Electroosmotic Permeability Research Articles

A LABORATORY-SCALE STUDY OF APPLIED VOLTAGE AND CHELATING AGENT ON THE ELECTROKINETIC SEPARATION OF PHENOL FROM SOIL

The influence of the chelating agent (1-hydroxyethane-1, 1-diphosphonic acid) (HEDPA) on the electroosmotic flow (EF) in natural, sod-podzolic soil contaminated with 0.003 g phenol per 1 g of dry soil was studied. An introduction of a small amount of HEDPA increased the electroosmotic permeability of soil from 4 × 10−5 to 11.2 × 10−5 cm2/V·s. Up to 80–95% of the phenol was removed from the soil by the EF during 30 to 50 hours of treatment with the average intensity of the EF remaining constant throughout the tests. The study confirmed that certain hazardous organic contaminants (e.g., phenol) could be successfully extracted from the soils of low permeability by combined application of a direct-current electric field and specific complexing agents.

Effect of an ac Perturbation on the Electroosmotic Behavior of a Cation-Exchange Membrane. Influence of the Cation Nature

The effect of an ac sinusoidal perturbation of known amplitude and frequency superimposed on the usual dc applied electric voltage difference on the electroosmotic flow through a typical cation-exchange membrane has been studied using different monovalent electrolytes. As a general trend, the presence of the ac perturbation increases the value of the electroosmotic flow with respect to the value in the absence of ac perturbation. A dispersion of the electroosmotic permeability on the frequency of the applied ac signal has been found for the three studied electrolytes, observing that the electroosmotic permeability reaches maximum values for some characteristic values of the frequency. This behavior may be related to the different relaxation processes in heterogeneous mediums.

Remediation of TCE contaminated soils by in situ EK-Fenton process

The treatment performance and cost analysis of in situ electrokinetic (EK)-Fenton process for oxidation of trichloroethylene (TCE) in soils were evaluated in this work. In all experiments, an electric gradient of 1 V/cm, de-ionized water as the cathode reservoir fluid and a treatment time of 10 days were employed. Treatment efficiencies of TCE were evaluated in terms of the electrode material, soil type, catalyst type, and catalyst dosage and granular size if applicable. Test results show that graphite electrodes are superior to stainless steel electrodes. It was found that the soil with a higher content of organic matter would result in a lower treatment efficiency (e.g. a sandy loam is less efficient than a loamy sand). Experimental results show that the type of catalyst and its dosage would markedly affect the reaction mechanisms (i.e. “destruction” and “removal”) and the treatment efficiency. Aside from FeSO 4, scrap iron powder (SIP) in the form of a permeable reactive wall was also found to be an effective catalyst for Fenton reaction to oxidize TCE. In general, the smaller the granular size of SIP, the lower the overall treatment efficiency and the greater the destruction efficiency. When a greater quantity of SIP was used, a decrease of the overall treatment efficiency and an increase of percent destruction of TCE were found. Experimental results have shown that the quantity of electro-osmotic (EO) flow decreased as the quantity of SIP increased. It has been verified that the treatment performances are closely related to the corresponding EO permeability. Results of the cost analysis have indicated that the EK-Fenton process employed in this work is very cost-effective with respect to TCE destruction.

Effects of electrode materials and current intermittence in electro-osmosis

The effects of electrode materials and current intermittence on the coefficient of electro-osmotic permeability and the voltage loss at the soil-electrode interfaces are investigated using a marine soil. An electro-osmotic testing cell is designed and fabricated to measure the electro-osmotic induced flow under known boundary conditions. Six pairs of electrodes are tested for the voltage loss at the soil- electrode interfaces and for the coefficient of electroosmotic permeability. The losses in the applied voltage are found to be dependent on the anode material and are less in metallic anodes (steel or copper) than carbon anodes. The coefficients of electro-osmotic permeability are relatively independent of the electrode materials and are controlled by the effective electric field intensity in the soil. The application of current intermittence generates a higher electro-osmotic flow than continuous d.c. for the same applied voltage and the open electric circuit is superior to the short electric circuit configuration. The coefficient of electro-osmotic permeability is maximum using current intermittence of 2 min on/1 min off and open-circuit configuration for the soil tested. Nous étudions, en utilisant un sol marin, les effets des matériaux des électrodes et de l'intermittence de courant sur le coefficient de perméabilitéélectro-osmotique et la perte de tension aux interfaces sol-électrode. Nous avons conçu et fabriquéune cellule d'essai électro-osmotique pour mesurer le flux provoquépar électro-osmose en conditions limites connues. Nous testons six paires d'électrodes pour la perte de tension aux interfaces sol-électrodes et pour le coefficient de perméabilité électroosmotique. Nous constatons que les pertes de tension appliquée dépendent du matériau de l'anode et sont moindres avec les anodes métalliques (acier ou cuivre) qu'avec les anodes en carbone. Les coefficients de perméabilité électro-osmotique sont relativement indépendants du matériau de l'électrode et sont fonction de l'intensité du champ é lectrique effectif dans le sol. L'application d'un courant intermittent produit un flux é lectro-osmotique plus e levéque l'application d'un courant direct continu pour la même tension appliquée; et le circuit é lectrique ouvert est supérieur àla configuration de circuit é lectrique court. Le coefficient de perméabilitéé lectro-osmotique est à son maximum quand on utilise un courant intermittent activé pendant 2 minutes et désactivépendant 1 minute et une configuration à circuit ouvert pour le sol testé

電位‐動水勾配併用による土壌からの汚染物質の浄化に関する一考察

Restoration of contaminated soils to an environmentally acceptable condition is important. Various methods currently used have advantages and limitations in remediating contaminants in soils. In fact, most successful in-situ remediation technologies are restricted to soils with relatively high hydraulic conductivity so that they can not be used for fine-grained deposits. One of the newer techniques in soil remediation is a method based on electrokinetic phenomena in soils. Electrokinetic soil remediation is an effective in-situ separation and removal technique used for extraction of heavy metals and some organic compounds from fine-grained, low permeability soils. However, electrokinetic method is slow in soils that have limited surface conductivity and appreciable permeability. Therefore, it is important to increase the cleanup efficiency. This research has investigated the possible use of electrokinetic phenomena coupled with hydraulic gradient for increasing the cleanup efficiency of contaminants from low permeability soils.In the present study, the contaminant removal from low permeability soils by coupled electric-hydraulic gradient is carried out using a theoretical model. Low permeability soils containing cadmium and trichloroethylene(TCE) are used as the contaminated sources. The results obtained in this study are summarized as follows:The coupled electric-hydraulic gradient can be effectively utilized to remove cadmium from soils with relatively high hydraulic conductivity compared with clayey/silty soils, but can not be effectively utilized to remove cadmium from clayey/silty soils. Meanwhile, in the removal of TCE from clayey/silty soils, the cou-pled electric-hydraulic gradient can be effectively utilized. Macmullin number and coefficient of electroos-motic permeability affect the cleanup efficiency of cadmium. Meanwhile, in the removal of TCE, the effect of Macmullin number is negligible, but the effect of coefficient of electroosmotic permeability is significant.

Electrokinetic Remediation Using Surfactant-Coated Ceramic Casings

Electrokinetic remediation is an emerging technique that can be used to remove metals from saturated or unsaturated soils. In unsaturated soils, control of the medium's water content is essential. Previously used electrode designs have caused detrimental soil wetting due to excess electroosmotic flow out of ceramic-encased anodes. We tested a method to reverse the electroosmotic flow at the anode by treating the ceramic casing with the cationic surfactant hexadecyltrimethylammonium (HDTMA). Laboratory tests showed the untreated ceramic had an electroosmotic permeability of 2.4 × 10−5 cm2 V−1 s−1. Ceramic treated with HDTMA had an electroosmotic permeability of −1.3 × 10−5 cm2 V−1 s−1. Under an applied electric potential, electroosmotic flow was reversed in the HDTMA-treated ceramic, indicating a reversed zeta potential due to formation of an HDTMA bilayer on the ceramic surface. Field tests conducted over a 6-month period showed negligible water loss from HDTMA-treated ceramic (0.03 L h−1) compared to untreated ceramics (up to 6 L h−1). The results indicated that a surfactant treatment to the anode ceramic casing can greatly improve the application of electrokinetics in unsaturated environments.

Flow through Porous Media XVI: Electrokinetic Transport Coefficients of Aqueous Solutions of Mercuric Chloride and Glycine through a Sintered Disc Impregnated with a Cellulose Acetate Membrane under a Magnetic Field

The effect of the magnetic field on the electrokinetic transport coefficients (permeability coefficient and electro-osmotic permeability coefficient) of water and aqueous solutions of mercuric chloride and glycine through a sintered disc impregnated with cellulose acetate at different potentials, concentrations, and magnetic fields varying up to 21 kg/cm2 are reported at 308.15 K. The phenomenological coefficients characterizing the electro-osmotic flow and the membrane characteristics are also estimated for the various solutions with the object of determining the efficiencies of electrokinetic energy conversion and ζ potential. The effect of magnetic field has been attributed to the molecular orientation of dipoles in solutions and to the change in the structure of the membrane.

Removal and degradation of phenol in a saturated flow by in-situ electrokinetic remediation and Fenton-like process

In this laboratory study, a sandy loam soil saturated with phenol solution was treated by in-situ electrokinetics-Fenton process incorporated with a permeable reactive wall of scrap iron powder (SIP). The soil was contaminated and saturated with aqueous phenol solution of 90–115 mg/kg in concentration. It was then placed in a soil cell. The soil cell was assembled with an anode reservoir and a cathode reservoir at its ends. A bed of SIP (1.05–32.69 g) was inserted in the soil cell at a distance of 5 cm from the anode reservoir compartment. For the test runs, 0.3% H 2O 2 was used as the anode reservoir fluid, whereas de-ionized water was used as the cathode reservoir fluid. An electric gradient of 1 V/cm was applied to enhance the saturated flow in the soil cell for a period of 10 days. Experimental results have shown that the electroosmotic (EO) flow quantity decreased as the amount of SIP increased. This phenomenon was in good agreement with the results showing the value of EO permeability increased with a decreasing amount of SIP. Results also showed that throughout the test period the cumulative, consumed mass of H 2O 2 in the anode reservoir increased as the amount of SIP decreased. On the other hand, the cumulative, increased mass of phenol in the cathode reservoir was found to increase with a decreasing amount of SIP. Meanwhile, the residual phenol concentration in the soil cell was found to decrease with a decreasing amount of SIP. When 1.05 g scrap iron powder was used, an overall removal and destruction efficiency of phenol of 99.7% was obtained. Therefore, it is evident that an in-situ combined technology of electrokinetic remediation and Fenton-like process is capable of simultaneously removing and degrading the phenol in a saturated flow.

Bistability and Electrokinetic Oscillations

Nonlinear dynamic behavior and electrokinetic oscillations have been investigated for the membrane systems (a) 0.1 N NaCl/KCl ∥ Millipore filter ∥ 0.01 N NaCl/KCl; (b) 0.1 N NaCl/KCl ∥ Whatman Inorganic filter ∥ 0.01 N NaCl/KCl; and (c) 0.1 N NaCl/KCl ∥ silver-coated filter ∥ 0.01 N NaCl/KCl, from the viewpoint of testing the theories for the phenomena and elucidating the mechanism. To achieve these objectives, studies on hydrodynamic permeability, electroosmotic permeability, bistability, and electrokinetic oscillations were undertaken. Relaxation time for buildup and decay of electroosmotic pressures was experimentally determined. Bistability was not observed showing that it is not a prerequisite for oscillations and nonlinear relations between (Jv)Δρ=0 and Δφ involving cubic or higher-order terms are necessary for bistability. The oscillations were studied at different current strengths. The period is found to be independent of current, while amplitude A is found to be linearly related to current I which is the bifurcation parameter. The bifurcation point occurs at ∼0.4 mA. Studies have also been made with membranes of different pore size that show that amplitude increases with increase in pore size of the membranes. The validity of the two-variable model of Teorell was examined by comparing the experimental results with computer simulation based on parameters determined experimentally. Theory does not meet expectation and the results suggest that modification of theory is needed. The weakness of the theory has been critically examined.

Abiotic Degradation of Nitrates Using Zero-Valent Iron and Electrokinetic Processes

Nitrate transformation in artificial saturated soils made from sand and/or clay mixed with nitrate-contaminated water was investigated using (1) zero-valent iron treatment, (2) electrokinetics treatment alone, and (3) electrokinetics coupled with an iron treatment wall placed near the cathode or anode. Approximately 75–98% of the nitrates were transformed using zero-valent iron to treat the artificial soils. The major products in the zero-valent–assisted transformation were nitrogen gases (75–81%) and ammonia–nitrogen (2–18%). Nitrite–nitrogen was less than 1% in all these experiments. With electrokinetics alone, some nitrates were transformed (about 30%). Nitrate transformation was about 60% with the iron wall placed near the cathode, and was about 95% with the iron wall placed near the anode. The major products were nitrogen gases and ammonia. Nitrite-nitrogen was less than 1% in these runs. Electroosmotic permeability (Ke) variation appeared to be dependent on the voltage in the reactor. The pH variations over time in electrokinetics (control and iron wall near cathode) indicated the movement of a small acid front. However, the presence of an iron wall near the anode tended to increase the pH slightly. The pH variations over time in the electrokinetics coupled with an iron wall depend on the location of the iron wall. This study demonstrates that electrokinetics coupled with an iron wall near the anode is capable of remediating nitrate contamination in low permeability soils. Key words: Electrokinetics; treatment wall; zero-valent iron; nitrates; groundwater remediation

Electroosmotic Transport through a Cation-Exchange Membrane: Effect of the Stirring on the Dependence of the Electroosmotic Permeability on the Temperature

The electroosmotic flux through a cation-exchange membrane has been obtained in different situations. From these measurements, the apparent electroosmotic permeability,W,of a cation-exchange membrane has been determined as a function of the temperature,T,and the stirring rate,v, of the solutions. In all the experimental situations studied,Wdecreases whenvincreases, while it can increase or decrease withTdepending on the temperature range considered. For this last reason, the (T,W) curves show a minimum whose value and position depend on the experimental conditions established. The influence of the concentration polarization effect in the value ofWand in its dependence withvandTis studied and quantified.

Effect of the Temperature on the Electroosmotic Permeability of a Cation-Exchange Membrane

The water electroosmotic flux,JV, through a cation exchange membrane has been measured as a function of the temperature,T, with various values of the electrolyte concentration and for different current densities. From these measurements the electroosmotic permeability,W, of the membrane has been determined under different experimental conditions. In the studied temperature range, 282 K ≤T≤ 308 K, a clear dependence ofWonTwas observed, so that,Wdecreases whenTincreases at the lowest values ofT, whereas the opposite behavior occurs at the highest values ofT. For this reason the (T,W) curves show a minimum in most of the studied cases. The position of this minimum as well as the value of the minimum of the electroosmotic permeability depends clearly on the concentration and the current density.

Effect of aqueous phase properties on clay particle zeta potential and electro-osmotic permeability: Implications for electro-kinetic soil remediation processes

The influence of aqueous phase properties (pH, ionic strength and divalent metal ion concentration) on clay particle zeta potential and packed-bed electro-osmotic permeability was quantified. Although pH strongly altered the zeta potential of a Georgia kaolinite, it did not significantly change that of a Wyoming bentonite. The zeta potential for the kaolinite ranged from +0.7 mV at pH = 2 to −54 mV at pH = 10 (0.01 M KCl) while the bentonite zeta potential changed by only 5 mV (−31 to −36 mV) over the same pH range. For both clays, ionic strength was found to have a weak effect while divalent cations made the zeta potential markedly more positive. Charge reversal was observed for kaolinite at 100 ppm Pb 2+ (pH = 5) with a background ionic strength of 0.01 M KCl and only 10 ppm Pb 2+ with a background of 5 × 10 −4 M KCl. A theoretical relationship between the electro-osmotic permeability coefficient for packed clay beds and particle zeta potential was developed and experimentally verified for kaolinite. For example, both the electro-osmotic permeability coefficient and particle zeta potential were found to be three times greater at pH = 5 than at pH = 3. As a result, rapid zeta potential analyses can be used to predict electro-osmotic performance for expected site conditions as well as to select electrolyte control strategies to optimize an electro-kinetic soil remediation process.

Scale-up aspects of the Lasagna ™ process for in situ soil decontamination

A novel integrated in situ remediation technology called Lasagna ™ is being developed coupling electrokinetics with in situ treatment zones. The first field test of the process was successfully completed in May of 1995 at a DOE site in Paducah, KY, which has clayey soil contaminated with trichloroethylene. This paper focuses on the scale-up characteristics of the Lasagna process from bench to pilot scale. The study was critical for developing predictive models that aided in the design of the field test. Key parameters such as electrokinetic characteristics, soil temperature, cathode effluent pH and conductivity, and treatment zone spacing were evaluated under controlled conditions. Experiments were conducted with both kaolin clay and the actual Paducah soil using various treatment zone configurations. The obtained data support the feasibility of scaling up this technology with respect to electrokinetic parameters such as electro-osmotic permeability and energy consumption. The removal of the model organic compound p-nitrophenol from the soil was also very efficient (98% in one pass) in the pilot unit. A mathematical model was developed that successfully predicted the temperature rises observed in the soil as a function of the applied voltage gradients.

Zeta potential and electroosmotic permeability of clay soils

L'on etudie les permeabilites electro-osmotiques de six sols argileux et leurs potentiels zeta calcules en partant de la double couche Stern-Gouy. L'on trouve que la permeabilite electro-osmotique est proportionnelle au potentiel zeta, en accord avec le modele electrocinetique de Helmholtz-Smoluchowski communement accepte, a la condition de prendre en compte le caractere tortueux des capillaires du sol et une coupure du potentiel zeta. La technique presentee dans cette etude peut etre utilisee pour evaluer l'efficacite du procede electro-osmotique sur un sol d'un site specifique pour obtenir certaines proprietes du sol en partant du laboratoire.

Electrokinetic dewatering of a phosphate clay

The principles of electrokinetic dewatering are: (1) electrophoresis, the movement of colloidal particles in a direct current electric field; (2) dielectrophoresis, the movement of colloidal particles in a non-uniform electric field; and (3) electro-osmosis, the water flow in porous media in a direct current electric field. Electrokinetic dewatering of a phosphate clay was investigated in an experimental program. The results show that the velocity of sedimentation is controlled by the applied current density and that electro-osmotic permeability dominates the effectiveness of electrokinetic consolidation. The intermittent current and polarity reversal can significantly improve the effectiveness of electrokinetic dewatering and reduce energy consumption and adverse electrode reactions.

Zeta potential and electroosmotic permeability of clay soils

Zeta potential and electroosmotic permeability of clay soils

Nonlinear Dynamics of Membrane Processes: Bistability and Oscillations in Electrokinetic Phenomena

Bistability and oscillations have been studied for a C 1 |membrane| C 2 system, where C 1 and C 2 represent the concentrations of dilute and concentrated solutions of NaCl/KCl. In this context (i) hydrodynamic permeability, (ii) electroosmotic permeability, (iii) streaming current, and (iv) diffusion current (current due to concentration difference on the two sides of the membrane) have been measured to test the assumptions of existing theories. Bistability data do not support the existing theories. The ratio of the slopes does not correspond to C 1/ C 2 as predicted by the theory of Kobatake et al. A semiempirical correlation has been proposed for the interpretation of data. Data on electrokinetic oscillations in (i) a Pyrex membrane-aqueous electrolyte system and (ii) a Millipore filter-aqueous electrolyte system have been reported in order to test certain features of the existing theories. The results show that the time period depends on the geometrical factors describing the system and is independent of the current strength, which is in conformity with the theory of Teorell et al. as well as that of Meares et al. It has been shown that previous theory also leads to an equation of the Van der Pol type. An attempt has been made to examine the correlation between bistability and oscillations. It is found that bistability can occur when electroosmotic permeability is a function of potential difference and conductance is a function of volume flux. On the other hand, oscillations can occur when conductance is a function of volume flux, provided certain dynamic conditions are satisfied.

Electrokinetic Studies of Urine-Urea Mixture Across Bladder Membranes

Purpose We ascertain the role of urea in urine and its probable effects on the polarizable behavior of bladder interfaces. Materials and Methods Urine was systematically diluted, keeping overall volume the same. The methodology of nonequilibrium thermodynamics was used, which involves measurements of hydrodynamic permeability, electro-osmotic permeability, streaming potential and streaming currents, respectively. Results Effective pressure terms (alpha 1) and polarizability terms (alpha 2) were computed, making use of higher order phenomenological coefficients, and their concentration dependence was examined. Abrupt changes in the values of alpha 1 and alpha 2 are supported by trends in higher order phenomenological coefficients. Conclusions The polarizable behavior of the bladder is maintained up to certain concentrations of urea in urine and then it undergoes drastic changes. The role of the bladder in situations of improper functioning of the liver and diets without protein may provide an explanation.

On the Fixed Charge Concentration and the Water Electroosmotic Transport in a Cellulose Acetate Membrane

The ionic permeselectivity of a cellulose acetate membrane prepared in our laboratory has been studied from membrane potential and electroosmotic flux measurements. The obtained results show that, at low values of the external salt concentration, the membrane behaves in a cationic-exchange way. The membrane fixed charge concentration has been estimated from the membrane potential measurements as ∼10-2 mol/liter. Electroosmotic transport decreases notably when the concentration increases, even reversing its sign at concentrations higher than ∼10-1 mol/liter. The weak cationic selective character of the membrane and the fact that the anion mobility is higher than the cation mobility in the membrane phase are both considered responsible for the observed significant sign reversal of the electroosmotic permeability.