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PubMed2002

Removal of arsenic from groundwater using point-of-use reverse osmosis and distilling devices.

Ground water in both the northeastern and southwestern coast areas of Taiwan may contain high concentrations of arsenic. Since no central water supply system is available in some of those areas, point-of-use (POU) water purification devices are considered as an option for providing safe drinking water. In this study, removal of arsenic, using two types of POU purification devices, reverse osmosis (RO) systems and distillers, was investigated. Three commercially available RO systems and two distillers were selected to test their removal efficiency of arsenic from synthetic and real ground water. Experimental results of the three RO systems using synthetic ground water showed that only one system had good removal efficiency for arsenic. In subsequent experiments using real ground water with 0.7 mg l(-1) arsenic, only one RO system was able to meet the drinking water standard after producing about 1,000 l of treated water. For the distilling systems, 99% of the arsenic was removed from both synthetic and real groundwater. The arsenic concentrations in the finished water of both distillers were all below the standard for drinking water. Although systems with higher arsenic removal efficiency seemed to have better removal of total dissolved solids (TDS), no correlation could be found after analysis.

Arsenic↗
PubMed2001

Application of nanofiltration and reverse osmosis membranes to the salty and polluted surface water.

Nanofiltration (NF) (TFC-S) and reverse osmosis (RO) (TFC-HR) membranes were evaluated for the treatment of salty and polluted Kucukcekmece Lake used as a drinking water reservoir for the Istanbul City. A thin film composite type of spiral wound membrane (2 m2 area) was used. Experiments were conducted at different pressures, pH ranges and temperatures. Flowrate was about 300 l/h. The flux decreased with increasing pH. Highest rejections were obtained for all anionic and cationic ions in the pH range of 6.0-8.5. Several permeation runs were carried out for the pressure range of 6-12 bar for TFC-S and TFC-HR membranes. According to the Spiegler-Kedem model, the permeate flux (Jv) is linearly related to the applied hydraulic pressure (deltaP). Lp values were calculated by linear regression. Salt rejection was seen to increase with the increasing of operating pressure due to increase of solvent flux. Na+, Mg+2, Ca+2, Cl- and SO4(-2) rejections and z1 and z2 constants have been determined and z values of cations were in the order of zMg > zCa > zNa and similarly those of anions were in the order of zSO4 > zCl. The Spiegler-Kedem model was able to correlate well the experimental data by fitting different best values of P and sigma, respectively for all ions. Best fit values of P and sigma were obtained by regression of the data according to the model.

Filtration↗
PubMed2002

Effect of operating conditions on the separation of ammonium and nitrate ions with nanofiltration and reverse osmosis membranes.

This paper presents the pilot scale membrane separation studies on the Elmali Lake raw water in Istanbul, which is highly polluted by discharging of sewage waters. Low pressure nanofiltration (NF) and reverse osmosis (LPRO) membranes having the surface area of 2 m2 have been used during the experimental runs. Experiments were conducted at different pressures, temperature and pH ranges. Feed flow rate was about 300 L/h. As a result, flux values increased linearly with increasing pressure. Ammonia and nitrate ion rejections also increased with increasing pressure and characteristics of rejection were similar for the both types of membranes. Permeate flux value increased proportionally with the temperature. The temperature changing has also influenced the rejection rate of ammonia and nitrate ions. Both ammonia and nitrate ion rejections at neutral pH values were very high. Therefore, neutral pH value is suitable for TFC-S and TFC-HR membranes to remove ammonia and nitrate ions.

Filtration↗
PubMed1989

Osmosis in leaky pores: the role of pressure.

Osmosis in leaky pores is often considered to involve gradients of pressure that originate from concentration gradients at the pore wall. These postulated surface pressures are incompatible with the Boltzmann equation and result from an incorrect application of the Gibbs-Duhem equation to binary solutions near surfaces. Such pressures would give rise to tensions in the surface phase that are not observed experimentally. Application of the argument to the swelling of porous systems and gels shows that this phenomenon cannot involve internal pressures within the fluid phase.

Hydrostatic Pressure↗
PubMed1983

Electrodialysis and reverse osmosis as a regeneration system for hemofiltrate.

The separation of urea from the hemofiltrate (or from spent dialysis fluid) must be considered the critical step in all regeneration systems. A promising solution for this problem is the combination of electrodialysis and reverse osmosis. A mathematical stimulation of the process and in vitro experiments have been carried out in order to determine operating conditions and design specifications. The experiments confirmed the predicted performance of the regeneration system with respect to the separation of urea and the recovery of electrolytes. As expected, some ionic toxins, such as uric acid, and some middle molecules are recovered also. These substances, however, can be easily removed by a small adsorption cartridge.

Adsorption↗
PubMed2003

Contact deformation of liposome in the presence of osmosis.

The role of osmotic pressure on the geometry of adherent liposome remains an intricate question in the mechanics of supramolecular structures. In this study, confocal reflection interference contrast microscopy in combination with cross-polarized microscopy was applied to probe the geometry of deformed liposome on fused silica substrates through the determination of a vesicle-substrate separation profile. In parallel, a theoretical model which describes the large deformation of the lipid bilayer membrane under both out-plane bending and in-plane shear forces is developed. Then, the global deformation geometry of the adherent liposome is rigorously compared with our experimental data. It is shown that the adhesion contact area increases in dimension, the liposome volume decreases, and the vesicle height decreases under the reduced osmotic pressure. The coupling of experimental data and a modified theoretical framework of the adherent liposome provides a more explicit result in comparison with previous studies and demonstrates the possibility of modeling the change of liposome mechanics under the influence of osmosis.

Adsorption↗
PubMed1968

Charge-mosaic membranes: enhanced permeability and negative osmosis with a symmetrical salt.

Charge-mosaic membranes are prepared by embedding a single layer of alternating cation and anion exchange beads in silicone resin. Membranes made in an identical manner but containing only one type of exchanger serve as controls. The mosaic membranes are 50 to 100 times more permeable to potassium chloride than the controls; and furthermore they give rise to net volume flow from concentrated to dilute solutions of potassium chloride in the absence of a pressure gradient ("negative osmosis"), whereas the controls exhibit normal osmotic behavior. The negative reflection coefficients of the mosaics suggest potential applications in desalination.

Ion Exchange↗
PubMed1973

Synthesis of reverse osmosis membranes by plasma polymerization of allylamine.

The polymerization of allylamine in a radio-frequency electrodeless plasma to form thin polymer films on microporous filter media provides very effective dry composite membranes for reverse osmosis. Salt and urea rejections as high as 98 percent and 46 percent, respectively, have been achieved from a solution containing 10 grams of sodium chloride per liter and 10 grams of urea per liter. The plasma conditions and polymerization technique are discussed.

Membranes, Artificial↗
PubMed1973

Fluid shifts associated with gas-induced osmosis.

It has been proposed that equilibration of nitrous oxide with blood plasma increases osmotic pressure and thereby causes hemodilution. However, calculations show that the 250-torr osmotic gradient produced by 0.7 atmosphere of nitrous oxide dissolved in blood plasma (separated from the other body fluids by a membrane permeable only to water) would be eliminated by a water shift which would dilute the plasma by only 4 percent. Permeability of the membrane to nitrous oxide would further reduce the shift. In vivo measurements confirmed the smallness of any osmotically induced shifts by demonstrating no significant transient changes in hematocrit value when 0.7 atmosphere of nitrous oxide was added to or removed from an inhaled anesthetic mixture in man. These results cast doubt on the suggestions that gas-induced osmosis is an important factor in dysbarism or in clinical anesthesia.

Anesthesia, Inhalation↗
PubMed1991

Gastrointestinal health effects associated with the consumption of drinking water produced by point-of-use domestic reverse-osmosis filtration units.

During a prospective epidemiological study of gastrointestinal health effects associated with the consumption of drinking water produced by reverse-osmosis domestic units, a correlation was demonstrated between the bacterial counts on R2A medium incubated at 35 degrees C and the reported gastrointestinal symptoms in families who used these units. A univariate correlation was found with bacterial counts on R2A medium at 20 degrees C but was confounded by the bacterial counts at 35 degrees C. Other variables, such as family size and amount of water consumed, were not independently explanatory of the rate of illness. These observations raise concerns for the possibility of increased disease associated with certain point-of-use treatment devices for domestic use when high levels of bacterial growth occur.

Canada↗
PubMed1999

Osmosis, osmometry, and osmoregulation.

The maintenance of adequate body fluid volume and the correct distribution of this fluid between the body compartments is a critical part of homeostasis. The process of osmosis plays an important role in movement of fluid within the body and the use of osmometry is an important part of the management of many patients. In addition to the application of osmometry to the measurement of body fluids, most commonly plasma and urine, osmotic action plays a part in some therapeutic actions of drugs and its strength needs to be quantified in fluids administered to patients. Unfortunately confusion often exists in the various terms that are used in the field of osmometry. This review aims to explain the different terms used, the laboratory methodology involved in osmometry, and the clinical application and interpretation of the results obtained.

Homeostasis↗
PubMed2003

Osmosis: a macroscopic phenomenon, a microscopic view.

At present, physical chemistry employs the tools of thermodynamics to treat osmosis across a semipermeable membrane. We propose a model in terms of momentum transfer, the inherent asymmetry of which leads quantitatively to the van't Hoff relationship; qualitatively, the solute molecules can be looked upon as micropumps that suck solvent through the pores in the membrane.

Models, Biological↗
PubMed1978

Osmosis, diffusion, convection.

We present a tutorial on the mechanisms of and connections among osmosis, diffusion, and convection. For simplicity, we consider only two-component nonelectrolyte solutions under isothermal conditions. Further, we confine our attention to laminar convection with application to the case of flow through narrow channels, as might occur in membranes containing pores or slits. The application of equilibrium and near-equilibrium thermodynamics to flow processes is just like considerations of mechanics with friction, or hydrodynamics. The description of flow processes of more than two atomistic components, either solutions or suspensions, is identical in the dilute limit to the description we give, except possibly when the curvature of the flow field (at the velocity profile) is significant. Flow fields, therefore, naturally divide into three regimes: 1) "one-dimensional" flow fields, e.g., solutions or suspensions in extended regions, whose velocity profile is macroscopically flat (compared to the atomistic curvature); 2) flow fields with significant curvature, e.g., Poiseuille or turbulent fields; and 3) high curvature fields, e.g., narrow flow channels.

Biophysical Phenomena↗
PubMed1987

Solvent flow in osmosis and hydraulics: network thermodynamics and representation by bond graphs.

A tutorial introduction to network thermodynamics and bond graphs as a modeling technique for any physiochemical system is presented with a particular emphasis on reaction diffusion systems. It combines the generality of nonequilibrium thermodynamics with the advantages of a graph theory. It is applied to the representation of osmotic and hydraulic flows across a semipermeable membrane on the basis of the solvent diffusion theory of osmosis. This theory allows for an easy derivation of the van't Hoff law of osmotic pressure from the Fick law of diffusion. Molar flows and volume flows are transformed into one another by transducers, the modulus of which is the partial molar volume of water, in such a way that power is conserved by a reciprocal transformation between the chemical potential and the pressure. Osmotic and hydraulic resistances are calculated, and their dependence on pore size is estimated.

Diffusion↗
PubMedDate not supplied

Discovering the movement of life: osmosis and microstructure in 1826.

RJH Dutrochet (1776-1847) may be remembered for his discovery of osmosis in 1826. This essay explores the meanings of that discovery within the science of the early nineteenth century, including contemporary ideas on plant and animal microstructure and on physical explanations for the phenomena of life. Dutrochet is revealed as a 'romantic' exponent of 'organic physics'.

Animals↗
PubMed2003

Design of a reverse osmosis plant for leachate treatment aiming for safe disposal.

Leachate treatment is one of the major environmental issues faced by landfill owners. One promising method for reduction of pollutant discharge is reverse osmosis (RO). RO technology was tested at a pilot plant at Hedeskoga Landfill in southern Sweden. This landfill receives municipal solid waste (MSW) and industrial, commercial and institutional (IC&I) waste, and produces about 3000 m3/ha of leachate annually. Annual variations in the volume of leachate produced, estimated from changes in leachate electrical conductivity, were relatively small and should therefore have a minor effect on the main performance parameter of an RO plant, i.e., the achievable volume reduction. The volume reduction (V(permeate)/V(feed)) of polluted water achieved in batch experiments with 200-1000 litres of raw leachate was more than 80% (4MPa) and the remaining 20% was left as retentate. However, raw leachate caused severe fouling problems in a continuous flow run and after 24 hours, the flux had decreased to about 20% of the initial value. By pre-treating the leachate in a storage pond combined with a wetland, the situation was significantly improved and the decrease in membrane flux was only 0.2% per hour during a 200 hour run. The retention in terms of total solids and chemical oxygen demand was 90%, and for ammonia, it was 82%, at a volume reduction of 50%. The HELP-model was used for prediction of the water balance for the Hedeskoga landfill, with special focus on estimation of potential evapotranspiration. With different types of vegetation and a volume reduction of 75% in the RO plant, it was found possible to achieve safe disposal by irrigating 25% to 40% of the leachate-producing landfill area with pre-treated leachate. Pre-treatment with wetlands and nature based systems reduce the need of detergents for cleaning of the membranes and water only can be used. Short pre-treatment by aeration is not sufficient to bring leachate to a condition sustainable for RO-treatment. In that case, it was found necessary with alkaline-acid-alkaline treatment to restore the permeability. The total treatment cost for a full scale treatment plant at Hedeskoga was estimated to be approximately 30 SEK/m3, of which 25 is capital and 5 is operational costs. This can be compared to the total treatment costs for municipal sewage in Sweden, which is 8 SEK/m3.

Detergents↗
PubMed2001

On the micro-space theory of osmosis osmofiltration, "active" water-flow in membrane-gaps.

The author revised the conclusion drawn from his former experiments and recognized a complex phenomenon that he named osmofiltration. This phenomenon occurs by way of the inhibition of the diffusion within a micro-gap bordering the experimental membrane in the model. It may have a significance as a basic biological phenomenon in similar biological membranous structures, and even, it may have a medical importance. The author discusses his working hypothesis about the micro-space theory of osmosis.

Cell Membrane↗
PubMedDate not supplied

Rejection of emerging organic micropollutants in nanofiltration-reverse osmosis membrane applications.

The rejection of emerging trace organics by a variety of commercial reverse osmosis (RO), nanofiltration (NF), and ultra-low-pressure RO (ULPRO) membranes was investigated using TFC-HR, NF-90, NF-200, TFC-SR2, and XLE spiral membrane elements (Koch Membrane Systems, Wilmington, Massachusetts) to simulate operational conditions for drinking-water treatment and wastewater reclamation. In general, the presence of effluent organic matter (EfOM) improved the rejection of ionic organics by tight NF and RO membranes, as compared to a type-II water matrix (adjusted by ionic strength and hardness), likely as a result of a decreased negatively charged membrane surface. Rejection of ionic pharmaceutical residues and pesticides exceeded 95% by NF-90, XLE, and TFC-HR membranes and was above 89% for the NF-200 membrane. Hydrophobic nonionic compounds, such as bromoform and chloroform, exhibited a high initial rejection, as a result of both hydrophobic-hydrophobic solute-membrane interactions and steric exclusion, but rejection decreased significantly after 10 hours of operation because of partitioning of solutes through the membranes. This resulted in a partial removal of disinfection byproducts by the RO membrane TFC-HR. In a type-II water matrix, the effect of increasing feed water recoveries on rejection of hydrophilic ionic and nonionic compounds was compound-dependent and not consistent for different membranes. The presence of EfOM, however, could neutralize the effect of hydrodynamic operating condition on rejection performance. The ULPRO and tight NF membranes were operated at lower feed pressure, as compared to the TFC-HR, and provided a product water quality similar to a conventional RO membrane, regarding trace organics of interest.

Disinfection↗