United States
Environmental Protection
Agency
Water Engineering Research
Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-85/138 Jan. 1986
&ER& Project Summary
Cost and Performance
Evaluation of In-Plant
Trihalomethane Control
Techniques
J. S. Taylor, D. Thompson. B. R. Snyder, J. Less, and L. Mulford
A study was conducted to evaluate
the costs and performance of new
technology for reducing trihalometh-
anes (THM) in drinking water on a
bench-, pilot-, and plant-scale. The four
Florida plant sites that were selected for
study used highly organic surface or
ground water supplies and served popu-
lations of fewer than 30,000 or fewer
than 10,000. Low-pressure membrane
processes (ultrafiltration), polyvalent
aluminum chloride (PACI) coagulation,
flotation, lime softening succeeded by
alum coagulation, and conventional
lime softening and alum coagulation
were investigated for THM reduction at
these sites.
This Project Summary was developed
by EPA's Water Engineering Research
Laboratory, Cincinnati. OH. to an-
nounce key findings of the research
project that is fully documented in a
separate report of the same title fsee
Project Report ordering information at
back).
Introduction
The purpose of this cooperative study
was to demonstrate the performance and
costs of possible new technologies rel-
ative to conventional technologies for
trihalomethane (THM) control in drinking
water. The scope of work was to identify
new technology for THM control, identify
sites where THM control was needed,
and execute in-plant studies with the
necessary cost documentation.
The technologies selected for this proj-
ect were polyvalent aluminum chloride
(PACI) coagulation, sequential treatment
of alum coagulation preceded by lime
softening, membrane processes, and
flotation. The selection of sites was
coordinated with EPA Region IV and
limited to Florida because the varying
water supplies and THM problems in that
state allowed more technologies to be
investigated within the project budget.
Coordination with the Florida Depart-
ments of Environmental Regulation and
Public Health resulted in the survey of
more than 50 potential sites. Following
plant visits, four sites were selected: (1)
The Village of Golf, Florida (VOG), a small
lime-softening plant serving 2000 sea-
sonal residents with water containing
THM's averaging more than 700yug/L; (2)
the Acme Improvement District (AID), a
lime-softening plant serving slightly few-
er than 10,000 residents and averaging
THM's of 380 //g/L (both AID and VOG
are near West Palm Beach, Florida, and
use ground waters); (3) the Olga water
treatment plant (near Ft. Myers, Florida),
an alum plant that uses Caloosahatchee
River water, has THM's of 700 yug/L, and
serves about 18,000 people; and (4)
Venice, Florida (the alternative site), a
water treatment plant that serves 13,000
with a blended water from lime softening
and reverse osmosis (RO) plants.
Plant Optimization
Optimization of existing plant processes
for THM reduction was conducted at all
four sites to develop comparable cost data
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and for the benefit of the plants. Bench-
scale and pilot-plant membrane process-
es were investigated at VOG, AID, and
Olga. Flotation experiments were con-
ducted at Olga. Pilot-plant sequential
treatment was done at AID. Seasonal
PACI/alum coagulation was studied on a
plant-scale at Olga.
Bench- and plant-scale investigations
for plant optimization were conducted at
three lime softening plants located in
VOG, AID, and Venice, Florida. The bench
tests clearly showed that the organic
parameters studied-color, dissolved or-
ganic carbon (DOC), trihalomethane for-
mation potential (THMFP), and total or-
ganic halogen formation potential
(TOXFP) could be reduced by increasing
softening pH. These plants typically soft-
ened at pH 10.3 to a total hardness (TH) of
100 ±50 mg/L as CaCOs and removed
20% to 30% of the raw color, DOC,
THMFP, and TOXFP. The jar tests indi-
cated an additional 1% to 2% DOC
removal for every 0.1 pH unit increase in
the reaction pH from 9.5 to 11.5. Gen-
erally, the THMFP reduction was greater
than the DOC reduction because CI2
demand was decreased as a result of the
lower DOC. The jar test studies also
indicated that 20 mg/L or less of alum
would increase organic removal 5% to
10% during softening and would not be
present in the finished water.
As a result of the bench-scale studies,
plant-scale investigations were imple-
mented at each of the lime-softening
plants. Similar process changes were
made at the three sites, including (1)
raising the reaction pH during softening
from 10.3 to 11.0-11.3, (2) reducing the
chlorine dose by eliminating chlorine as a
means of color removal and pH reduction,
and (3) adding H2SO4 to offset the in-
creased softening pH. At all three sites,
THM's were reduced by nearly half, as
were TOX and DOC relative to normal
operations. Generally, 80% of the color
was removed during softening, and hard-
ness was increased 50 to 80 mg/L. THM's
at AID and VOG averaged 240 and 330
fjg/L, respectively, during the plant test,
and were therefore above the maximum
contaminant level (MCL). Venice reduced
their THM's to 85 fjg/L during the plant
test and has adopted a high-pH softening
process for THM control. The additional
cost of high-pH softening ranged from
$0.02/1000 gal atVenice to $0.22/1000
gal at VOG. The percentage of unit cost
increase for high-pH softening was 2% at
Venice, 19% at AID, and 20% at VOG,
which corresponded with 32%, 50%, and
45% THM reduction, respectively.
PACI and Alum Treatment
The PACI and alum investigations were
made on both a bench- and a plant-scale
at the Olga water treatment plant in Lee
County, Florida, for both the wet and dry
seasons. The organic parameters inves-
tigated were DOC, THM, TOX, and color
as a result of coagulant dose and pH.
Aluminum residuals, turbidity, sludge
volumes, and dry-season softening were
also investigated.
The raw water color averaged about 57
chloroplatinate units (cpu) during the dry
season tests and increased 228% to 130
cpu during the wet season tests. Raw
water DOC averaged 19.6 mg/L during
the dry season plant tests and increased
9% to 21.4 mg/L during the wet season
tests. The raw turbidity averaged 6 NTU
during the wet season and 4 NTU during
the dry season. The alkalinity and hard-
ness during the wet season were ap-
proximately 140 and 110 mg/L as CaC03,
and they increased to 250 and 160 mg/L
as CaC03 during the dry season. The raw
water used during both plant tests was a
low-turbidity, high-color water that would
normally be treated by sweep coagulation
for color removal only. Two PACI coag-
ulants—1 DOS,* a sulfate chloride base,
and 190, a chloride-based coagulant-
plus alum were compared for organic
removal.
Jar testing during the wet and dry
seasons demonstrated that the optimum
coagulation pH was 5.0 to 6.0 for DOC
and color removal for all coagulants. PACI
100S was superior to PACI 190 for the
removal of DOC and color in jar tests; thus
it was selected for plant testing. DOC
removal increased with increasing coag-
ulant dose between pH 5.0 and 6.0, but it
appeared to approach a limiting value.
Coagulant doses of 117 mg/L as alum
removed 60% of the DOC and 90% of the
color in the wet and dry season jar test.
Increasing the coagulant dose to 175
mg/L increased DOC removal 5% to 10%
and had less effect on color removal. The
percentages of color and DOC removal
during the wet season were slightly
higher (<5%) than during the dry season
for all coagulants. However, the actual
DOC concentration and, to a less extent,
the color remaining in each season were
approximately the same at equivalent
conditions for each coagulant. Wet-sea-
son THMFP reduction was very similar to
DOC removal. The optimum pH range for
•Mention of trade names or commercial products
does not constitute endorsement or recommenda-
tion for use.
THMFP reduction was 5.0 to 6.0 for all
coagulants, and increasing the coagulant
dose increased the THMFP reduction in
all jar tests. Doses of 117 to 175 mg/L as
Alz(S04)3-14H20 realized 90% of the max-
imum THMFP reduction during coagula-
tion.
In all the jar testing, alum generally
removed slightly more «5%) DOC, color,
and THMFP than PACI. The seasonal jar
tests did not indicate a major difference in
coagulant demand for organic removal,
possibly because of the small DOC in-
crease during the wet season. Aluminum
residuals after coagulation with either
PACI-100S or alum were typically less
than 0.4 mg/L aluminum and were
controlled by coagulation pH. These levels
would not cause post-precipitation prob-
lems. Removal of DOC and THMFP during
coagulation should exceed 60% and be
accompanied by more than 90% color
removal. Although DOC, THMFP, and
color removal vary directly with equiva-
lent coagulation dose and pH, DOC is the
better indicator of THMFP than color.
Plant tests using alum and PACI were
conducted in the dry and wet season for
approximately 30 days each. The alum-
inum residuals in the distribution system
were generally less than 0.2 mg/L. The
aluminum residuals of 5 mg/L occurred
in the distribution system under the
normal plant process of using alum in
conjunction with softening. The seasonal
plant data demonstrated that finished
aluminum residuals are controlled by
coagulation pH, which should be 5.5 to
6.5 for minimum aluminum residuals. No
significant difference existed between the
sludge volumes produced during alum or
PACI coagulation during the plant tests
for equal operating conditions. The tur-
bidity carryover from the settled water
using either alum or PACI coagulation
was typically less than 2 NTU and ex-
hibited no differences between the two
coagulants. A PACI-100S dose of 80
mg/L was not sufficient to produce a
settleable floe during the plant test. An
equal alum dose produced a settleable
floe.
Softening preceded coagulation during
the dry-season plant test. Although soft-
ening removed 20% of the DOC and 43%
of the color, the succeeding alum or PACI
coagulation produced no more color or
DOC removal than if coagulation had
been used alone. The addition of 1.2
meq/L of alkalinity to the softening
process reduced the calcium hardness to
only 100 mg/L as CaC03 although the
alkalinity and total hardness were bal-
anced. The softening pH varied from 9.5
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to 10.6, with 10.0 achieving the lowest
hardness.
During the wet season, the DOC aver-
age reduction was 57% to an 8.6 mg/L
residual by PACI and 58% to a 7.0 mg/L
residual by alum. The dry season DOC
removals averaged 48% (to a 10.1 mg/L
residual) for alum and 39% (to a 12.1
mg/L residual) for PACI. This lower reduc-
tion during the dry season was due to a
higher coagulation pH caused by a hard
CaC03 scale in the reactor. The THM's at
the plant tap during the wet season
averaged 235 jug/L for PACI and 248
fjg/L for alum. The dry-season THM's at
the plant tap averaged 204 jug/L for PACI
and 175pg/Lforalum, which represented
a decrease of 13% to 30% in the dry
season. However, TOX for alum or PACI
were 710 and 714 fjg/L during the wet
season, and they decreased to 421 and
380 /ug/L during the dry season. Color
removal was similar to DOC removal,
reaching levels of 91% to 94% for PACI
and alum during the wet season and 78%
to 89% for PACI and alum during the dry
season.
The DOC:THM:TOX ratios averaged
1:32:94 during the wet season and
1:16:39 during the dry season. The
THM:TOX ratio did not vary as much as
the DOC:THM:TOX ratio, since both THM
and TOX are directly affected by CI2 dose.
The THM:TOX ratio was 1:2.9 and 1:2.4
during the wet and dry seasons, respec-
tively.
The operation cost increased from
$1.07/1000 gal to $1.16/1000 gal when
the maximum alum dose was used during
the wet season. This 8% cost increase
decreased plant THM's by 72%. The
operational cost during the wet season
for PACI was $1.62/1000 gal, and similar
THM reductions were obtained. The cost
of producing water was less during the
dry season because of relativley constant
labor and power costs and increased
production. The plant costs were in-
creased from $0.60/1000 gal to $0.787
1000 gal using the maximum alum dose.
This cost increase of 23% reduced THM's
by 39%. Dry-season PACI costs were
$1.02/1000 gal and decreased THM's by
29%.
Sequential Treatment
Lime softening followed by alum coag-
ulation was investigated on a bench- and
pilot-plant scale at the AID water treat-
ment plant. Jar tests were conducted to
determine the best sequence of softening
and coagulation for THM precursor re-
moval. Pilot plant testing was executed in
two unused reactors that were serially
connected for the project. The raw water
contained no turbidity. The hardness and
alkalinity were typically 350 mg/L as
CaC03, with color and DOC values of
approximately 40 cpu and 15 mg/L,
respectively.
The initial bench-scale sequential treat-
ment work indicated that 60% of the DOC
could be removed by sequentially treating
AID raw water with softening and coag-
ulation, regardless of order. However, if
pH was adjusted to 5.5 during coagula-
tion, this DOC removal was increased
25%. Color removal was 85% to 90% and
varied directly with removals of DOC and
THM precursors. THMFP was reduced to
a range from 167 to 217 fjg/L by softening
at pH 11.0 and coagulation at pH 5.5,
which represented an increased average
reduction of 45% relative to softening
only at pH 10.3. TOX formation was
generally three times THM formation.
The sequential treatment isopleths
showed that softening at pH 11.0 aver-
aged41 % DOC, 67%THMFP, 65%TOXFP,
and 63% color removal. These were
increased removals relative to softening
at pH 10.3 (+11 % DOC, +3% THMFP, +8%
TOXFP, +3% color). Following lime soften-
ing with alum coagulation also increased
organic removal. The optimum pH and
dose were 5.0 to 6.0 and 117 mg/L alum.
The DOC, THMFP, TOXFP, and color were
reduced an additional 30%, 13%, 23%,
and 30%, respectively. Alum coagulation
following softening at pH 10.3 increased
the percentage of removal for all the
organic parameters more than alum
coagulation following softening at pH 11.
However, the lowest concentrations of
DOC, THMFP, TOXFP, and color were
from samples softened at pH 11.0 and
coagulated at pH 5.0 to 6.0, although
these differences were typically less than
5%.
Plant testing of sequential treatment
was conducted by softening at pH 10.3
and 11.0 followed by alum coagulation
from pH 7.0 to 5.0. The alum dose was
varied from 60 to 109 mg/L. The results
demonstrated, as did the jar tests, that
alum coagulation following softening will
decrease the DOC, THMFP, TOXFP, and
color relative to softening alone. The
maximum DOC and color removals ob-
tained in the plant tests were approx-
imately 70% for DOC and 93% for color.
The THMFP and TOXFP were reduced
from 20% to 25%. Slightly better removal
occurred for all parameters when pH 11
rather than pH 10.3 softening preceded
coagulation. The organic removal
achieved in sequential treatment indi-
cates that DOC, THMFP, and TOXFP can
be reduced an additional 20% to 25%
when alum coagulation is used in series
with softening. The chemical cost in-
crease would vary from $0.10 to $0.157
1000 gal, which would increase AID O&M
cost ($0.35/1000 gal) by 30% to 43%.
These data do indicate that, relative to the
coagulation testing at other sites, adding
softening to a coagulation process could
not increase organic removal.
Membrane Processes
Bench-scale (1000 gpd) and pilot-scale
(25,000 gpd) investigations of membrane
processes were conducted at two sites
that used ground water supplies—VOG
and AID. Bench-scale investigations were
also conducted at one site (Olga) that
uses a surface supply. Initially, one RO
and six ultrafiltration (UF) low-pressure
membranes were purchased and tested
for product (permeate) water quality on a
bench-scale level. The UF membranes
are designed for operation up to 100 psi,
whereas the RO membrane is intended to
operate at 200 to 250 psi. Bench results
from all three sites demonstrated that
only two membranes could produce a
water from these highly organic sources
that would meet the THM MCL and
maintain a CI2 residual—the Filmtec UF
membrane (N-50) and the Filmtec RO
membrane (BW 3030).
The nominal molecular weights re-
jected by each membrane were supplied
by each manufacturer and ranged from
40,000 to 100. Bench-scale testing indi-
cated that a molecular weight rejection of
2,000 would typically pass 50% of the
raw DOC but only 20% of the color. The
resulting product THMFP was generally
800 A/g/L for the surface water source
and 400 jug/L for either ground water
source. The ultrafilter with a molecular
weight rejection of 400 passed less than
10% of the DOC and 3% of the color at any
site, and it typically produced a THMFP of
less than 50 /ug/L at the ground water
sites and approximately 100 jug/L at the
surface water sites. The product was
essentially colorless, and the DOC was 2
mg/L or less at all three sites. The color,
DOC, and THMFP of the RO membrane
were approximately equal to the color,
DOC, and THMFP of the best UF mem-
brane. However, the RO membrane oper-
ated at 200 psi and rejected species with
a molecular weight of 100 or greater as
opposed to the UF membrane, which
rejected species with a molecular weight
of 400 or greater at a pressure of 100 psi.
The RO membrane rejected a much
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higher inorganic fraction than did the UF
membrane. The RO membrane rejected
more than 90% of the total dissolved
solids (IDS), total hardness (TH), chloride
(CO, and sodium (Na+) at all sites, wher-
eas the UF membrane inorganic rejection
varied from 50% to 70% for the various
parameters. Since the N-50 was the
membrane that operated at the lowest
pressure and still produced a water that
met the THM MCL, it was selected for
extended operation.
The N-50 ultrafilter was installed at
Olga in a bench-scale unit capable of
producing 1000 gpd, and it operated for
740 hr over a 45-day period. An opera-
tional percentage of recovery and feed
pressure matrix was developed to deter-
mine the extended study operating condi-
tions. Over matrix conditions of 60 to 120
psi feed pressure and 60% to 90% recov-
ery, product water quality improved at
high pressure (105+ psi) and lower recov-
ery (60%). The matrix results indicated
the THM MCL could be met if the opera-
tional conditions were 105 psi with 60%
recovery. At these conditions, product
water quality and the percentage of
rejections were 1.6 mg/L DOC (92%), 3
cpu color (93%), 172 mg/L TDS (64%), 78
mg/L as CaCO3 TH (65%), 60 mg/L CI"
(40%), and 68 mg/L as CaC03 alkalinity
(59%) with pH 7.8. During the extended
operation, pressure was varied from 60 to
100 psi with recoveries of 60% to 90%.
The THM MCL was met for 105 psi and
60% recovery, and for 75 psi and 60%
recovery immediately after the membrane
was chemically cleaned. The flux de-
creased with time during the extended
study from 18 to 14 gpd/ft2 over 150 hr of
operation. After cleaning with the pres-
sure at 95 psi, the flux declined from 22 to
16 gpd/ft2, but the product quality re-
mained constant. Flux was independent
of recovery during the extended study.
The water quality and percentage of
rejection for the conditions meeting the
THM MCL were 2.7 mg/L DOC (88%),
156 fjg/L TOXFP (80%), and 3 cpu color
(98%). The inorganic water quality was
145 mg/LTDS (65%), 68 mg/L Cf(32%),
85 mg/L as CaC03TH(64%), and 7 mg/L
as CaC03 alkalinity (58%). The pH was
7.8, and the water was stable.
A 25,000-gpd mobile UF pilot plant
using the N-50 membrane was built in a
30-ft trailer. The UF plant was housed in
the 20- by 8-ft rear section of the trailer
and equipped for antiscalant feed, acid
feed, chlorination, stabilization, prefiltra-
tion, and storage as well as UF with
variable recovery (50% to 90%) and feed
pressure (80 to 120 psi). This plant was
installed and operated at VOG for 365 hr
from January 2 to March 3,1985. Initially,
an operational test matrix was developed
for water quality and flux from varying
percentages of recovery and pressure.
Product water DOC, color, and THMFP
were independent of recovery and pres-
sure over the test conditions and averaged
less than 2 mg/L, 1 cpu, and 50 fjg/L,
respectively. Product water TDS and TH
increased with increasing recovery, were
independent of pressure, and varied from
25% to 75% of the raw water value.
Operating conditions at VOG were set at
90 to 105 psi and 75% recovery to produce
a water with a TH of 150 mg/L as CaC03,
essentially no color, and THMFP of 50
/jg/L or less. During the VOG operation,
the product water quality and the per-
centage of rejection from the raw water
were 1.9 mg/L DOC (88%), 3 cpu color
(97%), 27 yug/L THMFP, and 47 /ug/L
TOXFP. The raw water TDS, TH, and
alkalinity were reduced to 195 mg/L
(60%), 142 mg/L as CaCO3 (62%), and
135 mg/L as CaC03(60%), respectively.
The final pH was 7.5, and the water was
stable. The product water flux declined
32% during the VOG operation from 20 to
13.4 gpd/ft2. The water temperature was
approximately 25°C and essentially did
not vary during the operation.
On March 3, 1985, the UF pilot plant
was moved from VOG to AID and oper-
ated until May 31,1985, with an elapsed
time of operation of 1020 hrs. A second
operational test matrix was developed
and showed that color, DOC, and THMFP
removal were independent of product
recovery and feed pressure over the test
conditions (50% to 90% product recovery
and 80 to 120 psi). Product water color,
DOC, and THMFP were typically less than
2 cpu, 2 mg/L, and 30/ug/L, respectively.
TH and TDS removals were independent
of pressure and dependent on product
recovery, and they varied from 25% to
75% of the raw water value. Long-term
operating conditions varied from 90 to
103 psi and 67% to 83% recovery. The
product water quality and percentage of
rejection from the raw water were 1.5
cpu color (97%), 2.0 mg/L DOC (86%), 50
fjg/L THMFP, and 48 fjg/L TOXFP. The
product water TDS, TH, and alkalinity
values and percentage of rejection were
282 mg/L (43%), 187 mg/L as CaC03
(40%), and 180 mg/L as CaC03 (37%),
respectively. The pH averaged 7.5, and
the product was stable.
The UF pilot plant was designed with
the membranes in four pressure vessels
connected two each in series. The aver-
age pressure drop in the first pressure
vessel was 32 psi (11 psi/membrane)and
41 psi (13 psi/membrane) in the second
pressure vessel. The flux at AID rose
slowly from the range of 14 to 15 gpd/ft2
during the first 150 hr of operation. After
a chemical cleaning, it rose to slightly
more than 20 gpd/ft and remained there
for the duration of the study.
Cost of construction of a UF plant
should be slightly less than an equivalent
RO plant because of less expensive
membranes and lower pressure require-
ments. Power costs should generally
decrease from 75% (100 psi/400 psi) to
50% (100 psi/200 psi). The construction
and O&M costs were estimated at $0.29
and $0.47/1000 gal for a 1-MGD UF
plant.
Flotation
Bench-scale investigations of dissolved
air flotation (DAF) in conjunction with and
after alum coagulation of a high-color,
low-turbidity water were conducted using
a small DAF pilot plant supplied by
Komline Sanderson. After contact with
DAF, alum floe was found to shear,
solubilize, and post-precipitate after
sampling was complete. DOC and color
removal following DAF of alum-coagulat-
ed waters were less than those having
only alum coagulation. Foam flotation
using alcohol-based surfactants common
to the mining industry did not remove
DOC from the same high-color, low-tur-
bidity potable water source.
Summary of Results
The DOC removal from each of the
processes investigated was different.
Lime softening typically removed 10% to
30% of the raw DOC at normal reaction
pH's of 9.0 to 10.3. The DOC removal
during softening could be generally in-
creased to 40% to 50% by raising the
reaction pH. Alum or PACI coagulation
should remove 60% to 70% of the raw
DOC if the reaction pH is 5.0 to 6.5 and
the coagulant dose is adequate—80 to
180 mg/L as AlzfSO^a'IAH^ in the
waters investigated. Sequentially treating
water with lime softening and alum
coagulation would remove 60% to 70%
DOC and offers essentially the same
removal as alum coagulation. RO at 200
psi or UF at 100 psi with selected
membranes will generally remove 90% or
more of the initial DOC. No process other
than membranes can achieve this high
removal for a prolonged period. These
general statements concerning DOC re-
movals are supported by the test results
of investigations conducted on a low-
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turbidity, high-color surface water and on
a low-turbidity, high-color ground water.
Although DOC is a better surrogate
than color for THM or TOX formation,
DOC cannot be used indiscriminately as a
surrogate for chlorinated organic forma-
tion. These results and others have
suggested that DOC's of less than 4 mg/L
following conventional coagulation or
softening are required to meet the THM
MCL. Indeed, when the DOC was reduced
to a range of 5 to 6 mg/L by coagulation,
THMFP's of less than 200 yug/L were
recorded. The DOC could not be reduced
any lower by coagulation or softening of
these waters. However, DOC's below 2
mg/L achieved by UF hadTHMFP's above
100/ug/L. The results indicated that DOC
is the best THM surrogate on a process
basis. DOC from membrane processes is
generally more reactive than DOC from
precipitative processes. The THM reduc-
tion is significantly greater than the DOC
removal because of the reduced chlorine
demand, which also reduces THM's. The
plant experiences indicate that a 30%
reduction inTHM is possible if the process
is tuned for increasing organic removal
and minimizing chlorine dose.
Conclusions
Plant Optimization
• DOC, THMFP, TOXFP, and color are
reduced as the reaction pH during
softening is increased.
• If the THM's are 150//g/L or less, the
THM and CI2 residual MCL can prob-
ably be met in a lime-softening plant
by increasing the reaction pH and
lowering the CI2 dose.
• Optimizing a lime-softening plant for
THM control will increase product
hardness by 75 mg/L as CaCO3, or
more.
PAC I/Alum Coagulation
• PACI has less base-neutralizing ca-
pacity than alum, which would gener-
ally be a disadvantage for organic
removal from a low-turbidity, high-
color water because of the importance
of a low-coagulation pH.
• Color, DOC, THMFP, and TOXFP re-
duction by either PACI or alum coag-
ulation was maximized near pH 5.5.
• Aluminum residuals after PACI or alum
coagulation were dependent on co-
agulation pH and minimized from pH
5.0 to 6.0.
• DOC was a better surrogate parameter
for THM and TOX than was color.
• Unit cost depended more on seasonal
water demand than on chemicals
required for optimum organic removal.
• Preceding either PACI or alum coag-
ulation with lime softening does not
increase the organic removal during
coagualtion.
• THM:TOX ratios were less variable
than DOC:THM:TOX ratios because of
the effect of chlorine dose on THM and
TOX.
• Alum floe was more settleable at low
coagulant doses (80 mg/L) than was
PACI floe.
• Alum was slightly superior to PACI for
color, DOC, and THMFP reduction.
Sequential Treatment
• The order of lime softening and alum
coagulation was not significant for
maximizing organic removal if alum
coagulation is added to an existing
lime-softening plant.
• Alum coagulation added to an existing
lime-softening process significantly
increases the organic removal and
reduces the THMFP; however, lime
softening will not increase the organic
removal when added to an existing
alum coagulation process.
Membranes
• A 150-day pilot-plant UF study of two
highly organic ground waters (both of
which produced more than 400 /ag/L
THM's when conventionally treated)
produced a finished water that easily
met the MCL's for CI2 residual and
THM's.
• Compared with membranes, no other
process has the same practical capac-
ity for the removal of THM precursors.
• The vast majority of THM precursors
were rejected by a membrane that has
a molecular weight cutoff of less than
2000 but greater than 400.
• The effect of recovery percentage and
feed pressure on product water quality
was site-specific.
• Flux was site-specific, ranging from
approximately 20 to 10 gpd/ft2, and it
was generally independent of the
recovery percentage.
• Caloosahatchee River water needs
more elaborate pretreatment than
single-pass sand filtration to maximize
N-50 permeate flux. Flux values during
the extended study were 12 to 18
gpd/ft2, and they decreased contin-
uously with time of operation.
• N-50 permeate quality is a function of
feed pressure, percentage of recovery,
and membrane surface condition. The
best inorganic and organic rejection
occurred at the highest pressures, the
lowest recoveries, and the cleanest
membrane condition. With the Caloo-
sahatchee water, the THM MCL was
met only at the 105 psi, 60% recovery
and the 75 psi, 60% recovery condi-
tions for a cleaned membrane. Mem-
brane surface conditions appear to be
as important as the pressure-recovery
setting for organic rejection. Poor
permeate quality during extended op-
eration was primarily due to mem-
brane fouling.
• Inorganic parameters such asTDS and
TH were reduced approximately 40%
by UF at approximately 100 psi and
75% recovery.
• The product water at VOG, AID, and
Olga exhibited low DOC and color
values that would not require addi-
tional color removal through chlorine
bleaching.
• The organic quality produced during
the VOG and AID UF pilot-plant tests
were independent of the percentage of
recovery and feed pressure for the test
conditions.
• The inorganic quality produced during
the UF pilot-plant tests at VOG and AID
were independent of the feed pres-
sures and improved as the percentage
of recovery decreased.
• UF with the N-50 membrane produced
a stable, noncorrosive water.
• The operation of the UF membrane
pilot plant required less effort and skill
than the operation of the other pro-
cesses investigated, and it produced a
vastly superior organic water quality.
Flotation
• DAF of alum sludge caused floe shear
and post-precipitation. It removed no
more organics than did conventional
alum coagulation.
• Foam flotation using conventional
alcohols common to the mining indus-
try removed no DOC from the raw
water.
Recommendations
• PACI studies should be expanded to
include high-turbidity and/or low-alk-
alinity waters.
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• DOC could be used as a surrogate for
THM formation on a site-specific basis.
• Specific organic rejection by mem-
brane processes should be investigat-
ed to include priority pollutant remov-
als and other organics capable of
adverse health effects.
• Cost and performance information on
membrane processes should be made
available to the water utility industry
as soon as possible so that they can be
considered in planning for plant ex-
pansion or new plant construction.
• A national survey of membrane plants
should be conducted to determine (1)
the cost of construction, operation,
maintenance, (2) operating conditions
and problems, (3) raw and finished
water quality, and (4) brine disposal
and membrane life.
• Further bench and pilot-plant testing
using UF and RO membranes should
be conducted on surface and ground
waters of varying organic quality to
ascertain the relationships among
water q ual ity, recovery, pressu re, flux,
membrane cleaning, membrane mater-
ials, and membrane life.
• Newly constructed membrane plants
using raw waters normally treated by
lime softening or coagulation should
be monitored for cost, water quality,
and operating conditions, and that
information should be published for
the water utility industry.
• A permanent membrane plant that
uses UF and RO should be constructed,
operated, and monitored for 2 to 5
years to provide for a small community
(fewer than 3,000 residents) water
that does not exceed the THM MCL.
Such a project could (1) establish mem-
brane processes as a practical means
of organic control, (2) provide the best
possible data on cost, water quality,
and operation, and (3) demonstrate the
ease of operation, modular expand-
ability, operator skill required, and
consistency of membrane processes.
• A mobile, pilot-plant-scale, hybrid sys-
tem of low-pressure RO and UF mem-
branes should be constructed and
operated to assess organic control and
production of waters with suitable
hardness values. Also, saltwater-in-
truded, high-organic waters could be
studied, particularly the coastal wat-
ers.
• Research and development should
continue on molecular-weight rejec-
tion by membranes. This work has
indicated that significant THM pre-
cursor rejection is accomplished be-
tween molecular-weight rejections of
400 and 2000. A membrane that has a
molecular weight rejection greater
than 400 may have as good a THM
precursor rejection and be less ex-
pensive to operate.
The full report was submitted in fulfill-
ment of Cooperative Agreement No. CR-
811039-01-0 by the University of Central
Florida under the sponsorship of the U.S.
Environmental Protection Agency.
. S. GOVERNMENT PRINTING OFFICE:1986/646-l 16/20752
-------
J. S. Taylor, D. Thompson, B. R. Snyder, J. Less, and L. Mulford are with the
University of Central Florida, Orlando. FL 32816.
J. Keith Carswell is the EPA Project Officer (see below).
The complete report, entitled "Cost and Performance Evaluation of In-Plant
Trihalomethane Control Techniques." (Order No. PB 86-130 515/AS; Cost:
$34.95, 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
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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