Understanding electrochemical inactivation of contaminants in water

Persistent Link:
http://hdl.handle.net/10150/191268
Title:
Understanding electrochemical inactivation of contaminants in water
Author:
Wang, Jiankang
Issue Date:
2004
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
This research investigated the mechanism, kinetics, and feasibility of chlorinated aliphatic compounds inactivation by electrochemical reduction using nickel and iron electrodes. Reactions of trichloroethylene (TCE) and tetrachloroethylene (PCE) with zerovalent iron were investigated to determine the role of atomic hydrogen in their reductive dechlorination using Tafel analysis and electrochemical impedance spectroscopy (EIS). Comparison of iron corrosion rates with those for TCE reaction showed that TCE reduction occurred almost exclusively via atomic hydrogen at low pH values and via atomic hydrogen and direct electron transfer at neutral pH values. In contrast, reduction of PCE occurred primarily via direct electron transfer at both low and neutral pH values. The EIS data showed that all the rate limitations for TCE and PCE dechlorination occurred during the transfer of the first two electrons. Carbon tetrachloride (CT) reductive dechlorination was studied at a nickel rotating disk electrode using chronoampermetry (CA) and EIS. Only trace levels of methylene chloride and chloromethane were produced, indicating that sequential hydrogenolysis was not the predominant pathway for methane production. EIS showed that the ratelimiting step for CT reduction was the transfer of the first electron to a physically adsorbed CT molecule. The feasibility of an electrochemical reductive dechlorination method for removing CT from potable water was carried out in a flow-through reactor using bare and polymer coated porous nickel electrodes. Destruction of half-life values for CT with the bare nickel electrode ranged from 3.5 to 5.8 minutes for electrode potentials ranging from -652 to -852 mV with respect to the standard hydrogen electrode (SHE). Faradic current efficiencies could be increased by 100 to 360% by coating the electrode with a silicone polymer. This research also investigated electrochemical oxidation of triclosan, a biocidal agent, using Ebonex® and boron-doped diamond (BDD) film anodes. Product analysis showed that breaking the ether linkage was easier than opening the aromatic ring. Microtox® testing indicated that residual triclosan accounted for nearly all the toxicity in the treated water, despite the fact that chlorinated byproduct concentrations were significantly higher than those of triclosan itself.
Type:
Dissertation-Reproduction (electronic); text
Keywords:
Hydrology.; Electrolytic reduction.; Water -- Pollution.
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Chemical and Environmental Engineering; Graduate College
Degree Grantor:
University of Arizona
Committee Chair:
Farrell, James

Full metadata record

DC FieldValue Language
dc.language.isoenen_US
dc.titleUnderstanding electrochemical inactivation of contaminants in wateren_US
dc.creatorWang, Jiankangen_US
dc.contributor.authorWang, Jiankangen_US
dc.date.issued2004en_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractThis research investigated the mechanism, kinetics, and feasibility of chlorinated aliphatic compounds inactivation by electrochemical reduction using nickel and iron electrodes. Reactions of trichloroethylene (TCE) and tetrachloroethylene (PCE) with zerovalent iron were investigated to determine the role of atomic hydrogen in their reductive dechlorination using Tafel analysis and electrochemical impedance spectroscopy (EIS). Comparison of iron corrosion rates with those for TCE reaction showed that TCE reduction occurred almost exclusively via atomic hydrogen at low pH values and via atomic hydrogen and direct electron transfer at neutral pH values. In contrast, reduction of PCE occurred primarily via direct electron transfer at both low and neutral pH values. The EIS data showed that all the rate limitations for TCE and PCE dechlorination occurred during the transfer of the first two electrons. Carbon tetrachloride (CT) reductive dechlorination was studied at a nickel rotating disk electrode using chronoampermetry (CA) and EIS. Only trace levels of methylene chloride and chloromethane were produced, indicating that sequential hydrogenolysis was not the predominant pathway for methane production. EIS showed that the ratelimiting step for CT reduction was the transfer of the first electron to a physically adsorbed CT molecule. The feasibility of an electrochemical reductive dechlorination method for removing CT from potable water was carried out in a flow-through reactor using bare and polymer coated porous nickel electrodes. Destruction of half-life values for CT with the bare nickel electrode ranged from 3.5 to 5.8 minutes for electrode potentials ranging from -652 to -852 mV with respect to the standard hydrogen electrode (SHE). Faradic current efficiencies could be increased by 100 to 360% by coating the electrode with a silicone polymer. This research also investigated electrochemical oxidation of triclosan, a biocidal agent, using Ebonex® and boron-doped diamond (BDD) film anodes. Product analysis showed that breaking the ether linkage was easier than opening the aromatic ring. Microtox® testing indicated that residual triclosan accounted for nearly all the toxicity in the treated water, despite the fact that chlorinated byproduct concentrations were significantly higher than those of triclosan itself.en_US
dc.description.notehydrology collectionen_US
dc.typeDissertation-Reproduction (electronic)en_US
dc.typetexten_US
dc.subjectHydrology.en_US
dc.subjectElectrolytic reduction.en_US
dc.subjectWater -- Pollution.en_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineChemical and Environmental Engineeringen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.chairFarrell, Jamesen_US
dc.contributor.committeememberArnold, Robert G.en_US
dc.contributor.committeememberEla, Wendellen_US
dc.identifier.oclc225863629en_US
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