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Water Technologies & Solutions fact sheet

many municipalities tap into benefits of EDR water treatment

Figure 1: EDR Water Treatment System

No one wants to drink radium. Or nitrates. Or arsenic. Or perchlorate. But, if not for some technologically advanced methods of removing these contaminants, methods like electrodialysis reversal (EDR), we all might be sipping on some very unhealthy water. (Figure 1)

Just ask the citizens of Washington, Iowa. In 1979, Washington was notified by the Iowa Department of Natural Resources that the city was in violation of the radium standard for drinking water. Even then, radium was recognized as a dangerous carcinogen. Washington evaluated a number of options for improving the water quality and removing the radium from the water. They decided on implementing the process known as EDR, a relatively new variation on the electrodialysis process which had been commercialized by SUEZ in the 1950s. Thanks to that technology, the city has literally seen its way clear to having no water quality problems. Other mid-western sites are now using EDR systems as large as 6.2 mgd to treat for radium and hardness reduction at water recoveries up to 85%.

Today, there are many other examples of cities, towns and municipal organizations that have found EDR demineralization to be an economical, high

performance way to transform non-potable water into high-quality, safe drinking water.

a self-cleaning process

The electrodialysis process uses a driving force of direct current (DC) power to transfer ionic species from the source water feed water through cation (positively charged ions) and anion (negatively charged ions) transfer membranes to a concentrate wastewater stream, creating a more dilute stream. EDR is a variation on the electrodialysis process, in that it uses electrode polarity reversal to automatically clean membrane surfaces. EDR works the same way as electrodialysis, except that the polarity of the DC power is reversed two to four times per hour. When the polarity is reversed, the source water dilute and concentrate compartments are also reversed. The alternating exposure of membrane surfaces to the product dilute and brine concentrate streams provides a self-cleaning capability that enables purification and recovery of up to 94% of source water the feed water.

There are currently a number of alternatives to the EDR technology for treating and reducing contaminants in drinking water. Probably the most well known of these is reverse osmosis (RO). Both EDR and reverse osmosis use semi-permeable membranes to filter out dissolved ions from water. But where RO uses the application of pressure to overtake osmotic pressure and force water through the membrane, EDR uses voltage potential and polarity reversal to remove unwanted constituents by pulling them through the membranes.

The RO process, itself, often has a capital cost advantage over EDR, but can require extensive pretreatment, higher pumping power, more chemicals, and more frequent membrane replacement. RO also has a lower water recovery rate if the water has positive scaling tendencies or higher silica. Depending on the project specifics, the overall economic advantage can fall on the side of EDR.

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an evolving technology

Over the last ten to fifteen years, numerous advances in membrane and system technology have made EDR an especially attractive technology, both in terms of performance and cost-effectiveness. Improved membrane technology now allows for one-step machine manufacture of ion exchange membranes, reducing costs and lowering membrane resistivity. And new high performance spacers (placed between the membranes) allow over 90% to 95% transport of contaminants like nitrates, arsenic and perchlorate speeding the process, reducing the number of membrane stacks required and shrinking costs.

Major improvements to EDR system design have taken shape in the form of the next generation SUEZ EDR 2020 product line. This new design streamlines the process flow with simpler hydraulics and standardized components, substantially lowering the capital and operating costs of EDR demineralization. It features the new spacer technology, as well as a more compact design that’s easy to install in a variety of configurations.

a clearly popular choice

With this new design and field-tested track record of success, the growing popularity of the next generation EDR systems among municipalities comes as no surprise. Recent examples of municipalities and organizations turning to SUEZ’s new EDR technology abound.

In recent years, completely new EDR installations have taken place around the world for a variety of applications. At the Ruth Fisher School in Arizona, an EDR system was installed with the objective to remove inorganic components from groundwater and reduce nitrates to meet US EPA drinking water standards. The nitrate concentration in the feed is over 130 mg/l, but the EDR system produces water with extremely low total dissolved solids and nitrate concentrations.

At the Bermuda Water Works, EDR is used to reduce hardness in the island’s existing water supply. The brackish water lens under the island is contaminated from septic tank leach fields, making nitrate removal essential. The 600,000 gpd plant removes 86% of the nitrates, while achieving 90% water recovery.

And in Kazusa Town, Japan, concerns were high about nitrate levels as high as 80 mg/l in the water supply. A SUEZ EDR system works to reduce the nitrates to less than 27 mg/l in order to provide safe, great tasting drinking water to the city.

Today there are numerous plans in the works to install new EDR systems to address a wide range of water treatment needs. SUEZ has been awarded a job in Lajitas,

Texas in which their new EDR technology is being used to remove contaminants like arsenic, iron and radionuclides from a well water hot spring.

After years of proven performance in Washington, IA, other Iowa municipalities have installed EDR, with ever larger capacities to treat groundwater for radium, hardness and salinity reduction. Mt. Pleasant, Iowa, installed 2.5 mgd worth of EDR in 1997. Following the old adage that success breeds success, Fairfield, Iowa, built an EDR plant in 2002 to desalt high sulfate and hardness groundwater which is then blended with existing lime softened water for up to 4.0 mgd of product water.

A 2002 installation near Albuquerque, New Mexico is using EDR with a very deep well water source that has limited flow capacity. This EDR installation is removing salinity, arsenic, iron and manganese for the supply of drinking water. With EDR, 92% water recovery is achieved. In fact, EDR was selected for this application since RO could not operate from an efficient recovery standpoint with the anticipated level of silica and other membrane scale-forming components in the raw water supply.

In actual field operations at other sites, EDR is now showing over 90% reduction of arsenic and perchlorate in well water supplies, delivering product waters down to less than 1 ppb of As and ClO4 without any special chemical pretreatment.

a healthy package

As EDR technology evolves and improves and efficiencies increase, one thing is becoming increasingly clear: EDR has a very bright future. EDR systems are now simpler and more reliable than ever, which means that the demineralization of difficult-to-treat water is easier for municipalities to handle. And the costs, initial and long-term, are easier to swallow as well.