United States
Environmental Protection
Agency
Water Engineering Research
Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-85/119 Nov. 1985
&ERA Project Summary
Trihalomethane Precursor
Removal by Coagulation
Techniques in a Lime-Softening
Plant (A Three-Phased Study)
J. C. Thurrott, H. Zwart-Duryea, K. McGurn, and K. Riger
A study was conducted to identify
and evaluate a new method for treating
drinking water to reduce trihalomethane
(THM) formation during water treat-
ment. The study method coagulated
THM precursor materials with a new
polymeric coagulant and removed them
before the water was chlorinated.
Bench tests, pilot tests, and plant-scale
tests were conducted on Daytona
Beach, Florida, groundwater to com-
pare a conventional lime-softening
process with the new process, which
used lime softening with a new poly-
meric coagulant.
The experimental coagulant system
reduced THM levels 50 percent more
than did the conventional treatment
methods, but the projected costs were
too high to warrant its continuous, full-
scale use in Daytona Beach.
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 (see
Project Report ordering information at
back).
Introduction
This research program identified and
evaluated a drinking water treatment
scheme that reduced the formation of
trihalomethanes (THM) during the treat-
ment process by coagulating the THM
precursor materials and removing them
before chlorination. The process was
evaluated in bench testing, in an 18.9-
L/min pilot plant test, and ultimately in a
plant-scale trial. These trials simultan-
eously compared the potential for pre-
cursor removal from Daytona Beach,
Florida, groundwater by conventional
lime softening and by lime softening with
a new polymeric coagulant (XE-392,
Rohm & Haas).*
The Daytona Beach water system was
composed of two lime-softening plants
and normally produced a finished water
with average THM concentrations of 100
fjg/L at the plant and more than 200/jg/L
in the distribution system. Treatment
processes included lime softening, coag-
ulation, f luoridation, chlorination to a free
residual, and mixed-media filtration.
Previous studies of this system were
directed toward reducing THM concentra-
tions through a change in the point of the
chlorination and improvements in the
coagulation process. In a 1981 pilot plant
investigation, the experimental polymeric
coagulation showed promising removals
of organic THM precursor materials.
Procedures
The current research program eval-
uated the use of XE-392 by itself and in
conjunction with conventional coagu-
lants. Bench-scale tests screened a num-
ber of coagulant combinations. The most
promising treatment scheme was then
evaluated in an 18.9-L/min (5-gal/mm),
"Mention of trade names or commercial products
does not constitute endorsement or recommenda-
tion for use.
-------
trailer-mounted pilot plant on loan from
the U.S. Environmental Protection Agency
(EPA). Following successful pilot plant
operation using XE-392, ferric sulfate,
and a non-ionic polymer in a lime-soften-
ing process, the same treatment scheme
was evaluated on a full-scale basis. A
flow of 0.13 m3/s (3 mgd) was treated at
the Ralph Brennan Water Treatment
Plant in Daytona Beach for 30 days. An
additional pilot plant run was later per-
formed using an improved analog of XE-
392, which was designated XE-513.
Results and Conclusions
Effluent THM concentrations from the
EPA pilot plant were identical to those
obtained during the full-scale trial at XE-
392 doses of 18 mg/L (see Figure 1).
Thus the pilot unit accurately simulated
the full-scale lime-softening process at
the Brennan Water Plant.
Extensive analytical data were collected
throughout the pilot plant and plant-scale
trials. Results indicated that coagulation
with XE-392 and XE-513 produced sub-
stantial reductions in THM concentra-
tions, both immediately after chlorination
and after a 24-hr storage period used to
approximate distribution system resi-
dence time. Figure 2 compares 24-hr
trihalomethane formation potentials
(THMFP's) for both raw and finished
waters in the jar tests, pilot tests, and
plant-scale tests.
The correlation of total organic carbon
(TOC) and ultraviolet (UV) absorbance
with total trihalomethanes was investi-
gated to establish an easily performed
process control test. Reductions in TOC
and UV absorbance correlated well with
reduction of THM's. In general, THMFP
reductions were less than UV absorbance
reductions but greater than TOC reduc-
tions. The use of UV may lend itself to the
development of a continuous stream
analyzer to monitor THM control practic-
es.
No secondary deterioration in water
quality was noted from the experimental
treatment scheme, and no major opera-
tional problems were experienced during
the trial. The experimental coagulant
system reduced THM concentrations 50
percent more than did the conventional
treatment methods used in the Daytona
Beach Treatment Plants. Results of the
pilot run using XE-513 indicated that
lower polymeric coagulant doses could be
used to achieve the desired THM pre-
cursor removal.
A cost estimate was prepared for the
use of the experimental treatment alter-
200
150
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Figure 1.
15 20
Coagulant Dose (mg/L)
Effect of experimental coagulant dose on finished water THM concentration.
35
Condition 1 - Jar Tests. XE-392 20 mg/L
Condition 2 - Pilot Plant, XE-392 17.7 mg/L
Condition 3 - Plant-Scale Test. XE-392 18 mg/L
Condition 4 - Pilot Plant. XE-513
a-18 mg/L coagulant dose
b-10 mg/L coagulant dose
c-5 mg/L coagulant dose
24-hr THMFP in
Raw Water
24-hr THMFP in
Finished Water
Figure 2. Summary of experimental results.
-------
native. XE-513 is expected to cost approx-
imately $6.00/lb when purchased in bulk.
Current operating cost for lime softening
in the Daytona Beach water plant (in-
cluding solids handling) is approximately
$0.33/1000 gal (1984 cost). If the exper-
imental coagulation process is used, the
XE-513 cost is expected to be $0.38/1000
gal, assuming a dose of 7.5 mg/L. Based
on the treatment of 0.53 mVs (12 MGD),
water plant operating costs would there-
fore exceed $0.70/1000 gal. These pro-
jected costs are considered too high to
warrant the use of this polymeric coag-
ulant on a continuous, full-scale basis in
Daytona Beach, Florida.
The full report was submitted in fulfill-
ment of Cooperative Agreement No. CR
810676 by the City of Daytona Beach, FL,
under the sponsorship of the U.S. Environ-
mental Protection Agency.
-------
J. C. Thurrott, H. Zwart-Duryea, and K. McGurn are with City of Daytona Beach,
Daytona Beach, FL 32015; andK. Riger is with Russet & Axon. Daytona Beach.
FL 33020.
O. Thomas Love, Jr. was the EPA Project Officer.
The complete report entitled "Trihalomethane Precursor Removal by Coagulation
Techniques in a Lime-Softening Plant (A Three-Phased Study)," (Order No. PB
86-115 029/AS; Cost: $ 11.95, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
For further information, Richard J. Miltner 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
Off iciaf Business
Penalty for Private Use $300
EPA/600/S2-85/119
0000329 PS
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