Enhanced Reactant-Contaminant Contact through the Use of Persulfate In Situ Chemical Oxidation (ISCO)

A fundamental study was conducted to investigate the activation and persistence of persulfate in the subsurface with the overlying objective of evaluating the potential for contact between the oxidant source and contaminants. Mechanistic investigation of persulfate activation by naturally occurring iron oxides, manganese oxides, clay minerals, trace minerals, base, iron chelates, and organic compounds was investigated using reaction specific probe compounds hydroxyl radical and sulfate radical scavengers, and electron spin resonance spectroscopy. In addition, the effect of activated persulfate formulations on the permeability and morphology of subsurface minerals and subsurface solids was investigated using falling head permeameters, xray computed tomography, x-ray diffraction, and surface area analysis. Diffusion and transport of different persulfate formulations into low permeability matrices was investigated using specially designed soil columns filled with kaolinite and a low permeability soil. Results of activation studies showed that most minerals do not activate persulfate particularly in the concentrations commonly found in the subsurface. Iron chelate-activated persulfate and base-activated persulfate generate hydroxyl radical, sulfate radical, and reductants and provide the basis for widespread treatment of different classes of contaminants in the subsurface. Many organic compounds activate persulfate including phenoxides and ketones. Because soil organic matter contains phenolic and ketonic moieties, it is a potent activator of persulfate. Depending on the acidity of the soil organic matter, it may activate persulfate with minimal addition of base. Persulfate formulations have varied effects on subsurface morphology.