Water Disinfection (1): UVA rays. SODIS

DON’T you have clean TAP WATER?

Does the water in your rural WELL have BACTERIA or VIRUSES?

DISINFECTS water with the SUN!

Remove pathogenic microorganisms from water by taking advantage of solar UV.

Drinking Water purification

Water purification process has to cover all causes of NOT drinking:

• Bacteria, viruses (disinfection)
• Toxis minerals and metals (in the form of particles or dissolved)
• Deposits or particles in suspension (mud, etc.)

The disinfection process can be done in multiple ways: chemical (eg chlorine) or physical media (eg, photocatalysis, electron radiation, etc). In this post I will try only with ultraviolet disinfection.

Disinfection of water with UV-A (SODIS)

The solar water disinfection, also known as SODIS is a method of disinfecting water using only the sun and adequate water clear bottles.

UV-A rays destroy the cellular structure of bacteria and produce reactive forms of oxygen that destroy pathogens. In addition, infrared radiation heats the water, helping to destroy microorganisms.

The steps for proper disinfection through plastic bottles are:

• Choose good clean bottles of clear plastic PET (Other plastics are degraded).
• Fill them 3/4 parts of water free of sediments and stir for 20 seconds. Fill the bottle completely and cap.
• Expose the bottle to direct sunlight (preferably on a roof) for 6 hours (or up to two days if there is little sun).
• Keep unopened bottles. Drink directly from bottles or clean glasses.

Advantages of SODIS

• You do not need any technology making it very economical.
• No electricity required, a common situation in remote rural areas.
• Simple to explain and to apply.

Limitations of PET bottles disinfection

• The productions are very short and needs manual intervention
• If drinking from a cup, it should be washed with disinfected water.
• Sometimes it can be hard to find really clean PET bottles.

In a later post I will explain other disinfecting system combining solar thermal with UVA radiation.

Did you know this already water disinfection system for UVA? Your opinions are welcome.

Related articles

• Solar water disinfection – SODIS (wikipedia)
• Water purification (wikipedia)
• Common Kitchen Ingredient Helps Clean Drinking Water (treehugger.com)
• Research opens doors to UV disinfection using LED technology (phys.org)
• Go ahead – make a splash! SA’s gushing hydrants good, clean fun (kens5.com)