Fouling control of different pretreatments on ceramic fouling ultrafiltration: a review

Abstract

Ceramic ultrafiltration membrane filtration has made great progress in water purification. In terms of operational stability, ceramic ultrafiltration membranes have more obvious advantages than polymer membranes. However, membrane fouling is still a key factor hindering the development of ceramic ultrafiltration membranes. In order to alleviate membrane fouling, relevant pretreatment methods have been paid more and more attention. With the in-depth study of the interaction between filtration and coagulation, oxidation, adsorption and other processes, the combination of different technologies to alleviate membrane fouling and improve water purification efficiency has been recognized. It is necessary to make a comprehensive review on the control of ceramic ultrafiltration membrane fouling by different pretreatment methods. In this paper, the latest progress in the mechanism of ceramic ultrafiltration membrane fouling control by different pretreatments is reviewed, and the effects of the combination of various pretreatment methods are discussed. This study can provide a reference for the development of ceramic ultrafiltration membranes in practical applications.

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Water impact

The existing ceramic ultrafiltration membrane system has a high operating cost, and one of the main reasons for this phenomenon is the effect of membrane fouling. This paper comprehensively discusses the control behavior and mechanism of ceramic membrane pollution by mainstream pretreatment technology, which is of great significance for the development of water treatment technology, energy saving, emission reduction and carbon footprint reduction.

1. Introduction

With the continuous improvement of drinking water quality standards, ultrafiltration technology has been increasingly emphasized and applied.¹ Ultrafiltration technology is widely used in the pulp and paper industry, textile industry, petrochemical industry, food industry, pharmaceutical industry, mining industry and other fields.² It has been shown that ultrafiltration produces higher throughput and consumes less energy than nanofiltration and reverse osmosis.³ However, membrane fouling and cost are still the key challenges that cannot be ignored in the development of ultrafiltration technology.⁴ Organic ultrafiltration membranes have harsh operating conditions and are prone to membrane pore clogging during operation, resulting in decreased water permeability, requiring frequent backwashing or replacement of the membrane and high costs. Compared with organic membranes, inorganic ceramic membranes have the advantages of high mechanical strength, good chemical/heat resistance, easy membrane cleaning, resistance to sterilization technology, good antibacterial performance and long service life.⁵ In addition, inorganic ceramic membranes can withstand higher COD levels and effectively retain biomolecules, oils, dyes and other substances in water.⁶ The trend of the influence of solution chemistry on the fouling behavior of ceramic membranes is basically the same as that of polymer membranes, but the degree of influence varies depending on the water quality parameters. Akash et al. reported the application of ceramic membranes in mining and petrochemical industries; ceramic membranes showed high reliability for petroleum mixtures, chemical mixtures, liquefied formation minerals in the petrochemical industry, and the operating cost of polymer membranes in the mining industry was 55% higher than that of ceramic membranes per year.⁷ Ceramic membranes also have advantages over polymer membranes in terms of fouling resistance and fouling removal,⁸ and the lower fouling tendency and higher cleaning efficiency further contribute to the potential application of ceramic membranes in surface water treatment.⁹ How to further improve the effluent quality and effectively reduce ceramic membrane fouling is the key to the current membrane water treatment field.¹⁰

Some studies have shown that adding a pretreatment process before the ultrafiltration process can improve the quality of ultrafiltration feed water and reduce the degree of membrane fouling.¹¹ At the same time, the pollutant removal efficiency can be effectively improved by a combination of different pretreatment processes for the type of target pollutants. Common pretreatment methods mainly include coagulation, adsorption, oxidation, biological methods and integrated treatment, etc.^12–14 The report elucidates the mechanism of membrane fouling control on the basis of a combination of different pretreatment methods in ceramic membrane ultrafiltration. In addition, the review of ceramic membrane ultrafiltration pretreatment methods provide background support for research and practical applications of ceramic membrane ultrafiltration.

2. Fouling types and mechanisms

2.1 Types of membrane fouling

Fouling of ceramic ultrafiltration membranes can be categorized according to the type of contaminant as follows:¹⁵

• Fouling of ceramic ultrafiltration membranes caused by particulate contaminants can be explained by the four classical clogging models mentioned below.¹⁶ Large particles of pollutants in the membrane surface accumulate; particles with size smaller than the membrane pore size can be adsorbed on the inner wall of the membrane pores; pollutant particles pile up on the surface of the membrane that is caused by media stacking fouling; membrane fouling has the most severe impact on the permeate flux. When more pollutant particles are deposited on the membrane surface to form a filter cake layer, it does not necessarily aggravate membrane fouling. For example, Liu et al.'s study found that the filter cake layer formed by coagulation can absorb and intercept HA with larger molecular weight. By adjusting the characteristics of the floc and the corresponding filter cake layer, the pollutant removal effect can be simultaneously optimized and the membrane fouling can be alleviated.¹⁷

• Membrane fouling caused by natural organic matter (NOM). NOM such as humic substances, proteins and polysaccharides are important causes of ultrafiltration membrane fouling. The fouling of ceramic ultrafiltration membranes caused by NOM was similar to that of organic membranes, both of which were bovine serum albumin (BSA) > sodium alginate (SA) > humic acid (HA), but ceramic UF membranes had a very high backwash efficiency compared to polymer UF membranes, suggesting that ceramic UF membranes have a higher degree of hydraulic reversibility.¹⁸

• Membrane fouling caused by organisms in the water. Studies have shown that algal material can directly or indirectly affect membrane flux and transmembrane pressure difference, and NaOCl is more effective than NaOH in removing Microcystis aeruginosa from the membrane surface.¹⁹

2.2 Membrane fouling mechanism

Membrane fouling caused by dead-end filtration of ceramic ultrafiltration membrane under constant pressure can be explained by four fouling models:^15,16

1. Complete blocking: complete blockage occurs when the size of the pollutant molecules or particles is comparable to or larger than the pore size of the ceramic membrane. These molecules or particles can fully enter the membrane pores due to interactions such as van der Waals forces, which cause them to accumulate within the pores, obstructing the passage of solvents or smaller molecules. Over time, this accumulation leads to a rapid decrease in filtration flux.

2. Standard blocking: standard blockage occurs when contaminants are adsorbed onto the membrane surface and membrane pores. Contaminants can be adsorbed and intercepted even if the particle size of the contaminant is smaller than the pore size of the membrane. These molecules may interact with the pore walls through chemisorption or physisorption mechanisms. For example, van der Waals forces or electrostatic attraction can cause contaminants to adsorb on the pore walls, gradually reducing the effective diameter of the pore and leading to a continuous decrease in filtration flux.

3. Intermediate blocking: pollutant molecules on the membrane surface are combined into a whole through the bridging effect to be intercepted by the membrane, and the situation that the pollutant molecules do not completely enter the membrane pore is called intermediate blockage. This stacking may be due to interactions among pollutant molecules, such as electrostatic repulsion or attraction, leading to the formation of a thicker layer of pollutants on the membrane surface. This layer impedes the passage of solvents and smaller molecules, and as the accumulation of pollutants continues, the filtration flux decreases progressively.

4. Cake filtration: filter cake layer fouling involves the accumulation of pollutant particles on the membrane surface to form a thick layer known as a filter cake. This layer forms due to the interactions among pollutant molecules, such as hydrogen bonding or van der Waals forces, as well as interactions with the membrane material, which cause them to form a stable structure on the membrane surface. The formation of a filter cake layer significantly reduces the membrane's filtration efficiency because solvents and smaller molecules must pass through this thicker layer of pollutants to get through the membrane. These four fouling models are shown in Fig. 1.

Fig. 1 Schematic diagrams of four filtration models: (a) complete blocking, (b) standard blocking, (c) intermediate blocking, and (d) cake filtration.²⁰

3. Pre-coagulation

NOM in raw water will lead to membrane fouling, accelerate the decrease of membrane flux, and reduce the working efficiency of the ceramic ultrafiltration membrane.²¹ Coagulation pretreatment before the ultrafiltration process can effectively reduce membrane fouling and ensure effluent quality and operation effect, which has been confirmed in drinking water treatment.²² The effect of coagulation pretreatment on ceramic ultrafiltration membrane fouling is complex, which is mainly reflected in the difference of coagulation agents and coagulation methods.²³ After coagulation of Al-based and Fe-based coagulants, the coagulant increases the collision frequency and instability of the particles. Then, due to the relatively uneven structure of the filter cake layer formed by adsorption electric neutralization, adsorption bridging, network sweeping, and compression of the electric double layer, the membrane is polluted as a filter cake layer after coagulation.²⁴ Different coagulants will produce different forms of flocs in the coagulation process, and the filter cake layer after coagulation pretreatment does not necessarily have a bad effect on ceramic ultrafiltration membrane fouling. The flocs are intercepted by the ultrafiltration membrane to produce a filter cake layer. Some structural filter cake layers can play a certain adsorption effect and reduce membrane fouling to some extent. Meng et al. discussed the effect of coagulant dosage on membrane flux during in situ coagulation (Fig. 2(a)). It was found that the membrane flux reached the best performance when the coagulant concentration was 20 ppm. The use of too high concentration of coagulant will lead to more serious reversible pollution caused by coagulant residues. The addition of low concentration coagulant will also cause a rapid decline in membrane flux, which is attributed to the residual organic matter caused by insufficient coagulant dosage. As shown in Fig. 2(b), in situ coagulation showed better results than pre-coagulation. This phenomenon may be due to the filter cake layer formed by flocs in front of the membrane playing a pre-filtration role to reduce membrane fouling.²³

Fig. 2 (a) Effect of coagulant dosage on membrane fluxes. (b) Effect of coagulant dosing method on membrane fluxes.²³

As can be seen from Fig. 3, for the most common aluminum-based coagulants, the different forms of Al also have different effects on ceramic membrane fouling. Polymeric aluminum chloride (PACl) is a product of partial hydrolysis of Al(III) and is classified into three types: monomeric substances (Ala), intermediate polymeric species (Alb) and colloidal or solid substances (Alc). Ala is mainly composed of monomeric species such as Al³⁺, Al(OH)²⁺, and Al(OH)₂⁺; Alb is the intermediate polymer species formed during Al(III) hydrolysis; Alc is the inert large polymer or colloidal species formed during Al(III) hydrolysis.²⁵ In the study of Feng et al., the form of aluminum has a certain effect on the strength and compaction of flocs. Different types of Al combine with pollutants in different ways, which will lead to different properties of flocs and different degrees of membrane fouling. It can be seen that the flux of Alb coagulation effluent is significantly higher than that of Ala and Alc. The experimental results showed that the membrane flux of Alb coagulation effluent was significantly higher than that of Ala and Alc, that is, the membrane fouling degree of Alb coagulation pretreatment was lighter than that of Ala and Alc. It is found that the influence of flocs on flux depends on the shear resistance of flocs. The pressure in the membrane unit can cause the floc to break, leading to more severe fouling. Therefore, the membrane flux is higher because the flocculants formed by Alb have stronger shear resistance.²⁶

Fig. 3 Influence of the morphology of elemental aluminum on membrane fluxes.²⁷

Jang et al. studied the effect of pre-coagulation on membrane fouling in the ultrafiltration process of oil–water separation. As shown in Fig. 4, the pre-coagulation reduced the zeta potential of oil droplets, weakened the electrostatic force between oil droplets and the surface of the ceramic membrane, increased the size of oil droplets, and formed cake layer fouling. The decrease of hydrophobicity of oil droplets by pre-coagulation also weakens the hydrophobic interaction between oil droplets and membrane surface. Therefore, pre-coagulation weakens the adhesion between oil droplets and membrane surface, which can significantly increase the flux and increase the proportion of reversible membrane fouling.²⁸

Fig. 4 The proposed schematic of mechanisms of ceramic membrane fouling for O/W emulsion separation without pre-coagulation.²⁸

4. Pre-oxidation

Pre-oxidation has attracted much attention because it can significantly change the composition and properties of feed water through chemical reactions. Chemical oxidation is different from coagulation, adsorption and pre-filtration because it can lead to changes in the chemical structure and valence of organic/inorganic composite pollutants, inactivation of microorganisms, partial mineralization of organic matter and production of by-products.²⁹ As shown in Fig. 5(a), ozone is the oxidant of most concern, followed by permanganate and chlorine.

Fig. 5 The ratio of studies according to oxidants (a) and membrane material (b) in surveyed literature.³⁰

In addition to these traditional oxidants, some new oxidation processes, such as electro-oxidation (EO), electron beam irradiation, and advanced oxidation processes (AOPs) based on peroxymonosulfate (PMS)/persulfate (PS) and ultraviolet (UV) catalysis, have also been studied to improve membrane performance.

Fig. 5(b) shows the proportion of studies by membrane material. Despite the advantages of ceramic membranes in terms of oxidation resistance, more than two-thirds of the investigations were carried out using polymer membranes, possibly due to their widespread use in the water industry and the convenience of laboratory research.³⁰ Due to the advantages of ceramic membranes in terms of oxidation resistance, this section will explore the effects of mainstream oxidation methods on ceramic ultrafiltration membrane fouling.

Song et al. found that both ozone pre-oxidation and in situ ozonation treatment can effectively reduce the ceramic ultrafiltration membrane fouling caused by colloidal natural organic matter. For ozone pretreatment, the dosage and dosing method of oxidants are the main factors determining membrane fouling. Ozonation effectively decomposes high molecular weight organic matter into low molecular weight organic matter. Under low ozone dosage, pre-ozone has better anti-fouling performance than in situ ozone, while under high ozone dosage, in situ ozone has better anti-fouling performance. In terms of hydraulic irreversible fouling control, regardless of ozone dosage, in situ ozonation is more effective than pre-ozonation. The mitigation of membrane fouling by pre-ozonation and in situ ozonation is mainly attributed to the mitigation of cake layer fouling and the integration of ceramic membrane filtration. The catalytic ozone decomposition increases the formation of hydroxyl radicals, further strengthens the oxidation of accumulated pollutants on the membrane surface and in the membrane pores, and thus effectively alleviates hydraulic reversible and irreversible fouling.³¹

The mixed treatment of ozonation and ceramic membrane successfully alleviated the ceramic membrane fouling caused by protein and polysaccharide by decomposing high molecular weight organic matter into low molecular weight organic matter, resulting in a decrease in the rejection of high molecular weight organic matter by the membrane. Ferrate(VI) is a powerful oxidant that can alleviate and degrade many pollutants in water and wastewater treatment without any disinfection by-products³² such as NOM, phenol, chlorobenzenes, pharmaceuticals and personal care products (PPCPs) and heavy metals.³³ Compared with the use of ferrate(VI) or ozone alone, the ferrate(VI)–ozone integrated process in water and wastewater treatment will be more suitable and preferred for NOM removal and subsequent membrane fouling control, and also enhance the oxidation performance, which is attributed to the fact that Fe(VI) particles such as γ-Fe₂O₃ and γ-FeOOH will catalyze ozone decomposition and promote the production of ·OH.^34,35 Compared to conventional advanced oxidation processes (AOPs), the ferrate(VI)–ozone integrated process will simultaneously oxidize, disinfect and coagulate in the same unit.³⁶

UV/TiO₂ treatment is an alternative method for the degradation of organic matter in water without the use of chemical reagents (green environmental protection) to avoid the generation and disposal of sludge.³⁷ In 2001, Lee et al. proposed a photocatalytic membrane reactor to remove HA from water and increase membrane flux.³⁸ Yang et al. found that according to the different pretreatment time of UV/TiO₂, the mechanism of membrane fouling development can be speculated by the growth stage of the filter cake layer, transition fouling, intermediate pore blockage and other factors. With the extension of UV/TiO₂ pretreatment time, the length limitation stage of the filter cake layer is advanced, and hydraulic reversible fouling is effectively controlled. In this case, more HPI humic substances with high molecular weight are produced. These organic substances have the opportunity to mix with TiO₂ particles to form a porous filter cake layer. When backwashing, these organic substances can be easily rinsed off. The mechanism is shown in Fig. 6.

Fig. 6 Working mechanisms of the membrane fouling mitigation by UV/TiO₂ pretreatment.³⁹

Cheng et al. systematically studied the performance of sulfate radical-based advanced oxidation process (SR-AOP) pretreatment in alleviating ceramic ultrafiltration membrane fouling caused by algae extracellular organic matter (EOM). Their research shows that SR-AOP pretreatment can promote the removal of DOC and UV₂₅₄. Their performance is in the order UV/Fe(II)/PMS > Fe(II)/PMS > UV/PMS, and the mechanism is mainly to degrade macromolecular biopolymers into small molecular biopolymers. Fe(II)/PMS had a significant mitigation effect on both reversible and irreversible fouling, and UV/PMS alleviated only reversible fouling.⁴⁰ Liu et al. studied the photocatalytic reduction of ultrafiltration membrane fouling caused by intracellular organic matter (IOM) in Microcystis aeruginosa cells by Bi-doped TiO₂ nanocomposites loaded on powdered activated carbon (Bi₂O₃–TiO₂/PAC). They found that excessive photocatalytic oxidation (90–120 min) would aggravate the degree of ceramic ultrafiltration membrane fouling. Photocatalytic oxidation significantly reduced the electronegativity of IOM, increased the hydrophilicity of the deposition layer on the membrane surface, and transformed the hydrophilicity of the membrane surface.⁴¹

5. Pre-adsorption

For the pre-adsorption process before ultrafiltration membrane separation, the two most important factors are the choice of adsorbent and the way of adsorption. Excellent adsorbents should have the characteristics of large-scale preparation and be insoluble, non-toxic, low cost and renewable.⁴² The most important advantage of the combination of adsorption and membrane filtration technology is the reduction of membrane contamination and cleaning frequency. It also makes the size of the micropollutants smaller, and the adsorbent can be more easily adsorbed in the system, so that more pollutants are intercepted by the membrane. While more and more pollutant legislation and public awareness have aroused widespread attention to micropollutants, the effect of adsorbent quality on membrane fouling has also become a controversial issue. Some of the adsorbent particles will enter the membrane pore, and some of them will form cake layer fouling. The weight of fouling type remains to be discussed.⁴³ Below we will report the mainstream adsorption methods and the effects of adsorption agents on ceramic ultrafiltration membrane fouling.

Powdered activated carbon (PAC) has been widely used in the removal of pollutants in wastewater treatment and can be used to prepare particles with specific particle size and pore size.⁴⁴ Among the various strategies of ultrafiltration membrane pretreatment, PAC adsorption pretreatment can significantly improve the removal rate of organic matter.⁴⁵ Other studies have shown that the removal rate of organic matter by the adsorption–ultrafiltration hybrid process increases with the dosage of PAC.⁴⁶ Wang et al. studied the mitigation of ceramic membrane fouling caused by humic acid (HA), sodium alginate (SA) and Yangtze River water by PAC. PAC has a good mitigation effect on membrane fouling caused by HA, but it will aggravate membrane fouling caused by SA. For Yangtze River water, PAC can also effectively alleviate membrane fouling, which is mainly due to the adsorption of fulvic acid (FA) and HA by PAC, which are the main organic pollutants in Yangtze River water.⁴⁷ Xing et al. studied the effect of UV/Cl-enhanced PAC pretreatment on membrane fouling. Their results showed that UV/Cl/PAC significantly reduced reversible and irreversible fouling resistance, and UV/PAC reduced reversible fouling. Therefore, UV/Cl oxidation may be a way to improve the efficiency of PAC adsorption pretreatment before ultrafiltration.⁴⁸

6. Combined process

A single pretreatment technology still has certain challenges for the mitigation of ceramic ultrafiltration membrane fouling. For the removal of NOM, coagulation is still the most common pretreatment method and is the most economical.⁴⁹ For some new trace pollutants, advanced oxidation technology is a better choice. Each pretreatment method has its own advantages and disadvantages. Combined pretreatment can more effectively alleviate membrane fouling and remove target pollutants. This part will focus on the effect of combined pretreatment process on ceramic ultrafiltration membrane fouling.

The eutrophication caused by excessive reproduction of algae in water is an important reason affecting water quality. Some algae species release toxins, such as microcystins (MCs), which pose a serious threat to human health.⁵⁰ The control of algae organic matter is often related to coagulation process and sand filtration process. In the coagulation process, the cell integrity of algae should be guaranteed as much as possible. All cells are completely removed by the surface charge neutralization of polyaluminium chloride (PACl). In the process of floc storage, the protective effect of EPS produced by M. aeruginosa cells was destroyed or decomposed, and PACl caused obvious damage to cells, resulting in a large release of MCs.⁵¹ In the process of filtration, algae cells and extracellular substances can easily block the membrane pores and cause membrane fouling. The traditional coagulation process has been found to have no obvious effect on alleviating this kind of membrane fouling. The effects of permanganate pre-oxidation and persulfate/iron(II) enhanced coagulation pretreatment on ceramic ultrafiltration membrane fouling caused by manganese and algae were compared. Studies have shown that compared with potassium permanganate, PMS/Fe²⁺ has a more obvious mitigation effect on ceramic membrane fouling, and potassium permanganate has a more significant removal effect on manganese. Studies have shown that soluble Fe²⁺ can activate PMS and produce ·OH or SO⁴⁻· for advanced oxidation. In the PMS/Fe²⁺ system, ·OH is considered to be the main contributor to the oxidation of pollutants. The removal effect of PMS/Fe²⁺ on UV₂₅₄ was more significant.⁵⁰ This may be due to the fact that PMS/Fe²⁺ can remove more humus, which is one of the main causes of membrane fouling.⁵²

As the main source of drinking water, groundwater has received extensive attention due to the weathering of metal minerals and rocks as well as the unreasonable discharge of some industrial wastewater; high levels of dissolved manganese (Mn) and iron (Fe) often coexist naturally in groundwater.⁵³ Antibiotics in drinking water have potential ecological risks and cause water quality problems easily due to their presence.^54,55 However, it is difficult to remove antibiotics in water by conventional processes;⁵⁶ advanced oxidation technology can effectively degrade antibiotics in water.⁵⁷ Du et al. found that the mixed pretreatment process as shown in Fig. 7 can achieve the purification of drinking water containing a variety of pollutants (Fe²⁺, Mn²⁺ and antibiotics). During the in situ oxidation/coagulation process, Fe²⁺, Mn²⁺ and antibiotics produced a large number of aggregates which can be effectively separated by the ceramic ultrafiltration membrane. In situ oxidation/coagulation can make pollutants form crystalline iron hydroxide or manganese precipitates in groundwater without NOM, which helps to mitigate membrane fouling; the presence of NOM weakens the crystalline structure of the aggregates, which can lead to more severe membrane fouling.⁵⁸

Fig. 7 Schematic of the fate of manganese, ferrous and antibiotics in groundwater during combined process.⁵⁸

Conventional water treatment processes have limited effects on the removal of complex organic compounds such as antibiotics. Advanced oxidation processes (AOPs) have been used to remove refractory organic pollutants in drinking water.⁵⁹ Du et al. studied the combination of PMS-assisted iron electrolysis/iron coagulation and ceramic ultrafiltration to treat surface water containing antibiotics.⁶⁰ In the process of electrooxidation, dissolved antibiotics can be converted into small molecular organic matter. These small molecular substances and inorganic particles flocculate to produce precipitation. Their study found that under the optimal PMS-assisted EO/EC pretreatment conditions, coagulation produces larger flocs (206–275 μm), which effectively alleviates membrane fouling. Compared with direct ultrafiltration, porous ceramic membrane-assisted electrooxidation/coagulation technology can remove a large number of antibiotics and a small amount of organic matter, and reduce membrane fouling.

7. Conclusion and outlook

Since the inception of membrane technology, the issue of membrane fouling has emerged as a central theme in numerous research endeavors. Membrane fouling not only impacts the service life and cleaning frequency of the membrane but also poses a challenge to the overall efficiency of filtration systems. Ceramic ultrafiltration membranes, recognized as one of the most promising membrane types, have become indispensable across a spectrum of applications, including the food industry, pharmaceuticals, bioengineering, industrial and municipal water treatment, seawater desalination, and drinking water purification. Despite their advantages, the inevitability of membrane fouling necessitates ongoing research to mitigate its effects on ceramic membranes. Current research primarily targets fouling caused by organic and inorganic pollutants, while comparatively less attention has been given to biological fouling and the impact of emerging pollutants. Future research should concentrate on the synergistic integration of advanced pretreatment technologies with ceramic membranes to address the limitations of current methodologies.

In addition to refining pretreatment processes, the modification of existing membranes and the innovation of novel membrane materials present exciting opportunities. Surface modifications, such as the introduction of anti-fouling coatings or nanomaterials, could potentially reduce energy consumption and lower operational costs during the water purification process. Moreover, the exploration of nanotechnology in membrane fabrication may pave the way for membranes with enhanced selectivity and permeability. Another critical area for future research is the development of intelligent monitoring systems that can predict and respond to fouling events in real-time, thereby extending the intervals between cleaning cycles and improving the overall lifespan of the membrane. Furthermore, the study of membrane biofouling, which involves the accumulation of microorganisms on the membrane surface, should be intensified to develop effective strategies for its control.

In summary, this report elucidates the control mechanisms of various pretreatment technologies for ceramic membrane fouling, providing valuable insights for the advancement of ceramic membrane technology. As technology progresses, it is anticipated that the challenges associated with membrane fouling will be more effectively managed. This will facilitate the broader application of ceramic membranes across diverse sectors, enhancing their role as a key component in sustainable water treatment solutions.

Data availability

No primary research results, software or code have been included and no new data were generated or analysed as part of this review.

Author contributions

Yimu Qiao: methodology, original draft preparation. Xue Han: writing – review & editing. Feiyong Chen: reviewing. Cuizhen Sun: funding acquisition. Linxu Xu: investigation. Jiaxin Yao: writing – review & editing. Yaqi Wu: data curation. Zhen Qi: data curation. Rupeng Liu: funding acquisition. Xue Shen: validation, supervision, reviewing, funding acquisition.

Conflicts of interest

There are no conflicts to declare.

Acknowledgements

This work was funded by Shandong Provincial Natural Science Foundation (No. ZR2021QE198); Shandong Top Talent Special Foundation (No.0031502)-Research and development of key technologies and high-end equipment of water environment health in the Yellow River Basin (Shandong) and the Doctoral Research Fund of Shandong Jianzhu University (No. X21076Z).

Notes and references

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