Potassium Permanganate for Industrial Water Purification |
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Potassium permanganate has a long history of successful application in industrial water purification, providing both primary and secondary benefits.
It is widely used by facilities to help meet regulatory rules and public pressures to produce quality drinking water. |
What is Potassium Permanganate? |
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Potassium permanganate is a strong oxidant used in combination with other treatment technologies to solve specific industrial water purification problems caused by organic and inorganic
contaminations in both ground (well) and surface water supplies. It converts oxidizable chemicals, such as ferrous iron, into their corresponding oxides that are removed by subsequent
treatment steps or remain soluble and no threat.
Oxidation is described as a chemical “burning up” of organic
matter converting contaminants into less odorous, harmless
by-products. |
Is Permanganate New for Drinking Water
Purification? |
Potassium permanganate was first discovered in 1659, but was not developed for commercial use until the 1800s, when it became a common household and institutional disinfectant.
It was first used for industrial water purification in 1910
in London, but did not begin to grow in use until the 1960s
when successful application for taste and odor control was publicized.
Since then, permanganate has been accepted by the water industry
as one of the most versatile oxidants available. |
What Permanganate Helps Control in Drinking Water |
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With industrial water purification of ground waters, permanganate is primarily used to help control iron, manganese, sulfides, and color. In addition, it is used in conjunction with manganese-treated greensand to reduce high concentrations of radionuclides and arsenic.
With industrial water purification of surface waters, permanganate is applied
primarily for problems with taste and odor, manganese, and trihalomethane
(THM). However, a number of other benefits
are reported by users. These include improved coagulation,
color improvement, and zebra mussel control. |
How Widely Is Permanganate Used for Industrial Water Purification? |
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The latest American Water Works Association(AWWA)/American Water Works Association Research Foundation(AWWARF) survey of surface water treatment plants serving >10,000 people shows that 36.8% use potassium permanganate for Pretreatment/Pre-oxidation/Organics Removal, second only to chlorine.
Thousands of very small groundwater treatment plants use permanganate for industrial water purification. The estimate
is that about 25% of the plants practicing iron/manganese
removal are employing permanganate. |
Is Permanganate a Cure-All
for Industrial Water Purification? |
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No single treatment process or product is a cure-all for industrial
water purification. Each product or process has advantages
and disadvantages. Problems can vary throughout the seasons
and from year to year, especially with surface supplies. The
most cost-effective process will sometimes include combinations
of all of the available technologies, each being applied at
the most strategic point in the plant. At times permanganate,
followed by activated carbon will be most effective. Other
water problems may require chlorine addition after permanganate.
Although the USEPA has established Best Available Technologies
(BATs) for controlling specific contaminants, very seldom
is there only one problem being addressed at a time. It takes
combinations of complementary products and processes to treat
complex industrial water purification problems and to do so
in the most cost-effective manner. |
Odors Most Effectively Controlled by Permanganate |
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Customers report that the fishy, grassy, septic, phenolic,
sulfur, and cucumber odors are easily controlled by potassium permanganate. Earthy, musty, and some flowerly type odors
are more difficult to control using permanganate alone in
industrial water purification.
Combinations of permanganate with activated carbon have been reported to be used very successfully to produce an acceptable odor level when MIB (methyl iso borneal) and Geosmin were found in raw waters.
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Color Removal in Drinking
Water with Permanganate |
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Most raw water color is caused by decayed vegetation and minerals such as manganese. Anaerobic conditions in raw water reservoirs cause leaching of the bottom sediments that contain many of these contaminants. Because the problem was caused by reducing conditions, an oxidizing agent can be very effective in treating colored waters. Some raw water color is effectively treated by good coagulation.
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Trihalomethanes (THM) in Drinking Water |
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The main cause of Trihalomethanes (THMs) is chlorination of drinking water that
contains precursors, primarily humic and fulvic acids. By
delaying the chlorination to an application point after coagulation,
the formation of THMs can be reduced 40% to 70%. This change
in chlorination point must be coupled with good coagulation
to remove the precursors. The addition of an alternate oxidant
to the pretreatment step is advisable. Preoxidation with potassium permanganate will maintain an oxidizing environment, control
taste and odor, oxidize manganese, and assist with the removal
of the precursors. An additional 5%, up to as much as 40%,
Trihalomethanes (THM) control has been reported by industrial water purification plants
utilizing permangante.
Permanganate is listed by the USEPA in the Federal Register
as one of the alternative oxidants that can be used for THM
control in industrial water purification.
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Does Permanganate Have Disinfection Properties? |
Potassium permanganate is not registered with the EPA as
a disinfectant. CT credits are not available with use of permanganate
for industrial water purification. |
Alternative Benefits of Permanganate Treatment |
When permanganate reacts it forms manganese dioxide. This
precipitate is heavy and with its negative charge, acts as
a nucleus for floc formation. It attracts positive ions and
can help in the removal of some compounds that cause taste
and odors in drinking water. It has also been shown to increase
settling which may lead to lower coagulant usage. |
How much permanganate is needed to do the job? |
The effective dosage is determined by running laboratory jar tests.
More highly contaminated drinking water will need higher
dosages. The average dosage is about 1 mg/L, but dosages as
high as 10 mg/L may be needed during sieges of “bad” water.
Jar testing will give a good idea of the approximated dose
needed in a given situation. When running the jar tests, the
effective dosage is determined through “ permanganate profiling,”
that is, finding out how much will react in a given period
of time. This is done by setting up raw water jar samples,
dosing them with permanganate, measuring the residual at given
time intervals, and plotting the data. The effective dose
is the amount used up in the time that it would take the raw
water to pass from the intake (or other feed point) to the
rapid mix where the coagulants are added. |
Cost of Using Permanganate for Industrial Water Purification |
Although permanganate sells for more than $1/lb, the dosage
usually does not exceed 1 mg/L, for a cost of less than one
penny for every thousand gallons of treated water. When compared
to other technologies for industrial water purification, the
cost of using permanganate is very competitive, and in combination
with other technologies, the total cost of treatment is often
less than any single technology.
A Western purification utility had used an average of 25
mg/L of powdered activated carbon to control a persistent taste and odor problem with their drinking water. By incorporating
1 mg/L of permanganate into the treatment ahead of the carbon,
the activated carbon dose was reduced dramatically to 8 mg/L.
The resultant cost of the combination treatment was reduced
to $30/MG, a savings of $36/MG, or at 40MGD, a savings of
more than $1400/day. There was no change in drinking water
quality with the addition of permangante to the purification
process, but there was significant reduction in total treatment
cost.
Not every case will be this dramatic or even this successful.
The case history does point out the value of having different
complementary technologies and to choose the most cost-effective
combination for specific industrial water purification problems. |
