Typical Fixed-Bed Carbon Adsorption System
Liquid phase carbon adsorption is a full-scale technology in which ground
water is pumped through one or more vessels containing activated carbon to which dissolved
organic contaminants adsorb. When the concentration of contaminants in the effluent from
the bed exceeds a certain level, the carbon can be regenerated in place; removed and
regenerated at an off-site facility; or removed and disposed. Carbon used for explosives-
or metals-contaminated ground water probably cannot be regenerated and should be removed
and properly disposed. Adsorption by activated carbon has a long history of use in
treating municipal, industrial, and hazardous wastes.
The two most common reactor
configurations for carbon adsorption systems are the fixed bed (see figure) and the pulsed
or moving bed. The fixed-bed configuration is the most widely used for adsorption from
liquids. Pretreatment for removal of suspended solids from streams to be treated is an
important design consideration. If not removed suspended solids in a liquid stream may
accumulate in the column, causing an increase in pressure drop. When the pressure drop
becomes too high, the accumulated solids must be removed, for example, by backwashing. The
solids removal process necessitates adsorber downtime and may result in carbon loss and
disruption of the mass transfer zone.
Modification of GAC, such as silicone impregnated carbon, could increase removal
efficiency and extend the length of operation. It may also be safer to regenerate.
The duration of GAC is usually short-term; however, if concentrations are low enough,
the duration may be long-term. The duration of operation and maintenance is dependent on
contaminant type, concentration, and volume; regulatory cleanup requirements; and metal
Activated carbon; Carbon filtration.
DSERTS Code: F20 (Carbon Absorption)
The target contaminant groups for carbon adsorption are hydrocarbons,
SVOCs and explosives. Limited effectiveness may be achieved on halogenated VOCs and
pesticides. Liquid phase carbon adsorption is effective for removing contaminants at low
concentrations (less than 10 mg/L) from water at nearly any flow rate, and for removing
higher concentrations of contaminants from water at low flow rates (typically 2 to 4
liters per minute or 0.5 to 1 gpm). Carbon adsorption is particularly effective for
polishing water discharges from other remedial technologies to attain regulatory
compliance. Carbon adsorption systems can be deployed rapidly, and contaminant removal
efficiencies are high. Logistic and economic disadvantages arise from the need to
transport and decontaminate spent carbon.
The following factors may limit the applicability and effectiveness of the
- The presence of multiple contaminants can impact process performance. Single component
isotherms may not be applicable for mixtures. Bench tests may be conducted to estimate
carbon usage for mixtures.
- Streams with high suspended solids (> 50 mg/L) and oil and grease (> 10 mg/L) may
cause fouling of the carbon and may require frequent treatment. In such cases,
pretreatment is generally required.
- Costs are high if used as the primary treatment on wastestreams with high contaminant
- Type, pore size, and quality of the carbon, as well as the operating temperature, will
impact process performance. Vendor expertise for carbon selection should be consulted.
- Carbon used for explosives- or metals-contaminated ground water is not regenerated.
- Highly Water-soluble compounds and small molecules are not adsorbed well.
- All spent carbon eventually need to be properly disposed.
A detailed discussion of these data elements is provided in Subsection 2.2.2 (Data Requirements for Ground Water,
Surface Water, and Leachate).
The major design variables for liquid phase carbon
applications are empty bed contact time (EBCT), usage rate, and system configuration.
Particle size and hydraulic loading are often chosen to minimize pressure drop and reduce
or eliminate backwashing. System configuration and EBCT have an impact on carbon usage
rate. When the bed life is longer than 6 months and the treatment objective is stringent
(ratio of effluent concentration,Ce, to influent concentration, Co,
<0.05), a combination of single beds operating in parallel is preferred. For a single
adsorber, the EBCT is normally chosen to be large enough to minimize carbon usage rate.
When less stringent objectives are required (Ce/Co<0.3), blending
of effluents from partially saturated adsorbers can be used to reduce carbon replacement
rate. When stringent treatment objectives are required (Ce/Co<0.05)
and bed life is short (less than 6 months), multiple beds in series may be used to
decrease carbon usage rate.
Adsorption by activated carbon has a long history of use as a treatment
for municipal, industrial, and hazardous wastestreams. The concepts, theory, and
engineering aspects of the technology are well developed. It is a proven technology with
documented performance data. Carbon adsorption is a relatively nonspecific adsorbent and
is effective for removing many organic, explosive, and some inorganic contaminants from
liquid and gaseous streams.
Costs associated with GAC are dependent on wastestream flow rates, type of
contaminant, concentration of contaminant, mass loading, required effluent concentration,
and site and timing requirements. Costs are lower with lower concentration levels of a
contaminant of a given type. Costs are also lower at higher flow rates. At flow rates of
0.4 million liters per day (0.1 mgd), costs increase to $0.32 to $1.70 per 1,000 liters
($1.20 to $6.30 per 1,000 gallons) treated.
Additional cost information can
be found in the Hazardous, Toxic, and Radioactive Wastes (HTRW) Historical Cost Analysis
System (HCAS) developed by Environmental Historical Cost Committee of Interagency Cost
Technologies: Field Scale Demonstration Project in North America, 2nd
of Remediation Case Studies, Volume 4, June 2000, EPA
Guide to Documenting and
Managing Cost and Performance Information for Remediation Projects - Revised
Version, October, 1998, EPA 542-B-98-007
1994. Technology Application Analysis: Petroleum Product Recovery and
Contaminated Groundwater Remediation Amoco Petroleum Pipeline Constantine, MI, prepared
by Stone & Webster Environmental Technology & Services.
1994. Technology Application Analysis: Recovery of Free Petroleum ProductFort
Drum, Fuel Dispensing Area 1595 Watertown, New York, prepared by Stone &
Webster Environmental Technology & Services.
EPA, 1986. Mobile Treatment Technologies for Superfund Wastes,
EPA, 1990. Innovative and Alternative Technology Assessment Manual,
EPA, Office of Water Program Operations, EPA/430/9-78/009.
EPA, 1993. Approaches for the Remediation of Federal Facility Sites
Contaminated with Explosive or Radioactive Wastes, EPA/625/R-93/013.
Federal Remediation Technologies Roundtable, 1995. Remediation
Case Studies: Groundwater Treatment, EPA/542/R-95/003.
Zappi, M.E., B.C. Fleming, and C.L. Teetar, 1992. "Draft - Treatability of
Contaminated Groundwater from the Lang Superfund Site", USAE-WES.
Zappi, M.E., C.L. Teeter, B.C. Fleming, and N.R. Francingues, 1991. "Treatability
of Ninth Avenue Superfund Site Groundwater", WES Report EL-91-8.
- Verona Wellfield Battle Creek, MI
- U.S. Coast Guard Traverse City, MI
- Love Canal Niagara Falls, NY
- Milan AAP Milan, TN
- Fort Drum, Watertown, NY
Petroleum Pipeline, Constantine, MI
- Commencement Bay, South Tacoma Channel (Well 12A), Phase 2, Tacoma, WA
Drum, Fuel Dispensing Area 1595, Watertown, NY
Points of Contact:
General FRTR Agency Contacts
Technology Specific Web Sites:
Government Web Sites
A list of vendors offering
Ex Situ Physical/Chemical Water Treatment is available from EPA
REACH IT which combines information from three established EPA databases,
the Vendor Information System for Innovative Treatment Technologies (VISITT),
the Vendor Field Analytical and Characterization Technologies System (Vendor
FACTS), and the Innovative Treatment Technologies (ITT), to give users access to
comprehensive information about treatment and characterization technologies and
Health and Safety: