Effect of sequestration on PAH degradability with Fenton's reagent: roles of total organic carbon, humin, and soil porosity.

The phenomenon of contaminant sequestration-and the physicochemical soil parameters which drive this process-has recently been studied by several authors with regard to microbial contaminant degradation. Very little work has been done to determine the effects of contaminant sequestration on the chemical treatability (oxidizability) of soil contaminants; the current study was conducted to address this data gap. A suite of six model soils, ranging in organic matter content from 2.32 to 24.28%, were extensively characterized. Measured parameters included: (1) levels of total organic carbon (TOC); (2) contents of humic acid (HA); fulvic acid (FA) and humin; and (3) total porosity and surface area. Each soil was then spiked with coal tar and, after varying periods of aging/sequestration, subjected to slurry-phase Fenton's reagent oxidation. Percent recoveries of 12 PAHs, ranging from 3 to 6 aromatic rings, were determined. Results indicated that the susceptibility of each PAH to chemical oxidation was a function of TOC in four of the soils (those with TOC greater than approximately 5%), but was strongly dependent on soil porosity for low-TOC soils. The importance of these two parameters changed with increasing sequestration time, with the relative contribution of porosity-mediated sequestration becoming more important over time. Porosity-mediated effects were more rapid and significant with lower-molecular-weight PAHs (e.g. those with three or four aromatic rings) than with higher-molecular-weight, more hydrophobic compounds. These observations are discussed in light of current physicochemical models of the contaminant sequestration process.

Inclusion of vegetable oils in Fenton's chemistry for remediation of PAH-contaminated soils.

Pre-treatment with vegetable oils prior to treatment with Fenton's reagent led to increased oxidation by the latter of polycyclic aromatic hydrocarbons (PAHs) in a pair of model manufactured gas plant soils. This effect was frequently most pronounced in the cases of high-molecular-weight (HMW) PAH species, indicating a preferential "targeting" of oxidative equivalents toward these compounds. In both cases, addition of oils--either corn oil containing unsaturated lipids or palm kernal oil (PKO) comprised primarily of saturated fats--at the 5% dosage was required; supplementation with 1% oil apparently did not sufficiently facilitate PAH desorption and mass-transfer to have a notable effect on degradation efficiency. In PKO-supplemented reactions, replacement of H2O2 with calcium peroxide (CaO2) further increased the extent of PAH removal. Again, this was most pronounced in the cases of several HMW PAHs; among a suite of four 5- and 6-ring PAH (benzo[a]pyrene, dibenz[a, h]anthracene, benzo[g, h, i]perylene and indeno[c, d]pyrene), average removal efficiency increased from 5% in PKO-supplemented reactions in which H2O2 served as the oxidant, compared to 44% in CaO2-containing reactions. This last finding is consistent with other reports which have indicated that slower-release oxidants are better suited to degradation of contaminants which, despite vegetable oil treatment, remain soil-sorbed.