Iron

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Iron
1. Rocks soils Ferric oxides (Fe2O3) Ferric hydroxides (Fe(OH)3)
2. Natural waters Ferrous bicarbonate Fe(HCO3)2) Ferrous hydroxide Ferrous sulphate(FeSO4) Organic Iron

• GWs containing soluble iron (ferrous) are clear
  colorless when it is first drawn
• Upon contact with air, a yellowish to reddish
  brown precipitate of ferric hydroxide is formed.
• Stain the porcelain fixtures laundry.
• Iron bacteria utilise ferrous iron as energy
  source precipitate ferric hydroxide, that may
  cause pipe clogging.

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Manganese

• Rocks soil

1. Natural waters It appears with iron. Manganous bicarbonate Mn(lCO3)2 Manganous chloride(MnCl2) Manganous sulphate(MnSO4)

• Causes Stain, bad taste growth of microorganisms

Iron Mn Removal

• Oxidation Ppn
• Aeration at high pH by lime addition coagulation
  ppn
• Selective Ion exchange Resins

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Iron Mn Removal

• Aeration, Sedimentation Filtration
• Tray type aerators, frequently contain coke/Stone
  contain beds to speed up oxidation reactions.

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• 2) Aeration, Chemical Oxidation, Sedimentation
  Filtration
• Aeration Strips out chemically oxidised gases
  adds O2
• Iron Mn are chemically oxidised by Cl2 /KMnO4
• 1 mg/L of KMnO4 oxidises 1.06 mg/L of iron 0.52
  mg/L of Mn
• (Fe2 M22) (soluble Irons) O2 Cl2/KMno4
  (FeOx ? MnO2?) (Insoluble oxides)
• Filtration is needed to remove Flocculent metal
  oxides
• 3)Mn Zeolite Process
• It is a natural green sand coated with manganese
  dioxide that removes soluble iron Mn from soln
• Zeolite bed is regenerated with KMnO4
• A pressure filter with media i.e Anthracite
  Manganese Zeolite bed.

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Iron Mn removal

• Impart a bitter characteristic, metallic taste
• Oxidised precipitates cause yellowish brown to
  black
• Staining of plumbing fixtures laundered
  materials can also result
• Carrying capacity of pipelines in distribution
  system is reduced due to deposition of iron oxide
  bacterial slimes due to growth of iron bacteria
  in iron bearing water
• Con of iron in excess of 0.2 0.3 mg/L may cause
  nuisance

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Sources Nature

• Occur on certain underground water springs
  alone or in association with organic matter
• Discharge of industrial wastes or mine drainage
• Iron exits in water in two levels of oxidiation
  (Fe2 Fe3)
• In ?W, if it is present , it is in Fe2 (Ferrous
  iron)
• Ferric iron is in precipitated form
• Manhanese is present in water in 2 oxidation
  states (biralent quadrivalent, which is
  sparingly soluble)
• Iron forms complexes with bicarbonate, sulphate,
  phosphate, cyaride or halide
• Water of high alkalinity have low iron Mn than
  water of low alkalinity
• If water contains H2O, little or iron or Mn is
  found in soln as it is precipitated

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Removal Methods

• Oxidation by aeration
• Use of Cl2, ClO2, KMnO4 followed by filtration
  alone by settling filtration
• Use of Zeolities as well as Catalytic Oxidation

• Precipitation
• 4Fe2 O2 10H2O ? 4 Fe(oH)2 ? 8H
• 4X 56 mg Fe2 2X 16 mg O2
• 1 mg Fe2 0.14mgO2
• Iron or Mn in water in reduced form os converted
  to insoluble ferric
• Mn compounds by oxidation
• Reaction time is 5 min, _at_ pH 7 7.5, 0.14 mg of
  O2 is needed to convert
• 1mg Ferrous iron to Ferric hydroxide
• Water is allowed to trickle over coke or crushed
  stone
• Contact beds 23 m deep _at_ SLR of 40 70 m3/d/m2
  with contact medium of sizes 50-150mm
• Accumulated iron Mn are Flushed out by rapid
  drainage
• Sedimentation before filtration is needed when
  iron content exceeds
• 10mg/L

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• Settling period 2-3 h
• Water pass through filters (gravity or pr. Type)
  with 75 cm depth of sand or sand anthracite
• Filters rates 6-9 m3/h/m2
• All organic material to be oxidised before ppn.
  Of iron
• Chlorination of many iron bearing water can bring
  about oxidation of organic matter other
  reducing agents facilitating oxidation of ferrous
  iron
• Addition of lime to raw or preaerated waters, co2
  could be brought down to zero, resulting high pH
  will promote flocculation of iron Mn
• Washing of filter medium 5-10 cm filter medium
  washing it manually with water to free it from
  sediment replace the same in position
• Coke medium needs washing once in 6-24 months
• Mn removal requires pH adjustment upto 9.4 -9.6
• 0.29 mg o2 is needed to convert 1 mg Mn
• 6Mn2 O2 6H2O ? 2ltn3O4 12 H
• 2Mn3O4 2O2 ? 6MnO2(Blau)
• 6Mn2 3O2 6H2O ? 6MnO2 12H
• 1mg Mn2 0.29mgO2
• Prechlorination to free residuals upto 0.7
  1mg/L will effect oxidation of ppn of Mn

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Contact beds

• To facilitate oxidation of iron or Mn through
  catalytic action of previously precipitated
  oxides of these minerals on gravel or ore
• Mn ore (pYro ludite), an oxide of Mn\
• Upward flow rates _at_ 9.6 m/h
• Bed depth 1.8m
• Regeneration of beds by backwashing with
  potassium permanganate
• Mn Zeolite, an effective contact material
• ClO2 KMno4 are strong oxidants for Mn.o

Zeolite

• Percolation of water through bed of zeolite which
  takes up iron Mn by IX
• Base exchanger siliceous, carbonaceous,
  synthetic resin type
• Air should be excluded

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Catalytic Method

• Percolating water through contact materials that
  oxidise iron Mn

Defluoridation of Water

• Dental fluorosis
• skeletal or bone fluorosis
• High con in AP, TN, Bihar, Gujarat, Kerala, etc.
• Range 1.5 6 mg/L, 16 18 mg/L, 36 mg/L

Removal Method

• 1)Fluoride exchanges
• Degreased alkali treated bones posses ability
  to remove fluorides
• Bone charcoal
• Tricalcium phosphate removes 0.7 kg of fluoride/n3

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• 2) Anion Exchanges
• Basic formaldehyde resin quaternary aluminum
  type in hydroxide or chloride from
• 3)Activated Carbon
• Carbonising paddy husk or saw dust, digesting
  under prenine with alkali quenching it in 2
  alum soln
• The spent material could be regenerated by
  soaking it in 2 alum soln for 14 h
• A granular iron exchange material (De
  fluoronz)a sulphunated coal.
• 4) Magnesium salts
• Excess lime treatment for softening effecrs
  removal of fluoride due to its adsorption by
  Magnesium hydroxide floc.
• 5) Al. Salts
• Filter alum activated aluminum alum treated
  cation exchanges have shown benefical effects
• Filter alum during coagulation baring about some
  removal of fluorides from water
• Coagulant aid like activated silice clay (300
  500 mg/L of alum) is required to bring down
  fluoride from 4 to 1 mg/L
• With coagulant aid, fluorides were reduced from 6
  to 1 mg/L _at_ alum dose of 100 mg/L
• Alum treated polystyrene cation exchanges
  sulphonated coals were used
• Calcinated or activated alumina in granular from
  can bre osed for fluoride removal

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Iron Mn Removal

• Basic principles of iron Mn removal are the
  same.
• The basic approach for Iron Mn removal involves
  oxidation removal of suspended material by
  either sedimentation or filtration.
• The most successful approach involves pH
  adjustment, chlorination direct filtration on a
  monomedia anthracite filter.

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• Oxidation Removal
• 4Fe2 2H O2 gt 4Fe3 2OH- ( 7mg
  Fe / mg O2)
• 2Fe2 Cl2 gt 2Fe3 2Cl- (1.6mg
  Fe / mg Cl2)
• 3Fe2 MnO4- 4H gt 3Fe3 MnO2 2H2O (1.6
  mg Fe / mg MnO4)
• Mn2 2H ½O2 gt Mn4 H2O (3.5
  mg Mn / mgO2)
• Mn2 Cl2 gt Mn4 2Cl-
  (1.3 mg Mn / mg Cl2)
• 3Mn2 2Mn7 gt 5Mn4
  (0.52 mg Mn / mg MnO4)

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• Oxidation Removal (cont.)
• Selection of media for filter unit is important.
• Media should have large effective size (gt1.5mm)
  to reduce head loss should have low UC.
• Use of green sand, a natural zeolite allows for
  more rapid oxidation removal of iron Mn
• Coal works well for this application.
• Recovery of backwash water disposal of sludge.

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• 2)Ion Exchange
• Use of water softeners for iron Mn removal is
  fairly common.
• Due to divalent nature of iron Mn, they are
  removed.
• The problem is that these materials are oxidised
  by DO in water thus media can be watered
  fouled.
• 3)Polyphasphates
• In special cases, use of polyphosphates is
  applied.
• Polyphosphates react with iron Mn hold it in
  solution, so that consumer is not aware of its
  presence.
• Polyphosphates are dosed _at_ 2 times con of iron
  Mn.

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Chemical injection
filter
Raw Water
To System
.
Backwash
Detention tank
Sludge to sewer
Backwash holding tank
Reclaimed backwash
Typical iron and manganese removal system
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Lime
Soda ash
CO2
Filter
settling
settling
Filter soft effluent
Sludge handling
Lime soda softening system
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Design Criteria for Iron and Manganese Control
S.No Elemment Units
1. Detention time 5-30 min at average flow after chemical feed
2. Filter media Uniformity coefficient Q/A Backwash Q/A 1.5 mm effective size or greater anthracte 1.2 1.4 5 gpm/ft2 to 10 gpm/ft2 15-25 gpm/ft2
3. Backwash tank size 20 min flow at 5 times normal Q/A
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Defluoridation
1. 1.5 2 mg/L Dental Fluorosis Discolored, blackened teeth permanent brown to grey discoloration of enamel
2. 3 6 mg/L Skeletal Fluorosis Severe permanent bone joint deformations
3. gt 10 mg/L Crippling Fluorosis

• High fluoride con. in GL in 23 countries
• Fluoride bearing minerals viz., fluorite,
  apatite, rock phosphate, etc.
• Fluorosis is an irreversible disease, there is no
  cure.
• Non skeletal fluorosis leads to gastro
  intestinal problems neurological disorders,
  kidney thyroid injury death
• Fluorosis can be detected in neck, spine, knee,
  pelvis, shoulder, small joints of hands feet
• Gastro intestinal problems include abdominal
  pain, diarrhea constipation.

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Methods of Defluoridation

1. Activated Alumina or Bone char
2. RO
3. Nalgonda Technique

• Nalgonda Technique
• It uses Al. salt for removing fluoride
• Raw water is mixed with lime
• Alum soln. is then added water is stirred
  slowly for 10 min allowed to settle for 1 h

• Activated Alumina or Bone char
• Water is percolated through insoluble granular
  media
• Regeneration of bone char consists of backwashing
  with 1 soln. of caustic soda then rinsing the
  bed.
• Regeneration of alumina involves backwashing with
  caustic soln.

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Defluoridation

• Both lime softening alum coagulation are
  effective.
• The only acceptable method of defluoridation is
  Adsorption onto Activated Alumina or Bauxite.
• The water is filtered through a bed of Activated
  Alumina
• The regeneration of alumina bed involves
  backwashing, regeneration by NaOH soln, Rinising
  with water neutralisation
• The major equipment include
• An activated Alumina bed
• Acid base feed
• pH adjustment control system
• 5raw water filtration backwash system
• Alumina bed regeneration
• Neutralisation systems

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Fluoride Removal

• Lime softening, Alum Coagulation Ion exchange
  with Activated Alumina.
• Ion exchange with Activated Alumina is the only
  method that can economically reduce fluorides
  levels to below drinking water stds.
• Lime softening
• An insoluble ppt is formed with Co-ppn. with
  Magnesium hydroxide (Mg(OH)2)
• Water high in Mg that would be softened can have
  significant fluoride reduction by co-ppn.
• Fresidual Finitial (0.07 Finitial X vMg)
• To reduce Fluoride from 5 to 1.5 mg/L,100 mg/L of
  magnesium is needed.

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• 2) Alum Coagulation
• It reduces fluoride levels to acceptable level,
  but requires very large amounts of alum.
• Fluoride reduction 3.6 to 1.4 mg/L requires 250
  mg/L of alum during conventional treatment.
• Optimum pH 5.5 7.
• Large amount of sludge is produced.
• 3) Activated Alumina
• Since 1930s, this is practiced.
• Activated Alumina is used in same way as IX
  resins .
• Activated Alumina is an amphoteric substance
  its isoeletric point is pH 9.5.
• It will remove anions below this pH cations
  above .
• When treated with an acid soln., alumina behaves
  like an anion exchanger will readily replace
  fluoride from alumina.

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• Optimum pH 5 8
• Commercial available alumina is in 4 typical size
  ranges
• 8 10, 14 28, 28 48 48 100 mesh.
• Registration methods include backwash (10 15
  min) followed by NaOH elution of fluoride
  neutralisation of bed by rinsing with the bed
  with water for removal of excess NaOH followed by
  rinsing with an acid soln. (H2SO4/ HCl).
• Disposal of regenerant waste is a problem.