Grantee Research Project Results
2003 Progress Report: Chemical, Physical, and Biological Processes at the Surface of Palladium Catalysts Under Groundwater Treatment Conditions
EPA Grant Number: R828772C004Subproject: this is subproject number 004 , established and managed by the Center Director under grant R828772
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
Center: Solutions for Energy, AiR, Climate and Health Center (SEARCH)
Center Director: Bell, Michelle L.
Title: Chemical, Physical, and Biological Processes at the Surface of Palladium Catalysts Under Groundwater Treatment Conditions
Investigators: Reinhard, Martin , Westall, John C.
Institution: Oregon State University
EPA Project Officer: Aja, Hayley
Project Period: January 1, 2002 through December 31, 2003
Project Period Covered by this Report: January 1, 2003 through December 31, 2004
RFA: Hazardous Substance Research Centers - HSRC (2001) Recipients Lists
Research Category: Hazardous Waste/Remediation , Land and Waste Management
Objective:
The objectives of this research project are to: (1) evaluate the impacts of groundwater on catalyst activity; (2) elucidate the chemical and physical mechanisms responsible for changes in catalyst activity; (3) investigate potential biofouling issues that may result from biological activity expected in long-term treatment applications; and (4) develop convenient and economical methods to regenerate catalysts in situ.
Rationale. Batch studies with supported palladium catalysts have demonstrated the potential of the palladium (Pd)/hydrogen process for treating groundwaters or effluent streams that are contaminated by halogenated compounds. These studies yielded virtually complete reductive dehalogenation of chlorinated ethylenes to ethane at room temperature in short contact times, with reaction rates that are orders of magnitude higher than zero-valent iron. Other batch studies have shown the ability of Pd to catalyze the reaction of a range of compounds: all six species of chlorinated ethylenes, carbon tetrachloride, chloroform, 1,2-dibromo-3-chloropropane, Freon 113, chlorobenzene, naphthalene, and lindane. Laboratory column studies and field tests, however, have indicated that catalyst activity may decline over time, thereby potentially affecting the economic competitiveness of this process. Research is needed to optimize the catalyst and operating parameters for the field by determining the causes of activity loss and the means for preventing or minimizing such effects.
Approach. This research project approaches optimization of the Pd process through: (1) testing the catalyst kinetics and responses during operation in a laboratory-scale version of the field system; and (2) observing changes in the catalyst surface during treatment. Laboratory reactors have been constructed and used to remove trichloroethylene (TCE), a model substrate, from water sources of varying quality, such as deionized (DI) water or groundwater; various regenerants are being compared. The kinetic experiments use a column reactor with a dispersed catalyst, which is typical of catalysts used in field applications. The surface studies use a batch reactor with a model catalyst, which is more amenable to spectroscopic analyses and therefore should yield more insight into surface phenomena; samples are removed from the reactor periodically over the course of treatment for spectroscopic characterization. The research is being undertaken in collaboration with a field study at Edwards Air Force Base (EAFB) near Lancaster, CA.
Progress Summary:
The laboratory reactor system with the dispersed Pd catalyst successfully removed TCE from EAFB groundwater. Observed deactivation was consistent with sulfide poisoning, and sodium hypochlorite was able to fully regenerate the catalyst. The sulfide was attributed to sulfate-reducing bacteria, whose growth was promoted by storing the reactor feed water under hydrogen pressure. As a result, the system was modified so that feed water was stored under helium (i.e., conditions were more representative of the aerobic field site and less favorable for the growth of sulfate-reducing bacteria). This modified system successfully removed TCE from DI water for 4 months with no deactivation. The catalyst then was deactivated with a solution of roughly 0.04 mg/L of sulfide, and several regenerants were compared: sodium hypochlorite, hydrogen peroxide, and air-saturated water. Air-saturated water and a 20 mM hydrogen peroxide solution both resulted in 50 percent recovery of the catalyst activity; further exposure of the catalyst to 200 mM hydrogen peroxide yielded no additional recovery. As in the case of the groundwater, 20 mM sodium hypochlorite fully regenerated the catalyst.
X-ray photoelectron spectroscopy (XPS) was performed on the model catalyst after exposure to EAFB groundwater and sodium hypochlorite. Preliminary analyses are consistent with earlier experiments with dispersed catalyst. Those experiments indicated that organics accumulate on the catalyst surface upon exposure to water, but there was no strong correlation to activity. The preliminary data also suggest that sulfide may bind to the Pd surface and may be oxidized to sulfate with hypochlorite treatment. The sulfide/sulfate data, however, were not cleanly reproduced in a concurrent replicate system, possibly because of differences in catalyst handling; more experiments are needed to verify accuracy and reproducibility.
Future Activities:
We will confirm the above XPS data and correlate chemical changes in the model catalyst to activity. In addition, regeneration will be optimized with respect to concentration, exposure time, and total dose. Finally, results will be compared with kinetic data from the field study. This study commenced on January 1, 2002, and is authorized for a 2-year period ending on December 31, 2003.
Journal Articles:
No journal articles submitted with this report: View all 1 publications for this subprojectSupplemental Keywords:
palladium catalyst, groundwater, trichloroethylene, TCE, surface science, environmental chemistry, international cooperation, waste, environmental engineering, groundwater remediation, hazardous, hazardous waste, advanced treatment technologies, carbon tetrachloride, chlorinated ethylene, contaminated groundwater, hazardous waste treatment, naphthalene., RFA, Scientific Discipline, INTERNATIONAL COOPERATION, Waste, Environmental Chemistry, Hazardous Waste, Groundwater remediation, Hazardous, Environmental Engineering, carbon tetrachloride, hazardous waste treatment, chlorinated ethylenes, napthalene, advanced treatment technologies, palladium catalysis, catalysts, contaminated groundwater, groundwater contamination, palladium catalystsRelevant Websites:
http://wrhsrc.oregonstate.edu/ Exit
Progress and Final Reports:
Original AbstractMain Center Abstract and Reports:
R828772 Solutions for Energy, AiR, Climate and Health Center (SEARCH) Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
R828772C001 Developing and Optimizing Biotransformation Kinetics for the Bio- remediation of Trichloroethylene at NAPL Source Zone Concentrations
R828772C002 Strategies for Cost-Effective In-situ Mixing of Contaminants
and Additives in Bioremediation
R828772C003 Aerobic Cometabolism of Chlorinated Aliphatic Hydrocarbon Compounds with Butane-Grown Microorganisms
R828772C004 Chemical, Physical, and Biological Processes at the Surface of Palladium Catalysts Under Groundwater Treatment Conditions
R828772C006 Development of the Push-Pull Test to Monitor Bioaugmentation
with Dehalogenating Cultures
R828772C007 Development and Evaluation of Field Sensors for Monitoring
Bioaugmentation with Anaerobic Dehalogenating Cultures for In-Situ Treatment of
TCE
R828772C008 Training and Technology Transfer
R828772C009 Technical Outreach Services for Communities (TOSC) and Technical Assistance to Brownfields Communities (TAB) Programs
R828772C010 Aerobic Cometabolism of Chlorinated Ethenes by Microorganisms that Grow on Organic Acids and Alcohols
R828772C011 Development and Evaluation of Field Sensors for Monitoring Anaerobic Dehalogenation after Bioaugmentation for In Situ Treatment of PCE and TCE
R828772C012 Continuous-Flow Column Studies of Reductive Dehalogenation with Two Different Enriched Cultures: Kinetics, Inhibition, and Monitoring of Microbial Activity
R828772C013 Novel Methods for Laboratory Measurement of Transverse Dispersion in Porous Media
R828772C014 The Role of Micropore Structure in Contaminant Sorption and Desorption
The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.
Project Research Results
Main Center: R828772
168 publications for this center
69 journal articles for this center