Velocity Profiling Versus Checkpoint Bioassay for Performance Testing of UV Disinfection Systems

As the recycled water industry is shifting from the use of theory based design of UV disinfection systems to a performance based design approach, there must be method for correlating the performance of one pilot-scale UV disinfection system to that of a full-scale system. Two methods for using existing performance data for the design and operation of future UV systems are presented in this paper.The first method, is velocity profiling. This is the method outlined in the Ultraviolet Disinfection Guidelines for Drinking Water and Water Reuse (2003 UV Guidelines) for applying the performance of a smaller validated reactor to full-scale reactors that have not undergone full biological validation. An alternative method, the checkpoint bioassay, is emerging as a more definitive means for applying the performance of a smaller validated reactor to that of a full-scale reactor. This method, with the proper provisions, has been accepted by some regulating agencies as an acceptable substitution for velocity profiling. Two case studies are presented in this paper to illustrate two potential applications of the check point bioassay method for determining the disinfection performance of full-scale and larger scale UV systems as it relates to the original full biological validation.