Q - ISOTEC Modified Fenton's Process
Is the modified Fenton's process patented or otherwise unique; what is the difference between ISOTEC and other vendors that provide similar services?
ISOTEC modified Fenton’s Process is a patented remediation technology covered by U.S. Patents 6,319,328; 4,591,443 and 5,741,427. Additional patents are currently pending. Although based upon the fundamental principles of Fenton’s chemistry, our technology vastly differs from conventional Fenton-based chemical oxidation technologies. Some of the major differences are outlined as below.
Circum-neutral pH Conditions: Conventional Fenton-based processes function only under acidic conditions because of the inability of the iron catalyst to remain dissolved in the natural subsurface pH range of 6-7. ISOTEC’s modified Fenton’s process utilizes specially developed catalysts composed of active components that chelate the iron and keep it in dissolved form as an organometallic complex that functions effectively in the circum-neutral pH range (i.e. pH @ 7.0) for contaminant destruction.
Mobility Characteristics: One of the biggest challenges of in-situ oxidation is to ensure that the injected reagents travel to the location of contamination without being subjected to losses caused by precipitation or surface fixation. Iron, which is the key component required to promote Fenton’s reaction, will precipitate within inches from the point of injection when introduced as solution of any of its typical salts. For example, a ferrous sulfate catalyst tends to precipitate to its oxidized form (Ferric), thereby, making hydroxyl radical generation magnitudes slower. Typically, 95% to 97% of a ferrous sulfate catalyst gets sorbed to the soil allowing only the remaining 3% to 5% of the catalyst to be utilized for hydroxyl radical generation. Acidified iron solution will remain in solution longer than regular iron solution; however, the low pH is quickly buffered by the native soil to its natural circum-neutral pH resulting in iron precipitation. Furthermore, acidification of the entire contaminated aquifer is not only impractical but may also result in permanently increasing the corrosivity of groundwater. ISOTEC’s catalysts have superior mobility compared to conventional Fenton’s catalysts and as discussed in (1), they function under natural subsurface conditions. The chelating components prevent precipitation or fixation of iron to native soil, thereby promoting its availability for hydroxyl radical generation from peroxide.
Control Agents: ISOTEC also developed stabilizers and mobility control agents that control the formation and dispersion of hydroxyl radicals. ISOTEC’s stabilizers significantly enhance the longevity of peroxide when introduced into the subsurface.
Research: ISOTEC developed its reagents through years of research – both in-house as well as through affiliated academic institutions. The injection technology has been fine-tuned through years of laboratory and field experimentation. ISOTEC’s reagents are especially designed for in-situ application. ISOTEC performs a field pilot program based on the results of laboratory testing conducted on site-specific samples. Laboratory bench tests are conducted in an effort to determine the stoichiometric molar ratio of ISOTEC reagents best suited to achieve maximum contaminant destruction at the subject site.
What is your experience with the production of interim daughter products and their toxicity?
ISOTEC has not experienced the production of any toxic interim daughter products at sites utilizing their modified Fenton’s process. The ISOTEC modified Fenton’s process is a chemical oxidation technology that destroys organic compounds in the subsurface. Upon injection of the reagents, hydroxyl radicals are generated. The modified Fenton’s process is non-specific; meaning that when a free radical is formed, it will oxidize any oxidizable organic compound it comes in contact with, producing carbon dioxide and water, and chloride ions if chlorinated compounds are being treated. After a short period of time, the catalyst is oxidized to simple ferrous/ferric ions, which adsorb to the soil matrix.
What are the effects of in-situ pretreatment pH and temperature on your process, including reaction kinetics?
Lab studies and corresponding field treatment programs can be performed at sites with varying subsurface conditions such as acidic pH levels to alkaline levels. ISOTEC’s patented catalysts allow for the generation of hydroxyl radicals and chemical oxidation to occur throughout the pH range of 2-10. ISOTEC’s 4000 series modified Fenton’s catalysts are designed to function under natural subsurface conditions (i.e. pH of 7). Therefore, no acidification of the subsurface is required. Temperature increases of up to 10 degrees Celsius may be noted during treatment programs for a short time period (<24 hours).
Our typical project approach starts in the laboratory where we develop a strategy to ensure that the ISOTEC process is optimized for your specific site conditions. A laboratory treatability study is conducted to test several types and concentrations of our patented catalysts and oxidizers on saturated soil and groundwater samples obtained from a site. Following the treatability study, a field pilot program is designed to evaluate not only the efficiency of our reagents, but also the distribution of the reagents within the impacted media. The data generated during the pilot program is used to design the most effective full-scale remediation program for your site. At some sites, appropriate geology and contaminant types allow ISOTEC to mobilize directly to the field and begin full-scale remediation.
Q - Chemistry 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 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.
Q - Installation of the Pilot System
How are bench-scale test results used to develop full scale-up recommendations?
A specific stoichiometry will be determined through a bench-scale lab study, with preliminary treatment quantities calculated. Application is typically tested in the field during a pilot program to determine the efficiency and radial extent of treatment, which varies depending on the site’s subsurface characteristics. Based upon a successful lab study and pilot program, design and implementation of full-scale remediation is proposed (if required).
The addition of acid to water generates heat. Also, the dissociation of hydrogen peroxide is exothermic. PVC is not capable of withstanding the heat of reaction. Practical experience has shown that PVC wells will melt, collapsing and becoming unusable.
PVC does not decompose until the temperature reaches a high of 148-149oC (or 298-300oF). Under normal treatment conditions, ISOTEC modified Fenton’s reaction temperatures rarely exceed a high of 10oC over background groundwater temperatures, which is significantly lower than the temperatures of concern. Furthermore, ISOTEC has used PVC injection points at numerous sites in the past and has found evidence of PVC melting only at sites with free product or high organic loading such as a peat layer, which can cause an aggressive reaction upon contact with hydrogen peroxide. Stainless steel wells are recommended in those instances. An additional point to note is that the ISOTEC process does not involve adding concentrated acid to the subsurface aquifer and therefore, will not generate such high reaction temperatures.
Injecting the H2O2 under hydrostatic pressure may only succeed in treating the area immediately around the injection point…H2O2 should be applied under moderate pressure.
It is true that hydrostatic pressure may not be adequate to attain the desired radial effect if permeability is low. ISOTEC designs its injection points for low to moderate pressure application where it is considered necessary. As mentioned before, a pilot study is performed to determine the conditions that are most suited for full-scale remediation of the site.
What information on full-scale processes have you implemented in residential areas or other areas that are populated (shopping centers, roadways, etc.)?
The ISOTEC process has and is currently being implemented within numerous residential areas. Full-scale programs have been completed from a small project within a residential dwelling basement where a former AGST spill occurred (See Lake Front Residence, New Jersey case study), to larger ongoing treatments within a warehouse (case study not completed) where total site VO’s (TCE/PCE) levels have been reduced from 151 ppm to 3 ppm after 2 treatment applications. Several ISOTEC case studies have been enclosed in the case studies section of this web site.
Q - Treatment Application
How are temperatures and pressures encountered with aproposed process during treatment controlled? Will standard PVC injection wells be utilized or will special well casing be required?
As stated earlier, an ISOTEC reagent combination utilized at a site is first tested during a bench-scale lab study. The ISOTEC process utilizes low concentration reagents under a gravity or slight pressure injection with constant off-gas releases through a site-specific injection apparatus. Reagents utilized are stabilized and at a low concentration, with injection in a controlled manner to reduce the possibility of any hazard occurring. Pressure and temperature measurements are not typically collected due to ISOTEC’s non-aggressive reactions. Temperature rises of upto 10 degrees Celsius are noted for a short period (<24 hours), and slight applied pressure is used only within less permeable aquifers. Standard PVC injection points are sufficient with the ISOTEC process. Treatment program activities are limited to the specific areas within the known contaminant plume, with injection of treatment chemicals controlled at the surface during the application. A site engineered injection apparatus is used to control flow of treatment chemicals into the subsurface via the chosen injection pathway.
In the injection of reagent into the contaminated subsurface, what percentage of pore volume is necessary for making adequate contact with contaminants of concern? Is there a concern with the displacement/forced migration of contaminants associated with adding significant volume of liquid to the subsurface? If so, how is this displacement/forced migration controlled?
The first part of the question should be answered by the stoichiometric ratio determined in the bench-scale lab study, along with several other factors as discussed above. The ISOTEC process injection rate and volume of discharge are extremely complex and interrelated to the reaction rates of hydroxyl radicals with the contaminants, the contaminant distribution coefficients in the subsurface systems, and the rate of hydrogen peroxide decomposition within the subsurface. The rate at which any flow can be injected into the subsurface is determined by the soil/aquifer characteristics. The treating flow will be discharged under hydrostatic or an applied pressure based on the engineering and construction of the injection system and receiving aquifer. The volume of discharge varies based on the specific stoichiometry determined in the lab study, level of contamination, volume of area to be treated, and subsurface soil and ground water characteristics.
The following should address the requested information on the actual destruction of contaminants versus possible displacement/forced migration. The ISOTEC process is a contact treatment that actually changes the chemical composition of the compound in-situ and occurs instantaneously. When ISOTEC chemicals are injected into the subsurface, a reaction transpires which immediately produces free radicals (via modified Fenton’s reagent or activated persulfate). The free radicals are non-specific oxidants that react with most organic contaminants at diffusion controlled rates. As the free radical comes into contact with organic compounds, oxidation occurs. A complete oxidation of the organic compound results in the production of carbon dioxide and water. Therefore, no displacement/forced migration occurs, only the chemical oxidation of organic compounds within the area being treated. In addition, subsurface aquifers consist of large quantities of liquid totaling in the millions of gallons. The addition of a few hundred/thousand gallons of ISOTEC catalysts and oxidizers within a particular area would not cause any significant decrease in contaminant levels due to dilution.
How are such parameters as pH and alkalinity manipulated as part of the full-scale treatment process in order to optimize performance of the injected reagents? Provide details.
Laboratory treatability studies and corresponding field treatment programs can be performed at sites with varying subsurface conditions such as low acidic pH levels to higher alkaline levels. ISOTEC’s patented catalysts allow for the generation of free radicals and chemical oxidation to occur through most of the pH scale (i.e. pH = 2-10). ISOTEC’s 4000 series catalysts are designed to function under natural subsurface conditions (i.e. pH of 7) and are suitable for majority of the sites using modified Fenton’s or persulfate. Therefore, no manipulation is required.
Are ISOTEC reagents prepared on site? What happens to these chemicals when injected into the subsurface?
ISOTEC catalysts consist of a site-specific chelated iron complex. ISOTEC typically uses H2O2 and sodium persulfate at a concentration of 5%-20% during injection activities. Permanganate is used at concentrations ranging from 1% to 10%. Typically, the H2O2 is shipped directly to the site and stored in DOT approved 55-gallon drums with an initial concentration of 50%. Sodium persulfate is shipped to the site in a dry form in 55 lb bags. Potassium permanganate is shipped in dry form in 100 kg pails while sodium permanganate is shipped in liquid form in DOT approved 55-gallon drums at an initial concentration of 40%.
Field dilution and addition of ISOTEC’s proprietary non-hazardous stabilizers and mobility control agents are performed as determined during our bench scale studies. All reagent components are premixed in a dry form and packaged prior to shipment to any site. The reagent additives will be mixed/ diluted on-site and added during dilution activities. The ISOTEC series catalysts consist of a chelated iron complex. The iron complex is similar and at levels comparable to that of naturally occurring metals within the soil matrix. ISOTEC catalysts include proprietary chelating agents, which keep the catalyst in dissolved form until adequate dispersion is completed and at levels to that of naturally occurring metals within the subsurface. The oxidizer slowly consumes the catalytic components before a gradual liberation of catalyst throughout the treatment area occurs. This process allows the catalyst to distribute evenly within subsurface before finally adsorbing to the soil particles. After a short period of time, the catalyst is oxidized to simple ferrous/ferric ions. For modified Fenton’s, the hydrogen peroxide oxidizer is itself reduced to water and oxygen. For activated persulfate, the sodium persulfate oxidizer is reduced to sulfate. For permanganate, MnO2 formation occurs, which precipitates as a dark brown to black solid that adsorbs to the soil matrix.
Since the hydroxyl ions which are generated are not selective, some of them will be wasted on other carbon sources such as the peat layer beneath the site. Besides the PCE, there are other contaminants, such as waste oils (PAHs) and phthalates, which will react with the oxidants.
It is true that hydroxyl radicals generated during the reaction are non-specific and will react with any organic material including peat and free product. Our bench test will test low to high reagent concentrations to evaluate the reagent quantities needed for contaminant treatment for the site-specific soil and groundwater and will include volumes to offset scavenging losses. A pilot study is primarily conducted to obtain a better idea of the overall site-specific factors affecting the process efficacy. Typically, ISOTEC uses a conservative correction factor while estimating the reagent quantities in order to account for losses such as those caused by the scavenging materials (such as peat) in the native soil. The reaction with the free product results in its gradual depletion from the subsurface, which is beneficial for the site.
When injecting modified Fenton’s reagent into DNAPL areas, a conversion from DNAPL into dissolved phase will occur. This raises an important question on how will this conversion take place. Do the reagents they will be adding to the groundwater will include surfactants to bring the DNAPL into solution.
ISOTEC modified Fenton’s process does not utilize any surfactants as part of its reagents. The critical ingredients are hydrogen peroxide and chelated iron complex. The conversion of DNAPL into dissolved phase will occur because of DNAPL desorption from the soil matrix and subsequent transfer to groundwater phase when groundwater contacts desorbed DNAPLs. Desorption occurs because the hydroxyl radicals non-selectively attack the soil-based organic matter binding these contaminants to the soil. The extent of transfer will depend upon the solubility of contaminants and their associated distribution coefficient.
Fenton-reaction involves forced injection of air into the subsurface which may result in pressure buildup that may create hydraulic fracturing resulting in preferential pathways.
Air injection into the subsurface, forced or otherwise is not performed at majority of ISOTEC sites. At sites with extremely tight subsurface conditions (such as tight clayey soils), pneumatic fracturing of the subsurface using pressurized air/nitrogen injection may sometimes be performed to promote distribution of reagents but only after a thorough investigation of the feasibility and potential effects have been completed.
Safety is a priority with the ISOTEC process, which uses relatively non-aggressive reaction chemistry. Possible side effects such as surface breakout or lateral migration of treatment reagents and/or off-gases occur with aggressive reaction type oxidative processes utilizing high concentration of reagents under a constant pressurized condition. ISOTEC does not utilize this approach. Reagents utilized by ISOTEC are stabilized and at a low concentration, with injection in a controlled manner to reduce the possibility of surface breakout or lateral migration. Furthermore, at sites with shallow depth of ground water, extreme caution is exercised while injecting reagents as the mounding effect created raises the ground water elevation to close proximity of the surface. This mounding effect will be monitored in the field by collection of continuous water levels shortly after injection of reagents. It should be noted that the mounding effect offers a potential benefit by treating contaminants present in the “smear” or vadose zone.
Q - Treatment Costs
What type of a model would you use for determining full-scale costs?
ISOTEC estimates project costs based on numerous site factors. A specific stoichiometry is first determined through a bench-scale lab study, with preliminary treatment quantities calculated. Application is typically tested in the field during a pilot program to determine the efficiency and radial extent of treatment, which varies depending on the site’s subsurface characteristics. Based upon a successful lab study and pilot program, design and implementation of full-scale remediation is proposed (if required). The following factors are considered in estimating the full-scale treatment costs: number of injection points required, amount and extent of delineated groundwater contaminant plume/ soil contamination, oxidant to be utilized, subsurface geology, and estimated volume of reagents required.
How do your cost estimates for full-scale treatment address remedial action objectives?
The ISOTEC process is typically a three-step process from laboratory-scale to pilot-scale to full-scale. Each step requires input from the previous. Full-scale treatment typically requires several applications, with each subsequent application treating a smaller area within the former plume. Each treatment application is followed by specific site monitoring to obtain information related to the treatment process, subsurface characteristics and remedial goals.
Initial estimates will reflect the cost of applying the ISOTEC process throughout the entire area of concern. ISOTEC typically performs a pilot study prior to site wide remediation to determine actual radial effects of treatment. The radial treatment estimates contained within any proposal are based upon ISOTEC fieldwork conducted in the past at facilities with similar geology. Actual radial treatment effects are site specific and can only be determined during actual remedial activities. Actual injection point locations will be determined upon a review of subsurface utility maps.
Q - Contaminant Treatment
Where do I get information if my contaminants of concern have been treated by ISOTEC in the past?
A few example contaminants that are amenable to ISOTEC technologies include petroleum related compounds e.g. BTEX, MTBE, Naphthalene, chlorinated alkenes e.g. PCE, TCE, DCE and VC, chlorinated alkanes e.g. 1,1,1-TCA and Carbon Tetrachloride, 1,4-Dioxane, MGP related compounds e.g. PAHs, metals e.g. Hexavalent Chromium, pesticides e.g. Lindane and Chlordane, pharmaceutical related compounds e.g. Sulfonamides and Barbiturates as well as various other contaminants. For information about contaminants present at a specific site please contact us.
What is your experience with the mobilization and control of DNAPLs resulting from your process?
The ISOTEC chemical oxidation process is a contact remedial treatment and works through contaminant desorption from the soil phase followed by oxidation in the aqueous phase. When injecting ISOTEC reagents into DNAPL areas, a conversion from DNAPL into dissolved phase will occur. Therefore, a thorough investigation must be completed at a site prior to remedial activities to determine the plume contaminant mass in the area to be treated. Once the plume mass has been calculated, a sufficient amount of reagents can be calculated to treat the contaminants in these areas.
ISOTEC has noted on some projects an increase in VOC concentrations after a chemical oxidation application. This scenario indicates the presence of large amounts of residual contamination bound to the soil matrix in the vicinity of treatment area or monitoring points. Such increases are caused by the desorption process of organics from the site soils and initial reagent quantities calculated not being sufficient to oxidize all organic contamination which may have been present in the treatment area. This is overcome by additional injection points and/or treatment applications, plus an increase in reagent volume injected.
If an unknown quantity of DNAPL is present in the portion of the site area tested, it is difficult to calculate the exact number of injections and/or quantity of reagent required to complete a remedial cleanup using chemical oxidation. However, ISOTEC will be better able to determine these amounts once the treatment program has commenced and initial data and trends can be evaluated.
Q - Reporting
When will final laboratory and pilot reports be available?
Laboratory treatability study report is typically available within five to six weeks from the date of sample submission to ISOTEC. Pilot program reports are typically available within two weeks after receipt of post-treatment sampling results by ISOTEC from the analytical laboratory.
Q - Health, Safety and Regulatory Concerns
What is your experience with ISCO reagents in states where it is not widely accepted to attain state standards, including any precedents for injecting ISCO reagents into potential drinking waters?
The ISOTEC processes are regularly accepted by numerous state agencies as a remedial treatment alternative. Most state agencies now consider modified Fenton’s reagent (MFR), sodium persulfate and permanganate as acceptable technologies. State agencies may ask for a lead time ranging from one month to one year prior to commencement of the project to complete review of the proposed remedial action. To date, we have completed projects in almost every state within the United States and internationally in Japan, Germany, Canada, Holland and the Caribbean.
Q - Proposal Request Information
What information does ISOTEC typically require in order to prepare a budgetary estimate or treatment program proposal?
To ensure ISOTEC may develop a proper estimate, accurate information pertaining to a site must be analyzed. We require site specific data to better understand the issues that may affect job performance and cost. These parameters include: geology (boring logs/drill logs), hydrology (depth to water, pH, hydraulic conductivity, etc..), a contaminant list (including, soil and groundwater concentrations), project remedial goals, site map(s) indicating estimated treatment areas and any subsurface/overhead utilities that may inhibit potential remediation at the site, vertical depth interval where majority of impacts exist, a history of any laboratory bench-scale studies completed at the site and any other past/current remedial technologies utilized.
All pertinent site data can be submitted to ISOTEC by filling out and submitting the Proposal/ Budgetary Estimate Request Form.