Ultraviolet disinfection of particle-associated viruses in water

Viruses are frequently attached onto or enmeshed within a variety of particles in natural waters and wastewaters, however relatively little is known about the impact of this viral particle-association on water treatment processes. This thesis focuses on the impact of particle-associated viruses on ultraviolet (UV) disinfection, a disinfectant currently gaining widespread popularity in the drinking water industry in North America.;Dual-media filtration, which often precedes UV disinfection in surface water treatment, was shown to be an effective means of reducing the number of particle-associated phage. The breakthrough of particle-associated phage through an anthracite-sand filter was highest during periods of increased particle breakthrough (i.e. filter effluent turbidity > 0.3 NTU), especially at the end of the filter cycle. UV disinfection of phage in the filter effluent was negatively impacted during the end of filter cycle breakthrough conditions in some cases. In addition, it was observed that un-filterable humic acid particles smaller than 0.45 mum and/or humic acid coating of bacteriophage surfaces may have UV-protective effects.;The research findings also re-emphasize that viral disinfection studies should account for particle-associated viruses using techniques such as the physico-chemical blending method that was used in this research, since failure to do so can result in significant underestimation of the true virus concentrations. Further, multiple viral surrogates should be used in experimental studies whenever possible, since viruses vary significantly in their sizes, shapes, and surface charges, all of which can influence the adsorption of viruses to particles.;Particles smaller than 2 microns (mum) in diameter were shown to be large enough to enmesh and protect bacteriophages MS2 and T4 (model viruses) from UV light. This is smaller than the minimum particle size of 7-10 mum for the shielding of coliform bacteria from the UV disinfection of wastewater reported by earlier studies. In addition, particulate chemical composition, specifically UV-absorbing content such as organic or iron compounds, was a critical factor in the survival of particle-associated bacteriophage exposed to UV light. Particles such as humic acid floc, activated sludge floc, and iron precipitate particles were observed to protect attached phage from UV light.