Grantee Research Project Results

2004 Progress Report: DNAPL Source Control by Reductive Dechlorination with Fe(II)

EPA Grant Number: R831276C001
Subproject: this is subproject number 001 , established and managed by the Center Director under grant CR831276
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
Center: Organotypic Culture Models For Predictive Toxicology Center
Center Director: Rusyn, Ivan
Title: DNAPL Source Control by Reductive Dechlorination with Fe(II)
Investigators: Batchelor, Bill
Institution: Texas A & M University
EPA Project Officer: Aja, Hayley
Project Period: December 1, 2003 through November 30, 2004
Project Period Covered by this Report: December 1, 2003 through November 30, 2004
Project Amount: Refer to main center abstract for funding details.
RFA: Gulf Coast Hazardous Substance Research Center (Lamar University) (1996) RFA Text |  Recipients Lists
Research Category: Hazardous Waste/Remediation , Targeted Research

Objective:

Chlorinated hydrocarbons are one of the most important subsurface contaminants in the United States and the most persistent contamination occurs when they are present as dense nonaqueous phase liquids (DNAPLs). The presence of DNAPL results in extended times for remediation, because the DNAPL continuously dissolves to contaminate large volumes of groundwater. Therefore, effective remediation of a contaminated aquifer usually requires removal of DNAPL so that the source of contamination is eliminated. Several technologies can be applied to treating DNAPL in a source zone, but they tend to be capital intensive and poorly applicable to soils that are not highly permeable. An attractive alternative that could be applied more economically to smaller sites and to those sites with impermeable soils is abiotic reductive dechlorination. Degradative solidification/stabilization using ferrous iron (Fe-DS/S) is a treatment process that combines reductive dechlorination with immobilization. The process, however, has not been investigated as a technology for treating such compounds when they are present as DNAPLs. The overall objective of the research project is to demonstrate the ability of modified Fe-DS/S to remove chlorinated solvents present as DNAPL in source zones and to determine operational variables that will optimize the process.

Progress Summary:

The Quality Assurance Project Plan for the project was developed and submitted to the Center in December 2003. A graduate research assistant was hired to conduct analyses for iron and chlorinated organics. Iron (Fe(II), Fe(III), and total Fe) was analyzed by the Ferrozine method. Target compounds and degradation products (perchloroethane [PCE], trichloroethane [TCE], 1,1-dichloroethane [DCE], c-DCE, t-DCE) were analyzed by electron capture gas chromatography (GC-ECD) after extraction. A 50:50 mixture of methanol and hexane was evaluated as an extractant to improve extraction efficiency compared to hexane alone. Results of testing the extraction procedure showed near 100 percent extraction efficiency with the methanol:hexane extractant and demonstrated the importance of methanol to ensuring good extraction efficiencies of DNAPLs in the presence of solid phases.

The experimental plan was updated to consider research that has been conducted recently in our laboratories on development of Fe(II)-based dechlorinating agents that are prepared without use of Portland cement. These reductants offer the potential for preparing higher capacity treatment mixtures without the need for high levels of Portland cement. Kinetic experiments were conducted with 3 mM PCE and Fe(II)-Fe(III) reductant solids (960 mM Fe(II), 100 mM Fe(III)).

The effect of ferrous iron dose on kinetics of degradation of high concentrations of PCE was determined in batch reactor experiments conducted in triplicate. The iron dose for all experiments was 100 mM, and the initial concentration of PCE was 3.08 mM. Because this exceeds the solubility, a DNAPL would be present initially. Initial pH was adjusted to pH 12, and the reactors were placed in an anaerobic chamber. TCE was the only significant product, although some evidence of other compounds was detected by GC-ECD. From previous research, it is known that PCE can be dechlorinated by a beta-elimination pathway that results in formation of nonchlorinated products (acetylene, ethylene, ethane) without accumulation of chlorinated intermediates. It also can be degraded, however, by a hydrogenolysis pathway that can accumulate TCE, DCE, and vinyl chloride (VC) as intermediates. It appears that both pathways are operative in this system.

Future Activities:

The effects on degradation kinetics of target compound type (PCE, TCE, trichloroacetate), reductant type (Fe(II)-Fe(III) mixtures, Fe(II)-Portland cement), soil type (none, loamy sand, loam, silty clay), target compound concentration, and reductant dose will be evaluated in a series of batch experiments.

Supplemental Keywords:

abiotic dechlorination, waste, ecological risk assessment, environmental engineering, hazardous waste, advanced treatment technologies, bioremediation, contaminated waste sites, groundwater contamination, petroleum contaminants, hydrocarbon,, RFA, Scientific Discipline, Waste, Water, POLLUTANTS/TOXICS, Hazardous, Remediation, Environmental Chemistry, Contaminated Sediments, Hazardous Waste, Chemicals, Environmental Engineering, reductive dechlorination, contaminated sediment, chlorinated hydrocarbons, hazardous waste treatment, contaminated groundwater, groundwater remediation, contaminated soil, remediation technologies, iron based degradation, DNAPL, iron mediated reductive transformation

Relevant Websites:

http://dept.lamar.edu/gchsrc/ Exit
http://toxics.usgs.gov/highlights/dnapl_removal.html Exit

Progress and Final Reports:

Original Abstract

Final

Main Center Abstract and Reports:

CR831276    Organotypic Culture Models For Predictive Toxicology Center

Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
R831276C001 DNAPL Source Control by Reductive Dechlorination with Fe(II)
R831276C002 Arsenic Removal and Stabilization with Synthesized Pyrite
R831276C003 A Large-Scale Experimental Investigation of the Impact of Ethanol on Groundwater Contamination
R831276C004 Visible-Light-Responsive Titania Modified with Aerogel/Ferroelectric Optical Materials for VOC Oxidation
R831276C005 Development of a Microwave-Induced On-Site Regeneration Technology for Advancing the Control of Mercury and VOC Emissions Employing Activated Carbon
R831276C006 Pollution Prevention through Functionality Tracking and Property Integration
R831276C007 Compact Nephelometer System for On-Line Monitoring of Particulate Matter Emissions
R831276C008 Effect of Pitting Corrosion Promoters on the Treatment of Waters Contaminated with a Nitroaromatic Compounds Using Integrated Reductive/Oxidative Processes
R831276C009 Linear Polymer Chain and Bioengineered Chelators for Metals Remediation
R831276C010 Treatment of Perchlorate Contaminated Water Using a Combined Biotic/Abiotic Process
R831276C011 Rapid Determination of Microbial Pathways for Pollutant Degradation
R831276C012 Simulations of the Emission, Transport, Chemistry and Deposition of Atmospheric Mercury in the Upper Gulf Coast Region
R831276C013 Reduction of Environmental Impact and Improvement of Intrinsic Security in Unsteady-state
R831276C014 Integrated Chemical Complex and Cogeneration Analysis System: Greenhouse Gas Management and Pollution Prevention Solutions
R831276C015 Improved Combustion Catalysts for NOx Emission Reduction
R831276C016 A Large-Scale Experimental Investigation of the Impact of Ethanol on Groundwater Contamination
R831276C017 Minimization of Hazardous Ion-Exchange Brine Waste by Biological Treatment of Perchlorate and Nitrate to Allow Brine Recycle
R831276C018 Integrated Chemical Complex and Cogeneration Analysis System: Greenhouse Gas Management and Pollution Prevention Solutions