Solar water disinfection

Consuming contaminated water can cause more or less dangerous illnesses which generally manifest themselves in weakness, vomiting and acute diarrhea. In a survival situation, consider using the SODIS process, a technique that will allow you to purify water in a simple and effective way using only solar energy.

The sun has a double effect on polluted water. It simultaneously causes an increase in temperature and exposure to radiation UV-A whose wavelength between 320 and 400 nm. The combination of these two effects helps to kill pathogenic microorganisms and thus promotes the disinfection and purification of contaminated water.

Solar water disinfection

There are certain precautions that you will need to take in order for the solar water disinfection process to be quick and effective.

  • The water must be clear and of low turbidity, so consider filtering it using a clean cloth and letting it settle before exposing it to the sun for disinfection.
  • Put the water in transparent plastic bottles and let them expose to the sun to destroy pathogenic organisms.
  • In ordinary times, the bottles should be left exposed to the sun’s rays for 6 hours, but if the temperature reaches or exceeds 50°C, one hour of exposure will suffice.
  • In cloudy weather, you will need 2 consecutive days of exposure to the sun to disinfect and purify the water.
  • To make the solar disinfection process more efficient, place the bottles on reflective surfaces such as aluminum or corrugated iron.
  • The sun produces oxygen free radicals and hydrogen peroxides which react better with hydrogen peroxide. Remember to aerate the water well before exposing it to the sun’s rays.
  • To aerate the water, fill the plastic bottle ¾ full and shake vigorously before filling it completely and leaving it exposed to the sun.
  • Once exposed to the sun, do not move the bottles any more because their agitation can negatively influence the efficiency of the process.

Choosing the material and shape of the bottle

Choosing the right bottle material is an essential step for successful solar water disinfection.

Glass : The iron oxide content in the glass determines its transmission of UV sunlight. For ordinary glass about 2mm thick, the transmission is almost zero. It is therefore not recommended to use this material for solar water disinfection.

PVC : Polyvinyl chloride (PVC) bottles are rich in stabilizing additives that protect their contents from oxidation as well as UV rays. However, PVC is not really considered the best material for the solar disinfection process.

The fart : PET bottles are not as rich in additives as PVC, they allow the passage of UV rays which activate cell molecules and destroy pathogenic micro-organisms thus promoting disinfection and solar purification of water.

The stages of solar water disinfection

To sanitize the water in a quick and effective way, you will need to follow these steps.

  1. Make sure the weather is sunny for the process to be faster and more efficient.
  2. Solar water disinfection takes time, from 2h to 48h depending on the climate, so try to collect a sufficient amount of PET bottles, around 4 bottles per person.
  3. Make sure the bottle is airtight and the cap is tightly closed.
  4. The water must be of low turbidity, try to filter it and treat it by decantation before exposing it to the sun.
  5. Leave the bottles exposed to the sun from dawn and make sure they are away from the shade.
  6. Put the bottles at an obtuse angle on a reflective surface like corrugated iron to speed up the process.

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