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Activated Alumina Activated alumina is a filter media made by treating aluminum ore so that it becomes porous and highly adsorptive. Activated alumina will remove a variety of contaminants including excessive fluoride, arsenic and selenium. The medium requires periodic cleaning with an appropriate regenerate such as alum or acid in order to remain effective. Activated Carbon (Granular or Solid Block) Granular activated carbon is a well established technology for the reduction of a wide range of aesthetic contaminants and is quite effective in the reduction of some health contaminants such as volatile organic compounds (benzene, trichloroethylene, and other "petroleum" based contaminants. Because of its molecular make-up, activated carbon can adsorb well, meaning it can take in or collect many organic molecules on its surface. Granular activated carbon filters are typically inexpensive and maintenance involves replacing six to twelve filter cartridges a year depending on the filter media and quality of the raw water. Specially designed solid block and precoat activated carbon filters are also available which are effective at reducing heavy metals such as lead and mercury. Solid block filters with a pore size smaller than 0.2 microns are often effective against biological contaminants as well. Anion exchange and cation exchange use the chemical ion exchange process to exchange anions or cations on a "resin" bed for cations or anions of the contaminant that needs to be removed from the water. For example, in cation exchange, a cation of a hardness mineral such as sodium, effectively removing most of the calcuim and softening the water. The anions or cations on the resin are eventually exhausted and replaced by the anions or cations of the contaminant being removed. When this occurs, the bed must be backwashed using a concentrated solution of the base cation or anion which recharges the bed and flushes the built-up contaminant. Anion exchange typically uses chloride or hydroxide anions and can be used to treat for mercury, nitrates, arsenic, and various staining agents. Ion exchange typically uses sodium or potassium chloride, and can also treat for some forms of lead and radium. It is also commonly used to soften water. Disinfection technologies kill or screen out biological contaminants present in a water supply. Chlorination, microfiltration, ozone and ultraviolet are the four major technologies used to disinfect water. Chlorination adds a concentration of the chemical chlorine or chloramine to a water supply where the oxidizing ability of this chemical "burns up" the organic contaminants in the water. Chlorine can effectively treat biological pathogens like coliform bacteria, legionella, and giardia, though it is ineffective against hard-shelled cysts like cryptosporidium. Chlorination also treats for organic related taste, color and odor problem. Chlorine is typically fed directly into a well or into a retention tank where concentration and contact time can be controlled. Chlorination is effective for treating pathogens like coliform bacteria and legionella, but the contact times and concentrations are usually too great for it to be used to treat hard-shelled cysts like cryptosporidium and giardia. Other chemicals like bromine and iodine can also be used to disinfect water through much the same process as chlorination, though they are not as frequently used. Microfiltration uses a filter media with a pore size smaller than 0.2 microns to physically prevent biological contaminants from passing through. Ceramic and solid block carbon are commonly used to provide microfiltration. Ceramic filters have an advantage in that they can often be cleaned and reused a number of times before they loose effectiveness. Carbon block media usually has to be disposed of after each use, however, this media provides additional treatment for a variety of other health and aesthetic contaminants (see activated carbon section). Microfiltration is effective for treating the full range of biological contaminants including hard-shelled cysts like cryptosporidium. Ozone treatment has typically been used in large-scale commercial and industrial applications, however, there has been a recent growth in the number of ozone units designed for use in a single home or business. Ozone treatment oxidizes organic contaminants in much the same way that chlorine does. An ozone generator converts the oxygen found in air into O3 or ozone. As with chlorination, proper concentrations and contact time is essential for disinfection. Ozone usually requires the use of a retention tank to accomplish this and can be used to provide partial treatment in pools. Ozone is effective for treating pathogens like coliform bacteria and legionella, though it is not as effective against hard-shelled cysts like cryptosporidium and giardia without using high concentrations and contact times. Ultraviolet (UV) light has treated water since the beginning of time through natural sunlight. Modern ultraviolet treatment units use a UV bulb in a clear quartz or Plexiglas housing around which passes the untreated water. The UV light kills the nucleus of pathogens like coliform bacteria and legionella which effectively neutralizes them by preventing them from reproducing. UV is not effective for the treatment of hard-shelled cysts like cryptosporidium and giardia. Distillation produces high quality, treated water by heating it until it turns into steam. The steam travels through a condensation coil where it is cooled and condensed back into liquid form in a separate section. Typically, the contaminants present when the water is converted into steam remain in the boiler section with the condensed water in the second section being substantially free of contaminants. Maintenance of a distillation unit usually involves cleaning out the built-up contaminants on the boiler side of the unit. Distillation typically provides a high degree of effectiveness against a broad range of health contaminants. Distillation is typically not effective for treating contaminants such as benzene and radon which give off harmful vapors that can move through the system with the steam. The energy requirement of distillation and a relatively long production time typically limits its use as to POU drinking water applications in the home and commercial markets. Some distillation units are also tested and approved for the reduction of biological pathogens. Reverse Osmosis (RO) is a common treatment technology that produces high quality water. The process works by forcing water under great pressure against a semi-permeable membrane, where ion exclusion occurs. With ion exclusion, water molecules form a barrier that allows other water molecules to pass through while excluding most contaminants. Typical contaminant rejection rates range from 85 percent to greater than 95 percent, and a gallon of highly treated water can usually be produced from two to four gallons of raw water depending on the initial quality of the water. Maintenance involves the replacement of the RO membrane cartridge every two or three years and the carbon filter cartridges six to twelve times per year. RO is effective for the reduction of a broad range of health and aesthetic contaminants, though it is typically not used for the reduction of biological pathogens. RO also incorporates an activated carbon filter which can provide added treatment for the VOCs not treated by the membrane itself. |