Retrofitting Existing WTPs with UV Disinfection for Microbial and DBP Rules Compliance


  • David Briley, Scott Alpert, Jay Jackson - Hazen and Sawyer

Some water systems are turning to UV disinfection for compliance with the new USEPA rules; Long-Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR) and the Stage 2 Disinfectant/Disinfection ByProducts Rule (DBPR). Water systems with Cryptosporidium hits in their water supplies may be required to meet higher levels of inactivation. This presentation will briefly present the Microbial Toolbox options available to water systems for achieving higher levels of Cryptosporidium inactivation. The advantages, disadvantages, and risks of each option will be discussed. In addition, water systems classified as Bin 1 (no additional Crypto. inactivation) according to the LT2ESWTR are also considering UV disinfection as a technology for DBP reduction. In this approach, UV disinfection would provide partial or full Crypto. and Giardia inactivation credit and allow a reduction in free chlorine contact within the plant; thereby reducing DBP formation at the point of entry into the distribution system.

There can be significant challenges with retrofitting existing water treatment plants with UV disinfection. Available head within the existing plant hydraulic profile is a key consideration since UV systems can have 2 to 4 feet of headloss. Site constraints can also be a significant challenge as plant sites may have been originally laid out for expansion, but not for additional treatment processes.

In this presentation, the key challenges and considerations for retrofitting existing WTPs will be discussed, including:
• Hydraulic considerations
• Site constraints and facility footprint
• Water quality and UV transmittance
• Electrical requirements
• Maintaining disinfection under adverse operating conditions

A brief update will also be provided on current trends in regulatory approval of UV disinfection systems for Crypto. and Giardia inactivation credit throughout the U.S.

For more information, please contact the author at

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Horizons Fall 2017 (pdf)

Horizons showcases significant water, wastewater, reuse, and stormwater projects and innovations that help our clients to achieve their goals, and can help you achieve yours. Articles are written by top engineers and process group leaders, demonstrating and explaining the beneficial application of a variety of technologies and tools.

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