United States
Environmental Protection
Agency
Water Engineering
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-87/011 Apr. 1987
&EPA Project Summary
Treatment Alternatives for
Controlling Chlorinated
Organic Contaminants in
Drinking Water
Mark A. Speed, Annette Barnard, Richard P. Arber,
George C. Budd, and Frank J. Johns, II
A pilot plant study was conducted by
the City of Thornton, CO, to evaluate
techniques for controlling chlorinated
organic compounds formed in drinking
water as a result of breakpoint, or free,
chlorination. The pilot plant was oper-
ated for 46 months using the raw water
sources available to the City's 20-mgd
Columbine Water Treatment Plant. The
treatment techniques evaluated in-
cluded conventional coagulation and
sedimentation, adsorption of organic
precursors on powdered activated car-
bon (PAC), adsorption of chlorinated or-
ganic compounds on granular activated
carbon (GAC), and alternative methods
of disinfection, including the use of
chloramines and chlorine dioxide in ad-
dition to the present practice of break-
point chlorination. The effectiveness of
the alternatives were assessed with re-
spect to formation or removal of total
trihalomethane (TTHM) and total or-
ganic halogen (TOX). In addition, the al-
ternative disinfectants were evaluated
for biocidal effectiveness.
Based on the study findings, a proc-
ess that employs chlorine dioxide in
combination with chloramination was
selected for full-scale evaluation. Nei-
ther GAC nor PAC was found to be ca-
pable of consistent or reliable control of
TTHM or TOX. The method of chlorami-
nation affected the extent of TTHM and
TOX formation and of bacteria inactiva-
tion. The method that resulted in the
lowest concentration of these chlori-
nated organic compounds had the low-
est biocidal efficiency as well and there-
fore was not considered acceptable.
A raw water monitoring program
was conducted concurrently with the
pilot plant program. Certain raw water
sources exhibited a chlorine dosage de-
pendency toward TTHM formation.
Procedures were therefore instituted
for determining the TTHM formation
potential (TTHMFP) that should be con-
sidered when analyzing for TTHMFP.
This Program Summary was devel-
oped by EPA's Water Engineering Re-
search Laboratory, Cincinnati, OH, to
announce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
Introduction
The City of Thornton, CO, located
along the South Platte River down-
stream of the metropolitan Denver area,
has historically experienced quality
problems in their raw water supply. In
1978, nitrite (NO^) concentrations ap-
proaching 2 mg/L as nitrogen were dis-
covered within the distribution system.
Based on data collected by the Thornton
laboratory, the source of the nitrite was
determined to be high concentrations of
ammonia in the raw water. The ammo-
nia was apparently being oxidized in the
distribution system by nitrifying bacte-
ria. This bacterial growth occurred de-
spite the fact that bacteriological stand-
ards were being met in the finished
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water. Because of the acute health ef-
fects associated with nitrite, Thornton
immediately began breakpoint chlorina-
tion for nitrogen removal.
Once the immediate water quality
problem was solved, evaluation of the
breakpoint chlorination process pro-
ceeded. Although no specific data were
available, the speculation was that high
concentrations of chlorinated organics
were being formed during the break-
point chlorination process. Initial test-
ing of the water following breakpoint
chlorination confirmed this suspicion
with instantaneous total trihalomethane
(TTHM) exceeding 100 jtg/L, total tri-
halomethane formulation potential
(TTHMFP) exceeding 250 |Ag/L, and in-
stantaneous total organic halogen
(TOX) exceeding 250 jtg/L, in the fin-
ished water from the Columbine Water
Treatment Plant. As a result of these
findings, a pilot plant study was recom-
mended to evaluate the effectiveness of
existing treatment processes as well as
additional processes for treating the
available raw water supplies.
The pilot plant was operated for 46
months using the raw water sources
available to the City's 20-mgd Colum-
bine Water Treatment Plant. Alterna-
tives that were evaluated for controlling
chlorinated organic compounds in-
cluded adsorption of organics on granu-
lar activated carbon (GAC) and pow-
dered activated carbon (PAC) and
alternative methods of disinfection, in-
cluding the use of chloramines and
chlorine dioxide in addition to the
present practice of breakpoint chlorina-
tion. The effectiveness of each alterna-
tive was assessed with respect to for-
mation or removal of TTHM, formation
or removal of TOX, and biocidal effi-
ciency.
Procedures
Pilot Plant
A 10-gpm pilot plant used for this
study consisted of a raw water rapid-
mix chamber, a two-stage flocculation
basin, a primary settling basin, a dual-
media filter, and a treated water storage
chamber. Carbon contactors used in
conjunction with the pilot plant con-
sisted of four 6-inch-diameter, 8-foot-
tall glass columns with sample taps at
six locations for monitoring organic
breakthrough. Each column had 5.5 feet
of coal-base GAC media. Two sets of
two columns each were operated in
series to provide a total empty bed con-
tact time (EBCT) of 16 minutes for each
set of columns.
Six different modes of operation were
used for the pilot plant during the pro-
gram. The first three modes used break-
point chlorination as the means of disin-
fection. The Mode 1 configuration
(control) was identical to the full-scale
Columbine Treatment Plant, with chlo-
rine added in the premix basin to
achieve breakpoint. The Mode 2 config-
uration located the breakpoint chlorina-
tion downstream at the clarifier effluent
to maximize the removal of precursor
material before the addition of chlorine.
The Mode 3 configuration was identical
to Mode 2 except that no PAC was
added. This mode allowed comparisons
to determine the effectiveness of PAC
on the removal of precursor material.
Modes 4 and 5 used two different
forms of chloramination. In the Mode 4
configuration, chlorine was added to
achieve breakpoint chlorination in the
premix basin, after which ammonium
sulfate was immediately added to form
chloramines. The Mode 5 configuration
included the addition of a preformed
chloramine solution that was prepared
off-line and added to the premix basin.
Mode 6 consisted of a dual disinfection
system using both chlorine dioxide and
preformed chloramines added at the in-
flow to the plant.
Raw Water Monitoring
A total of 16 sample locations were
selected for raw water monitoring. In-
cluded in the sampling were the four
current raw water sources for the
Columbine Treatment Plant, two possi-
ble future sources, and other locations
within the watersheds to monitor im-
pacts on the sources by wastewater
treatment plant discharges.
Results and Discussion
Study results show the correlation be-
tween the pilot plant and the full-scale
Columbine Water Treatment Plant, the
ability of a process or process train to
remove specific constituents, the differ-
ent levels of chlorinated organic forma-
tion among alternative disinfection
techniques, variations in bacteriological
quality produced by alternative disin-
fectants, and variations in raw water
quality.
Conventional Treatment
The average total organic carbon
(TOC) concentration of the raw water
entering the pilot plant was 5.2 mg/
TOC removal across the clarifier was a
proximately 11 percent and across th
filter approximately 8 percent.
With conventional treatment follov
ing breakpoint chlorination of the ra
water, approximately 40 percent of th
TTHMFP and 15 percent of the TOXF
was removed. By locating the point <
chlorination at the clarifier effluent, co
ventional treatment consisting of flo
culation and sedimentation removed 5
percent of the TTHM precursors and ;
percent of the TOX precursors.
Pilot Plant Correlation
An important part of the pilot plai
program was to determine whether th
pilot plant results were representativ
of full-scale operation. Data were con
pared for the full-scale filter effluent an
the pilot plant filter effluent for the fo
lowing parameters: TOC, instantaneoi
TTHM, TTHMFP, instantaneous TO)
and TOX formation potential (TOXFP
Each of these analyses showed a goo
correlation between the performance (
the full-scale plant and the pilot plant
Powdered Activated Carbon
During Mode 2 of the pilot plant ope
ation, PAC dosages of 5 to 10 mg/L wei
added to the premix basin, with brea
point chlorination occurring after clarrl
cation and before the filter. In Mode 31
the pilot plant operation, the proces
train remained identical to Mode 2 ope
ation except that the PAC was elim
nated to assess the effectiveness of PA
for removal of organic precursors.
Raw water quality was nearly equ
with respect to organic content, with a'
erage TOC concentrations of 5.7 and 5
mg/L for Modes 2 and 3, respective!1
The data indicate that PAC at thos
dosages is only slightly effective for n
ducing TOC concentration in the filt<
effluent. The filter effluent TOC concei
tration averaged 4.5 mg/L for Mode
and 4.7 mg/L for Mode 3. The averag
instantaneous TTHM concentration i
the filter effluent is approximately tr
same, regardless of whether PAC
used. The average TTHM concentn
tions were 33.7 (xg/L for Mode 2 an
35.8 jxg/L for Mode 3.
As with the TTHM data, the TOX coi
centration is not significantly differei
with or without PAC addition. The da'
showed a slightly higher average TO
concentration for Mode 2—189 |xg
compared with 142 jxg/L for Mode 3.
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Granular Activated Carbon
Performance
The performance of the GAC columns
was analyzed using data from Modes 1
and 4. The methods of disinfection used
were breakpoint chlorination in Mode 1
and breakpoint chlorination followed by
ammoniation in Mode 4. The GAC
columns were operated for 160 days
during these modes to determine the
breakthrough characteristics of the
columns. Samples that were analyzed
to determine GAC performance were
the effluent from column 10-6 (which
simulated a post-filtration GAC proc-
ess), the effluent from column 11-6
(which simulated a retrofit of the exist-
ing filters), and the effluent from
column 12-6 (which simulated replacing
the filters with a GAC process). The car-
bon columns were filled with virgin car-
bon at the beginning of each mode and
were backwashed weekly during opera-
tion.
The average TOC concentration of the
GAC influent was 4.6 mg/L for the
columns receiving clarifier effluent and
4.3 mg/L for the columns receiving filter
effluent. The average TTHM concentra-
tions during Mode 1 were 85 |xg/L for
clarifier effluent and 91 (xg/L for filter
effluent. The respective concentrations
during Mode 4 were 23 and 26 (xg/L.
Thus the two sets of carbon columns in
each mode received water with approx-
imately the same TOC and TTHM.
Results from the pilot studies indi-
cated that after a column was placed
into service with virgin GAC, the TOC
concentration in the effluent was low
and increased almost immediately until
it reached a steady state concentration.
In all cases, this steady state concentra-
tion was reached in approximately 50 to
60 days. The effluent concentrations
from Columns 10-6 and 12-6 were ap-
proximately equal (1 to 2 mg/L),
whereas the effluent concentration
from Column 11-6 was slightly higher (2
to 4 mg/L). The contact time through
Column 11-6 (8 minutes) was only half
the contact time through Columns 10-6
and 12-6 (16 minutes).
The GAC column performances for
TTHM removal differed from those for
TOC. The TTHM concentration in the ef-
fluent from the GAC columns remained
below 5 |xg/L for approximately 30 to 70
days, depending on the column. After
that period, the TTHM concentration in
the effluent began to increase and con-
tinued increasing for 30 to 50 days. The
'TTHM concentration then reached a
longer-term steady state, during which
a degree of removal could still be main-
tained.
TTHMFP is an important parameter
for judging the performance of the GAC
process. Since the water is dechlori-
nated during the GAC process, the efflu-
ent must be chlorinated before delivery
to the customer. The TTHMFP concen-
tration in the effluent from the GAC
columns began below 50 jxg/L and then
increased to a quasi-steady state con-
centration after 30 to 50 days for Mode
1 and after 40 to 90 days for Mode 4.
Because of the difference in contact
time, TTHMFP in the effluent from
column 11-6 began increasing sooner
and reached a higher level (100 to 150
jxg/L) than the effluents from columns
10-6 and 12-6 (50 to 90 (xg/L).
Alternative Disinfectants
The water quality of the pilot plant fil-
ter effluent was used to determine the
performance of the alternative disinfec-
tants. Formation of chlorinated organic
byproducts was determined using
TTHM and TOX analyses. Bacteriologi-
cal quality of the filter effluent was de-
termined using both total coliform and
standard plate count techniques. From
these, the bactericidal efficiency of the
alternative disinfectants could be deter-
mined.
Several batch studies were per-
formed to evaluate critical characteris-
tics with respect to disinfection and for-
mation of chlorinated byproducts over a
range of chlorination conditions. These
studies were intended to supplement
the pilot plant work by comparing differ-
ent chlorination approaches on the
same water sample. As such, the results
from these evaluations yielded a direct
comparison of these approaches. The
batch experiments were performed by
withdrawing 250-ml aliquots of a sam-
ple and placing each aliquot in a
headspace-free bottle with a chlorine
solution for a defined period of time.
The pH was controlled in the range of
7.5 to 8.0 to match conditions normally
encountered in the water distribution
system. Temperature was controlled to
match that of the finished water as an
approximation of conditions found in
the distribution system.
Chlorinated Organic Formation
The data evaluated were the TTHMFP
of the full-scale raw blend, the instan-
teous TTHM of the pilot plant filter efflu-
ent, and the terminal TTHM of the pilot
plant filter effluent. TTHMFP for the full-
scale raw blend was determined by
spiking the sample with chlorine at a
dosage of 2 mg/L greater than the 1-hr
demand. The sample was then stored
for a 5-day period before analysis.
The average instantaneous TTHM
concentration was approximately 80
p.g/L for Mode 1 (free chlorination), 25
(j.g/Lfor Mode4(post-ammoniation), 15
p,g/L for Mode 5 (preformed chlor-
amines), and 10 |xg/L for Mode 6 (dual
disinfection). The average terminal
TTHM concentration was approxi-
mately 190 (xg/L for Mode 1 and 40 (xg/L
for Mode 4. The higher concentration
for Mode 1 results from the free chlorine
present during sample storage; Mode 4
had no free chlorine because of post-
ammoniation. The data show no signifi-
cant difference in the instantaneous and
terminal TTHM values for Modes 5 and
6. The terminal values indicate the ex-
pected maximum concentration of
TTHM in the distribution system for
each mode of operation.
TOX is a nonspecific parameter for in-
dication of chlorinated organics. The
general trend for the TOX data is similar
to that observed for the TTHM data. The
average instantaneous TOX concentra-
tion in the pilot plant filter effluent was
270 M-g/L for Mode 1,130 jxg/L for Mode
4, 120 (xg/L for Mode 5, and 80 jxg/L for
Mode 6. The average terminal TOX con-
centration for the same four modes was
400, 400, 370, and 180 (xg/L. respec-
tively.
Bacterial Efficiency
Data for the pilot plant filter effluent
show that total coliforms were reduced
to levels below the detection limit in
nearly all cases for each alternative dis-
infectant. Thus because of its greater
sensitivity, the standard plate count
(SPC) was used as a means for examin-
ing the bactericidal efficiency of the al-
ternative disinfectants.
Probability distributions of the SPC
data show that with breakpoint, or free,
chlorination as practiced during Mode
1, an SPC of 10/mL was achieved ap-
proximately 98 percent of the time.
When chloramination was practiced
using the post-ammoniation method, as
in Mode 4, an SPC of 10/mL was
achieved only 87 percent of the time.
With the use of a chloramine solution
generated off-line, as practiced during
Mode 5, an SPC of 10/mL was achieved
only 76 percent of the time. When chlo-
rine dioxide was used as the primary
disinfectant in a dual disinfection sys-
tem, as practiced during Mode 6, an
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SPC of 10/mL was achieved approxi-
mately 97 percent of the time. The rela-
tive bactericidal efficiency of the alter-
native disinfectants is consistent with
that found in the literature.
Batch Studies
The general approach used in all
batch studies was to evaluate the char-
acteristics of concern at different loca-
tions along a breakpoint chlorination
curve. Those points located to the left of
the classic breakpoint lie within regions
where chloramines are the predomi-
nant form of total chlorine residual, and
those points to the right of the break-
point occur within the region of domina-
tion by free chlorine. Characteristics
that were evaluated include the biocidal
effectiveness of different methods of
chlorination and the formation of chlori-
nated byproducts, such as TTHM,
dichloroacetonitrile, TOX, and organic
chloramines.
The use of breakpoint chlorination to
achieve free chlorine results in the min-
imum bacteriological risk but maxi-
mizes the formation of chlorinated
byproducts, as indicated by TTHM,
dichloroacetonitrile, organic chlor-
amines, and TOX. Conversely, the use
of a preformed chloramine solution re-
sults in the formation of the lowest level
of byproducts but results in the highest
level of bacteriological risk. The use of
other alternative chloramination meth-
ods results in mixed levels of risk for all
parameters. The various chloramina-
tion modes result in a significant forma-
tion of chlorinated byproducts, particu-
larly TOX, with the exception of the use
of a preformed chloramine solution.
Raw Water Quality
Only those sources that are currently
used as a raw water supply for the
Columbine Water Treatment Plant or
are readily available for use in the near
future were considered for evaluation.
The parameters that were evaluated in-
cluded ammonia, nitrate plus nitrite,
total Kjeldahl nitrogen, turbidity, coli-
form, TOC, TTHM, and TOX. Based on
the data from these analyses, the raw
water sources were ranked by their
quality. This aided Thornton with their
water treatment planning.
Conclusions
1. The quality of the Thornton, CO,
raw water varies during the year
and follows a fairly predictable an-
nual cycle.
2. The raw water sources for the
Columbine Water Treatment Plant
exhibit a chlorine dosage depend-
ency with respect to TTHM forma-
tion.
3. A literature review shows that
TTHM formation can be related to
algae concentrations in the raw
water. A study conducted during
the pilot plant program showed
that TTHM produced by chlorina-
tion of proteins can be significant
during summer months of high
algae growth. TTHM is only one
example of organohalogen com-
pounds that can be produced by
chlorination of proteins. Algae can
be a significant source of these
proteins.
4. Compared with a conventional co-
agulation and sedimentation proc-
ess, PAC doses of 5 to 10 mg/L had
a minimal effect on the removal of
organics as measured by TOC.
TOC removal was approximately 6
percent greater with PAC than
without it. PAC addition did not ef-
fect the TTHM and TOX concentra-
tions in the filter effluent.
5. GAC is capable of removing TTHM
and TOX. These chlorinated organ-
ics reached a steady-state concen-
tration in the effluent from the GAC
columns, with breakthrough oc-
curring at certain intervals. The in-
terval of time to breakthrough was
not long enough for GAC to be an
economical alternative to using
other disinfectants for controlling
TTHM and TOX.
6. The conventional treatment proc-
esses could remove approximately
30 to 40 percent of the TTH M FP. By
moving the point of chlorination
downstream of conventional treat-
ment, a decrease in TTHM forma-
tion was realized. However, the
precursor removal by sedimenta-
tion was not adequate to consis-
tently allow Thornton to produce
water with less than 100 ng/L
TTHMFP.
7. Alternative chlorination schemes
can be characterized by the region
in which the chlorine species occur
along the breakpoint chlorination
curve. Each chlorination scheme
results in different water quality in
terms of bacteria and chlorinated
organic byproducts.
The chloramination procedure af-
fects the amount of disinfection
and the byproduct formation even
when the water following chlorar
ination contains the same type ar
concentration of chloramines.
8. Selection of the disinfectic
scheme should be based on tv
primary criteria: Disinfection c
pabilities and disinfection b
product formation. The goal is
maximize disinfection (i.e., to k
bacteria and other pathogen
and to minimize the formation
byproducts that have potential
adverse health effects.
9. None of the alternative chlorin
tion schemes produced both <
fective disinfection and minim
formation of chlorinated orgar
byproducts, as indicated I
TTHM and TOX, during the pil
plant study. The chlorinate
schemes that maximized disi
fection were those that result!
in higher byproduct concentr
tions. Those schemes that mil
mized byproduct formation hac
smaller degree of bacteria kill.
10. The use of chlorine dioxide as
disinfectant maximized bactei
kill and minimized the formati<
of chlorinated organic bypro
ucts. However, because the chl
rine dioxide residual is limited I
chlorite and chlorate formation
chlorine or chloramine solutii
must be added so that a disinfe
tant residual can be maintained
the distribution system.
Recommendations
1. The raw water monitoring pr<
gram should be continued to di
velop the data base further. Tr
program will allow for evaluatic
of water sources and provic
data relating to the variability <
the supply on an annual basis.
2. The evaluation and eventual d<
sign of a full-scale chlorine dio:
ide generation and feed systei
should be considered for th
Columbine Water Treatmet
Plant.
3. Alternative chlorination schenrn
should be evaluated for a wati
supply containing a low
ammonia concentration. The di
infection and byproduct form
tion results for a low-ammon
water may be different than tho;
found during this pilot plai
study.
4. When evaluating alternative di
infectants, water utilities shou
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consider more parameters than
those currently regulated under
the U.S. Environmental Protec-
tion Agency Primary Drinking
Water Standards. Other parame-
ters can provide a broader indica-
tion of disinfection byproducts
and bacteriological quality. For
example, when considering
chloramines as an alternative to
free chlorine, TOX should be
used along with TTHM as a mini-
mum indication of byproduct for-
mation. A more sensitive indica-
tor of bacteriological quality,
such as heterotrophic plate
count, should be used along with
the total coliform count.
5. Because different waters have
different characteristics in rela-
tion to TTHM formation, certain
parameters should be monitored
and reported when analyzing for
TTHMFP. These parameters in-
clude free and total chlorine
residuals, pH, temperature, and
storage period. In addition, since
some waters exhibit a dosage de-
pendency toward TTHM forma-
tion, TTHMFP analyses should be
conducted for at least two differ-
ent chlorine dosages.
The full report was submitted in fulfill-
ment of Cooperative Agreement CR-
809333-01 by the City of Thornton, CO
under the sponsorship of the U.S. Envi-
ronmental Protection Agency.
Mark A. Speed and Annette Barnard are with the City of Thornton. CO 80229;
Richard P. Arber, George C. Budd, and Frank J. Johns, II. are with Richard
P. Arber Associates. Denver,
Ben W. Lykins is the EPA Proje
CO 80206.
1 Officer (see below).
The complete report, entitled "Treatment Alternatives for Controlling Chlorinated
Organic Contaminants in Drinking Water," (Order No. PB 87-145 751 /AS;
Cost: $18.95, 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:
Water Engineering Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
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