Solar Water Purification
How To Use Solar Water Purification
A method for readying water for drinking purposes that is fast gaining popularity and acceptance is solar water purification. More commonly known as solar water disinfection, this method relies on the power of the sunlight and a readily available PET bottle to purify water enough to make it drinkable. A PET bottle is just a short name for polyethylene terephthalate which is the type of plastic that soda bottles are made out of, which makes them readily available. Because solar water purification is free and easily doable at the household level, the World Health Organization is recommending it for extensive use in third world countries where valuable water sources are rare and expensive.
Simply put, solar water purification involves placing water in PET bottles and exposing them to direct sunlight for a period of time. Experts who developed the method say that the action of ultraviolet radiation disinfects the water by killing bacteria that cause common gastric illnesses like diarrhea and cholera. The killing process is caused by the breakdown of dissolved oxygen in the water made possible by ultraviolet light. The broken down oxygen creates a reactive intermediate called free radicals that kill or neutralize pathogenic agents.
The World Health Organization suggests a minimum exposure time of 5 hours in the tropics and 6 hours in mid-to-high latitude countries order for solar water purification methods to be effective. This period of direct exposure to sunlight raises the water temperature to 100-110 degrees fahrenheit which also aids in the disinfection process.
The prescribed steps for household applications of solar water purification steps are as follows. First, prepare PET bottles that are properly cleaned, scratch free and with the labels removed to enhance exposure. PET bottles, with their transparent profile and temperature conduction properties are ideal for the job although other bottle types can also be used provided a long exposure time is maintained. Once the PET bottles are ready, water from suspected contaminated sources are then transferred to the bottles up to three-fourths in volume. Oxygen content inside the bottle is maximized by vigorously shaking the bottles for 20 seconds to promote oxygen dissolution into the water.
It should be remembered that the method does not do anything to remove suspended solids in the material, hence highly cloudy, opaque, or turbid water sources should first undergo some form of filtration to remove the solids. Depending on the degree of opacity of the water, up to three filtrations using clean cotton cloth should be done prior to proceeding with solar water purification.
For best results, sloping surfaces made of corrugated metal sheets such as roofs are ideal because they radiate the heat back into the bottle. After the prescribed exposure period, the water is now ready for direct consumption from the bottles. Data shows a reduction of 30-80% in diarrhea cases for people drinking water that is purified by solar means compared to those who consume water direct from the source.
Particular to third-world countries and especially in the summer when scarce water sources are most likely contaminated, solar water purification presents a viable form of water disinfection that is cost-free and effective. Households that have limited access to clean water sources would do well to practice using solar energy to purify water sources in order to limit the incidence of diseases.
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