Research Project 6
| EPA Grant Number: | R828771-0-01 |
| Title: | Zero-Valent Metal Treatment of Halogenated Vapor-Phase Contaminants in SVE Offgas |
| Investigators: | A. L. Roberts (PI) and H. Fairbrother (Co-PI) |
| Institution: | Johns Hopkins University |
| Project Period: |
October 1, 2001 to September 30, 2003 |
| Objectives: |
| This research will explore 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 is rapidly emerging as a highly promising
approach for in situ treatment of groundwater contaminants, but
its applicability to vapor phase contaminants has been virtually
unexplored. In this project we propose to complement and significantly
extend the scope of investigations recently initiated (though funding
obtained from other sources) that pertain to use of zero-valent metals
for treatment of anoxic landfill gases. Specifically, in this project we
intend 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 and hence
decreased reactivity, there is also 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. |
| Approach: |
| We propose to study reactions of selected organohalide contaminants with a variety of bimetallic reductants (or iron alone). Initial work (Task 1) will involve screening reductants for reactivity and selectivity in batch systems containing dissolved oxygen. Once promising candidates are identified, performance and longevity studies will be initiated in column reactors in which contaminants will be introduced to a gas phase containing O2 (Task 2). Reaction rates and products will be monitored over time for several different metal or bimetallic reductants. Specifically, we will explore the influence of the presence of oxygen on reactivity and selectivity. We will also examine whether reactivity declines over time as the composition of the metal or bimetallic reductant surface evolves. Analytical instrumentation to be purchased with this grant will allow us to assess how the changing composition of the solution phase affects reactivity of the metal or bimetallic reductant. In Task 3, the batch and column studies will be complemented by surface chemical investigations (involving surface infrared spectroscopy, scanning Auger electron spectroscopy, X-ray photoelectron spectroscopy, and in situ scanning electron microscopy). These studies will provide information concerning the composition of the reactive surface. |
| Expected Results: |
| It is expected that certain zero-valent metal or bimetallic reductants will degrade halogenated contaminants even in the presence of O2. This project will provide information needed to assess whether such treatment processes are cost-effective over the projected design life of the treatment process. |
| Improvements in Risk Management: |
| The proposed treatment of offgas from SVE systems represents a significant improvement over existing treatment technologies (e.g., adsorption onto granular activated carbon), which merely transfer contaminants from one medium to another. |
| Supplemental Keywords: |
| waste reduction, pollution prevention,
environmental engineering |