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At least 685 records · Page 38Linked to original sources
PubMed2003

Membrane technologies applied to textile wastewater treatment.

This paper describes the experimental results of a pilot-scale application of membrane technologies to textile wastewater advanced treatment, downstream of a biological activated sludge process, aimed at water reuse in textile technology processes. The chosen approach consisted of sand filtration as a pretreatment, a microfiltration (MF) or ultrafiltration (UF) membrane process, and a final separation treatment performed by means of a nanofiltration (NF) or a reverse osmosis (RO) membrane. An experimental study to compare spiral wound membranes, operating under pressure, to flat membranes, operating under vacuum was conducted. The technical results and a preliminary economic analysis indicate the possibility of technological transfer of the membrane technologies to an industrial scale for textile wastewater reclamation.

Journal Article↗
PubMed2003

Integrating photocatalysis and membrane technologies for water treatment.

Removal of organic contaminants in water may sometimes be more easily achieved with a pair rather than with a single unit operation. We explore here the combination of an ambient temperature, chemical oxidation photocatalysis (PC) process with physical separation via a membrane operation, microfiltration (MF), ultrafiltration (UF), or reverse osmosis (RO) using both a conceptual statement and a literature review format. Four configurations are noted and discussed here: (1) PC + MF for catalyst slurry recycle, (2) PC + UF for catalyst slurry and (polymer) reactant recycle, (3) immobilized PC and UF/RO for reactant recycle, and (4) immobilized PC on UF/RO membrane for membrane self-cleaning. Although the literature review is encouraging with respect to plausibility, the paucity of examples indicates a need for substantial effort to fully exploit the suggested possibilities for process development.

Journal Article↗
PubMed2003

Advances in solvent-resistant nanofiltration membranes: experimental observations and applications.

Nanofiltration (NF) and reverse osmosis (RO) are well-established membrane technologies for applications involving aqueous streams. The principles of NF transport (diffusion, convection, and Donnan exclusion) are effectively used to develop novel membrane materials and applications in aqueous medium. Use of NF in a non-aqueous medium holds strong potential for the food, refining, and pharmaceutical industries because of the low energy costs involved with such membrane processes. Further understanding and development of solvent-resistant NF membranes provides opportunities for various hybrid processing ranging from reactor-membrane to distillation-membrane combinations. This paper provides a comprehensive overview of literature results and our own work in the area of non-aqueous systems. For solvent-based systems, potential membrane swelling and solvent-solute coupling needs to be considered for membrane design and transport theories. A simplified transport theory for pure solvents has been developed using solvent (molar volume, viscosity) and membrane properties (membrane surface energy). This model and has been verified with literature data for both hydrophilic and hydrophobic membranes. Membrane characterization and preconditioning aspects need to be given serious consideration for evaluating membrane performance. In addition to permeability and separation results, some novel applications of NF in non-aqueous solvents are included in this paper.

Biotechnology↗
PubMedDate not supplied

Endotoxin and 'on line' production of substitution fluid in haemodiafiltration and haemofiltration.

In dialysis, machines intended for use in the treatment modes haemodiafiltration (HDF) and haemofiltration (HF) have been on the market about 10 years. These machines are equipped to be able to produce the substitution fluid to be used for direct infusion. In principle, this is done by using the reverse osmosis water of the clinic and mixing in concentrates as usual to form dialysis fluid. The dialysis fluid is then filtered in order to prepare it for use as substitution fluid. The volumes used when the substitution fluid is prepared on-line are usually 20-50 litres in HDF mode and 70-150 litres in HF mode. This means that a patient treated 3 times a week is exposed to a total volume of substitution fluid ranging from 3,000 litres to a maximum 23,000 litres a year. Where else in medicine do we see something coming close to this? Because of these large infusion volumes, the issue of endotoxin levels becomes as important as the issue of sterility.

Dialysis Solutions↗
PubMedDate not supplied

Routine disinfection of the total dialysis fluid system.

The importance of bacteria and endotoxin free, sterile dialysis fluid for long term, high quality haemodialysis treatment is obvious and very much demanded (1,2). Dead spaces and connections between units (segments) of fluid production and delivery in elder systems are a continuous source for bacteria growth, biofilm generation and endotoxin release (3). After varying success with routine disinfection of system components showing partly fast recovery and growth of bacteria (i.e. < 48 hours) we changed to routine disinfection of the entire fluid production and distribution system. We call this'system disinfection'. We report the methods and results from observation of practice over 28 months of disinfection. The fluid system is composed of a soft water tank, reverse osmosis (double RO), RO fluid loop, central bicarbonate production and delivery system and dialysis stations with and without ultrafilter and citric-thermal disinfection before and after each haemodialysis. The system disinfection is carried out bimonthly with peracetic acid 3.5% in > 0.1% solution at a mean temperature of > 15 degrees C and at a minimum of 60 minutes of disinfection time. Samples for microbiological testing and endotoxin measurement were assessed 3-4 monthly at 7 measurement points. The tests were carried out 7 times on the 11th day (mean value [MV]) after routine system disinfection. The result was in 0.2 CFU/ml (MV) in 40 tests. The endotoxin levels (IU/L) were all < 0.25 except one at 0.325 in RO water. Endotoxin was assessed 5 times in 26 tests over 28 months. Samples were taken at 10.5 (MV) days after system disinfection. The Gel Clot or turbometric method was used. Efficient and preventive routine system disinfection of an entire dialysis fluid production and distribution system as standard in modern equipment - can support sufficient quality in dialysis fluid produced and distributed by elder and composed systems.

Dialysis Solutions↗
PubMed1989

Mechanisms of water transport by epithelial cells.

Isosmotic transport of fluid across epithelial cell layers occurs by intraepithelial mechanisms that are not fully understood. Newer methods of measuring water flows across epithelia with higher resolution should now permit some key issues regarding solute-linked water transport to be clarified. Unstirred-layer effects are not likely to be serious sources of error in these measurements with judicious choice of experimental conditions. Progress in ultrastructural stereology has shown that in the proximal tubule most of the transporting membrane is located in the basal aspects of cells, making models based on a hyperosmolar lateral compartment less relevant. The current models of simple transcellular osmosis, though appealing for this simplicity, fail to account for some major experimental findings. Experimental design and methodological limitations have not yet achieved rigorous testing of whether or not epithelia can produce a perfectly isosmotic absorbate without any transepithelial driving forces. A better understanding of the mechanism of translocation of water through the lipid bilayer, the plasma membrane proteins, and special membrane structures like the tight junctions would significantly contribute to our knowledge of the mechanisms and intraepithelial routes by which water is transported by epithelia.

Animals↗
PubMed1967

Fixed charge in the cell membrane.

1. Focal electric field was generated by passing a current of 5 x 10(-7) to 1 x 10(-5) A from a micropipette into the culture medium. Movement of cells at a distance of 5-50 mu from the electrode tip was observed. In case of cells embedded in the culture only local deformation of the membrane was observed.2. The cell species explored included neurones, glia, muscle fibres, connective cells, malignant cells and erythrocytes. All cells responded in a similar manner to the electric field, and the current required was in the same range.3. Cells were attracted to a positive micropipette and repelled from a negative one: the only exception was observed in certain malignant cells which moved in the opposite direction.4. Movement and membrane deformation could be obtained with electrodes filled with various concentrated and isotonic solutions. The composition of the culture medium also had no qualitative influence on these effects.5. Metabolic poisons or rupture of the cell membrane had no effect on the movement. Isolated membrane fragments showed movement similar to that of intact cells.6. The possibility of artifacts due to proximity of the focal electrode is considered. It is shown that electro-osmosis cannot account for the present observations. Some other artifacts are also excluded.7. It is proposed that the most satisfactory way to account for the present observations is by a membrane carrying negative fixed charge of the order of 2.5 x 10(3) e.s.u./cm(2). Some physiological consequences of presence of negative charge in the membrane are briefly discussed.

Animals↗
PubMed1976

Chloride transport in human erythrocytes and ghosts: a quantitative comparison.

1. Homogeneous preparations of resealed ghosts with intracellular KCl concentrations between 15 and 900 mM could be prepared. Virtually all ghosts sealed to chloride. The chloride transport system was found not to be damaged: a quantitative comparison of the self-exchange of 36Cl- across intact and resealed membranes showed that both the transport capacity and a number of characteristic properties were identical (saturation kinetics, temperature dependence and the effect of inhibitors). 2. Due to the absence of intracellular titratable buffers intracellular chloride concentration in ghosts vary only slightly between pH5 and 11. The unidirectional exchange flux was constant between pH 7 and 11, showing that the transport system does not have a functionally important titratable group in the alkaline range, as previously assumed. The decrease of transport below pH 7 is similar in intact erythrocytes and ghosts. 3. Mean cellular volume of the resealed ghosts was a function of the amount of KCl added at 'reversal', before the ghosts are sealed. The ghosts shrank by osmosis when KCl was added to the suspension of 'unsealed' ghosts. The reflexion coefficient of sucrose (and therefore the osmotic effect) is larger than that of KCl. It was, therefore, possible to demonstrate that volume changes do not affect the chloride transport across the human red cell membrane. Unidirectional chloride fluxes at a KCl concentration of 165 mM were independent of ghost volume (100-40 mum3).

Biological Transport↗
PubMed2005

Water transport by Na+-coupled cotransporters of glucose (SGLT1) and of iodide (NIS). The dependence of substrate size studied at high resolution.

The relation between substrate and water transport was studied in Na+-coupled cotransporters of glucose (SGLT1) and of iodide (NIS) expressed in Xenopus oocytes. The water transport was monitored from changes in oocyte volume at a resolution of 20 pl, more than one order of magnitude better than previous investigations. The rate of cotransport was monitored as the clamp current obtained from two-electrode voltage clamp. The high resolution data demonstrated a fixed ratio between the turn-over of the cotransporter and the rate of water transport. This applied to experiments in which the rate of cotransport was changed by isosmotic application of substrate, by rapid changes in clamp voltage, or by poisoning. Transport of larger substrates gave rise to less water transport. For the rabbit SGLT1, 378+/-20 (n=18 oocytes) water molecules were cotransported along with the 2 Na+ ions and the glucose-analogue alpha-MDG (MW 194); using the larger sugar arbutin (MW 272) this number was reduced by a factor of at least 0.86+/-0.03 (15). For the human SGLT1 the respective numbers were 234+/-12 (18) and 0.85+/-0.8 (7). For NIS, 253+/-16 (12) water molecules were cotransported for each 2 Na+ and 1 thiocyanate (SCN-, MW 58), with I- as anion (MW 127) only 162+/-11 (19) water molecules were cotransported. The effect of substrate size suggests a molecular mechanism for water cotransport and is opposite to what would be expected from unstirred layer effects. Data were analysed by a model which combined cotransport and osmosis at the membrane with diffusion in the cytoplasm. The combination of high resolution measurements and precise modelling showed that water transport across the membrane can be explained by cotransport of water in the membrane proteins and that intracellular unstirred layers effects are minute.

Animals↗
PubMed2006

Water transport by GLUT2 expressed in Xenopus laevis oocytes.

The glucose transporter GLUT2 has been shown to also transport water. In the present paper we investigated the relation between sugar and water transport in human GLUT2 expressed in Xenopus oocytes. Sugar transport was determined from uptakes of non-metabolizable glucose analogues, primarily 3-O-methyl-D-glucopyranoside; key experimental results were confirmed using D(+)-glucose. Water transport was derived from changes in oocyte volume monitored at a high resolution (20 pl, 1 s). Expression of GLUT2 induced a sugar permeability, P(S), of about 5 x 10(-6) cm s(-1) and a passive water permeability, L(p), of 5.5 x 10(-5) cm s(-1). Accordingly, the passive water permeability of a GLUT2 protein is about 10 times higher than its sugar permeability. Both permeabilities were abolished by phloretin. Isosmotic addition of sugar to the bathing solution (replacing mannitol) induced two parallel components of water influx in GLUT2, one by osmosis and one by cotransport. The osmotic driving force arose from sugar accumulation at the intracellular side of the membrane and was given by an intracellular diffusion coefficient for sugar of 10(-6) cm(2) s(-1), one-fifth of the free solution value. The diffusion coefficient was determined in oocytes coexpressing GLUT2 and the water channel AQP1 where water transport was predominantly osmotic. By the cotransport mechanism about 35 water molecules were transported for each sugar molecule by a mechanism within the GLUT2. These water molecules could be transported uphill, against an osmotic gradient, energized by the flux of sugar. This capacity for cotransport is 10 times smaller than that of the Na(+)-coupled glucose transporters (SGLT1). The physiological role of GLUT2 for intestinal transport under conditions of high luminal sugar concentrations is discussed.

Animals↗
PubMed1996

Aspects of the mechanics of lobed liposomes.

Hotani has studied, by means of dark-field light microscopy, morphological transformations which unilamellar liposomes undergo when their interior volume decreases steadily with time as a consequence of osmosis. In a previous paper, we made a theoretical study of the initial buckling of an originally spherical vesicle into the observed oblate spheroidal shape; and we argued that some in-plane shear elastic stiffness is required-in addition to the well-known flexural stiffness of the lipid bilayer-in order to explain the observed phenomena. In the present paper, we consider a later stage in the chain of morphological transitions observed by Hotani, when a series of cudgel-shaped lobes have sprung out of a previously axisymmetric, biconcave-shaped vesicle. Specifically, we compare the observed shapes of such lobes with half of a series of "peanut"-shaped vesicles that are an equilibrium conformation of an initially spherical liposome under reduced internal volume. We find that the shapes do not match well. On the other hand, the observed lobe forms do match satisfactorily portions of "undulating tube" shapes which evolve from a hypothetical cylindrical vesicle, according to some simple calculations. In view of this agreement, we are led to propose that the formation of cudgel-shaped lobes requires some sliding of one lipid monolayer over another. This conflicts, of course, with the Love-Kirchhoff hypothesis which is normally invoked at the outset of analyses of lipid vesicles by means of classical thin-shell theory; but it is in accord with previous suggestions in the context of more obviously severe distortion of the lipid bilayer.

Computer Simulation↗
PubMed2005

Elimination of botulinum neurotoxin (BoNT) type B from drinking water by small-scale (personal-use) water purification devices and detection of BoNT in water samples.

Seven small-scale drinking water purification devices were evaluated for their capacity to eliminate botulinum neurotoxin (BoNT) type B from drinking water. Influent water inoculated with toxic Clostridium botulinum cultures and effluent purified water samples were tested for the presence of BoNT by using a standard mouse bioassay and two commercial rapid enzyme immunoassays (EIAs). The water purification devices based on filtration through ceramic or membrane filters with a pore size of 0.2 to 0.4 microm or irradiation from a low-pressure UV-lamp (254 nm) failed to remove BoNT from raw water (reduction of < 0.1 log10 units). A single device based on reverse osmosis was capable of removing the BoNT to a level below the detection limit of the mouse bioassay (reduction of > 2.3 log10 units). The rapid EIAs intended for the detection of BoNT from various types of samples failed to detect BoNT from aqueous samples containing an estimated concentration of BoNT of 396,000 ng/liter.

Animals↗
PubMed1978

Characterization of a partially purified methanol-soluble heat-stable Escherichia coli enterotoxin in infant mice.

While studying the involvement of cyclic adenosine 3',5'-monophosphate (cAMP) in the fluid secretion caused by heat-stable enterotoxin (ST) from Escherichia coli P16 in infant mice, it was noted that the culture filtrate containing ST also contained large amounts of cAMP. The present paper details attempts to obtain a cAMP-free ST preparation. The organisms were grown in a defined medium, and the heated culture filtrate was concentrated by reverse osmosis. After methanol extraction of the filtrate, which removed 80% of the nonactive solids, the methanol-soluble ST was further purified by gel filtration through a Sephadex G-10 column. The first fraction recovered after gel chromatography contained ST with a negligible amount of cAMP. Treatment with methanol did not adversely affect the enterotoxic activity. Certain parameters of the infant mouse model have been investigated, and using our ST preparation it has been found that animals remain responsive up to 15 days of age with an optimum assay time of 2 h after toxin challenge.

Age Factors↗
PubMed1993

Cation flux studies of the lesion induced in human erythrocyte membranes by the thermostable direct hemolysin of Vibrio parahaemolyticus.

Vibrio parahaemolyticus, an important agent of seafood-borne gastroenteritis, expresses several putative virulence factors that could account for the disease symptoms of infected humans, namely, diarrhea, nausea, and abdominal cramps. The pathogenicity of V. parahaemolyticus correlates well with the Kanagawa phenomenon (the hemolytic ability of strains grown on Wagatsuma blood agar), implicating the thermostable direct hemolysin (TDH) as the predominant toxin responsible for pathogenicity. TDH-induced hemolysis could be inhibited by the addition of the osmolyte sorbitol to the extracellular solution, supporting the hypothesis that hemolysis occurs through colloid osmosis secondary to an increase in the cation permeability of the membrane. The effect of TDH on cation permeability was investigated by measuring K+ (congener, 86Rb+) influx into human erythrocytes in which the endogenous cation transporters had been blocked (by use of ouabain, bumetanide, and nitrendipine). TDH increased K+ influx into these cells; this increase was rapid in onset and constant in magnitude, suggesting a direct action by TDH on the membrane. The kinetics of leak generation were examined; the relationship between counts accumulated and hematocrit indicated that the TDH-induced lesion is multihit in nature. TDH-induced K+ influx was sensitive to Zn2+. Time courses of hemolysis in isosmotic solutions of monovalent cation chlorides were used to obtain the selectivity series for the TDH-induced leak: Cs+ > Li+ > K+ > Rb+ > Na+. Both the Zn2+ sensitivity and this selectivity series were obtained for crude culture supernatants, suggesting that TDH is the predominant leak-inducing agent. Thus, we have identified several features of the TDH-induced leak likely to be important in the diarrhetic action of V. parahaemolyticus in the human intestine.

Adult↗
PubMed2005

Method for rapid identification and differentiation of the species of the Mycobacterium chelonae complex based on 16S-23S rRNA gene internal transcribed spacer PCR-restriction analysis.

Members of the Mycobacterium chelonae complex (MCC), including M. immunogenum, M. chelonae, and M. abscessus, have been associated with nosocomial infections and occupational hypersensitivity pneumonitis due to metalworking fluid (MWF) exposures. In order to minimize these health hazards, an effective and rapid assay for detection of MCC species and differentiation of MCC species from other species of rapidly growing mycobacteria (RGM) and from one another is warranted. Here we report such a method, based on the variable 16S-23S rRNA gene internal transcribed spacer (ITS) region. Mycobacterium genus-specific primers derived from highly conserved sequences in the ITS region and the flanking 16S rRNA gene were used. Specificity of the primers was verified using the MCC member species, 11 non-MCC RGM species, 3 slow-growing mycobacterial (SGM) species (two strains each), and 19 field isolates, including 18 MCC isolates (from in-use MWF) and one non-MCC isolate (from reverse osmosis water). The ITS amplicon size of M. immunogenum varied from those of M. chelonae and M. abscessus. Sequencing of the approximately 250-bp-long ITS amplicons of the three MCC member species showed differences in 24 to 34 bases, thereby yielding variable deduced restriction maps. ITS PCR-restriction analysis using the in silico-selected restriction enzyme MaeII or HphI differentiated the three MCC members from one another and from other RGM and SGM species without sequencing. The enzyme MaeII discriminated all three member species; however, HphI could only differentiate M. immunogenum from M. chelonae and M. abscessus. Use of an optimized rapid DNA template preparation step based on direct cell lysis in the PCR tube added to the simplicity and adaptability of the developed assay.

Bacterial Typing Techniques↗
PubMed2006

Injectable self inflating hydrogel pellet expanders for the treatment of orbital volume deficiency in congenital microphthalmos: preliminary results with a new therapeutic approach.

BACKGROUND/AIM: Children with congenital microphthalmos are usually able to wear an eye prosthesis but the cosmetic aspect is determined by the size of the orbital volume deficiency. Instead of using a ball shaped standard hydrogel expander or a regular orbital implant, which would necessitate enucleation of the microphthalmic eye, this study investigates the feasibility of volume augmentation with injectable pellet expanders, as formerly suggested for acquired anophthalmos in adults only. METHOD: The pellet expander is made from a self inflating hydrogel that takes up water by osmosis (dry state: length 8 mm, diameter 2 mm, volume 0.025 ml; in vitro hydrated state after around 1 day: length 15 mm, diameter 4 mm, volume 0.24 ml; swelling capacity: 9.6-fold). This report concerns six patients (two girls and four boys) aged between 4 months and 42 months with unilateral microphthalmos who were treated by injection of 4-14 pellet expanders into the retrobulbar orbital tissue. Volume augmentation was 1-3.5 ml. The pellets were injected using a customised trocar and placed behind the microphthalmos directed into the intraconal space. RESULTS: The increasing orbital volume was noticeable within 2 days and was confirmed by ultrasonography and magnetic resonance imaging. The final result can be anticipated by the volume augmentation effect produced by the amount of saline solution injected in the orbital apex region. All patients were fitted with an artificial eye, which was subsequently enlarged every 3-5 months. Anophthalmic enophthalmos was fully compensated with this technique. No complications have been encountered to date. CONCLUSIONS: Orbital volume augmentation with injectable self inflating hydrogel expander pellets is apparently a safe, quick, and minimally invasive technique for various indications in orbital reconstructive surgery-for example, to treat an enophthalmic appearance in microphthalmos and congenital or acquired anophthalmos.

Child, Preschool↗
PubMed1985

Current arrangements for teaching medical ethics to undergraduate medical students.

Those teachers in contact with medical students from pre-clinical days onwards will impart their ethical views by example and by precept, but such learning by 'osmosis' is insufficient. There is a knowledge base to be imparted which will enrich the understanding of ethical judgements on clinical problems seen during the undergraduate years. However, the learning process continues after qualification and in particular the doctor's capacity to make ethical clinical judgements will evolve with maturity and experience. It is essential therefore that students see their teachers willing and able to debate ethical issues at the postgraduate level.

Curriculum↗
PubMed1987

Some effects of water quality on the performance of high yielding cows in an arid climate.

The water from wells in Saudi Arabia is often high in mineral content. The cows in this study had been receiving water containing between 4000 and 5000 ppm total dissolved solids. Four groups of 16 cows were calved down and milked under similar conditions in the hot summer months. Two of the groups were given normal well water and the other two groups received water after desalination in a reverse osmosis plant. One group on each type of water also had their water cooled. The groups of cows receiving treated water drank more water, consumed more concentrate and produced significantly more milk than the groups given normal well water. A similar effect on feed intake and milk production was seen when treated water was given to a 1000-cow unit with a similar number of control cows.

Animals↗