On the Contrary

Nov. 14, 2003
UV-based technology combats waterborne pathogens in drinking water

About the author: Keith Bircher is principal engineer for Calgon Carbon Corp., and Walter Tramposch, Ph.D., is business development manager for UV Systems for Calgon Carbon Corp. For more information visit www.calgoncarbon.com or call 412/787-6700.


Since 1993, increased and more stringent water treatment rules by the U.S. EPA have intensified the need for a comprehensive, cost-effective solution to treat Cryptosporidium, Giardia and other waterborne pathogens in drinking water.

The solution was not chlorine, as it did not have an effect on Cryptosporidium unless applied in such toxic levels that it became dangerous to humans. Furthermore, independent research and testing sponsored by the water treatment industry confirmed that ultraviolet (UV) radiation was ineffective for fighting Cryptosporidium except in extremely high doses, making UV treatment economically unfeasible.

In 1996, the Calgon Carbon Corp. took a different approach and tested a new theory that showed Cryptosporidium and other parasites, including Giardia, could be effectively treated using low dosages of UV.

In the course of finding a solution for treating Cryptosporidium, the testing and research showed that at low doses, UV would inactivate Cryptosporidium and other similar parasites by preventing them from replicating and causing infection. This was a major research achievement because UV's effectiveness within this treatment range had not been previously demonstrated.

In fact all previous research, including that published after Calgon Carbon's announcement, taught a conclusion contrary to that of the company's approach.

Prior to announcing the results of the research, Calgon Carbon filed for a patent covering the inactivation of Cryptosporidium and similar parasites at UV doses between 10 mJ/cm2 and 175 mJ/cm2. This patent was granted to the company in October 2000.

The scope of the patent essentially covers all usage of UV technology in water treatment for the inactivation of Cryptosporidium and similar parasites.

In March 2002, the Canadian government also issued the company a Notice of Patent Allowance. In early 2003, Calgon Carbon was granted patents covering its inactivation treatment process in New Zealand and the Netherlands. Finally, in May 2003, the company was granted its second U.S. patent for preventing infection from Cryptosporidium and Giardia at UV doses of 1-175 mJ/cm2.

UV reactor validation

With the third-party testing and EPA's verification of Calgon Carbon's breakthrough inactivation method complete, the company's research efforts became focused on UV reactor validation to ensure water plant operators of continuously effective levels of UV radiation.

Working with Carollo Engineers, Calgon Carbon assisted in funding the first U.S. based UV validation facility in Portland, Ore. Within months of completing the testing facility, validation testing was conducted on the company's 48-in. Sentinel UV Disinfection System at flow rates of up to 40 million gallons of water per day (mgd), making this the largest UV validation test ever conducted.

Prior to validating the Sentinel reactor, the largest validated flow rate in the water industry was 18 mgd.

The Sentinel 48-in. UV Disinfection System was the first UV reactor to be in compliance with the U.S. EPA's Microbial-Disinfectants and Disinfection Byproducts Rules for the treatment of Cryptosporidium, Giardia and other viruses in drinking water under the Long-Term 2 Enhanced Surface Drinking Water Treatment Rule. 

This large-scale validation process was a significant advancement for the water treatment industry. For the 48-in. Sentinel to be validated at 40 mgd was unprecedented, and such a system could offer cost savings to municipalities and provide them with safe, high-quality drinking water.

Having complete control

Prior to Calgon Carbon's discovery, application of UV for disinfection of drinking water, including complete control of bacteria, viruses, and protozoa, was not considered an economically viable technology.

Many municipalities were considering expensive filtration and ozone technologies that would have cost substantially more than the Sentinel UV technology.

Since then, the water industry has been able to take advantage of UV designs providing for more efficient and affordable multiple-barrier systems.

The final information required by state regulators to grant disinfection credits for UV technologies is operational data. Calgon Carbon has developed detailed guidelines and CDF modeling for design engineering issues. Control and command features, system maintenance, and operator training are based on the company's experience with over 250 UV installations treating municipal wastewater, contaminated groundwater, industrial wastewater and drinking water. 

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