Variations in wastewater quality parameters influencing UV disinfection performance: Relative impact of filtration

The water-quality parameters influencing the performance of a UV disinfecti on system in the tailing region (typically apparent at doses greater than 3 0 mW . s/cm(2) in wastewater secondary effluents) are the inactivation rate coefficient (k) and the number of particles with associated coliform bacte ria (N-p). In this research, the natural variations of k and N-p in a waste water secondary effluent and the relative impact of filtration on reducing the variability of these two parameters was investigated. The coefficient o f variation (COV) of k in the effluent of a secondary clarifier, a sand fil ter, and a disc filter was roughly 39% for all three effluents. The sand an d disc filters reduced the COV of N-p in the secondary effluent from 112% t o 63% and 68%, respectively. Thus. filtration can be used to reduce the var iability in N-p to improve the long-term performance of a UV disinfection s ystem. The type of filtration system necessary was found to be dependent on the average log reduction in N-p required to meet the discharge requiremen t at the wastewater treatment plant.