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Practivistas rainwater 2014/Literature Review
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== Types of Filters == This section discusses the different filters used to clean water and the possible treatments we will consider in our examination of La Yuca. '''Carbon/Activated Carbon:''' "Activated carbon chemically bonds with and removes some contaminants in water filtered through it. Carbon filters vary greatly in effectiveness: Some just remove chlorine and improve taste and odor, while others remove a wide range of contaminants including asbestos, lead, mercury and volatile organic compounds (VOCs). However, activated carbon cannot effectively remove common "inorganic" pollutants such as arsenic, fluoride, hexavalent chromium, nitrate and perchlorate. Generally, carbon filters come in two forms, carbon block and granulated activated carbon."<ref name="nittygritty">THE NITTY GRITTY OF FILTER TYPES AND TECHNOLOGIES. (2013, February 27).. Retrieved June 8, 2014, from http://web.archive.org/web/20150120211400/http://www.ewg.org:80/report/ewgs-water-filter-buying-guide/filter-technology</ref> '''Carbon Block:''' "Carbon block filters contain pulverized activated carbon that is shaped into blocks under high pressure. They are typically more effective than granulated activated carbon filters because they have more surface area. Their effectiveness depends in part on how quickly water flows through."<ref name="nittygritty" />'''Granulated Activated Carbon:''' "These filters contain fine grains of activated carbon. They are typically less effective than carbon block filters because they have a smaller surface area of activated carbon. Their effectiveness also depends on how quickly water flows through."<ref name="nittygritty" />'''Ceramic:''' "Ceramic filters have very small holes throughout the material that block solid contaminants such as cysts and sediments. They do not remove chemical contaminants."<ref name="nittygritty" />'''Deionization:''' "These filters use an ion exchange process that removes mineral salts and other electrically charged molecules (ions) from water. The process cannot remove non-ionic contaminants (including trihalomethanes and other common volatile organic compounds) or microorganisms. EWG's water filter guide does not include any filters based on this technology."<ref name="nittygritty" />'''Distillation:''' "This technology heats water enough to vaporize it and then condenses the steam back into water. The process removes minerals, many bacteria and viruses and chemicals that have a higher boiling point than water. It cannot remove chlorine, trihalomethanes or volatile organic chemicals (VOCs). EWG's water filter guide does not include any filters based on this technology."<ref name="nittygritty" />'''Ion Exchange:''' "This technology passes water over a resin that replaces undesirable ions with others that are more desirable. One common application is water softening, which replaces calcium and magnesium with sodium. The resin must be periodically "recharged" with replacement ions."<ref name="nittygritty" />'''Mechanical Filters:''' "Like ceramic filters, these filters are riddled with small holes that remove contaminants such as cysts and sediments. They are often used in conjunction with other kinds of technologies, but sometimes are used alone. They cannot remove chemical contaminants."<ref name="nittygritty" />'''Ozone:''' "Ozone kills bacteria and other microorganisms and is often used in conjunction with other filtering technologies. It is not effective in removing chemical contaminants. EWG's water filter guide does not include any filters based on this technology."<ref name="nittygritty" />'''Reverse Osmosis:''' "This process pushes water through a semi-permeable membrane that blocks particles larger than water molecules. Reverse osmosis can remove many contaminants not removed by activated carbon, including arsenic, fluoride, hexavalent chromium, nitrates and perchlorate. However, reverse osmosis does not remove chlorine, trihalomethanes or volatile organic chemicals (VOCs). Many reverse osmosis systems include an activated carbon component than can remove these other contaminants. Quality can vary tremendously in both the membrane system and the carbon filter typically used with it. Consumers should also be aware that reverse osmosis filters use 3-to-20 times more water than they produce. Because they waste quite a bit of water, they are best used for drinking and cooking water only."<ref name="nittygritty" />'''UV (ultraviolet):''' "These systems use ultraviolet light to kill bacteria and other microorganisms. They cannot remove chemical contaminants. EWG's water filter guide does not include any filters based on this technology."<ref name="nittygritty" />Also, a note on sand filtration: "A simple household sand filter can be made wherever fine sand is available. Just remember that the water must pass through at least two feet (but preferably more) of sand and the rate of flow shouldn't exceed four gallons per square foot per hour."<ref>FILTERING WATER THROUGH SAND. Countryside & Small Stock Journal, 83. Retrieved June 9, 2014, from the EBSCO database.</ref>
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