| Iron release from corrosion scales in iron/steel pipes is the principal cause of “colored water” problems in drinking water distribution systems. The interaction of corroded iron pipe surfaces with water, however, is not well understood. In this dissertation, the composition and structure of corrosion scales from old iron/steel water distribution pipes was characterized with the objective to understand their role in metal ion release to water under different water quality conditions.; Most corrosion scales have characteristic structural features such as a loosely-held top surface layer, a shell-like layer and a porous core. Goethite (α-FeOOH), magnetite (Fe3O4), maghemite (γ-Fe 2O3), lepidocrocite (γ-FeOOH), and siderite (FeCO 3) were the primary crystalline phases present in the scales. The composition and structure of corrosion scales was different for scales formed in two dissimilar water distribution systems. Based on findings in this research, it was concluded that iron is released from corroded iron pipes primarily by dissolution of the corrosion scales. The microstructure and composition of corrosion scales are key parameters that determine the amount of iron released from such systems. The role of water quality parameters, such as dissolved oxygen, pH, alkalinity, and orthophosphates, in decreasing iron release was also evaluated.; A conceptual model was developed to address the issues of the formation and growth of iron corrosion scales, and their reactions that lead to colored water problems. According to the model, iron release from corrosion scales can be controlled, in general, by either (a) promoting a denser scale microstructure, or (b) inhibiting dissolution of corrosion scale components. It is anticipated that the conceptual model will be used as a basis for changing water quality to minimize colored water formation, and as a guide for further research. |
