United States
Environmental Protection
Agency
Municipal Environmental Research
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-82-037 August 1982
Project Summary
Alternative Water Disinfection
Schemes for Reduced
Trihalomethane Formation:
Volume I. Prototype Studies
Charles A. Sorber, Robert F. Williams, Barbara E. Moore, and Karl E. Longley
The potential adverse health effects
of organohalides, particularly trihal-
omethanes, in drinking water are of
serious national concern. Trihalome-
thanes (THM) are formed primarily by
the reaction between organic precur-
sors in the water and chlorine, the
halide most widely used for disinfec-
tion of potable water.
The primary objective of this study
was to develop techniques to reduce
or eliminate THM in finished water
without compromising the microbio-
logical quality of the water. To this
end, a prototype rapid mixing system
was employed and a number of alter-
native disinfection systems were
investigated. From these data, both a
general predictive model was devel-
oped and the role of algae and humic
acids as THM precursors was
evaluated.
Results of this study support the
contention that in disinfection prac-
tice a tubular plug flow reactor can be
used to advantage in reducing bacte-
rial populations in the water. An added
advantage is that use of this type reac-
tor will result in minimal THM forma-
tion when chlorine is used as the
disinfectant.
Experiments with standard plate
count (SPC) organisms and seeded
Escherichia co//showed that the disin-
fection systems of chlorine, chlorine
followed by ammonia, and chlorine
dioxide were very effective when used
with hydraulic mixing. Chlorine diox-
ide was shown to be the best disinfec-
tant under the conditions of this study.
Organisms used in this research var-
ied in their resistance to chlorination,
the least resistant being E. coli lys
147; next was £. coli C. SPC organ-
isms were more resistant than either
of the £. coli seed organisms, and bac-
teriophage f 2 was the most resistant of
all. SPC data were used to develop the
disinfection model presented in this
summary and the full report.
An important finding was the sub-
stantial reduction in THM production
observed with the prototype system.
The lower chlorine doses required for
effective disinfection resulted in sig-
nificantly lower THM production. The
two best systems for minimizing THM'
production were chlorine dioxide and
ammonia followed by chlorine, but
very substantial reductions of THM
concentration were achieved by chlo-
rine followed by ammonia. For exam-
ple, a 1.5 mg/L dose of chlorine alone
produced 119 /ug/L of THM, whereas
1.5 mg/L of chlorine followed by
ammonia produced about 7 //g/L of
THM. A dose of 1.5 mg/L of chlorine
added after ammonia produced as low
as 0.4/jg/L of THM, and 1.5 mg/L of
chlorine dioxide produced 0.8 fjg/L of
THM.
This Project Summary was devel-
oped by EPA's Muncipal Environmen-
tal 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
The use of chlorine as a disinfectant
in potable water has been based on its
long and successful history of rendering
water sufficiently free of pathogenic
organisms to minimize the probability of
waterborne disease among the con-
suming public. Because of its relative
ease of application and low cost, chlori-
nation has become synonymous for dis-
infection. The widespread use of
chlorine has been one of the most
important public health control mea-
sures of this century. Recently, potential
dverse health effects have been linked
to organohalides, particularly trihal-
omethanes (THM), in drinking water.
These organohalides are formed pri-
marily by the reaction between organic
precursors in the water and the chlorine
introduced into the water stream.
The primary objective of this investi-
gation was to develop techniques to
reduce or eliminate THM and other
organ chlorine compounds in finished
water without compromising the micro-
biological quality of the water. To
accomplish this goal, a prototype rapid
mixing system employing a plug flow
reactor was examined with several dis-
infectants. THM production and the dis-
infection efficiency resulting from the
use of alternative disinfectant schemes
were compared with those resulting
from the use chlorine. The alternative
disinfectant schemes were chlorine
dioxide, ammonia followed by the addi-
tion of chlorine, and chlorine followed
by the addition of ammonia.
Procedure
Water Treatment Plant
A new water treatment plant (WTP)
(at Boerne, Texas) located at a newly
constructed reservoir was the study
site.
The treatment train of the 6056 mVd
(1.6 mgd) WTP consists of prechlorina-
tion, alum coagulation and sedimenta-
tion through an upflow clarifier,
pressure sand filtration, and post chlori-
nation. Gas fed chlorinators are used for
chlorination, and facilities are available
for fluoridation. Sludge, filter backwash
water, and other plant liquid waste
streams are piped to two evaporation
ponds for disposal.
The filtered, nondisinfected water
was fed to a 1890-L (500-gal) storage
tank and pumped through the prototype
system at a f lowrate of 4.7 L/s (75 gal/
min) (Figure 1). Provisions were avail-
able for "seeding" the water stream
before disinfection. Seeding require-
ments for the prototype system were
based on the levels of indigenousorgan-
isms found in the test water. Seeding
experiments were performed to evalu-
ate the prototype system since indigen-
ous organism levels were insufficient to
ensure statistical significance in the
evaluation of disinfection effectiveness.
Aqueous chlorine, chlorine dioxide,
and ammonia were peripherally in-
jected into one of two plug-flow proto-
type mixers, which had internal throat
diameters of 20 mm (0.8 in.) and throat
lengths of 0.91 m (3 ft). Downstream
from each mixer, the water stream
passed through an energy recovery sec-
tion of 0.91 m (3 ft) into a 100-mm(4.0-
in.) internal diameter pipe (PVC,
schedule 80). The total length of the
prototype system was 37.36 m (122.6
ft). For a f lowrate of 4.7 L/s (75 gal/
min), the Reynolds numbers of the 20-
mm (0.8-in.) and 100-mm (4.0-in.) sec-
tions are 370,000 and 74,200,
respectively. Studies involving adding
chlorine followed by ammonia or ammo-
nia followed by chlorine were done by
adding the second chemical into the
second mixer located 8.78 m (28.8 ft)
downstream from the first mixer. This
permitted 15-sec mean contact with
free chlorine or ammonia before chlo-
ramine formation began. Total mean
contact time between the addition of the
disinfectant and the discharge of the
water stream was approximately 60
seconds.
Seed organisms (£. coli lys 147, £. coli
C, and phage fa) were added at the suc-
tion side of the system pump (organisms
were not introduced into the holding
tank).
Sampling
Samples having a contact time of
approximately 1 sec were collected at
the end of the mixer throat, and samples
with a mean contact time of 60 sec were
collected at the discharge of the pipe
contactor. Samples with desired contact
times greater than 60 sec were col-
lected in glass or plastic containers, as
appropriate, at the discharge point.
After the predetermined contact time
had elapsed, a suitable reducing agent
was added to quench the disinfecting
agent. Additionally, the sample col
lected at a sampling port immediate!
before the second mixer (the point o
ammonia or chlorine addition) allowei
the disinfectant residual and THM for
mation to be evaluated immediatel
before either chlorine or ammonia addi
tion for the chloramination studies
Overall control samples were obtainei
from a sample port immediately up
stream from the first mixer.
Bacteriological Analyses
Bacteriological samples were col
lected in sterile 500-ml polypropylene
bottles and placed in wet ice at 4°C unti
analysis. SPC organisms were mea
sured using the techniques in Standan
Methods. Total coliforms (TC) wen
determined by the membrane filtratior
technique (Standard Methods). The coli
form seed bacteria, E. coli lys 147, con
tained a phage that became active anc
lysed the bacteria after a 3 to 4 hour ex
posure at 42°C. These coliforms wer<
counted by a technique . in whict
plaques in an overlying £ coli laye
were enumerated after 18 hours c
35°C incubation following the 42°C ex
posure. Other plates without the £. co>
overlayer were heated to 42°C to lysi
the seed organism and then incubate*
for 48 hours at 35°C to determine SP(
less the £. coli lys 147. Bacteriophage f
was determined using soft agar overla'
plates with £ coli Hf r Hayes as the hos
organism.
Disinfectant Systems
For all bacteriological and THM analy
ses, sodium thiosulfate was used t
quench the disinfectants at the desire
times. The quantity of reducing ager
depended upon the disinfectant dos
but was always in excess.
Disinfectants were introduced int
the mixers through a vacuum ejectoi
and chlorine and-ammonia were fed a
gases. Chlorine dioxide was fed as a
aqueous solution prepared by reactin
sodium chlorite with hydrochloric aci
in a contact chamber filled with glas
beads (5-min detention time).
Field analyses for residual chlorine
total chlorine, chloramines, and chic
rine dioxide were performed by eithe
amperometric titration or colorimetri
determination with N, N-diethyl
phenylene-diamine sulfate (DPD). Am
monia determinations in the field wer
done colorimetrically with Nessler'
reagent.
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Plug flow
contacting sections
Test disinfectant
Pump
Seed"
storage
tank
Filtered water storage
Sample port (SP)
Figure 1. Schematic of prototype disinfection system.
Chemical Analyses
Temperature and pH were measured
in the field at WTP sampling points. For
prototype runs, these parameters were
measured at the field location as well as
after transport to the analytical labora-
tory. All samples for routine chemical
analyses were collected in 1-L plastic
bottles and stored at 4°C for transport to
the laboratory.
Trihalomethane Analyses
Samples were collected in 40-ml
vials with (Instant THM) or without (Ter-
minal THM) sodium thiosulfate and
sealed with Teflon®-faced* septums.
Instant THM samples were stored at 4°C
and Terminal THM samples were stored
at room temperature in the dark until
'Mention of trade names or commercial products
does not constitute endorsement or recommenda-
tion for use
analysis or until the designated times
for quenching by thiosulfate.
THM samples were analyzed by gas
chromotography using the gas sparging
technique. Samples (5 ml) were
sparged for 20 min at 25°C with a 30
ml/min flow of grade six helium carrier
gas and collected on a Tenax trap (30.5
cm long; 0.318 cm OD; 0.293 cm ID).
Thermal desorption at 210°C with a 20
ml/min helium flow onto a 50°C analy-
tical Tenax column (60/80 mesh; 2.4
cm long; 0.31 cm OD; 0.216 cm ID) was
then accomplished. The analytical
column was held isothermally for 6
min and temperature-programmed to
250°C at a rate of 10°C per min. Typical
retention times of 14.40, 16.38, 18.24,
and 20.02 min for chloroform, dichloro-
bromomethane, chlorodibromomethane,
and bromoform, respectively, were ex-
hibited for this analytical column. All
analyses were performed on a Varian
3700 gas chromatograph equipped
with a flame ionization detector and a
CDS 111C reporting integrator.
Results
Water Treatment Plant
Baseline data collected during the
normal operation of the WTP showed
little variability in chemical or bacterio-
logical parameters during the testing
period. The variations in operating con-
ditions were primarily because of prob-
lems associated with bringing the plant
on-line and developing experience to
provide the most effective operation.
After this initial period of fluctuation
(approximately 6 months), the chemical
parameters showed almost no changes.
Table 1 illustrates the ranges of bac-
teriological and THM data observed at
the site since the sampling program
began in early 1979. All of the high coli-
form and SPC values were observed
during the first 6 months of operation.
Since September 1979 there has been
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Table 1. Range of Bacteriological and Trihalomethane Data at Sampling
Sites in Boerne WTP from February 1979 to August 1980
Total Coliform Standard Plate Count Total THM
Sampling Site
Reservoir (Site 1)
Pretreatment (Site 2)
Post-coagulation (Site 3)
Post-filtration (Site 4)
Post-chlorination (Site 5)
(cfu/1OOml)
<0.33 - 150
0.33 - 38
0.33 - 52
5-60
<0.33 - 4
(cfu/ml)
51 -9000
80 - 380
0.6 - 430
10- 1700
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90
c
s
I
I
2
I
"5
B
99
99.9
99.99
99.999
99.9999
SPC
Dose (CLN) = 1.5 mg/L
pH = 7.6
Temp. = 17.2°C
I
SPC
\
I
I
0 10 20 30 40 50 60
Contact time, seconds
70 0 20 40 60
Contact time, hours
Figure 3. Prototype disinfection experiment with chlorine followed by a gravimeter
equivalent of ammonia after 15 seconds of contact time.
15-sec flowtime downstream of the
chlorine injection point (CLN). In both
experiments (CLN and NCL), the E coli
lys 147 population experienced a reduc-
tion greater than 99.999% in 1 sec or
less. The SPC organism population was
not nearly as susceptible to disinfec-
tion. A dose of 1.5 mg/L of chlorine
followed by ammonia inactivated 99%
of the SPC organisms in 1 min, but 1.5
mg/L of chlorine injected after ammo-
nia attained only 50% inactivation in 1
min. Both of these systems gave over
99.99% inactivation of SPC organisms
in 24 hr. At a 5.0-mg/L chlorine dose,
however, no significant differences
existed between the SPC organism
populations subjected to the CLN or
NCL disinfection schemes.
Disinfection results for SPC organ-
isms obtained in a single experiment
using chlorine dioxide as the disinfect-
ant at doses of 0.235, 0.390, and 1.49
mg/L indicated that SPC organisms in-
activation for all doses was similar—
90% inactivation was achieved in 1 min.
After 24-hr contact time, however,
99.3% inactivation was achieved with
the 0.135 mg/L CI02 dose, and greater
than 99.8% inactivation was achieved
with the 0.390 and 1.49 mg/L doses.
Figure 4 depicts a'single experiment in
which 0.25 mg/L doses of chlorine di-
oxide and chlorine were compared for
their efficacy as disinfectants. Chlorine
dioxide was the superior disinfectant for
SPC organisms achieving approximately
98.8% inactivation in 1 min compared
with only 55% for chlorine. After 1-hr
contact time, the activation achieved by
chlorine dioxide remained at 98% and
chlorine inactivation of the SPC organ-
isms increased to approximately the
same level. Both disinfectants reduced
the seeded E. coli lys 147 populations by
greater than 99.999% in approximately
20 sec.
The relationship between disinfec-
tant residual and SPC organism
inactivation was evaluated relative to
the residual's interaction with contact
time. Three models were developed to
express the residual: contact time rela-
tionship. When chlorine or chlorine fol-
lowed by ammonia were used in the
disinfection scheme, the data were fit to
the models separately using both free
and total residuals.
Model A: y = b0Rblt (1)
Model B: y = b0(Rt)bl (2)
Model C: y = b0Rbnb2 (3)
where: R = disinfectant residual, mg/L
t = contact time, sec
y = survival fraction of SPC
organisms
bo, bi, b2 = regression
coefficients
The statistics for the models are
shown in Table 2. Model A does not
describe the experimental data. How-
ever, Models B and C both provide signi-
ficant descriptions of the experimental
data as shown by associated correlation
coefficients and Fisher (F) test values.
The correlation coefficient and Fisher
test value are both directly related to
error in model fit; however, both are
shown for convenience. For those
experiments where chlorine or chlora-
mination was used. Model B appears to
be superior to Model C since the expres-
sion, (Rt)b , describes 40% to 63% of
"y"; whereas, the expression, Rbltb2,
associated with Model C describes only
16% to 40% of "y."
A disinfection experiment with 4 to 6
x 106 pfu/ml of a virus seed (bacterio-
phage f2) was performed at two chlorine
doses. At the low chlorine dose, 1.5
mg/L, disinfection of the phage to 7
orders of magnitude took place in 1 min.
Disinfection of indigenous organisms
from 770 to 3.3 cfu/ml occurred in 15
sec. At the higher chlorine dose, 5.0
mg/L, the phage was inactivated by 7
orders of magnitude within 30 sec and
the SPC was eliminated within 1 sec of
contact time.
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90
§
1
I
I
I
."*
i
I
99.9
99.99
99.999
99.9999
o-
1 \ Symbol Organism pH
H O SPC 7.5
\\ • SPC 7.6
\\ A f. CG////S 147 7.5
\\ A f. Colilys147 7.6
Temp. °C
21.0
23.5
21.0
23.5
Disinfectant
C12
CI02
Clt
C102
ft
0 /O 20 30 40 50 60
Contact time, seconds
70 0 2O 40 60
Contact time, minutes
Figure 4. Prototype disinfection experiments with a 0.25 mg/L dose of chlorine
dioxide compared with a 0.25 mg/L dose of chlorine.
Chemical Parameters—
The same chemical parameters that
were determined for the normal opera-
tion of the WTP were determined for the
prototype operation. Regardless of
disinfectant system or dose, there were
no substantial differences between the
values obtained for the prototype system
and those obtained for the WTP. The
only chemical parameter that was sig-
nificantly affected by operation of the
prototype system, compared with that of
the WTP, wasTHM production. Compar-
ison of the THM values with those
observed for the normal plant operation
show lower overall values for the proto-
type system. Similar results were ob-
served for the chlorine followed by
ammonia, ammonia followed by chlo-
rine, chlorine dioxide, and chlorine
(lowest effective disinfectant dose) dis-
infectant systems. In all cases, effective
disinfection occurred and lower
concentrations of Terminal THM were
observed.
The THM production was also deter-
mined for those prototype experiments
in which seed organisms were present.
No differences were observed in the
presence or absence of microorganism
seed. Table 3 shows the Total THM
values obtained in several disinfectant
systems. The duplicated data for chlo-
rine and chlorine followed by ammonia
at doses of 0.5 and 1.5 mg/L illustrates
the THM production observed without
added seed organisms.
As with disinfection, several models
were examined for THM production. The
model best expressing THM production
relative to time and chlorine residual is
given by equation 4.
Z = bo (I R,t) b1 (4)
i = 1
where: Z = THM concentration, //g/L
R, = free chlorine residual at
end of contact interval, mg/L
t, = contact interval, sec
M = number of contact
intervals
Bo' bi = regression coefficients
Application of test system data to the
above model yielded equation 5.
Z = 0.281 (I R,t,} 0466 (5)
i = 1
The correlation coefficient for 25 data
points was 0.815, significant at greater
than the 99% level, and the regression
coefficient, bi, was significant at
greater than the 99% level. Obviously,
use of the model is specific for the test
system from which it was derived.
Discussion
Analysis of the chemical data for the
Boerne Reservoir indicates that the
reservoir resembles a young, oligotro-
phic lake with no significant waste
inputs that currently affect water qual-
ity. Examination of the present and pro-
jected population and land use patterns
indicates that no significant industrial
or agricultural growth is expected in the
water shed and that future development
would be primarily residential and
recreational. Bacteriological data col-
lected also indicate no significant
human pollution at this time. Conse-
quently, the THM produced upon
clorination arose only from natural
organic material that was delivered to
the reservoir by runoff.
The overallTOC levels observed in the
reservoir were low, thus relative
similarity between systems indicates
that the rapid mixing techniques and the
addition of a biological seed does not
appreciably alter the chemical param-
eters characteristic of the water.
The effect of the prototype rapid mix-
ing system upon the added bacteriologic
seeds (E. coliC,E. coli\ys 147, and bac-
teriophage f2> was pronounced. Opera-
tion of the prototype without
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Table 2. Statistics Summary for Disinfection Models
Correlation Fisher
Data Model Regression Coefficients Coefficient Test
Source" Number b0 bi b2 r(R) F
CI2.-FAC A 3.66xW'3 6.223 — 0.163 0.527
CI2:TAC A 2.90x1Q-3 0.477 — 0.114 0.250
CLN.FAC A 9.10x10~A -1.114 — -0.430 2.043
CLN:TAC A 5.26x10'3 -2.681 — -0.649" 6.544*
CI02 A 7.50x1Q-3 1.659 — 0.279 1.353
CI2:FAC B 0.629 -0.301 — -0.587° 9.443C
CI2:TAC B 0.590 -0.275 — -0.558" 8.117*
CLN.-TAC B 0.447 -0.588 — -0.744" 11.179C
CLN.-TAC B 0.432 -0.481 — -0.611* 5.356*
CI02 B 0.214 -0.280 — -0.623C 10.1 39C
CI2:FAC C 0.398 -0.849 -0.277 0.731" 9.749"
CIZ:TAC C 0.376 -0.870 -0.240 0.693" 8.056"
CLN.-FAC C 0.163 -1.323 -0.357 0.943" 31.957"
CLN.-TAC C 0.354 -2.219 -0.165 0.981" 102.606"
CIOz C 0.222 -0.247 -0.278 0.673" 4.757"
a Disinfectant Systems: Clz - chlorine only; CLN - chlorine followed by ammonia;
CIOz - chlorine dioxide.
Residual Chlorine: FAC - free available chlorine; TAG - total available chlorine.
"95% level.
"99% level.
Table 3. THM Production from Several Disinfectant Systems
THM Production fag/L)
Disinfectant Disinfectant Total
Dosefmg/L) System CHCh CHCkBr CHCIBrz CHBr3 THM
0.00 None <0.1 <0.1 <0.1 <0.1 <0.1
0.25 Chlorine 1.06 1.80 1.43 <0.1 4.29
Chlorine Dioxide* 0.24 0.11 <0.1 <0.1 0.35
0.50 Chlorine 1.87 2.17 1.18 1.07 6.29
4.17 6.46* 8.22" 2.42" 21.6*
1.20 0.22 0.50 1.70 3.99
Chlorine + Ammonia* 0.99 0.87 0.61 <0.1 2.47
0.40 0.53
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other bacterial species present in most
raw or potable waters. In this study,
both E. coli C and F. coli lys 147 were
rapidly inactivated within 15 sec after
exposure to all test disinfectants. Similar
inactivation kinetics have been
observed by others. The SPC bacteria,
on the other hand, comprise a diverse
group of organisms that was found to be
considerably more resistant to disinfec-
tion during this study. Thus, the use of
SPC bacteria appears to be more desir-
able in defining the efficacy of potable
water disinfectants.
Of importance was the substantial
reduction in THM production observed
with the prototype system. As shown in
Table 3, lower disinfectant doses pro-
duced lower Total THM levels for chlo-
rine. There was, however, less of a
difference between Total THM formed
in the chlorine followed by ammonia
system (0.93 /jg/L to 10.24 fjg/L) than
was observed with the chlorine system
(6.29 fjg/L to 179.3 /jg/L) for the same
doses. The 15 sec of contact with free
chlorine before ammonia addition pro-
duced higher levels of Total THM when
compared with the addition of ammonia
followed by chlorine at the same dose
but the 15 sec of contact with free
chlorine also showed better disin-
fection. Thus, the ammonia addition
was able to prevent additional THM
from being produced.
The two best systems for minimizing
THM production were chlorine dioxide
and ammonia followed by chlorine. The
low level THM observed for chlorine
dioxide may have been due to low level
chlorine contamination in the system
produced because of the method of
generation of the chlorine dioxide.
Significant reduction of THM were ob-
served with chloramine and chlorine
dioxide as the disinfectants. A 17-fold
reduction in THM production was ob-
served at a 1.5 mg/L dose of chlorine
followed by ammonia when compared
with the same dose of chlorine alone. A
275-fold reduction in THM production
was observed for ammonia followed by
chlorine under the same conditions.
The prototype system was operated
with two chemical seeds to determine if
the rapid mixing system affects the THM
production in a predictable manner.
Three doses of humic acid and one dose
of chlorophyll-a were added to the
prototype system during the study
period. Both seed systems show
increased THM levels over the back-
ground indicating that these materials
do contribute to the THM production.
The smaller increases of THM observed
for the chlorophyll-a experiment are
consistent with the low level of seed
used. Experiments with humic acid did
not exactly parallel either the normal
plant operation nor the static laboratory
experiments with regard to time course
of THM production. The prototype sys-
tem did appear to affect the THM pro-
duction.1 This observation may be
explained by the kinetics of the reaction
of the disinfectant with the THM pre-
cursors. If diffusion of the disinfectant
to the organic precursor is rate-
controlling, increasing the mixing rate
will increase the reaction rate up to a
plateau value. If the reaction is not con-
trolled by diffusion, however, the reac-
tion rates will be independent of mixing.
For the present system, the THM pro-
duction is slower than that observed in
other systems. This can be interpreted
as a build-upof higher concentrations of
intermediate chlorinated compounds by
achieving the diffusion plateau. These
intermediates then break down more
slowly to produce THM because of self-
interaction or then follow other path-
ways to materials other than THM. At
long disinfectant residence times, the
levels of THM are comparable between
the laboratory and prototype experi-
ments.
Conclusions
1. Chlorine dioxide was a better disin-
fectant than chlorine for standard
plate count (SPC) organisms in the
prototype rapid mixing system.
2. For contact times greater than 1
hour, the chlorine followed by am-
monia disinfection system proved to
be a better disinfection system than
the chlorine dioxide and chlorine
disinfection systems on a gravimet-
ric basis.
3. Bacteriophage f2 was effectively in-
activated with chlorine under the
rapid mixing conditions used.
4. Highly turbulent mixing of chlorine
followed by ammonia addition
resulted in reduced THM levels (10-
20//g/L with THM formation poten-
tial of approximately 130//g/L) with
effective SPC organism reduction.
5. The prototype mixing system effec-
tively reduced THM initially and
maximized disinfection. Prolonged
contact chlorine produced addi-
tional THM if a free residual per-
sisted.
6. Soluble humic materials may be
responsible for a significant portion
of THM formation potential in the
Boerne reservoir water.
7. Chlorophyll-a was responsible for a
small but real portion of THM forma-
tion potential in the Boerne
reservoir water.
Recommendations
1. The chlorine, chloramination, anc
chlorine dioxide disinfection sys-
terns evaluated for bacteria
disinfection efficiency in this stud\
should be further evaluated for virus
disinfection efficiency.
2. The effects of mixing on mactivatior
of virus should be evaluated for dif
ferent disinfectant systems.
3. Specific mixing parameters shoulc
be evaluated to determine the
appropriate geometry and energy
input parameters applicable to en
gineering design of the mixing sys
tern; this would permit design of £
cost effective mixing system.
4. Isolation of endogenous organic
materials in raw reservoir water anc
the examination of their THM forma
tion potentials is needed.
5. The effect of higher added doses oj
chlorophyll-a on the production o'
THM should be evaluated.
The full report was submitted in fulfill
ment of Grant No. R-806046-01 -0 ty
the Center for Applied Research anc
Technology, the University of Texas a
San Antonio, under sponsorship of the
U.S. Environmental Protection Agency
8
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Charles A. Sorber, Robert F. Williams, Barbara E. Moore, and Karl E. Longley
were with the Center for Applied Research and Technology. The University of
Texas, San Antonio, TX 78285. (Sorber and Longley are presently with the
College of Engineering. The University of Texas, Austin, TX 78712 and Strauss
and Roberts are with Consulting Civil Engineers, Inc., Porterville, CA 93257.)
Gary S. Logsdon is the EPA Project Officer (see below).
The complete report, entitled "Alternative Water Disinfection Schemes for
Reduced Trihalomethane Formation: Volume I. Prototype Studies," (Order No.
PB 82-227 471; Cost: $ 12.00, 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
*USGPO:1M2-559-092-460
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