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                        and is withdrawn at the bottom of the column.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
                                                         Excelence fh tompfance through optfhial tethnltal solutfons
                                                         MUNICIPAL  TECHNOLOGY BRANCH

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