vvEPA
United States
Environmental Protection
Agency
Office of Water
Washington, D.C.
EPA832-F-00-017
September 2000
Waste water
Technology Fact Sheet
Granular Activated Carbon Adsorption and Regeneration
DESCRIPTION
Granular activated carbon (GAC) adsorption has
been used successfully for the advanced (tertiary)
treatment of municipal and industrial wastewater.
GAC is used to adsorb the relatively small
quantities of soluble organics (See Table 1) and
inorganic compounds such as nitrogen, sulfides,
and heavy metals remaining in the wastewater
following biological or physical-chemical
treatment. Adsorption occurs when molecules
adhere to the internal walls of pores in carbon
particles produced by thermal activation.
TABLE 1 ORGANIC COMPOUNDS
AMENABLE TO ADSORPTION BY GAC
Class
Example
Aromatic solvents
Polynuclear aromatics
Chlorinated aromatics
Phenolics
Aromatic amines & high
molecular weight aliphatic
amines
Surfactants
Soluble organic dyes
Fuels
Chlorinated solvents
Aliphatic & aromatic acids
Pesticides/herbicides
Benzene, toluene, xylene
Naphthalene, biphenyl
Chlorobenzene, PCBs,
endrin, toxaphene, DDT
Phenol, cresol, resorcinol,
nitrophenols,
chlorophenols, alkyl
phenols
Aniline, toluene diamine
Alkyl benzene sulfonates
Methylene blue, textiles,
dyes
Gasoline, kerosene, oil
Carbon tetrachloride,
percholoroethylene
Tar acids, benzole acids
2,4-D, atrazine, simazine,
aldicarb, alachlor,
carbofuran
GAC systems are generally composed of carbon
contactors, virgin and spent carbon storage, carbon
transport systems, and carbon regeneration systems
(See Figure 1). The carbon contactor consists of a
lined steel column or a steel or concrete rectangular
tank in which the carbon is placed to form a "filter"
bed. A fixed bed downflow column contactor (See
Figure 2) is often used to contact wastewater with
GAC. Wastewater is applied at the top of the
column, flows downward through the carbon bed,
and is withdrawn at the bottom of the column. The
carbon is held in place with an underdrain system at
the bottom of the contactor. Provisions for
backwash and surface wash of the carbon bed are
required to prevent buildup of excessive headloss
due to accumulation of solids and to prevent the
bed surface from clogging.
SJui
_. JufryPump 7 -
Bin f Slurry
Transport Pump
Water
Transport
Wattr Mxi-
Source: U.S. EPA, 1984.
Source: WEF MOP 8, 1998.
FIGURE 1 GAC ADSORPTION
SCHEMATIC
Expanded bed and moving bed carbon contactors
have been developed to overcome problems
associated with headloss buildup experienced with
fixed bed downflow contactors. In an expanded
bed system, wastewater is introduced at the bottom
of the contactor and flows upward, expanding the
carbon bed, much as the bed expands
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during backwash of a fixed bed downflow
contactor. In the moving bed system, spent carbon
is replaced continuously so that the headloss does
not build up. Carbon contactors may be operated
under either pressure or gravity flow. The choice
between pressure and gravity flow generally
depends on the available pressure (head) within the
wastewater treatment plant and cost.
Air scour discharge
Backwash effluent
Spent carbon out
Backwash influent
Source: Tchobanoglous and Burton, 1991.
FIGURE 2 TYPICAL DOWNFLOW
CARBON CONTACTOR
All carbon contactors must be equipped with carbon
removal and loading mechanisms to allow spent
carbon to be removed and virgin or regenerated
carbon to be added. Spent, regenerated, and virgin
carbon is typically transported hydraulically by
pumping as a slurry. Carbon slurries may be
transported with water or compressed air,
centrifugal or diaphragm pumps, or eductors.
When the carbon contactor effluent quality reaches
minimum water quality standards, the spent carbon
is removed from the contactor for regeneration.
Small systems usually find regeneration of their
spent carbon at an off-site commercial reactivation
facility to be the most convenient and economical
method. In this case, the spent carbon is
hydraulically transported from the contactor to a
waiting truck. Regenerated or virgin carbon is then
hydraulically transported from a second truck or
from a separate compartment in the first truck to the
contactor, then to a commercial reactivation facility.
Generally, systems which contain at least one
million pounds of carbon find on-site regeneration
to be cost effective.
Carbon regeneration is accomplished primarily by
thermal means. Organic matter within the pores of
the carbon is oxidized and thus removed from the
carbon surface. The two most widely used
regeneration methods are rotary kiln and multiple
hearth furnaces. Approximately 5 to 10 percent of
the carbon is destroyed in the regeneration process
or lost during transport and must be replaced with
virgin carbon. The capacity of the regenerated
carbon is slightly less than that of virgin carbon.
Repeated regeneration degrades the carbon particles
until an equilibrium is eventually reached providing
predictable long term system performance. See
Figure 3 for a schematic of the carbon regeneration
process.
SPENT CARBON
FROM CARBON
COLUMNS
CARBON FINES
BACK TO
PROCESS
REGENERATED
CARBON TO CARBON
COLUMNS
Source: WEF MOP 8, 1998
FIGURE 3 REGENERATION SCHEMATIC
APPLICABILITY
Typically, GAC adsorption is utilized in wastewater
treatment as a tertiary process following
conventional secondary treatment or as one of
several unit processes composing physical-chemical
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treatment. In wastewater treatment plants utilizing
biological secondary treatment, GAC adsorption is
generally located after filtration and prior to
disinfection. When utilized in a physical-chemical
treatment process, GAC adsorption is generally
located following chemical clarification and
filtration and prior to disinfection. In addition,
GAC adsorption systems have a relatively small
footprint making them suitable for facilities with
limited land availability.
The successful application of carbon adsorption for
municipal wastewater treatment depends on the
quality and quantity of the wastewater delivered to
the adsorption system. For a carbon contactor to
perform effectively, the feed water to the unit
should be of uniform quality (suspended solids
concentrations less than 20 mg/1) and without
surges in flow. Wastewater constituents that may
adversely affect carbon adsorption include
suspended solids, BOD5, and organics such as
methylene blue active substances or phenol and
dissolved oxygen. Environmental factors that must
be considered include pH and temperature because
they may impact solubility, which affects the
adsorption properties of the wastewater components
onto carbon (WEF MOP 8, 1998).
ADVANTAGES AND DISADVANTAGES
Before deciding whether carbon
adsorption/regeneration meets the needs of a
municipality, it is important to understand the
advantages and disadvantages of both the
adsorption and regeneration process.
Advantages (Adsorption)
• For wastewater flows which contain a
significant quantity of industrial flow, GAC
adsorption is a proven, reliable technology
to remove dissolved organics.
Space requirements are low.
GAC adsorption can be easily incorporated
into an existing wastewater treatment
facility.
Advantages (Regeneration)
• Systems are reliable from a process
standpoint.
Reduces solid waste handling problems
caused by the disposal of spent carbon.
• Saves up to 50 percent of the carbon cost.
Disadvantages (Adsorption)
• Under certain conditions, granular carbon
beds may generate hydrogen sulfide from
bacterial growth, creating odors and
corrosion problems.
Spent carbon, if not regenerated, may
present a land disposal problem.
• Wet GAC is highly corrosive and abrasive.
• Requires pretreated wastewater with low
suspended solids concentration. Variations
in pH, temperature, and flow rate may also
adversely affect GAC adsorption.
Disadvantages (Regeneration)
• Air emissions from the furnace contain
volatiles stripped from the carbon. Carbon
monoxide is formed as a result of
incomplete combustion. Therefore,
afterburners and scrubbers are usually
needed to treat exhaust gases.
• The induced draft fan of a multiple hearth
furnace may produce a noise problem.
The process is most effective when operated
on a 24-hour basis, requiring around-the-
clock operator attention.
The process is subject to more mechanical
failures than other wastewater treatment
processes.
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DESIGN CRITERIA
Prior to the design of GAC systems, a pilot plant
study should be performed to determine if the
technology will meet discharge permit requirements
and to quantify optimum flow rate, bed depth, and
operating capacity on a particular wastewater. This
information is required to determine the dimensions
and number of carbon contactors required for
continuous treatment.
The sizing of carbon contactors is based on contact
time, hydraulic loading rate, carbon bed depth, and
number of contactors. The carbon contact time
typically ranges from 15 to 35 minutes depending
on the application, wastewater constituents and
desired effluent quality. Hydraulic loading rates of
4 to 10 gpm/sq.ft are typically used for upflow
carbon columns. For downflow carbon columns,
hydraulic loading rates of 3 to 5 gpm/sq.ft are used.
Carbon bed depth varies typically within a range of
10 to 40 feet depending on carbon contact time
(Tchobanoglous, 1991).
The number of contactors should be sufficient to
ensure enough carbon contact time to maintain
effluent quality while one column is off line during
removal of spent carbon or maintenance. The
normal practice is either to use two columns in
series and rotate them as they become exhausted or
to use multiple columns in parallel so that when one
column becomes exhausted, the effluent quality will
not be significantly affected (WEF MOP 8, 1998).
Regeneration facilities are typically sized based on
carbon dosage or use rate. The dosage rate depends
on the strength of the wastewater applied to the
carbon and the required effluent quality. Typical
dosage rates for filtered, secondary effluent range
from 400 to 600 Ibs/mil.gall., while typical dosage
rates for coagulated, settled and filtered raw
wastewater (physical-chemical) range from 600 to
1800 Ibs/mil.gall.
PERFORMANCE
Niagara Falls Wastewater Treatment Plant
Niagara Falls, New York
The Niagara Falls Wastewater Treatment Plant
(NFWTP) has been operating as a physical-
chemical activated carbon secondary treatment
facility since 1985. With a design average daily
flow capacity of 48 mgd, it is the largest municipal
physical-chemical activated carbon wastewater
treatment plant in operation in the United States.
The treatment process consists of chemically
assisted primary sedimentation, granular activated
carbon adsorption, oxidation, and disinfection. The
influent pH can be adjusted to compensate for
industrial discharge. The current average daily flow
is 35 mgd. Industrial flow to the plant is
approximately 17 percent of the total flow.
The activated carbon system at NFWTP includes 28
carbon beds which are 17.3 feet wide by 42 feet
long. Each carbon bed is approximately 8.5 feet in
depth and contains 180,000 pounds of carbon.
Primary effluent percolates downward by gravity
through the GAC bed. Each carbon bed provides
chemical adsorption of pollutants from the
wastewater, physical filtration of solids, and
biological degradation from the incidental
anaerobic activity that occurs within.
The carbon beds at NFWTP operate in parallel.
During dry weather, there are typically 17 carbon
beds in operation with a primary effluent
application rate of approximately 2.2 gpm/sq.ft.
During wet weather, additional beds are placed in
operation. All beds are operated at an application
rate of approximately 3gpm/sq.ft (Roll, 1996).
Backwash of the carbon beds is based on headloss.
Regeneration of the spent carbon is performed on-
site in a multiple hearth furnace. Each filter bed is
separately removed from service and emptied of
carbon. The carbon is fed to the furnace at a rate of
about 2,000 Ibs/hr. The regenerated carbon is kept
in storage until an empty bed becomes available.
Normal operating losses, which average 5.5
percent, require the addition of virgin carbon to
maintain inventory levels. At present, the four
month regeneration process to regenerate all of the
carbon is performed once per year.
Three storage tanks are used during on-site
regeneration. The spent carbon storage tank has a
capacity of 2.5 carbon beds; the regenerated carbon
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storage tank can hold 1.5 beds of carbon and the
virgin carbon storage tank has a capacity of 1
carbon bed. Carbon is moved about the plant in a
slurry through an eductor system.
With GAC adsorption, the NFWTP has achieved
very low effluent organic compound concentrations.
On a daily basis, the facility receives approximately
800 pounds of influent priority pollutants which are
reduced by the treatment process to 12 pounds in
the effluent to the Niagara River. The effluent
discharge permit issued to NFWTP by the New
York State Department of Environmental
Conservation includes effluent limitations for
volatile compounds, acid compounds, base/neutral
compounds, pesticides, metals, and cyanide.
Millard H. Robbins Reclamation Facility,
Upper Occoquan Sewerage Authority,
Centreville, Virginia
The Millard H. Robbins Reclamation Facility
(MHRRF) provides biological, tertiary treatment to
an average daily wastewater flow of 24 mgd.
Industrial flow to the plant is approximately 10
percent of the total flow. The treatment process
consists of primary sedimentation, conventional
activated sludge with nitrification, lime addition for
phosphorous removal, clarification, two-stage
recarbonization, flow equalization, multimedia
filtration, GAC adsorption, post filtration and
disinfection. The MHRRF discharges its effluent
to Bull Run which flows into the Occoquan
Reservoir. This reservoir serves as raw water
storage for the potable water supply to portions of
northern Virginia.
The activated carbon system at MHRRF includes
32 upflow carbon columns which are 10 feet in
diameter and 40 feet tall. Each column has a
capacity of Imgd and contains approximately
75,000 pounds of carbon. Flow is pumped through
the columns by a pump station which also serves
the multimedia filters and post filtration system.
Post filtration is provided following the GAC
columns to remove carbon fines from the effluent to
maintain the Virginia Pollutant Discharge
Elimination System (VPDES) permit requirement
for turbidity of 0.5 NTU.
The carbon columns at MHRRF are operated in
parallel. During average daily flow periods,
approximately 24 columns are in operation with the
remaining eight columns brought on line during
daily peak flow periods. During wet weather, flows
in excess of 32 mgd are stored in a 90 million
gallon pond.
Regeneration of the spent carbon is performed on-
site in a multiple hearth furnace. The regeneration
process takes approximately 8 to 10 weeks to
regenerate approximately one-third of the carbon in
all 32 columns and is performed twice each year.
Consequently, it takes approximately 18 months
(three regeneration cycles) to regenerate the total
quantity of carbon in the columns. Spent carbon is
removed from the bottom of each column and
transported to the regeneration furnace through an
eductor system. The regenerated carbon is then
added at the top of each column. The cost for on-
site regeneration atMFIRRF is approximately $0.35
per pound. Normal operating losses, which average
5 to 7 percent of the total quantity of GAC in use,
require the addition of virgin carbon to maintain
inventory levels. Most of the carbon attrition
occurs during regeneration with approximately 10
to 12 percent of the total carbon regenerated lost
during the regeneration process. Carbon is moved
about the plant in a slurry through an eductor
system.
GAC adsorption is utilized at MHRRF to remove
non-biodegradable, soluble organics. COD is used
as the surrogate indicator of non-biodegradable
organics removal by the GAC columns. Currently,
the Virginia Pollutant Discharge Elimination
System (VPDES) discharge permit limit for COD is
10 mg/1. Following GAC regeneration, effluent
COD concentrations range from 6 to 7 mg/1, which
corresponds to approximately 50 percent removal of
COD. As the GAC in the columns becomes
exhausted, the percentage removal of COD declines
to approximately 25 percent. When the effluent
COD concentration has increased to 9 mg/1, GAC
regeneration is initiated.
OPERATION AND MAINTENANCE
The proper operation and maintenance of GAC
adsorption and regeneration systems ensures the
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efficient removal of soluble organics from
secondary effluent. A routine O&M schedule
following manufacturer's recommendations should
be developed and implemented for any GAC
adsorption and regeneration system. Regular O&M
includes the following:
Backwash of carbon contactor based on
headloss or flow.
• Flush carbon transport piping to prevent
clogging.
Backwash frequently after loading carbon to
minimize clogging of backwash nozzles by
carbon fines.
Store an adequate supply of spent carbon to
allow continuous operation of the
regeneration furnace.
Test and calibrate instrumentation and
controls on a routine basis.
COSTS
The construction and operation and maintenance
costs of carbon adsorption and regeneration depend
on the characteristics of the wastewater to be
treated, the capacity of the plant, and the plant site.
Therefore, the designer is responsible for selecting
a system that will meet the National Pollutant
Discharge Elimination System NPDES permit
requirements at the lowest cost possible. Once the
optimum flow rate, bed depth, and operating
capacity of GAC for a particular wastewater are
determined, comparative costs for different carbon
contactor configurations and the cost of on-site
regeneration versus off-site regeneration can be
estimated. Following a thorough engineering and
economic analysis of alternatives, the final
equipment configuration can be selected.
Construction costs include the carbon contactors,
carbon transport system, carbon storage tanks,
carbon regeneration system (if applicable), influent
wastewater pumps (if applicable) and contactor
backwash system. Operation and maintenance
costs include the purchase of virgin carbon, on-site
regeneration or purchase of regenerated carbon,
electrical power to operate pumps and controls,
flushing of carbon slurry piping, and replacement of
parts. Currently, the cost of virgin carbon ranges
from $0.70 to $1.20 per pound and the cost to
purchase regenerated carbon ranges from $0.50 to
$0.78 per pound.
Operational costs depend on the characteristics of
the influent wastewater and the adsorption capacity
of the GAC. For example, influent wastewater
which contains suspended solids concentrations
greater than 20 mg/1 will require more frequent
backwashing of the contactor to prevent clogging of
the carbon bed.
REFERENCES
Other Related Fact Sheets
Other EPA Fact Sheets can be found at the
following web address:
http://www.epa.gov/owmitnet/mtbfact.htm
1. "Activated Carbon Absorption &
Adsorption." [http://www.scana.com/
sce%26g/business_solutions/technology/
ewtwaca.htm].
2. Gulp, Russel L., Wesner, George Mack, and
Culp, Gordon L., 1978. Handbook of
Advanced Wastewater Treatment, 2nd Ed.
Van Nostrand Reinhold Co., NY.
3. Naylor, William F. and Rester, Dennis O.,
1995. Determining Activated Carbon
Performance. Pollution Engineering, July
1.
4. Perrich Jerry R., 1981. Activated Carbon
Adsorption for Wastewater Treatment,
CRC Press, FL.
5. Roll, Richard and Crocker, Douglas,
"Evolution Of A Large Activated Carbon
Secondary Treatment System", WEFTEC,
1996, WEF Annual Conference, Dallas.
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6. Tchobanoglous, George and Burton,
Franklin L., 1991. Wastewater Engineering
Treatment Disposal, Reuse, Metcalf and
Eddy Inc., 3rd Ed.
7. U.S. EPA, 1984. Granular Activated
Carbon Systems Problems and Remedies,
U.S. EPA 800/490/9198, U.S. EPA,
Washington, D.C.
8. Water Environment Federation, Design of
Municipal Wastewater Treatment Plants,
MOPNi. 8, 1998.
ADDITIONAL INFORMATION
Calgon Carbon Corporation
Dan Brooks
P.O. Box 7171
Pittsburgh, PA 15230-0717
Department of Wastewater Facilities
Wastewater Treatment Plant
Richard R. Roll, P.E., D.E.E
1200 Buffalo Avenue, P.O. Box 69
Niagara Falls, NY 14302-0069
William Naylor
Senior Applications Engineer
Norit America, Inc.
Marshall, TX 75671
The mention of trade names or commercial
products does not constitute endorsement or
recommendation for use by the U. S. Environmental
Protection Agency.
For more information contact:
Municipal Technology Branch
U.S. EPA
Mail Code 4204
1200 Pennsylvania Avenue, NW
Washington, D.C., 20460
MTB
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MUNICIPAL TECHNOLOGY BRANCH
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