Compiled by Walter Sorochan Posted July 02, 2011
Polluted drinking water: Millions of people become sick each year from drinking contaminated water. Approximately 4 billion cases of diarrhea are reported annually, of which 2.5 million end in death. Every day around 6000 children die due to the lack of safe drinking water. Children are especially susceptible. An estimated 1.5 billion cases of diarrhea occur each year, resulting in the death of nearly 2 million children. Worldwide, about 1.3 billion people do not have access to safe drinking water, including nearly half the population of sub-Saharan Africa. Aristanti:SODIS – Solar Water Disinfection Developed by the Swiss Institute for Environmental Science and Technology (EAWEG), the method, called solar water disinfection, or SODIS, uses the sun’s UV-A rays and heat to decontaminate water. The disinfection method they advocate involves filling a transparent container with contaminated water. So far, up to two million people in 20 countries have used it, though Benin is one of the few West African countries to trial the method. Irin: Sunshine makes clean water The SODIS method is more straightforward. Users take a clear plastic bottle with a maximum size of three liters, fill it with water and put it on the roof or a corrugated iron sheet to soak up the sun’s rays. Between six hours and two days later, depending on the strength of the sun, the water should be purified. Irin: Sunshine makes clean water According to officials at EAWEG, the sun’s UV-A rays kill the pathogenic organisms in the water while its heat has a pasteurizing effect. The combined effect can kill up to 99.9 percent of the micro-organisms that cause cholera and diarrhea. Irin: Sunshine makes clean water The chart below indicates the temperatures at which the most common waterborne pathogens are rapidly killed, thus resulting in at least 90 percent of the microbes becoming inactivated in one minute at the given temperature. (The 90 percent reduction is an indicator frequently used to express the heat sensitivity of various microbes.) Thus, five minutes at this temperature would cause at least a 99.999 percent (5 log) reduction in viable microbes capable of causing disease. (Significant inactivation of these microbes actually starts at about 5°C (9°F) below these temperatures, although it may take a couple of minutes at the lower temperature to obtain 90 percent inactivation.) Metcalf: kill water germs
Problem with SODIS: One problem in this method is it's current reliance on plastic bottles. When the plastic these bottles are made from (Polyethylene terephthalate) react with the heat & UV radiation from the sun, chemicals in the plastic can be absorbed into the water. Another problem with the use of plastic bottles is the threads in the cap and spout of the bottle. This is one spot on the bottle that can not be disinfected by the sun because the cap is covering it! So if the bottle is used to scoop up water from a dirty source, and then disinfected with the SODIS method, the water will only be re-contaminated by the threads of the bottle once poured out. It is important to keep in mind of any possible points of recontamination (i.e. dirty hands, dirty containers). Ensminger: Caution - SODIS not totally safe Additional application: Solar Water Disinfecting Tarpaulin References: ClimateLabBeta, "Solar Water Treatment," ClimateLabBeta. ClimateLab: safe water Ensminger Karl , "Uv water treatment," June 8,2010. Ensminger: Caution - SODIS not totally safe Irin, "BENIN: Sunshine + plastic bottle = clean water," Irin,July 10, 2008. Irin: Sunshine makes clean water Metcalf Bob, "Water pasteurization," Waikia, Metcalf: kill water germs Olsen Eric, "innovative design of an easy-to-carry device for transporting and purifying water," Bustler, Olsen: innovation clean water Waters Ilana, "How to Purify Water when Traveling Overseas," eHOW, January 13, 2011. Walters: Purifying water when traveling |