United States
Environmental Protection
Agency
Municipal Environmental Researc
Laboratory
Cincinnati OH 45268 /
Research and Development
EPA-600/S2-82-046 August 1982
Project Summary
Pilot Scale Evaluation of
Biological Activated Carbon
for the Removal of
THM Precursors
William H. Glaze, James L. Wallace, Kenneth L. Oickson, Douglas P. Wilcox,
K. R. Johansson, Eichin Chang, Arthur W. Busch, Bobby G. Scalf, Roger K.
Noack, and David P. Smith, Jr.
This project evaluates a method for the
removal of trihalomethane (THM) pre-
cursors from surface water sources. The
site of the project. Cross Lake in Shreve-
port, Louisiana, represents sources in
the southern United States with high
concentrations of THM precursors. In
one phase of the project, a pilot plant
was operated for 80 weeks to test the
combination of ozone and granular acti-
vated carbon (GAC) for THM precursor
removal. An important objective of the
pilot study was to investigate the possi-
bility of microbiological degradation of
precursors In the GAC columns and the
effect of preozonation on this process.
The combination of ozone and GAC is
sometimes referred to as biological
activated carbon (BAG).
Analysis of the pilot plant data shows
microbiological activity to be a significant
contributor to the removal process for
total organic carbon (TOO and trihalo-
methane formation potential (THMFP) in
GAC columns under the conditions
tested. In the initial stages, the removal
mechanism appears to be primarily
adsorption. But, after 50 x 103 bed
volumes of water have been processed,
only microbiological removal remains.
During the Interim period, both adsorp-
tion and microblal processes appear to
contribute to TOC and THMFP removal.
Comparison of costs associated with
the addition of GAC and BAG to traditional
water treatment plants of 100-, 10-,
and 1 -mgd capacities shows that, for the
conditions of this study, the addition of
ozone was not cost effective in extend-
ing the time between reactivations of
the GAC.
In a second phase of the project, studies
were conducted at Shreveport's Amiss
treatment plant complex to define the
extent of their THM problem. Results
there showed high concentrations of
THM's. Alternatives for lowering the
concentrations to less than 0.10 mg/L
Include addition of GAC and conversion
to chloramination. In either case, some
type of oxidant will be required for man-
ganese control.
This Project Summary was developed
by EPA's Municipal Environmental Re-
search Laboratory, Cincinnati, OH, to
announce key findings of the research
project that Is fuHy documented In a sep-
arate report of the same title (see Project
Report ordering information at back).
Introduction
Following the passage of the Safe
Drinking Water Act by the U.S. Congress
in 1974, the U.S. Environmental Protec-
tion Agency (EPA) proceeded to act
under the authority of this legislation to
promulgate National Interim Primary
Drinking Water Standards. These stan-
dards set maximum contaminant limits
for several inorganic elements and com-
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pounds, organic pesticides, radioactivity
levels, and microbiological parameters.
Furthermore, they were applied to essen-
tially all water supplies serving popula-
tions in the United States. Recently,
these standards were amended to include
the establishment of maximum contami-
nant levels for four organic substances
known as the trihalomethanes (THM's).
Trihalomethanes are known to be formed
by the disinfection process that uses
chlorine, the most disinfectant used in
water treatment in the United States.
The reaction of chlorine with naturally
occurring organic compounds, called
THM precursors, is well known to result
in the formation of a variety of chlori-
nated organic compounds, including the
THM's. Four THM's are now regulated
by the requirements of the Safe Drinking
Water Act—chloroform, bromodichloro-
methane, dibromochloromethane, and
bromoform. As of November 29, 1981,
the combined levels of these four THM's
were not permitted to exceed 0.10 mg/L
in water supplies serving populations
greater than 75,000. This limit will apply
to all water systems serving populations
of 10,000 to 75,000 as of November
29, 1983. Trihalomethane limits are
expected to be extended to cover essen-
tially all U.S. water supplies in the future.
Methods for controlling THM levels
include modification of the disinfection
process (including substitution of an
alternative disinfectant), removal of
THM's once formed by advanced treat-
ment processes including adsorption
and aeration, and removal of THM pre-
cursors before the use of chlorine as a
disinfectant.
Among the treatment methods avail-
able for the removal of THM precursors,
GAC adsorption has emerged as the
most promising alternative. Various
studies have shown that GAC can re-
move natural organic compounds from
groundwaters and surface waters with
great efficiency. The principal disadvan-
tage of the use of GAC is the need to
replace or reactivate it periodically to
renew its adsorption capabilities. The
relatively high cost of this process has
discouraged its wide application as a
water treatment process. A recent dis-
covery suggests the possibility of ex-
tending the lifetime of GAC columns for
water treatment. This discovery involves
the recognition that microbiological pro-
cesses occur on GAC much as they do in
trickling filters used for wastewater
treatment. The fact that bacterial colo-
nies proliferate on GAC has been known
for some time, but only recently has it
been appreciated that this presence may
be used beneficially to remove organic
substances from the influent water.
Naturally occurring organic compounds
in water supplies (sometimes referred to
as aquatic humus) are relatively refrac-
tory materials, and their biological degra-
dation is usually a relatively slow process.
Thus in the application of microbiological
processes to GAC, various workers have
proposed to increase the biodegrada-
bility of these substances by the applica-
tion of an oxidation pretreatment process.
Ozone has been the most favored oxidant
for these purposes. The combination of
ozone followed by GAC for the removal
of organic substances in water has been
termed the biological activated carbon
(BAC) process. Proponents of this pro-
cess contend that BAC can extend the
life of granular activated carbon columns
almost indefinitely, provided microbio-
logical colonies can be maintained. Treat-
ment efficiencies during such extended
lifetimes ordinarily do not equal those of
fresh carbon, but the proponents of the
BAC process contend that longer empty
bed contact times in the carbon can be
used to obtain desirable treatment effi-
ciencies. According to this view, the
increased capital costs associated with
longer GAC contact times and the addi-
tion of an oxidant are more than offset
by the avoidance of GAC reactivation or
replacement costs.
Most of the data on which these con-
clusions are based have evolved from
the application of ozone and GAC adsorp-
tion in European waterworks. Few cases
have been studied in which the perfor-
mance criteria match those required by
U.S. drinking water regulations; that is
to say, the operational criteria used in
Europe to evaluate the BAC process do
not correspond to the minimization of
the THM's. For this reason, EPA is spon-
soring several pilotscale investigations
to evaluate GAC adsorption for the direct
removal of THM's or THM precursors.
This report describes the results of
one such investigation. The study was
conducted in the southern part of the
United States in Shreveport, Louisiana.
The test water is taken from Cross Lake,
the principal water supply for the city of
Shreveport. Cross Lake contains relatively
high levels of THM precursors, but it is
relatively uncontaminated by anthropo-
genic sources. A pilot study was carried
out to evaluate GAC adsorption with and
without preozonation as a means for re-
moving these high levels of precursors.
A variety of chemical and microbiological
parameters were measured in the pilot
plant and in associated laboratory exper-
iments to obtain more information on the
physical, chemical, and biological pro-
cesses that occur in GAC filters. Parallel
to this effort, studies were taking place
in the Thomas L. Amiss treatment plant
of the city of Shreveport to help municipal
authorities develop approaches for mini-
mizing trihalomethanes in the city water
supply.
Conclusions
The pilot-scale portion of this study
has shown that GAC columns may be
operated for extended lifetimes by opti-
mizing the physical and microbiological
processes that occur in these columns.
With the trihalomethane formation po-
tential (THMFP) as the principal analytical
criterion, water from a southern U.S.
reservoir has been treated effectively for
a period of 1 year using a combination of
alum flocculation, multi-media filtration
and 24 min of contact with Filtrasorb-
400* GAC. During this period the THMFP
of the product water was less than the
0.10 mg/L maximum contaminant level
except on two occasions.
Engineering and cost analyses have
been conducted for the addition of GAC
adsorption with a 24 min contact time to
an existing plant using the same reservoir
as the water source. The analysis shows
that costs of this additional treatment
are not unreasonable. For 1-, 10-, and
100-mgd plants, additional costs per
1000 gal were computed to be $0.33,
$0.20, and $0.13, respectively.
The addition of ozone before GAC
adsorption may extend the lifetime of
GAC columns, presumably by direct oxi-
dative reduction of THMFP and by en-
couragement of microbiological removal
mechanisms in the GAC columns. Under
the conditions used in this study, the
addition of ozone was not cost effective
in extending the time between reactiva-
tions of the GAC.
An analysis of the chemical and micro-
biological data from the pilot study sug-
gests that the following conclusions
may be drawn regarding the pilot plant
operation.
1. Traditional treatment consisting of
alum flocculation, sedimentation
and mixed-media filtration results
•Mention of trade names or commercial products!
does not constitute endorsement or recommenda-"
tion for use.
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in the removal of 30% to 40%
THMFP, with more efficient removal
occurring in the summer periods.
Except for occasional periods in the
winter months, the product of this
treatment has THMFP values well
in excess of 0.10 mg/L.
2. Oxidation with ozone is not an effec-
tive method per se for the removal
of THMFP. For the relatively low
doses (applied ozone dose range =
2.0 to 6.3 mg/L) used in this work,
5% to 20% destruction of THMFP
was observed. When combined with
traditional treatment, ozonation
produced water that met the 0.10
mg/L THMFP criterion only 20% of
the time.
3. The addition of GAC columns to
traditional treatment is an effective
means for controlling THM precur-
sor levels. Various data point to the
following mechanisms as those re-
sponsible for the sustained removal
of natural organics from the GAC
columns:
(a) Physical Adsorption. This pro-
cess is prevalent during the early
stages of operation and shows
the expected decline in rate as
macropore sites become satu-
rated and the process is limited
by pore diffusion. But as other
workers have shown, the ca-
pacity of GAC for natural organ-
ics is very large if the micropore
capacity is fully utilized.
(b) Microbiological Degradation. This
process is temperature depen-
dent and accounted for the re-
moval of approximately 0.21
moles of carbon/m3 GAC-hr (or
approximately 0.13 mg THMFP/
m3 GAC-hr) during its optimum
period.
These two processes combine to yield
a sustained period of THMFP removal.
During the early stages, the removal is
largely due to physical adsorption; but in
the latter part of the study, microbiologi-
cal processes appear to prevail. The in-
termediate period (referred to by some
as a pseudo-steady-state period) is
apparently due to a combination of the
two processes.
4. Results of the parallel study at the
T. L. Amiss plant are incomplete, but
they suggest the following conclu-
sions:
(a) Instantaneous THM concentra-
tions in the Amiss distribution
system are extremely high by
Federal standards, ranging ap-
proximately from 0.10 mg/L in
the winter to 0.35 mg/L in the
summer.
(b)A substantial fraction of the
THM's is produced upon pre-
chlorination—a common practice
at the Amiss plant. During sum-
mer months, concentrations
above 0.10 mg/L often occur
after a detention time of only 10
to 20 min beyond prechlorina-
tion.
(c) Elimination of prechlorination
results in more effective coagu-
lation of precursors in the sedi-
mentation basins. The result is
not only lower THM concentra-
tions leaving the Amiss plant,
but lower ultimate values in the
distribution system.
(d) Control of pH levels after lime
stabilization is an ineffective
means of minimizing THM for-
mation.
(e) Control of chlorination practice
alone cannot solve the THM
problem in systems such as the
Amiss plant. Other measures
that may be used are GAC ad-
sorption (as indicated by the
pilot study) and substitution of
an alternative disinfectant for
chlorine.
(f) If chloramination is to be used in
place of chlorination, it must be
substituted throughout the plant,
at least during summer periods.
The control of primary producers
in the plant basins, taste and
odor problems, and manganese
levels in the product water then
become management problems
that will require renewed atten-
tion.
Recommendations
This project has shown that biologically
enhanced removal of THM precursors is
possible. Full-scale studies should be en-
couraged to optimize the process. Par-
ticular attention should be given to the
development of regimes for partial reac-
tivation of the GAC beds in some type of
rotary fashion so that biological and
physical adsorption can be coordinated
and the entire process optimized.
The full report was submitted in fulfill-
ment of Cooperative Agreement No. CR-
806157 by The University of Texas at
Dallas, Richardson, Texas, under the
sponsorship of the U.S. Environmental
Protection Agency.
William H. Glaze is with the University of Texas at Dallas, Richardson, TX 75080;
James L. Wallace, Kenneth L. Dickson, Douglas P. Wilcox, K. R. Johansson.
Eichin Chang, and Arthur W. Busch are with North Texas State University,
Denton, TX 76203; Bobby G. Scalf, Roger K. Noack, and David P. Smith, Jr., are
with Henningson, Durham and Richardson, Dallas, TX 75230.
J. Keith Cars well is the EPA Project Officer (see below).
The complete report, entitled "Pilot Scale Evaluation of Biological Activated
Carbon for the Removal of THM Precursors," (Order No. PB 82-230 301; Cost:
$16.50, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Municipal Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
« U.S QOVERNMEm-pRIMTINO OFFICE: 1»K-559-017/0767
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