher hydrophilicity.

Optimized coagulation pretreatment alleviates ultrafiltration membrane fouling: The role of floc properties and slow-mixing speed on mechanisms of chitosan-assisted coagulation

To alleviate ultrafiltration (UF) membrane fouling, the pre-coagulation of poly-aluminum chloride (PACl) with the aid of chitosan (CTS) was conducted for synthetic humic acid-kaolin water treatment. Pre-coagulation of three molecular weights (MW) CTSs (50-190 kDa (CTS_L), 190-310 kDa (CTS_M) and 310-375 kDa (CTS_H)) was optimized with slow-mixing speeds of 30, 60 and 90 r/min, respectively. The removal efficiency and floc properties as well as membrane fouling were analyzed, and were compared to results obtained by conventional coagulation with PACl. Results showed that variations in floc properties could be ascribed to the coagulation mechanisms of CTS_L/CTS_M/CTS_H at different slow-mixing speeds, resulting in reduced UF membrane fouling. Specifically, at the low speed of 30 r/min, all three CTS types produced flocs with similar properties, while CTS_L resulted in the lowest removal efficiency and aggravated irreversible fouling. At the appropriate speed of 60 r/min, CTS_M generated the most compact flocs with the combined effects of bridging and path mechanisms. The compact cake layer formed could alleviate irreversible fouling, which was beneficial for prolonging the operation of the UF membrane. At the high speed of 90 r/min, CTS_H formed fragile flocs and aggravated irreversible membrane fouling. We considered membrane fouling to be affected by floc properties and the resultant removal efficiency, which was governed by the MW of the CTS used and the slow-mixing speed applied as well.

Application of a hybrid gravity-driven membrane filtration and dissolved ozone flotation (MDOF) process for wastewater reclamation and membrane fouling mitigation

This study proposed a novel membrane filtration and dissolved ozone flotation integrated (MDOF) process and tested it at pilot scale. Membrane filtration in the MDOF process was operated in gravity-driven mode, and required no backwashing, flushing, or chemical cleaning. Because ozone was added in the MDOF process, ozonation, coagulation, and membrane filtration could occur in a single reactor. Moreover, in situ ozonation occurred in the MDOF process, which differs from the conventional pre-ozonation membrane filtration process. Significant enhancement of turbidity removal was further achieved through the addition of membrane filtration. Membrane fouling was mitigated in the MDOF process compared to the MDAF process. In situ ozonation in the MDOF process decreased the fluorescence intensity and transformed the high MW dissolved organics into small MW compounds. For the fouling layer, the extracellular polymeric substance (EPS) contents and cake layer morphology were analyzed. The results indicated that the contents of EPS decreased. Furthermore, a thinner and more loosely structured cake layer formed in the MDOF process. Because coagulation and ozonation occurred simultaneously in a single reactor, the generation of hydroxyl radicals was enhanced through the catalytic effect of Al-based coagulants on ozone decomposition, which further alleviated membrane fouling in the MDOF process.

In situ extracting organic-bound calcium: A novel approach to mitigating organic fouling in forward osmosis treating wastewater via gradient diffusion thin-films

Forward osmosis (FO) has gained increasing interests in wastewater treatment and reclamation. However, membrane fouling has become one major obstacle hindering FO application. A novel mitigation approach for FO membrane fouling via in situ extracting Ca²⁺ binding with the organic foulants using the gradient diffusion thin-films (DGT) was proposed in this study. The DGT could effectively adsorb the Ca²⁺ binding with the sodium alginate via the chelation of the Chelex functional groups, and its adsorption amount of Ca²⁺ correspondingly increased as a function of the Ca²⁺ concentration in the feed solution. Owing to the extraction of Ca²⁺ from the fouling layer by the DGT, the FO membrane fouling was effectively mitigated evident by significant enhancement of water flux, and at the same time, foulants became easily removed by physical cleaning. The alleviation of FO membrane fouling by the DGT could be attributed to the fact that the structure of the fouling layer became more porous and looser after in situ removing Ca²⁺ from the alginate-Ca²⁺ gel networks. The feasibility of fouling control strategy via in situ removing Ca²⁺ binding with the foulants in the fouling layer was demonstrated, which provides new insights into fouling control mechanisms during FO treating wastewater.