POTASSIUM PERMANGANATE: AN ALTERNATIVE
TO PRECHLORINATION
LE PERMANGANATE DE POTASSIUM, UNE ALTERNATIVE A LA
PRECHLORATION
by KENNETH J . FICEK, manager-Technical Services, M a r k e t i n g D e p a r t m e n t
JOHN E. BOLL, Senior Technical Service Representative, M a r k e t i n g D e p a r t m e n t ,
C a r u s Chemical C o m p a n y , 1500 Eighth Street, L a Salle, Illinois 61301. 815/223-1500
Significant changes in water treatment practices are now being considered as a result of the passage of the National
Interim Primary Drinking Water Regulations. Potassium permanganate, a strong oxidant. is being investigated in order to define
the role it may play in helping water treatment plant operators meet the new Total Trihalomethane standards.
This paper summarizes some of the currently available laboratory and field data on the use of potassium permanganate as a
substitute for prechlorination. The discussion centers around the relocation of the point of prechlorination to reduce TTHM
concentrations; and the use of permanganate as an alternate oxidant to control taste and odors, oxidize manganese, control algae,
slime and marine growths. and to oxidize THM precursors.
The oxidation of phenol with KMnO, is discussed as a possible explanation for some of the increases in TTHM concentrations
found when permanganate was applied together with free chlorine.
Summary:
Des modifications significatives dans les procedes de traitemem de l’eau sont actuellement A letude depuis le vote du
Reglement national interimaire de l’eau potable primaire. Le permanganate de potassium, oxydant energique, est etudie en vue de
definir le rBle qu’il pourrait jouer en aidant les exploitants des stations de traitemem de I’eau a atteindre les nouvelles normes du
trihalomethane total.
Le rapport resume quelques unes des donnees de laboraroire et d’exploitation acquises sur I’emploi du permanganate de
potassium comme substitut de la prechloration. La ditcussion e5t centree sur la redefinition du point de prechloration pour require les
teneurs en TTHM, et sur I’emploi du permanganate comme oxydant alternatif pour lutter contre les g o h et odeurs, pour oxyder le
manganese, pour lutter contre les algues. les dep6tc vicqueux et les animaux marins, et pour oxyder les precurseurs du THM.
L’oxydation du phenol par KMnO, est discutee comme explication possible de I’augmentation des teneurs en TTHM constatee
quand le permanganate etait utilise en meme tempc q u e du chloce Itbre.
Resume:
Introduction
The passage of the National Interim Primary Drinking Water
Regulations now limits the concentration of Total Trihalomethanes (TTHMs) in drinking water to 0. IO milligrams/liter
(100 parts per billion) on a running annual average. This
requirement has led treatment plant supervisors to consider
major changes in water treatment practices ( I ) . Most notable
of the changes is the elimination of raw surface water treatment
with free chlorine. This chlorination technique has been shown
to be the main reason for the formation of trihalomethanes.
The chemical interaction between chlorine and the commonly
present, natural humic substances (the precursors) produces
chloroform and the other haloform compounds (2).
Many studies have now shown that by altering the point of
chlorine addition and improving the coagulation step, a
marked reduction in T T H M formation can be achieved. For
example, in Cincinnati, Ohio, a reduction in TTHMs from 300
ppb to 20-50 ppb was reported by Superintendent Richard
Miller, when they stopped chlorinating the influent to the presettling basins (2). In Huron, South Dakota, Harms and
Looyenga reported a 75% reduction in chloroform concentration by changing the prechlorine application point (3).
Further experimenting showed that by substituting chloramine
treatment for free chlorine, the TTHM concentration was
reduced from an average of 154 ppb in the finished water to
37 ppb (4).
These examples illustrate two of the many techniques under
investigation that can be employed to lower the finished water
concentration of TTHMs: first, the elimination of prechlorination, or alternately, the application of chloramines.
However, delaying the point of chlorination must be considered very carehlly before imp!emen:ation, since all benefits
of prechlorine treatment would be lost. In addition to
disinfection, these include algae/slime control, tastdodor
control, or ironlmanganese oxidation. By altering the point of
prechlorination and not providing a substitute oxidizing
chemical, serious problems, unrelated to the TTHM problem,
can occur. Some of these can be solved by chlorinating later in
the treatment, or by installing granular activated carbon
filters, but these solutions may not:
1) prevent algae and slime from growing in intake lines,
2) oxidize and coagulate the manganese in the raw water,
3) keep the sludge from going “sour” in the settling basin,
or
4) provide adequate taste and odor control.
Aqua No. 1. 1980
Marlborough Publishing Lid. 1980. Printed in England
However, by applying an oxidant other than chlorine, these
problems can be prevented without the production of THMs.
An alternate oxidant-potassium permanganate
The application of an alternate oxidant, while not a complete
substitute for prechlorination, can solve some of the problems
created by the chlorine relocation. One of the oxidants worthy
of consideration is potassium permanganate.
As a result of the TTHM regulation, the use of permanganate
as a substitute for prechlorination is seriously being investigated at many locations. For example, C. Blanck, in an article
published in the Journal of the American Water Works
Association, reported that a 76% reduction in finished water
TTHMs was achieved by a twofold treatment where the point
of chlorination was moved from the raw water, and potassium
permanganate was substituted (5).
But such treatment schemes are not new. Potassium
permanganate has been applied in this manner for twenty
years. Before 1960, it was being used to solve specific taste and
odor problems. Later, its main application was for the
oxidation of iron and manganese, where the permanganate
was used on ground waters in conjunction with pressure
filters using manganese treated greensand (6). As permanganate was used at more and more treatment plants, it was seen
that it would better solve many of the problems that were
originally controlled by free chlorine. In many cases where
potassium permanganate was applied for taste and odor
control, a reduction in chlorinous odors in the finished water
was noticed (7). Research based upon finished water threshold
odor numbers showed that permanganate was particularly
effective when applied before any chlorination. With the
advent of :he chlorinated organic problem, the study of
permanganate as an alternate pre-oxidant to reduce TTHM
formation was initiated.
These years of practical experience coupled with the new
data generated through trihalomethane research clearly show
that permanganate will be important for: the oxidation of
THM precursors; some pre-disinfection; control of slimes,
algae, etc. . .; control of taste and odor; and the oxidation of
manganese (8, 9).
Permanganate oxidation of THM precursors
The use of KMnO, to oxidize the precursors of the trihalomethanes was first studied by the U.S. EPA in Cincinnati,
Ohio. Their work was limited in scope to laboratory tests on
0153
Ohio River water. They found a 5-20% reduction of TTHM
concentrations when KMnO, was added in dosages of 0.7 to
5.0 mg/l, followed by chlorination after any excess KMnO,
was reduced. With permanganate treatment under extreme
conditions ( I O mg/l KMnO, at pH 11.5 for 21 hours), followed
by chlorination, a 40% reduction in TTHM concentration was
achieved (IO).
O t h e r laboratory and field studies substantiated the
oxidation of precursors with KMnO, and showed reductions in
TTHM concentrations of 5-40'70, attributable to permanganate application ( I I).
Singer e l a / , studied the application of potassium
permanganate in waters collected in North Carolina. He
reported that when these waters had been pretreated with 2 to
10 mg/l KMnO, before chlorination, less chloroform was
produced, compared to the same waters treated with chlorine
only (12). (See Figs. 1-2.) The potassium permanganate
treatment (at the dosages tested) did not oxidize all of the
precursors, and its application alone, without moving the
point of chlorination, would not reduce the THM concentration to required levels. The combined treatment changes,
however, along with improved coagulation would result in
finished water that met the TTHM regulation.
I
1
I
250
I
I
I
I
H ^ ^ ^II
I
'
0
1
2
3
4
5
6
7
CHLORINE CONTACT TIME - DAYS
Fig. 1.
r
I
I
I
I
I
I
1
I
1
KMnO,
'DOSE
DURHAM SETTLED WATER
I
-"it
TURBIDITY 6 4NTU
I
I
1
2
1
3
1
4
I
5
6
I
7
I
CHLORINE CONTACT TIME - DAYS
Fig. 2.
A report from the Frankfurt Water Plant in West Germany
indicated a n overall reduction of 50% in haloform generation
due to a shift in the point of chlorination, and raw water
permanganate addition. Further work is being conducted on a
combination of permanganate and biological treatment to
completely replace chlorination and further suppress T T H M
formation (13).
Studies of permanganate raw water addition and chlorine
relocation conducted by Carus personnel in the field, verified
the reduction of final T H M concentrations, but showed that
the lower levels were mainly due to the elimination of raw
water chlorination. In addition, an increase in T T H M
concentration was noted on several occasions when KMnO,
and free CI, were present simultaneously.
In one such test in California, chlorination of the raw water
produced a concentration of 83 ppb TTHM. By eliminating
prechlorine, adding KMnO,, coagulating, filtering, and then
post-chlorinating, the final T T H M concentration was reduced
t o between 30 and 40 ppb. By adding KMnO, and chlorine
0154
together (no coagulation or filtration) the final T T H M concentration was increased to 99 ppb, higher than that produced by
chlorination of the raw water alone. This test indicated that
thepermanganate should be added, the water coagulated, and
only then should the water be chlorinated t o produce the best
results (14).
One explanation for the TTHM increase in the previously
mentioned case might be found in the work done by the
Russian scientist, V. N. Bobkov (15). In his work on the
oxidation of phenol by potassium permanganate, Bobkov
showed that some of the intermediate oxidation products were
humic substances. Production of humic substances was
greatest at a permanganate to phenol weight ratio of 4: 1.
The permanganate oxidation of phenol t o carbon dioxide
and water is shown below. The weight ratio for this reaction is
15:7 parts KMn0,:I part phenol, the theoretical maximum.
3 C,H,OH + 28 KMnO, + 5 H,O
18 CO, + 28 KOH
+ 28 MnO,
-.
According to Bobkov, where permanganate was added at
less than the 4: 1 ratio, the humic substances increased. Beyond
the 4: I ratio, the humic substances began to decrease until they
are completely undetectable at the ratio of about 15:l (See
Fig. 3 . ) Other oxidation products were identified at various
ratios of KMnO, to phenol. These included formic acid, oxalic
acid, tartaric acid, and carbon dioxide. (See Fig. 4, 5 . 6 . )
These oxidation products and the ratios are important
because, if indeed humic substances are produced as a result of
inadequate oxidant additions, chlorination of these oxidation
products could produce high concentrations of TTHMs. In
other words, chlorination of phenol might only produce
chlorophenol, which may be objectionable due to its disagreeable odor. But the partial oxidation of phenol by
permanganate and subsequent chlorination could produce a
substantial trihalomethane concentration This theory is to be
studied in more detail in our laboratory and in the field.
The information available at this point indicates that, when
using permanganate, the most effective means of minimizing
the formation of trihalomethanes is to:
1) add the permanganate to the raw water, and allow it t o
react completely,
2) coagulate and settle turbidity and suspended solids, and
3) chlorinate before or after filtration, depending upon
bacterial properties of the water and local regulation
regarding chlorine contact time.
Tastes, odor, slime, algae
It has long been recognized that chlorination of raw surface
water has provided some degree of taste and odor control, as
well as keeping intake lines and basins free of algae and slime.
At times, chlorination of raw water also could intensify taste
and odor problems by forming odorous, chlorinated organics,
as is the case with phenol. Many plants in the early 1960s
minimized or eliminated prechlorination in favor of permanganate treatment to control these taste and odor problems.
Excellent odor control was achieved at a Virginia supply when
1.75 mg/l KMnO, was substituted for 6 mg/l CI,. The finished
threshhold odor number was reduced from a 6 TON (chlorinous) t o a 1.2 TON, which was not considered objectionable
when post-chlorinated (7).
The application of permanganate prior to chlorination in
many cases reduced the chlorine demand, indicating that the
KMnO, was reacting with contaminants in the raw water.
Without KMnO,, these products would probably have reacted
with CI,-possibly being oxidized, but more than likely simply
being chlorinated. In the early 1960s the technical expertise
was not available t o detect these chlorinated products.
However, odor tests and consumer acceptance of water pretreated with KhlnO, supported its successful application.
In those cases where prechlorination is providing oxidation
of the taste- and odor-producing organics, the elimination of
this step, without substitution of another oxidant, could lead to
inadequate control. The water may be low in TTHM concentration, but unacceptable because of tastes and odors.
Permanganate oxidation along with other treatment tech.niques, such as the addition of activated carbon, may help
in some of these situations. It is, however, not a cure-all, and
Fig. 3.
8
5
t
I
404
1
”
\
00
\
0 0
0,
20
”\
I
2
6
0
\
,
1
I
10
I
9
14
m KMn0,l m C,H,O
Fig. 5.
1.2
m KMn0,l m CH
,O
,
Fig. 6.
I
E-
m KMn0,l m CH
,O
,
Figs. 3-6: The composition of the reaction by-products, when
phenol is oxidized by potassium permanganate at different
ratios of the initial reactants-a) humic substances: b) oxidized
combination treatments should be studied to achieve the
optimum in quality and economy.
In addition to the oxidation of taste- and odor-producing
organic contaminants, KMnO, is being used to solve some of
the other previously mentioned problems. A water plant using
Lake Michigan water continuously feeds a dosage of 0.25 mg/l
of KMnO, to the raw water at the intake, which is several miles
from the plant. This low dosage completely controls the slime
and algae build-up in the line. Prior to the KMnO, treatment,
CI, had been applied to keep the line free of growths (16).
Another case is in Alabama, where KMnO, is added every
spring to rid a raw water line of the Asian clam, Corbicula.
The permanganate, at a dosage of 4 mg/l, is introduced
primarily for taste and odor control at the intake structure,
approximately 1 % miles from the treatment plant. Shortly
after the KMnO, is started every spring, the clams begin to
“slough off” and within two to three weeks, the line is free of
the Corbicula and a corresponding increase in flow rate of
about 9-10Vo is ,achieved. The superintendent claims that “if
they fed KMnO, at 20 mg/l, he could accomplish the tasks
more quickly, but they would have a problem with the excess
residual permanganate in the plant”. Similar results (i.c.
ridding the line of the clam) can be achieved with chlorine, but
they prefer permanganate for the taste and odor control (17).
m KMn0,l m CH
,O
,
phenol; c) formic acid; d) oxalic acid; e) tartaric acid; and
f) carbon dioxide. From V. N. Bobkov. “Study of the
Oxidation of Phenol by Potassium Permanganate.” (1975).
Manganese oxidation
The application of permanganate for the oxidation of soluble
manganese is well documented and widely used. Whether
treating surface or ground water, most manganese is
controlled with permanganate dosages from 0.25 mg/l to 2.5
mg/l. Chlorine can also be used to oxidize manganese, but the
necessaiy conditions are more critical, and a high pH is usually
required.
Research and field work has indicated that the formation of
trihalomethanes is pH-dependent. As the p H of a water to be
chlorinated increases, the tendency to produce trihalomethanes also increases. I f a pH of greater than nine is
required for the oxidation of manganese by chlorine, the
conditions become more favorable for high TTHM formation.
The oxidation of manganese by permanganate is also
somewhat p H dependent. The reaction rate is faster at higher
pHs, but under normal treatment plant conditions (pH 7-8) it
is already extremely fast. Therefore, manganese removal with
permanganate oxidation in place of chlorination will minimize
trihalomethane formation, due to the pH change alone.
This was verified at a plant in West Virginia where these two
manganese oxidation techniques were studied (18). In separate
tests, pretreatment with free chlorine was compared to permanganate oxidation and chlorination just ahead of the filters.
In addition to complete manganese control, the following
TTHM results (See Fig. 7) were obtained:
0155
TTHM Concenirations
Chlorination Only
KMnO, & Chlorination
Range
50-330 ppb
43-82 ppb
Average
127 ppb
56 PPb
WEST VIRGINIA WATER
COMPARISON O F T T H M FORMATION
PRE-CI, vs KMnO, FOLLOWED BY CI,
DATE
11-1
11-2
11-6
11-8
11-9
11-13
11-16
11-17
I 1-20
11-21
11-21
1 1-24
11-27
11-28
11-29
11-30
12-1
12-4
12-5
12-6
12-7
12-12
12-13
AVERAGE
FINAL T T H M CONCENTRATION
PRE-CI, ONLY KMnO, FOLLOWED BY CI,
115 ppb
330
148
130
90
86
86
78
53
78
150
94
157
99
123
162
127 ppb
Figure 7.
Conclusion
Test work in the laboratory and the field has now shown that
by relocating the point of prechlorination, or by substituting
chloramine treatment, TTHMs can be substantially reduced.
By doing so, however, a variety of problems, unrelated to
trihalomethanes, may occur.
Potassium permanganate, while not the ultimate answer to
all of these problems, can be used effectively in combination
with other treatment techniques to produce a water, not only
low in T T H M concentration, but also free of manganese and
taste and odor producing compounds. It can also be beneficial
in controlling algae, slime, and other marine growths. The
-carus
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Division of Carus Corporation
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0156
data strongly indicates that potassium permanganate addition
should be considered as one of the alternatives t o prechlorination treatment.
References
1. USEPA. National Interim Primary Drinking Water
Regulations. 44 Fed. Reg., 231:141.12 (29 November
1979).
2. DALLAIRE, GENE, assoc. ed. “Arecities Doing Enough
to Remove Cancer-Causing Chemicals From Water?,”
Civil Engineering-ASCE. (September 1977), p. 88-94.
3. HARMS, L. L., LOOYENGA, R. W. “Chlorination
Adjustment to Reduce Chloroform Formation,” Journal
American Water Works Association. (Huron, South
Dakota: May 1977), p. 258-263.
4. NORMAN, T. S., HARMS, L. L., LOOYENGA, R. W.
“The Use of Chloramines To Prevent Trihalomethane
Formation,” JournalAmerican Water WorksAssociation.
(Huron, South Dakota: March 1980), p. 176-180.
5. BLANCK, C. A. “Trihalomethane Reduction in Operating Water Treatment Plants,” Journal American Water
Works Association. (September 1979), p. 525-528.
6. FICEK, K. J. “Potassium Permanganate for Iron and
Manganese Removal and Taste and Odor Control.” In
Water Treatment Plant Design For the Praciicing Engineer.
Sankes, R. L., ed. (Michigan: Ann Arbor Science 1978),
461-479.
7. WELCH, W. A. “Potassium Permanganate in Water
Treatment,” Journal American Water Works Association.
(Reprint-June 1963), p. 735-741.
8. FLETCHER, W. H. C. “In Golden, Colorado-One
Answer to Slime Problems in Coagulation,” Water Works
and Wastes Engineering. (March 1965).
9. MUCHMORE, C . B. “Algae Control in Water-Supply
Reservoirs, ” JournalAmerican Water WorksAssociation.
(May 1978). p. 273-279.
10. STEVENS, A. Personal Communication. U S E P A ,
Cincinnati, Ohio.
11. “Potassium Permanganate Reduces Trihalomethanes,”
Public Works. (January 1979), p. 107.
12. SINGER, P . C., BORCHARDT, J . H., COLTHURST,
J. M. “Effects of Permanganate Pretreatment On Trihalomethane Formation In Drinking Water.” Presented
at 98th Annual Convention, American Water Works
Association. (June 1979).
13. MACK, E. Personal Communication. T h . Goldschmidt
A.G., Mannheim, West Germany (August 1979).
14. Personal Communication. Carus Chemical Company.
15. BOBKOV, V. N . “Study of the Oxidation of Phenol by
Potassium Permanganate.” (1975). CA86:215 1511.
16. Personal Communication.
17. Personal Communication.
18. Personal Communication.