Solar water disinfection in rural puerto rican counties


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Solar water disinfection in rural puerto rican counties

  1. 1. Solar Water Disinfection in Rural Puerto Rican Counties<br />Adriana Rivera, Iván García, Javier Arce<br />RISE Program, Biology Department, Universidad de Puerto Rico-Cayey<br />16th of May of 2011<br />Abstract:<br />Most developing countries and rural counties have very limited sources of potable and clean water. Reasons for these can be any of the following: poverty, lack of an adequate aqueduct, contaminated rivers and streams, and isolation. Potable and clean water is one of the most basic of humane necessities and is one vital for optimal, or at least better, living conditions. Most streams and rivers in isolated and rural areas, as well as in developing countries, contain high concentrations of total coliforms (these are used to measure the overall quality of water) and of E. coli. Water from the rural Guavate River in Cayey, Puerto Rico, was tested to see overall quality and how effective can SODIS be in disinfecting the obtained water from any E. coli. It was hypothesized that direct sunlight (UV rays) was the cause of the disinfection process of SODIS and not the temperature accumulated from the direct exposure to sunlight. After many variables and several tests, results showed that a slightly higher temperature caused by sunlight had little or no effect in the disinfection process; furthermore it was insinuated that temperature actually created a suitable environment for the bacteria to repopulate. The hypothesis was proved and it was determined that UV rays did most of the disinfection process of SODIS. <br />_____________________________________________________________________________________<br />Introduction:<br />SODIS is a method for water disinfection using nothing but PET bottles and sunlight. SODIS stands for Solar Water Disinfection. This method was first publically used in Switzerland. A worldwide problem, especially for developing countries, is the access to potable water on a constant basis. Most developing countries don’t have a developed aqueduct system nor have the access to a source of potable, or at least clean, water. A SODIS experiment was conducted on the UPR-Cayey Campus and dealt with the problem of finding a clean source of water or to at least disinfect water from a nearby stream or river. Water was collected from the nearby Guavate River. It was known that this river has a high concentration of total coliforms and E. coli concentration in its waters. E. coli and total coliforms are used as a measuring standard to verify how contaminated that source of water is, this measuring system of total coliforms was established by the EPA around 1989 (EPA, 2010). E. coli is very common bacteria found in the human body and in most bodies of water. At low concentration most E. coli are harmless, but in high concentrations they can cause adverse health effects. A Colilert test was used to determine the concentration of total coliforms and E. coli. Colilert is a product from Idexx© which is used to detect total coliforms and E. coli on water samples as a measure of water quality (Idexx Laboratories, 2011). Experiments performed in Haiti proved that during a one day period of normal sunlight, about 52% bacterial inactivation was observed (Oates, 2002). With SODIS not only can drinkable water be obtained in times of emergency (after an earthquake, hurricane) in which water supplies are cut off, but drinkable water can also be obtained for a lower price than commercially sold water. This can also serve a stepping stone for developing countries to start and continue their development healthier and with a constant source of potable and disinfected water. <br />Methodology: <br />SODIS was made with the intention of being relatively simple to do and with the minimal amount of materials. SODIS requires a minimum of six hours of direct sunlight in order to be effective in the disinfecting process. Fourteen, 12 ounce, PET bottles were used in this experiment. Around 8am the water recollecting process was done at the Guavate River. Eight of these bottles were covered in aluminum foil to create one of the variable groups. This aluminum foil group was used to test if it was UV rays or heat that made the SODIS process effective. The control group was never exposed to sunlight nor heat and these two bottles where maintained in ice for the total length of the experiment. The six remaining bottles were left unprotected and maintained in ceiling receiving sunlight. Every two hours two bottles were taken off the ceiling and put into ice. One of these two bottles that were removed every two hours was from the aluminum foil variable group and an unprotected bottle. This was performed every two hours until 5pm. A total of three removal stages were done. After all the removals, a colilert test was started. After all the bottled samples were put in the colilert test strips, the strips were put in an incubator at 35°C for twenty-four hours. After the twenty-four hour incubation, the strips were taken out and examined under a blue UV light. <br />Figure 1 shows the usual setup for water bottles and the water thermometer. <br />Results and Observations:<br />The experiment finished with surprising results. The two control groups had a total amount of total coliforms and very high concentrations of E. coli. All the bottles which were wrapped in aluminum foil, regardless of how much time they spent under direct sunlight, had little or no disinfection at all. Out of all the other bottles, which had no aluminum foil and were left for various hours under sunlight, only one showed significant disinfection when compared to the rest of the bottles. It can be deducted that it is UV rays the real disinfectors in the SODIS process. It was even observed that the water bottles covered in aluminum foil were over-saturated; implying that the temperature created under these conditions actually favored a repopulation of the E. coli bacteria in those water samples. <br />Graph 1 shows how water disinfection varied from water removed from sunlight at various hours.<br />Water removed later on during the day showed greater disinfection, this implies that the longer the water receives direct sunlight, more disinfection will occur. The experiment was not conducted to its full potential due to weather problems. SODIS requires a minimum of six hours of constant and direct sunlight. During the day of experiment the bottles received approximately two hours of direct sunlight since the weather turned rainy and cloudy. It is possible that if the experiment would be conducted in direct sunlight or if the bottles were left for six to eight more hours sitting outside, then maybe the disinfection would’ve been higher. <br />Conclusion:<br />SODIS has the potential to be an affordable and accessible method for water disinfection. The SODIS method is especially useful in developing countries that don’t have easy access to potable and clean water. This method can also be useful after a natural disaster when it is common for aqueducts to stop functioning for an undetermined time. SODIS is a very easy water disinfection method and this experiment proved that water can be disinfected by using the SODIS method. It was also determined that our hypothesis (UV rays are the source of disinfection in SODIS and not temperature) was proven by showing the difference between a bottle covered with aluminum foil (which reflected UV rays away from the bottle) and an uncovered bottle (which absorbed all the UV rays), that showed that the covered bottle had no disinfection whatsoever and most likely even had a repopulation of bacteria due to an adequate temperature for bacteria to grow, while the uncovered bottle showed significant disinfection when compared to the covered bottles. SODIS is well on its way to become a global water treatment process (Sommer, 1997).<br />Bibliography:<br /><ul><li>EPA. "Total Coliform Rule (TCR) | Total Coliform Rule | US EPA." Index | Water | US EPA. EPA, 13 Aug. 2010. Web. 12 May 2011. <>.
  2. 2. Laboratories, Idexx. "Collilert Idexx." 2011. Web. <http://>.
  3. 3. Oates, Peter M. "Solar Disinfection (SODIS): Simulation of Solar Radiation for Global Assessment and Application for Point-of-use Water Treatment in Haiti." ScienceDirect. 29 Oct. 2002. Web. 12 May 2011. <http://>.
  4. 4. Sommer, B. "SODIS: an Emerging Water Treatment Process." 1997. Web. 12 May 2011. <>.