Stage III Update
All water produced by Central Iowa Water Works continues to meet all safe drinking water standards.
We continue to see the nitrate levels remain stubbornly high on both the Raccoon and Des Moines Rivers but the concentrations in the gallery are decreasing.
How does the nitrate removal facility work?
The Fleur Nitrate Removal Facility uses a process called ion exchange. Fleur’s facility involves eight ion exchange vessels each rated for 1,000 gallons per minute or 1.4 million gallons per day. Each vessel is filled with a special media, called resin. In Fleur’s process, we saturate that resin with a salt (NaCl) solution. Then as the water with nitrate passes through the resin it exchanges the nitrate (NO3-) ion for a chloride (Cl-) ion. The nitrate ion stays trapped in the resin. Over time the number of available chloride is reduced, thus reducing the system’s ability to remove more nitrate. That is when the vessel must be regenerated. To regenerate, the trapped nitrate is flushed out and the resin is resaturated with sodium chloride, thereby returning its ability to remove nitrate. The flushed-out nitrate and chloride is then wasted to the Des Moines Metropolitan Wastewater Reclamation Authority (WRA). The treated water coming out of the nitrate removal facility is typically less than 1 mg/L Nitrate-N. Because the nitrate removal facility has a limited treatment capacity, not all water that is treated in the plant passes through the nitrate removal facility. This low nitrate water is then blended back into the plant flow to ensure the overall nitrate concentration meets or exceeds the standard. When
But what does the WRA do with the waste stream? – You can find the answer here: https://www.kcci.com/article/what-happens-to-nitrates-after-they-are-removed-from-drinking-water-in-central-iowa/65179925
