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408 Lawrence K.Wang et al.

Table 4
Applicability of CAS Selected Contaminants
CAS
typically
Contaminant class Examples effective Comments
Aromatics Benzene, toluene Yes Standard application of GAC
Aliphatics Hexane, heptane Yes Standard application of GAC
Halogenated hydrocarbons Chloroform Yes Standard application of GAC
Light hydrocarbons Methane, Freon No Will not adsorb
(MW < 50 or BP <20ºC)
Heavy hydrocarbons Glycols, phenols No a Will not desorb or will not be
(MW > 200 or BP >200ºC) adsorbed due to steric
constraints
Oxygenated compounds Ketones, aldehydes No b Fire hazard
Certain reactive organics 1,1,1-Trichloroethane, No Will react with and degrade GAC
organic acid
Bacteria Coliform Yes Requires silver-impregnated GAC
Radioisotopes 131 I Yes Requires coconut-shell carbon
Certain inorganics Hydrogen sulfide, Yes Requires impregnated GAC
ammonia,
hydrochloric acid
Mercury — Yes c Requires impregnated GAC
a Nonregenerable carbon systems may work.
b Not all oxygenated compounds are a problem.
c High levels of sulfur dioxide may blind the charcoal and reduce Hg removal efficiencies.
Source: US EPA.

capacity. Some problems the emissions stream may pose for the GAC system are plug-
ging, fouling, and corroding the system. However, these problems can be overcome
with pretreatment devices, which will increase the total system cost.
Some of carbon adsorption technology limitations can be alleviated with pretreatment.
The emission stream prior to carbon adsorption system should have low solids and par-
ticulates to prevent fouling and plugging of the system. The emission stream should
contain less than 1000 ppmv inorganics. Particulate filter can be used to lower levels in
the emission stream prior to adsorption system. Relative humidity of emission stream prior
to carbon adsorption system should be below 50%. As relative humidity in the emission
stream rises above 50%, the efficiency of VOC adsorption decreases rapidly. By increas-
ing the temperature of the emission stream, the relative humidity of the stream can be
lowered, but this can affect the removal efficiency. At a moderate temperature range from
100ºF to 130ºF, VOC adsorption occurs readily on carbon.
Table 4 summarizes the effectiveness of the carbon adsorption system (CAS) for
various classes of compound, and Table 5 provides the adsorption capacities of carbon
for some HAPs. Also, adsorption capacities of carbon can be calculated as a function of
temperature and inlet concentration. Additionally, it is known that CAS is very effective
for radon gas reduction (15, 21), but at this time, GAC’s adsorption capacity for radon
gas reduction is unknown.