In-Situ Chemical Oxidation (ISCO) Services
Hydrogen Peroxide ISCO Process
Although hydrogen peroxide can be used alone for the oxidation of organic compounds, Fenton´s reagent provides a much more powerful oxidation potential. Fenton´s reagent is a mixture of hydrogen peroxide, a catalyst (ferrous sulfate), and an optimum pH (3-5) adjuster (sulfuric acid). The ISCO process involves injecting hydrogen peroxide and other amendments as required directly into the source zone and downgradient into the contaminant plume.
The appropriateness of ISCO technology at a site depends on matching the oxidation and delivery systems to the site contaminants and site conditions. Site specific geochemical data are required to estimate chemical dosage, to establish baseline conditions prior to treatment, and to evaluate the effectiveness of treatment in soil/ground water. Site specific technology feasibility testing is typically conducted during the early design stage, referred to, as a treatability study commonly conducted at the laboratory scale. Typically, the results of bench-scale testing are used to prepare for a field test of the technology at the site in question.
Persulfate ISCO Process
The ISCO approach for remediation of a Site using a modified Fenton´s Chemistry/reaction includes the addition of persulfate as an oxidant. Persulfate has a longer half life than hydrogen peroxide and will be able to reach the impacted areas to oxidize the organic compounds in the pore waters of the aquifer materials in the subsurface.
Sodium persulfate is a stable, highly soluble, crystalline material, which upon activation generates the persulfate radical, a very strong oxidant, capable of oxidizing a broad range of recalcitrant compounds. Free radical initiation can be achieved through the application of heat, transition metal catalysts, hydrogen peroxide, chelated metal EDTA complex, or sodium hydroxide. Knoll has successfully implemented NaOH as the activation reagent of sodium persulfate because alkaline persulfate has proven to have broad reactivity.
The application process of persulfate for oxidizing petroleum compounds in ground water include the preparation of activated persulfate solution by mixing solid persulfate, activation reagents, and water; and then injection into the impacted aquifer. Reaction of persulfate with organic contaminants oxidizes the gasoline compounds to carbon dioxide and persulfate after reaction and decomposes to bisulfate. The levels of sulfate in ground water will return to background concentrations within a month or so. Thus, the reaction does not create any toxic compounds.
The closure of the site to meet the state cleanup standards involved the following:
- The Fenton´s Reagent process
- Bench Scale Treatability Study
- Applicability of Fenton´s Reagent to petroleum hydrocarbons
- Areas to be treated (focused area)
- Injection equipment
- Injector Well installation
- Performance and process monitoring
- Treatment program procedures
- Reporting and Permitting