UV Disinfection Sizing: A Method for Comparing Apples to Oranges

As ultraviolet (UV) light technology for wastewater disinfection has evolved, various methods have been used to size UV systems to meet discharge permit requirements for bacterial limits. Many of these methods have resulted in inappropriately sized UV systems, leaving agencies and design engineers with the need for an objective approach. Using third-party validated bioassays is one option; however, there are variations in the various bioassay validation methods, which can make a direct comparison of the delivered dose among various equipment manufacturers difficult. One of the goals of the Colorado Springs Utilities' (SU) Las Vegas Wastewater Treatment Facility (LVWWTF) Alternative Disinfection design build project, was to develop an objective and comprehensive approach to evaluate the UV design dose proposed by various UV manufacturers. This case study presents the simplified approach developed to select an appropriate dose based on projected plant flows, third-party validation relationships, and observed UV transmittance (UVT).