Credit: Photo: Stanley Consultants
Workers position one of the 96 EDR membrane units installed at the Mason City water plant. The EDR process uses an electric current to separate dissolved minerals, including radium, from the water.
In 2000. Mason City, Iowa, began planning an upgrade of its water treatment system in order to meet the regulations established by the U.S. Environmental Protection Agency's Final Radionuclide Rule. Until the new standard became effective on Dec. 8, 2003, the city's treatment for drinking water had consisted of aeration, chlorination, and fluoridation. In order to lower the concentration of radium in their raw water to meet the levels set by the new regulation, Mason City replaced this system as part of an $18 million water project.
The city chose to hire Stanley Consultants, an AEC firm in Muscatine, Iowa, to provide the engineering services for design and construction of the project. In addition, Stanley provided guidance in acquiring funding for the project.
“Stanley Consultants acts as the ‘coach,' training, showing, and participating as clients work with their appropriate representatives and senators,” said Herb Ohrt, senior vice president for Stanley. “To date this process has generated a total of $6.75 million of federal grants for Mason City.”
This project, completed in June 2004, included a new central water treatment plant, new raw and treated water mains, a new booster pump station, and well rehabilitation. In designing the treatment method for the new plant, several options were considered. “Lime softening and reverse osmosis was determined to be too expensive,” said Chip Hendrickson, water operator for Mason City. “Also, with lime softening you have the problem of what to do with the sludge.”
In the end, Ohrt said, “One central water treatment plant using the electrodialysis reversal (EDR) treatment process was recommended by Stanley Consultants and approved by Mason City.” This process is supplied by Ionics Inc.—based in Watertown, Mass.—and involves the use of voltage potential and polarity reversal to remove unwanted constituents by pulling them through membranes.
Transitioning from a simple treatment system to a more complicated one can be challenging. “Stanley Consultants prepared a construction sequencing plan, which allowed the existing water treatment process to continue to operate while the new treatment processes were constructed,” said Ohrt. “The old treatment processes were removed or converted when able, to allow the new process to come on line to provide city water supply.”
The city is now working to learn the new system and is fine-tuning it to improve operations. One unexpected result has been the “dropping out” of calcium carbonate in the EDR units. “If pH builds up, we find that within a couple of days the pressure through the system gets too high,” said Hendrickson. “Then we perform clean-in-place maintenance by running water and acid through the system and allowing the solution to sit over night to break down the calcium carbonate.”
To neutralize the pH in the EDR units, an anti-scalant system, using a weak acid, will be installed. “Once the anti-scalant system goes in, we will only have to perform cleaning once a month,” said Hendrickson.
The new system has softened the water, allowing citizens and business to abandon their individual softening systems. “The economic benefits of the water softening have been significant for large water users that maintained their own water treatment plants,” said Ohrt. “Local industries have seen a reduction in their costs to treat water for boilers and chillers. This is a significant savings for existing industry and an incentive for companies considering a move to Mason City.”