Abstract
Fenton’s reaction-based chemical oxidation is in principle a method that can be utilized for all organic fuel residues thus making it a potential all-purpose, multi-contaminant, in situ application for cases in which storage and distribution of different types of fuels have resulted in contamination of soil or groundwater. Since peroxide breakdown reactions are also expected to lead to a physical transport of the target compound, this secondary physical removal, or rebound concentrations related to it, is prone to be affected by the chemical properties of the target compound. Also, since soil conditions are seldom optimal for Fenton’s reaction, the balance between chemical oxidation and transport may vary. In this study, it was found that, with a high enough hydrogen peroxide concentration (5 M), methyl tert-butyl ether–spiked groundwater could be treated even under suboptimal conditions for chemical mineralization. In these cases, volatilization was not only contributing to the total removal but also leading to rebound effects similar to those associated with air sparging techniques. Likewise for diesel, temporal transport from soil to the aqueous phase was found to lead to false positives that outweighed the actual remediation effect through chemical mineralization.
Highlights
According to surveys performed in 2013, there are 23,000 sites in Finland that are either suspected to be polluted, declared as such, or have already been treated for contamination
The largest peroxide dose alone decreased pH to level 5.6. These changes were likely contributing to the performance level in each individual case as the results were obtained under highly varied pH conditions (Fig. 1)
No similar peak in volatilization was observed in the 1-L scale, where reduction through some physical mechanism would have had to happen either after a lag period of 4 h or through continuous, moderately increased volatilization without a distinguishable peak. These results suggest that volatilization is either cancelled out or covered under the primary mechanism of chemical oxidation, and that the effect would be negligible in favourable conditions
Summary
According to surveys performed in 2013, there are 23,000 sites in Finland that are either suspected to be polluted, declared as such, or have already been treated for contamination. One method that in principle allows for simultaneous treatment of multiple contaminants with differing characteristics and in different media is chemical oxidation. In a reaction based on Fenton’s chemistry, the chemical breakdown of hydrogen peroxide is catalysed by ferrous iron, and hydroxyl radicals and hydroxide ions are released whilst the ferrous iron is oxidized to ferric iron (Neyens and Baeyens 2003). This first reaction is followed by a series of reactions in which the varying reactive radicals degrade organic compounds, including hydrocarbons (Petri et al 2011)
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