Decreased Release of PAHs from Soils as a Result of Field Bioremediation

In this study, the relationship between the release characteristics of contaminants from soil and the biodegradability of the contaminants was evaluated. The soils used were from a large-scale field site. A batch rate of release procedure was used to quantify the release of polynuclear aromatic hydrocarbons (PAHs) from manufactured gas plant site soils before and during bioremediation in a field land treatment unit (LTU). This evaluation assessed the performance of the field-scale LTU with respect to changes in the soil PAH concentrations and to changes in chemical release parameters. The practical implications of the evaluation are discussed. During 147 days of LTU operations, the concentrations of specific PAHs were reduced 39–93%. ROR studies were conducted on LTU soil samples obtained at Days 0, 58, 72, and 147 of treatment. As a result of 147 days of treatment in the LTU, the fraction of a PAH released rapidly (F) had decreased for 8 of 10 PAHs, and the value of k2 (the first-order rate constant describing slow release) had decreased for 5 of 10 PAHs. There were no increases in F or k2 for any of the PAHs as a result of treatment in the field LTU. The results indicated that (1) only a fraction of the total concentration of the individual PAHs in the LTU samples was readily available to be released from the soil; (2) the remainder was released at a much slower rate; and (3) the mass of PAH released from the LTU soils to the aqueous phase decreased considerably. In addition, the fraction of the chemical released rapidly (F) for the Day 0 soil sample provided a reasonable prediction of the extent of PAH loss during 147 days of biological treatment in the field LTU.