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Research on Chemical Oxidation/In-situ Chemical Oxidation
In-Situ Chemical OxidationIn-situ chemical oxidation (ISCO) is developing quickly and is the most rapidly growing remedial technologies applied at EPA hazardous waste sites. Project managers are utilizing ISCO on both new and old sites. ISCO involves the introduction of a chemical oxidant into the subsurface for the purpose of transforming ground water or soil contaminants into less harmful chemical species. ISCO results in the transformation of a wide range of environmental contaminants, enhances mass transfer, and is being used at old sites specifically to reduce the contaminant mass flux from source areas to downgradient pump and treat systems, and/or to reduce anticipated cleanup times required for natural attenuation and other remedial options.
There are several different forms of oxidants that have been used for ISCO; however, the most commonly used oxidants include: permanganate (MnO4-), Fenton's (hydrogen peroxide (H2O2) and ferrous iron (Fe+2)) or catalyzed hydrogen peroxide (CHP), ozone (O3), and persulfate (S2O82-). The two most commonly used forms of injected oxidants are permanganate and H2O2.
The type and physical form of the oxidant indicates the general materials handling and injection requirements. The persistence of the oxidant in the subsurface is important since this affects the contact time for advective and diffusive transport and ultimately the delivery of oxidant to targeted zones in the subsurface. For example, permanganate persists for long periods of time and therefore, both diffusion into low-permeability materials and greater transport (advective) distances through porous media are possible. H2O2 has been reported to persist in soil and aquifer material for minutes to hours, and the relativel diffusive and advective transport distances will be limited. Radical intermediates formed using H2O2, S2O82-, and O3 are generally considered to be responsible for contaminant transformations. These intermediates react very quickly and persist for very short periods of time (< 1 sec).
Permanganate-based ISCO is more fully developed than the other forms of oxidant. Widespread use of in-situ permanganate oxidation involving a diversity of contaminants and geological environments under well documented pilot- and field-scale conditions, in conjunction with long term monitoring data and cost information, has contributed to the development of the technology and the infrastructure needed to support decisions to design and deploy permanganate ISCO systems.
In-situ permanganate oxidation involving the
emplacement method of oxidant delivery.
However, additional research and development is still needed. Fenton oxidation involves the injection of H2O2 alone, or in combination with other co-injected chemical reagents including various forms of iron (Fe+2), acid, and chelating agents. The main Fenton reactions have been previously investigated, however, side and competing reactions that may play major roles in contaminant transformations have not been fully investigated, thus requiring additional research. Complex heterogeneous systems involving aquifer materials,soils, and ground water introduce potential treatment inefficiencies due to non-ideal reactive conditions. Consequently, scientific investigations at GWERD are focused on both fundamental and applied aspects of chemical oxidation to identify and understand site conditions and treatment process variables that contribute to effective and efficient treatment methods. Fenton-driven ISCO has been deployed at a large number of sites and involves a variety of approaches and methods.
Conceptual model of in-situ Fenton/catalyzed hydrogen peroxide oxidation and potential
fate and transport mechanisms.
In general, Fenton chemistry and in-situ Fenton oxidation are complex, involves numerous reactive intermediates and mechanisms, and technology development has been slower. Ozone is a strong oxidant that has been used in the subsurface but in much more limited application than permanganate and Fenton-driven oxidation. Persulfate (S2O82-) is a relatively new form of oxidant that has mainly been investigated at bench-scale. However, considerable research and the applied use of this oxidant is being conducted at an increasing number of laboratories and field sites, resulting in the rapid development of this technology.
- Technical point of contact - Dr. Scott G. Huling (huling.scott@epa.gov).
- Technical Support and Technology Transfer, contact Dr. David Burden (burden.david@epa.gov)
- Link to technical support website (http://www.epa.gov/ada/tsc.html)
Adsorption/Oxidation
A Fenton-driven mechanism for regenerating spent granular activated carbon (GAC) has been proposed and tested. The technology involves the combined, synergistic use of two treatment technologies - adsorption on activated carbon and Fenton oxidation. During carbon adsorption treatment, environmental contaminants are immobilized and concentrated on the GAC, and subsequently transformed by ·OH or other reaction byproducts (oxidants and reductants) generated by the Fenton mechanism. The objective of the treatment process is to transform the contaminants into less toxic byproducts, re-establish the sorptive capacity of the carbon for the target chemicals, increase the useful life of the GAC, and reduce costs for GAC regeneration and water or air treatment. The adsorption/oxidation technology can be applied in both above- and below-ground configurations.
MTBE-spent activated carbon used in Fenton-driven
regeneration studies
Activated carbon is the most commonly used adsorbent in the US today. In 2001, the US consumption of activated carbon was 400 million pounds per year and growing. The international market is greater. Activated carbon is used as a broad-spectrum adsorbent to purify air, water and wastewater in numerous environmental programs implemented via the EPA (Clean Water, Clean Air, Drinking Water, RCRA, UST, CERCLA, etc.). Similarly, the breadth of environmental contaminants that react with moderately high rates with ·OH, a strong but nonspecific oxidant, and with other H2O2-derived reactants (·O2-, HO2-), is large. Therefore, a wide range of contaminant classes are amenable to treatment via the adsorption/oxidation process. The technology could be used on-site and in-situ (i.e. in the above-ground adsorber unit, or below grade) providing an efficient means by which to destroy a wide range of toxic compounds. This treatment process yields high quality treatment effluent and can be deployed under a variety of applications. Preliminary results indicate low costs and favorable economics and feasibility suggesting this is a viable alternative to conventional thermal regeneration where costs can be high due to transportation, treatment, air pollution control, and process inefficiencies.
EPA is seeking collaborative partners to further develop and deploy this technology
(http://www.epatechmatch.com/epa/index.aspx)
- Technical point of contact - Dr. Scott G. Huling (huling.scott@epa.gov).
- Technical Support and Technology Transfer, contact Dr. David Burden (burden.david@epa.gov)
- Link to technical support website (http://www.epa.gov/ada/tsc.html)
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Contact Information
Scott G. Huling, Ph.D., P.E.
U.S. Environmental Protection Agency
Robert S. Kerr Environmental Research Center
P.O. Box 1198
Ada, OK 74820
(580) 436-8610 Phone
(580) 436-8614 FAX
huling.scott@epa.govP. Kyle Jones
U.S. Environmental Protection Agency
Robert S. Kerr Environmental Research Center
P.O. Box 1198
Ada, OK 74820
(580) 436-8873 Phone
(580) 436-8614 FAX
jones.kyle@epa.gov