Grantee Research Project Results
1998 Progress Report: Fenton-Like Reductions for the Enhanced Desorption and Degradation of Biorefractory Contaminants
EPA Grant Number: R826163Title: Fenton-Like Reductions for the Enhanced Desorption and Degradation of Biorefractory Contaminants
Investigators: Watts, Richard J. , Hess, Thomas F. , Teel, Amy L.
Current Investigators: Watts, Richard J. , Teel, Amy L. , Hess, Thomas F.
Institution: Washington State University
EPA Project Officer: Aja, Hayley
Project Period: February 1, 1998 through January 31, 2001
Project Period Covered by this Report: February 1, 1998 through January 31, 1999
Project Amount: $307,481
RFA: Exploratory Research - Environmental Engineering (1997) RFA Text | Recipients Lists
Research Category: Safer Chemicals , Land and Waste Management
Objective:
The project objectives are: to investigate the process conditions that promote the generation of reductants and nucleophiles in Fenton-like reactions, to identify these reactants and the products of their reactions with oxidized organic contaminants, and to evaluate the enhanced desorption of these contaminants from soils by the reactants.Progress Summary:
The use of modified Fenton's reactions (hydrogen peroxide and transition metal or mineral catalysts) recently has been shown to effectively oxidize a wide range of sorbed and biorefractory contaminants in soils and groundwater. Under appropriate process conditions, sorbed contaminants can be oxidized within hours, much faster than they would desorb naturally. However, the mechanism of this enhanced degradation of sorbed contaminants has not been elucidated. Furthermore, recent results have shown that in Fenton-like reactions, as in other advanced oxidation processes, reductions as well as oxidations may occur. These reductions may be important mechanisms when using Fenton-like reactions to degrade compounds, such as 2,4,6-trinitrotoluene (TNT), in which oxidant-resistant products are produced. Moreover, a correlation has been found between these reductant-generating conditions and the conditions that promote the enhanced degradation of sorbed contaminants. Therefore, the overall objective of the proposed research was to investigate the occurrence, reactivity, and kinetics of Fenton-like reductions and to determine the role of these reductions in enhancing the degradation of sorbed contaminants. Of the five objectives proposed, three have been nearly completed and the remaining two are under current/future study.The occurrence of nonhydroxyl radical mechanisms was investigated in modified Fenton's systems. Vigorous Fenton-like reactions using varying concentrations of hydrogen peroxide showed that the highest concentration of hydrogen peroxide used, 0.6 M, resulted in 90 percent degradation of carbon tetrachloride (CT), a highly oxidized compound not reactive with hydroxyl radicals. A standard Fenton's reaction using dilute hydrogen peroxide did not degrade CT, confirming its minimal reactivity with hydroxyl radicals. Degradation of CT in the vigorous Fenton-like reaction was confirmed by chloride analysis, which showed that an average of 3.9 chlorides were released per molecule of CT degraded. A central composite rotatable design experiment determined the optimum conditions for CT degradation at pH 3 to be 0.6 M hydrogen peroxide at 2 mM iron (III) catalyst.
To determine the mechanism responsible for the degradation of CT, a range of scavengers was used. The addition of excess isopropanol to scavenge hydroxyl radicals did not inhibit CT degradation, confirming that hydroxyl radicals were not the reactive species. Addition of excess nitrate to scavenge aqueous electrons also did not inhibit CT degradation, indicating that aqueous electrons were not the species responsible for CT reduction. However, addition of excess chloroform to scavenge reductants quenched CT degradation completely, indicating that a reductant other than aqueous electrons was responsible for the degradation of oxidized compounds in vigorous Fenton-like reactions.
Future Activities:
Because oxygen effectively scavenges reductants (ke- = 1.2 x 1010 M-1 sec-1), it will compete with contaminants if they are degraded by a reductive pathway. A key to making modified Fenton's reactions more efficient, through improving the stoichiometry and minimizing hydrogen peroxide costs, is the addition of an oxygen scavenger or electron donor.Characterization of the reduction and/or oxidation products will provide a basis for under- standing the nature of the coexisting oxidation-reduction reactions. Product characterization will be performed under conditions in which: (1) both hydroxyl radicals and the reductant are present (i.e., no scavengers); (2) the hydroxyl radicals are scavenged with excess tert-butyl alcohol; and (3) the reductant is scavenged with excess chloroform. A range of oxygen scavengers and electron donors (e.g., thiosulfate, sulfite, sulfide, ethylene diamine tetra-acetic acid, nitrilo triacetic acid) will be evaluated using three-level central composite rotatable experimental designs. The three levels of variables will be catalyst concentration, hydrogen peroxide concentration, and scavenger concentration. The probe compounds, hexachloroethane (HCE) and 1,3,5-trinitrobenzene (TNB), will be used and dissolved oxygen, oxidation-reduction potential, and hydrogen peroxide consumption will be monitored and compared to systems without the oxygen scavengers.
Journal Articles on this Report : 2 Displayed | Download in RIS Format
Other project views: | All 12 publications | 6 publications in selected types | All 6 journal articles |
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Teel AL, Warberg CR, Atkinson DA, Watts RJ. Comparison of mineral and soluble iron Fenton's catalysts for the treatment of trichloroethylene. Water Research 2001;35(4):977-984. |
R826163 (1998) R826163 (Final) |
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Watts RJ, Bottenberg BC, Hess TF, Jensen MD, Teel AL. Role of reductants in the enhanced desorption and transformation of chloroaliphatic compounds by modified Fenton's reactions. Environmental Science & Technology 1999;33(19):3432-3437. |
R826163 (1998) R826163 (Final) |
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Supplemental Keywords:
hazardous waste treatment, remediation, cleanup, Fenton's reagent., Scientific Discipline, Toxics, Water, Waste, Chemical Engineering, Contaminated Sediments, Environmental Chemistry, HAPS, Environmental Engineering, Groundwater remediation, degradation, biorefractory contaminants, sediment treatment, soil sediment, contaminated sediment, sorbed contaminants, Chloroform, enhanced desporption, kinetic studies, remediation, hydroxyl radicals, reactivity, Fenton's reagentProgress and Final Reports:
Original AbstractThe 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.