Solar Water Purification System

Colegio Ingles de Puebla has been celebrating the Science Fair for 15 years, each year students will have a team in which they will have to elaborate a project about a special subject. This year one of the projects will be a Solar Water Purification System(SODIS).

Solar water disinfection is a low-technology, simple process of purifying water using the power of the sun’s UV rays and solar radiation. SODIS technology was first introduced in 1980. The method for SODIS involves clear PET bottles and a location that is exposed to the sun, most commonly the roof top of a residence. The size of the bottles should be 2 liters or less, and the water is filled in the bottles to leave 2.5 cm of space in order to permit enough oxygen for the process, then shake the bottle of water to fully oxygenate the water. The process involves exposure to the UV-rays and temperature, the higher the temperature the water reaches in the bottle the faster the disinfection process. If it is sunny or up to 50% cloudy, the water is disinfected in 6 hours of exposure. If it is 100% cloudy then the bottles need to be exposed for 2 days.6 If water temperature goes above 50 the disinfection process is complete in 1 hour.7After this time period, the water is disinfected and ready to drink. These simple calculations of sunlight and temperature make this method of water purification very accessible.

SODIS kills many water borne pathogens including bacteria, viruses, and the giardia and cryptosporidia parasites. These pathogens are related to many health issues including cholera, typhus, diarrhea, polio, hepatitis, stomach cramps, fever, among others. Most likely, UVA-rays kill these pathogens most by damaging the respiratory system through radiation, but this is still in question. Because the UVA-rays play such a vital role in disinfection, the process happens even when the temperature is cool. The process is ineffective, however, during periods of heavy rainfall and many recommend rainwater harvest and filtration during this time. Furthermore, it is important that the water is relatively clear in order for the rays to penetrate and disable the functions of the pathogens. Waters of higher turbidity must be filtered before SODIS treatment to ensure proper purification.