Electrokinetic Transport

Edwards [105] has extended the macrotransport method, originally developed by Brenner [48] and based upon a generalization of Taylor-Aris dispersion theory, to the analysis of electrokinetic transport in spatially periodic porons media. Edwards and Langer [106] applied this methodology to transdermal dmg delivery by iontophoresis and electroporation. 

Electrokinetically enhanced bioremediation is an in situ process for the treatment of soils and groundwater contaminated with petroleum hydrocarbons and other compounds easily biodegraded under anaerobic conditions. Bench-scale tests have shown that the apphcation of an electric field provides electrokinetic transport of nutrients and biodegrading bacteria to areas of contamination. In addition, microbial growth is enhanced, nitrate transport can be predicted, and beneficial temperature increases can be achieved to areas of contamination. 

Electrokinetic transport is a patented, in situ, commercially available technology for the bioremediation of organic contaminants in aquifer soils and groundwater. The technology involves the application of a direct electrical current across the area to be treated to facilitate the movement of biodegrading bacteria to the site of contamination. 

Electrokinetics has been used to mobilize metals and dissolved contaminants to in situ treatment or recovery zones. Electrokinetic transport uses these mechanisms to move bacteria through the subsurface to the contaminated media. The technology can be used to treat organic contaminants that adsorb to aquifer soils including halogenated hydrocarbons and non-aqueous-phase liquids (NAPLs). 

This technology is not suitable for very dense, low-permeability soils and sediments. However, electrokinetic transport could be used to remediate contaminated clay formations within a more permeable aquifer. 

Masliyah, J. H., Electrokinetic Transport Phenomena, Alberta Oil Sands Technology and Research Authority, Edmonton, Alberta, Canada, 1994. (Graduate and undergraduate levels. An excellent introduction to transport processes relevant to applications of electrokinetic phenomena. Most of the material is accessible to undergraduate students. Chapter 12 presents some very practical applications of electrokinetic phenomena of interest to engineers.)... 

Future developments that may facilitate ocean measurements from vessels or buoys include miniaturization of chromatographic equipment (so less solvent is needed per analysis), new solvent transport systems, such as electrokinetic transport, to reduce power requirements on the pumps, and more sensitive detectors for liquid chromatography. Certain combinations of very short columns and flow injection analysis are also promising for real-time studies. 

DeFlaun, M. F. and Condee, C. W. (1997) Electrokinetic Transport of Bacteria f Journal of Hazardous Materials, Special Edition on Electrochemical Decontamination of Soil and Water, Edited by Yalcin B. Acar and AkramN. Alshawabkeh, pp. 263-278. 

Masliyah, J.H. Electrokinetic Transport Phenomena, Alberta Oil Sands Technology and Research Authority Edmonton, AB, 1994. 

Ermakov, S.V., Jacobson, S.C., Ramsey, J.M., Computer simulations of electrokinetic transport in microfabricated channel structures. Anal. Chem. 1998, 70(21), 4494M504. 

Griffiths, S.K., Nilson, R.H., Modeling electrokinetic transport for the design and optimization of microchannel systems. Micro Total Analysis Systems, Proceedings 5th [lTAS Symposium, Monterey, CA, Oct. 21-25, 2001, 456 158. 

Instead of directly using the charged or otherwise electrically activated species in a chemical reaction, the option exists to use charges to enhance mass transport. This can be achieved by transporting the chemical species, if charged, themselves, or by transporting the medium in which the chemical species are contained. This electrokinetic transport exists in different forms, which will be highlighted below. 

J.H. Masliyah, Electrokinetic Transport Phenomena, Aostra, Alberta, 1994, p. 99. 

Joseph, S. and Aluru, N.R. (2006) Hierarchical Multiscale Simulation of Electrokinetic Transport in Silica Nanochannels at the Point of Zero Charge. Langmuir, 22, 9041-9051. 

For examples of electrokinetic transport models as applied to ion-exchange membranes, see [151, 153, 154]. 

Figure 3. Microfluidic Device. (A) Time lapse illustrating repulsion the ejection of 1.9 pm fluorescent polystyrene microsphere particles from an electroactive microwell. After dissolution of the membrane, the fluorescent particles can be seen in the well. White hnes outline the gold electrodes features. Images are taken every 2 s (total of 10 s). (B) Schematic of the electroactive microwell drug delivery system developed here. Scale bar represents 2 mm. (C) Micro fluidic device with electrical leads connected to thin copper wires. Inset Magnified view of microchip from above looking at the region near the membrane. (D) To illustrate the electrokinetic transport processes involved in the ejection stage, a finite element analysis of time-dependent species transport of the system is shown. Images show cut view of species concentration every 60 s up to 300 s after the ejection process.

Masliyah, J. H. Electrokinetic Transport Phenomena Technical Publication Series 12 Alberta Oil Sands Information Services, Alberta Energy Edmonton, Canada, 1994. 

The classical H-S equation is used to predict the electro-osmotic velocity of the fluid as a function of the electric field and the electrokinetic potential of the clay. Both of these parameters vary during electrokinetic transport, and result in a nonlinear process. New models have been developed that uncouple the electro-osmotic velocity from the applied field taking that surface conductivity and the resulting proportion of the current transferred over the solid-liquid interface are used as intrinsic properties of the clay to describe the velocity (Chapter 2). The pH changes affect the zeta potential, and thereby electro-osmotic conductivity. Thus, electro-osmotic conductivity changes as the dynamic changes in soil pH occur. 

When solving how problems numerically, a Neumann boundary is described as an insulated boundary (or impermeable boundary), which means that there is no fiux at the boundary, while a Dirichlet boundary indicates that the value of head (potential, concentration, etc.) is constant at the boundary. Constant boundary conditions are not able to describe the nature of the electrokinetic transport realistically due to the existence of fiux boundaries caused by the electrode reactions and advection of fluid. In Cao s model, the boundary conditions apphed at the inlet and outlet of the soil column maintained the equahty between the flux of solute at the inside of the column and the flux of solute immediately outside of the column. The following boundary condition was used at the inlet (Lafolie and Hayot, 1993) ... 

Figure 2.14. Distribution of the ORP across a saturated clay specimen measured with and without nanoiron during electrokinetic transport (Pamukcu, Hannum, and Wittle, 2008).

Electrokinetics is a very effective technique to transport nitrate and fluoride, although the transport characteristics of anionic contaminants such as nitrate and fluoride are quite different from the transport of cationic metals. In electrokinetic restoration of saline soil, the electrokinetic transport of cationic salts, as well as nitrates, should be considered. Changes in pH near electrodes after electrokinetic treatment of saline soil are the disadvantages of electrokinetic restoration however. 

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