Osmotic transport

Fig. 5-8 Total adhesion loss of a 500-/xm-thick coating of EP (liquid lacquer), 0.2 M NaCI, galvanostatic = -1.5 /tA nrr, 5 years at 25"C. Left coating with a pin pore loss of adhesion due to cathodic disbonding. Right pore-free coating loss of adhesion due to electro-osmotic transport of H O. In both cases the loose coating was removed at the end of the experiment.

Ions permeating the membrane carry solvating water molecules in their hydration shell. Also, osmotic transport of water from the dilute to the concentrated chambers can occur. 

Cherepy, N.J. and Wildenschild, D. (2003) Electrolyte management for effective long-term electro-osmotic transport in low-permeability soils. Environ. Sci. Technol. 37,3024-3030. 

Equations (6.292) and (6.293) are the formulations of nonequilibrium thermodynamics and describe the osmotic transport of solute and water across the membrane. These equations can be linearized for small chemical potential differences, and we obtain... 

Osmotic transport through pores, cracks, or drilled holes... 

It must be stressed that the individual mass-transfer coefficients, determined using Eqs (21)-(23), include both the diffusive and the osmotic transport components. Qf, and Qf, i, Qe, and Qe, i, Qr, and Qr,, represent the changes in the quantities of the solute, that is, in the concentrations and volumes between sampling time i, and i, i. Therefore, experimental determination of the osmotic pressure gradients. An, and calculation of osmotic mass-transfer coefficients, FQ, may be excluded. Overall mass-transfer coefficients of solute species through the BAHLM system are calculated using Eqs (8) and (9). 

The electro-osmotic transport of water during EOD leads to very high energy efficiencies for example, the observed efficiencies of 5.6 ml/mAh (1.55 ml/C) are equivalent to 8300 moles of water per Faraday of electricity, so that EOD is extremely cost effective. 

A well-documented field application of electrochemical remediation is reported to address the problem of chlorinated solvent (TCE) in clay soil at the DOE site in Paducah, Kentucky. This process is known as Lasagna (Terran Corporation, Beavercreek, OH) and it combines the electro-osmotic transport of TCE in pore water and degrades it in vertical curtains installed along the flow path within the soil that are filled with iron filings and kaolin clay. Pore water accumulated at the cathode is recycled by gravity back to the anode as makeup water and neutralize the acid formed at the anode. Overall, the treatment is found to be effective. The implementation and performance results are presented in detail in Chapter 30. The same Lasagna process is implemented very recently at another site contaminated with TCE in Fonde du Lac, Wisconsin, and performance is being monitored (Chapter 30). 

The sorption and desorption of chlorinated pesticides limits the potential success of electro-osmotic transport. The sorption of hydrophobic organic compounds (HOCs) is a partitioning type of process and can be represented by linear isotherms until aqueous phase solubility is approached (Chiou, Peters, and Freed, 1979). Karickhoff (1981) reported that the sorption isotherm was linear for HOCs up to half of the aqueous phase solubility level of the solute. Although HOCs adsorb to mineral surfaces mainly due to van der Waals forces (Schwarzenbach, Gschwend,... 

Cosolvent-enhanced electrokinetic remediation of chlorinated pesticides has yet to be explored. Few studies have shown enhancements in the transport of polycyclic aromatic hydrocarbons (PAHs) when cosolvents were used (Maturi and Reddy, 2008 Reddy and Saichek, 2003). The potential success of cosolvents depends on their ability to mobilize the HOCs and to increase the EOF. It was shown that 10% n-butylamine generated the greatest EOF, followed by 20% n-butylamine and water (Maturi and Reddy, 2008). The sorption of solvents to the soil matrix may not be as high as the surfactants, which cause a better solubilization with the same amount of electro-osmotic transport. 

It is worth emphasis that the verification of isotonic transport for a particular model necessitates the solution of Eqns. 5 and 6. In general, the simple calculation of (Cr)o, the reabsorbate concentration with exactly equal bathing media, is not sufficient. Nevertheless, (Cr)q is an important theoretical aspect of a model and has been used to define the coupling coefficient of osmotic transport [ 15] by... 

Thus, the osmotic coupling coefficient is the ratio of the actual volume flow observed with equal bathing media relative to the virtual volume flow that would be necessary for reabsorption to be isotonic. In the models we shall consider, 0 < y < 1. For tight couphng, Y 1 in an uncoupled system y = 0. y has also been termed the efficiency of osmotic transport [16]. 

Osmotic transport of water to or from the contact electrolyte. 

As explained, there are endoelectrogenic soiu-ces in the cell membranes. However, it is quite likely that some macroscopic membranes around organs are also the sites of electricity sources. Nordenstr0m (1983) proposed that there are closed DC circuits in the body with the well-conducting blood vessels serving as cables (e.g., a vascular-interstitial closed circuit). These DC currents can cause electro-osmotic transport through capillaries. Dental galvanism is the production of electricity by the metals in the teeth. 

The transniembrane transport of sodium is coupled with co-electro-osmotic transport of water which dilutes the caustic soda formed. Perfluorocarboxylic membranes can be substituted by perfluorosulphonic membranes for reducing the water transport. 

If vegetables are being cooked, it is advantageous to add salt to the water, as vegetables themselves contain salt. This way, the osmotic transport of water into the vegetables is prevented, which would lead to a significant loss of taste. 

Because EY5 is equal to k the mass transfer coefficient, is strongly dete. There are two other effects that influences the performance of the process as well, i) osmotic flow and ii) less effective Donnan exclusion. Osmotic flow is inherently part of the process and can not be avoided. Since ions are transferred from one compartment to another an osmotic pressure difference is generated and this drives the osmotic transport of water from the diluate to the concentrated side. Secondly, in case of high ionic concentrations the Donnan exclusion becomes less effective. This effect and the less favoured energy consumption at high concentrations makes the process of electrodialysis mote competitive at relatively low concentrations. 

These have the advantage of high membrane flux, which results from the very small thickness of the organic membrane. However, there are a number of operational difficulties. The first of these concerns the osmotic transport of water across the membrane as a result of different ionic concentrations in the two aqueous phases. This causes the membrane drops to swell and ultimately to break down, mixing the strip and feed solutions. Another difficulty arises with the ultimate breaking of the emulsion and separation of the two phases that can give rise to entrainment problems. In addition, the overall process is much more complex than that of the supported liquid membrane. 

Qiao R, Alum NR (2003) Transient analysis of electro-osmotic transport by a reduced-order modelling approach. Int J Numer Methods Eng 56(7) 1023-1050... 

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