Application
This technology has been proven effective in reducing concentrations of volatile organic compounds (VOCs) and semi-volatile organic compounds (SVOCs). In-Situ Chemical Oxidation (ISCO) is generally more cost effective when applied in the source area of contamination.

Site-specific conditions and parameters, in conjunction with oxidant-specific characteristics, must be carefully considered to determine whether ISCO is a viable technology for deployment relative to other candidate technologies, and to determine which oxidant is most appropriate. These issues and the advantages and disadvantages should be considered. The breadth of ground-water contaminants amenable to transformation via various oxidants is large. That is, many environmental contaminants react at moderately high rates with these oxidants. Therefore, a wide range of contaminant classes are amenable to chemical oxidative treatment. Mixtures of contaminants may require treatment trains involving the sequential application of technologies to accomplish the treatment objective. Chemical oxidation can be deployed under a variety of applications, i.e., in either the unsaturated or saturated zones, or possibly above-ground, and under a variety of hydrogeologic environments. There are potential advantages and disadvantages of ISCO that should be assessed when considering the deployment of this technology..

Operation Principles (Back to Top)
In-situ Chemical Oxidation (ISCO) is a process in which the oxidation state of a substance is increased. In general, the oxidant is reduced by accepting electrons released from the transformation (oxidation) of target and non-target reactive species. Oxidation of non-target species, including reduced inorganics in the subsurface, also involves the loss of electrons; however, the main target during ISCO involves organic chemicals. Oxidation of organic compounds may include oxygen addition, hydrogen abstraction (removal), and/or withdrawal of electrons with or without the withdrawal of protons. The main objective of chemical oxidation is to transform undesirable chemical species into species that are harmless or nonobjectionable.

For example, oxidation of trichloroethylene (TCE) and perchloroethylene (PCE) may produce reaction byproducts that include dichloroacetaldehyde and dichloroacetic acid, compounds with lower toxicity. Similarly, oxidation of phenolic compounds may produce an assortment of carboxylic acids (Huling et al. , 1998) that are nontoxic. Oxidation of these byproducts to CO 2 and H 2 O could be accomplished through additional oxidative treatment and expense, but may not be practical for economic purposes. These reaction byproducts may also serve as microbial substrate for natural attenuation processes.

Some of the factors that determine the effectiveness of ISCO are:

System Design (Back to Top)
Bench-scale treatability studies and pilot tests can be useful to gain insight on the feasibility of contaminant oxidation prior to field-scale applications. In complex, heterogeneous sys­tems it is difficult to predict specific reactions, oxidation efficiency, oxidation byproducts, or whether any of the potential limitations apply. The methods and materials of bench-scale treatability studies may vary based on the oxidant used and the objectives. It is important to recog­nize the physical differences between bench and field-scale systems. The use of bench-scale treatability results from simplified systems to design field-scale ISCO sys­tems must be heavily scrutinized. Physical and chemical characteristics of the subsurface environment (hydrogeology, geology, geochemistry) vary from site to site and impact the fate and transport of the injected oxidant and reagents. Site characterization is critical to the feasibility assessment of ISCO and in the planning and design of pilot- and full-scale ISCO systems.

Advantages and Disadvantages (Back to Top)