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: Gulf Coast HSRC (Lamar)
Center Director: Ho, Tho C.
Title: DNAPL Source Control by Reductive Dechlorination with Fe(II)
Investigators: Batchelor, Bill
Institution: Texas A & M University
EPA Project Officer: Lasat, Mitch
Project Period: 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 main sources of sub-surface contamination in the U.S. and the most serious type of contamination occurs when they are present as dense non-aqueous phase liquids (DNAPL). The presence of contaminant DNAPL, results in extended times for remediation, because the DNAPL continuously dissolves and thereby contaminates large volumes of groundwater. Therefore, effective remediation of a contaminated aquifer usually requires removal of DNAPL in order to remove the source of contamination. 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 more economically applied to smaller sites and to those sites with impermeable soils is abiotic reductive dechlorination. Iron-based degradative solidification/stabilization (fe-ds/s) is a treatment process developed with funding initiated by the GCHSRC that combines reductive dechlorination with immobilization. Immobilization is achieved by reactions of Portland cement, which is the primary reagent used by conventional solidification/stabilization. Dechlorination is achieved by a compound formed by reaction of ferrous iron with components of Portland cement. Current research indicates that it will be possible to produce this dechlorinating agent directly using specific chemicals so that Portland cement will not be required. Research has shown that fe-ds/s can effectively dechlorinate compounds such as PCE when they are present in aqueous solution. However, the process has not been investigated as a technology for treating such compounds when present as a DNAPL in source zones.

The overall goal of the proposed research 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.

Approach:

This goal will be achieved by a two-part experimental plan. The first task will determine optimal conditions for producing active reductants for DNAPL dechlorination. The effects on reductive activity of Fe(II)/Fe(III), OH/Fe(III), C1/Fe(III), A1(III)/Fe(III), SO4/Fe(III) and reaction time will be investigated in batch reactors. Activity of the dechlorinating agent will be quantified in batch reactors as the amount of PCE removed after a specific reaction time. More extensive kinetic experiments will be conducted to measure rate constants for dechlorinating agents with highest activity. The second research task will determine the effectiveness of fe-ds/s in remediating chlorinated organics present as DNAPLs. Solid-phase experiments will be conducted with contaminated soils. Experimental variables to be investigated are: soil type (loamy sand, loam, silty clay), target chlorinated organic type (PCE, TCE, TCA), target organic concentration (3,000, 10,000 mg/kg), reductant type (Fe(II), preformed reductant), and reductant dose (3, 10, 30, 100 times stoichiometric). Portland cement doses will be chosen to achieve optimal porewater pH. Samples will be taken over time and target compounds and products will be analyzed by electron-capture gas chromatography after solvent extraction. Kinetic coefficients will be determined by non-linear regression using an appropriate rate model (first-order, modified Langmuir-Hinshelwood). Partitioning experiments will be conducted so that kinetic coefficients can be reported as being independent of the sorption capacity of the soil. Products of dechlorination reactions will be measured to document effective destruction.

Expected Results:

The fe-ds/s process should have costs that are similar to that of conventional s/s, which range from $60 to $290/ton. They would be on the order of $10/ton higher due to costs of the reductant. This project will take 3 years to complete.

Supplemental Keywords:

RFA, Scientific Discipline, Waste, Water, POLLUTANTS/TOXICS, Contaminated Sediments, Remediation, Environmental Chemistry, Chemicals, Hazardous Waste, Hazardous, Environmental Engineering, hazardous waste treatment, DNAPL, remediation technologies, contaminated sediment, chlorinated hydrocarbons, contaminated soil, groundwater remediation, reductive dechlorination, contaminated groundwater, iron mediated reductive transformation, chlorinated solvents

Progress and Final Reports:

  • Final

  • Main Center Abstract and Reports:

    CR831276    Gulf Coast HSRC (Lamar)

    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