AWWA WQTC58970

The objective of this research was to evaluate the effect of two water quality parameters, chloride and orthophosphate, on the release of iron from an old cast iron pipe section removed from a drinking water distribution system and on the properties of the resulting suspensions. Experiments were conducted using a section of cast iron pipe (approximately 90 years old) removed from the drinking water distribution system of the City of Cincinnati, Ohio. The pipe was approximately 8 cm (3.15 inches) in height and 10.2 cm (4 inches) in diameter. Approximately 1.3 centimeters (0.5 inches) of the original effective inside diameter was lost to corrosion deposits. One end of the pipe was closed with a rubber seal and hose clamp fastener. Cincinnati tap water served as the base water for the experiments. The pipe section was "conditioned" with Cincinnati tap water for one year prior to the start of data collection. All chemicals used in this study were Analytical Reagent (AR) grade. The amount of ultrapure nitric acid, HNO3, used to preserve samples for metals analysis, and sodium chloride and sodium phosphate (Na3PO4C12H2O) were used to adjust water chemistry. The paper names various instruments for measuring: pH; dissolved oxygen; reduction-oxidation potential; metals content; color, total iron, orthophosphate, and free chlorine; total iron; and, turbidity. Syringe filters (0.45, 0.2 :m) were used to separate colloidal iron during color and iron measurements. Two liters of Cincinnati tap water were collected in glass beakers after flushing the laboratory faucet for 5 minutes. If applicable, sodium chloride and sodium phosphate were added at this time and the water was mixed. The pH, reduction-oxidation (REDOX) potential, orthophosphate, and free chlorine in the tap water were immediately measured, and water samples were collected for metals analysis. The remaining volume of test water was then pumped through 6.4 mm (0.25 inch) plastic tubing into the pipe section (standing vertically) at a slow rate of 50 mL/min from the bottom of the pipe. Excess water was allowed to overflow from the pipe section. Dissolved oxygen (DO) was measured with a dissolved oxygen probe suspended at the center of the pipe during flushing. The pipe section was loosely covered with a glass plate to reduce interaction with the outside environment and allowed to sit undisturbed for approximately 23.5 hours during weekdays and 72 or 96 hours over weekends. The glass cover was carefully removed at the end of stagnation. The dissolved oxygen was first measured as before. Samples were then carefully drawn for pH, REDOX potential, turbidity, color, total iron, orthophosphate, and free chlorine and measured immediately, and a sample was taken for ICAPS analysis. Statistical comparisons between means of treatment groups were made using unpaired test when data sets passed normality test or the Mann-Whitney Rank Sum Test when data sets failed normality test ("=0.05). Normality was tested using the Kolmogorov-Smirnov test. All statistical calculations were made using Sigmastat£ (version 2.0). Includes 22 references, tables, figures.