Solar water disinfection

From Wikipedia, the free encyclopedia

This article or section is in need of attention from an expert on the subject.
Please help recruit one or improve this article yourself. See the talk page for details.
Please consider using {{Expert-subject}} to associate this request with a WikiProject

Solar Water Disinfection, or SODIS, is a method to disinfect water using sunlight and PET bottles.

1 Steps
2 How SODIS works
3 Notes
4 Cautions
5 Applications
6 References
7 External links

[edit] Steps

Obtain a clear plastic or glass bottle (transparent PET bottles of up to 3L volume are adequate)
Fill the bottle with clear water.
Leave the sealed bottle in direct sunlight for at least 6 hours, preferably lying on a highly reflective surface, for example a corrugated iron sheet.
If the weather is cloudy, you need to leave the bottles out for 2 consecutive days.
After cooling down, the water is disinfected and drinkable.

[edit] How SODIS works

Sunlight is treating the contaminated water through three synergistic radiation mechanisms.

UV-A (wavelength 320-400nm) which react with oxygen dissolved in the water produces highly reactive forms of oxygen (oxygen free radicals and hydrogen peroxides) in the water. These reactive forms of oxygen kill the microorganisms.
UV-A also interferes with the reproduction cycle of bacteria by damaging their DNA
Infrared heating the water. If the water temperatures raises above 50°C, the disinfection process is three times faster.

The combined effect of all three mechanisms is greater than that of each individual components.

[edit] Notes

SODIS efficiency depends on the physical condition of the plastic bottles. Mechanical scratches and aging due to photoproducts, reduce the efficiency of SODIS. Heavily scratched or old, blind bottles should be replaced.

If the sun is less strong, due to clouds or in a less sunny climate, a longer time in the sun is necessary.

[edit] Cautions

If not left in strong sun for the proper length of time (due to carelessness, impatience or urgent thirst) the water may not be safe to drink and could cause illness.

There is concern over whether plastic drinking containers can leach chemicals or toxic components into water, a process possibly accelerated by heat.^[1]

[edit] Applications

SODIS is very valuable where fuel or cookers are not available for boiling, or where this is expensive. (Even where fuel is available, however, SODIS is a more economical and environmentally friendly option).

In theory it could be used in disaster relief or refugee camps. However, supplying bottles may be more difficult than alternatives such as supplying disinfecting tablets containing chlorine, bromine, or iodine. Additionally, in some circumstances, it may be difficult to guarantee that the water will be left in the sun for the necessary time.