ENVE 201
Dr. Aslıhan Kerç
Problems in groundwater, surface water 
certain seasons.
Some underground waters are free of Fe, Mn, but
some have
Biochemical changes effect Fe, Mn content
Changes in environmental condition brought by
biological reactions effect Fe, Mn content.
Fe,Mn  insoluble form in soil  how converted
to soluble?
Fe is found in soils and minerals as :
insoluble ferric oxide
ironsulfide (pyrite)
(slightly soluble) Ferrous carbonate (siderite)
Mn  in soil as manganese dioxide (insoluble) in water
containing CO2
Under anaerobic cond. : oxidation state changes
These changes occur due to biological rxns:
1) G.W. containing Fe, Mn low D.O high CO2
in the form Fe2+ , Mn2+
High CO2 bacterial oxidation of organic matter.
Absence of D.O anaerobic cond.
2) Wells producing good water change to poor
quality in time. What is the reason?
Organic wastes discharge aroundanaerobic
conditions occur in soil.
3) In surface waters (reservoirs) anaerobic conditions
occur in hypolimnion.
Fe,Mn released from bottom mud. Distributed to the
whole lake during fall overturn.
4) Mn (IV) , Fe (III) stable oxidation states for aerobic.
Reduced to soluble Mn(II) , Fe(II) under highly
anaerobic conditions.
G.W. contain CO2
FeCO3 + CO2 + H2O  Fe2+ + 2HCO3-
like dissolution of calcium and magnesium carbonates
More problems w/ insoluble ferric compounds.
Under anaerobic (reducing) condition :
Fe3+  Fe2+
(ferric) (ferrous)
5) Certain bacteria use Fe (III) and Mn(IV) as electron
acceptor. (?)
When O2 containing water injected into G.W for
recharge  soluble Fe content may increase.
O2 consumed by pyrite FeS2  leading to anaerobic
conditions again
2FeS2 + 7O2 + 2H2O  2Fe2+ + 42SO42- + 4H+
Environmental Significance
No harmful affect in drinking water
 When exposed to air become turbid, form colloidal
unaccepted aestheticaly
oxidation rate  not rapid
Form stable complexes with humic substances more
resistant to oxidation
Interfere with laundering.
Environmental Significance
Difficulties in distribution sys.  growth of iron bacteria
 Imparts taste to water
Fe: 0.3 mg/L
Mn: 0.05 mg/L
Measurement of Iron
(Phenanthroline Method)
Interferences : Phosphate
Heavy metals
1,10 phenonthroline combines with Fe2+ to form
complex ion orange in red color
Color produced confirms Beer’s Law
 Visual
 Photometric comparison
Phenanthroline Method
Sample exposed to atmospfere contains Fe2+ , Fe3+ , ppt of
ferric hydroxide.
All iron  must be in soluble form
HCl is used
Fe(OH)3 + 3 H+  Fe3+ + 3 H2O
1,10 phenonthroline  specific for measuring Fe(II)
Fe3+ is reduced to Fe2+
Hydroxylamine is used as reducing agent
4Fe(III) + 2 NH2OH  4Fe(II) + N2O + H2O + 4 H+
3 molecules of 1,10 phenantrhroline complex with each
Manganese measurement
method  depend upon oxidation of
Mn to  VII
forms highly colored permanganete ion
Obeys Beer’s Law
Visual or photometric comparison
 Colorimetric
Manganese measurement
(Persulphate Method)
Ammonium persulphate  oxidizing agent
Cl- interference: Because of reducing action in acid medium.
use Hg2+ for interference. HgCl2 complex is formed
Ag2+ is used as catalyst
Oxidation of Mn in lower valence to permanganete by persulfate.
2Mn2++5S2O82- +8H2O  2MnO4- +10SO42- +16H+
(permanganete colored)
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