Central Iowa Water Works has a nitrate removal facility that ensures safe and reliable drinking water in times where nitrate in source water is above the EPA safe drinking water standard.

That standard is 10 ppm. Final treated water will always meet EPA nitrate requirements, and if it doesn’t your utility is required to tell you.

In Cedar Rapids, water has to be blended. In Des Moines, they have another tool located in the Fleur Nitrate Removal Facility.

Ion Exchange

The facility sends a portion of the plant’s water through a process called ion exchange. Ion exchange containers have resin inside which is saturated with a salt solution. As water passes through the resin, it exchanges the nitrate ion for a chloride ion. In other words, water with nitrate flows in; Cleaner water flows out. Water has about 1 ppm of nitrate after the ion exchange treatment.

The Fleur facility has eight ion exchange vessels each rated for 1,000 gallons per minute, or 1.4 million gallons per day.

Where does the water go?

Low nitrate water treated by ion exchange is blended back into the plant flow. This dilution helps to even nitrate levels out. This is more efficient and cost effective than running all water through the ion exchange system, especially since the system does cost extra to run.

At this point, the nitrate ion is trapped in the resin and it has to be removed. The trapped nitrate is flushed out and the resin is refilled with sodium chloride.

Where does the nitrate go?

CIWW sends the flushed out nitrate to the Des Moines Metropolitan Wastewater Reclamation Authority (WRA) for further treatment. It’s essential to reduce nutrients in the wastewater so that they are not released back into waterways.

At the reclamation facility, “activated” sludge consumes pollution in the water. What makes it activated? Bacteria. In this stage of the wastewater process, the water moves through six basins, where the bacteria removes ammonia-nitrogen, nitrate-nitrogen, and phosphate. The WRA helps the bacteria live by aerating the wastewater with oxygen.

After that, water flows to a clarifier, where solids can settle. Some of those solids then move onto anaerobic digestion.

In the anaerobic digestion step, two products are made: biogas which can be used as natural and renewable energy, and sludge which can be used as fertilizer for crops after further treatment.

You can take a virtual tour of the WRA facility here.