S.C. Kehoe

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 the solar disinfection of drinking water, inactivation process. The effects of periodic agitation, covering the rear surface of the container with aluminium foil, container volume and turbidity on the solar inactivation kinetics of Escherichia coli (starting population = 10(6) CFU ml(-1)) were investigated. It was shown that agitation promoted the release of dissolved oxygen from water with subsequent decrease in the inactivation rates of E. coli. In contrast, covering the rear surface of the solar disinfection container with aluminium foil improved the inactivation efficiency of the system. The mean decay constant for bacterial populations in foil-backed bottles was found to be a factor of 1.85 (std. dev. = 0.43) higher than that of non-foil-backed bottles. Inactivation rates decrease as turbidity increases. However, total inactivation was achievable in 300 NTU samples within 8 h exposure to strong sunshine. Inactivation kinetics was not dependent on the volume of the water container for volumes in the range 500-1500 ml.

Batch solar disinfection inactivates oocysts of Cryptosporidium parvum and cysts of Giardia muris in drinking water

Aim:  To determine whether batch solar disinfection (SODIS) can be used to inactivate oocysts of Cryptosporidium parvum and cysts of Giardia muris in experimentally contaminated water.

Effects of simulated solar disinfection of water on infectivity of Salmonella typhimurium.

To determine whether cells of Salmonella typhimurium rendered nonculturable by simulated solar disinfection retain infectivity for mice. Bacteria suspended in water were exposed to UVA irradiation for up to 8 h. Culturability, determined by colony forming unit and Most Probable Number counts, fell by six log10 units, while cellular activity determined by the Kogure cell elongation test was retained by approximately 5% of the cells present after 8 h. Intraperitoneal doses of nonculturable cells and active but nonculturable (ABNC) cells exceeding the LD50 of the test organism and BALB/c mouse host, respectively, by 4 and 3 orders of magnitude failed to produce detectable infections. Culturable cells that had been irradiated for 1·5 h were less infective (virulent) than their nonirradiated counterparts. Nonculturable and ABNC cells of Salm. typhimurium produced by UVA irradiation do not retain infectivity for mice. Although ABNC cells could be produced by low cost solar disinfection systems, they do not appear to pose a potential infection hazard.

Solar disinfection of poliovirus and Acanthamoeba polyphaga cysts in water – a laboratory study using simulated sunlight

Aims:  To determine the efficacy of solar disinfection (SODIS) in disinfecting water contaminated with poliovirus and Acanthamoeba polyphaga cysts.

Batch process solar disinfection is an efficient means of disinfecting drinking water contaminated with Shigella dysenteriae type I

Aims:  The mortality and morbidity rate caused by Shigella dysenteriae type I infection is increasing in the developing world each year. In this paper, the possibility of using batch process solar disinfection (SODIS) as an effective means of disinfecting drinking water contaminated with Sh. dysenteriae type I is investigated.

Effect of Batch-Process Solar Disinfection on Survival of Cryptosporidium parvum Oocysts in Drinking Water

ABSTRACT The results of batch-process solar disinfection (SODIS) of Cryptosporidium parvum oocysts in water are reported. Oocyst suspensions were exposed to simulated sunlight (830 W m−2) at 40°C. Viability assays (4′,6′-diamidino-2-phenylindole [DAPI]/propidium iodide and excystation) and infectivity tests (Swiss CD-1 suckling mice) were performed. SODIS exposures of 6 and 12 h reduced oocyst infectivity from 100% to 7.5% (standard deviation = 2.3) and 0% (standard deviation = 0.0), respectively.