Liquid-Phase
Granular Activated Carbon Adsorption
Description
Liquid-phase Granular Activated Charcoal (GAC) Adsorption is
a treatment technology to remove contaminants
from groundwater.
Groundwater is pumped through one or more vessels containing GAC. The thermal
processing of carbon, often derived from ground coconut shells, creates small porous particles
with a large internal surface area. This attribute makes it activated. The
activated carbon attracts and adsorbs organic
molecules as well as certain metal and inorganic
molecules. Dissolved contaminants sorb onto the
surfaces of the activated carbon. Water is passed through the vessels
relatively quickly. When the concentration of contaminants in the water exiting
the vessels exceeds a certain level, the carbon must be replaced. Spent carbon
can be regenerated in place, removed and regenerated at an off-site facility,
or most commonly, removed and disposed.
Limitations
and Concerns
Groundwater with suspended solids or oil and grease may cause fouling of the
carbon. The chemical characteristics of the contaminants must be known prior to
implementation. In many cases pretreatment may be required to ensure the
treatment's effectiveness.
Costs are high if used as the primary treatment for groundwater with high
concentrations of contaminants. Often, GAC is phased in after a different
technology is used.
Some degradation products, such as vinyl chloride and smaller molecules, are
not sorbed well. Consequently the effluent must be monitored carefully.
All spent carbon eventually needs to be disposed in landfills or
regenerated. There are few regeneration facilities. Although activated carbon
is a well-established technology for removing organic compounds, its use in the
removal of inorganic contaminants has not been as widespread due to its low
capacity as well as the difficulty of regeneration and cost of disposal. Also,
the presence of iron may promote fouling of the carbon.
Most regeneration systems release sorbed contamination to the air. There is
a concern by many communities that GAC, while removing contamination from the
groundwater (or air in a vapor phase system), spreads the contamination to
other areas. In the Western U.S., one regeneration facility is located on an
Indian reservation.
Carbon used for some contaminants (e.g., explosives or metals) may not be
regenerated.
If used to remove radioactive contamination from groundwater, GAC does not
reduce radio-toxicity. In cases where the GAC is used to remove both
radionuclides and VOCs, the GAC may become mixed waste that will be
difficult to dispose.
Applicability
This technology is used to treat groundwater contaminated with VOCs, metals,
and explosives. GAC can also be used to treat certain radionuclides such as
uranium, cobalt-60, and ruthenium-106.
Technology
Development Status
The technology is well proven, and it is frequently included in remedial
designs. Innovations in regenerating GAC contaminated with high explosive
compounds are in the research phase.
Web Links
http://clu-in.org/download/citizens/activatedcarbon.pdf
http://www.frtr.gov/matrix2/section4/4-47.html
Other
Resources and Demonstrations
See the related descriptions of Vapor Phase GAC
and Sorption.
See Coupled Chemical and Biological Systems for Regenerating Activated
Carbon Contaminated with High Explosives,
Knezovich et al., 1996, UCRL-ID-103483-95.
See http://140.194.76.129/publications/design-guides/dg1110-1-2/entire.pdf
for ÒEngineer and Design: Adsorption Design GuideÓ (DG 1110-1-2), published by
the U.S. Army Corps of Engineers, March 2001. It provides practical guidance
for the design of liquid and vapor phase devices for the adsorption of organic
chemicals. The adsorptive media addressed include granular activated carbon
(GAC) and other alternative adsorption carbon media, such as powdered activated
carbon (PAC) and non-carbon adsorbents.