United States
Environmental Protection
Agency
Municipal Environmental Research
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-82-087 Nov. 1982
Project Summary
Feasibility Study of
Granular Activated Carbon
Adsorption and On-Site
Regeneration
Richard Miller and David J. Hartman
A cooperative study was under-
taken by the Cincinnati Water Works
(CWW) and the U.S. Environmental
Protection Agency (EPA) to investi-
gate the feasibility of municipal water
treatment using granular activated
carbon (GAC) adsorption and on-site
regeneration. The project was to
determine whether the use of GAC in
either deep-bed contactors or conven-
tional-depth gravity filters with on-
site carbon regeneration (reactivation)
would be a feasible means of removing
trace organics from Ohio River water
at a reasonable cost and without
adverse effects on the level of treat-
ment provided by the existing plant.
GAC removed a broad spectrum of
organics from Ohio River water, and it
functioned as well if not better than
sand in removing turbidity. Reactiva-
tion restored the GAC to its virgin
adsorptive capacity. Because GAC
removes all free chlorine and all but a
trace of combined chlorine, a post
chlorination facility and additional
clean/veil capacity would be needed
for adequate disinfection. Costs for
implementing GAC treatment at the
CWW facility were estimated to be
$12.5 million per year for the filter
option and $8.5 million per year for
the contactor option.
This Project Summary was developed
by EPA's Municipal Environmental
Research Laboratory, Cincinnati. OH.
to announce key findings of the
research project that is fully docu-
mented in a separate report of the
same title (see Project Report ordering
information at back).
Introduction
In August 1977, the CWW entered
into a cooperative agreement with the
EPA to pursue a feasibility study of
municipal water treatment using GAC
adsorption and on-site regeneration.
This project is one of only a few in the
country to use full-scale filters, post-
filtration contactors, and a granular
carbon regeneration (reactivation)
furnace, all on site.
The water treatment plant has a
design capacity of 10.2 mVsec (235
mgd), and is a typical alum coagulation,
rapid sand filter plant with two large
presettling basins having a combined
capacity of approximately 1.4 million m3
(372 million gallons) and a retention
time of 2 to 3 days. The resulting
finished water from the treatment plant
is low in turbidity and meets all
maximum contaminant levels (MCL's)
as established under the Safe Drinking
Water Act. Average daily pumping rates
are currently 6.1 mVsec (140 mgd). As
such, this system is the largest com-
munity water system on the Ohio River.
The main objective of the project was
to determine whether the use of GAC in
either post-filtration deep-bed contactors
-------
or conventional-depth, sand-replace-
ment gravity filters with on-site carbon
reactivation would be a feasible means
of removing trace organics from Ohio
River water at a reasonable cost and
without adverse effects on the quality of
treatment provided by the existing plant.
A secondary objective was the deve-
lopment of plant design and operating
parameters for full-scale plant conver-
sion to GAC treatment. Additional
aspects of the project included the study
of various filter-adsorber configurations
and types of activated carbon in pilot
and full-scale applications.
The project was divided into three
phases conducted over a period of 3.5
years. In the first phase of the project,
three existing rapid sand filters (1.7
L/sec • m2 or 5 mgd) were converted to
GAC filter adsorbers. Various GAC
types and bed depths were studied to
compare organic removal efficiencies,
bed lives, general water quality char-
acteristics, the need for a sand under-
layer, and operational problems.
The second phase involved the use of
pilot-scale components to investigate
the effects of reactivation on the
activated carbon's adsorptive ability and
to determine the reliability of pilot
columns as indicators of the performance
of full-scale components. The relative
performance of lignite and bituminous-
based GAC was also studied.
In the last phase of this project, the
relative performances of carbon filters
and 0.3 L/sec-m2 (1 mgd} post-filtration
carbon contactors were studied, the
most advantageous empty-bed contact
time for the GAC was determined, and
the effectiveness of on-site reactivation
was evaluated. Pilot columns were also
operated in parallel with the full-sized
units to assess again their usefulness
as predictors of full-scale operation.
Finally, a significant aspect of this
project was the development of prelimi-
nary cost estimates for full-plant
conversion to the GAC adsorption
process.
The first three GAC filter adsorbers
went on line in February 1978. While
data and experience were being gained
on GAC filters and pilot-scale filters and
contactors, contracts were negotiated
for the construction of plant-sized
contactors and a carbon reactivation
furnace. Contactor operations started in
October 1979, and furnace shakedown
operations commenced in March 1980.
All operations were carefully monitored
and recorded to permit a rational
evaluation of the costs, effectiveness.
and problems to be expected in full-
plant utilization of GAC with on-site
reactivation.
Significant Findings
1. GAC is effective in removing a
board spectrum of organics from
Ohio River water. Though many
specific organics were investi-
gated, they were generally present
in such low concentrations (ng/L
or parts per trillion) that evaluation
of the effects of GAC was possible
only with rather elaborate and
newly developed analytical tech-
niques GAC proved to be effective
on all but a few of the organics
investigated.
2. Since it is nearly impossible to
monitor daily for all of the com-
pounds present in the raw water
(many of which are naturally
occurring), more general criteria
were needed with which to deter-
mine the life cycle (or exhaustion)
of a GAC adsorber bed. The criteria
selected included the existing
MCL of 0.10 mg/L trihalomethanes
(THM's)and 1.0 mg/L total organic
carbon (TOC), which was developed
in accordance with design criteria
in the proposed EPA GAC regula-
tion (now rescinded), Control of
Organic Chemical Contaminants in
Drinking Water, Federal Register,
February 9, 1978.
3. GAC functioned as well as or
better than sand in removing
turbidity. Filter beds that contained
part sand and part GAC did not
function as well as either a full
sand or a full GAC bed. In all cases,
the filter medium was supported
by a coarse sand underlayer, and it
was virtually impossible to prevent
removing some of this sand with
the carbon for reactivation. A sand
separator was included in the
reactivation equipment, but it was
not efficient enough for this
application. Sand carryover caused
frequent shut-downs of the furnace
by plugging the fluidizing gas
ports. This problem was not asso-
ciated with contactor operations.
Data indicated that floe removal by
GAC filters had little effect on the
carbon's adsorptive capacity when
compared with a similar contact
time in a contactor.
4. Longer contact times resulted in
more than a proportionately longer
service life, thus affording more
efficient use of the GAC. Overall,
the data indicated that the optimum
empty-bed contact time was 7 to
15 minutes under average condi-
tions and greater than 15 minutes
during critical summer conditions.
These results tend to support the
use of contactors that can be
constructed with the optimum
contact time.
5. Reactivation restored the GAC to
its virgin adsorptive capacity with
respect to both the various organic
parameters and carbon character-
istics studied.
6. The cost of buying carbon to make
up for that lost in the process of
removing it from the bed (filter or
contactor), reactivating Jt, and
returning it to the bed would be a
significant factor in the overall
costs of implementing carbon
treatment. The average bed-to-
bed GAC loss for nine reactivation
cycles for contactors was 15.3%
compared with 18.5% for six
reactivation cycles for filters. By
contrast, earlier estimates by
furnace manufacturers and the
EPA were about 5%.
7. The National Institute of Occupa-
tional Safety and Health (NIOSH)
conducted a survey for working
conditions. GAC is not considered
hazardous, and the level of dust
present was well below the accept-
able level for nuisance dusts.
Though noise levels outside the
control room exceeded the stan-
dards for continuous exposure,
noise was not deemed a hazard
because the operators spend only
brief periods outside the control
room.
An independent laboratory under
contract sampled and analyzed
the furnace off-gases. The South-
west Ohio Air Pollution Authority
reviewed the laboratory's report
and determined that the emissions
were well within the limits estab-
lished for a process plant. In-house
analysis of samples from various
waste effluents contained no
contaminants at levels significant
enough to require special treat-
ment before disposal.
8. As expected, GAC removes all free
chlorine and all but a trace of
combined chlorine. These removals
permit the growth of bacteria
within the carbon bed with poten-
tial for carryover into the distribu-
tion system. Thus, though it may
not be necessary to increase the
-------
amount of chlorine used through-
out the entire treatment process, it
would be necessary to construct a
post-chlorination facility and add-
itional clearwell capacity to provide
sufficient chlorine contact time for
disinfection with full-scale GAC
conversion.
9. GAC implementation costs were
projected for the CWW facility as it
exists today. The annual cost of
GAC treatment will depend on
which treatment alternative is
selected — the application of GAC
in existing but modified filters or in
newly constructed contactors
following normal sand filtration.
Under the sand-replacement option,
about $37 million would be needed for
capital costs and about $8 million for
operating expenses (in 1981 dollars).
The annual amortization of the capital
expenditures would bring the total
annual cost to about $12.5 million,
adding about 180 per hundred cubic
feet to the cost of water to both city and
suburban customers.
Under the post-filtration contactor
option, about $38 million would be
needed for capital costs, but only about
$4 million for operating expenses (in
1981 dollars). The annual amortization
of the capital expenditures would bring
the total annual cost to about $8.5
million, adding about 130 per hundred
cubic feet to the cost of water.
The full report was submitted in
fulfillment of Cooperative Agreement
No. CR805443 by the City of Cincinnati
Water Works under the sponsorship of
the U.S. Environmental Protection
Agency.
Richard Miller and David J. Hartman are with the Cincinnati Water Works,
Cincinnati, OH 45232.
Jack DeMarco and Ben W. Lykins. Jr.. are the EPA Project Officers (see below).
The complete report consists of two volumes, entitled "Feasibility Study of
Granular Activated Carbon Adsorption and On-Site Regeneration."
"Volume 1. Detailed Report," (Order No. PB 83-121 731; Cost: $25.00,
subject to change)
"Volume 2. Supplemental Figures and Data," (Order No. PB 83-121 749;
Cost: $43.50, subject to change)
The above reports will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officers can be contacted at:
Municipal Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
-------
GOVERNMENT PRINTING OFFICE: 1982 659-O17/O869
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Postage and
Fees Paid
Environmental
Protection
Agency
EPA 335
Official Business
Penalty for Private Use $300
RETURN POSTAGE GUARANTEED
2
ION AGENCY
------- |