Community Chooses EDR Technology for Drinking Water Treatment

EDR (electrodialysis reversal) has been a technological mainstay in the desalination industry for over 30 years. In the spring of 2002, officials from Fairfield, IA — a growing community in the southeastern portion of the state — decided to upgrade their existing lime softening plant with an Ionics EDR 2020® system.

The Ionics EDR 2020® system installed at Fairfield, IA, produces 1.95 mgd of drinking water.

"EDR is a much better process for removing [minerals] than lime softening," said Dennis Langstraat, General Superintendent for Fairfield Water Works. "The combination of lime softening and EDR works out very well and produces a nicely blended product."

Fairfield is known for its strong economic base that includes over a dozen manufacturing plants (from washing machine factories to hay-handling equipment), several software developing companies and two of the largest telecommunication firms in the United States. With such a solid economic base combined with an increasing college community, the population is growing and currently stands at approximately 10,000 people.

With the growth in population, a great amount of pressure has been placed on the maintenance and improvement of community services, which includes public drinking water. Until June 1999, approximately 75% of Fairfield's water came from three area lakes, while the remaining 25% was obtained from the Jordan aquifer, a 2,200-foot-deep, water-bearing sandstone formation that lies under much of eastern Iowa. All of these water sources were treated with a lime softening procedure to remove hardness, turbidity, iron and color.

Over the years, the surface water of the area lakes began to create several significant problems for the city of Fairfield, which resulted in complaints based on the water quality, color, odor and taste. These problems — coupled with increasingly strict state and federal surface-water regulations — forced the city to review its current water technologies, as well as proposals for various technological enhancements.

The Fairfield, IA, drinking water treatment plant serves a community of approximately 10,000 people.

The increase in population also contributed to problems associated with the city's surface-water supply. The rising number of families and businesses relocating to the community led to an increase in the amount of chemicals (such as lawn fertilizers) being used, which caused the city to provide stronger water treatment applications to neutralize any additional problems associated with water quality.

With increased chemical demand loads, "we knew we needed another water supply," Langstraat said.

After conducting thorough research and reviewing various water treatment options, city officials determined that by adapting and repositioning their current technologies, they could draw more heavily from the Jordan aquifer. The aquifer would be a more stable source of water year-round and would be less susceptible to impurities than surface water from the area lakes.

In June 1999, Fairfield stopped using water from the lakes and began depending fully upon the Jordan aquifer as the community's primary drinking water source. After a few years, however, city officials still found evidence that the existing lime softening plant was not effective on its own as their primary water-treatment method.

EDR System

Enter Ionics in the spring of 2002 with its EDR 2020® system. Electrodialysis (ED) employs a driving force of direct current (DC) voltage to transfer ionic species from the feedwater through cation (positively charged ions) and anion (negatively charged ions) transfer membranes to a concentrate stream, creating a more dilute stream.

EDR is a variation on the electrodialysis process that uses electrode polarity reversal to automatically clean membrane surfaces. In the reversal process, the polarity of the DC voltage is reversed two to four times per hour. When the polarity is reversed, the dilute and concentrate compartments are also reversed. The alternating exposure of membrane surfaces to the dilute and concentrate streams provides a self-cleaning capability that enables purification and recovery of up to 85% of the feedwater.

Ionics' EDR technology had been operating on the Jordan aquifer and serving neighboring communities for last 10 years, and its performance was a key factor in its selection as the technology for Fairfield, according to community officials. City officials purchased the EDR system for approximately $3 million and construction of the new plant began in the spring of 2002.

Officials selected a masonry building, rather than metal, to house the new system.

"Our old existing lime softening plant is constructed of steel, and there is a lot of humidity which causes rust and increases maintenance costs," Langstraat said.

Although it is slightly more expensive upfront, Fairfield's engineers estimated a higher return on investment with the masonry housing selection. There was also an aesthetic consideration, said Langstraat, as "in 20 to 30 years the brick will still look very nice."

The Ionics system used in Fairfield incorporates major improvements to prior generation EDR systems in that it is a lower-cost system with a more flexible design and layout. The new design streamlines the process flow with simpler hydraulics and standardized components. It also has new high-performance spaces that enhance demineralization, increasing salt removal per stage and lowering DC power consumption, substantially lowering the capital and operating costs of EDR demineralization process.

Completed in the spring of 2003, the new system has been instrumental in significantly increasing both water quality and capacity. An input of 2.29 mgd of raw water has resulted in 1.95 mgd of drinking water. The EDR product water is blended with an additional 2.05 mgd to produce up to 4 mgd of drinking water containing less than 750 ppm of total dissolved solids — well below established limits.

The plant operates 24 hours a day, with a representative on staff each day from 6 a.m. to 5 p.m. Monitoring equipment was installed to provide alarm capability, alerting staff immediately if the EDR system were to malfunction in any way.

"Most problems have been very minor," said Langstraat.