Fouling Of Microfiltration Membranes Research Articles

Clarification of raw rice wine by ceramic microfiltration membranes and membrane fouling analysis

Ceramic membrane capacity during the filtration of raw rice wine is typically limited by fouling, which can occur by pore blocking, pore constriction or caking. In this study three modified fouling models were used to describe flux decline behavior during microfiltration accounting for these three classical fouling mechanisms. The fouling mechanism was identified by estimation of the model parameter according to a nonlinear regression optimization procedure. Analysis by the models indicated cake filtration to be the dominant mechanism and pore constriction to be the secondary fouling mechanism. In the fixed operating conditions of transmembrane pressure (TMP) and cross-flow velocity (CVF), the fouling mechanism evolves from a pore constriction to a cake filtration. Membrane fouling was also investigated using Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). FTIR analysis revealed that polysaccharides, long chain protein and some phenolics appear to be primarily responsible for fouling. The main physico-chemical characteristics of rice wine were evaluated in order to select membrane pore size and material that supply the highest permeation flux and best clarified rice wine.

Comparison of membrane fouling in dead-end microfiltration of denitrifying granular sludge suspension and its supernatant

Nowadays, membrane biofouling remains a big challenge in application of membrane bioreactor (MBR) for wastewater reclamation. This study investigated an alternative for alleviating the membrane fouling by a combination of denitrifying granular sludge and microfiltration. The dead-end microfiltration performances of denitrifying granular sludge suspension and its supernatant were evaluated. Results showed that the permeate flux of denitrifying granular sludge was 2.35–9.4 times higher than that of suspended denitrifying sludge. It was further revealed that the superior filtration performance of denitrifying granular sludge was due to its big size, reduced surface charge and soluble polysaccharides (sPS). Microfiltration of the supernatant obtained from the suspension showed that the substances in the supernatant was mainly responsible for the membrane pore blocking in the microfiltration of denitrifying granular sludge, while the cake layer helped to remove the pore blocking-causing substances. It appears from this study that the combination of denitrifying granular sludge with membrane filtration would be an attractive alternative for high-efficiency nitrogen removal as well as for control of membrane biofouling.

The hydrodynamic effect of microparticles on membrane resistance

The membrane technique of microfiltration (MF) was used to investigate the degree of reduction of the membrane resistance. The application of dolly-particles seems very beneficial for some MF processes with conventional equipment. A pile of bakelite enhanced the local shear near the membrane surface. This phenomenon depends greatly on the components and properties of the feed suspension; the shear force is dependent on the radius and the amount of the particles. This approach has been successful in increasing fluxes of MF. The larger particles induce a much higher shear-induced diffusion and therefore dramatically improve mass transfer. Increasing size of the bakelite particles could be associated with increasing flux. To prevent the fouling of MF membranes during the processing of chalk-dust solutions, a high degree of turbulence should be introduced in the membrane surface. The application of microparticles (bakelite) as dolly-particles was investigated for this purpose. The experiments were carried out in MF/K1 equipment. The influence of the microparticles on the flux was investigated with a 0.45μm tubular ceramic membrane. The size of the bakelite particles used was 90–125 μm, 125–160 μm, 160–200μm or 200–400 μm. It was concluded that in all cases the applied bakelite increased the permeate flux. Increasing size of the bakelite particles was associated with an increasing flux. The largest Bakelite particles (200–400 μm) caused the highest fluxes and the smallest cake resistance (RCake) and total (RT) resistance. This work has yielded new experimental results in an alternative approach for the reduction of fouling.

Particle Size Distribution, Count Rate, and Membrane Fouling in Hollow-Fiber Microfiltration

Particle Size Distribution, Count Rate, and Membrane Fouling in Hollow-Fiber Microfiltration Author(s)Josh SmeraldiRajagopalan GaneshJana SafarikDiego RossoSourceProceedings of the Water Environment FederationSubjectSession 11: FoulingDocument typeConference PaperPublisherWater Environment FederationPrint publication date Jan, 2010ISSN1938-6478SICI1938-6478(20100101)2010:5L.518;1-DOI10.2175/193864710798217115Volume / Issue2010 / 5Content sourceMembranes ConferenceFirst / last page(s)518 - 519Copyright2010Word count12

Investigation of membrane fouling in cross flow microfiltration of non-alcoholic beer and modeling of tubular membrane flow

In the present work, numerical simulation of cross flow microfiltration of non-alcoholic beer in a tubular membrane has been studied theoretically and verified experimentally. Finite element method was used as a powerful tool for simulation. The feed stream, which flows mainly tangentially to the porous membrane surface, is modeled by the Navier–Stokes equations whereas the porous wall conditions are described by the Darcy equation that relates the pressure gradient within a flow stream to the flow rate through the permeable wall. A new model that considers transient behavior of the membrane due to fouling was used to estimate the permeate flux reduction. A pilot-scale cross flow membrane filter was developed to verify the model results in which ceramic tubular membranes were used. The cross flow velocity of the feed solution was controlled in the laminar region. It was shown that the model results have good agreement with experimental observations and therefore the model developed in this work can be used for design or optimization of the microfiltration of non-alcoholic beer.

Filtration characteristics and membrane fouling in cross-flow microfiltration of BSA/dextran binary suspension

Filtration characteristics and membrane fouling in BSA/dextran binary suspension cross-flow microfiltration is studied. An increase in cross-flow velocity or transmembrane pressure leads to higher pseudo-steady filtration flux due to less membrane fouling or higher driving force. The fouled membrane pore size and fouled layer thickness under various conditions are estimated using a theoretical model based on the Hagen–Poiseuille law. The fouled membrane pore size decreases with increasing transmembrane pressure due to ever increasing fouling. The fouled layer thickness becomes thicker and invariant with operating conditions under a lower pressure drop through the fouled membrane. Molecular adsorption occurs on the pore walls until a specific wall shear stress is reached in the membrane pores. However, the fouled layer becomes thinner when the pressure drop exceeds a critical value. An increase in cross-flow velocity results in a larger fouled membrane pore size and a thicker fouled layer in such condition. The dextran molecular deformation under higher transmembrane pressure causes a thinner fouled layer and an ultimate equilibrium adsorption in the membrane pores. Furthermore, an increase in cross-flow velocity leads to higher BSA and dextran rejection due to the sweeping effect on the membrane surface. The BSA rejection increases with transmembrane pressure due to the reduction in membrane pore size, while the decrease in dextran rejection under higher transmembrane pressure is attributed to the molecular deformation. The “coil-stretched” deformation of dextran molecules can be indicated using the Deborah number. The fouled membrane pore size and dextran rejection decrease with increasing Deborah number and remain constant as the Deborah number exceeds a critical value. Taking the filtration flux and solute rejection into consideration, operating a cross-flow microfiltration system under lower cross-flow velocity and higher transmembrane pressure is more efficient from the selectivity and mean dextran mass flux view points.

Prediction of microfiltration membrane fouling using artificial neural network models

In this study, artificial neural network (ANN) models were applied to predict the performance of microfiltration (MF) system for water treatment. A series of bench scale experiments were conducted at critical flux and supra-critical flux conditions with various permeate fluxes and feed water qualities. The effects of operating parameters on membrane performance were evaluated based on the comparison of transmembrane pressure (TMP) as a function of operating time. The ANN models used five input variables including permeate flux ( J w), feed water turbidity (Tur f), UV 254, time (h), and backwash frequency for predicting corresponding TMP. The modeling results indicated that there was an excellent agreement between the experimental data and predicted values. Nevertheless, selection of database for training is important for the accuracy of ANN prediction. Relative weights of each input variable were calculated to find out key operational factors affecting the performance of MF system.

Direct-flow microfiltration of aquasols: II. On the role of colloidal natural organic matter

Natural organic matter (NOM) has been considered a major contributor to the fouling of microfiltration (MF) and ultrafiltration (UF) membranes employed in water treatment. However, the fouling potential of NOM has often been assessed in terms of its size or chemical composition. The colloid’s chemical properties have often been ignored. In this study, a chemical attachment-based (CAB) model established previously was used in conjunction with a variety of analytical techniques to investigate the existence of three major components of an aquatic NOM and their role in the fouling of a polyvinylidene fluoride MF membrane. The results suggest that colloidal NOM relevant to membrane fouling has a broader size distribution and variations in chemical properties than proposed previously. For the model aquatic NOM used in this research, fouling was primarily contributed by both non-humic and humic colloidal fractions. The non-humic colloids were larger in size and probably adhered to the membrane regardless of the solution chemistry, while humic colloids had variable size and stickiness depending on solution chemistry. The fouling caused by organic colloids was mostly hydraulically irreversible, as a consequence of favorable surface interactions. The CAB model provided a useful way to understand the role of organic colloids in membrane fouling.

Membrane regeneration and filtration modeling in treating oily wastewaters

Traditional membrane cleaning methods generate waste cleaning waters; whose disposal costs are an increasing concern. The use of backflushed coalescing microfiltration for the pre-treatment of oily wastewaters prior to ultrafiltration is an interesting technique offering potential as a physical pre-treatment method. The concept of this technique is to pre-treat oily wastewaters with a large pore microfiltration membrane operated with backflushing where the oils are partly coalesced in the pores of the membrane. The permeate from this membrane can then be treated by ultrafiltration. The coalescing membrane must eventually be regenerated in order to maintain a desirable permeate flux. The present work investigates environmentally friendly physical membrane cleaning methods, such as backflushing with hot water or steam followed by pressurized air. The treatment of oily wastewater containing half seawater using a microfiltration (MF)/ultrafiltration (UF) hybrid system was studied in this work. The beneficial effects for steam cleaning were quite evident. The results were also modeled using four traditional fouling models and a combined filtration model. They indicate that fouling of microfiltration membranes is due to the presence of oil and grease and seawater colloids in membrane pores. Optimal cycle times between physical cleanings were found to be in the range of 1.6–2.2 h.

Whey protein fouling of large pore-size ceramic microfiltration membranes at small cross-flow velocity

Microfiltration of whey protein solutions by tubular ceramic membranes, under constant cross-flow and trans-membrane pressure, with periodic backwashing, is investigated using a fully instrumented pilot unit. Relatively large nominal membrane pore size (0.8 μm) insures very high protein transmission, which is desirable in applications such as microbial load reduction. In the first of a sequence of three filtration-backwashing cycles, irreversible and reversible fouling are identified, over the tested pressure range of 5–17.5 psi. Early in the first cycle, especially at the higher pressures, a pore constriction/blocking mechanism appears to be responsible for the irreversible fouling. In the other two cycles only the reversible fouling is significant, possibly due to some kind of protein layer formation on the membrane surface. The permeate flux level tends to increase by increasing trans-membrane pressure up to a near-optimum value of 10 psi, beyond which pressure has a negative effect. This interesting trend is attributed to the interplay of cross-flow velocity, which tends to reduce fouling by promoting re-suspension and breakage of colloidal protein agglomerates, with the trans-membrane pressure (and related flux) which leads to protein layer formation on the membrane and may impose compressive stresses, thereby increasing its resistance to permeation.

Characterization of floc size and structure under different monomer and polymer coagulants on microfiltration membrane fouling

The characteristic of aggregates pre-coagulated by inorganic monomer alum, polymer aluminium chlorohydrate(ACH) and polyaluminium chloride(PACl) coagulants impose major impact on the removal of humic acids (HAs) and the reduction of microfiltration (MF) membrane fouling. The fractal dimension of flocs formed by ACH and PACl is higher than that by monomer alum, indicating Keggin structure produced by polymer coagulants is much more compact compared with hexameric ring structure of alum hydrolysis species. Correspondingly, cake layer specific resistance is far higher and the MF membrane flux deteriorates much more severely when pre-coagulated by ACH and PACl than by alum. Moreover, the higher basicity contains in PACls, the cake layer fouling is more serious for producing more proportion of dense hydrolysis species Al 13. Thus, the polymer coagulant ACH and PACl seems not adapt to the pre-coagulation–MF process for cake layer resistance increase two to three times although they save 60–70% dose in comparison with alum for HAs removal. Additionally, for three Al-based coagulants under sweep coagulation condition, insufficient dose result in lower HAs removal and produce more small particles caused higher cake layer specific resistance according to Carman–Kozeny relationship. On the other hand, coagulant hydrolysis species as direct contaminant loading aggravated cake resistance on the MF membrane when overdosed. The optimum dose should keep the minimum to provide better HAs removal efficiency, and produce lower cake layer specific resistance and higher membrane filterability for pre-coagulation–MF hybrid process.

Low-pressure membrane filtration of secondary effluent in water reuse: Pre-treatment for fouling reduction

Fouling in the low-pressure membrane filtration of secondary effluent for water reuse can be severe due to the complex nature of the components in the water. Pre-filtration, coagulation and anion exchange resin were investigated as pre-treatments for reducing fouling of microfiltration (MF) and ultrafiltration (UF) membranes in the treatment of activated sludge-lagoon effluent. The key fouling components were determined using several analytical techniques to detect differences in the organic components between the feed and permeate. Pre-filtration (1.5 μm) enhanced the permeate flux for MF by removing particulates, but had little effect for UF. Marked flux improvement was obtained by coagulation pre-treatment at 5 mg L −1 Al 3+ with internal membrane fouling being substantially alleviated. Anion exchange resin removed >50% of effluent organic matter but did not improve the flux or reduce irreversible membrane fouling. These results, together with detailed organic compositional analyses, showed that the very high-molecular weight organic materials (40–70 kDa) comprised of hydrophilic components such as soluble microbial products, and protein-like extracellular matter were the major cause of membrane fouling.

Mathematical models of membrane fouling in cross-flow micro-filtration

The greatest difficulty arising during cross-flow micro-filtration is the formation of a cake layer on the membrane surface (also called fouling), thereby affecting system performance. Fouling has been related to permeate flux decay resulting from changes in operating variables. Many articles have been published in an attempt to explain this phenomenon but it has not yet been fully understood because it depends on specific solution/membrane interactions and differing parameters. This work was aimed at presenting an analytical review of recently published mathematical models to explain fouling. Although the reviewed models can be adjusted to any type of application, a simple “concentration polarisation” model is advisable in the particular case of tropical fruit juices for describing the insoluble solids being deposited on membrane surface.

Pre-treatments to reduce fouling of low pressure micro-filtration (MF) membranes

Despite the fact that natural organic matter (NOM) is significantly smaller than the pore size of microfiltration (MF) membranes, fouling due to organic compounds has emerged as a problematic issue for both potable water and wastewater membrane filtration. Pre-treatment of the feed water can be a useful strategy for reduction or mitigation of these fouling effects. The aim of this investigation was to evaluate various combined pre-treatment methods for reducing NOM fouling of laboratory scale micro-filtration (MF) membranes, including treatment with adsorbents such as MIEX ® (MIEX ® is a registered trademark of Orica Australia Pty. Ltd.) and powdered activated carbon (PAC) as well as coagulation with alum. High performance size-exclusion chromatography (HPSEC) was applied to determine molecular weight (MW) distribution and proved to be a simple analytical technique, capable of detecting the onset of fouling by observation of the >50,000 Da ‘colloidal’ peak in the water sources examined. Results obtained showed that treatments that reduce the majority of bulk water dissolved organic carbon (DOC) of all MW ranges, including ‘colloidal’ (very high MW) material successfully prevented short-term fouling of MF, where treatments that removed most of the DOC but did not remove the colloidal components, were unable to prevent fouling.

Membrane fouling by cell‐protein mixtures: In situ characterisation using multi‐photon microscopy

Fouling of the membrane by cell and protein mixtures can result in severe flux declines, leading to the eventual need to clean or replace the membrane. In this study multi-photon microscopy, a fluorescence-based technique is used to 3-D image in situ the fouling of microfiltration membranes by suspensions containing combinations of washed yeast, bovine serum albumin (BSA) and ovalbumin. Appropriate fluorescent labelling allows the three foulant species to be clearly identified. Images correlate well with filtration data and clearly show the cake of yeast cells capturing protein aggregates. The proteins exhibited very different filtration behaviour. When filtering washed yeast together with ovalbumin and/or a 50:50 mixture by mass of BSA and ovalbumin, the ovalbumin fouling dominates the system. Capture of aggregates by the cake did not reduce fouling of the membrane by the protein and increased the resistance of the cake. For mixtures of BSA and washed yeast, the presence of a cake of yeast cells did reduce fouling of the membrane by the protein, however, the extra resistance due to the cake resulted in a flux lower than that when filtering BSA alone.

Fouling of microfiltration membranes by natural organic matter after coagulation treatment: A comparison of different initial mixing conditions

The flux declines in the low-pressure membrane filtration of waters pre-treated by chemical coagulation using different initial mixing conditions were compared and the influence of natural organic matter (NOM) on the fouling of membranes was investigated. It was suggested that organic matter in the molecular weight ranges 300–2000 and 20,000–40,000 Da were mainly responsible for the fouling. The fouling was greater for hydrophobic than hydrophilic membranes. ATR–FT-IR analysis of the fouled hydrophobic membranes indicated aliphatic amide and alcoholic compounds as well as polysaccharides contributed to significant membrane fouling. These adsorptive foulants are considered as neutral fractions present in hydrophobic and hydrophilic NOM components. In the case of similar hydrophilic fractions, pre-coagulated water with a high hydrophobic content resulted in greater flux decline, which was presumed to be due to the organic matter with neutral properties contained within the hydrophobic fraction. The relative concentrations of each NOM fraction in coagulated water are important. Mechanical mixing for chemical coagulation, with a backmixing-type, rather than pump diffusion mixing, with an in-line type, is likely to be more effective at reducing the fouling caused by NOM.

In Situ Three-Dimensional Characterization of Membrane Fouling by Protein Suspensions Using Multiphoton Microscopy

Fouling of microfiltration membranes leads to severe flux declines and the need to clean or replace the membrane. In situ 3D characterization of protein fouling both on the surface and within the pores of the membrane was achieved using multiphoton microscopy. Time-lapse images of the fouled membrane were obtained for single suspensions and mixtures of fluorescently labeled bovine serum albumin and ovalbumin. Deposited protein aggregates were visible on the membrane and evidently play an important role in fouling. A combination of 3D images and resistance versus time data was used to identify the dominant fouling mechanism. Fouling is initially internally dominated, but after 1 and 15 min for ovalbumin and bovine serum albumin, respectively, the fouling becomes externally dominated. This is in good agreement with two-stage protein fouling models.

Membrane Fouling of Submerged Membrane Bioreactors: Impact of Mean Cell Residence Time and the Contributing Factors

In this study, four bench-scale pre-anoxic submerged membrane bioreactors (MBR) were operated simultaneously at different mean cell residence times (MCRTs) (3, 5, 10, and 20 days) to systematically elucidate the contributing factors of membrane fouling. Severe membrane fouling was first observed in the 3-day followed by the 5-day MCRT MBRs. Minimal membrane fouling was detected in the 10 and 20-day MCRT MBRs. The fouling of microfiltration membrane was not controlled by mixed liquor suspended solids concentration or zeta potential of biomass. Instead, membrane fouling rate increased with increasing soluble microbial products and extracellular polymeric substances concentrations, which both increased with decreasing MCRT. Total organic carbon, protein, carbohydrate, and UV254 absorbance in the mixed liquor supernatant increased with decreasing MCRT and were consistently higher than those of the effluent. Accumulation of carbohydrates rather than proteins in the mixed liquor supernatant was found to decrease with increasing MCRT. Normalized capilliary suction time value rather than the capilliary suction time value would indicate membrane fouling potential of a mixed liquor. Image analysis of the fouled membrane using scanning electron microscope and confocal laser scanning microscope showed that biofilm formation was the cause of membrane fouling.

A three mechanism model to describe fouling of microfiltration membranes

Mathematical modeling of flux decline during filtration plays an important role in both sizing membrane systems and in the understanding of membrane fouling. Protein fouling is traditionally modeled using one of three classical fouling mechanisms: pore blockage, pore constriction or cake filtration. Here, we have developed a mathematical model to describe flux decline behavior during microfiltration accounting for all three classical fouling mechanisms. Pore constriction was assumed to first reduce the size of internal pores. Pore blockage then occurs at the top of the membrane, preventing further fouling to the interior structure. Finally the foulants at the top of the membrane form a cake, which controls the late stages of the filtration. The model prediction shows excellent agreement with experimental data for 0.25 μm polystyrene microspheres filtered through 0.22 μm Isopore membranes (where pore constriction is expected to be minimal) as well as non-aggregated bovine serum albumin solution through hydrophobic Durapore membranes (where pore constriction is expected to dominate). The effects of different fouling mechanisms on the flux decline were characterized by the ratio of characteristic fouling times of the different mechanisms. In this way the model can provide additional insights into the relative importance of different fouling mechanisms as compared to an analysis by a single mechanism model or by derivative plots, and it can be used to provide important insights into the flux decline characteristics.

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.