Grantee Research Project Results

2002 Progress Report: Zero-Valent Metal Treatment of Halogenated Vapor-Phase Contaminants in SVE Offgas

EPA Grant Number: R828771C006
Subproject: this is subproject number 006 , established and managed by the Center Director under grant R828771
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
Center: Center for the Study of Childhood Asthma in the Urban Environment
Center Director: Hansel, Nadia
Title: Zero-Valent Metal Treatment of Halogenated Vapor-Phase Contaminants in SVE Offgas
Investigators: Roberts, A. Lynn , Fairbrother, D. Howard
Institution: The Johns Hopkins University
EPA Project Officer: Aja, Hayley
Project Period: October 1, 2001 through September 30, 2002
Project Period Covered by this Report: October 1, 2001 through September 30, 2002
Project Amount: Refer to main center abstract for funding details.
RFA: Hazardous Substance Research Centers - HSRC (2001) Recipients Lists
Research Category: Hazardous Waste/Remediation , Land and Waste Management

Objective:

This research project explores the use of zero-valent metals and bimetallic reductants for treating vapor phase organohalides found in offgas from soil vapor extraction systems. Zero-valent metal technology has emerged as a promising approach for in situ treatment of groundwater contaminants, but its applicability to vapor phase contaminants has been virtually unexplored. This research project significantly extends the scope of investigations currently underway (through funding obtained from other sources) that pertain to use of zero-valent metals for treatment of anoxic landfill gases. The main objective of this research project is to test whether similar treatment systems could prove useful for treating organohalides in gas streams that contain O₂. Although it might be anticipated that the presence of O₂ could lead to more rapid passivation of reactive surfaces due to the formation of a thick coating of iron oxides and decreased reactivity, there also is ample reason to believe that the presence of O₂ will not significantly impair treatment system performance, provided that the reactive surface is judiciously selected. If successful, an approach based on zero-valent metals or bimetallic reductants could be used to treat offgases obtained from soil vapor extraction (SVE) systems. Results will form the basis of process models that can be used to design aboveground treatment systems for SVE offgases that contain organohalides.

Progress Summary:

Preliminary work focused on screening the reactivity of various iron-based, bimetallic reductants. The reaction rates of cis-1,2-dichloroethylene (cis-DCE), a "model" organohalide, with a variety of bimetallic reductants, were compared in batch studies. Initial experiments compared the rates of Ni/Fe, Co/Fe, and Cu/Fe reductants to that of Fe alone. These studies revealed significant differences between the various reductants. Although Co/Fe and Cu/Fe exhibited slightly accelerated rates of reaction as compared to Fe alone, the reactions with Ni/Fe were significantly faster. Given our initial successes with the Ni/Fe reductants, we have focused solely on this system in subsequent experiments. Additional batch reactors were used to investigate the effect of nickel loading on the observed rates of reaction. We have developed a methodology for the controlled production of the bimetallic reductants with variable loadings of the catalytic metal using electroless deposition. We used auger electron spectroscopy to determine the average nickel loading on the iron particles. Correlation of the reaction rate data from the batch reactor studies with the surface composition information indicates that the nickel loading has a significant impact on the rate of reduction of cis-DCE. At low Ni loadings, the rate of cis-DCE removal increases quickly with nickel concentration, but at higher Ni loadings, the rate increases more slowly. At maximum, the Ni/Fe system exhibited rates of cis-DCE reduction that were an order of magnitude greater than those of Fe.

Current efforts are focused on testing the applicability of the Fe and Ni/Fe bimetallic reductants to the treatment of gas phase contaminants in column reactors. Plexiglass columns, fitted with a series of gas sampling ports along their lengths, were packed with either iron or nickel-plated iron, filled with water, and drained gravimetrically. cis-DCE is introduced to the gas phase by bubbling a 50:50 mix of carbon dioxide and nitrogen through a saturated solution of the organohalide. The concentration of the organohalide can be accurately manipulated by varying the ratio of the cis-DCE-containing gas stream with a second water-saturated gas stream. The gas stream was introduced to the columns several weeks ago, and samples are periodically taken for gas chromatographic analysis. Preliminary results indicate that the gas phase concentration of cis-DCE is decreasing along the length of the columns. Product species such as ethene and ethane are growing in, suggesting that the contaminant is partitioning into the aqueous phase and undergoing reductive dehalogenation at the iron or bimetallic surface. Additionally, it is clear that the rate of formation of products in the Ni/Fe system is approximately an order of magnitude faster than the rate observed in the column with Fe alone.

Future Activities:

The column reactors will remain continuously operational for an extended period of time to allow us to study the longevity of these reductants. Additional sampling ports on the columns will allow us to remove iron or bimetallic grains for analysis. If the efficiency of the columns appears to change with time, surface analysis of the reductant grains using Auger electron spectroscopy and/or x-ray photoelectron spectroscopy will allow us to correlate changes in the surface composition of the reductants with changes in the reaction kinetics. Additional columns will be added in the future to allow us to explore the effect of variables such as flow rate, specific water retention, nickel loading, concentration of cis-DCE, and the presence of other atmospheric constituents in the gas stream. In particular, the effect of O₂ on the efficiency of this treatment system will be explored.

Journal Articles:

No journal articles submitted with this report: View all 4 publications for this subproject

Supplemental Keywords:

waste reduction, pollution prevention, environmental engineering, metal, zero-valent metals, bimetallic reductants, vapor, vapor gas, vapor extraction., RFA, Scientific Discipline, Water, Waste, Hazardous, Chemical Engineering, Ecological Risk Assessment, Health Risk Assessment, Environmental Chemistry, Engineering, Chemistry, & Physics, Analytical Chemistry, Contaminated Sediments, Hazardous Waste, Geochemistry, Hydrology, Ecology and Ecosystems, Environmental Engineering, contaminant transport, adsorption, heavy metals, contaminated sediment, soil vapor phase contaminants, offgas, fate and transport , hazardous waste treatment, soil vapor extraction, electrochemical technology, chemical detection techniques, fate and transport, groundwater, contaminant dynamics, soil extraction, zero valent metal treatment, vapor phase organohalides, chemical kinetics, heavy metal contamination

Relevant Websites:

http://www.jhu.edu/hsrc/ Exit

Progress and Final Reports:

Original Abstract

Final

Main Center Abstract and Reports:

R828771    Center for the Study of Childhood Asthma in the Urban Environment

Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
R828771C001 Co-Contaminant Effects on Risk Assessment and Remediation Activities Involving Urban Sediments and Soils: Phase II
R828771C002 The Fate and Potential Bioavailability of Airborne Urban Contaminants
R828771C003 Geochemistry, Biochemistry, and Surface/Groundwater Interactions for As, Cr, Ni, Zn, and Cd with Applications to Contaminated Waterfronts
R828771C004 Large Eddy Simulation of Dispersion in Urban Areas
R828771C005 Speciation of chromium in environmental media using capillary electrophoresis with multiple wavlength UV/visible detection
R828771C006 Zero-Valent Metal Treatment of Halogenated Vapor-Phase Contaminants in SVE Offgas
R828771C007 The Center for Hazardous Substances in Urban Environments (CHSUE) Outreach Program
R828771C008 New Jersey Institute of Technology Outreach Program for EPA Region II
R828771C009 Urban Environmental Issues: Hartford Technology Transfer and Outreach
R828771C010 University of Maryland Outreach Component
R828771C011 Environmental Assessment and GIS System Development of Brownfield Sites in Baltimore
R828771C012 Solubilization of Particulate-Bound Ni(II) and Zn(II)
R828771C013 Seasonal Controls of Arsenic Transport Across the Groundwater-Surface Water Interface at a Closed Landfill Site
R828771C014 Research Needs in the EPA Regions Covered by the Center for Hazardous Substances in Urban Environments
R828771C015 Transport of Hazardous Substances Between Brownfields and the Surrounding Urban Atmosphere