Control Membrane Fouling Research Articles

Peracetic acid integrated catalytic ceramic membrane filtration for enhanced membrane fouling control: Performance evaluation and mechanism analysis

Endowing ceramic membrane (CM) catalytic reactivity can enhance membrane fouling control in the aid of in situ oxidation process. Peracetic acid (PAA) oxidant holds great prospect to integrate with CM for membrane fouling control, owing to the prominent advantages of high oxidation efficacy and easy activation. Herein, this study, for the first time, presented a PAA/CM catalytic filtration system achieving highly-efficient protein fouling alleviation. A FeOCl functionalized CM (FeOCl-CM) was synthesized, possessing high hydrophilicity, low surface roughness, and highly-efficient activation towards PAA oxidation. Using bovine serum albumin (BSA) as the model protein foulant, the PAA/FeOCl-CM catalytic filtration notably alleviated fouling occurring in both membrane pores and surface, and halved the flux reduction degree as compared with the conventional CM filtration. The PAA/FeOCl-CM catalytic oxidation allows quick and complete disintegration of BSA particles, via the breakage of the amide I and II bands and the ring opening of the aromatic amino acids (e.g., Tryptophan, Tyrosine). In-depth investigation revealed that the in situ generated •OH and 1O2 were the key reactive species towards BSA degradation during catalytic filtration, while the organic radical oxidation and the direct electron transfer pathway from BSA to PAA via FeOCl-CM played minor roles. Overall, our findings highlight a new PAA/CM catalytic filtration strategy for achieving highly-efficient membrane fouling control and provide an understanding of the integrated PAA catalytic oxidation - membrane filtration behaviors.

Mitigation of membrane fouling of alginate with combined actions of aeration and powdered activated carbon: Fouling behaviors and mechanisms.

A laboratory-scale flat-sheet ceramic microfiltration membrane system was developed to investigate the membrane fouling behaviors and mechanisms of sodium alginate (SA) in the presence of aeration and powdered activated carbon (PAC). When the SA concentration increased from 20 to 500 mg/L, the permeate flux decreased by 81.7%, and the transmembrane pressure (TMP) and resistance increased 1.7 and 24.5 times, respectively. At an SA concentration of 500 mg/L, it was found that the membrane fouling tended to decrease with the increase in the aeration rate, indicating high control of the fouling by air scouring, while PAC-aeration scouring produced a significant improvement in the permeate flux with substantially reduced fouling. In the microfiltration of 500 mg/L SA at an air flow rate of 2.2 L/min and PAC concentrations of 40, 100, and 250 mg/L, the flux increased by 179.3%, 238.0%, and 302.7%, the TMP decreased by 32.6%, 34.8%, and 45.7%, and the cake and pore blocking resistance decreased by 78.0%, 85.1%, and 87.9%, respectively, compared to the corresponding values without PAC-aeration scouring. Intermediate blocking and complete blocking models were confirmed to elucidate the effect of aeration scouring and PAC-aeration scouring on the mitigation of membrane fouling by SA. PRACTITIONER POINTS: Air scouring was effective at mitigating membrane fouling of sodium alginate. The addition of PAC could alleviate membrane fouling of SA. Synergistic scouring by aeration and PAC offers a promising means for more-efficient and cost-effective control of membrane fouling. The fouling mechanisms in various scenarios were elucidated.

Effect of Fe(II)-Activated Peroxymonosulfate (PMS) on the Performance of Ultrafiltration (UF) Process for Secondary Effluent Treatment and Reuse

The secondary effluent of the wastewater treatment plant is considered as one of the reused water sources and needs advanced treatment to meet increasingly stringent water treatment standards. Ultrafiltration, as one of the most widely used advanced treatment technologies, is limited due to membrane fouling, and coagulation and pre-oxidation have received extensive attention as pretreatment methods to alleviate membrane fouling. This research proposes a new method of Fe(II)-activated peroxymonosulfate (PMS) coagulation and a pre-oxidation system coupled with ultrafiltration (UF) to treat secondary effluent from sewage plants, separately evaluating the treatment effect under different molar ratios of Fe(II)/PMS. The Fe(II)/PMS decontamination mechanism and membrane fouling control effect were elucidated through pollutant removal efficiency, membrane morphology, membrane flux trend, and membrane fouling resistance distribution. According to the experimental results, the optimal effect of organic matter removal and membrane fouling mitigation was achieved at the Fe(II)/PMS dosage of 60/60 μM/μM (molar ratio 1:1). The efficiency of pretreatment methods in removing organics and fluorescent components and mitigating membrane fouling followed the order of Fe(II)/PMS > Fe(III) > inactivated PMS. Fe(II)/PMS could produce a synergistic effect in a high concentration state (60 μM), relying on the dual effects of coagulation and oxidation to alleviate membrane fouling. Coagulation and pre-oxidation by Fe(II)/PMS significantly reduced the clogging of membrane pores and the proportion of irreversible resistance, effectively controlling membrane fouling and improving effluent quality. SEM images further confirmed its effectiveness, and EPR results unequivocally indicated that its synergistic mechanism was mediated by •OH and SO4•−. The research results can provide ideas for advanced wastewater treatment and secondary effluent reuse.

Ultrafiltration of aerobic granular sludge bioreactor effluent: Fouling potentials and properties

The integration of low-pressure membrane filtration and aerobic granular sludge (AGS) reactor leads to a novel environmental biotechnological process with great potential to control membrane fouling and demonstrate good wastewater treatment performance. However, membrane fouling mechanisms in the AGS-based membrane bioreactor (MBR) lack systematic elaboration. In the present work, a bench-scale AGS reactor was operated for 8 months to investigate the effects of granule evolution, initial water flux, and membrane material on membrane fouling behavior and reversibility. After 143 days of operation, complete granulation was successfully achieved in the AGS reactor, which showed 97.6 ± 1.7% organic degradation, 94.3 ± 2.0% NH3-N removal, 90.6 ± 0.8% total nitrogen removal, and 98.9 ± 1.0% PO4-P removal. The remarkable AGS effluent quality reduced the fouling layer formation compared to the filtration occurred before complete granulation. The combined cake-complete model demonstrated that the dominant fouling mechanism is cake layer formation. The polyethersulfone (PES) membrane exhibited a better antifouling performance than the polyvinylidene fluoride membrane, regardless of the AGS effluent composition. The experimental data suggest the existence of a threshold flux for fouling reversibility when PES membrane is applied to treat the AGS effluent. Combining physical cleaning and operating under the threshold flux can effectively control the fouling degree in treating the AGS effluent by UF membrane. This, in turn, can reduce the operating cost caused by chemical cleaning and membrane replacement. Overall, the results provide comprehensive insights into the membrane fouling mechanisms and control strategy in a side-stream AGS-MBR and will contribute to the large-scale application of AGS-MBR technology in wastewater treatment.

PAC-UF Process Improving Surface Water Treatment: PAC Effects and Membrane Fouling Mechanism.

In this study, the water purification effect and membrane fouling mechanism of two powdered activated carbons (L carbon and S carbon) enhancing Polyvinylidene Fluoride (PVDF) ultrafiltration (UF) membranes for surface water treatment were investigated. The results indicated that PAC could effectively enhance membrane filtration performance. With PAC addition, organic removal was greatly enhanced compared with direct UF filtration, especially for small molecules, i.e., the S-UF had an additional 25% removal ratio of micro-molecule organics than the direct UF. The S carbon with the larger particle size and lower specific surface area exhibited superior performance to control membrane fouling, with an operation duration of S-UF double than the direct UF. Therefore, the particle size and pore structure of carbon are the two key parameters that are essential during the PAC-UF process. After filtration, acid and alkaline cleaning of UF was conducted, and it was found that irreversible fouling contributed the most to total filtration resistance, while the unrecoverable irreversible resistance ratio with acid cleaning was greater than that with alkaline cleaning. With PAC, irreversible UF fouling could be relieved, and thus, the running time could be extended. In addition, the membrane foulant elution was analyzed, and it was found to be mainly composed of small and medium molecular organic substances, with 12% to 21% more polysaccharides than proteins. Finally, the hydrophilicity of the elution was examined, and it was observed that alkaline cleaning mainly eluted large, medium, and small molecules of hydrophilic and hydrophobic organic matter, while acid cleaning mainly eluted small molecules of hydrophilic organic matter.

Theory of oil fouling for microfiltration and ultrafiltration membranes in produced water treatment

Due to the complexity of oil-in-water emulsions, the existing literature is still missing a mathematical tool that can describe membrane fouling in a fully quantitative manner on the basis of relevant fouling mechanisms. HypothesisIn this work, a quantitative model that successfully describes cake layer formation and pore blocking is presented. We propose that the degree of pore blocking is determined by the membrane contact angle and the resulting surface coverage, while the cake layer is described by a mass balance and a cake erosion flux. ValidationThe model is validated by comparison to experimental data from previous works (Dickhout et al. 2019; Virga et al., 2020) where membrane type, surfactant type and salinity were varied. Most input parameters could be directly taken from the experimental conditions, while four fitting parameters were required. FindingsThe experimental data can be well described by the model which was developed to provide insight into the dominant fouling mechanisms. Moreover, where existing models usually assume that pore blocking precedes cake layer formation, here we find that cake layer formation can start and occur while the degree of pore blocking is still increasing, in line with the more dynamic nature of oil droplets filtration. These new conceptual advances in the field of colloid and interface science open up new pathways for membrane fouling understanding, prevention and control.

Pilot plant demonstration of temperature impacts on the methanogenic performance and membrane fouling control of the anaerobic membrane bioreactor in treating real municipal wastewater

A 5,000-L anaerobic membrane bioreactor (AnMBR) fed with actual municipal wastewater was employed to study the impact of temperature drops on methanogenic performance and membrane fouling. With temperature dropped from 25 °C to 15 °C, the methane yield decreased from 0.244 to 0.205 NL-CH4/g-CODremoval and the dissolved methane increased from 29% to 43%, resulted in the methanogenic performance reduced by 25%. The membrane rejection offset the deteriorated anaerobic digestion at low temperatures and ensured the stable COD removal efficiency of 84.5%-90.0%. The synergistic effects of the increased microbial products and viscosity and the residual inorganic foulants aggravated the membrane fouling at lower temperatures. As the organic fouling was easily removed by NaClO, the inorganics related to the elements of S, Ca and Fe were the stubborn membrane foulants and required the enhanced acid membrane cleaning. These findings obtained under the quasi-practical condition are expected to promote the practical applications of mainstream AnMBR.

The effect of aeration mode on the operational effectiveness and membrane bioreactors for greywater treatment and membrane fouling

This study aims to investigated the effect of aeration mode on membrane bioreactors (MBRs) using a self-designed integrated hollow fiber MBR and flat sheet organic MBR for rural greywater treatment. The pollutant removal efficiency, characteristics of activated sludge and mixed liquor, and mechanisms of membrane fouling were systematically analyzed under intermittent aeration and continuous modes. The results indicate that the permeability of MBRs in intermittent aeration mode is higher than that in the continuous aeration mode when operating at the same aeration rate. Due to the higher extracellular polymeric substance (EPS) and soluble microbial product (SMP) concentrations. The removal rates of TN and TP by both MBRs at the intermittent aeration mode were higher than those in the continuous aeration mode due to the difference in the aeration environment. Compared to the flat-sheet organic membrane, the hollow-fiber membrane surface was more likely to form biofilms, which cause biological fouling.The relative abundance of Thermomonas showed a positive correlation with the EPS concentration, indicating that Thermomonas participates in EPS synthesis. This study provides a theoretical basis for evaluating the influence of aeration modes on MBRs,and would be a useful guide for the better control of membrane fouling and treatment of rural greywater.

Understanding the influence of hydraulic conditions on colloidal fouling development by using the micro-patterned nanofiltration membrane: Experiments and numerical simulation

Surface patterning has emerged as a promising method to control membrane fouling by disturbing the flow field on the membrane surface. In this study, fouling development was non-destructively characterized by optical coherence tomography (OCT), while the micro hydraulic conditions and particle migration trajectories were investigated by using Computational Fluid Dynamics (CFD). Preliminary results demonstrated remarkable anti-fouling performance of the MNF membrane, and CFD simulation revealed that the local flow velocity on the apex area of patterns was greatly accelerated and the vortex among the valley regions was continuously generated. These hydraulic characteristics resulted in the enhancement of the hydrodynamic lift force (fL) and decrease of the permeation drag (fD) enforced on the retained foulants by the MNF membrane. Moreover, particle trajectories simulation integrated with comprehensive forces allowed to understand the influence mechanism of the flow field around MNF membrane surface on particle deposition. This study presents a new understanding of the anti-fouling mechanism of the MNF membranes and provides new insights into the design of self-cleaning membranes.

Performance enhancement and fouling alleviation by controlling transmembrane pressure in a vibration membrane system for algae separation

Although transmembrane pressure (TMP) has proven to be a significant factor in the separation of microalgae by the vibration membrane process, there is a lack of systematic research on this factor. This study introduced a multi-angle insight by analyzing hydrodynamic interaction acting on algae, compressibility of the cake layer, and quantitative evaluation of the membrane fouling performance to assess the relationship between TMPs and membrane fouling in the vibration membrane system. Supported by a collision-attachment model which illustrated the algae/membrane hydrodynamic interactions under different TMPs, the critical point in TMP was confirmed as at or beyond which membrane fouling became serious. Then, after analyzing the main membrane fouling indicators of polysaccharides and proteins, the results demonstrated that TMP had a greater effect on reversible fouling. Furthermore, using the theory of algae deposition, the study verified that the increase of TMP would lead to a greater compressibility of the cake layer, and the operation at the critical point could cause more serious membrane fouling. Finally, energy consumption and the technique for order preference by similarity to ideal solution combined with grey relational analysis (TOPSIS-GRA) could quantitatively evaluate membrane fouling performance, and the results showed that a lower TMP, especially below the critical point, was a good choice for sustainable control of membrane fouling. Over all, this insight into TMP elucidated the importance of employing lower TMP during the algae separation process under specific vibration conditions, providing a theoretical basis for the selection of TMP. • The collision-attachment model was applied to explore the critical point in TMP. • The analysis of membrane fouling indicators demonstrated TMP exhibited a greater effect on reversible fouling. • The theory of algae deposition was used to verify a higher TMP led to a greater compressibility of the cake layer. • Quantitative assessment methods were applied to confirm operation below a critical point was economical and effective.

Incorporating catalytic ceramic membrane into the integrated process of in situ ozonation, membrane filtration and biological degradation: Enhanced performance and underlying mechanisms

The integrated process comprising of in situ ozonation, ceramic membrane filtration and biologically active carbon filtration has a bright application prospect in wastewater reclamation to confront the global water crisis. Additionally, ceramic membranes of stronger catalytic activity are highly desirable so as to further increase the process cost-efficiency. In this study, a Mn-loaded catalytic membrane was tested by conducting pilot-scale experiments of the integrated process to measure its performance in enhancing pollutant removal and in alleviating membrane fouling. Lab-scale experiments were also conducted in order to investigate the underlying mechanisms in which the conventional Al2O3 membrane was used for comparison. Results showed that the integrated process with an incorporated catalytic membrane performed very well in that at a water flux as high as 80 L/m2/h and an ozone dosage of 5 mg/L, the treated water satisfied the guideline values for indirect potable reuse and membrane fouling was minimal. Reducing the ozone dosage to 4 mg/L can still achieve significant membrane fouling control effects, and maintain good effluent quality. Catalytic ozonation could lead to the generation of hydroxyl radicals, and the catalytic ozonation effect was much stronger when the catalytic membrane was used. Catalytic ozonation took place in both the membrane tank and membrane pores, with comparable contributions to the pollutant removal and membrane fouling control. Redundancy analysis (RDA) of membrane fouling characteristics showed that residual ozone concentration in membrane tank was an essential parameter and catalytic ozonation could be more effective in abating irreversible fouling than reversible fouling. RDA also confirmed that a lower ozone dosage would be sufficient for membrane fouling control when the catalytic membrane was used. This study evidently suggested the advantage of using catalytic ceramic membrane in the integrated process for efficient while economic treatment and reclamation of wastewater.

Study on the Control of Membrane Fouling by Pulse Function Feed and CFD Simulation Verification.

A complex-function fluid controller placed in front of a membrane module was used to control the velocity change with feed fluid and reduce membrane fouling. Using humic acid as the simulated pollutant, the effects of the square wave function, sine function, reciprocal function, and power function feeding on the membrane flux were investigated. For sine function feeding, the membrane-specific flux was the largest and was maintained above 0.85 under the intermittent frequency of 9 s. Compared with the final membrane-specific flux with steady-flow feeding of 0.55, functional feeding could significantly reduce membrane fouling. SEM results showed that sine feeding led to slight contamination on the membrane surface. Furthermore, the Computational Fluid Dynamics (CFD) simulation results showed that the shear force of sine function feeding was about three times that of the steady flow (6 × 105 N). Compared with steady feeding, functional feeding could significantly improve the shear force on the membrane surface and reduce membrane fouling.

An integrated separation technology for high fluoride-containing wastewater treatment: Fluoride removal, membrane fouling behavior and control

The high concentration of fluoride in aqueous, which exacerbated by the discharged wastewater from semiconductor, electroplating, metallurgical and ceramics industries, has gone far beyond the World Health Organization (WHO) standard and seriously affected the health of human life. This study aims to validate the deep removal of fluoride from high fluoride-containing wastewater by using an integrated precipitation/crystallization/ultrafiltration (UF)/reverse osmosis (RO) system. The system enables an extremely low residual fluoride concentration (down to 0.25 mg L−1) qualified WHO standard, which was much lower than those of other reported membrane-based processes. In particular, the application of crystallization rather than conventional coagulation/flocculation was demonstrated to be effective in reducing fluoride, turbidity and sludge water content. Membrane fouling analysis indicated that UF membrane scaling was attributed to the CaF2 particles deposition at recovery rates of 70%–90%. RO membrane fouling behaviors were identified at recovery rate of 50% (organic fouling), 70% (inorganic scaling occurred and organic fouling) and 80% (inorganic scaling and organic fouling). Meanwhile, UF/RO membrane scaling/fouling could be removed by pure water cleaning (UF) and Na2CO3/NaOH/HCl cleaning (RO). Results of this work shall provide useful information on the application of a precipitation/crystallization/UF/RO system to purify and recover high fluoride-containing wastewater.

Membrane distillation treatment of landfill leachate: Characteristics and mechanism of membrane fouling

Landfill leachate (LFL), which contains organic and inorganic contaminants in high concentration, poses a detrimental hazard to the ambient environment. Although membrane distillation (MD) shows great potential in wastewater treatment, the membrane fouling in LFL treatment is still a rarely reported. In this study, the membrane fouling was systematically investigated in a real LFL treatment by a direct contact MD system. Various characterization methods, such as scanning electron microscopy, scanning electron microscopy with energy-dispersive X-ray spectroscopy, and attenuated total reflection Fourier transform infrared spectroscopy were adopted in membrane fouling identification. Increasing membrane fouling was observed with the increasing feed pH. The analysis of membrane autopsy and differential log-transformed absorbance spectroscopy revealed that the increase of feed pH strengthened the deprotonation of carboxyl groups in organic matter, contributing to the formation of organo-inorganic complexation. The interaction between magnesium-related substances and humic-like matter might be the culprit of organo-inorganic membrane fouling in alkaline feed condition based on correlation analysis (R2 = 0.996). The results enhance the understanding of the mechanisms by which pH affects membrane fouling and lay the foundation for controlling membrane fouling in the LFL treatment.

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).

Composition and Accumulation of Fouling during Leachate Reverse Osmosis Membrane Treatment in both a Typical Incineration Plant and a Landfill

Reverse osmosis (RO) membrane process has been extensively used for leachate treatment both in incineration plants and landfills. However, operation and maintenance costs caused by membrane pollution limit the wide application of RO membrane. In order to further understand membrane fouling, this study analyzes the influent, effluent, concentrated liquid pollutants and membrane fouling of typical waste incineration plants and landfills in Chongqing, a city in the west of China based on the comparison of three-dimensional excitation and emission matrix fluorescence (3DEEM) and nanometer particle size. In addition, this paper discusses the change law of chemical oxygen demand (COD) and main pollutants in membrane fouling in the disc tube reverse osmosis (DTRO) system in a single operation cycle, analyzes the main components of membrane fouling, and draws the accumulation of RO membrane pollutants, in order to provide a reference for understanding the composition, formation and control of membrane fouling.

Electrical-based ultrafiltration processes enhanced by in-situ generation of Fe(III): Significance of permanganate oxidation

In this study, a permanganate-assisted electrocoagulation-ultrafiltration (PEC-UF) process was proposed to control membrane fouling in the treatment of secondary effluent. Four comparable systems, i.e., UF, electro-UF (E-UF), electrocoagulation-UF (EC-UF), and PEC-UF, were investigated to systematically clarify the role of permanganate and electrocoagulation in mitigating membrane fouling. Results revealed that the formation of a dense cake layer containing concentrated solutes was the primary reason for membrane fouling. Electrocoagulation significantly mitigated membrane fouling and resulted in the reduction of the normalized transmembrane pressure of the EC-UF and PEC-UF systems by 35.0% and 44.6% compared with the UF control system, respectively. However, the retention of a considerable amount of iron oxyhydroxide precipitates on the membrane surface aggravated inorganic fouling in the in-situ EC-UF system. Furthermore, the enhanced formation of Fe(III) by oxidation of Fe(II) with permanganate promoted the coagulation process. Hence, increased generation of Fe(III) and enhanced coagulation promoted by formed MnOx accelerated the formation of a hydrophilic cake layer with high porosity and thereby reduced the occurrence of both organic and inorganic membrane fouling. These results demonstrated the potential application of permanganate-assisted in-situ electrical-based methods to control UF membrane fouling during advanced wastewater treatment.

Pre-coagulation for membrane fouling mitigation in an aerobic granular sludge membrane bioreactor: A comparative study of modified microbial and organic flocculants

Coagulation has become a hotspot for membrane fouling control; however, there is a gap in research regarding the application of modified microbial flocculants (MMFs) to mitigate membrane fouling. Herein, we prepared an MMF and compared it with conventional organic flocculants for their effects on mitigating membrane fouling in an aerobic granular sludge membrane bioreactor (AGMBR). The results showed that electrical neutralization played a dominant role in the flocculation process of polymeric aluminum chloride (PAC)/MMF, which exhibited the optimal performance for the removal of pollutants and membrane fouling control. Moreover, the characteristics of the fouled membrane and the fitting of membrane fouling models indicated that the cake layer formation was the main fouling mechanism underlying membrane fouling, and MMF could mitigate the accumulation of foulants on the membrane surface, forming a loose and porous cake layer. Based on the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory, the largest energy barriers of the membrane-foulant and foulant-foulant interactions were observed in the PAC/MMF-AGMBR hybrid system. Furthermore, correlation analysis revealed that total phosphorus, polysaccharide, zeta potential, and particle size had the greatest correlation with the fouling resistance. Thus, this study shows that MMF pre-coagulation is feasible and provides a new method for membrane fouling mitigation in an AGMBR. • The MMF was used for the first time to mitigate membrane fouling. • The cake layer was the major mechanism of membrane fouling in the MMF-AGMBR system. • The MMF promoted the formation of a loose, porous, and thin cake layer. • The MMF reduced the foulants deposited on the virgin/fouled membranes. • TP, PS, zeta potential, and particle size remarkably affect the fouling resistances.

Critical Flux and Fouling Analysis of PVDF-Mixed Matrix Membranes for Reclamation of Refinery-Produced Wastewater: Effect of Mixed Liquor Suspended Solids Concentration and Aeration.

Fouling tends to cause a significant increase in hydraulic resistance, decreased permeate flux, or increased transmembrane pressure (TMP) when a process is operated under constant TMP or constant flux conditions. To control membrane fouling and maintain sustainable operation, the concept of critical flux has been discussed by several researchers. Various fouling mechanisms, such as macromolecule adsorption, pore plugging, or cake build-up, as well as hydrodynamic conditions, for example aeration, can take place at the membrane surface. This study aimed to investigate the effects of mixed liquor suspended solid (MLSS) concentration and air bubble flow rate (ABFR) on the critical flux and fouling behavior, when treating refinery-produced wastewater. To determine the critical flux values, the experimental flux-steps were the following: (1) the filtration began with a 30 min step duration at a low flux (10 to 20 L/m2h); (2) at the end of this step (after 30 min), the permeate flux was increased, (3) this step was repeated until the TMP did not remain constant at the constant permeate flux, (4) the critical flux was then achieved. A critical flux model with an R2 of 0.9 was, therefore, derived, which indicates that the particle properties were regulated by the suspended solids. The increase of MLSS concentration, from 3 mg/L to 4.5 mg/L, resulted in a decrease of the permeate flux by 18%. Moreover, an increase in ABFR, from 1.2 mL/min to 2.4 mL/min, increased the permeate flux, but this decreased with a greater flow rate of aeration. To assess the stability and reversibility of fouling during critical flux (Jc) determination using a mixed matrix membrane, flux-step methods were utilized. A step height of 14.3 L/m2h and 30 min duration were arbitrarily chosen. The flux increased to 32.5 L/m2h with a slight increase of trans membrane pressure (TMP), while the rate of increase became significant at a higher flux of 143.6 L/m2h, due to fouling. Overall, this study proved that the response of MLSS concentration and aeration affected the membrane performance, based on the critical flux and fouling behavior.

Flux modulation: A novel approach for ultrafiltration fouling control

Control of membrane fouling is critical for the long term production of water in a membrane system. Backwashing with or without relaxation is the most common method to control fouling in-situ with ultrafiltration (UF) hollow fiber membrane systems. The inclusion of relaxation is intended to assist with decompression of the membrane cake layers and assist with backwashing. However, it also results in a loss of membrane productivity. This study aimed to investigate the effect of flux modulation with single and dual mode cycles, as well as relaxation, on the performance of an UF membrane with respect to fouling control. Results demonstrated that modulating the flux in place of relaxation results in a substantial improvement in control of membrane fouling while still maintaining membrane productivity. By modulating the flux at different levels compared to a control of flux of 36 LMH, the fouling index values decreased by over 80% while specific water production only dropped 8% (2489 vs 2702 L/m2). Incorporating a relaxation step had minimal impact (<8%) on the performance of a given flux cycle with regards to fouling control. Therefore, high membrane performance can be achieved without the need for a relaxation step, as long as an appropriate flux modulation cycle is selected. This research demonstrates the potential for significant fouling control on an UF membrane by alternating the stress on the membrane surface through flux modulation.