Current and impending regulations, such as the Stage 2 Disinfectant / Disinfection Byproduct Rule and the Long Term Enhanced Surface Water Treatment Rule, require reduction in the formation of disinfection byproducts and have generated growing interest in the use of UV disinfection. UV disinfection is the process of using ultraviolet light to alter cellular molecular components essential to cell function. Altering the cell function inactivates the pathogen, which prevents the cell replication (and infection). EPA has expressed its belief that UV disinfection is an “available and feasible” technology (Maggi et al., 2001).

UV disinfection has been used to treat water and wastewater for many years. As of 1996, Europe had over 2,000 UV disinfection systems to treat drinking water (USEPA, 2003). The first UV disinfection system was used in Marseille, France, in 1910. The first UV system in the United States was built in 1916 in Henderson, Kentucky. The current interest in UV disinfection started in 1998 when it was found that UV disinfection is effective in inactivation of Cryptosporidium and Giardia at economically feasible doses. Prior to 1998, it was believed that very high doses of UV were required to disinfect protozoa. The high dose requirements were based on in vitro viability assays which were found to greatly “overestimate the UV doses required to prevent infection” (Clancy et al., 1998; Bukhari et al., 1999; Craik et al., 2000). Results using in vivo assays (e.g., mouse infectivity) and “cell culture techniques to directly measure infectivity” has shown Cryptosporidium and Giardia can be inactivated at much lower doses which are economically feasible.

UV disinfection has several benefits for small public utilities. In addition to inactivating Cryptosporidium and Giardia, there is little or no formation of known disinfection byproducts (DPBs). In addition, the cost is less compared to other methods of disinfection. UV disinfection systems can be installed and retrofitted into existing facilities.

Studies, research, and USEPA guidance relating to UV disinfection are continuing to help the water industry understand the UV process as well as develop new equipment and guidelines to assist implementation of UV disinfection into water treatment plants. In the development of this educational module many of these studies were reviewed.

Studies by Passantino (2001), Linden (2002), and Christensen (2002) evaluated water quality impacts on MS2 Dose-Response Curves and the UV disinfection process by suspended particles, algal content, and turbidity. Craik (2001), Mofidi (2001) and others researched the use of UV radiation to inactivate Cryptosporidium.

As more utilities consider the addition of UV disinfection to their water treatment plant, manuals and guidelines have been written and continue to be written. These include the NWRI (2000) UV Disinfection Guidelines for Drinking Water and Reuse, Ultraviolet Light in Water and Wastewater Sanitation by Masschelein (2002), as well as the recently released USEPA draft Ultraviolet Disinfection Guidance Manual (2003). Maggi (2001), Wright (2001, 2002), Duke (2002), Brauer (2002), and Kolch (2002), have done research and studies that range from the design considerations for UV systems, the validation and certification process, to dose delivery monitoring. Hilmoe (2002), Hebberd (2002), Swaim (2002) and others are providing information on the decision-making process and steps involved in adding a UV system to aid other facilities that are considering UV disinfection as a disinfectant alternative.

This module is intended to be an educational tool in the use of ultraviolet disinfection of drinking water for small water systems.

Calgon Carbon patents for Cryptosporidium and Giardia inactivation

Calgon Carbon Corporation has been granted two patents for the use of ultraviolet light for Cryptosporidium and Giardia treatment. Details of the two patents can be found by clicking this link for details of the patents. Essentially, Calgon Carbon claims a patent on using low pressure and medium pressure lamps to prevent infection by Cryptosporidium oocysts and to prevent replication of Cryptosporidium oocysts or Giardia cysts in drinking water treatment. It was well known before the ‘invention’ that high dosages of UV would kill Cryptosporidium and Giardia but Calgon Carbon claims that its research discovered that it is not necessary to kill these microorganisms. Rather, its patents claim the discovery or invention that lower, economical UV doses will disrupt the cellular machinery of the microorganisms and thus prevent their replication and infection. Calgon has also been granted patents in Canada and the Netherlands (www.uswaternews.com/archives/arcquality/2calcar4.html). Calgon Carbon is licensing its patented technology to utilities at a rate of $0.01 to $0.02/1000 gallons treated (http://www.mwhglobal.com/reg_analysis/reg_analysis_217.asp).