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Escherichia coli and some salmonellas were exposed in seawater and freshwater to natural sunlight, visible light of comparable intensity, and light containing a similar proportion of u.v. as natural sunlight but of a much lower intensity. Direct viable bacterial counts and culturable counts on selective and non-selective media were made at intervals. The rate of decrease in numbers of culturable bacteria was significantly faster in seawater than in freshwater when exposed to natural sunlight. No significant difference was found between the rates of decrease in numbers of culturable bacteria in seawater and those in freshwater when bacteria were exposed to light with a small u.v. component of similar intensity. The effect of salinity no loss of culturability is, therefore, more significant in the presence of u.v. radiation. Direct counts by the acridine orange direct viable count method decreased much more slowly than the culturable counts in seawater but comparably with culturable counts in freshwater in natural sunlight. Direct viable counts and culturable counts decreased at a similar rate in seawater and in freshwater in visible light. This may signify the evolution of enteric bacteria towards a viable but non-culturable form in seawater when exposed to natural sunlight. The presence of humic acids significantly reduced loss of culturability but only in low salinity conditions. Salinity appears to be an important factor influencing culturability in bacteria exposed to sunlight.

The coagulant and disinfectant qualities of Moringa oleifera and Citrus paradisi were investigated on various water samples acquired from sachet water (packaged water), borehole water, river water and well water. The results revealed that Moringa oleifera functioned adequately at settling time beyond 2 h in highly turbid river water but was more effective when combined with Citrus paradisi. Moringa oleifera or its combination with Citrus paradisi is less effective for turbid water treatment but effective for river water (sample) purification. The number of total Coliforms and Escherichia coli reduced with the increasing treatment time.

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Results are reported from a comprehensive series of experiments in which the survival characteristics of a range of indicator bacteria, pathogenic bacteria and bacteriophages was compared in fresh and seawater in the light, and at a range of temperatures, nutrient concentrations and salinities in the dark. Survival of the following organisms was studied: E.coli, faecal streptococci, maroon faecal streptococci, Salmonellatyphimurium 12, 12a and 110, S. anatum, Shigellasonnei, Sh. flexneri, Yersinia enterocolitica, Campylobacter fetus, Coliphages MS 2 and f 2. The data shows that in the light the survival of E.coli was very poor compared to that of Salmonellae. In the light, survival was best in fresh water, but in the dark survival in seawater was usually better. A linear relationship was demonstrated for T,90 and light intensity, and log T90 and temperature, but non-linear responses occurred for a range of salinities and nutrient concentrations.