Impact of particle aggregated microbes on UV disinfection. I: Evaluation of spore-clay aggregates and suspended spores

Aggregation of microbes with particles can reduce the effectiveness of ultraviolet (UV) disinfection. This study evaluated the comparative impact of dispersed spores, dispersed spores mixed with clay particles (nonaggregated), spore-spore aggregates, and spore-clay aggregates on UV disinfection performance in simulated drinking waters. Aggregates were induced by flocculation with alum and characterized by particle size analysis (count, volume, and surface area) of dispersed and aggregated systems, scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis. It was concluded that spores within aggregates of the spore-clay system were protected from UV irradiation compared to nonaggregated spores and the difference between these systems was found to be statistically significant throughout the UV range tested. In addition SEM-EDX analysis suggested that aggregate composition is nonhomogeneous with respect to the ratio of spores and clay particles among aggregates. It was estimated that 30-50% of the spores in the aggregates tested were protected from UV irradiation.