FREQUENTLY ASKED QUESTIONS
Laboratory Bench-Scale Study
Although oxidation of organic compounds can occur at neutral to slightly acidic conditions, the optimum pH for oxidation of organic compound is between 2 and 4...There is no mention in the lab study of how this acidification was accomplished...Does the chelated-iron catalyst used by ISOTEC's modified Fenton's process provides the free Ferrous iron?
The chelated iron catalyst used by ISOTEC provides required iron concentration needed to catalyze the hydroxyl radical formation from hydrogen peroxide. While the optimal pH needed may be in the acidic range in conventional Fenton’s chemistry, it has to be noted that the ISOTEC process is a modified Fenton-based process that has been designed to function at natural subsurface conditions (i.e. pH @ 7). The chemical constituents ISOTEC uses to attain the targeted process conditions are proprietary. No pH modification of the aquifer is conducted.
Provide a detailed breakdown of the number of samples to be analyzed. How many different concentrations of reagent will be evaluated in the determination of the optimum dosage?
In order to evaluate site conditions, ground water and/or soil samples, which exhibit elevated levels of contamination, are collected and shipped to ISOTEC’s research laboratory. The optimum reagent combination obtained from previous central composite optimization experiments performed on the contaminants of concern is used as the basis for each laboratory study. Specific concentrations and volumes of the reagents to be injected in the field are determined based on a series of experiments, which test several catalyst and oxidizer amendments.
Why is a 1:1 slurry of ground water and soil analyzed in the treatability study instead of a ratio more representative of in-situ conditions?
ISOTEC has been utilizing the 1:1 slurry within ground water/soil lab study samples as a general representation of in-situ site conditions. The ratio is typically dependant on site soil conditions (i.e. moisture content, porosity, etc.) within the saturated zone. ISOTEC can perform the ground water/soil lab study at any ratio, and will work with the client to provide the best available information.
Should the lab study indicate that the ISOTEC process could not successfully treat…". Please identify factors and conditions that you understand or suspect present at the site that would be revealed during the lab study, which may render ISOTEC’s process ineffective for field-testing.
ISOTEC processes including modified Fenton's, activated persulfate or permanganate may not be effective on samples containing high concentrations of heavier end (i.e. Carbon-10 or greater) aliphatics, polychlorinated alkanes and certain polyaromatic compounds. These contaminants are strongly adsorbed to the soil and are not easily available for treatment by the aqueous generated hydroxyl radicals. In addition, samples from wells that contain free product will require free product to be removed prior to initiating one of ISOTEC’s processes. Contaminants such as TCE, PCE and BTEX can be treated due to the presence of carbon-carbon double bonds within the target contaminants that are vulnerable for attack by free radicals during the reaction. Factors such as native pH and total organic carbon (TOC) content of the site soils are also critical. Samples containing unusually high or low pH may not provide conditions conducive for effective reaction propagation and contaminant oxidation. Such sites will require pH treatment prior to initiating ISOTEC reagent injection. Most sites with the native subsurface pH in the range of 2.5 to 8.5 are suitable for ISOTEC treatment. Sites with total organic carbon (TOC) content of soils >75,000-ppm result in high oxidant wastage due to competition provided by TOC. This limit is higher for sites where a significant portion of TOC can be attributed to contamination that is already present within the subsurface.
While field tests with the modified Fenton’s technology have been shown to be successful, due to heterogeneity and uncertainties in the subsurface, the in-situ reaction is never as complete as bench and batch scale studies would suggest.
It is true that ISOTEC laboratory study is performed as a controlled batch process that differs from the heterogeneity associated with a subsurface. While the main objective of our laboratory bench test is to determine the contaminant destruction efficacy using one of ISOTEC’s processes, concerns associated with field application are usually addressed during the pilot study. In fact, the principal objective of the pilot study is to evaluate the injection mechanism, radial effects, and site-specific chemical formulation. Information obtained from laboratory study provides a basis to initiate the pilot program.
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