Conference Papers | 2001 Conference Papers
REMOVAL IN DRINKING WATER SYSTEMS
Ravi Raveendran -
Operations Improvement Coordinator,
South Gippsland Water
Brian Ashworth -
South Gippsland Water
Bryan Chatelier -
South Gippsland Water
exists naturally in some soils and enters into ground
water or is washed down to surface water reservoirs.
If not oxidised, manganese(II) ions will escape through
water treatment processes into the supply system. Once
in the system, the ion is gradually oxidised to insoluble
manganic dioxide causing dirty water problems.
can be oxidised to insoluble manganic dioxide and removed
by clarification and filtration. Oxidation can be achieved
by aeration, chlorination or chemical oxidation using
Gippsland Region Water Authority (SGRWA) has manganese
problems in most of their surface water reservoirs.
This paper shares the experiences of SGRWA in removing
manganese and compares the advantages and disadvantages
of alternate oxidation methods with plant scale data.
Manganese, Aeration, Potassium permanganate, Chlorine,
Sodium Hypochlorite, pH, detention time, dosage
Gippsland Region Water Authority (SGRWA) owns and operates
ten water treatment plants and supplies 21 small towns.
The main water supply for the treatment plants is surface
water. Four SGRWA plants obtain their water directly
from rivers. The remaining plants source their water
from reservoirs. Since manganese exists naturally in
the South Gippsland region as insoluble manganic oxide
and soluble manganese ion almost all the plants have
manganese problems. Although the storage reservoirs
supply water of a consistent quality for most parameters,
the manganese levels in the raw water vary significantly
with time. The insoluble manganic dioxide in the raw
water tends to settle to the bottom of the reservoirs.
Where dissolved oxygen levels are low the manganese
ion is released into the water from the manganic oxide.
Manganic dioxides that have not settled in the reservoir
can be readily removed by coagulation, sedimentation
and filtration processes. However, since the removal
of soluble manganese cannot be achieved by such processes,
the soluble manganese which enters the supply system
is gradually oxidised to manganic dioxide by the disinfection
process causing problems for customers. Generally customer
complaints are received at manganese concentrations
as low as 0.03 mg/L. According to the Australian Drinking
Water Guidelines (ADWG) manganese is not a health consideration
unless the concentration exceeds 0.5 mg/L.
The descriptions of complaints resulting from manganese
in the supplied water vary from dirty water, black water,
or brown water. Where bleach is added to laundry, manganese
ions are oxidised to manganic dioxide forming stains
on washed clothes. Maintenance of the water supply pipeline
is also a problem. Low levels of iron and manganese
in the supply water enhance the growth of iron bacteria
that produce black slimes.
slimes increase the chlorine demand and reduce the available
chlorine residual in the distribution system. They also
cause taste and odour problems. If not flushed regularly
the bacteria slimes and manganic oxide sediments accumulate
in the pipes. During peak demand periods they slough
off and cause problems. As a result normal water flushing
at the hydrant is not sufficient to maintain pipelines.
Regular air scouring of the mains is required and undertaken
In addition, manganic dioxide also stains the sample
pipelines and on-line monitoring equipment such as pH
probes, turbidity meters and chlorine residual analysers.
The sample lines coated with manganic dioxide absorb
and release manganese ions. Where long sample lines
exist this results in misleading manganese levels being
manganese can be oxidised to manganic dioxide and then
removed by coagulation, sedimentation and filtration.
Oxidation can be achieved by aeration or by oxidation
agents such as chlorine, sodium hypochlorite or potassium
2.0 OXIDATION OF MANGANESE
Aeration can be used to oxidise manganese ions to manganic
dioxide. However, the kinetics of oxidation by oxygen
is slow in typical water treatment conditions and so
a long detention time is required (AWWA, 1990). Aeration
is useful as an option to oxidise manganese in reservoirs.
Manganic dioxide can release manganese ions back into
the water at DO levels as high as 4 mg/L. Generally
aeration involves high capital costs and high running
costs. Aeration alone cannot completely oxidise all
manganese. Aeration is ineffective in oxidising organically
bound manganese. As a result aeration can only be used
as a preliminary treatment to oxidise manganese. Where
further oxidation is necessary an oxidising agent must
be introduced to reduce the manganese levels.
is used in several SGRWA reservoirs to provide artificial
destratification to control algal blooms, iron and manganese.
However, manganese levels in the raw water can increase
significantly on occasions. Increasing levels have been
observed where algal blooms have been treated using
algaecide. It is believed that this is due to oxygen
depletion resulting from the sudden death and decomposition
of the algal cells (AWWA research Foundation, 1995).
Chlorine is a stronger oxidising agent than oxygen.
Chlorine forms hypochlorous acid when dissolved in water.
For manganese oxidation chlorine needs to be added at
the head works or just before filtration. Pre-chlorination
has a higher potential to react with organic compounds
and to produce trihalomethane (THM) which is carcinogenic.
At SGRWA chlorine gas is delivered in cylinders to the
water plants. Chlorinators and appropriate safety equipment
are required to dose chlorine.
Sodium hypochlorite also forms hypochlorous acid when
dissolved in water. The sodium hypochlorite reaction
slightly increases the pH whereas the reaction of chlorine
gas slightly reduces the pH. Commercially available
sodium hypochlorite has a concentration of 12.5 %. Even
though sodium hypochlorite is about twice the cost as
equivalent chlorine gas, sodium hypochlorite is used
only in small systems at SGRWA due its ease of handling
Potassium permanganate is a stronger oxidant than chlorine
and sodium hypochlorite. Whilst it is effective in oxidising
manganese, it has also been used for the treatment of
taste and odour problems in water supplies (AWWA Research
Foundation, 1995). Unlike chlorine, the reaction of
potassium permanganate with organic compounds will not
produce trihalomethanes but will actually reduce them
permanganate is supplied as a powder in 50 kg drums.
Potassium permanganate is mixed on site with water to
a concentration between 0.5 to 2.0 % before dosing.
The stoichiometric equation for manganese ion oxidation
by potassium permanganate is given as below.
to the stoichiometric equation, it would require 1.92
mg of potassium permanganate to oxidise 1 mg of manganese
ion. A comparison of the oxidants required to oxidise
manganese according to stoichiometry is given in Table
Table 1: Comparison of Oxidants
for oxidation of manganese
though, the stoichiometric requirement of chlorine and
hypochlorite is less than potassium permanganate, in
practice the chlorine requirement has been found to
be much higher due to the chlorine demand by organic
JAR TEST STUDIES
series of jar tests were completed to compare the effectiveness
of potassium permanganate and sodium hypochlorite to
oxidise manganese. The pH, oxidant dosage and detention
time were identified as the controlling parameters for
manganese removal. The tests were designed to simulate
the conditions at a water plant where levels of manganese
were high. The jar testing procedure performed is as
1) Initial pH adjustment to the required pH;
2) Mixing at 100 rpm;
3) Oxidant addition (potassium permanganate or sodium
4) Mixing at 100rpm for the required detention time;
5) Alum addition (40mg/L concentration for all jars);
6) Rapid mixing at 100 rpm for 1 minute;
7) Slow mixing at 60 rpm for 5 minutes;
8) Slow mixing at 10 rpm for 10 minutes;
9) Settling time (10 minutes);
10) Decanting 50ml of sample from the top of the jars;
11) Filtration of sample through 0.45um filter;
12) Analysis of filtrate for manganese.
Jar test results are summarised in Table 2. The objective
of the tests was to reduce the manganese concentration
below 0.02 mg/L.
The pH of the water is the most important parameter
for manganese removal. Required levels of manganese
removal occurred above a pH of 7.5. Pre pH adjustment
was made using a 10% soda ash solution. The lowest manganese
concentration of 0.026 mg/L was obtained at an initial
pH of 8.3 (Test No.12). Alum addition decreased the
pH to approximately 5.8.
3.2 Detention Time
Generally a detention time of 5 to 15 minutes is recommended
for manganese removal (Sank, 1980). According to a study
by Desjardins, oxidation of manganese by potassium permanganate
occurred in less than 5 minutes where the manganese
was not in a complexed form (AWWA Research Foundation
, 1995). Jar tests were performed at 2 to 3 minute intervals
to simulate the conditions of the existing plant where
the maximum available detention time during average
demand is approximately 3.0 minutes. Results from the
tests indicated no significant difference in manganese
removal for the time range tested.
Experience in one SGRWA plant, (Lance Creek WTP), indicates
that a detention time of 10 minutes is adequate to provide
complete oxidation of manganese with potassium permanganate.
It should be noted however that the detention time for
manganese oxidation has to be provided before alum addition.
After alum addition, the pH drops below 7.0 slowing
the kinetics of potassium permanganate oxidation.
The theoretical potassium permanganate dosage required
is approximately double the concentration level of manganese
in the raw water. Manganese in the raw water varied
between 0.15 to 0.38 mg/L during the tests. Best results
were obtained using a potassium permanganate dosage
of 0.4 to 0.5 mg/L.
overdosing of permanganate (up to 0.1 mg/L) has been
found not to cause any adverse effects. Currently, potassium
permanganate is used at five of the water treatment
plants at SGRWA to remove manganese. Installation of
dosing systems at the remaining water treatment plants
is presently occurring.
3.4 Sodium Hypochlorite Dosage Trials with the addition
of sodium hypochlorite indicated that sodium hypochlorite
was not effective within short detention times. The
kinetics of oxidation by chlorine is very slow and therefore
longer detention times are required.
chlorination is not preferred because of THM formation
especially for high coloured raw water.
2: Jar Tests Results
tests can give an indication of the pH and dosage requirement
for manganese removal. However, jar tests alone cannot
exactly predict the treated water manganese level. This
is because filtration simulated in the jar tests uses
0.45um filter paper whereas water treatment plant filtration
involves granular media filtration.
media filters play a major role in manganese removal.
Manganic dioxide solids that are deposited on the granular
media during filtration act as catalysts in manganese
oxidation reactions. The manganic dioxide is also found
to adsorb the manganese ion which will be eventually
oxidised in time (Water Quality and Treatment, 1990).
4.1 Korumburra Ness Creek Reservoir
The Korumburra Reticulation System provides water for
the township of Korumburra with a population of 4200.
The system also includes two industrial customers, (Korumburra
Saleyards and Burra Foods), and a hospital.
raw water is sourced from three reservoirs, Coalition
Creek, Bellview Creek and Ness Creek as shown in Figure
1. Coalition Creek Reservoir is the only storage used
all year round. Water from the other two reservoirs
is pumped as required.
the summer of 2000-2001, the Korumburra Township had
to be placed on water restriction due to inadequate
water at the reservoirs. Unfortunately the manganese
level in Ness Creek Reservoir increased to a level where
it was not possible to use the water without contaminating
the water supply in the Coalition Reservoir. Therefore
as a temporary solution it was decided to treat the
manganese at the reservoir by oxidation and settling.
Once treated the water would then be pumped to the Coalition
Samples were taken at the reservoir at different locations
and depths to determine the manganese levels in the
reservoir. The Ness Creek Reservoir has a floating off-take
approximately 1m deep. The manganese level at this off-take
was measured at 0.38 mg/L.
3: Manganese Testing at Korumburra Ness Creek Reservoir
4.2 Potassium Permanganate Dosing
Potassium permanganate dosing in the reservoir was considered
as an immediate and viable option. However, potassium
permanganate as a long-term solution was not preferred
because of the total mass of manganese compounds that
would settle and remain in the reservoir. Therefore
as a trial a small amount of potassium permanganate
was dosed. Approximately 15kg of potassium permanganate
was dissolved in approximately 900L of water. This solution
was then sprayed into the reservoir from a boat to give
an overall potassium permanganate concentration of 0.19
total water volume in the reservoir at the time of application
was approximately 80ML. Samples taken after two days
indicated that the manganese levels had increased to
0.5 mg/L at 1m sampling depth. Most of the manganese
appeared to be in a dissolved form. This is most likely
due to the mixing effect of the boat in the reservoir
which increased the manganese concentration at the surface
of the water.
Temporary aeration was introduced into the basin as
a second step to reduce the manganese. Samples were
taken at the reservoir weekly. Initially the manganese
levels increased, however, after three weeks, the soluble
manganese concentration decreased below 0.5 mg/L. Whilst
the total manganese level was still high at approximately
0.5 mg/L, this indicated that most of the manganese
has been oxidised to manganic dioxide and remained in
The manganic dioxide in the reservoir could now be removed
by coagulation, clarification and filtration treatment.
However, transferring manganic dioxide solids into the
main reservoir was still not considered as a good option.
4.4 Alum addition
Flocculating the manganic dioxide solids with alum addition
was considered in order to settle as much manganese
as possible in the reservoir. Approximately 800 kg of
alum powder was evenly distributed from a boat to achieve
an overall alum concentration of approximately 10 mg/L
in 80 ML of water. After alum addition aeration was
continued for one more day to provide adequate mixing.
The aerator was then turned off to allow settling of
the manganic dioxide-alum flocs. A week later the measured
manganese levels had decreased below 0.1 mg/L. The water
from the Ness Creek Reservoir was then pumped to the
Coalition Creek Reservoir, the main reservoir that feeds
the water treatment plant.
Treating the water at the reservoir was considered as
a temporary, emergency option. Providing a permanent
aeration system at the Ness Creek Reservoir is currently
Comparison of oxidants to remove manganese brought the
at the reservoir should be considered as primary
treatment. However, aeration alone cannot oxidise
all of the manganese and therefore oxidising agents
are necessary at the treatment plants to reduce
manganese to low levels.
permanganate dosing is very effective. However,
if the raw water manganese level fluctuates significantly,
adjusting the permanganate dosing according to manganese
levels may be operationally difficult. Slight overdosing
of permanganate (up to 0.1 mg/L) has been found
not to cause any adverse effects.
pH (pH above 8) resulted in improved manganese removal.
However, if the resulting pH after alum addition
is above 6.5, alum coagulation would be affected.
Whilst alum coagulation is good at a slightly acidic
pH (5.5 to 6.5), it is not always economical to
add more pH correcting chemical. Plant performance
indicates that a pre pH correction up to 7.5 to
8.0 with a detention time of 10 minutes before alum
addition gives adequate manganese removal.
is not as effective as potassium permanganate in
oxidising manganese. The chlorine requirement has
been found to be in excess of the stoichiometric
requirement. This is due to chlorine demand by organic
The authors wish to acknowledge Bill Dilg and Robert
Cook from the Operations Group for their assistance
in completing jar tests and Kevin Mitchell and Peter
Bentick for carrying out manganese removal operations
at the Korumburra Ness Creek Reservoir.
Water Works Association (1990), Water Quality and
Treatment, Fourth Edition, p 698 -700, McGraw-Hill,
American Water Works Association Research Foundation
and Lyonnaise des Eaux (1995), Advances in Taste
and Odour- Treatment and Control
and ARMCANZ (1996), Australian Drinking Water Guidelines,
National Water Quality Management Strategy, Canberra
L.R.(1980), Water Treatment Plant Design for the
Practising Engineer, p461-477, Ann Arbor Science
Publishers Inc, Michigan, USA.
P.C.; Borchardt, J.H; and Colthurst, J.M. (1980), The
Effects of Permanganate Pretreatment on Trihalomethane
Formation in Drinking Water, Journal AWWA, Vol 10: