In situ chemical oxidation

In situ chemical oxidation (ISCO), a form of advanced oxidation processes and advanced oxidation technology, is an environmental remediation technique used for soil and/or groundwater remediation to reduce the concentrations of targeted environmental contaminants to acceptable levels. ISCO is accomplished by injecting or otherwise introducing strong chemical oxidizers directly into the contaminated medium (soil or groundwater) to destroy chemical contaminants in place. It can be used to remediate a variety of organic compounds, including some that are resistant to natural degradation. Chemical oxidation is one half of a redox reaction, which results in the loss of electrons. One of the reactants in the reaction becomes oxidized, or loses electrons, while the other reactant becomes reduced, or gains electrons. In ISCO, oxidizing compounds, compounds that give electrons away to other compounds in a reaction, are used to change the contaminants into harmless compounds. The in situ in ISCO is just Latin for 'in place', signifying that ISCO is a chemical oxidation reaction that occurs at the site of the contamination. The remediation of certain organic substances such as chlorinated solvents (trichloroethene and tetrachloroethene), and gasoline-related compounds (benzene, toluene, ethylbenzene, MTBE, and xylenes) by ISCO is possible. Some other contaminants can be made less toxic through chemical oxidation. A wide range of ground water contaminants react either moderately or highly with the ISCO method, and ISCO can also be used in a variety of different situations (e.g. unsaturated vs saturated ground, above ground or underground, etc.), so it is a popular method to use. Fenton's reagent (hydrogen peroxide catalyzed with iron) and potassium permanganate are the oxidants that have been used the longest, and are now used the most widely. The systems of using hydrogen peroxide were based on the work of H.J.H. Fenton, who used iron salts to catalyze the compound. Hydrogen peroxide was first used in 1985 to treat a formaldehyde spill at Monsanto's Indian Orchard Plant in Springfield, Massachusetts. At this site, a 10% solution of hydrogen peroxide was injected into a formaldehyde plume. Fenton's reagent was initially used to treat hydrocarbon sites where benzene, toluene, and ethylbenzene were present. As the industry shifted its focus to the remediation of chlorinated solvents, hydrogen peroxide was found to be effective in both the hydrocarbon industry and the chlorinated solvent industry. Scientists also found that permanganate could be used on chlorinated solvents. Permanganate based ISCO started to be used in the late 1990s. At this time, ISCO had also become an established remedial technology. The development of sodium persulfate for ISCO began in the late 1990s because of the limitations in using peroxide or permanganate as oxidants. Peroxide has such a short life that it can not be transported properly. Permanganate only treats chlorinated solvents with double bonds and is easily used up by organic material in soil. Persulfate is more stable, treats a wider range of contaminants, and is not used up by soil organics as easily.