A PLASTIC bottle provides a cheap way to harness the power of the Sun to
disinfect emergency supplies of drinking water after natural disasters.
This week Oxfam discussed using solar disinfection in Assam, India, where the
floods earlier this month left 5 million people homeless. The charity says that
chlorination tablets for disinfecting drinking water are in short supply.
The idea of using plastic bottles for solar disinfection鈥攐r
SODIS鈥攈as been developed by researchers at the Swiss Federal Institute for
Environmental Science and Technology in Duebendorf. To disinfect water, people
simply fill clear plastic bottles with water and leave them in the sun. The heat
warms up the water and the combination of warm water and ultraviolet radiation
kills most microorganisms.
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鈥淪ODIS efficiently inactivates bacteria and viruses,鈥� explains project leader
Martin Wegelin. He says that tests have shown that 99.9 per cent of the
Escherichia coli in a sample of contaminated water were killed when the sun
heated the water beyond 50 掳C.
At this temperature, the process can take as little as an hour, says Wegelin.
Painting half the bottle black and laying it on a corrugated metal sheet
shortens the time taken to warm up the water.
Wegelin and his colleagues have been testing the effectiveness of SODIS in
several rural parts of Asia, Africa and South America, where water-related
illnesses claim 5 million victims every year. The results are encouraging. SODIS
is particularly good at killing Vibrio cholerae, the bacterium that
causes cholera. SODIS also inactivated some common human parasites such as
cryptosporidium that cause severe diarrhoea.
The technology could also be a boon in the developing world鈥檚 growing urban
areas, where water supplies are often contaminated鈥攁s a result, sales of
bottled drinks are soaring among the rich. 鈥淭he target population of the soft
drinks industry are well off people who buy the bottles. The target population
of SODIS are the poor who are interested in empty bottles,鈥� he explains.
鈥淏ottles go from rich to poor, reducing the waste in urban areas.鈥�
Their idea does have its drawbacks, says Tricia Jackson of the water
engineering and development centre at Loughborough University. 鈥淭here may be a
lack of suitable plastic containers in emergency areas,鈥� she says. Alan Reed of
Oxfam says that the main problem is the absence of education about hygiene. 鈥淚f
there is little water and people have to travel a long distance to get it, they
don鈥檛 tend to worry what it contains.鈥�
But Wegelin is optimistic that with proper education, people will use SODIS.
Wegelin says that in a trial of SODIS, 84 per cent of people said they would
continue to use it. 鈥淲e are now in the process of promoting SODIS at a national
level in Asia and South America.鈥�