Standardized Collimated Beam Testing Protocol for Water/Wastewater Ultraviolet Disinfection

Ultraviolet (UV) irradiation has emerged as a viable alternative for water/wastewater disinfection. Laboratory dose-response data from collimated-beam tests are commonly used as a basis for determining the necessary delivered UV dose for full-scale UV systems as measured by UV intensity and exposure time. While researchers often think that germicidal dose can be estimated confidently in a collimated beam system, the reported dose-response relationships vary considerably. Numerous factors may affect the test results to some extent. They include apparatus setup, column dimensions, UV lamp type and output, intensity measurement, shutter type and operation, petri dish specifications, sample volume and depth of the liquid, mixing condition, laboratory settings, microbial organism preparation and testing, and water quality. The methodology used to calculate the UV dose for collimated beam tests is also a critical factor. To ensure reproducibility or to have a meaningful comparison of results from different collimated beam tests, a standardized protocol for collimated beam testing and its dose calculation is necessary. The standardized collimated beam test can then serve as a tool to “calibrate” the dose calculation models for field-scale UV reactors and, consequently, to meaningfully compare the dose values derived from these models. A comprehensive standardized collimated beam testing protocol is warranted to advance applications of UV disinfection for water/wastewater. However, development of such a protocol is a significant research effort that will require input from researchers of various technical and disciplinary backgrounds. In addition, some technical issues still need to be clarified by further research. This paper presents important issues associated with collimated beam testing in the context of developing a standard protocol as well as future research needs. The main objective is to serve as a starting point for development of a standardized collimated beam testing protocol that is universally acceptable by researchers, industries, and regulatory agencies.