Carbon has long been used to absorb pollutants and is probably the most powerful absorber known to man! A pound of activated carbon has a total of 125 acres of surface area (!) and can actually absorb thousands of different chemicals. Activated carbon is carbon that is slightly more electropositive, which makes it even better at trapping pollutants and chemicals. Contaminants in the water flowing through the positively charged activated carbon are attracted to its surface.
Activated carbon filters that are used for residential purposes generally contain granular activated carbon or powdered activated carbon blocks. Although both are effective, the activated carbon blocks have a higher removal rate of contaminants from water. The two most important facts affecting effectiveness of activated carbon are the amount of carbon in a filtration device and the amount of time the filtered water spends in contact with the carbon. The more carbon, the better. Similarly, the lower the water flow through the filter, the longer impurities will be in contact with the carbon, resulting in a higher absorption rate. The particle size also affects the contaminant removal rate.
Activated carbon filters are typically rated by the size of particles they are able to trap. This size is measured in microns and generally ranges from 50 microns (less effective) down to 0.5 microns (most effective). A typical faucet filter or undercounter system contains between 350 and 700 grams of activated carbon. The most common types of carbon used in water filtration are coal, charcoal and coconut shell charcoal. The latter is generally about 20% more expensive than the others, but it is considered the most effective of the three.
There are two primary methods that carbon removes contaminants: absorption and catalytic reduction, a process by which negatively charged contaminant ions are attracted to the positively charged activated carbon. Organic compounds are removed by absorption while sedimentary disinfectants such as chlorine and chloramines are removed by catalytic reduction.
Activated carbon filtration is very widely used, especially in home water filtration systems. A carbon filter can be used alone to remove unpleasant taste and odor from municipal water (which is pre-treated and chlorinated), resulting in much better quality water. It is also used to pre-treat water as a part of a reverse osmosis system (which will be discussed next).
Activated carbon filters remove or reduce concentration of many volatile organic compounds, pesticides and herbicides as well as chlorine, benzene, trihalogen methane compounds, radon, solvents and hundreds of other man-made chemicals that may be found in tap water. Some activated carbon filters are moderately effective at removing some, but not all heavy metals. Additionally, the highly compressed carbon blocks in water filters remove particles as small as 0.5 microns, including Giardia or Cryptosporidium cysts, turbidity and pollen.
Carbon filters are not effective in removing dissolved inorganic contaminants or metals such as salts or minerals (contaminants that cause sediment or water hardness), antimony, arsenic, asbestos, barium, beryllium, cadmium, chromium, copper, fluorine, mercury, nickel, nitrates and nitrites, selenium, sulfates, thallium, or certain nuclides. The removal of these contaminants requires a reverse osmosis filter or distillation.
Activated carbon does not remove sediment or dust very effectively, which is why it is often preceded in a filtration system by a sediment pre-filter. Sediment pre-filters further extend the life of an activated carbon cartridge by trapping particles that would otherwise clog the carbon filter, reducing its filtering surface and absorption capacity.
- Myth 7: Reverse Osmosis Is Too Expensive
- Myth 6: Reverse Osmosis Wastes a lot of Water
- Myth 5: Reverse Osmosis generates very acidic water with low pH
- Myth 4: Reverse Osmosis Sucks Minerals Out of Body
- Myth 3: Reverse Osmosis Removes Healthy Minerals From Water
- Myth 2: Reverse Osmosis is a NASA technology.
- Myth 1: Reverse Osmosis Produces Unhealthy Water