Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Chemical and Biochemical Engineering

Supervisor

Herrera, Jose

Abstract

The presence of lead in drinking water is a common issue for utilities where lead pipes are used as service lines in drinking water distribution systems. Dissolved lead concentrations have been linked to the destabilization of stratified lead corrosion scales formed at the inner walls of lead pipe used as drinking water service lines. To develop a framework for lead dissolution control, it is necessary to fully describe the characteristics of the surface layer of the lead corrosion scale in direct contact with drinking water. In the first part of this thesis, a thorough lead corrosion scale characterization is carried using lead pipes collected from four Canadian drinking water systems. The results obtained are contextualized in terms of the preferential presence of lead oxides and aluminosilicates at the surface layer of the corrosion scales. The different phases identified are linked to the corresponding water quality, particularly pH values and dissolved silicate concentrations. In the second part of this work, PbO2 dissolution processes in the presence of monochloramine were studied. A detailed chemical synthesis protocol, characterization for the PbO2 solid, analysis of monochloramine decomposition and corresponding lead dissolution profiles have enabled us to identify a surface reaction between PbO2 and NH2Cl. Two different reaction regimes for this interaction were revealed. At high PbO2/NH2Cl molar ratios, where NH2Cl is the limiting reagent and the presence of PbO2 accelerated the decomposition of NH2Cl. PbO2 was reduced only by water, resulting in the release of limited amounts of dissolved lead (<10 >μg/L). In contrast, at low PbO2 solid to NH2Cl molar ratios, monochloramine decomposition rates were similar to those observed for its auto-decomposition. The monochloramine decomposition process triggered the formation of defects in PbO2, resulting in elevated levels of dissolved lead released to the aqueous phase. The activity of PbO2 for monochloramine decomposition is determined by its crystal structure, crystallite size, and surface properties in the form of defects. Based on these observations, a proton-containing species in PbO2 is proposed as the active species for monochloramine decomposition.

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