EFFICACY OF IN-SITU OZONATION FOR THE REMEDIATION OF PAH CONTAMINATEDSOILS

Polycyclic aromatic hydrocarbons (PAHs) are of environmental concern b ecause many PAHs are either carcinogens or potential carcinogens. Petr oleum products are a major source of PAHs. The occurrence of PAH conta mination is widespread and novel treatment technologies for the remedi ation of contaminated soils are necessary. Ozone has been found to be extremely useful for the degradation of PAHs in soils. For these compo unds, the reaction with molecular ozone appears to be the more importa nt degradation pathway. Greater than 95% removal of phenanthrene was a chieved with an ozonation time of 2.3 h at an ozone flux of 250 mg h(- 1). After 4.0 h of treatment at an ozone flux of 600 mg h(-1), 91% of the pyrene was removed. We have also found that the more hydrophobic P AHs (e.g. chrysene) react more slowly than would be expected on the ba sis of their reactivity with ozone, suggesting that partitioning of th e contaminant into soil organic matter may reduce the reactivity of th e compound. Even so, after 4 h of exposure to ozone, the chrysene conc entration in a contaminated Metea soil was reduced from 100 to 50 mgkg (-1). Ozone has been found to be readily transported through columns p acked with a number of geological materials, including Ottawa sand, Me tea soil, Borden aquifer material and Wurtsmith aquifer material. All of these geological materials exerted a limited (finite) ozone demand, i.e. the rate of ozone degradation in soil columns is very slow after the ozone demand is met. Moisture content was found to increase the o zone demand, most likely owing to the dissolution of gaseous ozone int o the pore water. As once the initial ozone demand is met, little degr adation of ozone is observed, it should be possible to achieve ozone p enetration to a considerable distance away from the injection well, su ggesting that in-situ ozonation is a feasible means of treating uncont aminated soils. This is substantiated by two field studies where in-si tu ozonation was apparently successful at remediating the sites. (C) 1 997 Elsevier Science B.V.