Factors affecting particle-microorganism association and UV disinfection: Effect of source water, organics, and particle characteristics

Abstract

Ultraviolet (UV) disinfection is usually applied following filtration to reduce particulate concentrations and improve disinfection effectiveness. However, there is a desire to avoid costs associated with pre-treatment for small and resource-limited treatment facilities. Lack of pre-treatment can increase the degree of particle-microorganism association and inhibit disinfection by UV. As such, there is a need to quantify the degree to which unfiltered water conditions may decrease UV performance. In this study, a range of water quality was produced at bench scale to simulate extreme water conditions. Overall, particle type primarily impacted UV disinfection, particularly at lower turbidity (<5 NTU). The composition of turbidity-causing material was reported as the controlling factor in particle-microorganisms association and disinfection achieved by UV. In particular, it was observed that the surface charge of particulates governs the proportion of microorganisms associated with particles and the resulting loss of disinfection efficiency. Multiple linear regression analysis of UV disinfection results showed incorporating zeta potential in conjunction with commonly used indicators increased the accuracy of predicting UV disinfection achieved. The results of this study highlight some of the risks of UV disinfection of unfiltered supplies and can be used to optimize UV disinfection in small-scale or resource-limited water treatment plants.