Cross-flow Rate Research Articles

Cross-flow microfiltration of oil-in-water emulsions using low cost ceramic membranes

Low cost ceramic membranes (M1–M3) were prepared using uniaxial compaction method using different compositions of low cost inorganic precursors and clays. Along with good combinations of acidic and basic corrosion resistance, the prepared membranes possessed an average pore diameter of 0.45 to 1.30μm, porosity of 23 to 30%, water permeability of 0.37–3.97×10−6m/skPa and flexural strength of 10–34MPa. Cross-flow microfiltration experiments were conducted using oil–water emulsion concentration of 100mg/L at five distinct pressures (69–345kPa) and three different cross flow rates (2.78–13.9×10−7m3/s). During cross-flow microfiltration, the maximum rejection values have been observed to vary from 89 to 97% with permeate flux of 1.33–1.91×10−5m/s, for all the membranes. Amongst these membranes, membrane M2 provided a good combination of permeate flux and rejection (5.54×10−5m/s and 87% at a cross flow rate of 13.9×10−7m3/s and trans-membrane pressure of 207kPa). Also, the experimental flux decline data has been analyzed using various pore blocking models and it was evaluated that cake filtration model provided the best fitness towards the experimental data. These observations indicate the competence of the developed membranes towards the treatment of oil-in-water emulsions.

The modeling and calculation of sound radiation from facilities with gas flowed pipes

Computer modeling of industrial facilities like chemical plants, refineries, or other production areas is the first and most important step in the calculation of sound exposure in the environment. The pipework with gas flows is often contributing relevant to the sound radiation of the complete facility. This radiation can be determined applying the methods described in technical papers like VDI 3733 and ISO 15664. On the basis of these descriptions a software tool was developed that allows to create pipework in 3D models with line sources and to calculate the sound propagation with methods like ISO 9613-2. The line sources are linked with the technical parameters like pipe cross section, flow rate, pressure, density, and temperature of the gas and material parameters of the pipe wall. The sound power emission from the pipe to the environment and the internal flow of sound power—linked to the next section of piping—is calculated on the basis of these parameters. The same technique is used to calculate the sound emission of cooling towers, electric and fuel driven motors, gears pumps, and other devices. This powerful technique allows creating sustainable models that can be adapted to different operation conditions with minimum time and effort.

Removal of Phenol from Coke‐Oven Wastewater by Cross‐Flow Nanofiltration Membranes

This study investigated the phenol rejection characteristics of some nanofiltration membranes during treatment of coke wastewater. Four different types of composite polyamide commercial nanofiltration membranes (Sepro, USA) were tested under different operating conditions including transmembrane pressure, pH and recovery rate. When pressure was increased from 4 to 16 bars, the percentage of rejection of phenol in the permeate increased from 72.5% to 97.7% while yielding a high flux of 118 litres per square meter per hour(LMH) at a volumetric cross flow rate of 800 litres per hour at pH 10 (in recirculation mode) in case of NF1 membrane. The effect of recovery rate on the rejection coefficient of phenol and flux was also studied in concentrated mode and found that a recovery rate of up 55% nanofiltration was successfully operated without much decline of flux and rejection coefficient. Finally, nanofiltration had great efficiency in phenol removal from industrial wastewater and was considered suitable regarding its operation.

Removal of fluoride from contaminated groundwater by cross flow nanofiltration: Transport modeling and economic evaluation

A modeling and simulation study along with economic evaluation was carried out for removal of fluoride from contaminated groundwater in a flat sheet cross flow nanofiltration membrane module. Mathematical model was developed based on extended Nernst–Planck equation and with the help of ‘concentration polarization modulus’ equation. Linearized approach in modeling reduced computation time significantly. Effects of transmembrane pressure, cross-flow rate, pH and concentration of the solute of interest on membrane charge density, solute rejection and solvent flux were investigated. The membrane module was successful in yielding a pure water flux as high as 158lm−2h−1 removing more than 98% of the fluoride at a transmembrane pressure of only 14kgfcm−2 and at a pH of 10.01 for a volumetric cross flow rate of 750Lh−1. The membrane module not only removed fluoride effectively but also brought down high pH of groundwater to the desired level. The developed model corroborated well with the experimental findings as reflected in the very low relative error (<0.1) and high value of overall correlation coefficient (R2>0.98). Economic analysis indicated that such a membrane filtration system could be quite promising in purifying fluoride-contaminated groundwater at low cost.

Selective Separation of Nickel (II) and Cobalt (II) from Waste Water by Using Continuous Cross-Flow Micellar Enhanced Ultrafiltration with Addition of Chelating Agent

The performance of continuous cross-flow micellar enhanced ultrafiltration (MEUF) is evaluated for the selective separation of nickel (Ni2+) and cobalt (Co2+) from the aqueous stream using anionic surfactant sodiumdodecyl sulfate (SDS) and the mixture of the anionic and nonionic surfactant (SDS+TritonX-100) with the addition of iminodiacetic acid (IDA) as a chelating agent. Operating parameters like operating time (upto 100 min), cross flow rate (100–175 mL/min.), pH of the feed solution (3-6), molar concentration ratio of the chelating agent to metals (C/M ratio, 0.5–2.5), and molar concentration ratio of the surfactant to metals (S/M ratio, 5–9) were studied to investigate the effectiveness of the process on selective separation. For the single surfactant system at all empirically selected parameters, 92% Ni2+ in the permeate and 94% Co2+ in the retentate was achieved whereas for the mixed surfactant system 93% Ni2+ in permeate and 84% Co2+ in retentate was achieved. Flux variation for single and mixed surfactant system was studied. Flux observed for the single surfactant system was 36 L/m2.h and for the mixed surfactant system was 31.5 L/m2.h. Flux measurement also indicates insignificant fouling of the membrane.

Separation of praseodymium(III) from aqueous solutions by nanofiltration

The increased demand for rare earth elements in commercial products is increasing their production, which in turn increases public exposure to rare earth elements. The objective of the present work is to study the separation of praseodymium from aqueous solutions by a commercial nanofiltration membrane (NF-300) at various operating conditions. The permeate and feed samples were analysed with inductively coupled plasma atomic emission spectrometry (ICPAES) to find praseodymium [Pr(III)] concentration. The results indicated that the separation of Pr(III) ions increased with increase in applied pressure (2–10 bar) and cross flowrate (4–16 L min−1); and decreased with increase in feed concentration (10 mg L−1 PrCl3 – 100 mg L−1 PrCl3). The highest observed separation of the Pr(III) was found to be 89·07 and 84·20% for an initial feed concentration of 10 and 100 mg L−1 PrCl3 respectively. It was also observed that separation of Pr(III) increases to 99·28 and 99·30% in complexation step by using ethylene diamine tetra aceticacid (EDTA) and diethylene triamine penta aceticacid (DTPA) respectively, as the chelating agent has generally influenced by pH (2 –10).La demande accrue d’éléments de terres rares dans les produits commerciaux augmente leur production, ce qui, à son tour, augmente l’exposition du public aux éléments de terres rares. Le but de ce travail est d’étudier la séparation du praséodyme à partir de solutions aqueuses au moyen d’une membrane commerciale de nanofiltration (NF-300) sous diverses conditions d’utilisation. On a analysé les échantillons de perméat et d’apport au moyen de la spectroscopie d’émission atomique avec plasma induit par haute fréquence (ICPAES) afin de déterminer la concentration du praséodyme [Pr(111)]. Les résultats indiquaient que la séparation d’ions de Pr(111) augmentait avec une augmentation de la pression appliquée (2–10 bar) et de la vitesse de l’écoulement transversal (4–16 L min−1) et diminuait avec une augmentation de la concentration de l’apport (10 mg L−1 PrCl3 – 100 mg L−1 PrCl3). On a trouvé que la valeur la plus élevée de séparation observée pour le Pr(111) était de 89·07 ou de 84·20% pour une concentration initiale de l’apport de 10 ou de 100 mg L−1 de PrCl3, respectivement. On a également observé que la séparation du Pr(111) augmentait jusqu’à 99·28 ou 99·30% dans une étape de complexation en utilisant de l’acide éthylènediaminetétracétique (EDTA) ou de l’acide diéthylènetriamino-pentaacétique (DTPA), respectivement, comme agent chélateur, influencé généralement par le pH (2–10).

A novel implementation of water recovery from whey: “forward–reverse osmosis” integrated membrane system

As a result of its emerging contribution to water recovery and clean water production, forward osmosis (FO) in integrated membrane system has recently especially been preferred by research communities on membrane science and desalination technology. In this study, the effectiveness of FO reverse osmosis (RO) integrated membrane system in whey dewatering was investigated in laboratory scale experiments in which FO and RO were utilized for whey concentration and water recovery, respectively. FO experiments were carried out at different conditions of cross-flow rate, temperature, membrane kind, membrane orientation mode, and microfiltration (MF) pretreatment. A single-step RO system was applied for water recovery from the FO draw solution. In the FO process, about 1.6 L water of 3 L whey was withdrawn into 3M NaCl draw solution during 6 h operating time, and a sufficiently high performance in whey concentration was obtained, with the solid content being increased from 6.8 to 14.3%. However, the process resulted in a high salt permeation into the whey, in addition to some soluble organics being permeated into the draw. RO process are operated with relatively low performances due to excessive salt concentration of the FO draw solutions, which indicates that there is a need for RO implementation in two or three sequential levels for achieving an absolute success in the water recovery from whey. Despite the fact that MF pretreatment to some extent decreased the FO performance, it could be used for directly productive activities intended to recover fats from whey. Results have proved that prior to whey powder production, the integrated system could be effectively employed for whey concentrations up to a solid content of 25–35%. Accordingly, FO–RO system can be utilized as a novel alternative in concentrating whey compared to ultrafiltration-RO combined system widely used worldwide. However, before practical implementation of the system, an optimization between alleviating the salt concentration in FO draw and multi-step RO implementation should have to be considered concurrently with the economics of the investment.

Optimization and evaluation of asymmetric flow field-flow fractionation of silver nanoparticles

Asymmetric flow field-flow fractionation (AF4) in combination with on-line optical detection and mass spectrometry is one of the most promising methods for separation and quantification of nanoparticles (NPs) in complex matrices including food. However, to obtain meaningful results regarding especially the NP size distribution a number of parameters influencing the separation need to be optimized. This paper describes the development of a separation method for polyvinylpyrrolidone-stabilized silver nanoparticles (AgNPs) in aqueous suspension. Carrier liquid composition, membrane material, cross flow rate and spacer height were shown to have a significant influence on the recoveries and retention times of the nanoparticles. Focus time and focus flow rate were optimized with regard to minimum elution of AgNPs in the void volume. The developed method was successfully tested for injected masses of AgNPs from 0.2 to 5.0μg. The on-line combination of AF4 with detection methods including ICP-MS, light absorbance and light scattering was helpful because each detector provided different types of information about the eluting NP fraction. Differences in the time-resolved appearance of the signals obtained by the three detection methods were explained based on the physical origin of the signal. Two different approaches for conversion of retention times of AgNPs to their corresponding sizes and size distributions were tested and compared, namely size calibration with polystyrene nanoparticles (PSNPs) and calculations of size based on AF4 theory. Fraction collection followed by transmission electron microscopy was performed to confirm the obtained size distributions and to obtain further information regarding the AgNP shape. Characteristics of the absorbance spectra were used to confirm the presence of non-spherical AgNP.

Modeling of the initial deposition of individual particles during the cross-flow membrane filtration

This study is devoted to the modeling of the deposition of individual particles onto a clean membrane surface in cross-flow filtration systems. Comprehensive force analysis approach is applied, which accounts for the random Brownian force and the polar component of the particle–membrane interactive forces. The inclusion of the polar interactive force is important in that when a hydrophilic membrane is involved, it can easily predominate over the rest of lateral forces in the near-field. The repulsive polar particle–membrane interaction can greatly decrease the stability of the particle on the membrane surface. In the far-field that is about 0.1μm or farther away from the membrane, the particle transport is primarily dictated by the hydrodynamic lift and drag forces and the Brownian force. In sharp contrast to semi- or non-Brownian particles, the transport trajectory of Brownian particle is hardly definitive. The filtration flux and the cross-flow velocity can influence the particle transport trajectory of all sizes. Nevertheless, the existence of critical flux or critical cross-flow velocity is more evident for non-Brownian particles. Above the critical cross-flow rate or below the critical flux, particle deposition is minimized. Under appropriate operational conditions, a force-balanced level exists in the viscous sub-layer for a particular particle size, which is independent of the initial position of the particle. The model can be expanded further for more complicated water filtration conditions.

Intensification of microfiltration using a blade-type turbulence promoter

Intensification of microfiltration has been accomplished using motionless mixers consisting of a series of pairs of semielliptical blades as turbulence promoters. Blade mixers of two aspect ratios 2.5 and 1.3 were tested in the microfiltration of milk (0.1μm membrane). The permeate fluxes are substantially increased by application of blade mixers due to a reduction of both reversible and irreversible fouling. The highest flux improvements of 500–650% for the same cross-flow rate (relative to the conventional operation) were obtained by application of the blade mixer of aspect ratio 1.3.When compared for the same hydraulic dissipated power mixer of aspect ratio 2.5 proved to be slightly more efficient because it causes the lower pressure drop. Despite to the increased pressure drop, the energy savings obtained by application of blade mixers are considerable compared to the conventional operation and to the operation using some other mixers. In the membrane fitted with a blade mixer the flow field changes in a manner which afford the intensive disruption of boundary layer, scouring and removal of fouling forming material. The flow field is characterized by the high cross-flow velocities at membrane wall, alternation of stream line path and swirling motion. Therefore, the application of blade mixers affords an operation under the several times lower initial cross-flow velocity.

Purification of lactic acid from microfiltrate fermentation broth by cross-flow nanofiltration

Experimental investigations were carried out on cross-flow nanofiltration of microfiltrate fermentation broth of lactic acid during membrane-integrated fermentative production of monomer grade lactic acid. Three types of composite polyamide nanofiltration membranes (NF2, NF3 and NF20) manufactured by Sepro Co. (USA) were used in nanofiltration. Lactic acid fermentation broth produced by fermentation of sugar cane juice by Lactobacillus plantarum in a membrane-integrated hybrid reactor system was filtered by NF membranes after preliminary filtration through microfiltration membranes for cell separation and recycle. Effects of cross flow rate, transmembrane pressure and pH on flux and rejection of both acid and unconverted sugars for recycle were analyzed. NF3 membrane was successful in retaining 94% unconverted sugars while allowing 32% lactic acid to permeate at a flux of 113Lm−2h−1 at pH 5.5, temperature 37°C, transmembrane pressure of 13bar and cross-flow velocity 2.48ms−1. The study shows that integration of a properly selected nanofiltration membrane with a cell-recycle fermentation unit and lactate conversion unit can yield l (+) lactic acid with an optical purity of 85.6% through an economically attractive route by recovering and recycling of unconverted sugars. The nanofiltration combine with bipolar electrodialysis in downstream purification can replace the multiple purification steps by two steps while yielding a monomer grade lactic acid from a mixture of unconverted sugars and lactic acid.

Hydrodynamic radius determination with asymmetrical flow field-flow fractionation using decaying cross-flows. Part I. A theoretical approach

Direct determination of hydrodynamic radius from retention time is an advantage of the field-flow fractionation techniques. However, this is not always completely straight forward since non-idealities exist and assumptions have been made in deriving the retention equations. In this study we investigate the effect on accuracy from two factors: (1) level of sophistication of the equations used to determine channel height from a calibration experiment and (2) the influence of secondary relaxation on the accuracy of hydrodynamic radius determination. A new improved technique for estimating the channel height from calibration experiments is suggested. It is concluded that severe systematic error can arise if the most common channel height equations are used and an alternative more rigorous approach is described. For secondary relaxation it is concluded that this effect increases with the cross-flow decay rate. The secondary relaxation effect is quantified for different conditions. This is part one of two. In the second part the determination of hydrodynamic radius are evaluated experimentally under similar conditions.

Application of flow field-flow fractionation (FlFFF) for size characterization of carbon black particles in ink

The size and distribution of the carbon black particles play important roles with respect to application in diverse areas. When used in inks, the smaller the particle size, the better the carbon black particles are dispersed, and thus the glossiness of ink increases. Asymmetrical flow field-flow fractionation (AsFlFFF) has shown to be applicable for size characterization of various types of colloidal particles. In the present study, AsFlFFF was employed to analyze the size of carbon black particles used in ink. Carbon black suspensions were prepared by dispersing carbon black powder in aqueous media containing various types of copolymeric dispersing agents of hydrophobic (styrene) and hydrophilic (acrylic or maleic acid) monomers. Experimental parameters of AsFlFFF including the type of the surfactant added to the carrier liquid, the channel and the cross flow rates, and the ionic strength were varied to find an optimum condition for analysis of the carbon black particles. It was found that the use of FL-70 as an additive to the carrier liquid resulted in the best elution profile among the tested surfactants (cationic, anionic, and nonionic surfactant). Although the mean sizes obtained by AsFlFFF and dynamic light scattering (DLS) were generally in good agreements, DLS failed to distinguish between the carbon black suspensions having different size distributions, whereas AsFlFFF was able to differentiate easily. Results indicated that the carbon black particles were dispersed better with the copolymeric dispersing agents having the hydrophobic content of 2 to 3 times higher than the hydrophilic molecules. At the styrene:acrylic acid of 1:1, the carbon black particles tend to have larger mean sizes and the size distributions tend to become broader, probably due to poor dispersion. Furthermore, it was observed that as the mean size of the carbon black particles decreased and the size distribution became narrower, the ink became clearer and glossier.

Combined effects of operational parameters on electro-ultrafiltration process characteristics

The aim of the present study was to identify the influence of process parameters and their interactions on the electro-ultrafiltration performance during the filtration of alumina suspensions at low cross-flow rates. Overall, a weak flux-pressure dependence was observed in the absence of an electric field, indicating mass transfer limitation. A clear enhancement of flux was achieved by superimposing an electric field on the transmembrane pressure. As the feed pH increased from the acidic range to the vicinity of the isoelectric point of the particles, the beneficial effect of the electric field on permeate flux decreased significantly. Statistical analyses showed that in addition to the experimental parameters, some of their interactions were quite influential for determining the performance of the electro-ultrafiltration (EUF) process. Thus, the electric field induced flux enhancement became less pronounced as the initial ionic strength of the feed solution increased. In addition, the three studied response factors were noticed to be interrelated, whereby inevitable pH and conductivity changes associated with the electrode reactions during the electrofiltration process were also important in determining the permeate flux and quality. Overall, the results indicated that a clear understanding of the EUF performance is only possible when considering different effects (such as flux improvement and pH shift) simultaneously.

Clarifications of stevia extract using cross flow ultrafiltration and concentration by nanofiltration

Cross flow ultrafiltration was employed to clarify the pretreated stevia extract. Two practical modes of cross flow ultrafiltration, namely, steady state under total recycle mode and batch concentration mode, were used. A detailed investigation of effects of the operating conditions on the permeate flux and permeate quality was undertaken. It was observed that the significant flux enhancement was achieved with transmembrane pressure drop and cross flow rate. Maximum 200% flux enhancement with cross flow rate and 140% with transmembrane pressure drop were attained in the range of operating conditions studied herein. Effects of cross flow rate on the permeate properties were marginal but that of the transmembrane pressure drop was significant. Recovery of stevioside in the permeate was in the range of 30–56% for various transmembrane pressure drop and it was maximum for lower operating pressure, 276kPa. However, the recovery of stevioside decreased to 38% at 276kPa pressure after 10h of operation. Nanofiltration was employed to concentrate the ultrafiltered liquor. During nanofiltration, the ultrafiltered feed was concentrated maximum twice at 1241kPa and 1500rpm of stirrer speed within 1h of operation. Maximum overall (ultrafiltration followed by nanofiltration) purity and recovery of 60% is obtained for a particular set of operating conditions.

Molecular characteristics of native sago starch and isolated fractions determined using asymmetrical flow field‐flow fractionation

AbstractThe apparent average molar masses (Mw,app), apparent average radii of gyration (Rg,app), of native sago starch and fractions were determined using asymmetrical flow field‐flow fractionation coupled with multi‐angle light scattering and refractive index detectors (AF4/MALS/RI). Amylose‐type (Fraction A) and amylopectin‐type (Fraction B) were chemically separated from native sago starch. Native sago starch and Fractions (A–B) were dissolved in 1M KSCN using a high pressure microwave vessel. The effect of varying cross flow rates at a fixed channel flow rate upon the Mw,app and Rg,app distributions of native sago starch and Fractions (A–B) were investigated. The average Mw,app values of native sago starch, Fraction (A) and Fraction (B) were 60 × 106, 1.5 × 106 and 60 × 106 g/mol, respectively, with average Rg,app values of 142, 75 and 127 nm, respectively. The sphere‐equivalent hydrodynamic radii (Rh) values for native sago starch and fractions were determined from AF4 experimental parameters.

Characterisation of normal corn starch using asymmetrical flow field‐flow fractionation

AbstractThe apparent average molar masses (Mw,app), apparent average radii of gyration (Rg,app), diffusion co‐efficients (DT), and hydrodynamic radii (Rh) of normal corn (maize) starch and fractions were determined using asymmetrical flow field‐flow fractionation coupled with multi‐angle light scattering and refractive index detectors (AF4/MALS/RI). AM‐type (Fraction A) and AP‐type (Fraction B) were chemically separated from normal corn starch. Normal corn starch and Fractions (A–B) were dissolved in 1 M KSCN using a high pressure microwave vessel. The effect of varying cross flow rates at a fixed channel flow rate upon the Mw,app and Rg,app distributions of normal corn starch and Fractions (A–B) were investigated. The average Mw,app of normal corn starch, Fractions (A) and Fraction (B) were 41 × 106, 1.4 × 106 and 39 × 106 g/mol, respectively, with Rg,app values of 129, 60 and 129 nm, respectively.

Determination of molar mass distribution of tapioca starch using asymmetrical flow field flow fractionation

AbstractThe apparent average molar masses (Mw,app) and apparent average radii of gyration (Rg,app) of native tapioca starch and fractions were determined using asymmetrical flow field flow fractionation (AF4) coupled with multi‐angle light scattering and RI detectors (AF4/MALS/RI). AM‐type (Fraction A) and AP‐type (Fraction B) were chemically separated from native tapioca starch. Native tapioca starch and Fractions (A and B) were dissolved in 1 M KSCN using a high pressure microwave vessel. The effect of varying cross flow rates at a fixed channel flow rate upon the Mw,app and Rg,app distributions of native tapioca starch and Fractions (A and B) were investigated. The average Mw,app values for native tapioca starch, Fraction (A) and Fraction (B) were 59 × 106, 2.1 × 106 and 19 × 106 g/mol, respectively, with average Rg,app values of 165, 73 and 87 nm, respectively. Hydrodynamic radii (Rh) values for native tapioca starch and fractions were determined directly from AF4 experimental parameters.

Twisted tapes as turbulence promoters in the microfiltration of milk

This study is concerned with the application of a twisted tape, as low pressure loss turbulence promoter, in the microfiltration of milk. By application of twisted tapes both reversible and irreversible fouling are reduced and the permeate fluxes are remarkably increased. The flux improvement increases with decrease of an aspect ratio of twisted tape. The highest flux improvements (relative to the conventional operation) were obtained by application of the tightest twisted tape of aspect ratio 1.0, 400–600% for the same cross-flow rate and 25–82% at the same hydraulic dissipated power. Considerable energy savings can be obtained by application of twisted tapes as compared to the conventional operation and to the operation with some other promoters such is KM Kenics™ mixer. The high efficiency of twisted tapes as turbulence promoters is contributed to the intensive promotion of turbulence and low pressure loss compared to some other turbulence promoters. Alternation of streamline path from straight to helically shaped proved to be more efficient in disruption of the fouling layer than just an increased axial cross-flow velocity. In the membrane fitted with twisted tape turbulence is the most intensive at the membrane wall were the helically shaped streamline path is the longest. This contributes to the intensive disruption of boundary layer and scouring of fouling forming material.

Evaluation of the importance of various operating and sludge property parameters to the fouling of membrane bioreactors

A single-fibre microfiltration system was employed to investigate the importance of various operating and sludge property parameters to the membrane fouling during sludge filtration. The sludge was obtained from a submerged membrane bioreactor (SMBR). A series of comparative and correlative filtration and fouling tests were conducted on the influence of the operating variables, sludge properties and the liquid-phase organic substances on the membrane fouling development. The test results were analysed statistically with Pearson's correlation coefficients and the stepwise multivariable linear regression. According to the statistical evaluation, the membrane fouling rate has a positive correlation with the biopolymer cluster (BPC) concentration, sludge concentration (mixed liquor suspended solids, MLSS), filtration flux and viscosity, a negative correlation with the cross-flow velocity, and a weak correlation with the extracellular polymeric substances and soluble microbial products. BPC appear to be the most important factor to membrane fouling development during the sludge filtration, followed by the filtration flux and MLSS concentration. The cross-flow rate also is important to the fouling control. It is argued that, during membrane filtration of SMBR sludge, BPC interact with sludge flocs at the membrane surface to facilitate the deposition of the sludge cake layer, leading to serious membrane fouling.