It is now almost five years since UV disinfection technology from Aquionics was selected to provide Cryptosporidium-free drinking water for the City of Henderson in Nevada. Henderson, the second largest city in Nevada, decided to upgrade and modernize its water treatment system in 2001 to enhance water quality and meet increasing demand. It was the first surface water plant in the USA to be specifically designed for Cryptosporidium inactivation with approval from the State and the USEPA.
“We were very proud to be the first plant in the USA to utilize this technology for Cryptosporidium inactivation,” says Mike Morine, Manager of Technical Services. “We take our commitment to the health and safety of our residents very seriously and we implemented this project to provide the best possible disinfection for our community. We saw UV as a cost-effective way of achieving this and since its installation almost seven years ago the Aquionics plant has helped us to exceed the USEPA’s water quality regulations. It has certainly exceeded our expectations.”
Treating 15 million gallons per day (mgd), the UV disinfection plant consists of four medium pressure UV chambers, each with an independently validated capacity of 5 mgd. Three chambers are in constant use, with the fourth on standby. The plant is completely automated with UV dose control, fail-safe features and reliable automatic cleaning for ease of maintenance. The water, which originates from Lake Mead, is coagulated with ferric chloride then flocculated and filtered before passing through the UV chambers prior to distribution. The Aquionics system provides at least 99 percent inactivation of Cryptosporidium oocysts, the infective stage of the organism which is resistant to chlorine.
Cryptosporidium is a single-celled parasite that invades the human digestive and respiratory systems, causing cryptosporidiosis. While the disease is often asymptomatic, intestinal cryptosporidiosis can cause severe diarrhea lasting two to four days in adults or up to four weeks in children.
UV disinfection is among only a few proven methods for rendering Cryptosporidium harmless, and it does so without the use of chemicals. UV light has been used successfully for disinfection of industrial process water and municipal effluent worldwide and for drinking water treatment for many years. Recent research documenting the effectiveness of UV disinfection against Cryptosporidium oocysts and Giardia cysts has made the technique a powerful and cost-effective alternative to ozone disinfection and other methods for water treatment.