Wastewater Process Modifications for Addressing TSS to Improve UV Disinfection

This paper focuses on total suspended solids (TSS) in wastewater effluent, which can have two major negative impacts on ultraviolet (UV) disinfection. First, an increase in TSS may cause a decrease in the disinfection rate, especially at lower UV doses, and second, tailing of the dose-response curve can be attributed to suspended solids. While the concentration of suspended solids (total weight measurement) is typically used to evaluate the potential performance of a UV disinfection system, correlations between suspended solids concentrations and UV performance are often inconsistent. Past research has shown that suspended solids size has an important impact on UV disinfection efficiency with larger particle size fractions, resulting in lower disinfection efficiency than smaller fractions. A summary of particle size distribution data from several different types of wastewater facilities will be presented, showing the relationship between type of biological treatment process and particle size distribution. Additionally, a case study of a wastewater treatment plant in Massard, Arkansas, will be described in which UV was selected as the disinfection process following a trickling filter, a biological treatment process that can produce solids with a high fraction of large particles. A discussion of the biological process improvements that were implemented to improve TSS conditions making such UV disinfection feasible is also provided.