Intermediate Water Treatment

Iron and Manganese

Removal
Natural Iron and Manganese

Did you know that Iron is the 4th most abundant element in Earth’s
crust?

Because of that, and the lack of oxygen in the earth’s crust, iron will
easily solubilized into water and is found in groundwater and aquifers.

It is also due to erosion and weathering of rocks and minerals.

Un- natural Iron and Manganese

Iron and Manganese can enter waterways by means of:

• Acidified mine drainage

• Landfill leachates
• Sewage effluents
• Iron- related industries
 Iron and Manganese

Generally…

 Low in surface waters such as

rivers and lakes
 Found frequently in well
waters or deep aquifers
 Varying concentrations of iron
and/or manganese
 CDWQG Limits

 Iron (Fe) AO = <0.3 mg/L

 Manganese (Mn) MAC = 0.12 mg/L.

Health Basis of MAC: Effects on neurological development and

behavior; deficits in memory, attention, and motor skills.

NOTE: The AO for Manganese is <0.02 mg/L

 Clothes
laundered
come out
stained

Best way to determine if

there is a problem is to
observe staining on fixtures
 Sample Collection and Analysis

 Accurate results are difficult to

obtain
 Loose scales on pipe walls
may break loose
 Particles get dislodged and
enter into the sample bottle
 The error can be large
 Iron and Manganese Sample Analysis

Correct procedure:
 Take 3 samples and use an average
 Purge plastic sample lines
 ~1 minute per 10 feet of line

Colorimeter/Spectrophotometer
https://www.youtube.com/watch?v=fM2Et xfq8r0
 Iron and Manganese Sample Analysis

 Must be done within 48 hours

 If sample cannot be analyzed in time, then sample
preservation must be undertaken

Sample preservation
 Acidify the sample with nitric acid
(2 mL/L per sample)
 Reduce pH to less than 2
 Iron Bacteria

 Obtain there energy from the spontaneous chemical

reactions that occur between iron and manganese
and dissolved oxygen, O2(2-)
 These bacteria use ferrous iron, Fe(2+) and oxidize
the iron and use the energy for reducing carbon
dioxide to organic forms (slimes)
 The manganous ion, Mn(2+)is used in a similar
fashion
 Bacterial Growth

 Cause thick slimes to grow inside the

distribution piping
 form deposits of "rust," bacterial cells, and
a slimy material that sticks the bacteria to
well pipes, pumps, and plumbing fixtures.
 Can cause flow disruptions and loose
scale
 Results in colour, taste and odour
problems
Iron and Manganese Maintenance

• By having a regular flushing program,

the build-up of iron and manganese
articles can be minimized or
prevented.
• Maintain a free chlorine residual
throughout the distribution system

Pipe Cleaning Using Pigs – YouTube

 Monitoring Treated Water

Controlling iron and manganese by aeration or chemicals

requires:

1. Close monitoring of product wate r

2. Correct sampling procedures
3. Correct lab testing procedures
 Control Methods

3.2.2.2 Phosphate Treatment

3.2.2.3 Removal by Ion exchange
3.2.2.4 Oxidation by Aeration
3.2.2.5 Oxidation by Chlorination
3.2.2.6 Oxidation by Permanganate
 Phosphate Treatment

 Iron <0.1 mg/L

 Manganese <0.3 mg/L
 Can be treated with polyphosphates with
reasonable efficiency
Polyphosphates should be added a few minutes
before chlorine application
 Iron and Manganese Scale Inhibitors

Phosphate delays the Commonly fed at the raw

precipitation of oxidized water source to allow for
manganese and iron, the longest contact time
thereby greatly reducing
the layer of scale that
forms on the pipe due to The effect is called
precipitation. Sequestration.
 Sequestration/Chelation

A chemical forming or joining together of metallic

cations (such as iron) with certain inorganic
compounds such as phosphate

Also called Chelation

Polyphosphate Treatment

• Chlorine usually must be fed

along with the polyphosphates
to prevent the growth of iron
bacteria (<0.2 mg/l)

• This process also works best

for sequestering manganese

Figure 3.2 Polyphosphate

and chlorine system
Polyphosphate Treatment

When sequestering iron

and manganese from a
well, polyphosphates
should be injected into
the process right after
the water leaves the
well.
 3.2.2.3 Ion Exchange

• Uses the same resin as a

water softener
• Exchanges undesirable
cations (Fe2+ & Mn2+) with the
cations of sodium (Na+)
• Discussed further in
Softening
 Ion Exchange
Similar to a
down flow
pressure filter When the resin
becomes fouled
the exchange
capacity of the
 Enters the unit resin is reduced
through an inlet
distributor
When iron and
The unit must be manganese start
 Forced through regenerated to appear in the
the ion exchange treated water,
unit to the under
drain system

The resin must

then be
backwashed to
clean
 Ion Exchange

If the water to be treated contains no oxygen, then the

same resins that are used for water softening can be used.

Note:
If water contain dissolved
oxygen, the resin
becomes fouled with iron
and manganese
precipitates
 Ion Exchange

Advantages
• Highly automated
• Plant requires little attention
Disadvantages
• Danger of fouling the ion
exchange with oxides
• High initial cost
 Iron and Manganese Oxidation

Iron and manganese react with an oxidizer (dissolved

oxygen) to form a solid precipitate

Ferric hydroxide, Fe(OH)3 Manganese dioxide, MnO2

 Iron and Manganese Oxidation

Ferrous hydroxide, Fe(OH)2 Ferric hydroxide, Fe(OH)3

Manganese, Mn2+ Manganese, MnO2

 3.2.2.4 Oxidation by Aeration

pH is increased by aeration
due to the removal of
carbon dioxide, it is
important that the aeration
be as efficient as possible.
 Oxidation by Aeration
pH Reaction Acceleration

This reaction is accelerated by an increase in pH.

Figure 3.3 pH versus time to oxidize 99 percent iron following aeration
Aeration

 Detention time must be

controlled for proper aeration (30-
60 mins)
 Typically uses diffusers
 Other methods included forced
draft, multiple trays, cascades
and sprays
 DAFT Process works very well
 Reaction Basin

• A reaction basin follows the process

• Sometimes called a
sedimentation/detention basin
• This allows time for the oxidation
reactions to take place
• Sludge accumulation is an issue
due to the precipitates
• Sedimentation and/or filtration
takes place
 Process

 Flow through the process

requires careful control
 Carefully monitor levels of
Iron
 If iron is detected, the flows
must be reduced
 Oxidation by Aeration
Advantages
 No chemicals are required, unless pH increase adjustment is
required

Disadvantages
 Small changes in surface water pH will have a drastic effect
on iron removal efficiency
 Manganese oxidation efficiency is very low
 Higher costs
 Effect of pH on Solubility

-Insoluble
-Precipitate/rust
Alkaline
-Soluble

Acidic
-Ferric (Fe3+)
Iron(III) hydroxide -In solution
Fe(OH)3 -Ferrous (Fe2+)
Iron(II) hydroxide
Fe(OH)2
 Chemical pH Adjustment

Lime, soda ash or caustic can also be used to drive

up the pH as well as remove the carbon dioxide.

Calcium hydroxide (slaked lime), Ca(OH)2

Calcium oxide (quick lime), CaO
 3.2.2.5 Oxidation with Chlorine

 Chlorine is a strong oxidant

 Iron is converted to rust particles or ferric hydroxide
 Manganese is converted to a jet-black compound
called manganese dioxide
 These materials form a loose scale on the piping
 The insoluble scale can then be removed by filtration
 Chlorine Oxidation

 The higher the chlorine residual in the water, the faster

the reaction is.
 Often the water is first dosed with a residual between
5-10 mg/L
 The insoluble precipitates are then removed by
filtration before the water is de-chlorinated to an
acceptable residual for domestic use
 Chlorine Oxidation

 Do not use high doses of chlorine if the water contains

high amounts of organics or colour

 Excessive concentrations of total trihalomethanes

could develop
 De-Chlorination requirement

The water is de-chlorinated using reducing agents such as:

 Sulfur dioxide (SO2)

 Sodium sulfite (NaSO3)
 Sodium thiosulfate
 Sodium Bisulfite is commonly used because it is
cheaper and more stable than sulfite
 3.2.2.6 Oxidation with Permanganate

2 Methods of treatment:

1. Intermittent Regeneration
2. Continuous Regeneration

Discussed in Part 2
Intermediate Water
Treatment

Iron & Manganese

Removal

Part 2
 3.2.2.6 Oxidation with Permanganate

• Potassium Permanganate (KMnO4)

• Most common in Western Canada
• Strong oxidant
• Reacts to form insoluble precipitates
• Soluble ferrous iron (Fe2+), vs. insoluble ferric iron (Fe3+)
 Potassium Permanganate

Can remove up to 95% of iron and manganese

Iron above 10 mg/L or manganese above 5mg/L will
cause oxides to plug off the filter quickly
Efficiency drop
Pretreatment is recommended for iron removal
 Manganese Greensand

Potassium permanganate is Similar to conventional filter

often used with manganese but the media includes:
Greensand pressure filters
1. Anthracite coal
2. Manganese greensand
Filter is efficient in removing 3. Graded gravel
iron and manganese
Figure 3.4

Multimedia manganese
greensand filter (horizontal
flow shown in diagram)

Note: Flow rate is usually 2-3

gpm/ft2
 Manganese Greensand Filter Media

• Removes iron and manganese using

adsorption and oxidation

• Manganese greensand contains

much finer sand
• Slower filtration rate

• Slower backwash rate

• Backwashed according to head loss

 Manganese Greensand Filtration

The filter can be operated in 3 modes:

Method depends on iron and manganese concentrations*

1. Continuous regeneration (CR)

Ideal iron concentrations of 0.5 – 3.0 mg/L (ideal) up to 15 mg/L

2. Intermittent regeneration (IR)

Only or mostly manganese

3. Catalytic regeneration (will not be discussed)

 KMnO4 Performance

Permanganate reactions are highly dependent upon pH of the water.

High pH = reacts quickly

Low pH = reacts slower
 Greensand Efficiency

Rate of reaction to insoluble

pH iron hydroxide
 Greensand Efficiency

Oxidation potential of
pH chlorine and KMnO4
Figure 3.5 Flow diagram of a continuous regeneration (CR) greensand
process
Figure 3.5 Flow diagram of a continuous regeneration (CR)
greensand process

At the plant shown on page 228, raw water being pumped from
a well contains 3.0 mg/L iron and 0.75 mg/L of manganese and
it has a pH of 6.2.

Because the pH of the water in this example is 6.2, which is

the minimum recommended pH for the use of the CR
process, the pH is adjusted within the range of 6.5 to 6.8
Figure 3.5 continued

• After pH adjustment , the water is injected with chlorine

• It is then flash mixed, and flocculated for period of ten
minutes. This will oxidize most of the iron and any
sulfide.
• The chlorine dosage is equal to the iron concentration,
as shown in the following formula:
Figure 3.5 continued

• After chlorination, the water is injected with potassium

permanganate
• Oxidation of the remaining iron and manganese
• The KMnO4 dosage can be calculated using this formula:
 Demand can be caused by other oxidizable compounds

 including organic color, bacteria, and hydrogen sulfide.

 Insoluble iron and manganese oxides are filtered

 Excess permanganate is reduced to manganese

oxides, regenerating the manganese greensand
 Greensand Filtration

• Insoluble precipitates build up on the media and the bed

must be backwashed
• 10 – 15 minutes
• Backwash goes back to the front of the plant for reuse
• Air scour can be used to assist in Manganese oxide removal
• Sticky/gummy residuals
Continuous Regeneration
Advantages
 Can remove moderate concentrations of manganese and
iron from water

Disadvantages
 Requires the addition of chlorine and if required and a de-
• chlorination step
 Manganese oxidation efficiency is very low, not used when
manganese concentrations are high
 Intermittent Regeneration

Steps include:
 Suitable where mostly manganese
is present
 Shutting down the process
 Very little iron in the raw water
(small amounts of iron are also  Pour a saturated (~5%)
removed) KMnO4 solution onto the
 Oxidation occurs directly on the filters
greensand  Soak for 24 hours
 The filter is then backwashed when  Backwashing filter after 24
the head loss becomes too great hours and place in service
Intermittent Regeneration

Advantages
Good where manganese is the main treatment
Requires no chlorine/de-chlorination

Disadvantages
Can not treat water with high iron
 Dosage

 Determining the correct dosage can be

done by increasing the KMnO4 until
pink water just flows out of the
greensand media

 Then the KMnO4 should be decreased

until the pink colour just disappears
 Dosage

 If adequate potassium permanganate is being fed into the

process, the filter influent should have a slightly pink color
 If the dose is too small,someof the manganese in the water will
not be oxidized
 If the dose is too large, permanganate will enter the system
and produce pink colored water
 Customer complaints may follow
 Red water complaints

 Ensure Fe & Mn treatment is

Langelier Saturation Index
operating correctly
pH – pHs
 Then investigate the pHs = 9.3 + A + B – C - D
distribution
system for the cause  Positive (+) is scale forming
 Red water or dirty water can be (keep scale forming)
caused by corrosive water
 Negative (-) is corrosive
 Stabilize using the Langelier
Saturation Index  Zero (0) is stable water
 Cast Iron pipe and Iron Bacteria

Red or dirty water may be caused by iron bacteria, which can be

 Very troublesome
 Very difficult to eliminate
Slime growths can be controlled by
 Maintaining a free chlorine residual
 Developing a flushing program
 Mapping customer complaints
 Maintenance of a chemical feeder

• In small water treatment plants that remove iron and manganese, a

hypochlorite solution may be used instead of chlorine gas.

• When the solution is diluted using water containing carbonate

alkalinity, the resulting solution becomes supersaturated with calcium
carbonate

• This calcium carbonate tends to form a scale or coating on the poppet

valves in the solution feeder
 Maintenance of a chemical feeder

Calcium carbonate scale can be removed by using hydrochloric acid, HCl

(also known as muriatic acid) to solubilize the calcium scale back into the
solution.

1. Fill a 1-liter container half full with tap water

2. Add 50 mL of 30 – 37%
3. Finish filling the container to the top with tap water
4. Place the suction hose of the hypochlorinator in the jar and pump the entire
contents of the jar through the system
5. Return the suction hose to the solution tank and resume normal operation
 Videos

Read here for an article on Winnipeg switching water-

treatment chemical to fight brown water

Read here for an article on Onaway residents with pink

water!
 References
1. "river". Microsoft Word . Bing image search creative commons only . Accessed 20 August 2024.
2. "well". Microsoft Word . Bing image search creative commons only . Accessed 20 August 2024.
3. "Iron, Rust, Black Iron Bacteria, Manganese." The Water Hook-Up, www.waterhookup.com/site/837757/page/524531. Accessed 20 Aug.
2024.
4. Carnicom, Clifford E. "Morgellons - A Thesis." Ferrous Iron, www.bibliotecapleyades.net/CIENCIA/ciencia_morgellons23.htm. Accessed 20
Aug. 2024.
5. Carnicom, Clifford E. "Morgellons - A Thesis." Ferric Iron, www.bibliotecapleyades.net/CIENCIA/ciencia_morgellons23.htm. Accessed 20 Aug.
2024.
6. "Scale And Corrosion Inhibitor - Geopure 3005 For Industrial Use." IndiaMART, www.indiamart.com/proddetail/scale-and-corrosion-inhibitor-
geopure-3005-20647725062.html. Accessed 20 Aug. 2024.
7. Unknown. Pipe cleaning dirty water using pipe pig. Accessed 20 August. 2024.
8. "monitoring". Microsoft Word . Bing image search creative commons only . Accessed 20 August 2024.
9. Figure 3.2 Polyphosphate and chlorine system. Water Treatment Plant Operation. Seventh ed., vol. 2, Office of Water Programs, 2020.
10. "Whats the ion exchange method for softening water ." Lanlang Corp, www.lanlangcorp.com/info/what-s-the-ion-exchange-method-for-water-
softe-40035488.html. Accessed 20 Aug. 2024.
11. "ion exchange media". Microsoft Word . Bing image search creative commons only . Accessed 20 August 2024.
12. "pros and cons". Microsoft Word . Bing image search creative commons only . Accessed 20 August 2024.
13. "ion exchange media". Microsoft Word . Bing image search creative commons only . Accessed 20 August 2024.
14. "rust". Microsoft Word . Bing image search creative commons only . Accessed 20 August 2024.
15. "black compound". Microsoft Word . Bing image search creative commons only . Accessed 20 August 2024.
16. "surface aeration". Microsoft Word . Bing image search creative commons only . Accessed 20 August 2024.
 References

17. Figure 3.3 pH versus time to oxidize 99 percent iron following aeration. Water Treatment Plant Operation. Seventh ed.,
vol. 2, Office of Water Programs, 2020.
18. "surface aeration". Microsoft Word . Bing image search creative commons only . Accessed 20 August 2024.
19. "aeration". Microsoft Word . Bing image search creative commons only . Accessed 20 August 2024.
20. "Schema of an iron removal system." Lenntech, www.lenntech.com/schema-of-an-iron-removal-system.htm. Accessed
20 Aug. 2024.
21. "permanganate". Microsoft Word . Bing image search creative commons only . Accessed 20 August 2024.
22. Figure 3.4. Multimedia manganese greensand filter. Water Treatment Plant Operation. Seventh ed., vol. 2, Office of
Water Programs, 2020.
23. "hydrant flushing". Microsoft Word . Bing image search creative commons only . Accessed 20 August 2024.
24. """Winnipeg switching water-treatment chemical to fight brown water."" CBC News · Posted: Nov 16, 2018. Last
Updated: November 16, 2018"
25. Zeta Potential. , American Water College, 2017, www.youtube.com/watch?v=QKdX9HpQclE. Accessed 20 Aug. 2024.
26. Figure 3.2 Polyphosphate and chlorine system. Water Treatment Plant Operation. Seventh ed., vol. 2, Office of Water
Programs, 2020.
27. Onoway residents shocked by pink tap water." Global News · Posted: Mar 7, 2017.