Catalyzed hydrogen peroxide (H2O2) propagations (CHP; modified Fenton’s reagent) has been applied at hundreds of sites over the past few years. Practitioners have used a range of H2O2 concentrations and catalysts with and without the addition of acid. Results from CHP in situ chemical oxidation (ISCO) have been mixed: soluble, sorbed, and dense nonaqueous phase liquid (DNAPL) forms of contamination have been destroyed at some sites, while minimal treatment has been observed at other sites. It is widely believed that hydroxyl radicals are the only species important in contaminant treatment through Fenton-like reactions. However, other species formed in CHP reactions, such as superoxide anion and hydroperoxide anion, may provide important mechanisms for treating contaminants in sorbed and DNAPL states.
This research was based on the tenet that, in order for ISCO using CHP to be successful, the generation of an optimum mixture of hydroxyl radicals and other reactive transient oxygen species is necessary. Specific objectives focused on the generation of transient oxygen species from the catalytic decomposition of H2O2 by the different minerals contained in aquifer solids, the generation of transient oxygen species by soluble iron-catalyzed CHP reactions, the role of different oxygen species in the degradation of common organic contaminants, the potential for the treatment of contaminants in sorbed and DNAPL states, and the use of process chemistry to optimize reagent delivery.
The research aimed to provide a better fundamental understanding of CHP as an ISCO process. Two basic principles served as themes for the project: (1) that hydroxyl radicals, while necessary for the oxidation of soluble contaminants, are only partially responsible for the success of CHP ISCO, and (2) naturally occurring trace minerals may play an important role in CHP ISCO relative to soluble iron catalyst addition. Research focused on detecting the generation of three transient oxygen species in CHP reactions catalyzed by trace minerals or soluble iron: hydroxyl radical, superoxide anion, and hydroperoxide anion. The importance of each oxygen species was evaluated for DNAPL destruction and the treatment of sorbed contaminants. Finally, practical delivery and stoichiometry considerations were evaluated.
The project team is now applying state-of-the-art peroxygen (H2O2 and persulfate) ISCO process chemistry and phased optimization to a representative field site to demonstrate the full potential of peroxygen ISCO, validate its effectiveness, and give Department of Defense (DoD) remedial project managers knowledge of more effective process conditions for successful peroxygen ISCO implementation. A Final Report for this project is available.
Results of this research provide information on the site and process conditions necessary for the successful implementation of CHP ISCO for remediation of DNAPL at DoD facilities. (Project Completed – 2006)