Solar water disinfection (SODIS) has been in existence for more than 30 years. The technique consists of placing water into transparent plastic or glass containers (normally 2L PET beverage bottles) which are then exposed to the sun. Exposure times vary from 6 to 48 hours depending on the intensity of sunlight and sensitivity of the pathogens. Its germicidal effect is based on the combined effect of thermal heating of solar light and UV radiation.
Diagram of the SODIS technique
How it works
Transparent containers are filled with contaminated water and placed in direct sunlight for at least six hours, after which time it is safe to drink. Solar disinfection containers (reactors) can be glass or plastic (usually polyethylene-terephthalate – P.E.T.) – even plastic bags have been used. Plastic bottles are more robust than glass bottles since few glass bottles survive an off-road journey in the back of a 4-wheel drive vehicle or a fall from a roof. It is recommended that solar disinfected water should be consumed within 48 hours to avoid the possibility of post exposure re-growth. The efficiency of the basic protocol can be enhanced by adding a number of additional steps such as:
- Placing filled bottles on reflective surfaces to boost the amount of sunlight absorbed by the reactor (Kehoe et al. 2001, Mani et al. 2006).
- Painting the underside of the SODIS reactor black to enhance solar heating.
- Shaking a two-thirds filled bottle vigorously for 30 seconds before topping up and sealing, to increase initial levels of dissolved oxygen for solar induced oxidative inactivation..
- Filtering the water before filling the reactor.
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