Chemical oxidation efficiency for aged, PAH-contaminated sites: An investigation of limiting factors

In Situ Chemical Oxidation (ISCO) can be applied to soils contaminated by polyaromatic hydrocarbons (PAHs). PAH degradation yields are often rather low, because of different obstacles not clearly understood. These include the low availability of PAHs, the type and age of soil organic matter and the carbonate content of the soil. The aim of this work was to provide a better understanding of the influence of these limiting factors at a given oxidant dose. Batch experiments were performed on contrasted PAH-contaminated soils or matrices using permanganate, persulfate, modified Fenton's reagent and activated persulfate. PAH availability was estimated by a cyclodextrin-enhanced extraction method. Moderate amounts of oxidant were used in order to lower costs whilst minimizing environmental impacts. Results showed that chemical oxidation efficiency was mainly affected by PAH availability, particularly with low persistent oxidant. With permanganate, a correlation was found between PAH availability and degradation yield. With low persistent oxidants, degradation yields were significantly increased by sequential addition. The negative impacts of a high content of soil organic matter and/or carbonate were highlighted. For the aged contaminated soils, PAH degradation yields remained below 30% after most treatments except with permanganate (40-60%) and sequential addition of Fenton's reagent (40-70%). These results should have useful implications for the design of ISCO treatments.