Enhanced Solubilization and Destruction of Tetrachloroethylene by Hydroxypropyl-β-cyclodextrin and Iron

Hydroxypropyl-β-cyclodextrin (HP-β-CD) enhances the solubility of tetrachloroethylene (PCE) in water both in static and in flowing systems. HP-β-CD does not decrease the interfacial tension between PCE and water and, therefore, should not mobilize immiscible-phase PCE in the subsurface. Rates for the reaction of PCE with metallic iron were measured in HP-β-CD solutions under static conditions. In flowing systems, metallic iron removed PCE, and no other chlorinated ethylene species were observed in the column effluent. In several such systems, recycling of the HP-β-CD solution took place following the reaction with iron. No downward mobilization of the PCE pool in the generator column was observed. The solubility enhancement and reaction with metallic iron are consistent with reversible formation of a stoichiometric HP-β-CD/PCE complex. A theoretical treatment of the reaction rates of complexed PCE on an iron surface was developed. This treatment suggests that any material that enhances the solubility of low-solubility organic substances may slow down the rate of reaction in aqueous solution. In many cases, the rate retardation should equal the degree of solubility enhancement. The combination of HP-β-CD and iron metal appears to be a promising groundwater remediation technology.