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Technology Removing ions from solution as it is done with electrodialysis can be a much easier way to desalinate water versus the standard reverse osmosis or brine concentrator method. of clean water can be as high as 95 percent. This is extremely beneficial in industries such as oil and gas that have wastewater disposal volume concerns. By using capacitors to capture the ions instead of another flow channel, the device construction costs and energy usage are much lower. And because the flux rates (moles/min/cm2 membrane) are significantly higher, a given device can process a much higher inlet of total dissolved solids (TDS). The latest system designs for 8,000 to 10,000 ppm applications have capital costs less than 1/3 that of ED. The cost of ownership (energy, maintenance, depreciation, and disposal) is up to 70 percent less than the leading state-of-the-art technology for that particular TDS range. The latest CDI devices can process up to and greater than 150,000 ppm of water including water with over 50,000 ppm of hardness and low solubility species such as barium(Ba)/strontium(Sr)/calcium(Ca) sulfates and calcium carbonates. Because any dissolved ions can be removed, it is also effective at removing low concentrations of heavy metals such as mercury, arsenic, selenium, uranium, etc. Because of the ability to process complicated high TDS waters, CDI is making inroads into industries with very difficult, highly saline waters such as oil/gas produced water, frack water, mining wastewater, flue gas desulfurization (FGD)/cooling tower blowdown, and other industrial wastewaters. This is very helpful when treating water for discharge with stringent limits such as power and greenhouse industries. In some cases, the concentrated solution is the desired product. CDI can concentrate a solution to recover high-value metals, salts, acids, and bases. The system basis is the grouping together of large supercapacitors, similar to how RO tubes are organized. This positions CDI to be able to build high-capacity systems simply by duplicating the supercapacitors. Pretreatment is very important for any membrane process, including CDI. The requirements for total suspended solids (TSS), organics, and iron are very similar to RO and ED due to the very thin flow channels and fouling nature of organics and ferric iron. But because of CDI's ability to capture and remove low solubility salts safely, no antiscaling chemicals are needed. The origin of most current CDI devices is from a DARPA project from the DoD back in 2000-2004 to develop an alternative to desalination systems used to supply troops with fresh water. CDI is another example of a technology that was developed for one purpose, but found other market segments where its advantages were greater than expected. As system design and material properties continue to improve, the economics and performance capabilities of the CDI system will continue to improve and likely surpass all existing technologies in performance. These systems are starting to penetrate various markets and will continue to make inroads over the next decade. Patrick Curran, CEO and founder of Atlantis Technologies, has led the development and commercialization of many novel processes and products over his 25-year career, garnering seven issued and pending patents. He has a B.S. in chemical engineering from Drexel University. 30 wateronline.com ■ Water Online The Magazine