Identification of Distribution System Tastes and Odors Caused by an Iron and Manganese Removal Treatment Plant

摘要

A city in Western Washington had a 1.6 MGD treatment plant that uses ozone and filtration to treat iron and manganese. The City experienced large numbers of customer complaints of tastes and odors in the distribution system. Many of the complaints involved earthy, musty, and chlorinous odors. The City began an investigation to identify the cause of the taste and odor problems. The initial portion of the investigation focused on the treatment plant performance. Bench scale ozone dosing analysis indicated that the ozone dose was insufficient to oxidize all of the potential demand. Additional ozone equipment was procured and a full-scale pilot test was performed over the course of one summer to ascertain the effect of additional ozone. Water quality improved as evidenced by a decrease in the frequency of customer taste and odor complaints. However, additional testing revealed that customer complaints decreased even further when ozonation was discontinued suggesting that interactions between ozone and organic material or other contaminants in the water were contributing to tastes and odors. These additional tests used air injection to introduce ambient oxygen followed by filtration, which proved equally effective at removing manganese. Additional pilot testing using chlorine oxidation and pyrolusite media was also compared with the previously used filtration media. The pilot testing revealed that chlorination and filtration removed iron and manganese to non-detectable levels and resulted in fewer potential taste and odor problems and increased maintenance and operational efficiency. Full-scale conversion to chlorination and pyrolusite oxidation is also discussed.