How does the nitrate removal facility work?

Q. How does the nitrate removal facility work?

A. The Fleur Nitrate Removal Facility uses a process called ion exchange.  The facility includes 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, which is saturated 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 available chloride decreases, reducing the system’s ability to remove more nitrate. Consequently, 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). 

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, typically less than 1 mg/L Nitrate-N, is blended back into the plant flow to ensure the overall nitrate concentration remains below the safe drinking water standard of 10 mg/L.

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