Chemistry Reference
In-Depth Information
TABLE 1.8. Redox Potentials for the Oxidants/Disinfectants Used in Water
Treatment [291-294]
Oxidant
Reaction
E
o
(V/NHE)
Hydroxyl radical
•
OH + H
+
+ e
−
H
2
O
2.80
•
OH + e
−
OH
−
1.89
Sulfate radical
SO
+
NO e
−•
e
−
SO
2
−
2.43
4
4
Nitrate radical
2.30
•
+
−
NO
−
3
3
Manganate
MnO
2
−
+
4
H
+
+
2
e
−
MnO
+
2
H O
2.26
1.74
0.60
4
2
2
MnO
2
−
+
8
H
+
+
4
e
−
Mn
2
+
+
4
H O
4
2
MnO
2
−
+
2
H O e
+
2
−
MnO
+
4
OH
−
4
2
2
Ferrate(VI)
FeO
2
−
+
8
H
+
+
3
e
−
Fe
3
+
+
4
H O
2.20
0.70
4
2
FeO
2
−
+
4
H O e
+
3
−
(
Fe OH
)
+
5
OH
−
4
2
3
O
3
+ 2H
+
+ 2 e
−
O
2
+ H
2
O
2.08
Ozone
O
3
+ H
2
O + 2 e
−
O
2
+ 2OH
−
1.24
H
2
O
2
+ 2H
+
+ 2 e
−
2H
2
O
1.78
Hydrogen peroxide
H
2
O
2
+ 2 e
−
2OH
−
0.88
CO
−•
+
e
−
CO
2
−
1.59
Carbonate radical
3
3
Permanganate
MnO
−
+
8
H
+
+
5
e
−
Mn
2
+
+
4
H O
1.51
0.59
4
2
MnO
−
+
2
H O e
+
3
−
MnO
+
4
OH
−
4
2
2
Hypochlorite
HClO + H
+
+ 2 e
−
Cl
−
+ H
2
O
1.48
ClO
−
+ H
2
O + 2 e
−
Cl
−
+ 2OH
−
0.84
Peroxysulfate
HSO e
+
−
HSO
−
1.40
5
5
Perchlorate
ClO
−
+
8
H
+
+
8
e
−
Cl
−
+
4
H O
1.39
4
2
Chlorine
Cl
2
+ 2 e
−
2Cl
−
1.36
Dissolved oxygen
O
2
+ 4H
+
+ 4 e
−
2H
2
O
1.23
O
2
+ 2H
2
O + 4 e
−
4OH
−
0.40
Chlorine dioxide
0.95
ClO aq
(
) +
e
−
ClO
−
2
2
This suggests both Fe(VI) and Mn(VI) have strong oxidizing power, particu-
larly under acidic conditions.
Chlorine is a commonly used disinfectant in drinking water because it is
readily available and effective. However, chlorine can react with amino acids
and peptides to form DBPs, which have negative health effects [295-299]. The
kinetics and mechanisms of the formation of DBPs are presented in Chapter
3. The chlorination products of amino acids include cyanogen chloride, chlo-
roform, dichlroacetonitrile, monochloroamines, aldehydes, and nitriles [300-
303]. Chlorinated products of peptides are more stable than chlorinated
derivatives of amino acids; therefore, peptides in water are also of concern
[300]. The chlorination of waters containing bromide and iodide ions may
produce hypobromous (HOBr) and hypoiodous (HOI) acids [304, 305]. Thus,
both HOBr and HOI may also result in DPBs [304, 305].
Monochloroamine (NH
2
Cl) as a chlorine alternative is applied to reduce
the formation of DPBs. During chloramination, lower concentrations of DBPs,
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