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.

published_or_final_version / Zoology / Doctoral / Doctor of Philosophy

No description available.

No description available.

No description available.

Chapter one summarises the development of UK legislation for the protection of the aquatic environment, and highlights current EC legislative requirements for water quality. The need for on-line water quality monitoring and the alternative instrumental approaches to it are discussed, together with the philosophy of "easy care instrumentation" and water industry requirements for online analysers. A simple spectrophotometric FI system is proposed for the on-line determination of a range of water quality parameters. The following chapter details instrumentation used in the FI system, emphasising the solid-state photometric detector. Development of an FI manifold for the determination of aluminium in potable and treated waters is covered in the next chapter. The method, based on complexation of aluminium with pyrocatechol violet is compared with a standard Driscoll procedure. Details of the construction and testing of a fully automated FI instrument are also given. Chapter four describes the development of a modular automated FI monitor with a PC compatible STEbus based computer system. Successful operation of this monitor is illustrated by its application to the determination of residual coagulants (aluminium and iron). Full details of software routines for control, processing and validation are given together with results from a tap water trial for dissolved aluminium. The FI determination of residual iron by its complexation with ferene S, and the application of the optimised method in the STEbus based monitor is detailed in chapter five. In the final chapter the use of on-line FI oxidation procedures for the determination of dissolved organic carbon are examined. The oxidation of a wide range of organic species to carbon dioxide using a silver catalysed persulphate reaction, enhanced with UV irradiation and a stopped-flow procedure is described. The sequential determination of inorganic and organic carbon without separation of the fractions is also investigated.

Thesis (M. Sc.)--University of Hong Kong, 1996. / Includes bibliographical references (leaf 98-101).

No description available.

The Osoyoos Lake problem is one of excessive algal populations creating nuisance conditions for recreation and agriculture. During the summer of 19 68 (May 28 to October 14) an extensive water sampling program was carried out to determine phytoplankton communities present and some of the physical and chemical factors influencing their growth. The lake was monitored using a system of three transects at predetermined sections across the lake and four fixed sampling locations on each transect. The sites on each transect were sampled at intervals of approximately two weeks. Mud samples were collected at each site once a month. Samples were also collected on a two week basis from various waters which eventually enter Osoyoos Lake. The purpose of this was to gain some indication of nutrients contributed to the lake by inflowing waters. Osoyoos Lake gave rise to a major blue-green alga bloom which persisted throughout June and July. This Anabaena flos-aquae bloom was followed by smaller populations of Fragilaria crotonensis, Dinobryon sertularia, a late summer pulse of A. flos-aquae, and at the southern end of the lake considerably large populations of Melosira italiea and Oscillatoria acutissima. A discussion of the geological, physical, chemical and morphological factors possibly combining to create such growths in the lake is presented. It was generally concluded that high levels of nitrogen, phosphorus, calcium and dissolved solids were favouring the enhancement of eutrophication in Osoyoos Lake. Climate, lake morphology and the edaphic factor were also favourable to productivity. There is evidence to support the statement that sewage effluent and industrial wastes are sources of phosphorus and nitrogen build-up in the lake. In addition to these sources, sewage seepage, agricultural drainage and nitrogen fixation are believed to be contributing to the accumulation of lake nitrogen. The continuous application of water to the fertilized orchards surrounding the basin is thought to be instrumental in leaching fertilizers and minerals natural to the land into the lake at an accelerated pace. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

The operation and maintenance of highways contributes a variety of pollutants to surface and subsurface waters. Solids, heavy metals, nutrients, oil and grease, pesticides and bacteria can all be associated with highway runoff. Although the full extent of the effect of all these runoff constituents upon the quality of surrounding waters is not well defined, this study will mainly concentrate on nutrient contaminants (essentially phosphorus). The last decade has seen increasing efforts in research and development to abate contaminant discharges from highway runoff using a number of treatment facilities such as swale and detention/retention ponds. An evaluation of the effectiveness of these systems in removing phosphorus by physical, chemical and biological uptake is the aim of this research endeavor. This study represent the first step towards the determination of design criteria for swales and detention/retention ponds based on water quality improvement.