Impact of particles on ultraviolet disinfection of bacteria in water

When UV light is applied to disinfect drinking water, particles in the water can conceivably protect embedded microorganisms from disinfection. Earlier studies have investigated how turbidity and particles affect light scattering, and particle-associated protection of cultured microorganisms. Little attention has been devoted to the ability of natural particles in water supplies to protect indigenous microorganisms. This thesis focuses on humic-coating of bacteria, the optical properties of particles and particle-related protection of indigenous microorganisms.;The bulk LV254 absorbance by particulate material in 10 surface waters was found to be the same order of magnitude as particles from the secondary effluent of a municipal wastewater treatment facility. This implies that since wastewater particles can offer protection to embedded microorganisms from UV light, it is possible for surface water particles to offer similar protection, at least in terms of the optical properties of the particle material.;Particle-related protection of indigenous coliforms in untreated surface water from 3 sources (turbidity from 0.8 to 5.4 NTU) was observed with protection attributed to particles > 11 microm. However, despite this protection, at least 2.5-log inactivation of indigenous coliform bacteria was observed in all waters considered. In another untreated surface water (up to 1.3 NTU), no strong evidence of protection of indigenous coliforms or aerobic spores was found.;A final objective of this study was to use 14 months of hourly UVT data to evaluate the USEPA's Ultraviolet Disinfection Guidance Manual recommendations for UVT data collection and analysis for design of UV systems. In terms of sampling frequency, both hourly and daily (but not weekly) UVT data collection provided reliable data for UV reactor design.;A bench-scale proof-of-concept study found that both commercial (AHA) and aquatic humic acid (Suwannee River natural organic matter) appears to coat the surface of cultured bacteria hindering the effectiveness of UV disinfection. Both AHA and Suwannee River NOM were found to offer statistically significant (alpha = 0.05) protection of both E. coli and B. subtilis at concentrations of 50 and 120 mg/L. The concentrations of humic matter used in the study (10 to 120 mg/L) exceed those commonly found in surface waters.