Treatment of Four Biorefractory Contaminants in Soils Using Catalyzed Hydrogen Peroxide

Abstract

The treatment of soil contaminated with pentachlorophenol, trifluralin [2,6-dinitro-N, N-dipropyl-4-(trifluoromethyl) benzenamine], hexadecane, and dieldrin (3,4,5,6,9,9-hexachloro-1a,2,2a,3,6,6a,7,7a-octahydro-2,7:3,6-dimethanonaphth[2,3-b]oxirene) using catalyzed hydrogen peroxide [H₂0₂ and iron(II)] was investigated in a soil of low development with organic C ranging from 2000 mg kg^–1 to 16 000 mg kg^–1. Soil treatment was conducted at pH 3 with 240 and 400 mg L^–1 iron additions and 120 000 mg L^–1 H₂O₂. Pentachlorophenol and trifluralin degradation rates decreased as a function of soil organic C content. However, soil organic C had no effect on the degradation rates of dieldrin and hexadecane. In addition, the four contaminants degraded at equal rates with soil containing organic C > 10 000 mg kg^–1. The ratio of first-order rate constants for contaminant degradation to hydrogen peroxide consumption (k_contaminant/k_h2O₂) was used as an empirical measure of treatment efficiency. These ratios were sensitive to both the soil organic C content and to the concentration of iron added during treatment. The efficiency ratios were highest for treatment with no iron addition; these data suggest that iron minerals and H₂O₂ provide a system in which Fenton-like oxidations are catalyzed. The ability of iron minerals and H₂O₂ to oxidize pentachlorophenol was evaluated in goethite-, hematite-, and magnetite-silica sand at pH 3. Pentachlorophenol was degraded in the mineral-silica sand systems, which was verified by the loss of organic C and the stoichiometric recovery of chloride.