Characterization and Kinetics of Contaminant Oxidation and Hydrogen Peroxide Decomposition in the Presence of Subsurface MaterialEPA Grant Number: R823402
Title: Characterization and Kinetics of Contaminant Oxidation and Hydrogen Peroxide Decomposition in the Presence of Subsurface Material
Investigators: Valentine, Richard L.
Institution: University of Iowa
EPA Project Officer: Lasat, Mitch
Project Period: October 1, 1995 through September 30, 1998 (Extended to August 26, 1999)
Project Amount: $189,242
RFA: Exploratory Research - Engineering (1995) Recipients Lists
Research Category: Land and Waste Management , Engineering and Environmental Chemistry
Surface catalyzed decomposition of hydrogen peroxide in the subsurface environment leads to oxygen formation and potentially to the abiotic oxidation of organic contaminants. This research will improve of understanding of these processes by examining the role of different types of subsurface materials, important water quality parameters including pH and the presence of carbonate, and phosphate. The proposed research will provide information for the development of mechanistic descriptions and the testing of a proposed reaction model. An important overall objective is to determine if the model is: 1) generally applicable to a variety of mineral surfaces and a variety of contaminants, and 2) if it is consistent with known and hypothesized elementary reactions.
The primary approach is to simultaneously measure contaminant oxidation and hydrogen peroxide decomposition in the presence of materials that characterize the subsurface environment and in waters of different composition. Probe studies to identify radical pathways will also be conducted. Experiments are being conducted in both batch and fixed-bed reactors. Subsurface type material to be utilized includes collected aquifer material as well as synthesized model oxides. Model contaminants include several that are good candidates for probe compounds because their reaction products and kinetics with several radicals is established. Mathematical modeling will be based on the hypothesized scheme and will involve the use of non-linear parameter estimation methods and numerical integration.
Significant progress has been made on evaluating hydrogen peroxide decomposition kinetics and quinoline oxidation in the presence of three types of iron oxides believed ubiquitous in the subsurface environment. Hydrogen peroxide decomposition followed a rate expression first order in hydrogen peroxide and iron oxide concentration. The catalytic activity varied by over an order of magnitude on a mass basis, in the order of ferrihydrite > semi-crystalline oxide > Goethite. On a surface area basis, the catalytic activity however, was comparable, varying by only a factor of approximately two. This indicates that site density and site activity of these oxides were similar, even though their morphology greatly differed. In comparison, the catalytic activity toward quinoline oxidation was highest for Goethite, much less for the semi-crystalline material, and negligible in the presence of ferrihydrite. Carbonate and phosphate also reduced decomposition rates but did not affect the stoichiometry between quinoline degraded and hydrogen peroxide decomposed. It is hypothesized that a primary mechanism involves surface adsorption and catalytic site inactivation by adsorption or through effects on solution chemistry. A preliminary model for the effect of carbonate and phosphate adsorption on hydrogen peroxide decomposition in the presence of iron oxides has been developed. The formulation of the original reaction model has been expanded to include this and several other phenomena.