SODIS Description

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Photo Credit: SAKYIKROM

Description
The SODIS process involves filling transparent plastic bottles with water and exposing them to full sunlight for six or more hours so that a combination of UV-A radiation and increased water temperature disinfects the water. This process may be combined with solar reflectors or solar cookers to further increase water temperature.

Development
The Swiss Federal Institute for Environmental Science and Technology

Important SODIS Recommendations

"We do not recommend any more to paint the plastic half-side black."

"UV-A transparent bottles of 0.3 - 3 litres can be used for SODIS. The bottles also reduce the risk of a recontamination of the treated water as long as the water is stored in the bottle, consumed directly from the bottle and/or from a clean glass. I kindly ask you to disseminate this information order to avoid misleading recommendations."

Martin Wegelin
Email: [ martin.wegelin [at] eawag [dot] ch ]
Dept. of Water and Sanitation in Developing Countries (Sandec)
Duebendorf, Switzerland

Performance

Amount of Water Treated
SODIS requires 10 or fewer liters of water per container in order to be effective. The size and number of bottles used, as well as the length of exposure required given the sun’s availability, will determine the amount of water treated by SODIS.

Contaminant Removal
SODIS, without the use of reflectors or cookers, has been found to kill 99.4 percent of fecal coliform in a liter of water with one day of full light exposure and 91 percent under cloudy conditions. These removal rates heavily depend on sunlight intensity and duration, cloudiness, ambient temperature, and bottle quality, including how scratched and thick the plastic is. Removal rates for SODIS are lowered by the presence of organic matter, iron, sulfites, nitrites, and turbidity because these particles absorb UV radiation and shield microbes from being hit with UV rays. UV radiation does not treat chemical contamination or turbidity.

Ease of Use
SODIS is a very simple process to set-up, though SODIS users need to monitor the temperature of the water to ensure it is properly treated.

Benefits & Drawbacks

Benefits
  • Simple
  • Scientifically proven
  • Excellent microbial removal
  • Bottles widely available
  • Water is already contained in a safe storage vessel
Drawbacks
  • Treatment process is slow
  • May not remove pesticides, fertilizers, and other chemicals.
  • Effectively only for low turbidity water
  • Dependent on sunlight availability
  • Small volume of water treated


Ideal Situation
Communities with presence of an institution that can provide promotion of the technology.

Additional Considerations
Studies indicate that some users stop using SODIS because chemicals may leach from the bottles into the water, causing undesirable taste or smell.

Costs

The costs associated with SODIS are minimal because the only materials needed are plastic bottles. Solar reflectors and cookers can also be made cheaply using cardboard and aluminum foil.

Resources

Projects

Contact Information