- Carbon filtering
Carbon filtering is a method of filtering that uses a piece of
activated carbonto remove contaminants and impurities, utilizing chemical adsorption. Each piece of carbon is designed to provide a large section of surface area, in order to allow contaminants the most possible exposure to the filter media. One pound (454g) of activated carbon contains a surface area of approximately 100 acres. [cite book
title=Design of Remediation Systems
author=Jimmy Wong, Chin Hong Lim, Greg L. Nolen
accessdate=2008-09-05] This carbon is generally activated with a positive charge and is designed to attract negatively charged water contaminants. Carbon filtering is commonly used for
water purification, but is also used in air purifiers.
Carbon filters are most effective at removing
chlorine, sediment, and volatile organic compounds(VOCs) from water. They are not effective at removing minerals, salts, and dissolved inorganic compounds.
Typical particle sizes that can be removed by carbon filters range from 0.5 to 50
micrometres. The particle size will be used as part of the filter description. The efficacy of a carbon filter is also based upon the flow rate regulation. As water is allowed to flow through the filter more slowly, the longer contaminants are exposed to the filter media.
Types of carbon filters
There are two predominant types of carbon filters used in the filtration industry: powdered block filters and granular activated filters. In general, carbon block filters are more effective at removing a larger number of contaminants, based upon the increased surface area of carbon. Many carbon filters also use secondary media, such as
silveror KDF-55, to prevent bacteriagrowth within the filter.
History of carbon filters
Carbon filters have been used for several hundred years and are considered one of the oldest means of water purification. Historians have shown evidence that carbon filtration may have been used in ancient Egyptian cultures for both air and water sanitization.Fact|date=February 2007 2000 B.C. Sanskrit text refers to filtering water through charcoal (1905 translation of "Sushruta Samhita" by Francis Evelyn Place).Fact|date=September 2008 The first modern use of a carbon filter to purify
potablewater occurred in 1862.Fact|date=September 2008 Carbon filtration was further advanced in the mid 1970's when carbon powder was first manufactured into a porous block form for drinking water use.Fact|date=September 2008
Currently, carbon filters are used in individual homes as point-of-use
water filtersand, occasionally, in municipal water treatment facilities. They are also used as pre-treatment devices for reverse osmosissystems and as specialized filters designed to remove chlorine-resistant cysts, such as giardiaand cryptosporidium.
For small scale production of hydrogen water purifiers are installed to prevent formation of minerals on the surface of the electrodes and to remove organics and chlorine from utility water. First the water passes through a 20 micrometer interference (
meshor screen filter) filter to remove sand and dust particles, second, a charcoal filter ( activated carbon) to remove organics and chlorine, third stage, a de-ionizing filter to remove metallic ions.Fact|date=September 2008 A test can be done before and after the filter for proper functioning on barium, calcium, potassium, magnesium, sodiumand silicon.
Nuclear / Nuclear Medicine
Carbon filters are widely used on
hot cellsin conjunction with HEPA filters.Fact|date=September 2008 This allows expulsion of the extracted air into the atmosphere as all particles (or at least 99.99999%) along with any radioactivity, have been removed.
* [http://www.historyofwaterfilters.com/ Water filtration history] A guide to the history of water filters and current water treatment issues.
* [http://www.allaboutwater.org/ Water facts and information] Discusses water treatment alternatives and bottled water quality.
* [http://www.waterfilters.net/water-university/choose-water-filter.htm Common Carbon Water Filters] Describes various carbon filters and which contaminants they remove.
* [http://www.activecarbonfilters.com/Activecarbon/index.htm Active Carbon Filters Ltd.] Activated Carbon filter manufacturer.
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