Chemical oxidants most commonly employed to date include peroxide, ozone, and permanganate. These oxidants have been able to cause the rapid and complete chemical destruction of many toxic organic chemicals. The chemical oxidation process also commonly provides for partial degradation of contaminants as an aid to subsequent bioremediation. In general, the chemical oxidation process has demonstrated the capability of achieving high treatment efficiencies (e.g., > 90 percent) for unsaturated aliphatic (e.g., trichloroethylene [TCE]) and aromatic compounds (e.g., benzene), with very fast reaction rates (90 percent destruction in minutes). As is the case with technology application, the key to successful implementation and achieving performance goals lies in the matching of oxidant and in situ delivery system to the contaminants of concern (COCs).
Ozone and/or Concentrated Oxygen Injection
Technology Description: Ozone and/or concentrated Oxygen gas can oxidize contaminants directly or through the formation of hydroxyl radicals. Due to the high reactivity and instability of ozone’s and/or pure both are produced onsite using specialized generation equipment. The delivery system(s) generally require closely spaced injection points (e.g., air sparging wells). The resultant oxygen supply is commonly greater than the total oxygen demand. This fact allows for stimulation of In situ decomposition by indigenous chemotroph bacteria (biostimulation), for faster and more efficient site cleanup. Variations on the basic concept of concentrated oxygen injection form the basis of the bioventing and/or biosparging methodologies. Bioventing is primarily applied to the unsaturated (vadose) zone. In contrast to soil vapor vacuum extraction, bioventing uses low airflow rates to provide only enough oxygen to sustain microbial activity. Injection of oxygen into the saturated zone constitutes – biosparging. Both methods provide in situ remediation technology that stimulates the natural biodegradation of aerobically degradable compounds in soil.
Technology Description: Oxidation using liquid hydrogen peroxide (H2O2) in the presence of native or supplemental ferrous iron (Fe+2) produces Fenton’s Reagent which yields free hydroxyl radicals (OH-). These strong, nonspecific oxidants can rapidly degrade a variety of organic compounds. Fenton’s Reagent oxidation is most effective under very acidic pH (e.g., pH 2 to 4) and becomes ineffective under moderate to strongly alkaline conditions.
ORC (Oxygen Release Compound) Application
Technology Description: Regenesis Bioremediation Products, Inc. has developed 2 slow release compounds for the in situ treatment of contaminated groundwater that contains petroleum hydrocarbons from compounds such as gasoline and fuel oil, chlorinated solvents such as PCE, TCE and TCA, and heavy metals such as lead, hexavalent chromium, and arsenic. The products are applied into the ground using a high-pressure injection pump. The ORC chemically reacts with the groundwater to release oxygen for the treatment of petroleum products through an aerobic degradation process. The HRC releases lactic acid when it contacts groundwater. Resulting fermentation produces hydrogen that provides a mechanism for an accelerated breakdown of the chlorinated compounds. Both processes are accomplished with minimum disruption of site activities. The equipment used for the installation is typically a direct push rig that injects the appropriate product into the saturated zone using a high-pressure positive displacement pump. For brownfield sites a reinjectable point can be constructed to permit multiple applications without business disruption.
The rate and extent of degradation of a target COC are dictated by the properties of the chemical itself and its susceptibility to oxidative degradation as well as the matrix conditions, most notably, pH, temperature, the concentration of oxidant, and the concentration of other oxidant-consuming naturally occurring substances. Oxidant consuming substances include natural organic matter, reduced minerals as well as carbonate and other free radical scavengers. Given the relatively indiscriminate and rapid rate of reaction of the oxidants with reduced substances, the method of delivery and distribution throughout a subsurface region is of paramount importance. Oxidant delivery systems often employ vertical or horizontal injection wells and sparge points with forced advection to rapidly move the oxidant into the subsurface.
The application of Oxidation methods allows for the chemical conversion of hazardous contaminants to non-hazardous or less toxic compounds that are more stable, less mobile, and/or inert.
Two Case Studies