Nitrate Removal Facility
Location: Des Moines Water Works, Ames, IA
Featuring: Mike and Bill
Nitrate concentrations in the Raccoon and Des Moines Rivers present Des Moines Water Works with their biggest water quality problem. When nitrate exceeds the Environmental Protection Agency’s (EPA) maximum contaminant level (MCL) of 10 milligrams per liter (mg/L), water must be purified using a nitrate removal facility. which cost over $4 million to build. In 2015 alone, their plant had to operate for 177 days to bring DMWW into compliance with federal statutes defined by the Safe Drinking Water Act.
As nitrate-laden water passes through removal vessels filled with a sodium chloride-coated resin material is in each removal vessel, nitrate ions are captured and chloride ions are released into the water in a process known as ion exchange. This process is similar to a home water softener that removes calcium and magnesium ions from the water, exchanging them for sodium ions.
When the resin in these removal vessels is exhausted, it is regenerated with sodium chloride brine. Nitrate on the resin is exchanged for chloride, a reversal of the removal process. The spent brine containing the collected nitrate is diluted with partly-treated water and discharged back into the Raccoon River. DMWW has two National Pollutant Discharge Elimination System (NPDES) permits allowing for this nitrate discharge.