| 1. |
- Jönsson, Ann-Sofi, et al.
(författare)
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Colloidal fouling during ultrafiltration
- 1996
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Ingår i: Separation Science and Technology. - : Informa UK Limited. - 0149-6395 .- 1520-5754. ; 31:19, s. 2611-2620
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Tidskriftsartikel (refereegranskat)abstract
- Colloidal fouling causes serious problems in many membrane plants. Two different kinds of flux-reducing phenomena occur when treating colloidal dispersions, When treating stable dispersions the flux is reversible and can be restored after changing the operating parameters, such as the transmembrane pressure or the crossflow velocity. The flux reduction experienced when treating unstable colloidal dispersions is irreversible. In this study the DLVO theory, well-known from colloid chemistry, has been used to illustrate the mechanisms underlying the difference in filtration characteristics between stable and unstable colloidal dispersions.
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| 2. |
- Jönsson, Ann-Sofi, et al.
(författare)
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Influence of the concentration of a low-molecular organic solute on the flux reduction of a polyethersulphone ultrafiltration membrane
- 1997
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Ingår i: Journal of Membrane Science. - 0376-7388. ; 135:1, s. 117-128
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Tidskriftsartikel (refereegranskat)abstract
- Drastic flux reductions are sometimes encountered during ultrafiltration of solutes much smaller than the membrane pores. This usually occurs during ultrafiltration of hydrophobic, low-molecular solutes, such as fatty acids, alcohols and alkanes. The influence of the concentration of a carboxylic acid, octanoic acid, on the flux of a polyethersulphone membrane was studied in this investigation. The concentration was found to have a marked influence on the flux. The flux reduction was moderate at low concentrations, but became severe above a certain, critical concentration. Two fur-reducing mechanisms were evaluated; reduction of the effective pore radius by adsorption of solute molecules on the pore walls, and blocking of pores by capillary condensation. The adsorption of octanoic acid on a hydrophobic solid surface was studied by null ellipsometry.
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| 3. |
- Jönsson, Ann-Sofi, et al.
(författare)
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Ultrafiltration of colloidal dispersions - A theoretical model of the concentration polarization phenomena
- 1996
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 1095-7103 .- 0021-9797. ; 180:2, s. 504-518
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Tidskriftsartikel (refereegranskat)abstract
- A general thermodynamic model of the concentration polarization phenomena of colloidal particles at a membrane surface is presented. The model is based on the balance between a thermodynamic force, due to the osmotic pressure gradient, and a frictional force, due to the fluid flow around each particle. A cell model description is used to model the concentration dependence of the thermodynamic force as well as the how properties in the concentrated colloidal solution. Equilibrium thermodynamics of the colloidal system can be used in the cell calculations since local equilibrium is assumed in the neighborhood of each colloidal particle (i.e., in each cell). This means that the concentration dependence of the osmotic pressure can be obtained, either from an experimental determination or from a theoretical model of the bulk properties of the colloidal system. To exemplify the usefulness of the model when establishing the influence of different operating parameters, such as the transmembrane pressure, the fluid shear, or different solution properties, such as concentration, particle size, pH, and ionic strength, a model system of charged spherical colloidal particles is used. The interaction between the particles is in the presented examples assumed to be a combination of electrostatic interactions, calculated from the Poisson-Boltzmann equation, dispersion forces, calculated as additive 1/r(6) interactions, and a hard sphere interaction calculated from the Carnahan-Starling equation. (C) 1996 Academic Press, Inc.
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| 4. |
- Frenander, U, et al.
(författare)
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Cell harvesting by cross-flow microfiltration using a shear-enhanced module
- 1996
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Ingår i: Biotechnology and Bioengineering. - 1097-0290. ; 52:3, s. 397-403
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Tidskriftsartikel (refereegranskat)abstract
- Protein, produced by a bacterial culture of recombinant Vibrio cholerae, was separated from cells in a fermentation broth by cross-flow microfiltration. A new, mechanically agitated (rotational) shear filter, the DMF(TM) filter from Pall, was used to perform the separation. Higher protein recovery and permeate flux than commonly obtained during cell harvesting were demonstrated using sixfold concentration followed by twofold diafiltration. The transmembrane pressure only increased by 10 kPa when the flux was kept constant at 150 L/m(2) h during both concentration and diafiltration. The protein transmission was about 100% initially, and over 90% at the end of the concentration process. The protein transmission during the diafiltration was over 80%. The total recovery of protein was 97%. When using an enzymatic cleaning agent, no significant pure water flux decrease was detected during the course of the experiments. (C) 1996 John Wiley & Sons, Inc.
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| 5. |
- Jonsson, C, et al.
(författare)
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Influence of the membrane material on the adsorptive fouling of ultra-filtration membranes
- 1995
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Ingår i: Journal of Membrane Science. - 0376-7388. ; 108:1-2, s. 79-87
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Tidskriftsartikel (refereegranskat)abstract
- The hydrophilic/hydrophobic properties of the membrane material have an important influence on the membrane flux reduction when treating solutions containing hydrophobic solutes. Different methods of measuring the hydrophobic properties of membranes have been evaluated; measurement of the contact angle being the most commonly used method. In this investigation the flux reduction of eight membranes of approximately the same cut-off, but of different materials, was determined and related to the contact angle. A low-molecular weight hydrophobic solute (octanoic acid) was used as foulant. The flux of the hydrophilic membrane was only marginally reduced, whereas the flux reduction of hydrophobic membranes was significant. Membranes of polyvinylidene fluoride had the lowest flux reduction of the hydrophobic membranes. Differences between membranes of the same material (polyethersulfone), but from different manufacturers, were observed. No relation was found between the flux reduction and the contact angle of the membrane, the initial pure water flux or the retention of a hydrophilic macromolecule (PEG20). The pure water flux of two of the hydrophobic membranes increased significantly during the experiments, whereas the pure water flux of the other hydrophobic membranes decreased. A membrane of polyaramide, with a contact angle of the same order of magnitude as the other hydrophobic membranes, behaved as a hydrophilic membrane, with no influence on the flux at concentrations below the solubility limit of the hydrophobic solute, but experienced the most severe flux decline of all the membranes included in the investigation at the solubility limit. Two modified membranes were included in the investigation. The flux reduction of these membranes was not significantly lower than for the corresponding unmodified membranes of the same materials.
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| 6. |
- Jonsson, C, et al.
(författare)
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The influence of degreasing agents used at car washes on the performance of ultrafiltration membranes
- 1995
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Ingår i: Desalination. - : Elsevier BV. - 1873-4464 .- 0011-9164. ; 100:1-3, s. 115-123
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Tidskriftsartikel (refereegranskat)abstract
- The influence of washing chemicals used at car washes on the flux and retention of three ultrafiltration (UF) membranes has been studied. Eleven commercial degreasing agents, two shampoo agents and a wax were included in the investigation. The membrane performance when treating waste water collected at a car wash at different times of the year was also studied. The retention of the different chemicals varied greatly, but there was no significant difference in COD retention among the three UF membranes. The highest flux was observed when treating the alkaline degreasing agents and the shampoo solutions. The flux and COD retention when treating the waste water from the car wash were 30-50 l/m(2) h and 60%, respectively. One of the low-retention degreasing agents was treated by nanofiltration (NF). The retention was significantly higher when using NF, but the COD concentration in the permeate was still too high to allow the permeate to be discharged without further treatment.
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| 7. |
- Jönsson, Ann-Sofi
(författare)
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Concentration polarization and fouling during ultrafiltration of colloidal suspensions and hydrophobic solutes
- 1995
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Ingår i: Separation Science and Technology. - : Informa UK Limited. - 0149-6395 .- 1520-5754. ; 30:2, s. 301-312
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Tidskriftsartikel (refereegranskat)abstract
- Flux reductions experienced during ultrafiltration are due either to concentration polarization or fouling. It is usually difficult to distinguish between these two phenomena, but by using a turbulence-promoting module it is possible to determine the reversibility of a flux reduction, and thus distinguish between concentration polarization and fouling. By using a turbulence-promoting module, it is also possible to distinguish between different cases of fouling. In this paper, fouling caused by the deposition of material at the surface of the membrane is illustrated by results from tests with a silica sol, and fouling due to interactions in the membrane matrix is illustrated by results from ultrafiltration of a low-molecular organic solute.
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| 8. |
- Jönsson, Ann-Sofi
(författare)
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Fouling during ultrafiltration of a low molecular weight hydrophobic solute
- 1998
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Ingår i: Separation Science and Technology. - : Informa UK Limited. - 0149-6395 .- 1520-5754. ; 33:4, s. 503-516
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Tidskriftsartikel (refereegranskat)abstract
- The influence of a small hydrophobic solute (octanoic acid) on the flux reduction and the flux recovery of two ultrafiltration membranes was studied in this investigation. The two membranes were made of polyether sulfone and regenerated cellulose, both with a nominal molecular weight cutoff of 20,000 Da. The concentration of the octanoic acid solution was found to have a significant influence on not only the extent of flux reduction during treatment of the octanoic acid solution, but also on the flux recovery when the membrane was rinsed with deionized water. After treatment of the octanoic acid solution, a pure water flux increase of 1.5 times the pure water flux of the new, unused polyether sulfone membrane was observed. Different causes of the increased pure water flux after treatment of the octanoic acid solution are presented, and the serious consequences this apparent positive effect can cause in industrial applications are discussed.
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| 9. |
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| 10. |
- Jönsson, Ann-Sofi, et al.
(författare)
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Treatment of high-temperature rinsing water from a degreasing plant by reverse osmosis
- 1997
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Ingår i: Desalination. - 1873-4464. ; 114:2, s. 175-181
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Tidskriftsartikel (refereegranskat)abstract
- In the manufacture of heat-exchangers, it is of great importance that the heat-exchanger plates be thoroughly cleaned before being sealed. At a Swedish heat-exchanger manufacturer, oil, grease and other impurities are removed in a washing plant consisting of three stages: a degreasing tank and two rinsing tanks. The possibility of improving the cleanliness of the heat-exchanger plates, without increasing the need for fresh water, by treating the rinsing water in a reverse osmosis (RO) plant, was studied in this investigation. A new, high-temperature-resistant, thin-film RO membrane from Osmonics-Desal was used in the experiments. The influence of a lubricant, based on a block copolymer, and an alkaline degreasing agent on the membrane performance was studied. The flux reduction of a model rinsing solution with time was moderate. The flux after 500 h of continuous treatment at 65 degrees C and 4.0 MPa was 351/m(2) h, and the permeate quality fulfilled the demands of the heat-exchanger manufacturer.
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