Vapor-Phase Granular Activated Carbon Adsorption
Vapor-phase Granular Activated Charcoal (GAC) is a treatment technology that removes contaminants from air. Contaminated air is passed through one or more vessels containing GAC. Contaminants sorb onto the surfaces of the activated carbon grains. The thermal processing of carbon, often from coconut shells, creates small porous particles with a large internal surface area. This processing activates the carbon. The activated carbon attracts and adsorbs organic molecules as well as certain metal and inorganic molecules. When the concentration of contaminants in the vapor 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
Some degradation products such as vinyl chloride and smaller molecules are not sorbed well, and consequently must be monitored carefully.
All spent carbon eventually needs to be disposed in landfills or regenerated. There are few regeneration facilities.
Most regeneration systems release the sorbed contamination to the air. There is a concern by many communities that GAC, while removing contamination from the air (or water in a liquid-phase system), spreads the contamination to other areas. In the Western U.S., one regeneration facility is located on an Indian reservation.
The carbon used for some contaminants (e.g., metals) can not be regenerated.
Spent carbon transport may require hazardous waste handling.
Relative humidity greater than 50% can reduce carbon capacity
Elevated temperatures from soil vapor extraction (SVE) pumps (greater than 38° C or 100° F) inhibit adsorption capacity.
Some compounds, such as ketones, may cause carbon bed fires because they release heat upon adsorption.
Technology Development Status
The technology is well proven, and it is frequently part of remedial designs.
Other Resources and Demonstrations
See “Engineering and Design: Adsorption Design Guide” (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 and other alternative adsorption carbon media, such as powdered activated carbon (PAC) and non-carbon adsorbents.