Citation:

Lytle, D., M. Tang, A. Francis, A. O'Donnell, AND J. Newton. The Effect of Chloride, Sulfate, and Dissolved Inorganic Carbon on Iron Release from Cast Iron. WATER RESEARCH. Elsevier Science Ltd, New York, NY, 183:116037, (2020). https://doi.org/10.1016/j.watres.2020.116037

Impact/Purpose:

Iron corrosion in drinking water distribution systems causes water discoloration, water quality deterioration, hydraulic loss, and even pipe failures, which are usually influenced by scale structure, water hydraulics, water chemistry, and other factors. The objective of this work was to evaluate the effects of chloride, sulfate, and dissolved inorganic carbon (DIC) on iron release from a 90-year-old cast iron pipe section at water pH 8.0 under stagnant conditions. Experimental results showed that the addition of 150 mg/L sulfate to water significantly increased the mean total iron concentrations to 1.13-2.68 mg/L, relative to 0.54-0.79 mg/L for the baseline water with only 10 mg C/L DIC. Similar results were observed under conditions when chloride was added, and when sulfate and chloride were added together. In contrast, the mean total iron concentration was significantly reduced by 53-80% in waters with higher DIC of 50 mg C/L, as compared to similar waters with lower DIC of 10 mg C/L. Additionally, the Larson Ratio was generally a good indicator for iron release depending on the circumstances. Iron release was described by molecular radial diffusion modelling that accounted for water quality, scale characteristics, hydraulics, and other condition-related information. The results provided insightful information for water systems that have cast iron pipes and galvanized iron pipes and that might encounter changes in water treatment and water sources. More studies are needed to better understand the cast iron corrosion mechanisms under the examined water chemistries.

Description:

Iron corrosion in drinking water distribution systems causes water discoloration, water quality deterioration, hydraulic loss, and even pipe failures, which are usually influenced by scale structure, water hydraulics, water chemistry, and other factors. The objective of this work was to evaluate the effects of chloride, sulfate, and dissolved inorganic carbon (DIC) on iron release from a 90-year-old cast iron pipe section at water pH 8.0 under stagnant conditions. Experimental results showed that the addition of 150 mg/L sulfate to water significantly increased the mean total iron concentrations to 1.13-2.68 mg/L, relative to 0.54-0.79 mg/L for the baseline water with only 10 mg C/L DIC. Similar results were observed under conditions when chloride was added, and when sulfate and chloride were added together. In contrast, the mean total iron concentration was significantly reduced by 53-80% in waters with higher DIC of 50 mg C/L, as compared to similar waters with lower DIC of 10 mg C/L. Additionally, the Larson Ratio was generally a good indicator for iron release depending on the circumstances. Iron release was described by molecular radial diffusion modelling that accounted for water quality, scale characteristics, hydraulics, and other condition-related information. The results provided insightful information for water systems that have cast iron pipes and galvanized iron pipes and that might encounter changes in water treatment and water sources. More studies are needed to better understand the cast iron corrosion mechanisms under the examined water chemistries.

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