Activated carbon is made from any substance with
a high carbon content, and activation refers to the
development of the property of adsorption.
Activated carbon is important in purification
processes, in which molecules of various contaminants
are concentrated on and adhere to the solid
surface of the carbon. Through physical adsorption,
activated carbon removes taste and odorcausing
organic compounds, volatile organic compounds,
and many organic compounds that do not
undergo biological degradation from the atmosphere
and from water, including potable supplies,
process streams, and waste streams. The action can
be compared to precipitation. Activated carbon is
generally nonpolar, and because of this it adsorbs
other nonpolar, mainly organic, substances.
Extensive porosity (pore volume) and large available
internal surface area of the pores are responsible
for adsorption.
Processes used to produce activated carbons
with defined properties became available only after
1900. Steam activation was patented by R. von
Ostreijko in Britain, France, Germany, and the
U.S. from 1900 to 1903. When made from wood,
the activated carbon product was called Eponite
(1909); when made from peat, it was called Norit
(1911). Activated carbon processes began in
Holland, Germany, and the U.S., and the products
were in all cases a powdered form of activated
carbon mainly used for decolorizing sugar solutions.
This remained an important use, requiring
some 1800 tons each year, into the twenty-first
century.
In the U.S., coconut char activated by steam
was developed for use in gas masks during World
War I. The advantage of using coconut shell was
that it was a waste product that could be converted
to charcoal in primitive kilns at little cost. By 1923,
activated carbon was available from black ash,
paper pulp waste residue, and lignite. In 1919, the
U.S. Public Health Service conducted experiments
on filtration of surface water contaminated with
industrial waste through activated carbon. At first,
cost considerations militated against the widespread
use of activated carbon for water treatment.
It was employed at some British works before
1930, and at Hackensack in New Jersey. From that
time there was an interest in the application of
granular activated carbon in water treatment, and
its subsequent use for this purpose grew rapidly. As
improved forms became available, activated carbon
often replaced sand in water treatment where
potable supplies were required.
Coal-based processes for high-grade adsorbent
required for use in gas masks originally involved
prior pulverization and briquetting under pressure,
followed by carbonization, and activation. The
process was simplified after 1933 when the British
Fuel Research Station in East Greenwich, at the
request of the Chemical Research Defence
Establishment, began experiments on direct production
from coke activated by steam at elevated
temperatures. In 1940, Pittsburgh Coke & Iron
Company, developed a process for producing
granular activated carbon from bituminous coal
for use in military gas masks. During World War
II, this replaced the coconut char previously
obtained from India and the Philippines. The
large surface area created by the pores and its
mechanical hardness made this new material
particularly useful in continuous decolorization
processes. The Pittsburgh processes developed by
the Pittsburgh Activated Carbon Company were
acquired in 1965 by the Calgon Company. In late
twentieth century processes, carbon was crushed,
mixed with binder, sized and processed in lowtemperature
bakers, and subjected to high temperatures
in furnaces where the pore structure of
the carbon is developed. The activation process can
be adjusted to create pores of the required size for a
particular application. Activation normally takes
place at 800–900_C with steam or carbon dioxide.
Powdered activated carbon is suitable for liquid
and flue gas applications—the granulated form for
the liquid and gas phases, and pelleted activated
carbon for the gas phase. Granulated activated
carbon is used as a filter medium for contaminated
water or air, while the powdered form is mixed into
wastewater where it adsorbs the contaminants and
is later filtered or settled from the mixture.
Activated carbon has also been used in chemical
analysis for prior removal and concentration of
contaminants in water. Trade names for activated
carbon used in these processes are Nuchar and
Darco.
Activated carbon has been used in the largescale
treatment of liquid waste, of which the
effluent from the synthetic dye industry is a good
example. Synthetic dye manufacture involves reactions
of aromatic chemicals, and the reactants and
products are sometimes toxic. In addition to an
unpleasant taste and odor imparted to water, this
waste is also highly colored, complex, and invariably
very difficult to degrade. Fortunately, many of
the refractory aromatic compounds are nonpolar,
the property that permits adsorption onto activated
carbon. In the 1970s, three large dye-making
works in New Jersey used activated carbon to
remove aromatics and even trace metals such as
toxic lead and cadmium from liquid waste. In two
cases, powdered activated carbon was added to the
activated sludge treatment process to enhance
removal of contaminants. In a third case, following
biological treatment, the liquid effluent was
adsorbed during upward passage in towers packed
with granular activated carbon. The spent carbon
from this continuous process was regenerated in a
furnace, and at the same time the adsorbed waste
solute was destroyed.
In 1962, Calgon utilized activated granular
carbon for treating drinking water, and at the
end of the twentieth century, municipal water
purification had become the largest market for
activated carbon. The older methods that involved
disposal of spent carbon after use were replaced by
the continuous processes using granulated activated
carbon. By continuous reuse of the regenerated
activated carbon, the process is ecologically
more desirable. Apart from the inability to remove
soluble contaminants (since they are polar) and the
need for low concentrations of both organic and
inorganic contaminants, the cost of the carbon is
the greatest limitation in the continuous process.
Activated carbon also found wide application in
the pharmaceutical, alcoholic beverage, and electroplating
industries; in the removal of pesticides
and waste of pesticide manufacture; for treatment
of wastewater from petroleum refineries and textile
factories; and for remediation of polluted groundwater.
Although activated carbons are manufactured
for specific uses, it is difficult to characterize
them quantitatively. As a result, laboratory trials
and pilot plant experiments on a specific waste type
normally precede installation of activated carbon
facilities.
