Advancing UV Technologies for the Drinking Water Industry

Twenty years ago, ultraviolet (UV) technologies were primarily used in North America for the disinfection of wastewater effluents. Today, UV technologies provide drinking water disinfection at flows up to 2,000 mgd, advanced oxidation of taste and odor compounds, destruction of N-Nitrosodimethylamine (NDMA) and other nitrosamines in ground water, and disinfection and advanced oxidation with potable reuse. This expanded application of UV technologies has been driven by new regulations and guidance promulgated by the US Environmental Protection Agency (USEPA), UV projects funded by the Water Research Foundation (WRF) and other agencies, and technology advances and validation by UV system manufacturers. The Carollo Research Group (CRG) has been active in each of these areas and has provided leadership in promoting UV technology applications.

Developing the UV Validation Testing Facilities

In 2001, USEPA contracted with Carollo to develop the UV Disinfection Guidance Manual (UVDGM) for the Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR). At that time, there was very limited experience with drinking water UV disinfection, especially in the area of UV dose monitoring and validation. In response, Carollo worked with UV system manufacturers to develop the Portland UV validation test facility, located in Portland, OR. The facility opened in 2003 and has since conducted UV validation testing on over 80 commercial UV reactor products at flows ranging from 5 gallons per minute (gpm) to 70 million gallons per day (mgd) per reactor. The UV dose monitoring algorithms developed at the Portland test facility not only provided
a foundation for the UV monitoring requirements specified in the LT2ESWTR and the validation test protocol provided in the UVDGM, both published in 2006, but have also promoted confidence in UV technologies with utilities and their regulators.

Raising the Bar for UV Performance 

Since 2006, CRG has been the Principal Investigator (PI) or Co-PI for 11 UV projects funded by WRF. These projects have defined the state-of-the-art UV technologies resulting in better public health protection with lower capital and operation and maintenance costs. For example, WRF Project 2977 developed design and performance guidelines for UV sensor systems and UV dose monitoring. Prior to WRF 2977, UV dose algorithms provided indirect predictions of pathogen log inactivation based on UV validation conducted using a single surrogate, such as MS2 Phage. With indirect predictions of pathogen log inactivation, the UVDGM specified application of a reduction equivalent dose (RED) bias factor to account for prediction uncertainty. This factor was based on a “worst case” commercial reactor, and hence was highly conservative with many UV technologies. To address this issue, WRF Project 2977 defined UV dose algorithms based on validation conducted using multiple surrogates. These algorithms include a kinetic term for the microbe, which allows direct prediction of pathogen inactivation thereby eliminating the RED bias uncertainty. Since WRF 2977 was finalized, all of the major UV system manufacturers have adopted these algorithms for UV dose monitoring.

In 2020, USEPA published the document entitled “Innovative Approaches for Validation of Ultraviolet Disinfection Reactors for Drinking Water Systems” (EPA/600/R-20/094). Authored by CRG, the Innovative Approaches document acts as a compendium of new approaches for UV dose monitoring, validation, and implementation developed since the publication of the 2006 UVDGM. For UV dose algorithms that provide direct predictions of pathogen log inactivation, the document provides criteria for developing a robust validation test matrix, monitoring algorithm goodness of fit and quality assurance/quality control requirements, and standardized approaches for defining the validated range of UV reactors. To simplify UV system operation, the document provides approaches for UV dose monitoring algorithms that do not require an online UV transmittance monitor. The document also provides UV dose values for 6-log inactivation of Cryptosporidium, Giardia, and adenovirus that can be applied with UV technologies used for potable reuse.

Carollo’s work on advancing UV technologies continues to this day. In 2021, Carollo completed validation of a UV LED reactor for drinking water disinfection at flows up to 3.2 mgd, all in accordance with the USEPA UVDGM and Innovative Approaches document. UV LEDs provide a mercury-free alternate to low-pressure high-output (LPHO) and medium-pressure (MP) UV lamps used with many UV reactors. In 2022, based on UV dose models developed through WRF Project 4764, Carollo developed a UV dose calculator tool based on computational fluid dynamics (CFD) that quantifies the impact of lamp failures on UV dose delivery and public health protection with installed wastewater UV systems. The tool enables plant staff to develop strategies for addressing lamp failure with their system. These two examples show that new and exciting work is still going on in the world of UV.

Read more of this issue of Currents: Currents: Volume 4, 2022