The effectiveness of solar disinfection in treating roof-harvested rainwater contaminated with microorganisms was evaluated with a view to its use as a household technology. Coliform and heterotrophic bacteria inactivation kinetics were studied using bottles with different backing surfaces. The effects of various parameters such as turbidity, solar intensity, type of organisms (naturally occurring versus laboratory grown) and bottle volume on bacterial inactivation were studied. Complete inactivation of total coliforms was observed in 6 h when solar radiation exceeded ∼500 W/m2.Under high contamination and overcast conditions, prolonged exposure was needed. Moderate turbidity (38 NTU) did not reduce the inactivation efficiency, but slightly enhanced it. No regrowth of microorganisms was observed after 24 h following solar disinfection. No significant difference in the inactivation kinetics was observed for bottle sizes in the range of 0.5 to 2.0 L. Tests with naturally occurring and laboratory-grown organisms indicated that laboratory-grown organisms were inactivated faster than naturally occurring organisms.

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