Relationship between physiochemical properties, aggregation and u.v. inactivation of isolated indigenous spores in water

Aims: The objective of the study was to compare ultraviolet (u.v.) inactivation kinetics of indigenous aerobic spores in surface water with their laboratory-cultured spore isolates and to investigate the relationship between physicochemical characteristics and u.v. inactivation kinetics of spore isolates. Methods and Results: Lake water samples were analysed for the presence of indigenous aerobic spores. Different bacterial isolates from the heterogeneous indigenous population were genetically characterized, resporulated and examined for hydrophobicity, surface charge, particle size distribution and survival at different u.v. 254 nm fluence levels. Cultured isolated spores exhibited a three-stage inactivation curve consisting of shoulder, first order and tailing regions whereas indigenous spores exhibited only one stage of linear kinetics. Hydrophobicity of the Bacillus spore isolates was inversely related to the extent of u.v. inactivation before tailing occurred. Conclusions: Tailing in the u.v. inactivation curves results from aggregation of a portion of the spore population because of hydrophobic interactions, supporting the link between aggregation of spores, hydrophobicity and u.v. inactivation. Significance and Impact of the Study: Evidence of the link between spore physicochemical parameters and u.v. disinfection performance furthers the understanding of factors that affect inactivation of microbes in natural waters supplied to drinking water treatment plants.