Crossflow Filtration

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The objective of the study described in the present paper was to investigate transport and separation properties of ultrafiltration membranes for atrazine solutions in the presence of natural complexing agents (humic and tannic acids). Two ultrafiltration membranes made of various polymer materials were used in the tests. Atrazine concentrations in tested solutions amounted to1000 mg/m3. The influence of pH of atrazine solutions as well as the dose of humic and tannic acids on the process efficiency was investigated. The highest efticiency of separation (80%) was achieved for DS-GE membrane at the concentration of humic substances equal to 20 g/m'.

Arsenic occurs naturally in the ground and surface water and is not desired in the drinking water due to carcinogenic effect on human body. The common types of arsenic are arsenate (As V) and arsenite (As III). Although arsenate removal has been achieved by membranes, adsorption, ion exchange and coagulation, arsenite removal is difficult to decrease the concentration up to the standard level (below to 10 μg/L). In this study, nanofiltration (NF) and adsorption techniques have been compared to remove arsenite from drinking water. In nanofiltration study, different NF membranes and arsenite feed concentrations have been studied. Feed water was prepared synthetically and laboratory scale cross-flow mode filtration apparatus with a flat-sheet membrane cell was used for NF experiments. In the adsorption experiments with granular iron hydroxide (GIH), all studies were performed in the free water flow and at the normal pH of tap water. It was concluded that arsenite concentration was lowered to below 10 μg/L with adsorption. These results showed that GIH adsorption can be used to remove arsenite concentration of 0.1 and 0.5 g/L from water supplies.

The structure and microbial communities of biofilms developing on cross-flow nanofiltration (NF) membranes at different temperatures (20, 25 or 34 1C) and operation lengths (8 h-24 days) were studied. Feedwater comprised tertiary quality wastewater effluent or synthetic media mimicking effluents of intermediate quality. After each run, the membranes were autopsied for bacterial enumeration, bacterial community composition and microscopy visualization (SEM, CLSM and AFM/NSOM). Community composition was analyzed by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) coupled with sequence analysis of 16S rRNA gene fragments from dominant bands. Deposition of polysaccharides and initial bacterial colonization were observed within 8 h, whereas developed biofilms markedly affecting membrane permeability were evident from days 2-3 onwards. Regardless of applied conditions, the heterotrophic plate counts in the biofilm were 3-4 Â 10 6 CFU/cm 2 and the thickness of the biofouling layer was 20-30 mm. From a total of 22 sequences obtained from 14 independent experiments, most species identified were Gram negative (19 of 22 sequences). Proteobacteria were found to be a prevalent group in all cases (16 of 22 sequences) and among it, the b-subclass was the most predominant (8 sequences), followed by the g-subclass (5 sequences). Pseudomonas/ Burkholderia, Ralstonia, Bacteroidetes and Sphingomonas were the dominant groups found in most cases. Even though the microbial population might be important with respect to biofouling patterns, membrane permeability decline seems to be more substantially influenced by the formation and accumulation of exopolymeric substances (EPS).

Biofouling is a major impediment in reverse osmosis (RO) and nanofiltration (NF) cross-flow processes. Due to the cross-flow component, feedwater microorganisms are transported to the membrane surface where they adsorb, forming a fouling layer. Once attached, the microorganisms grow and multiply at the expense of feedwater 0 nutrients, forming a biofouling layer which reduces permeate fluxes and damages the membrane. Prefiltered secondary effluents and synthetic media simulating secondary effluents were applied for studying NF membrane biofouling, using 120 cm 2 area-polyamide tubular membranes of 200 Da MWCO. After operation the membranes were dismounted and segmented in slices which were analyzed by spectroscopic, microscopic and molecular techniques. Fully developed biofilm was found on the membranes and biofouling appears to be the predominant form of fouling composed of bacteria and extracellular polymers, while the size and composition of biofilm population seem to be convergent to finite number. Microbial populations identified by sequence homology corresponded phylogenetically to Flavobacterium sp, Pseudomonas, Ralstonia and Cytophaga regardless of the conditions applied. Microscopic observations revealed presence of protozoa as well. Bacterial counts in biofilm accounted for approx. 10 7 CFU cm À2 regardless of the feed applied. Although biofouling layer over the membrane reduced flux, biofouling development improved brine rejection (50-70%). FTIR spectra of the organic matter accumulated on the NF membrane showed the presence of proteins and amino acids and a high level of aliphatic and polysaccharide residues.

This study demonstrates the removal efficiency and the permeate flux behavior during cross-flow nanofiltration (NF) of aqueous solutions of five pharmaceutically active compounds (PhACs). Cephalexin, tetracycline, acetaminophen, indomethacin and amoxicillin were used as models of PhACs, and alginate was selected as model of natural organic matter (NOM). Two commercial composite NF membranes (SR2 and SR3) with different characteristics were used. The highest rejection was observed for tetracycline, i.e., 75-95% for membrane SR 2 and 95-100% for membrane SR 3, while the rejection was least for acetaminophen (32-36% for SR2 and 52-59% for SR3). As the pH of acetaminophen solution was increased (from 6 to 9) the rejection would increase. Changes of ionic content (from 10 to 20mM) lead to increase (from 89 to 93% for SR 3) or decrease (from 100 to 91% for SR2) of cephalexin rejection depending on the membrane used. The permeate flux would decrease with decreasing the pH solution and incr...

Energy recovery from a crossflow ultrafiltration (UF) membraneunit employed in order to improve the performance of an anaerobic contact digester for the treatment of brewery wastewater was assessed. The performance of the pilot-scale anaerobic UF membrane system was studied for over 15 months. At steady-state conditions, an organic loading rate of 28.5 kg COD m-3 d-1, a hydraulic retention time

Zwischen zwei rotierenden Zylindern entstehen, abhängig von den Winkelgeschwindigkeiten der Zylinder zueinander und den geometrischen Gegebenheiten, unterschiedliche Strömungsstrukturen. Grundlegende Untersuchungen dazu führte Taylor bereits 1923 durch. Der Übergang von laminarer Couetteströmung zu laminarer Taylorwirbelströmung wird durch die kritische Reynoldszahl beschrieben. Diese Stabilitätsgrenze wird von der Spaltweite, den beiden Winkelgeschwindigkeiten und der Viskosität des Fluids bestimmt. Bei der Überschreitung dieser Stabilitätsgrenze entstehen im Spalt ringförmige Wirbel über den gesamten Umfang. Die Anzahl dieser sogenannten Taylorwirbel ist in erster Linie abhängig vom Streckungsverhältnis des Systems. Das Streckungsverhältnis ist das Verhältnis von axialer Länge zur mittleren Spaltweite des Systems. Ein großes Streckungsverhältnis charakterisiert somit einen langen, schmalen Spalt zwischen den Zylindern. Da Taylorwirbel im Querschnitt näherungsweise eine kreisförmig...

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balance experiments with stream NOM show good recovery (99.7% ( 9.5%, n ) 67). Sorption losses are very low (on average, <2%) to RCL membranes but are higher for PES. Replicate precision is typically better than (5% for carbon. There are significant differences between PES and RCL membranes: permeate carbon levels are similar, but RCL predicts a larger >10 kDa fraction and carbon sorption is more significant on PES. These findings could be explained by greater hydrophobic interactions of dissolved organic carbon with PES and charge interactions with RCL. A strong negative correlation is observed between the percent of colloidal carbon (10 kDa -0.4 µm) and the log specific conductance of streamwaters (R 2 ) 0.71).

In the ultrafiltration (UF) of macromolecules, permeate flux increases with increase in the applied pressure until a critical value is reached where further increase in applied pressure does not cause any significant increment of the permeate flux. In this mass-transfer controlled region, film theory has been employed to study the flux behaviour during ultrafiltration of Polyethylene Glycol-6000 solution in a cross flow ultrafiltration module fitted with polyethersulphone membrane. Effect of feed velocity on flux and rejection behaviour have been studied. Mass transfer coefficient have been estimated using suitable correlation involving Reynolds no., Schmidt no. and Sherwood no. for the system. The concentration of the gel layer at the membrane surface has also been estimated. Studies have also been carried out in the pressure controlled region. A 38% increase in permeate flux have been found when the TMP has been increased to 1.0 kg/cm 2 to 2.5 kg/cm 2 .

A white wine was clarified by tangential microfiltration (MF) and ultrafiltration (UF). The permeation experiments were carried out in a Dow Lab-unit M20 with a membrane area of 0.036 m 2. Two membranes were tested, one of MF with a pore size of 1.0 mm and another of UF with a molecular weight cutoff (MWCO) of 100 kDa. They are both made of a fluor polymer and supplied by DSS-Denmark. The operating conditions (pressure and circulation flow rate) were optimised for both membranes. The MF and UF clarification experiments were performed at the same optimal conditions of 1× 10 5 Pa transmembrane pressure and 554 l h − 1 circulation flowrate. The results were compared in terms of permeate productivity, particle and polysaccharide removal. The polysaccharides were precipitated from the raw wine, the UF permeate and the UF concentrate. Potassium hydrogen tartrate crystallisation induction times were measured at 0°C using hydroalcoholic solutions with and without these polysaccharides. MF and UF presented similar permeate productivities and particle removal. The UF membrane proved to be easier to clean. Polysaccharide removal was low with both membranes: 10% for MF and 16% for UF. The polysaccharides retained by UF did not alter significantly the potassium hydrogen tartrate crystallisation induction times. These induction times are similar for the model solution with the polysaccharides from the raw wine and the UF clarified wine.

The efficiency of crossflow microfiltration processes is limited by membrane fouling and concentration polarization leading to permeate flux decline during operation. The experiments that were carried out in the laboratory were conducted to determine and investigate the performance, behaviour and the fouling susceptibility of new ceramic tubular microfiltration membranes during the crossflow filtration of yeast suspensions. The tubular membranes of nominal pore size 0.5 microns were fouled over a varied range of concentration, temperatures, pH, crossflow velocities and system pressures. The typical filtration conditions were at a temperature of 25°C, a system pressure of 1.5 bar and a concentration of 0.03 g/L yeast suspension. These parameters varied during subsequent investigations. After each experiment, the membrane and the rig were cleaned using a three stage cleaning process and was reused in order to replicate industrial filtration conditions. The effects of repeated fouling and cleaning cycles upon membrane flux over time and cleaning efficiency are investigated and their influence over time is also documented. For every experiment, the flux data was recorded over a 50 min period and the membrane was changed after the PWF declined considerably due to excessive fouling over time. Chemical cleaning consisted of a sequential application of a 1% caustic solution through the rig followed by a 2% hypochlorite solution and a 2% nitric solution, all at 50°C. The permeate flux was shown to decrease with filtration time during the development of the fouling layer. Once the fouling layer was developed and established, there appeared to be a leveling of permeate flux. The experimental results are presented in the report and the flux values at different conditions are presented.

A novel polyethersulfone (PES)/microcrystalline cellulose (MCC) composite membrane for humic acid (HA) removal in water was fabricated using the phase inversion method by blending hydrophilic MCC with intrinsically hydrophobic PES in a lithium chloride/N,N-dimethylacetamide (LiCl/DMAc) co-solvent system. A rheological study indicated that the MCC-containing casting solutions exhibited a significant increase in viscosity, which directly influenced the composite membrane’s pore structure. Compared to the pristine PES membrane, the composite membranes have a larger surface pore size, elongated finger-like structure, and presence of sponge-like pores. The water contact angle and pure water flux of the composite membranes indicated an increase in hydrophilicity of the modified membranes. However, the permeability of the composite membranes started to decrease at 3 wt.% MCC and beyond. The natural organic matter removal experiments were performed using humic acid (HA) as the surface water...

The removal of CrO 4 2− anions from aqueous solution using surfactant added hybrid powdered activated carbon (PAC) and crossflow microfiltration (CFMF) process was performed. Experimental runs were studied at various amounts of cetyl trimethyl ammonium bromide (CTAB) as cationic surfactant, PAC as adsorbent and CrO 4 2− ions in feed solution. CFMF unit was operated at constant values of the transmembrane pressure (150 kPa), crossflow velocity (1.18 m/s) and temperature (30 • C). Hybrid PAC/MF process performance was investigated in terms of CTAB and CrO 4 2− rejections and, the flux decline. It was shown that the flux declined with time and the rejections varied for various properties of feed solution. CTAB and CrO 4 2− rejections could be achieved as 91 and 97.2% at the conditions of 0.5 g PAC/L, 5 mM CTAB, 0.2 mM CrO 4 2− and 120-min process time. It was found that over the critic micelle concentration (CMC), both CTAB and CrO 4 2− rejections were in the higher values according to the values under the CMC. In addition, membrane blocking mechanisms were investigated to clarify the cake formation mechanism due to PAC. For all experimental conditions, the best results of blocking models obtained for cake filtration, intermediate blocking and standard pore blocking, respectively. It was understood that these blocking mechanisms occurred simultaneously on membrane surface in terms of high r 2 values. A cake layer formed on membrane surface (cake filtration). Pore entrance blocked partially due to particles bridging over pore opening (intermediate blocking). Free CTAB aggregates with or without CrO 4 2− anions, entered into the membrane pores, caused to a layer formation by adsorption and entrapment on the membrane's pore walls (standard pore blocking). Besides, cake resistance (R c), specific cake resistance (α), modified fouling index (MFI) and total dried solid mass of cake per unit membrane area (ω) were also determined to comprehend the reasons of clogging within the membrane and on the surface due to both CTAB aggregates and PAC, respectively. Membrane fouling (MFI) increased with the increasing of PAC, CTAB and CrO 4 2− amounts in feed solution. As a result, flux, rejections and fouling in membrane were shown as a dynamic function of PAC, CTAB and CrO 4 2− as the properties of the feed solution.

Membrane separation technology was proposed to confront the problem of inorganic dye pollutant treatment such as an indigosol dye. A modified ultrafiltration process known as micellar-enhance ultrafiltration (MEUF), was applied to remove three kinds of indigosol dye (Pink IR, Blue O4B, and vat brown). Surfactant at concentration above CMC was added to form micelle structure and solubilize the dye molecule in the feed solution. Maximum dye rejection was achieved by the MEUF of all three kinds of indigosol dye. The  rejection of indigosol pink IR, blue O4B, and brown VAT1 were 94,27%, 95,49% and 99,15%, respectively. In this research, it was found that the MEUF system leads to higher membrane flux, compared to the ultrafiltration system as shown in flux profiles. The difference was expected due to different dye molecular structure. Blocking mechanism was predicted by a mathematical model based on Hermia’s model and depicted a mechanism of complete blocking on most UF process and cake ...

In this work, polysulfone (PSF)-based ultrafiltration (UF) membrane with antibacterial and antifouling properties was prepared by the phase inversion technique. ZnO and eugenol were used as additives and introduced into the membrane matrix via the additive blending method. The additives could improve the performance of the PSF membrane due to their hydrophilic nature. The water contact angle (WCA) of the PSF membrane decreased from 67.7° ± 1.2° to 52.8° ± 0.8° when the additive loading was increased from 0 to 5%-wt. The PSF membrane with 5%-wt ZnO and 5%-wt eugenol had pure water permeability and humic substance rejection of 83.8 ± 3.7 L m−2 h−1 bar−1 and 95.6%, respectively. In addition, the additives were able to improve antifouling properties, e.g. a recovery ratio (FRR) of 85.4% and relative flux reduction ratio (RFR) of 30.2%. In the antibacterial assay, the membrane displayed 3 mm and 10 mm inhibition zones against Escherichia coli and peat water microorganisms, respectively, ...

The influence of various polymer concentrations on flux stability of polysulfone membranes was investigated. The polysulfone membrane was prepared by blending polysulfone in DMAc with 25%wt concentration of PEG400 and 4% wt concentration of acetone. It was found that the pure water flux was sharply decreased from 1230 to7 Lm-2 h-1 , when the polysulfone concentration was increased from 14% to 24%wt. Furthermore, the increase of polysulfone concentration also affects the fouling behavior of the membranes, in which almost of 90% of FRR was achieved by the addition of 18 %wt of polysulfone concentration. It was suggested that fouling formed on the membrane surface was dominated by reversible fouling, thus it could be easily cleaned by flushing method. In addition, the applied transmembrane pressure (TMP) also plays an important role in fouling behavior of polysulfone membrane. It was observed that irreversible fouling of organic matter was deteriorated by the increase of TMP, which contributed to the reduction of water flux. More stable membrane flux performance was achieved although it was operated at high TMP, when 20% wt concentration of polysulfone was added into membrane solution.

The present paper deals with the ultrafiltration (UF) of produced water using a polysulfone membrane. Membranes were prepared by the phase inversion technique using polysulfone (PSf) polymer base, poly vinyl pyrrolidone (PVP) additive and N-methyl-2-pyrrolidone (NMP) solvent. Prepared UF membranes were characterized by determining the surface morphology by scannaing electron microscopy (SEM), atomic force microscopy (AFM), porosity, (iii) water contact angle, equilibrium water content and pure water flux, whereas membrane performance was determined by measuring permeate flux and oil rejection using oily synthetic produced water. With the increase in trans-membrane pressure in the cell, the permeate flux increased significantly, but oil rejection showed a decreasing trend. The best UF membrane performance under different trans-membrane pressures was obtained by maintaining ≥90% oil rejection using an UF membrane with the following composition: PSf-15%, PVP-5% and NMP-80%.

Introduction Worldwide, the numerous challenges associated with inadequate access to safe drinking water are well known: 1.8 billion people use water contaminated with faecal pathogens [1] and 3 900 children die daily from diseases transmitted through unsafe water [2]. In Uganda, although piped water coverage has increased over the years, treatment of piped supplies is not guaranteed, and only 5 % of the population have access to a tap on their premises [3]. Residents without access to piped water use untreated sources, which are prone to contamination with enteric pathogens (Photo 1). As a result, 29 300 children die annually in Uganda from diarrhoeal diseases [4]. Ultrafiltration (UF) is a promising technology for decentralised water treatment in developing countries; yet, a major hindrance to long term operation of UF is membrane fouling. This leads to permeate flux losses, increased membrane cleaning routines and high operating costs. Several researchers have studied coagulation...

-L'influence des différents facteurs intervenant lors de la clarification d'un lactosérum d'emmental a été étudiée à "aide d'un plan d'expérience. Les facteurs étaient : la teneur en protéines totales (8-50 gokg-'), la teneur en calcium (0,4-4,2 gokg-'), la température initiale (2-30 OC), le pH (6,9-7,9) et la température finale (45-75 OC). Les réponses étudiées ont concerné la A Pierreet al upon optical density in Emmental clarified whey was initial calcium level followed by final temperature; initial temperature and pH had no significant etîects; total protein content had a depressive effect on clarification. Clarification of whey was performed for ail the protein contents investigated. A graphic representation of the optimal values of factors is presented for whey at 5 protein contents. Particle size of whey colloidal material responsible for Iight diffusion and opacity was measured by light scattering. Particles of 105-512 nm in diameter were predominant. In clarified whey, they disappeared and only small particles of 8 nm diameter were detected. The nature and composition of the different particles were not elucidated. Chemical analysis of treated whey and electrophoresis of proteins provided data for estimating the components in the precipitated material. Precipitation involved Ca, P including minerai P0 4 and organic P. The precipitation of f3-casein phosphopeptides of whey (PP5 and PP8) was demonstrated. The demonstration of milk fat globule membrane precipitation was not carried out; it was, however, observed that phospholipids were still present in clarified whey (qualitative analysis). whey 1clarification

La clarification du lactosérum doux de fromagerie a été étudiée en mettant à profit la propriété des lipoprotéines de s'agréger en présence de calcium ionisé sous l'effet d'un traitement thermique. L'examen systématique de la quantité de calcium ajoutée au lactosérum, du pH à maintenir, dans le mélange et de la température de thermisation (le temps de chambrage étant fixé à 20 s) a permis d'optimiser le procédé proposé c'est-à-dire I'obtention d'un lactosérum ayant une limpidité voisine de celle de l'ultra filtrat de <lait avec le minimum de pertes en protéines dans le sédiment. Ces pertes étaient limitées à environ 15 % des matières azotées initiales dans les conditions retenues, à savoir: ajout de 0,8 g.I::' de calcium (sous forme de CaClz), pH maintenu à 6,0 et température de traitement fixée à 78-79°C. L'agrégation et la réduction d'hydrophilie des complexes lipoprotéiques sous l'effet du traitement proposé entraîne leur décantation rapide à basse température. L'analyse des surnageants et des sédiments a permis de montrer que 80 % de la t1-lactoglobuline et 85 % de l'a-lactalbumine initialement présentes dans le lactosérum, restaient solubles dans le produit clarifié. Le lactosérum clarifié constitue une matière première idéale pour la préparation de boissons aromatisées ou pour la préparation d'une base pâtissière à pouvoir moussant très élevé. Du fait de sa composition et de ses propriétés fonctionnelles, notamment émulsifiantes, le sédiment devrait, aussi, quant à lui trouver de nom

Ultrafiltration of bovine serum albumin solutions using cellulose triacetate (CTA) and regenerated cellulose (RC) membranes showed that CTA membranes were more vulnerable to fouling than hydrophilic RC membranes. The flux decline for both membranes, which was more significant initially, could be attributed to concentration polarization near membrane surfaces and adsorption of the protein. Fouling of the membranes was characterized by the resistance of protein deposits to the permeation of pure water through fouled membranes. The CTA membranes gave more resistant protein deposits than the RC membranes and the resistance increased, two to three times, in the presence of salts but decreased substantially at higher temperatures.

Membrane technology has revolutionized the dairy sector. Different types of membranes are used in the industry for various purposes like extending the shelf life of milk without exposure to heat treatment, standardization of the major components of milk for tailoring new products as well increasing yield and quality of the dairy products, and concentrating, fractionation and purification of milk components especially valuable milk proteins in their natural state. In the cheese industry, membranes increase the yield and quality of cheese and control the whey volume, by concentrating the cheese milk. With the advancement of newer technology in membrane processes, it is possible to recover growth factor from whey. With the introduction of superior quality membranes as well as newer technology, the major limitation of membranes, fouling or blockage has been overcome to a greater extent.

Pineapple is a very appreciated tropical fruit due to its unique aroma and flavour. Pineapple juice was cold sterilised and clarified by crossflow microfiltration associated with an enzymatic treatment. A tubular polyethersulfone 0.3 pm pore size membrane with effective filtration area of 0.05 m* was used in the pilot system. Ten experiments were carried out under the same operational conditions, 25°C and 100 kPa, in order to evaluate the cold sterilisation and clarification of pineapple juice by microfiltration. It was observed that the permeate flux did not change significantly after fifteen minutes of processing time. It was stabilised around 100 L/hm'. The clarification process was considered very efficient due to the great reduction of haze and viscosity, and by showing no significant changes in pH, acidity, sugar and soluble solid content of the juice. The permeate of the process was collected in sterile bottles inside a laminar flow station and kept under refrigeration (8°C) for a period of 28 d. The samples were submitted to microbiological evaluations in intervals of seven days. The microbiological analysis of the microfiltered pineapple juice showed that it was in agreement with the requirements by the Brazilian Legislation for juices and drinks.

Reverse osmosis technique was applied in removing hexavalent chromium ions from artificial wastewater. Different operating conditions were studied to monitor the separation process using commercial Reverse Osmosis BW30XFR membrane. Different concentrations of hexavalent chromium; 5, 30, and 100 ppm were tested. Samples were subjected to incrementally increasing operating pressure; 10, 30, and 45 bar and flow rates; 2.2, 3.4, and 4.5 L/min under various temperatures; 25, 35, 45, and 55 °C. Collected permeate and concentrations were measured after each experiment using a UV spectrophotometer. Results obtained presented a higher rejection percentage at lower feed concentrations with a value up to 99.8% for 5 ppm in comparison to 94.3% for 30 ppm and 77.2% for 100 ppm concentration due to concentration polarization; however, it showed no effect of increasing operating flow rates. Moreover, the increase in feed temperature from 25 to 55 °C had positively increased permeate flux to more t...

In this paper, various parameters such as pressure, pH, and concentration levels were investigated. The Cr(VI) and sulfate concentrations chosen for the study were the same as the levels found in drinking water sources. The results indicated that a better rejection of Cr(VI) (96%) was obtained at basic pH and at an optimal pressure of 4 bar in 0.1 mg/L and no significant effect was found between 4 and 8 bar in 0.5 mg/L concentrations. Permeate fluxes were 12.8 and 10.53 L/m 2 h at 4 bar in 0.1 and 0.5 mg/L concentrations, respectively. In the presence of a fixed sulfate concentration, fluxes declined with the increasing ionic strength of Cr(VI) feed solutions. The simultaneous rejection of sulfate and Cr(VI) (varying from 90% to 100%) showed that the influences of the ionic strength of a mixed aqueous solution were found to be weak at the selected concentrations of both Cr(VI) and sulfate. The experiments also showed that the rejection was affected more by the ion strength of Cr(III) than by Cr(VI). To demonstrate the fate of the ions rejected, a mass balance analysis was developed under optimal experimental conditions.

The classical theory for the interactions between colloidal particles is the DLVO theory in which the interaction is presumed to consist of a repulsive long range electrostatic term and an attractive short range dispersion term. One important missing term is the e ect of the depletion force (known in the statistical mechanics community as the volume exclusion force). An approximate description of this term was obtained by Henderson and Lozada Cassou (HCL) from the theory of hard sphere mixtures. There has been some controversy about the manner in which this term was obtained. Some aspects of this question are discussed and an account of some recent work that has settled this controversy and that justi es the original result of HLC are reviewed.

Ion transport characteristics during nanofiltration (NF) were investigated by measuring effective osmotic pressure and diffusivity experimentally. Effective osmotic pressure and diffusivity were measured through lab-scale transport and diffusion tests. First, it was shown that the water flux across NF membranes decreased dramatically with increasing ionic strength because of the noticeable increase in effective osmotic pressure. Second, the results from transport experiments showed that the ion selectivity values, which were derived from the thermodynamic model, decreased with increasing ionic strength. Third, by analysing the data of measured osmotic pressure and diffusivity, it was demonstrated that the former and the latter increased and decreased, respectively, as ionic strength increased. The experimentally determined osmotic pressure across NF membranes was much lower than that calculated theoretically. At best, around 5% or less of the theoretical osmotic pressure was obtained under the experimental conditions investigated. The effective osmotic pressure and ion rejection decreased in the presence of nano-colloids. The influence of nano-colloids on ionic transport was found to be dependent on the concentration and size of the nano-colloids. Therefore, ion transport characteristics across NF membranes can be determined practically by measuring effective osmotic pressure and diffusivity as these reflect both feed water and membrane properties.

Introduction Worldwide, the numerous challenges associated with inadequate access to safe drinking water are well known: 1.8 billion people use water contaminated with faecal pathogens [1] and 3 900 children die daily from diseases transmitted through unsafe water [2]. In Uganda, although piped water coverage has increased over the years, treatment of piped supplies is not guaranteed, and only 5 % of the population have access to a tap on their premises [3]. Residents without access to piped water use untreated sources, which are prone to contamination with enteric pathogens (Photo 1). As a result, 29 300 children die annually in Uganda from diarrhoeal diseases [4]. Ultrafiltration (UF) is a promising technology for decentralised water treatment in developing countries; yet, a major hindrance to long term operation of UF is membrane fouling. This leads to permeate flux losses, increased membrane cleaning routines and high operating costs. Several researchers have studied coagulation...

Ultrafiltration is widely used for separation and purification of several biomolecules from various sources. However, the performance of ultrafiltration in terms of transmembrane flux, yield and purity vary with biomolecule and process parameters. In the present study, ultrafiltration was employed for the purification of R-Phycoerythrin from marine macroalga Gelidium pusillum. Parameters such as molecular weight cutoff (30, 50, 100 and 300 kDa), transmembrane pressure (1, 2 and 4 bar), pH (4, 5, 6 and 7), and ionic strength (control, 0.5 and 1.0 M) were standardised. Ultrafiltration in diafiltration mode and its integration with ammonium sulphate precipitation and aqueous two-phase extraction was also carried out to maximise R-PE purity. In-situ ultrasonication was employed to enhance the transmembrane (permeate) flux. Permeate flux was evaluated employing Hermia's model to have insight and understand membrane fouling that occurs during ultrafiltration. Integration of ammonium sulphate precipitation followed by diafiltration and aqueous two-phase extraction has resulted in 17 fold enrichment in R-PE purity with 61% yield and removal of more than 95% of soluble sugars. In-situ ultrasonication has resulted in increase of transmembrane flux by 10% to 47 L/m 2 /h. Hermia's model based analysis of permeate flux has revealed that cake formation is the predominant type of fouling.

This study presents the development of a simple correlation between modified fouling index (MFI) and crossflow sampler-modified fouling index (CFS-MFI) to assess fouling potential of feed under constant flux mode. The study was carried out using a bench-scale experimental setup with variables including crossflow effect, feed concentration, particle types and sizes, and the intrinsic resistance of membrane. From the forty-eight experimental data, upper and lower bounds of the correlation between MFI const.flux and CFS-MFI const.flux were successfully established. The permissible range of coefficient (1.007 ≤ m ≤ 1.561) for the correlation was further verified by the dataset reported in previous study.

The present paper deals with the ultrafiltration (UF) of produced water using a polysulfone membrane. Membranes were prepared by the phase inversion technique using polysulfone (PSf) polymer base, poly vinyl pyrrolidone (PVP) additive and N-methyl-2-pyrrolidone (NMP) solvent. Prepared UF membranes were characterized by determining the surface morphology by scannaing electron microscopy (SEM), atomic force microscopy (AFM), porosity, (iii) water contact angle, equilibrium water content and pure water flux, whereas membrane performance was determined by measuring permeate flux and oil rejection using oily synthetic produced water. With the increase in trans-membrane pressure in the cell, the permeate flux increased significantly, but oil rejection showed a decreasing trend. The best UF membrane performance under different trans-membrane pressures was obtained by maintaining ≥90% oil rejection using an UF membrane with the following composition: PSf-15%, PVP-5% and NMP-80%.

In order to recover cadmium ion from wastewater, a process based on enhanced ultrafiltration was finalised. The originality of the solution here proposed lies on the coupled use of ceramic membranes and of a surfactant added to the water to be treated. This paper deals with the study of the influence of experimental conditions upon permeation flux and selectivity of the separation. The process is efficient and flexible since a single stage treatment allows to reduce the concentration of cadmium in the effluent by a factor of about 750; this high performance in selectivity is on a par with high fluxes of permeate (roughly 170 L.h.−1.m−2 at 25°C and 3 × 105 Pa).

-Le phosphocaséinate natif (PPCN) était séparé du lait cru par microfiltration tangentielle sur membrane (diamètre des pores: 0,2 l1m) suivie d'une purification par diafiltration avec de l'eau. Le suivi analytique des liquides obtenus de part et d'autre de la membrane montrait une perméation conforme aux lois de la filtration des protéines majeures du lactosérum (j3-lactoglobuline et a-lactalbumine), du lactose et des sels minéraux solubles et au contraire, une rétention élevée des composants solubles à haut poids moléculaire ainsi que des protéoses-peptones. Le rétentat final était séché par atomisation. Ses teneurs en matière azotée (N x 6,38) et en cendres étaient respectivement de 89% et de 9% par rapport à la substance sèche. L'aptitude à la coagulation par la présure, de la solution reconstituée a été comparée à celle du lait cru. Le temps de coagulation est réduit de 53%; la cinétique d'organisation du. gel (appréciée par le K2Q) et la fermeté finale (appréciée à 30 min) sont également accrues de plus de 50%. La propriété de former un gel sous l'action de la présure après un traitement thermique de 100 oC-5 min est conservée, contrairement au lait qui, soumis au même traitement, ne coagule plus. microfiltration 1 phosphocaséinate 1 coagulation présure 1 traitement thermique Summary-Native micellar casein separation through cross flow membrane microfiltration. Native phosphocaseinate (PPCN) was separated from raw milk by tangential membrane microfiltration (pore diameter: 0.2 um) followed by purification through water diafiltration. Analytical survey of both tiquids issued by membrane treatment showed permeation rates matching mathematical laws for the main whey proteins (fJ-lactoglobulin and a-Iactalbumin), lactose and soluble mineraI salts. On the contrary, a high retention of high molecular weight soluble components and proteose-peptone fraction was observed. Finaldiafiltratedretentate was spray-dried. Its protein (N x 6.38) and ash contents in total solids were respectively 89% and 9%. Rennet coagulating ability of PPCN reconstituted solution was compared to that of raw milk. Coagulation time was reduced by 53%; gel development kinetics (estimated by Krol and final firmness (estimated at 30 min) were increased by more than 50%. When a severe heat treatment (100 oC-5 min) was applied, milk lost its ability to coagulate alter rennet action; PPCN solution did not, but ifs coagulation time was increased and the curd was slightly weaker.

Crossflow microfiltration experiments were performed on aqueous dispersions of rutile (titanium dioxide) through a 0.1 pm pore size ceramic membrane at various operating parameters. The initial transient flux decline follows deadend filtration theory, with the membrane resistance determined from the initial flux and tbe cake resistance determined from the rate of flux decline due to cake build-up. For a long time, the observed fluxes reached steady or nearly steady-state values, presumably as a result of the cake growth being arrested by the shear exerted at its surface. The steady-state fluxes increase with increasing inlet crossflow velocity and decreasing feed concentration. The steadystate permeate flux values were determined from the steady-state model based on the Kozeny-Carman equation for cake resistance and Darcy's law applied over the filter area to relate filtration rate to average pressure difference between the feed and permeate sides of the filter. The model includes a cake resistance of the cake layer, which was determined for the titanium dioxide dispersions by fitting the experimental flux data to the model. The apparent viscosity of the dispersion, which is an input parameter in the tlux model, is also adjusted to account for a model of the Herschel-Bulkley type. The resulting fluxes obtained from the model using simple values for the membrane resistance, cake resistance, and rheological parameters for each data set are in good agreement with the measured fluxes. Q 1998 Elsevier Science S.A.

The one-electron oxidation of N-methylphenothiazine in anionic, cation&and non-ionic micellar systems and in a water-methylene chloride microemulsion has been studied and correlated wrth cation radical stability followed by absorbancedecay and solute location shown by uv spectra. The NMeP/NMeP' redox couple keeps the same reversibility character in all the media studied without indication of specific adsorption or coupled chemical reaction. The oxidation potential shifts are explained as resulting from an increase or adecrease in the radical cation stability according to the properties of its microenvironment in the solutions. The presence of an hydrophobic barrier arising when the solute is located in the hydrocarbon core of the micelles or droplets is assumed. INTRODUCTiON Surfactant micelles, emulsions and microemulsions may provide a new medium for solubilising water insoluble compounds.

The sorption of seven endocrine disrupting chemicals (EDCs) to aquatic colloids was determined by cross-flow ultrafiltration (CFUF) followed by gas chromatography-mass spectrometry (GC-MS). Results show that the colloidal organic carbon normalized sorption coefficient (K coc) of EDCs to different aquatic colloids varies by a factor of 6-12 because such colloids are of different origin. Through characterization of colloidal samples, a significant relationship was established between K coc values and the molar extinction coefficient of colloids at 280 nm, whereas no other colloidal properties such as elemental ratios were correlated with K coc values. The results are consistent with other reports of the importance of the quality of sorbents such as their aromatic carbon content in sorbing various organic pollutants. The presence of a surfactant was found to increase K coc values for estrone (E1) and 17Rethynylestradiol (EE2). The method was subsequently applied for determining EDC concentrations in field samples, where both conventional and truly dissolved EDCs showed higher concentrations close to sewage outfalls than either upstream or downstream, confirming the sourceconcentration relationship. In addition, the truly dissolved EDC concentrations were lower than the conventional dissolved concentrations, confirming that there were interactions between aquatic colloids and EDCs. It is estimated that between 10 and 29% of EDCs are associated with aquatic colloids. As colloids are highly abundant in rivers and ocean, they will therefore play a significant role in the environmental behavior and fate of EDCs.

Cross-flow ultrafiltration (CFUF) was developed first for the isolation of natural colloids and subsequently for determining the partition of selected endocrine-disrupting chemicals (EDCs) between river colloids and dissolved phase. In this study, a 1-kDa Millipore Pellicon 2 cartridge type CFUF system was validated using a range of molecular probes spiked in natural waters. Results show that good retention (>80%) of high molecular weight (HMW, >1 kDa) molecules and low retention of low molecular weight (LMW, <1 kDa) molecules can be achieved at high concentration factor (cf) values in sampling mode or over long time scales in recirculation mode. The interactions between aquatic colloids and EDCs were studied by mixing EDCs, water, and colloids previously isolated by CFUF for a certain duration, followed by the separation of the target compounds between the truly dissolved and colloidbound phases by CFUF and analysis by gas chromatographymass spectrometry (GC-MS). The kinetics of EDCs binding to colloids were relatively rapid, reaching equilibrium within 5 min. The mass balance of chosen EDCs through CFUF system was fully investigated, with good recovery for the relatively polar EDCs such as estrone and 17estradiol. On the basis of EDC sorption by colloids, the partition coefficient normalized to colloidal organic carbon content (K coc) was 8.85 × 10 3 , 1.50 × 10 4 , 8.85 × 10 3 , 4.87 × 10 4 , and 1.59 × 10 4 mL/g for bisphenol A, estrone, 17estradiol, 17R-ethynylestradiol, and 16R-hydroxyestrone, respectively, which are comparable with the values reported in the literature. In addition, it has been shown that the K coc values of EDCs were relatively independent of their octanol-water partition coefficient (K ow) values, suggesting the important role of different binding mechanisms other than nonspecific hydrophobic interaction between EDCs and natural colloids. As the CFUF-GC-MS method can be used to quantify very low concentration of pollutants and is not limited to fluorescent compounds, it has the potential to be a widely applicable separation/analytical tool for determining the partition of organic pollutants between colloidal materials and dissolved phase.

Ultrafiltration and nanofiltration membranes that are traditionally used in baromembrane processes have become increasingly frequently applied in electromembrane and baroelectromembrane processes. In the latter case, two driving forces, an electric field and a pressure gradient, are simultaneously used. This study presents data on the specific electrical conductivity, diffusion permeability, and transport numbers of ions as well as current-voltage characteristics and chronopotentiograms of AMN-P and OPMN-P weakly ionized nanofiltration membranes and a number of track membranes in solutions of NaCl and CaCl 2. The relationship of obtained characteristics with the structure and exchange capacity of membranes is discussed. It is shown that both nanofiltration and track membranes can exhibit a quite high selectivity towards the electrical transport of ions with a certain charge sign. Such selectivity is especially high in respect of the transport of Ca 2+ ions. In the case of an AMN-P membrane, the transport number of Ca 2+ reaches 0.98, while it is noticeably lower for Na + ions. This result correlates well with a known fact about a higher rejection coefficient of doubly charged ions in comparison with singly charged ions in baromembrane processes. Track membrane #115 is also distinguished by high selectivity in respect of cations, the transport number of sodium ions in it is close to 0.96.

The treatment of a rejection of tannery effluent was carried out on an organic nanofiltration membrane. The rejection was recovered from a leather manufacturing plant in the area of Algiers (Rouiba). The effluent of the bath of tanning and liming charged with chromium ions was the subject of this study. In the case of synthetic solutions, the experimental variations of the retention ranged from 94-99.9% depending on initial feed concentration. For the tanning bath, the results indicated that chromium retentions of 60 and 30% were observed respectively in acid and basic medium. In acid medium, the rejection of the bath of liming has generated a retention of 15%. The use of the model of Nakao et al. [1] based on the extended modified Nernst Planck equation enabled us to compare the theoretical retention of chromium ions with the experimental results and to calculate the membrane pore radius.

Real-time measurement Membrane fouling characterization Nanofiltration (NF) membranes have found more frequent use in recent years for the desalination of seawater and other sources of brackish water because they can be used at lower pressures than more traditional reverseosmosis (RO) technologies, and thus provide overall energy savings. However, membrane fouling still presents a common and significant challenge in practical applications. Currently, the performance of membrane-based liquid separation processes is most often monitored by external, volumetric flow-based techniques that provide delayed information on fouling layer development. The delay between initial growth and the observation of fully established fouling reduces the efficacy of cleaning and remediation measures. The focus of this study is the use of ultrasonic time-domain reflectometry (UTDR) as a non-destructive method for real-time, in-situ monitoring of early-stage inorganic scaling layer formation on NF membranes. This work utilizes miniature-scale ultrasonic transducers that are internally integrated into a flat-sheet cross-flow filtration module and in contact with the membrane. Comparisons are made with results obtained from externally mounted UTDR transducers, a more commonly used arrangement. Results show that while the internal sensors can be somewhat more sensitive, the significance of this improvement can be negated by scaling deposition that is hindered by the presence of the sensor.

The paper presents the results of water treatment investigation, using UF/MF and a hybrid process coagulation-UF/MF. The experiments were conducted using capillary modules made of polyethersulfone (PES) for ultrafiltration and of polypropylene (PP) for microfiltration. Two coagulants, i.e. iron chloride (FeCl 3-6H 2O) and aluminum sulfate (A1 2(SO 4)3-18H 2O), were used during the coagulation. The hybrid water treatment process was carried out in coagulation-sedimentation-MF/UF and &quot;in-line&quot; coagulation (without sedimentation)-MF/UF systems. Unlike a direct UF/MF, the hybrid processes allow an improvement in water quality and reduction in fouling intensity. UF efficiency can be predicted employing relaxation and resistance models. The mechanism of fouling based on Hermia&#39;s equation was determined.

Our paper presents the results of investigations on the treatment of waters involved in unit process ultrafiltration, hybrid process-coagulation/sedimentation/ultrafiltration and in-line coagulation/ultrafiltration. in membrane filtration that we applied immersed capillary membranes. simulated water containing humic acids at 30 mg/l was ultrafiltered with a constant volumetric permeate flux amounting to 5.7×10-6 m 3 /m 2 •s. Four coagulants were tested, for which the optimal process parameters were determined experimentally. We determined the effectiveness of ultrafiltration and that of the hybrid system coagulation-membrane filtration, basing on measurements of the membranes' yield (permeate flux) and physico-chemical analysis of raw water and permeates. Also residual concentration of metal ions (Al and Fe) in permeates were determined. The application of the hybrid system, combining coagulation and ultrafiltration, offers better effects of the removal of organic pollution.

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