Effects of several surfactants and high-molecular-weight organic compounds on decomposition of trichloroethylene with zerovalent iron powder.

ABSTRACT

We investigated the effects of coexisting surfactants and high-molecular-weight organic compounds on the reductive dechlorination of trichloroethylene by zerovalent iron powder to determine whether these additives had utility as washing reagents for remediation of soil and groundwater pollution. During the dechlorination reaction, the amount of trichloroethylene decreased, and the formation of cis-1,2-dichloroethylene was observed. The decomposition of trichloroethylene was found to be first-order with respect to the trichloroethylene and zerovalent iron concentrations when the solution contained no additives. The rates of decomposition of trichloroethylene in the presence of the additives were lower than the rate in the absence of the additives the rate constant was reduced by a factor of 0.7 for the cationic surfactant cetyltrimethylammonium bromide; by a factor of 0.5 for the anionic surfactants sodium n-dodecylbenzenesulfonate, sodium n-dodecylsulfate, and sodium n-dodecanesulfonate and for the high-molecular-weight organic compounds soluble starch, beta-cyclodextrin, and polyethyleneglycol 6000; and by a factor of 0.2 for sodium laurate and the nonionic surfactants Triton X-100, Tween 20, Tween 60, Brij 35, and Brij 58. Comparison of the concentrations of the nonionic surfactants with their critical micellar concentrations indicated that the rate-reducing effect of these additives was due to solubilization of trichloroethylene into the micellar phase. The adsorption of trichloroethylene onto the zerovalent iron surface was also affected by the presence of the additives. Thus, our results indicated that the changes in the decomposition rate of trichloroethylene were determined by several factors.