PARTICLE SIZE DISTRIBUTION TESTING AS A DIAGNOSTIC TOOL FOR OPTIMIZING FILTRATION AND UV DISINFECTION SYSTEMS

Particle size distribution (PSD) testing is a diagnostic and a predictive tool that can be effectively utilized to more fully quantify the factors that impact filtration and UV disinfection performance. The results that will be presented during this paper have been obtained from several bench, pilot, and full scale filtration and UV disinfection studies. Through the use of PSD analyses it has been demonstrated that filtration performance of both cloth media and granular media filters is negatively affected by the presence of large quantities of smaller sized particles. It has also been demonstrated that the type of upstream biological treatment processes employed will have a significant effect on the secondary effluent PSD and turbidity levels. Biological treatment processes such as trickling filter-solids contact and pure oxygen activated sludge plants have been shown to produce a secondary effluent with a large concentration of smaller sized particles. To effectively treat secondary effluents from biological treatment process that produce large quantities of smaller sized particles, such that the Title 22 turbidity limits of 2 NTU can be satisfied, a coagulation, and flocculation step will be required. PSD analyses can also be used to ensure that a filter prior to a UV disinfection system is adequately removing larger sized particles that could shield coliform bacteria from UV light and result in residual coliform concentrations.