Effect of agitation, turbidity, aluminium foil reflectors and container volume on the inactivation efficiency of batch-process solar disinfectors

We report the results of experiments designed to improve the efficacy of th e solar disinfection of drinking water, inactivation process. The effects o f periodic agitation. covering the rear surface of the container with alumi nium foil, container volume and turbidity on the solar inactivation kinetic s of Escherichia coli (starting population= 10(6) CFU ml(-1)) were investig ated. It was shown that agitation promoted the release of dissolved oxygen from water with subsequent decrease in the inactivation rates of E. coli. I n contrast, covering the rear surface of the solar disinfection container w ith aluminium foil improved the inactivation efficiency of the system. The mean decay constant for bacterial populations in foil-backed bottles was fo und to be a factor of 1.85 (std. dev. =0.43) higher than that of non-foil-b acked bottles. Inactivation rates decrease as turbidity increases. However, total inactivation was achievable in 300 NTU samples within 8 h exposure t o strong sunshine. Inactivation kinetics was not dependent on the volume of the water container for volumes in the range 500-1500 ml. (C) 2001 Elsevie r Science Ltd. All rights reserved.