DDT, DDD, and DDE Dechlorination by Zero-Valent Iron

Traditionally, destruction of DDT [1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane] for environmental remediation required high-energy processes such as incineration. Here, the capability of powdered zero-valent iron to dechlorinate DDT and related compounds at room temperature was investigated. Specifically, DDT, DDD [1,1-dichloro-2,2-bis(p-chlorophenyl)ethane], and DDE [2,2-bis(p-chlorophenyl)-1,1-dichloroethylene] transformation by powdered zero-valent iron in buffered anaerobic aqueous solution was studied at 20 °C, with and without the presence of nonionic surfactant Triton X-114. The iron was successful at dechlorinating DDT, DDD, and DDE. The rates of dechlorination of DDT and DDE were independent of the amount of iron, with or without surfactant. The rates with surfactant present were much higher than without. Initial first-order transformation rates for DDT, DDD, and DDE were determined. For example, the initial first-order rate of DDT dechlorination was 1.7 ± 0.4 and 3.0 ± 0.8 day-1 or, normalized by the specific iron surface area, 0.016 ± 0.004 and 0.029 ± 0.008 L m-2 h-1, without and with surfactant, respectively. A mechanistic model was constructed that qualitatively fit the observed kinetic data, indicating that the rate of dechlorination of the solid-phase (crystalline) reactants was limited by the rate of dissolution into the aqueous phase.