| 1. |
- Brinck, J, et al.
(författare)
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Influence of pH on the adsorptive fouling of ultrafiltration membranes by fatty acid
- 2000
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Ingår i: Journal of Membrane Science. - 0376-7388 .- 1873-3123. ; 164:1-2, s. 187-194
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Tidskriftsartikel (refereegranskat)abstract
- Fatty acids are found in many solutions treated in ultrafiltration plants, for example, in dairy products, fermentation broth, oily waste water and bleach plant effluents from pulp mills. The influence of fatty acids on the fouling of membranes is often ignored because their concentration is rather low. However, during recent years the significant influence of fatty acids on the flux reduction of ultrafiltration membranes has attracted much attention. The pore radius of the membrane, the concentration of fatty acids and the pH of the solution all have a profound influence on the flux reduction when treating solutions containing fatty acids. In the work presented in this paper, the influence of pH on the flux reduction of an ultrafiltration membrane made of polyethersulphone was studied. It was found that there was no flux reduction under alkaline conditions, whereas the flux reduction under acidic conditions was severe. In order to elucidate the adsorption process, the adsorption of octanoic acid on a planar, hydrophobized silica surface was studied by means of in situ null ellipsometry. In the ellipsometry study a sharp increase in the amount adsorbed was observed when the concentration of undissociated acid approached the saturation concentration as the pH was decreased. This explains the observed flux reduction under acidic conditions. (C) 2000 Elsevier Science B.V. All rights reserved.
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| 2. |
- Byhlin, Henric, et al.
(författare)
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Influence of adsorption and concentration polarisation on membrane performance during ultrafiltration of a non-ionic surfactant
- 2003
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Ingår i: Desalination. - 1873-4464. ; 151:1, s. 21-31
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Tidskriftsartikel (refereegranskat)abstract
- Surfactants are present in almost all aqueous solutions-either as additives for different purposes, or because they occur naturally. Because of the common occurrence of surfactants in process water it is important to know how they behave in membrane processes. Ultrafiltration membranes allow almost complete passage of surfactant monomers, but reject micelles almost completely. Concentration polarisation during ultrafiltration of surfactant solutions is therefore mainly influenced by the presence of micelles. Operating parameters, e.g. the transmembrane pressure and the concentration of surfactant, as well as the pure water flux of the membrane, have a marked influence on the performance of hydrophilic membranes, as shown in this investigation. A distinct difference between the interaction of a non-ionic surfactant with hydrophilic and hydrophobic membranes was observed. The hydrophobic membrane showed a flux reduction already at concentrations below the critical micelle concentration (CMC), whereas no flux reduction was observed for a hydrophilic membrane with the same nominal molecular weight cut-off, below the CMC.
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| 3. |
- Falth, F, et al.
(författare)
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Ultrafiltration of effluents front chlorine-free, kraft pulp bleach plants
- 2001
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Ingår i: Desalination. - 1873-4464. ; 133:2, s. 155-165
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Tidskriftsartikel (refereegranskat)abstract
- Ultrafiltration has proven to be a useful technology for treating alkaline bleach plant filtrates in sulphite pulp mills. In this investigation the treatment of seven alkaline filtrates from kraft pulp mills were studied. The results include high fluxes and fair, or even good, removal of organic, as well as inorganic, substances. The flux seems to depend on the concentration of the bleach plant filtrate rather than its origin. The factor with the largest impact on flux is conductivity, i.e., the concentration of the low-molecular-weight inorganic substances. The retention of organic substances varies depending on the type of filtrate and the water management system of the mill. The retention is highest when treating filtrates from the first alkaline stage from traditional ECF mills. Filtrates from modem ECF and TCF mills contain a larger fraction of low-molecular-weight substances, which are not retained as efficiently. The treatment not only reduces the organic content of the filtrates but also increases the fraction that is biodegradable. The membranes retain a rather large fraction of the multi-valent ions, while the monovalent ions are let through.
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| 4. |
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| 5. |
- Into, M, et al.
(författare)
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Reuse of industrial wastewater following treatment with reverse osmosis
- 2004
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Ingår i: Journal of Membrane Science. - : Elsevier BV. - 0376-7388. ; 242:1-2, s. 21-25
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Tidskriftsartikel (refereegranskat)abstract
- The Perstorp, industrial park in southern Sweden is faced with water shortage problems. One way to reduce these problems is through the reuse of recycled water. In this paper the results of treating 240 m(3) per day wastewater in a reverse osmosis (RO) plant are presented. High-quality water, which is used as make-up water in cooling towers, is produced from a difficult and varying feed. Severe fouling problems during the first year of operation have been solved and the reliability of the RO plant is now good. The only pretreatment employed before the RO plant is a bag filter. Despite no cleaning of the membranes, the membrane lifetime is 16 months, which means that RO treatment is economically feasible. The savings made by using the RO plant emanate from reduced use of fresh water and lower discharge charges. (C) 2004 Elsevier B.V. All rights reserved.
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| 6. |
- Lindstrand, V, et al.
(författare)
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Fouling of electrodialysis membranes by organic substances
- 2000
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Ingår i: Desalination. - 1873-4464. ; 128:1, s. 91-102
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Tidskriftsartikel (refereegranskat)abstract
- In this investigation, the influence of various kinds of organic solutes on the fouling of an anion and a cation selective ED membrane was studied. Fouling by adsorption of organic matter onto the membrane was measured as an increase in the membrane resistance with time. Experiments were performed with a fatty acid (octanoic acid), two anionic surfactants (sodium octanoate and sodium dodecylbenzene sulphonate) and an alkaline bleach plant filtrate from a sulphate pulp mill. A marked difference was observed between the increase in the membrane resistance of the anion selective membrane and that of the cation selective membrane. The cation selective membrane was slightly fouled by the bleach plant filtrate, but was only marginally affected by the other organic solutes. The anion selective membrane, on the other hand, was markedly fouled by all solutes.
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| 7. |
- Lindstrand, V, et al.
(författare)
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Organic fouling of electrodialysis membranes with and without applied voltage
- 2000
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Ingår i: Desalination. - 1873-4464. ; 130:1, s. 73-84
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Tidskriftsartikel (refereegranskat)abstract
- In this investigation organic fouling of ED membranes was studied with and without applied voltage. Fouling without the application of voltage, i.e., adsorption, was observed as an increase in the membrane resistance, and fouling with the application of voltage, i.e., conventional ED, was observed as an increase in the voltage drop across the membrane. Experiments were performed with three different carboxylic acids (propanoic, octanoic and decanoic acid) and an alkaline bleach plant filtrate from a sulphate pulp mill. An anion-selective (Selemion AMV) and a cation-selective (Selemion CMV) membrane were used in the investigation. A significant difference was observed between the fouling of the two membranes. The membrane resistance and voltage drop across the cation-selective membrane did not increase in any of the experiments, i.e., the cation-selective membrane was not fouled. The anion-selective membrane, on the other hand, was fouled by all solutes except sodium propanoate.
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| 8. |
- Persson, A, et al.
(författare)
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Conversion of sodium lactate to lactic acid with water-splitting electrodialysis
- 2001
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Ingår i: Applied Biochemistry and Biotechnology. - 1559-0291. ; 94:3, s. 197-211
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Tidskriftsartikel (refereegranskat)abstract
- The conversion of sodium lactate to lactic acid with water-splitting electrodialysis was investigated. One way of reducing the power consumption is to add a conductive layer to the acid compartment. Doing this reduced the power consumption by almost 50% in a two-compartment cell, whereas the electric current efficiency was not affected at all. Three different solutions were treated in the electrodialysis unit: a model solution with 70 g/L of sodium lactate and a fermentation broth that had been prefiltered two different ways. The fermentation broth was either filtered in an open ultrafiltration membrane (cut-off of 100,000 Dalton) in order to remove the microorganisms or first filtered in the open ultrafiltration membrane and then in an ultrafiltration membrane with a cut-off of 2000 Dalton to remove most of the proteins. The concentration of sodium lactate in the fermentation broth was 70 g/L, as well. Organic molecules present in the broth (peptides and similar organic material) fouled the membranes and, therefore, increased power consumption. Power consumption increased more when permeate from the more open ultrafiltration membrane was treated in the electrodialysis unit than when permeate from the membrane with the lower cut-off was treated, since there was a higher amount of foulants in the former permeate. However, the electrodialysis membranes could be cleaned efficiently with a 0.1 M sodium hydroxide solution.
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| 9. |
- Persson, A, et al.
(författare)
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Separation of lactic acid-producing bacteria from fermentation broth using a ceramic microfiltration membrane with constant permeate flow
- 2001
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Ingår i: Biotechnology and Bioengineering. - 1097-0290. ; 72:3, s. 269-277
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Tidskriftsartikel (refereegranskat)abstract
- The influence of several operating parameters on the critical flux in the separation of lactic acid-producing bacteria from fermentation broth was studied using a ceramic microfiltration membrane equipped with a permeate pump. The operating parameters studied were crossflow velocity over the membrane, bacterial cell concentration, protein concentration, and pH. The influence of the isoelectric point (IEP) of the membrane was also investigated. In the interval studied (5.3-10.8 m/s), the crossflow velocity had a marked effect on the critical flux. When the crossflow velocity was increased the critical flux also increased. The bacterial cells were retained by the membrane and the concentration of bacterial cells did not affect the critical flux in the interval studied (1.1-3.1 g/L). The critical flux decreased when the protein concentration was increased. It was found that the protein was adsorbed on the membrane surface and protein retention occurred even though the conditions were such that no filter cake was present on the membrane surface. When the pH of the medium was lowered from 6 to 5 land then further to 4) the critical flux decreased from 76 L/m(2)h to zero at both pH 5 and pH 4. This was found to be due to the fact that the lowering in pH had affected the physiology of the bacterial cells so that the bacteria tended to adhere to the membrane and to each other. The critical flux, for wheat flour hydrolysate without particles, was much lower (28 L/m(2)/h) when using a membrane with an IEP of 5.5 than the critical flux of a membrane with an IEP at pH 7 (96 L/m(2)h). This was found to be due to an increased affinity of the bacteria for the membrane with the lower IEP. (C) 2001 John Wiley & Sons, Inc.
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| 10. |
- Persson, Anna, et al.
(författare)
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Transmission of BSA during Cross-flow Microfiltration: Influence of pH and Salt Concentration
- 2003
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Ingår i: Journal of Membrane Science. - 0376-7388. ; 223:1-2, s. 11-21
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Tidskriftsartikel (refereegranskat)abstract
- In many downstream processes microfiltration (MF) is used as the first step to separate the micro-organisms from the product-containing broth. The transmission of proteins through these MF membranes is of great importance, especially when a protein is the desired product. Usually, the largest fraction of the proteins retained in the membrane during the separation of micro-organisms is retained in the filter cake of micro-organisms that is built up on the membrane surface. However, this is not always the case. In some cases the transmission of proteins can decrease below 100% even though there are no micro-organisms present in the broth. In the present study the transmission of BSA through two different MF membranes (a nylon membrane, Pall Filtron Ultipore, Nylon66, 0.2 m, and a membrane made of polyether sulphone, Pall Filtron, Omega, 0.16 m) was investigated. The transmission of BSA was highest for the membrane that was said to be a low protein binding membrane (Omega) and it was affected by the pH in the solution. At pH 5, which is close to the IEP of the protein, the transmission was 100%, while at pH 3 and 7 the transmission was much lower (sometimes as low as 40%). However, when the ionic strength in the solution was increased the transmission of BSA through both MF membranes increased dramatically (at pH 3 and 7). This shows that the electrostatic interactions between the protein and the filter cake (made up of protein aggregates) and between the protein and the membrane affect the transmission. The increase in transmission when the protein is close to its IEP (at pH 5), is believed to be due to the lack of electrostatic repulsion between the proteins in the solution and filter cake of protein aggregates formed on the membrane. At high ionic strength the charged protein molecules are shielded from each other and from the membrane and the filter cake, by the ions in the solution. Due to this shielding effect the protein molecules act as if they were uncharged and the transmission of BSA is thus increased.
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