Environmental Engineering Reference
In-Depth Information
Fig. 8
Diurnal variations
of Fe(II) and Fe(III) in the
upstream waters (Site KR2,
Shouriki) on 21 August 2003
and in the downstream waters
(Site KR6, Hinotsume)
on 26 September 2003, in
the Kurose River, Japan.
Data Source
Mostofa and
Sakugawa (unpublished data)
[Fe(II)]
[Fe(III)]
SI
(a)
80
3.00
2.50
60
2.00
40
1.50
1.00
20
0.50
0
0.00
(
b)
250
3.00
2.50
200
2.00
150
1.50
100
1.00
50
0.50
0
0.00
Sampling period (Japan standard time, JST)
course of the experiment (Miller et al.
1995
). All the reported results suggest that
the photo-Fenton reaction under sunlight proceeds at the highest rate at noon in
natural waters, in correspondence with the peak values of Fe
2
+
and H
2
O
2
. The
diurnal changes in the concentrations of Fe(II) and H
2
O
2
are strongly correlated
to the losses in the DOM fluorescence: the latter was 28 % lower at noon than
before sunrise in the river waters (Mostofa et al.
2005
). However, the contribu-
tion of the photo-Fenton reaction to the production of HO
•
was minor (2-29 %)
as compared to NO
3
-
(3-70 %) and NO
2
-
(1-89 %) upon irradiation of river water
samples from Japan (pH 6.7-9.0) (Nakatani et al.
2007
). Interestingly, it has also
been shown that the oxidation of Fe
2
+
by H
2
O
2
is the key reaction step in the pres-
ence of high concentrations of Fe
2
+
; in contrast, the back reduction of Fe(III) by
superoxide is important at low initial Fe
2
+
concentrations and high pH (Pham and
Waite
2008
). It has also been suggested that precipitation of Fe(III) has a marked
effect on the overall Fe(II) oxidation, particularly at high pH. A recent study has
shown that the inhibition of the photo-Fenton degradation of organic material
(both synthetic phenol wastewater and an aqueous extract of Brazilian gasoline)
in the presence of chloride ions can be circumvented, by maintaining the pH of the
medium at or slightly above 3 throughout the process. In this way, it is possible to
limit inhibition of the oxidation reactions even in the presence of 0.5 M chloride
(Machulek et al.
2007
).
