Water Disinfection Using Solar
Radiation |
Document(s) 12 of 15
Introduction
Obtaining clean drinking
water is a constant challenge in many countries. Often the only water available
is rife with disease-causing bacteria, and must be disinfected to make it safe.
Conventional methods for disinfecting drinking water, including boiling and
adding chlorine compounds, can be time-consuming and expensive. In some regions,
it is difficult to ensure a reliable supply of chlorine, which can also give the
water an unpleasant taste. In many areas, there is little fuel available for
boiling water.
Drawing inspiration from water treatment practices developed in India as long
ago as 2000 B.C., researchers at the American University of Beirut in Lebanon
developed, with IDRC support, a
low-cost, practical means to provide safe drinking water in rural and urban
areas in developing countries. The key to this method lies in the ability of
direct sunlight to destroy bacteria. The treated water is suitable for drinking,
and can also be used to prepare Oral Re-hydration Therapy (ORT) solutions to
treat dehydration suffered by children with diarrhea. Solar radiation is a form
of renewable energy that is abundant and accessible in most southern countries.
The research focused on small quantities of drinking water, sufficient to
satisfy the daily requirements of a small family.
Sunlight with wavelengths of 315-400 nanometers (nm) on the ultraviolet (UV)
range of the electromagnetic spectrum is most effective at destroying bacteria.
Since colourless glass or plastic can transmit light in this near ultraviolet
range, they are the best materials for disinfection. Visible light (400-750 nm)
next in terms of efficiency, with the visible band of violet and blue light
(400-490 nm) is the most useful within this range. As a result, violet, blue,
and very light green-tinted glass follow colourless glass or plastic in order of
suitability.
More recent research carried out at Montreal's Brace Research Institute
(BRI), in collaboration with international colleagues, indicates that
transparent plastic bags are the best material for solar water disinfection.
Researchers report that six litres of St. Lawrence River water can be
disinfected in five hours during the summer. Research attention in this regard
has been focused on finding or developing plastics capable of transmitting
sunlight wavelengths below 400 nm.
Impact
Development of a simple, effective and economical method of water
disinfection using solar radiation - Earlier work by researchers in Lebanon
on developing suitable methods to disinfect water in developing countries is
being carried on at the Brace Research Institute. Identifying simple,
inexpensive plastic bags for use in disinfection has become a suitable method to
use in southern contexts. BRI researchers actively promote their findings
through a variety of networks, including the Global
Applied Research Network (GARNET).
Prerequisites
Containers made from
colourless or tinted glass, or transparent plastic; adequate sunshine (optimum
regions for solar radiation lie between latitudes 35°N and 35°S).
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