Theme: 01. Remediation Technology Innovations

Topic Area: 01i. In Situ Chemical Oxidation: Optimized Design Approaches and Lessons Learned

Formatted Title:

Ferrous Sulfide: A New Activation Chemistry for Persulfate

Background/Objectives:

Background/Objectives: In situ chemical oxidation using persulfate employs a variety of activators to increase the reactivity of persulfate and facilitate the mineralization of more recalcitrant compounds not treatable by persulfate alone. Unactivated persulfate anion (SO₄^-2) is a moderate strength oxidant stable in the subsurface (~3 months). However, when properly activated, persulfate provides not only the persulfate anion, but also a variety of other highly reactive radical species including both oxidizing (sulfate and perhydroxl radicals), and reductive species (hydroperoxide anion and superoxide radical).

Activation may be completed by a variety of methodologies, each subject to costs and limitations for field implementation. Traditional activation chemistries include multiple patented methodologies such as iron (native iron minerals or amended chelated iron), application of supplemental heat, decomposing hydrogen peroxide, raising the pH to greater than 10.5, application of carbohydrates, multivalent metals, ozone, and other methods.

Approach/Activities:

Approach/Activities: Terra Systems’ research program identified an activation chemistry using ferrous sulfide (FeS) termed ferrous sulfide activation or FSA. Terra Systems conducted a series of batch and column treatability studies confirming the increased performance of FSA relative to other activation chemistries for the successful treatment of a wide variety of constituents - gasoline-range organics (GRO, TPH-G), polycyclic aromatic hydrocarbons (PAHs), benzene, 1,4-dioxane, and chlorinated volatile organic compounds (CVOCs) including both the ethenes and ethanes

Results/Lessons Learned:

Results/Lessons Learned: This paper will present performance data from FSA studies and highlight the improvements obtained using FSA activation, compared to more expensive, traditional methods, notably:

Decreased activation mass required – less activator is required, thus improving site operations, decreasing operational footprint, and reducing the complexity of chemical storage, handling, mixing and application.
Application of activated persulfate, eliminating successive mixing of persulfate and activator improving the distribution of activated persulfate during initial injection and eliminating reliance on subsurface mixing.
Increasing the safety of the work environment and injection equipment throughout the injection process.
An unexpected low pH condition occurred during the injection of persulfate and FSA which caused corrosion of the injection rods. This condition was alleviated by simultaneous injection of a small volume of sodium hydroxide.
Results from a UST project in South Jersey with a persistent plume will be discussed.

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Gary Cronk