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Final Report: A Novel, In-Situ Delivery Method for Peroxide for Remediation of Organically Contaminated Soils
EPA Contract Number: 68D98121Title: A Novel, In-Situ Delivery Method for Peroxide for Remediation of Organically Contaminated Soils
Investigators: Inman, Maria E.
Small Business: Faraday Technology, Inc.
EPA Contact: Manager, SBIR Program
Phase: I
Project Period: September 1, 1998 through March 1, 1999
Project Amount: $69,338
RFA: Small Business Innovation Research (SBIR) - Phase I (1997)
Research Category: SBIR - Remediation , Hazardous Waste/Remediation
Description:
The purpose of the research was to electrochemically generate peroxide ions at an air-fed cathode, for subsequent electrokinetic dispersion through a contaminated site. This technology places a buried electrode at the contaminated site for point-source remediation. Furthermore, oxygen is utilized from the air and fed to the buried electrode. This novel technology eliminates the costly options of 1) transport of 30 wt% peroxide solutions to the affected area or 2) generating the peroxide at the site surface through a mini-chemical plant, for subsequent leaching through the surface layers of the contaminated site. The peroxide would provide an oxygen source in subsurface soil and groundwater, for either direct chemical oxidation or bioremediation of organic contaminants.Research Work Carried Out
Figure 1 shows a schematic of the design of the anode/cathode setup that was used in the Phase I program. The anode is a dimensionally stable anode mesh screen, which encircles the cathode. The air-fed cathode is based on the gas diffusion electrode used in the fuel cell industry. To fabricate the cathode, a mixture of carbon catalyst particles mixed in Teflon? is pressed or rolled onto a carbon support cloth. To simplify the construction of this cathode, we purchased carbon cloth impregnated with carbon black from Electrosynthesis, Inc. We tested two different carbon catalysts, Black Pearls 2000 and Vulcan XC-27R, which have different surface areas per gram of carbon. The carbon cloth is wrapped around a metal microfilter tube (Ron-Vik, Inc., MN). Oxygen gas is passed through the tube, and back pressure, due to a gas bubbler at the end of the tubing, forces some of the oxygen through the filter screen into the carbon cloth, which acts as a gas diffuser. The diffused oxygen and electrolyte (groundwater) meet at the surface of the carbon particles, which act as catalysts for the peroxide generation reaction. The top and bottom of the gas diffusion electrode are set in Struers mounting resin and sealed with Torrseal?, to prevent oxygen escaping from the ends of the cathode.
Figure 1: Schematic of the air-fed cathode and dimensionally stable anode arrangement.
As part of this program, we were to develop and calibrate an electrochemical measurement system for in-situ monitoring of the peroxide concentration in groundwater. Although this technique could be fully explored in future programs, it was felt that it potentially could take up a substantial part of the effort directed towards this program. Therefore, we have developed a simple chemical analysis method, that will take a small sample of groundwater from positions throughout the cell, and determine the peroxide concentration in that sample using a titration method. The method for the analysis of H2O2 by permanganate titration is as follows:
Principle
This method utilizes the reduction of potassium
permanganate (KMnO4) by hydrogen peroxide in sulfuric acid.
Scope
This method is suitable for measuring aqueous solutions of
H2O2 ranging from 0.25 to 70 wt.%, although useful values
may also be obtained as low as 0.05 wt.%.
Interferences
Any substance which reduces KMnO4 under
acidic conditions will produce a positive interference.
Reagents
1. Concentrated sulfuric acid, reagent grade
H2SO4 (sp.gr. 1.84).
2. Potassium permanganate, reagent
grade KMnO4.
3. Sodium oxalate, reagent grade
Na2C2O4.
Results
The maximum amount of peroxide generated in an experiment was 0.09 wt% in an alkaline solution at pH 12, containing 0.5 M Na2SO4, after approximately 1 hour. After 3 hours, the concentration of peroxide had dropped to 0.07 wt%. The current efficiency calculated for this experiment was slightly less than 10 %. An air-fed cathode fabricated using a high surface area carbon cloth such as Black Pearls 2000 (Electrosynthesis), appeared to give better performance than lower surface area electrodes (Vulcan XC-27R carbon cloth, Electrosynthesis). Significant amounts of peroxide were generated when the cathode was new or slightly used, suggesting aging of gas diffusion electrodes, leading to decreases in performance. The use of chemical additives such as magnesium sulfate or acetanilide, did not appear to result in stabilization of the peroxide generated during the experiments. In addition, the use of modulated electric fields did not result in an enhanced peroxide generation rate, although this may have been tainted by the fact that new cathodes were not used for any of those experiments. Finally, after consultation with an experienced environmental consulting firm, it has become apparent that the technology should be designed so as to funnel contaminated groundwater through a treatment zone, rather than attempt to electrokinetically disperse peroxide over a wide area. This shift in technology design will be examined during the Phase II program.
Potential Commercialization
Commercialization will occur in conjunction with an environmental engineering/site management company because logistics and remediation implementation are both required for successful commercialization of our groundwater remediation technology. As an example, most recently a collaborative team from one such company and Faraday Technology, Inc. traveled to the Oak Ridge National Laboratory (ORNL) reservation to participate in a site visitation of a contaminated burial site managed through the Department of Energy (DOE). The purpose of this visitation was to explore a potential joint project to assist the DOE in delivering an innovative containment/remediation technology to assist in the clean-up and ultimate preservation of the ORNL reservation site.
Field Demonstration - It is anticipated that during a Phase II program we will complete a field demonstration in conjunction with an environmental engineering/site management company. Most recently, under contract to one such company, we developed, fabricated, and tested, a soil column test facility that enabled simulation/prediction of in-situ chemical corrosion behavior for remediation of a US Army site containing buried, unexploded ordnance. Additionally, we most recently attended a nitrate destruction meeting held at the Los Alamos National Laboratory (LANL) to discuss continued development of, and eventual commercialization of a nitrate destruction technology under development by the DOE. The subject of our current work for delivering in-situ peroxide for point-source remediation of contaminated groundwater was discussed. Faraday Technology, Inc. and LANL have executed a mutual non-disclosure agreement for the purpose of further collaborative effort discussions.
Supplemental Keywords:Economic, Social, & Behavioral Science Research Program, Water, Scientific Discipline, Waste, Remediation, Engineering, Chemistry, & Physics, Chemistry, Environmental Engineering, Environmental Chemistry, Contaminated Sediments, Groundwater remediation, Bioremediation, Market mechanisms, organic pollutants, groundwater, oxidation, contaminated sediment, in-situ bioremediation, contaminants in soil, cost effective, groundwater contamination, bioremediation of soils, electrochemical methods, organic contaminants, sediment treatment, treatment technology, sediments, soil sediment, electrochemical technology, in situ remediation
Progress and Final Reports:
Original Abstract