Electrokinetic Removal of Chlorinated Pesticides

The transport of contaminants under an electrical field in soil is governed by several processes, including electromigration, electro-osmosis, diffusion, sorption, solubilization, and chemical and biological reactions. 

Electromigration is the movement of charged species under the electrical field. Anions move toward the anode and cations move toward the cathode. The degree of the electromigration depends on the mobility of the ionic species. Electromigration is negligible for most chlorinated pesticides since most of them are not ionized. 

Advective flow occurs either by electro-osmosis or hydraulic gradient. The flow due to hydraulic gradient is represented by Darcy s Law. 

Although some degree of advective flow is generated by electro-osmosis, the low solubilization of chlorinated pesticides in the aqueous phase and low desorption rates from the soils limit the movement of contaminants in soUs. As represented in Table 11.1, solubilities of the chlorinated pesticides are very low. Furthermore, the solubility of organic pesticides in most cases is rate limited, which causes even lower aqueous phase concentrations. 

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, 

---