Iron release from corroded, unlined cast-iron pipe

One goal of drinking water treatment is to minimize iron uptake from distribution systems in which old, corroded iron and steel pipes are used. This research evaluated the effects of changes in pH and alkalinity and the use of orthophosphates to minimize iron release. A pilot pipe-loop system was constructed using 100-year-old unlined cast-iron pipes. The composition and structure of the corrosion scales were characterized, and iron release was investigated for various water quality conditions. Results showed that iron release could be reduced over time by maintaining a stable water quality. When the pH of water was raised to 9.5, iron release during an 8-h stagnation period decreased from <1.5 mg/L to >0.3 mg/L within 6-8 months. Comparable results were obtained when an orthophosphate concentration of 3.0 mg/L as PO₄ was maintained in the influent to the pipes. Iron release was found to be sensitive and complementary to changes in the alkalinity of water.