Treatment of Four Biorefractory Contaminants in Soils Using Catalyzed Hydrogen Peroxide

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.