330charged 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
micrometers. 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. When the water is allowed to
flow through the filter at a slower rate, the contaminants are exposed to the filter media for
a longer amount of time.
In certain regions, the treatment of the water intended for potable purposes is not
necessary throughout the whole of the year. The presence of taste, odor and toxins is
dependent largely on the biological action in areas where lake or reservoir supply is
common. It is therefore often more cost-effective to use temporary or intermittent dosing
of activated carbon into the water only during times when treatment is required. During
these times, the use of Powdered Activated Carbon (PAC) is preferred as no costly fixed
bed filtration equipment is required. The PAC can be dosed directly to existing flocculent
tanks at a prescribed rate to achieve the level of removal of taste, odor and toxins as
required.
Following dosing of PAC, the activated carbon is removed as part of the flocculation
process, or subsequently filtered mechanically. The water is then disinfected for supply to
the distribution network.
Nonmetals in the 'near-metalloid' category include carbon, phosphorus, selenium and
iodine. They exhibit metallic luster, semiconducting properties and bonding or valence
bands with delocalized character.
This applies to their most thermodynamically stable forms under ambient conditions:
carbon as graphite; phosphorus as black phosphorus; and selenium as grey selenium.
These elements are alternatively described as being 'near metalloidal', showing
metalloidal character, or having metalloid-like or some metalloid(al) or metallic properties.
Carbon Group
The carbon group is a periodic table group consisting of carbon (C), silicon (Si),
germanium (Ge), tin (Sn), lead (Pb), and flerovium (Fl).
In modern IUPAC notation, it is called Group 14. In the old IUPAC and CAS systems, it
was called Group IVB and Group IVA, respectively.
In the field of semiconductor physics, it is still universally called Group IV. The group was
once also known as the tetrels (from Greek tetra, four), stemming from the Roman
numeral IV in the group names, or (not coincidentally) from the fact that these elements
have four valence electrons (see below). Elements in the group are sometimes also
referred as tetragens.