Fouling Mechanisms Research Articles

Dynamic pore modulation of contracted carbon fiber filter for wastewater treatment: Filtration performance and in-situ regeneration mechanism

Antifouling and selectivity are the major challenges in membrane separation technologies. Inspired by membranes with tunable pore sizes in filtration systems, we propose a contracted carbon fibrous filter (CCF) with an inversed-triangle structure (ITS) using commercial carbon fibers that can control the filter pore size by adjusting the external force loading. By increasing the force loading on fibers, CCF pores shrunk from 2.02 to 0.98 µm, while maintaining a high rejection efficiency of kaolin particles (>99%) at a water flux ranging from 679.7 to 354.9 L m-2 h−1. The role of the ITS and the filtration mechanism of the carbon fibers was revealed via computational simulations and experimental results. Various cleaning strategies were explored to regenerate CCF performance after fouling. A mean flux recovery of 99.6% could be achieved during the nine-cycle filtration by adjusting the pore size combined with electrocleaning. Additionally, a removal mechanism for internal fouling was proposed. This study demonstrates that the novel CCF provides a simple and reliable strategy for wastewater filtration.

Peroxymonosulfate enhanced Fe(III) coagulation coupled with membrane distillation for ammonia recovery: Membrane fouling control process and mechanism

Membrane fouling limited the application of membrane distillation (MD) process in resource recovery. In this research, the peroxymonosulfate (PMS) enhanced Fe(III) coagulation process was proposed and proved its effectiveness in eliminating natural organic matter (NOM) and emerging organic contaminants (EOCs). Fe(III)/PMS process significantly enhanced the removal of dissolved organic carbon (DOC), turbidity, and UV254, compared to conventional Fe(III) coagulation. Thiamphenicol (TAP) represented the EOCs in the digestate, and Fe(III)/PMS could significantly degrade TAP (86 % degradation). In this course, phenols/quinones served as electron shuttles to induce the Fe(III)/Fe (II) redox cycle. The activation of PMS was boosted, generating the primary reactive substance sulfate (SO4−) radical with intense oxidative properties. In addition, membrane distillation achieved recovery of 93 % of TAN from coagulation effluent without membrane fouling. No tryptophan-like, tyrosine-like, xanthate, and other soluble microbial byproducts were detected on the membrane surface following Fe(III)/PMS pretreatment. The innovation of this study was revealing that the complexation of Fe(III) with NOM could promote Fe (II) regeneration and enhance PMS activation, active substance formation and contaminants degradation. New insights into the role of NOM in the Fe(III)/Fe(II) redox cycle were gained and the development of advanced oxidation process (AOP) coupled membrane technology was promoted to mitigate membrane fouling.

Membrane fractioning of pre-treated waste activated sludge for the recovery of valuable biocompounds

The recovery of added-value biocompounds from waste activated sludge (WAS) is a promising alternative to its current management. In this study, WAS was partially wet oxidised producing a highly complex stream mainly composed of humic acids, proteins and carbohydrates. This stream was ultrafiltered to assess the influence of membrane material and molecular weight cut-off (MWCO) on its fractioning based on the different sizes of the biomolecules contained in the oxidised WAS.Flat-sheet polyethersulfone (PES), permanently hydrophilic polyethersulfone (PESH), and polyacrylonitrile (PAN) membranes with a MWCO of 50 KDa were evaluated. The best performance was obtained with PES membrane, achieving high retention values (around 70 % for proteins and carbohydrates, and 47 % for humic acids) and high differences in selectivity between proteins and carbohydrates with humic acids (around 23 %). For the size fractioning experiments, PES membranes of 10 and 3 kDa (PES10 and PES3) were used, obtaining the best results when filtering the PES50 membrane permeate with the PES3 membrane, retaining 83 % of carbohydrates, 87 % of proteins and 69 % of humic acids. These results open the possibility of separating carbohydrates, proteins and humic acids through an integrated membrane process.Besides, membranes were characterized by atomic force microscopy, infrared spectroscopy, and contact angle measurements.Multiple fouling models were assessed, and the main fouling in PAN membrane, and to a lesser extent in PES, was reversible. Conversely, PESH membrane fouling had a strongly irreversible character. Cake filtration can be considered the main fouling mechanism in all experiments.

Fouling mechanism and effective cleaning strategies for vacuum membrane distillation in brackish water treatment

Membrane scaling is an enormous challenge in the desalination of hypersaline water using membrane distillation (MD). In this study, vacuum membrane distillation (VMD) was employed for brackish water treatment, with an emphasis on scaling mechanisms and mitigation strategies. Four methods, including deionized water, hydrochloric acid, and acetic acid, ultrasonication, were utilized for membrane cleaning. The cleaning efficiency was assessed through a comprehensive analysis of residual foulant layers. It was determined that mineral scaling constituted the primary fouling mechanism, and a minor amount of organic fouling was present at the interface between scaling-scaling and scale-membrane. Calcium and magnesium carbonate were the primary scaling components observed in brackish water desalination, appearing as needle-like and block crystals. Notably, CaCO3 predominantly existed as the aragonite crystal structure. Ultrasonication and deionized water demonstrated limited effectiveness due to the alkaline nature of the scaling. Conversely, the application of dynamic hydrochloric acid and acetic acid treatments resulted in a significant reduction in scaling, with acetic acid demonstrating superior efficacy in removing carbonate scaling. The results presented in this study can provide valuable theoretical guidance for the treatment of brackish water using membrane desalination techniques.

The combination of precipitative softening and ozonation as a pretreatment of ultrafiltration in flowback water treatment: performance and fouling analysis

ABSTRACT Ultrafiltration (UF) technology is an efficient shale gas flowback water treatment method. However, severe membrane fouling is the primary restriction on the application of UF technology. Here, we studied the impact of three pretreatments: precipitative softening (PS), precipitative softening, followed by ozonation (PS-O) and ozonation, followed by precipitative softening (O-PS), on pollutants’ removal efficiencies and membrane fouling. The results showed that (1) the hardness, bacteria, scaling trend and compatibility with formation water exceeded the requirements for water reuse; (2) pretreatments effectively increased water flux and prolonged ultrafiltration membrane life, and both of them followed the order of PS-O process > O-PS process > PS process; (3) the fouling mechanism was changed from the complete blocking model to the standard blocking model by the PS process and the addition of ozonation enhanced the correlation of standard blocking model; (4) the quality of fracturing liquid prepared by the effluent treated by the PS-O-UF process was the best and satisfied the requirements of slick water. This paper indicated that the PS-O-UF process was suitable for the treatment of Changning shale gas flowback water for reuse.

Study on the Effect of Surface Properties of Non-Metallic Materials on the Growth Mechanism of Crystallization Fouling

In order to alleviate the serious problem of scaling in oilfield water injection pipelines, we developed a scale collection device and applied it in the field based on the idea to “change passive descaling to active descaling”, but the effect is not stable, so we need to improve the descaling effect. Firstly, this paper analyzed the effect of surface physical properties of eight non-metallic materials on CaCO3 scale growth and their mechanisms through shear experiments. Then, the influence of surface properties (roughness, contact angle, surface energy) on the scale growth characteristics was investigated. Finally, the influence of material surface properties on the friction coefficient was studied by a cyclic experiment. The results showed that except for PTFE (polytetrafluoroethylene), the fouling amount of the other seven materials changed abruptly at 18 h, and the maximum fouling amount of FRP was 2.05 g/m3. It was found by scanning electron microscopy that the fouling particles on the surface of FRP were interconnected and presented in the form of flakes, which was related to the larger surface wettability, surface energy, and roughness. At the same time, the surface properties of the material have a certain relationship with the friction coefficient, and the influence of the contact angle on the friction coefficient is greater than the surface energy and roughness.

Molecular mechanism of casein-chitosan fouling during microfiltration

In this study, the casein-chitosan complexes were subjected to microfiltration. The filtration property was analyzed, and the molecular mechanism of fouling was explained under different medium pH, casein-chitosan ratios and ionic strength. Results suggest that a higher pH and more polysaccharide can slow down the fouling growth rate, but a higher pH is unfavorable for long-term processing. Especially the effect of pH on the process was far more significant than the others. At pH 2.8, most of amino acid residues combined with chitosan to form the denser particles and to generate the gel consistency and yield stress. Thus, the severe fouling resistance was caused by the tight gel layer stacked on membrane surface. At pH 6.8–7.8, the electrostatic binding energy between casein and chitosan decreased. The complexes gel consistency and yield stress disappeared, and the incompact network was formed. Thereby, the cake layer density and the fouling growth rate were reduced. At pH 4.8, the amino acid residues of αS1- and β-casein bound to chitosan decreased. Although the complex exhibited the gel consistency and yield stress, the microfiltration efficiency was improved due to the decrease of binding sites. This work provides new evidences into understanding the membrane fouling mechanism.

Effect of fouling and cleaning upon the surface charge and porosity of polyethersulphone membranes during coffee brew decaffeination

Filtration processes could offer a viable alternative to use of solvents for the production of reduced caffeine coffee beverages (so called ‘half-decaf’) which have recently gained increased commercial attention. However fouling phenomena and membrane deterioration could significantly alter the process performance; hence fouling and cleaning mitigation strategies must be explored by monitoring key membrane properties such as porosity and surface charge. In this study, multiple cycle filtration of coffee brews for the selective reduction of caffeine has been performed. A commercially available synthetic tight ultrafiltration polyethersulphone (PES) membrane (GP95PP – Alfa Laval) and a bespoke loose nanofiltration mixed matrix PES membrane fabricated, were used for three consecutive fouling and cleaning filtration cycles. The impact and mechanisms of fouling and the cleaning protocol effectiveness were investigated using surface charge, porosity, membrane surface and membrane morphology characterization techniques. Streaming potential studies revealed negative surface zeta potential for the membranes in a pH range of ca. 3.5–8.0. The fouled membrane classes exhibited elevated negative charges, which were partially restored to the pristine levels when chemically cleaned, suggesting the presence of residual negatively charged foulants. Porosity studies revealed the presence of a porous cake layer with an increase of average pore size and pore volume, and a decrease of 10–20 % on the BET surface area of the fouled membranes. Presence of key compounds on the membrane surface and structure was confirmed via EDX and FT-IR spectroscopy. Surface roughness along with SEM microscopy verified the uniform deposition of the foulants with absence of bulky particles. The presence of a cake layer was confirmed via SEM cross-sectional images due to selective thick layer thickness increase of the fouled membranes. Flux differences between the membrane classes can be related to the thickness of the top layer. Flux decreases and flux recovery ratios were also reported over multiple cycles and linked with porosity and other surface properties.

Experimental Evaluation of the Process Performance of MF and UF Membranes for the Removal of Nanoplastics.

Despite the high removal ability of the wastewater treatment technologies, research efforts have been limited to the relatively large-sized microplastics, leaving nanoplastics outside the studied size spectrum. This study aims to evaluate the process performance of MF and UF membranes for the removal of single and mixed solutions of polystyrene nanospheres (120 and 500 nm) and BSA. The process performance was evaluated in terms of the rejection coefficient, the normalized flux, and the permeability recovery. The fouling mechanism of these pollutants was studied, evaluating the effect of different membrane materials, membrane pore sizes, and nanoplastic sizes, as well as the synergetic effect of the mixture of foulants. This study was complemented by surface membrane characterization. Polystyrene nanospheres were successfully removed with all the membranes studied, except for the MF membrane that obtained PS 120 nm rejection coefficients of 26%. Single nanoplastic particles were deposited in UF membranes creating a pore blocking and cake layer formation, whilst the nanoplastics of 120 nm were accumulated inside the MF membrane creating an internal pore blocking. In mixed solutions, the BSA acted in two different ways: (i) as a stabilizer, hindering the deposition of nanoplastics and (ii) as a main foulant that caused a substantial flux reduction.

Fouling of reverse osmosis membrane: Autopsy results from a wastewater treatment facility at central park, Sydney

Membrane fouling is an inevitable phenomenon and common issue in Reverse Osmosis (RO) membrane systems used for water reclamation. Severe membrane fouling in RO system could consequently increases the operation cost as it requires frequent membrane chemical cleaning process thus consuming more chemical agents and shorten lifespan of RO membrane module. In this study, potential foulants of RO membranes that are used at Sydney's urban wastewater recycling facility which treated for domestic and commercial wastewaters, were investigated via membrane autopsy method. The three-year-old spiral wound RO membrane modules were taken from the site for membrane autopsy and to investigate major fouling factors as well as in-depth study of fouling mechanisms throughout various characterization methods. Additionally, a flux recovery rate of fouled RO membranes via the chemical cleaning was also examined using different kind of chemical cleaning agents to find a most effective chemical cleaning combination.

A novel membrane bioreactor inoculated with algal-bacterial granular sludge for sewage reuse and membrane fouling mitigation: Performance and mechanism

In this study, a novel membrane bioreactor (MBR) inoculated with algal-bacterial granular sludge (ABGMBR) was established to improve pollutant removal and alleviate membrane fouling. The ABGMBR system showed higher pollutant removal rate and longer operation time (152 day) compared to the control MBR (AGMBR). Moreover, the contents of the pollutants such as granular sludges, extracellular polymeric substances (EPS), and soluble microbial products on the membrane were remarkably reduced, leading to the formation of a porous and loose cake layer on the membrane and a slow increase in transmembrane pressure. Standard blocking was the main mechanism of membrane fouling; however, the membrane pore blockage was significantly reduced in ABGMBR. The extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory suggested that the aggregation and adhesion of foulants on the membrane were greatly inhibited in ABGMBR. Furthermore, correlation analysis showed significant differences in membrane fouling characteristics between AGMBR and ABGMBR. The ABGMBR system effectively retarded sludge disintegration and increased the repulsion between the sludge and membrane owing to the favorable mixed liquor characteristics. This study showcases the superior operational efficiency and anti-fouling performance of ABGMBR, offering a novel perspective on sewage reuse and membrane fouling mitigation.

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

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

Comparative analysis of membrane fouling mechanisms induced by operation modes of membrane bioreactors with aerobic granular sludge

This experimental work investigated fouling characteristics induced by two different configurations of membrane bioreactor (MBR), which are submerged MBR and sidestream MBR with aerobic granular sludge. Submerged membrane bioreactor with granular sludge (Sub-MGSBR) ran the longest operation time 61 days with a steady overall TMP increase rate; Sidestream membrane bioreactor with granular sludge (SS-MGSBR) performed only 39 days, which exhibited Sub-MGSBR had more efficiently retarding membrane fouling. In both membrane bioreactors with flocculent sludge (MFSBRs) as a control, membrane foulants were compact, and cake resistance was the dominant fouling factor. In MGSBRs, however, pore blocking resistance turned out the key fouling factor. Especially in Sub-MGSBR, it went beyond 75%, and there was the most conglomeration of microorganisms of foulants with the highest porosity. Extracellular polymeric substances (EPS) content of foulants proved membrane fouling was hardly just for granules accumulation into cake but microorganisms’ growth in MGSBRs.

Investigation of factors affecting sodium alginate fouling mechanisms in a microfiltration process under non-constant-flux and non-constant-pressure conditions.

Variations in transmembrane pressure and permeate flux are closely related to membrane fouling. In this study, a laboratory-scale submerged microfiltration system was used to investigate the influence of sodium alginate (SA) concentration and peristaltic pump rotation speed on the fouling under the conditions of (1) the same driving force and non-aerated-PAC, (2) different driving forces and non-aerated-PAC, and (3) different driving forces and aerated-PAC. The results showed that the normalized transmembrane pressure (TMP') increased linearly with decreasing normalized permeate flux (J') during the early microfiltration stage regardless of the operating conditions, indicating that the SA microfiltration process controlled by the peristaltic pump was non-constant-flux and non-constant-pressure. The latter filtration stage was considered constant-pressure filtration when 200-1,200 mg/L of SA was filtrated at the same rotation speed. During filtration of 800 mg/L of SA under the non-aerated-PAC condition, the later filtration stage was considered constant-pressure filtration when the peristaltic pump rotated at slower speeds of 15 and 30 rpm. This approached constant-flux filtration when the peristaltic pump rotated at faster speeds of 60 and 90 rpm, and PAC-aeration scouring was an effective measure for mitigating membrane fouling by SA.

Gravity-driven membrane coupled with oxidation technology to modify the surface properties and biofilm formation: Biofouling mitigation

Biofilms caused by biological fouling play an essential role in gravity-driven membranes’ (GDMs) flux decline and rejection rate. The effects of ozone, permanganate, and ferrate (VI) in-situ pretreatment on membrane properties and biofilm formation were systematically studied. Due to the selective retention and adsorption of algal organic matter by biofilms and oxidative degradation, the rejection efficiency of dissolved organic carbon (DOC) in algae-laden water pretreated with permanganate by GDM was up to 23.63%. Pre-oxidation extraordinarily postponed flux decline and biofilm formation of GDM and reduced membrane fouling. The total membrane resistance decreased by 87.22%–90.30% within 72 h after pre-ozonation. Permanganate was more effective than ozone and ferrate (VI) in alleviating secondary membrane fouling caused by algal cells destroyed by pre-oxidation. Extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory revealed that the distribution of electrostatic force (EL), acid-base (AB), and Lifshitz-van der Waals forces (LW) interactions between M. aeruginosa and the released intracellular algogenic organic matter (IOM) and ceramic membrane surface was similar. The membrane and foulants are always attracted to each other by LW interaction at different separation distances. The dominant fouling mechanism of GDM combined with pre-oxidation technology shifts from complete pore blocking to cake layer filtration during operation. After pre-oxidation of algae-laden water by ozone, permanganate, and ferrate (VI), GDM can treat at least 131.8%, 37.0%, and 61.5% more feed solution before forming a complete cake layer. This study provides new insights into the biological fouling control strategies and mechanisms for GDM coupled with oxidation technology, which is expected to alleviate membrane fouling and optimize the feed liquid pretreatment procedure.

Co-pressing and co-sintering preparation of cost-effective and high-performance asymmetric ceramic membrane for oily wastewater treatment

High-performance asymmetric ceramic membranes have shown great potential in wastewater treatment. Nevertheless, high production cost, which results from expensive raw materials, high energy consumption, and complicated preparation process, hinders their large-scale production and application. Herein, a simple and cost-effective co-pressing and co-sintering method was proposed to prepare thin defect-free asymmetric ceramic membranes. This method overcomes the bottleneck of preparing thin asymmetric ceramic membrane by co-pressing. The membrane with a cornstarch content of 20 wt% and sintered at 1300 °C possessed large water permeance (3640 L·m−2·h−1·bar−1), high permeability (steady-state feed permeance > 1000 L·m−2·h−1·bar−1) and selectivity (rejection rate > 99.6%), as well as excellent oil fouling resistance and regeneration performance. The fouling mechanism of the membrane was in accord with cake filtration for the whole separation process (3 h), although multiple fouling mechanisms might occur simultaneously in the initial filtration stage. This study indicates that co-pressing and co-sintering is a quite promising method for fabricating high-performance and cost-effective ceramic membrane.

Revealing the fouling characteristics in membrane-based primary treatment (MPT) of municipal wastewater and the antifouling mechanism of influent conditioning

Membrane-based technology is becoming an attractive option for primary treatment of municipal wastewater (MW) due to its superior organic retention capacity and footprint savings. However, limited understanding of fouling mechanisms still hampered its practical application. This study aims to investigate the fouling characteristics in MPT and analyze anti-fouling mechanisms of influent conditioning. In the meantime, the differences between microfiltration (MF) and ultrafiltration (UF) are also discussed. Dozens of filtration experiments with different membranes (0.1 μm and 100 kDa), MW conditioning methods (coagulation and adsorption) were conducted. Results indicated that a hallmark of MPT is the protective ability of particulate matters present in the raw MW. The irreversible fouling rate was 2–4 times higher in the absence of particulates. Besides, the main irreversible foulant types and the cake growth patterns differed with different pore sizes. As for influent conditioning, coagulation and adsorption collaborate effectively in regulating cake characteristics. Polymeric aluminum chloride reduces the tendency of binding between foulants and membrane, while activated carbon increases the porosity of the cake layer.

X-ray Absorption Spectroscopy Reveals Mechanisms of Calcium and Silicon Fouling on Reverse Osmosis Membranes Used in Wastewater Reclamation

Reverse osmosis (RO) is widely employed to provide clean water from nontraditional sources (e.g., seawater or municipal wastewater). One of its key challenges is membrane fouling, which leads to reduced flux and increased operational costs. Despite its practical relevance, fundamental understanding of membrane fouling is limited. Toward this end, we investigated calcium (Ca) and silicon (Si) fouling under real RO feed conditions using μ-X-ray fluorescence (μ-XRF) mapping and μ-X-ray absorption near-edge fine structure (μ-XANES) spectroscopy. These techniques are distinctly suited to identify the spatial distribution and (local) chemical speciation of foulants, thereby providing unique insight into the mechanisms of fouling under realistic conditions. Specifically, we investigated RO membranes harvested from a pilot-scale RO system operated at the Orange County Water District (OCWD) Groundwater Replenishment System (GWRS) Advanced Water Purification (AWP) Facility, which received the same feed water as the full-scale plant. Both Ca and Si were found to be abundant in the fouling layer. Despite the use of a commercial antiscalant to inhibit mineral formation, several Ca minerals were present in the fouling layer as minority species, including sulfates, phosphates, and carbonates; most of these minerals were found in particles that were aligned with the feed spacer used to separate the membranes. In contrast, organic-bound Ca and silica occurred across the entire membrane. Our work provides novel insight into the synergistic mechanism of RO fouling by Ca, Si, and organics on RO membranes.

A novel membrane-based integrated process for baicalin recovery from TCM Pudilan wastewater

This study aimed to investigate the potential of membrane integration technology for the recovery of baicalin from Pudilan (PDL) industry wastewater. The impact of different membranes on permeate flux and separation efficiency was analyzed, with fouling mechanisms identified using both resistance-in-series and Hermia models. Results indicate that the CA50k and PES5k combination was suitable for the process. The retentate obtained from the UF membranes contained a significant amount of baicalin, which was subsequently recovered and purified using a straightforward acid precipitation method. The structure of the purified baicalin was identified using 1H NMR and 13C NMR spectra, achieving a maximum recovery rate of 26.15 % with a purity of 93.24 %. The findings of this study have significant implications for the resource utilization of traditional Chinese medicine (TCM) pharmaceutical wastewater.

A critical review on thermodynamic mechanisms of membrane fouling in membrane-based water treatment process

A critical review on thermodynamic mechanisms of membrane fouling in membrane-based water treatment process