Understanding the effect of particle-size on UV disinfection: Kinetics, mechanism and modeling

This study aimed to better understand the impact of suspended particles on ultraviolet disinfection of municipal effluents. The results showed that particles of sizes greater than 45 gm accounted for more than 90% of the surviving coliform in the tailing region of secondary effluent UV dose-response curve. Particles in larger size fractions also showed a greater tailing propensity---the probability of particle surviving UV doses beyond 30 mJ/cm2. In modeling the disinfection performance of secondary effluents, this was found to be the summation of the disinfection of all its particulate constituents. It was therefore possible to predict UV dose-response curve based on measurements of effluent particle-size distribution and particle disinfection kinetics. Finally, the tailing propensity was found to greatly depend on treatment processes. Trickling filter particles exhibited ten times greater tailing propensity than activated sludge particles, owing to their greater UV resistance and percentage viability.