CE 370

1
CE 370

• Iron and Manganese Removal

2
Fe and Mn

• Ferrous iron Fe and manganous manganese Mn
  are
• soluble
• invisible
• When exposed to air, they are oxidized to ferric
  iron Fe and manganic manganese Mn, which
  are
• insoluble
• visible

3
Oxidation

• The oxidation rate depends on
• pH
• alkalinity
• organic content
• presence of oxidizing agents
• If not removed from water, iron and manganese
  oxides create problem of brown color formation.

4
Oxidation

• Reduced iron in water promotes the growth of
  autotrophic bacteria in distribution mains.
• Elimination of iron bacteria is difficult and
  expensive.
• When decays, iron bacteria release foul taste and
  odor.
• Heavy chlorination followed by flushing proved to
  be successful in some case.
• Removal of iron and manganese from water is the
  best solution to that problem.

5
Oxidation of Iron and Manganese with Oxygen,
Chlorine, and Chlorine Dioxide
6
Treatment Alternatives
7
Aeration, Sedimentation, and Filtration

• Aeration (air oxidation) is the simplest
  treatment in removing iron. The reaction that
  takes place is in the form of
• Fe(ferrous) oxygen ? FeOx (ferric oxide)
• Soluble iron Insoluble iron
• Air oxidation can not remove manganese
  effectively. Increasing the pH to 8.5 can
  enhance the oxidation process. If manganese was
  not effectively removed from the water, it can
  cause problems with post-chlorination. When
  oxidized
• it can clog the solution-feed chlorinator
• it cause a staining water

8
Aeration, Chemical Oxidation, Sedimentation, and
Filtration

• This is a common method for removing iron and
  manganese from well water without softening
  treatment.
• Preliminary aeration strips out dissolved gases
  and adds oxygen.
• Iron and manganese are oxidized by free chlorine
  residual
• Fe Mn Oxygen ? FeOx MnO2
• Soluble ions Insoluble metal
  oxides
• or by potassium permanganate
• Fe(HCO3)2 KMnO4 ? Fe(OH)3 MnO2
• Ferrous bic. Potas. Perm. Ferric
  Hydrx. Mang. Diox.
• Mn(HCO3)2 KMnO4 ?
  MnO2
• Manganous bic Potas Perm Mang.
  Diox.
• Potassium permanganate oxidizes iron and
  manganese at rates faster than dissolved oxygen
  and its reaction is relatively pH independent.
• Since iron and manganese can not be completely
  removed by sedimentation, effective filtration is
  required.

9
Manganese Zeolite Process

• Manganese zeolite is a natural greensand coated
  with manganese dioxide. It has the capability to
  remove iron and manganese from solution. When
  manganese zeolite becomes saturated with metal
  ions, it can be generated using potassium
  permanganate. A continuos flow diagram is shown
  in the following Figure.

10
(No Transcript)
11
Reaction Equations
12
Manganese Zeolite Process

• KMnO4 is applied prior to filtration.
• The filter is a dual-media filter with anthracite
  is placed on top of the manganese zeolite.
• Iron and manganese are oxidized by KMnO4.
• The upper layer will remove the insoluble metal
  ions.
• Any iron and manganese ions not oxidized, it will
  be captured by the lower layer of manganese
  zeolite.
• Any surplus KMnO4 will regenerate the greensand.
• When the bed becomes saturated, it is backwashed
  by KMnO4 to remove particles from the upper layer
  and regenerate the greensand.

13
Water Softening

• Lime and soda ash, which are used in water
  softening, can remove iron and manganese from
  water.

14
Biological Treatment

• New process
• In the form of filters that support
• Iron-oxidizing bacteria
• Manganese-oxidizing bacteria
• Two separate filters are used
• pH and dissolved oxygen of the feed are critical
• Filtration rates are
• 25 to 40 m/h for iron
• 10 to 40 m/h for manganese
• Coarse sand is used

15
Sequestering

• Sequestering agents are used
• Sodium silicates
• Phosphates
• polyphosphates
• Agents are added
• In the form of colloidal complexes
• to bind iron and manganese and prevent them from
  forming color and turbidity
• In distribution system
• Chlorine is added simultaneously to oxidize iron
  and manganese
• Normal doses of silicates are 5 to 25 mg/l as
  SiO2
• Iron is sequestered more with silicates than
  manganese