AWWA JAW59057

The principal cause of colored water is iron release from corroded iron and steel pipes. In this research, a pilot pipe-loop system was constructed from 100-year-old unlined cast-iron pipes taken from the Massachusetts Water Resources Authority in Boston. The authors then evaluated the role played by water quality factors - pH, alkalinity, and orthophosphates - in controlling iron release. Results from the experiments showed that iron release was closely linked to turbidity, with turbidity directly proportional to iron concentration. Iron release was also found to be particularly sensitive to changes in alkalinity. In the pH range of 7.6 to 9.5, higher alkalinities (i.e., in the 10-60 mg/L as calcium carbonate range) were associated with lower levels of iron release. Overall, maintaining a stable water quality with constant pH and alkalinity proved the most important factors for reducing iron release. The water industry has often based its control strategies for iron release on information from corrosion in new iron pipes. However, older corroded iron pipes respond much differently to changes in water quality parameters, and corrosion scale chemistry and structure can dictate the iron release response in corroded pipes. By focusing on the old, unlined pipes prevalent in many distribution systems, this article provides new insight into the causes of iron release and the treatment options to control it. Includes 31 references, tables, figures.