Highlighting UV's Growing Legal Impact

Ultraviolet disinfection's new role in future U.S. drinking water regulations

Ultraviolet (UV) irradiation is a proven disinfection technology that has been used for almost a century. The technology is used to disinfect drinking water (municipal and consumer), wastewater (discharge and water reuse), indoor air, swimming pools, and industrial effluents from the food and beverage industries, cooling towers, fish hatcheries, ballast water, semiconductor fabricators, and pharmaceutical manufacturers.

UV was first used for municipal drinking water in 1906, in Marseille, France. However, due to poor equipment reliability and the prevalence of chlorine disinfection, its use remained anecdotal for decades. The technology's effectiveness and dependability improved in the late 1970s. Coupled with the discovery that chlorine disinfection may form harmful disinfection byproducts (DBPs), such as trihalomethanes (THMs), UV's use became more widespread for groundwater applications in Europe. In 1987, UV made its American municipal debut at Ft. Benson, Mont.'s, water treatment plant. By the mid-1990s, UV was used in several hundred public water supplies in Europe, whereas its primary use in North America remained for Point-Of-Use (POU)/Point-Of-Entry (POE) systems, with the exception of a few municipal groundwater systems.

Today, the use of UV in drinking water disinfection is seeing unprecedented interest as the global water industry faces a major dilemma: how to address the risky trade-off between microbial disinfection and the byproducts formed by commonly used disinfectants.

U.S. Regulatory Drivers
The U.S. Environmental Protection Agency (EPA) is currently developing a set of regulations that is expected to drastically alter water treatment practices. These regulations include the Stage 2 Microbials/Disinfection Byproducts (M/DBP) cluster of rules1 and the Groundwater Rule (GWR) 2.

The Stage 2 Microbials/Disinfection Byproducts (M/DBP) cluster of rules includes the Long-Term Two Enhanced Surface Water Treatment Rule (LT2ESWTR) 3 and the Stage 2 Disinfection Byproducts Rule (Stage 2 DBPR) 4. These rules build on the Interim Enhanced Surface Water Treatment Rule (IESWTR) 5 and the Stage 1 Disinfectant/Disinfection Byproducts (D-DBP) Rule6, which resulted in conflicting demands between higher requirements for disinfection and stricter limits on chemical DBPs7.

To date, EPA does not require groundwater systems to provide disinfection unless they are under the direct influence of surface water. The Groundwater Rule was developed to meet a requirement of the 1996 amendments to the Safe Drinking Water Act that require disinfection of groundwater systems "as necessary" to protect the public health.

The Long-Term Two Enhanced Surface Water Treatment Rule.

The LT2ESWTR applies to all public water systems that use surface water or groundwater under the influence of surface water (GWUI). The rule builds on the SWTR, IESWTR, and the LT1ESWTR by improving control of microbial pathogens, specifically Cryptosporidium. The rule bases treatment requirements on a system's source water Cryptosporidium concentration and type of treatment provided.

LT2ESWTR for Filtered Systems

All water systems using surface water or GWUI must monitor raw water for Cryptosporidium. Monitoring results may necessitate additional treatment and/or follow-up actions. EPA estimates the rule will affect more than 3,000 public water systems.

Under the LT2ESWTR, filtered systems will need to treat raw water to an additional 0-log to 2.5-log reduction for Cryptosporidium, based on risk bin assignment (4 bins). Filtered systems must also initially monitor source water for two years unless they provide treatment equaling 2.5-log inactivation, in addition to conventional treatment.

LT2ESWTR for Unfiltered Systems

Unfiltered systems will need to achieve 2-log or 3-log Cryptosporidium inactivation, depending on the source water concentration of Cryptosporidium. A minimum of two disinfectants must be used to fulfill the overall disinfection requirements of unfiltered systems.

The Stage 2 Disinfection Byproducts Rule.

The Stage 2 DBPR applies to all community water systems -- both ground- and surface water systems -- that add a disinfectant other than UV light. The rule requires systems to conduct a year-long initial distribution system evaluation (IDSE) to identify distribution system locations with high DBP levels. The rule no longer allows annual system averaging of total trihalomethanes (TTHM) and five haloacetic acids (HAA5). Rather, systems must comply with TTHM/HAA5 Maximum Contaminant Levels (MCLs) of 80/60 parts per billion (ppb) based on locational running annual averages (LRAA).

The regulations were initially proposed in 2003 and are expected to be promulgated by the end of 2005. The compliance deadline is six years after the promulgation of LT2ESWTR for systems serving 10,000 people or more and 8.5 years for systems serving fewer than 10,000 people. Numerous tasks will need to be performed within this timeframe, including Cryptosporidium monitoring and initial bin classification, process evaluation and planning, facility design, and construction and startup.

The Groundwater Rule.

In addition to the above rules that were developed for surface water and groundwater under the influence of surface waters, EPA also developed the GWR that applies to all public groundwater systems. The rule will apply to 147,000 systems serving more than 110 million people. Under the rule, which establishes multiple barriers to protect against bacteria and viruses, systems required to disinfect will need to ensure that they reliably achieve 4-log inactivation or removal of viruses. The GWR is expected to be promulgated by the end of 2005.

UV:The Best Available Compliance Technology
While a number of drinking water treatment technologies could be paired with one another to comply with the upcoming regulations, only UV can single-handedly address all three of them.


Research in the late 1990s proved that UV disinfection technology easily inactivates Cryptosporidium.8, 9 Contrary to chemical disinfectants, UV does not form harmful DBPs because the energy applied for inactivation of microorganisms is insufficient for breaking down chemical bonds. Accordingly, UV readily addresses the risky trade-off between microbial disinfection and the byproducts formed by chemical disinfectants.

UV can readily meet the additional Cryptosporidium inactivation requirements for both filtered and unfiltered systems. These requirements can be found in detail in the UV Disinfection Guidance Manual, or UVDGM.10 The UVDGM validation protocol has been laid out with two different levels of complexity: Tier 1 and Tier 2. Using the Tier 1 validation protocol, which is based on pre-set safety factors, EPA has developed Reduction Equivalent Dose (RED) targets for Cryptosporidium.

Based on Table 3, it is clear that a UV system certified at a commonly used UV dose of 40 mJ/cm2 will receive 2.5- to 3-log inactivation credits for Cryptosporidium (depending on the lamp technology).

At this dose, UV has been proven to be significantly more cost effective than alternative technologies, such as ozonation and membrane filtration processes11. In addition to its cost-effectiveness, UV has numerous advantages over these alternative technologies. 

UV for Stage 2 DBPR

As previously discussed, UV does not form harmful DBPs. It can be used as a stand-alone disinfection technology or in conjunction with chlorine or other chemical disinfectants, especially when a residual effect is needed. Its use can greatly reduce and, in some cases, eliminate the amount of disinfectants used. This, in turn, not only increases safety but also reduces the levels of DBPs and lowers chemical costs.

UV for GWR

As previously discussed, the GWR was developed to protect against bacteria and viruses since evidence shows that groundwater systems can quite easily be contaminated through runoff.

UV and membranes are two technologies that can help plants comply with the Rule. UV is extremely effective for protecting against bacteria and most viruses. UV doses required for inactivation of bacteria are extremely low and similar to the doses required for protozoa such as Cryptosporidium and Giardia. A UV dose of 20 millejoules per square centimeter (mJ/cm2) will successfully achieve 4-log inactivation of known pathogenic bacteria. For most viruses, the commonly used UV dose of 40 mJ/cm2 will readily achieve 4-log inactivation. However, adenovirus is an exception, as it is extremely resistant to UV. If using UV to treat this virus, the technology will need to be paired with a chemical disinfectant such as chlorine.

A Glimpse into the Future
Future regulations have piqued U.S. water treatment plants' interest in using UV technology as an additional barrier for municipal drinking water treatment. The discovery that UV readily inactivates Cryptosporidium has spurred numerous large facilities to begin installing the technology, including those in Pittsburgh; Henderson, Nev.; Seattle; New York City; and Cincinnati, to name a few.

UV's popularity is also rising north of the border; Vancouver is just one of many large Canadian municipalities preparing to install the technology. With a capacity of more than 500 million gallons per day, the Vancouver installation will be the largest UV system in the world.


  1. U.S. Environmental Protection Agency (EPA) 1999. Microbial and Disinfection Byproduct Rules Simultaneous Compliance Guidance Manual. Office of Water (4607), EPA 815-R-99-015, www.epa.gov/safewater/mdbp/simult.pdf .
  2. EPA 2002. "Proposed Groundwater Rule" EPA 815-F-00-003, April 2002. www.epa.gov/safewater/gwr.
  3. EPA 2003. "National Primary Drinking Water Regulations: Long-Term 2 Enhanced Surface Water Treatment Rule" Proposed Rule, 40 Code of Federal Regulations (CFR) Parts 141 and 142, Federal Register (FR)/ Vol. 68, No. 154, August 11, 2003, 47640-47795, www.epa.gov/safewater/lt2.
  4. EPA 2003. "Proposed Stage 2 Disinfectants and Disinfection Byproducts Rule," Office of Water (4607M), EPA 815-F-03-006, July 2003, www.epa.gov/safewater/stage2.
  5. EPA 1998. "National Primary Drinking Water Regulations: Interim Enhanced Surface Water Treatment, Final Rule" 40 CFR Parts 9, 141, and 142, FR/ Vol. 63, No. 241, December 16, 1998, 69478-69521, www.epa.gov/safewater/mdbp/ieswtrfr.pdf.
  6. EPA 1998. "National Primary Drinking Water Regulations: Disinfectants and Disinfection Byproducts Notice of Data Availability," 40 CFR Parts 141 and 142, FR, Vol. 63, No. 61, March 31, 1998, 15674-15692, www.epa.gov/safewater/mdbp/dis.pdf.
  7. Hargy, T. 2002. "Status of UV Disinfection of Municipal Drinking Water Systems in North America." Water Conditioning & Purification, June 2002, pp. 30-34.
  8. Bukhari, Z., T. Hargy, J. Bolton, B. Dussert, and J. Clancy 1999. "Medium-pressure UV Light for Oocyst Inactivation." American Water Works Association (AWWA) Journal, 91(3), pp. 86-94.
  9. Clancy, J., Z. Bukhari, T. Hargy, J. Bolton, and M. Marshall 2000. "Using UV to inactivate Cryptosporidium." AWWA Journal, 92(9):97-104.
  10. USEPA 2003. "Ultraviolet Disinfection Guidance Manual." Draft EPA Report No. 815-D-03-007. Office of Water, EPA, Washington, D.C.
  11. Cotton, C., D. Owen, G. Cline, and T. Brodeur 2001. "UV disinfection costs for inactivating Cryptosporidium." AWWA Journal, June 2001, pp. 82-94.

This article originally appeared in the 09/01/2005 issue of Environmental Protection.

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