Microfiltration Fouling Research Articles

Membrane fouling in microfiltration of oil-in-water emulsions; a comparison between constant pressure blocking laws and genetic programming (GP) model

Microfiltration of oil-in-water emulsion with different concentrations and TMPs was experimentally performed to investigate the fouling mechanisms of oil droplets. In this work, the performance of both blocking laws and genetic programming model was evaluated. Four individual and five combined blocking models were applied to determine if they would provide acceptable fits of the experimental data. In individual models, the best predictions were obtained by the intermediate model and the cake model failed to provide any fit of the experimental data in all data sets. Although the combined models used two fitted parameters, they did not provide better fits of the data than individual models. The intermediate model combined with the cake filtration model and standard model provided the same fit as the intermediate model alone. In addition, genetic programming as a novel approach in membrane fouling was used to predict both permeate flux and oil rejection. It was found that for the studied system, the GP model not only was able to provide better fits of experimental data, but also predicted the oil rejection with an acceptable accuracy. The dominant fouling mechanisms were also identified in different operating conditions.

Pre-treatments for removing colour from secondary effluent: Effectiveness and influence on membrane fouling in subsequent microfiltration

The effects of different pre-treatments for colour removal on membrane fouling in the microfiltration (MF) of a coloured activated sludge (AS) effluent were investigated. It was found that a 80% colour removal target could be achieved by pre-treatment of the raw AS effluent with either ozone (10mgO3L−1, 10-min contact time), a powdered activated carbon (150mgL−1, 30-min contact time), or a strong base anion exchange resin (10mLL−1, 20-min contact time). Of these pre-treatments, ozonation was the only method that resulted in a reduction in membrane fouling. The other two methods, while they showed high removals of dissolved organic matter, did not affect the membrane flux. The changes in the membrane foulants due to the pre-treatments were determined and were used to explain the differences in the membrane flux. The results showed that pre-treatments for fouling reduction in MF of secondary effluent should target the biopolymers (which contained polysaccharides and proteins) in the effluent.

Membrane fouling mechanism in dead-end microfiltration of denitrifying granular sludge mixed liquors developed in SBRs at different calcium concentrations

This study investigated membrane fouling mechanisms of various fractions of denitrifying granular sludge mixed liquors developed in three sequencing batch reactors (SBRs) operated at respective calcium concentrations of 0, 50 and 100mg/L. Results showed that supernatants caused the lower fluxes and more severe membrane fouling than their corresponding mixed liquors and granule solutions, indicating supernatants were the major contributors to membrane fouling in microfiltration of granular sludge mixed liquors. Cake layer formed by denitrifying granules on membrane surface was observed to serve as a prefilter which could reduce membrane fouling effectively by entrapping fine particles, colloids and soluble extracellular polymeric substances (sEPS). Such observation was further confirmed by the fact that cake, specific cake and total resistances of mixed liquors all decreased with increase of granule concentrations from 0 to 5000mg SS/L, and remained unchanged when granule concentrations were further increased to 13,000mg SS/L. The resistances of granular sludge mixed liquors were increased with concentrations of fine particle, colloid and sEPS in supernatant when granule concentration was kept constant. It was also revealed that the supplementation of calcium of 100mg/L in granulation process could greatly reduce the contents of fine particles, colloids and sEPS, leading to less membrane fouling.

Particles size-associated membrane fouling in microfiltration of denitrifying granules supernatant

The aim of this study was to investigate particle size-associated membrane fouling in microfiltration of supernatants separated gravitationally from three denitrifying granular sludge sequencing batch reactors (SBRs, named as R1, R2 and R3) fed with different calcium concentrations of 0, 50 and 100mg Ca2+/L, respectively. The permeate flux decline, membrane resistances and the relative contribution of cake resistance were determined and compared for particles in the ranges of 2.7–1.0μm, 1.0–0.45μm, 0.45–0.22μm and <0.22μm. Results showed that particles with the mean size of 1.0–2.7μm in R1–R3 supernatants formed thin and dense cake layer, contributing more severe fouling than other size particles. The relative contributions of particles with size of 1.0–2.7μm to the cake resistances were found above 86.82%. Membrane fouling of supernatant due to the particles smaller than 1.0μm was responsible to both cake and pore blocking. It was also found that the addition of calcium in SBRs could help to reduce concentrations of fine particles, colloids and soluble extracellular polymeric substances (sEPS), and subsequently led to the reduction of membrane fouling.

Characterization of membrane fouling in a microfiltration ceramic membrane system treating secondary effluent

Membrane filtration is one of the most promising technologies used for the advanced treatment of secondary effluents. Despite the number of fouling-control studies that have been conducted, membrane fouling remains a problem of utmost importance. In this study, pilot-scale ceramic microfiltration equipment was used to treat real secondary effluents from a wastewater treatment plant. Reversible fouling and irreversible fouling, which are defined based on backwashing, were characterized, and the effects of coagulation and membrane pore sizes on fouling evolution, as well as the composition of foulants, were also studied. The results showed that coagulation is an effective pretreatment for the control of microfiltration fouling, and that 5 mg aluminum per liter feed water is a cost-effective dosage for treatment. In terms of stable operating time and recovered water volume, the performance of the 0.1 μm ceramic membrane was the best. Results of pure water filtration experiments revealed that sodium hypochlorite solution washing recovered more flux than citric acid solution. The concept of a “trans-membrane pressure (TMP for short) turning point” was suggested as an operational signal for conducting membrane off-line chemical washing. After this point, both reversible and irreversible fouling increased drastically to maximum levels within a short span of time, resulting in difficulties in thoroughly cleaning the membrane.

Iron and manganese fouling in microfiltration as a pretreatment of seawater reverse osmosis processes

Two sets of pilot test were carried out to investigate the fouling behaviours of microfiltration (MF) system as a pretreatment for seawater reverse osmosis (SWRO) processes for about two years. One set used clean seawater as feed water while the other adopted surface water with lower quality than the seawater. Both systems introduced commercial hollow fiber MF modules from the same manufacturer. During the operation period, raw water quality parameters related to reverse osmosis (RO) performance were collected and analyzed. Regardless of raw water quality, the product water of both MF systems without coagulation exhibited high water quality as RO feed water. The MF system for SWRO pretreatment underwent more severe fouling than the MF system for surface water treatment although the tested seawater quality is much better than the tested surface water quality in terms of fouling potentials. Iron and manganese turned out to be main foulants through water analysis for discharged water from the chemical cleani...

Control of physically irreversible fouling in microfiltration by pre-coagulation

Control of physically irreversible fouling in microfiltration by pre-coagulation

Effect of processing parameters on the microfiltration fouling during the clarification of pomegranate juice.

The pomegranate juice with high nutritional value has turbid appearance that makes it difficult to preserve and concentrate. Microfiltration is useful process which can clarify it. One of the most important problems in this process is fouling phenomenon which affected by several parameters. The effects of fluid velocity, transmembrane pressure, membrane type and its pore size on membrane fouling were studied. The results showed that the membrane fouling increased with increase in the fluid velocity and transmembrane pressure. Also, more hydrophilic property and pore size resulted more membrane fouling due to greater flux which move more particles to membrane surface. Scanning electron microscopy (SEM) images support these results. Keywords: Clarification, Fouling, Membrane, Pomegranate juice

Membrane foulants and fouling mechanisms in microfiltration and ultrafiltration of an activated sludge effluent

Membrane fouling in microfiltration (MF) and ultrafiltration (UF) of an activated sludge (AS) effluent was investigated. It was found that the major membrane foulants were polysaccharides, proteins, polysaccharide-like and protein-like materials and humic substances. MF fouling by the raw effluent was governed by pore adsorption of particles smaller than the pores during the first 30 minutes of filtration and then followed the cake filtration model. UF fouling could be described by the cake filtration model throughout the course of filtration. Coagulation with alum and (poly)aluminium chlorohydrate (ACH) altered the MF fouling mechanism to follow the cake filtration model from the beginning of filtration. The MF and UF flux improvement by coagulation was due to the removal of some of the foulants in the raw AS effluent by the coagulants. The MF flux improvement was greater for alum than for ACH whereas the two coagulants performed equally well in UF. Coagulation also reduced hydraulically irreversible fouling on the membranes and this effect was more prominent in MF than in UF. The unified membrane fouling index (UMFI) was used to quantitatively evaluate the effectiveness of coagulation on membrane flux enhancement.

Clarification of aqueous corn extracts by tangential flow microfiltration

The effectiveness of tangential flow microfiltration for the solid/liquid clarification of aqueous corn endosperm and germ extracts was examined using recombinant type I human collagen (rCollagen) and green fluorescent protein (GFP) as model proteins. We identified the effects of transmembrane pressure (TMP), crossflow rate, protein molecular weight, and membrane chemistry on permeate flux, protein rejection, and internal membrane fouling in microfiltration. In dead-end filtrations, both endosperm and germ extracts formed highly compressible cakes that provided the dominant hydraulic resistance. For tangential flow filtration using a ceramic membrane, increasing the crossflow rate had a significant beneficial effect on the permeate flux for all TMPs examined. High fouling of the ceramic membrane occurred during the filtration and this was likely due to the presence of soluble corn starch in the feed. Filtration with a ceramic membrane resulted in low rejection (<10%) of both the host cell proteins (HCP) and GFP and very high rejection (∼90%) of rCollagen. In contrast to the ceramic membrane, tangential flow filtration using a poly(vinylidene fluoride) membrane resulted in much less internal fouling and no measurable rejection of HCP, GFP, or rCollagen. Microfiltration was an effective method for the solid/liquid clarification of corn protein extracts, except in cases where high internal membrane fouling resulted in increased rejection of large molecular weight proteins.

Comparison of 3DTA and VSEP systems during the ultrafiltration of sweet whey

Whey, a side-product of the cheese-making and casein industry, is a nutritious protein source. The nutritional, biological and functional properties of whey proteins make them attractive and explain why an active whey industry has been developing over the last 30 years. The preconcentration of whey at its production site is the major field of application of membrane separation. The high salt content of whey (8–20% dry matter) gives rise to numerous processing difficulties, a low lactose crystallization rate, and fouling in microfiltration (MF) and ultrafiltration (UF) performed to produce whey protein concentrates. In order to improve UF performance, it is advisable to limit fouling of the membranes by selecting an appropriate flux or shear stress ratio [1]. In this study, the performance of a vibratory shear-enhanced processing system (VSEP) for the concentration of cheese whey was assessed and compared with a classical, cross-flow, plate and frame membrane configuration system (3DTA) with the same membrane (i.e. a C30F UF regenerated cellulose UF membrane with a 30 kDa molecular mass cut-off). The temperature and pressure dependences of the permeate flux, the permeate flux reduction ratio, the resistances and the rejection values were investigated. Comparison of the two systems revealed a definite advantage for the VSEP system equipped with the same membrane and operated at the same pressure and temperature. The flux reduction ratio (J/J0) was 0.60 vs. 0.42, and the total resistances 2.87×1013 m-1 vs. 4.54×1013 m-1 for the VSEP and 3DTA system, respectively.

CFD and experimental studies of fouling of a microfiltration membrane

This paper reports Computational Fluid Dynamics (CFD) and experimental studies on microfiltration fouling of a Blue Indigo solution. A hydrophilic Polyvinylidene Fluoride (PVDF) membrane was used and experiments were carried out at three cross-flow velocities of 0.5, 1 and 1.3 m s −1. The fouled membranes were analyzed using simple photographs and precise Scanning Electron Microscope (SEM) micrographs. A 3-D CFD modelling was carried out using the commercial CFD code, FLUENT6.2. The predicted shear stress distributions upon the membrane were used to explain the observed fouling. In addition, the particles deposition pattern upon the membrane surface was predicted using discrete phase modelling.

High performance polyethersulfone microfiltration membranes having high flux and stable hydrophilic property

High performance polyethersulfone microfiltration membranes with a high flux and stable hydrophilic character were successfully prepared by vapor induced phase separation coupled with non-solvent induced phase separation method. Pluronic ®, a poly(ethylene oxide)- b-poly(propylene oxide)- b-poly(ethylene oxide) triblock copolymer and triethylene glycol (TEG) were used as hydrophilicity modification agent and non-solvent, respectively. Casting solution composition (non-solvent and additive content) and process condition (exposure time before coagulation and relative humidity) were optimized to obtain these membranes. The resulting membrane characteristics, which include hydraulic permeability, pore size distribution, surface hydrophilicity, chemical composition and membrane morphology, were investigated. The membrane performance was examined by investigation of adsorptive fouling and microfiltration using solutions of bovine serum albumin as the model system. The results suggest that the non-solvent content (TEG) and the exposure time were the most critical parameters to obtain high-flux membranes, whereas the concentration of Pluronic was important to obtain hydrophilic property. The increase in resistance towards both adsorptive and microfiltration fouling was clearly observed. The surface chemistry and wettability of the resulting membranes did not change after incubating in water (40 °C) for a period of 10 days.

Mechanism Involved in the Evolution of Physically Irreversible Fouling in Microfiltration and Ultrafiltration Membranes Used for Drinking Water Treatment

Control of membrane fouling is important for more efficient use of membranes in water treatment. Control of physically irreversible fouling, which is defined as fouling that requires chemical cleaning to be cancelled, is particularly important for reduction of operation cost in a membrane process. In this study, a long-term filtration experiment using three different types of MF and UF membranes was carried out at an existing water purification plant, and the evolution of physically irreversible fouling was investigated. The experimental results demonstrated that the extent of physically irreversible fouling differed significantly depending on the membrane type. Cleaning of the fouled membranes with various chemical reagents demonstrated that organic matter was mainly responsible for physically irreversible fouling. Organic matter that had caused physically irreversible fouling in the long-term operation was desorbed from the fouled membranes and was subjected to Fourier transform infrared and 13C nuclear magnetic resonance analyses. These analyses revealed that carbohydrates were dominant in the membrane foulant regardless of the type of membrane. Based on measurements of molecular weight distribution of organic matter in the feedwater and the permeates from the membranes, a two-step fouling mechanism is proposed to explain the dominance of carbohydrates in the foulant: hydrophobic (humic-like) components with small molecular weight are first adsorbed on the membrane and, consequently, narrow the size of micro-pores of membranes, and then hydrophilic (carbohydrate-like) compounds with larger molecular weight plug the narrowed pores or the hydrophilic compounds are adsorbed onto the membrane surface conditioned by the hydrophobic components.

Development of a Novel Metalworking Fluid Engineered for Use With Microfiltration Recycling

Membrane microfiltration is a promising technology that has been shown to extend metalworking fluid (MWF) life by eliminating contaminants while allowing the fluid to stay in use. However, the efficacy of this technology is compromised by the clogging of the filter pores in a process known as membrane fouling. In this paper the fouling issue is addressed by the development of a semi-synthetic MWF specifically designed to not foul microfiltration membranes. The composition of the designed MWF is discussed and compared with a commercial MWF. Cross-flow microfiltration fouling tests were carried out in low-pressure, high-velocity conditions on ceramic α-alumina membranes. Several common MWF components are shown not to be factors of membrane fouling on these membranes. The flux of the designed fluid was found to reach an immediate steady state at about twice the value of the steady-state flux of the tested commercial fluid. Scanning electron microscope imaging was used to further evaluate membrane fouling by each fluid. The machining capabilities of the designed fluid were examined in terms of cutting forces and machining temperature.

Effect of filamentous bacteria on membrane fouling in submerged membrane bioreactor

Membrane fouling is the major problem that hinders the practical application of membrane bioreactor (MBR) systems. Since the MBR system includes living microorganisms and their metabolites, the fouling mechanism is even more complex than that of conventional membrane separation processes. This paper provides an improved understanding of the influence of filamentous bacteria on membrane fouling in microfiltration of activated sludge wastewater. In order to make clear the membrane fouling mechanism of filamentous bacteria, the physicochemical characteristics of sludge flocs, including extracellular polymeric substance (EPS), zeta potential, relative hydrophobicity (RH) and floc morphology were systematically investigated. The results showed that the sludge flocs with negligible filamentous bacteria led to severe membrane pore blocking, and the sludge flocs with filamentous bacteria created the formation of a non-porous cake layer on the membrane surface. The excess growth of filamentous bacteria resulted in much more release of EPS, lower zeta potential, higher hydrophobicity of sludge flocs and more irregularly shaped flocs, which did great harm to membrane filtration. The sludge flocs with a small quantity of filamentous bacteria had a positive effect on membrane permeation. It is important to control filamentous bacteria concentration in the operation of MBRs.

A study on the fouling phenomena of a microfiltration membrane

The utilization of membrane processes for drinking water treatment has become more popular. However, fouling by source water probably is the major factor prohibits its widespread application. In this research, the fouling phenomena of a microfiltration (MF) membrane were studied. The interactions among colloidal particles, calcium ion, and dissolved organics, such as salicylic acid, humic acid, and alginic acid, on MF fouling were focused. A lab-scale single hollow fiber MF membrane, made of polyvinylidenefluoride (PVDF), module was used. The results show that, for single organic compound, the extent of fouling caused by humic acid was higher that of alginic acid. For the latter, the permeate flux decrease at lower pH was more significant than those at higher pH. For low MW salicylic acid, both rejection and flux decrease were minor. It seems that solubility have strong correlation with fouling rate. The higher the solubility is, the lower the fouling rate. For sole colloidal particle system, latex beads with diameter close to the pore size of MF membrane showed severe fouling. Adding Ca can aggregate the latex beads, and alleviate fouling. However, calcium ion also found to increase fouling of alginic acid on membrane under neutral or alkali pH condition, probably via charge neutralization and/or bridging. In conclusion, MF fouling seems to be strongly related to the type of organics, size of colloidal particles, and the existence of divalent ions, in the feed water.

The effect of varying transmembrane pressure and crossflow velocity on the microfiltration fouling of a model beer

Experiments were conducted to determine the fouling propensity during crossflow filtration of a model beer, primarily composed of dextrin and protein. The Carbosep™ filters of nominal pore size 0.45 μm were fouled over a range of transmembrane pressures and crossflow velocities at a constant temperature of 20 °C. After each experiment, the membrane was cleaned and re-used in order to replicate industrial filtration conditions. For each experiment, the flux decline data were obtained, together with the concentrations of the dextrin and protein in the permeate and retentate streams. Further data manipulation enabled retention ratios to be calculated for each component. The permeate flux was shown to decrease with filtration time during the development of the fouling layer. Once the fouling layer was established, the permeate flux became constant for a given set of experimental conditions. The steady-state flux increased with increasing transmembrane pressure and with increasing crossflow velocity. For a given crossflow velocity, an increase in transmembrane pressure resulted in a reduction in transmission of both the BSA protein and dextrin components of the model beer. This is attributed to an increase in the fouling layer thickness due to higher permeate fluxes, coupled with a decrease in fouling layer voidage at higher transmembrane pressures. The retention data suggest that higher transmembrane pressures lead to an increase in the proportion of BSA present in the fouling layer. For a given transmembrane pressure, an increase in crossflow velocity led to increased transmission of both the BSA and dextrin through the membrane. This is due to the inhibition of fouling layer development through the larger wall shear stress and thinner laminar sub-layer that are associated with an increase in crossflow velocity.

Protein fouling in microfiltration: deposition mechanism as a function of pressure for different pH

The influence of applied pressure on the fouling mechanism during bovine serum albumin (BSA) dead-end microfiltration (MF) has been investigated for a polyethersulfone acidic negatively charged membrane (ICE-450) from Pall Co. BSA solutions at pH values of 4, 5 (almost equal to the protein isoelectric point, IEP), and 6 were microfiltered through the membrane at different applied transmembrane pressures. Results have been analyzed in terms of the usual blocking filtration laws and a substantial change in the fouling mechanism was observed as the pressure was increased, this change can be related to the specific membrane–protein and protein–protein interactions.

Membrane fouling and cleaning in microfiltration of activated sludge wastewater

A major obstacle in the widespread application of membrane microfiltration for activated sludge wastewater treatment is the rapid decline of the permeation flux with time as a result of membrane fouling. In this study, a hollow fiber membrane microfiltration unit was employed to treat two types of activated sludge wastewater of different particle size distributions. Theoretical models were used to fit the experimental flux data to identify the predominant membrane fouling mechanisms during microfiltration of each type of the activated sludge wastewater. A novel membrane cleaning method using sonication technique was evaluated. The performance of a combination of the various membrane cleaning methods, such as clean water backwashing, sonication, and chemical cleaning, was investigated. The results show that the main types of membrane fouling in microfiltration of activated sludge wastewater were attributed to initial pore blocking followed by cake formation. Periodic sonication of the membrane microfiltration module effectively removed the cake from the membrane surface and thus significantly recovered the permeation flux. However, sonication was not effective in flux recovery for membrane fouling caused by other mechanisms, such as pore blocking, and therefore the extent of flux recovery decreased with each sonication cleaning cycle. A combination of clean water backwashing, sonication and chemical cleaning with alkali and acid could achieve almost complete flux recovery. The underlying cleaning mechanisms and the effectiveness of each of the different cleaning methods to the different types of fouling are discussed.