Remediation of PAH-contaminated soils and sediments: The peroxy-acid process

A new and innovative hybrid method employing a chemical process followed by a biological process was developed as an efficient and cost effective technique for degrading polycyclic aromatic hydrocarbons (PAHs) found, among other places, in soil and sediment. The chemical process involved the use of hydrogen peroxide and acetic acid to generate reactive hydroxyl radicals or cations as well as peroxy-acid compounds, which in turn oxidize the very stable PAHs. Laboratory optimization experiments were conducted to examine the transformation and/or degradation of alpha-methylnaphthalene and benzo(a)pyrene in two different sediment types and in kaolin. In all optimization experiments, where the volumes of hydrogen peroxide or acetic acid were varied, both alpha-methylnaphthalene and benzo(a)pyrene were degraded over a period of 24 hours. Specific sediment characteristics, such as organic carbon content and particle size distribution, were found to play an important role in the availability of the contaminant and the efficacy of the transformation during the peroxy-acid process for the PAHs investigated. The type of reagent ( i.e., peroxyacetic acid, premixed peroxyacetic acid, and peracetic acid) used also seemed to have a significant effect on the mechanism involved in the peroxy-acid process. Results demonstrated that the mechanisms of oxidation of PAHs may be different depending on the preparation of the solution of peroxyacetic acid used. Finally, authentic PAH-contaminated soils from Superfund sites were treated with the optimized peroxy-acid process (i.e., 3:3:9 v/v/v ratio of hydrogen peroxide:acetic acid:DI water). These experiments were performed both at a small scale where 5 g of soil was treated and at a larger scale where 4.4 kg of soil was treated. A degradation of more than 50% of all the components in this mixture of PAHs was achieved, therefore demonstrating the effectiveness of the process. A preliminary cost analysis showed that the peroxy-acid process would cost more than the Fenton's reagent if hydrogen peroxide and acetic acid were to be used separately. However, using peracetic acid or further optimizing the peroxy-acid process may reduce the cost for this PAH remediation technique.