Design, construction and use of solar stills for water purification: A study of their performance in two geographical regions in Swaziland

M.D. Dlamini, A.J. Varkey

Abstract


Clean water for drinking and other domestic purposes is becoming a scarce resource the world
over. The presence of pathogens such as Escherichia coli [E. coli] in contaminated water often leads
to health complications and at times death, particularly when they originate from human or animal
waste, and may give rise to gastro-intestinal diseases such as diarrhoea and cholera. Simple and
affordable water purification devices are therefore essential in rural and peri-urban areas without
municipal water supply. Two locally built solar stills, sometimes called solar distillers, were
designed and constructed at the workshop of the Physics Department of the Faculty of Science and
Engineering, University of Swaziland. They were installed at two locations in Swaziland with
different climatic conditions, one at Dvokolwako in the Lowveld and the other, at Etimpisini in the
Middleveld. Data on monthly variation of the amount of distilled water collected at each of the two
locations were recorded over a period of one year. The effect of the ambient temperature on the
water collection efficiency was also evaluated. The amount of distilled water collected at each of the
two locations was found to increase with ambient temperature. The collection efficiency was found
to be higher in the Middleveld in spring and summer [September to February], whereas it was lowest
in winter [June and July]. The percentage increase in the amount of water collected in the
Middleveld between July and September was approximately 75%. In the Lowveld, however, the
variation in the collection efficiency was only about 19%. On average, a still can produce about 2.75
litres of water per day in the Middleveld, compared to 2.6 litres in the Lowveld, using a still with a
base area of 1 m2. The raw and distilled water were tested at the Swaziland Water Services
Corporation [SWSC], Mbabane for the presence of E. coli and total coliform, as well as the levels of
pH and total hardness. Tests on cations and anions were carried out by the Department of
Geological Survey and Mines, Mbabane. Results of the water quality tests showed that the solar
stills had the capacity to eliminate E. coli and total coliform completely from the raw water and
reduce the levels of pH, total hardness, anions and cations significantly. The anions were reduced
by 22 % to 100 % and there was a 53% to 100% reduction in cations. All the parameters were found
to be within the South African [SA] and SWSC standards for water quality. Improvements for future
work have also been highlighted.

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