Iowa's first electrodialysis reversal water treatment plant

Abstract

In 1979 the City of Washington was notified by the Iowa Department of Natural Resources (IDNR) that the City was in violation of the radium standard for drinking water. The City of Washington authorized an engineering study to determine the most cost-effective and practical way to remove radium and, at the same time, improve overall water quality. Several possible treatment alternatives were evaluated. It was finally decided to utilize electrodialysis reversal (EDR). Washington obtains its water from three deep wells ranging in capacity from 600–780 gpm. The untreated water withdrawn from the wells first passes through the EDR units. There are three EDR units, each able to produce 285 gpm of finished water. In the future, another EDR unit can be easily added to the other three units, since the new plant was built and plumbed for an additional EDR unit if water demand increased. The Jordan aquifer supply is adequate for current and future needs. The average daily water usage in 1993 was 818,000 gal/d. In order to meet peak flows, it is possible to bypass the EDR units with part of the untreated water and then blend treated and untreated water. The treated water meets IDNR standards of 5.0 pC/L. After the EDR units, the water flows through an aerator where odor-causing gases and carbon dioxide are removed. Aeration reduces the amount of caustic soda and chlorine used in the finished water. The hydrogen sulfide gas leaves the water as it passes through the aerator, and this loss of gas creates less chlorine demand. Total and free chlorine residuals are now detected in every water main of the town, whereas before, the residuals would not be detected in certain area of Washington. Phosphates have been cut back from 7 pounds per day to one pound per day. Better water quality is now being achieved with fewer chemicals added to the finished water. Washington's water treatment plant is the first municipal EDR plant in the State of Iowa and one of the largest municipal installations in the United States.