By Michael Cochran

Summary: Previously regulated to very specific needs in water treatment, chlorine dioxide is expanding its wings within the industry. Unique technology, discussed here, is enabling the use of chlorine dioxide in new applications that call for prevention of microbial growth such as slimes and molds.


One set of new water treatment products on the market thisyear features chlorine dioxide in applications where the powerful disinfecting agent hasn’t been used before.

Chlorine dioxide has been used for many years as a bleaching agent and slimicide in the pulp and paper industry, as a disinfectant in municipal water treatment, and in many other industrial water-treatment operations. Significant capital and operating costs, however, have limited use of chlorine dioxide to large-scale applications. New technology now makes it practical to use the disinfecting agent in a wider range of water treatment applications.

Significant capital and operating costs, however, have limited use of chlorine dioxide to large-scale applications. For most applications, chlorine dioxide must be produced and used at the same location to realize its full potency. As a result, on-site chemical or electrochemical generation using complex and expensive equipment has been the only practical way to deliver this compound in its most effective form.

Investment in generating systems and precursor chemicals can be significant. Financial and time investments must also be made to train employees to operate the systems. Also, strict hazardous materials handling procedures may be required. Obviously, this approach is impractical for small-scale water treatment applications.

New technology now makes it practical to use the disinfecting agent in a wider range of water treatment applications by delivering chlorine dioxide in a safe, stable, easy-to-use powder. The powder features a controlled sustained-release mechanism that allows precise control of the concentration, strength and rate of release of chlorine dioxide.

Why chlorine dioxide?
Although the Cl2 and ClO2 share the name “chlorine,” their chemistries are very different. Unlike chlorine, chlorine dioxide doesn’t chlorinate. It works through oxidation and penetrates bacteria cell walls and reacts with vital amino acids in the cytoplasm of the cell to kill the organism.

Chlorine dioxide has up to 2.6 times the oxidizing power and 7 times the biocidal efficacy of chlorine. The only by-product of chlorine dioxide use is chlorite, which rapidly breaks down to form chloride—one of the chemicals in common table salt.

 Chlorine dioxide has been called the “ideal” biocide for a number of reasons:

  • It works against a wide variety of bacteria, yeasts, viruses, fungi, protozoa, spores, molds, mildews and other microbes. It’s especially effective in killing Giardia and Cryprosporidium.
  • It exhibits rapid kill of target organisms, often in seconds.
  • It’s effective at low concentrations and over a wide pH range.
  • It biodegrades in the environment.
  • Unlike chlorine, it doesn’t react with primary organics to form harmful trihalomethanes (THMs).

New technology applications
This new delivery technology can bring the power of chlorine dioxide to many other new applications without the expense and complication of on-site generation or high levels of training. The technology is offered in powders and tablets. The powders and tablets are contain activators that combine with chlorite salt contained in the powders to generate chlorine dioxide.

The powders produce chlorine dioxide only when they come into contact with water or when they are exposed to moisture in ambient air. Water or moisture provides the reaction bridge between the chlorite salt and the activator, allowing the generation of chlorine dioxide to proceed. When sealed in airtight containers, the powders can be stored and used when needed.

This technology can be custom formulated to deliver different levels of chlorine dioxide and release the biocide at specific rates. Tablets and sachets for use in solutions can be designed to begin releasing chlorine dioxide in as little as 10 seconds after being combined with water while continuing to release the biocide for up to four hours. A wider range of controlled-release parameters is available for dry applications.

These products will release chlorine dioxide independent of solution pH and volume. After the biocide is activated, the material safely reduces into common salts. For solution applications, the product is available in dissolvable tablets and sachets. Both product forms are USEPA-registered antimicrobials for hard surfaces, water surfaces, and recycle water for car washes and cooling towers.

Deodorizing and disinfecting
Chlorine dioxide technology is being incorporated into a number of new products for the water treatment market. The following are some examples:

  • Alamo Water Refiners’ tablets are designed to eliminate fouling microorganisms in home water softeners. The tablets generate chlorine dioxide when placed in contact with water and eliminate microbial buildup in resin beds. The chlorine dioxide generated by this tablet has 2.6 times the oxidizing power of chlorine without producing chlorine by-products such as THMs and haloacetic acids. The tabs also leave no chlorine residue in the softener and don’t attack the resin bed. Alamo is offering two versions—tablets for home use by consumers as well as use by Alamo dealers as part of regular softener treatment.
  • Ecolab Inc.’s new Ice Sentry™ sachet controls the formation of slime and odor-causing bacteria and fungi that are often associated with ice machines. It can be used to safely and effectively eliminate bacteria in hotel, restaurant, and food store ice machines. The sachet is hung inside the ice chamber of the icemaker where it inhibits the formation of bacteria and fungi.

Other exciting new applications for the technology in water treatment include treating bacteria in car-wash recycle water and cooling tower water. Additionally, Bio-Lab Inc.’s new SoftSwim Assist®, sold under the BioGuard® brand, offers consumers a way to eliminate white water mold and pink slime in their swimming pool plumbing. This technology enables pool owners to use Bio-Lab’s non-chlorinated products to keep their pools algae-free.

Interestingly, under an emergency exemption from the U.S. Environmental Protection Agency (USEPA), chlorine dioxide can also be used by government agencies to treat structures and property that may be contaminated with anthrax (see FIFRA, Section 18).

Conclusion
This new chlorine dioxide technology is one of the first commercial technologies to offer long-term or residual control of microbial contamination, such as unwanted slime and molds. For example, the ice-machine product will control slime in ice machines for up to 30 days. Other products are in development and additional regulatory approvals are being sought for emergency drinking water use. The commercial applications for this new method of delivering chlorine dioxide promise to be many and varied.

About the author
Michael Cochran is the business development manager for the Aseptrol technology at Iselin, N.J.-based Engelhard Corp., a surface and materials science company that develops technologies to improve customers’ products and processes. He can be reached at (732) 205-7082, (732) 205-6901 (fax) or email: michael.cochran@engelhard.com

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