Variations in Wastewater Quality Parameters Influencing UV Disinfection Performance: Relative Impact of Filtration

Abstract

The water-quality parameters influencing the performance of a UV disinfection system in the tailing region (typically apparent at doses greater than 30 mW⋅s/cm2 in wastewater secondary effluents) are the inactivation rate coefficient (k) and the number of particles with associated coliform bacteria (Np). In this research, the natural variations of k and Np in a wastewater secondary effluent and the relative impact of filtration on reducing the variability of these two parameters was investigated. The coefficient of variation (COV) of k in the effluent of a secondary clarifier, a sand filter, and a disc filter was roughly 39% for all three effluents. The sand and disc filters reduced the COV of Np in the secondary effluent from 112% to 63% and 68%, respectively. Thus, filtration can be used to reduce the variability in Np to improve the long-term performance of a UV disinfection system. The type of filtration system necessary was found to be dependent on the average log reduction in Np required to meet the discharge requirement at the wastewater treatment plant.