Use of Fenton's Reagent for the Degradation of TCE in Aqueous Systems and Soil Slurries

Abstract

Fenton's reaction is comprised of hydrogen peroxide (H2O2) catalyzed by iron, producing the hydroxyl radical (·OH), a strong oxidant. ·OH in turn may react with H2O2 and iron and is capable of destroying a wide range of organic contaminants. In this laboratory study, Fenton's reaction was observed in aqueous and soil slurry systems using trichloroethylene (TCE) as the target contaminant, with the goal of maximizing TCE degradation while minimizing H2O2 degradation. Fenton's reaction triggers a complex matrix of reactions involving ·OH, H2O2, iron, TCE, and soil organics. In soil slurries with a high fraction of organic carbon (fOC), iron tends to sorb to soil organics and/or particles. In aqueous systems the optimal ratio of H2O2:Fe2+:TCE to degrade TCE in a timely fashion, minimize costs, and minimize H2O2 degradation is 300 mg/L: 25 mg/L: 60 mg/L (19:1:1 molar ratio), while soil slurries with a fOC up to approximately 1% and a soil:water ratio of 1:5 (weight ratio) require about ten times the amount of H2O2, the optimal ratio being 3000 mg/L: 5 mg/L: 60 mg/L (190:0.2:1 molar ratio). TCE degradation rates were observed to decrease in soil slurries with higher fOC because of competition by soil organic matter, which appears to act as a sink for ·OH. H2O2 degradation rates tended to increase in soil slurries with higher fOC, most likely due to increased demand for ·OH by soil organics, increased available iron and other oxidation processes.