Environmental Engineering Reference
In-Depth Information
the differences in the reaction rates observed between estuarine waters of various
alkalinity and seawater diluted with water (Millero and Sotolongo
1989
).
A recent study demonstrates that the rates of the Fenton reaction do not vary
in the presence of chloride, nitrate and perchlorate. However, in the presence of
sulfate the rate of Fe(II) oxidation is higher and depends on pH and the concen-
tration of sulfate. This result has been obtained under dark conditions at pH < 3,
25
±
0.5 °C and controlled ionic strength (
≤
1 M) (Le Truong et al.
2004
). It has
also been shown that H
2
O
2
is more stable in Fenton-like than in Fenton's systems,
and that the lifetime of H
2
O
2
is highly affected by the solution pH. Indeed, pH-
buffered acidic conditions are preferred to ensure sufficient H
2
O
2
lifetime, which
is an important factor in the feasibility of Fenton's and Fenton-like reactions with
haematite and magnetite for soil and groundwater remediation (Jung et al.
2009
).
4.7 Photo-Fenton Reaction
•
The formation of HO
in the photo-Fenton reaction (Fe(III)
+
H
2
O
2
+
h
ν
) signifi-
cantly depends on light intensity, H
2
O
2
and Fe(III) concentration, and pH (Zepp
et al.
1992
; Voelker et al.
1997
; Southworth and Voelker
2003
; Vermilyea and
Voelker
2009
). Studies on the ferrioxalate system (air- and argon-saturated) sug-
gest that the Fe(II) photoproduction rates are not affected by the reducing interme-
diates (CO
2
•
-
, scavenger-derived radicals) produced in the aqueous solution
(Zepp et al.
1992
). The results demonstrate that the photolytically generated Fe(II)
can efficiently react with H
2
O
2
to produce HO
•
-
, O
2
•
in water at pH 3-8 (Zepp et al.
1992
). It has been shown that the Fe(II) concentration in upstream waters grad-
ually increased from zero (0530 h JST, Japan standard time) to 3.8
μ
M (1300 h
JST), and decreased to zero again after sunset (1900 h JST) (Fig.
8
a) (Mostofa
KMG and Sakugawa H unpublished data). In the meantime, pH varied from 7.0
to 7.6 (Mostofa and Sakugawa
2009
). In downstream waters, the Fe(II) concen-
tration increases from 2.3 (0530 JST) to 4.0
μ
M (1200 JST) and then decreased
to 2.2
μ
M (1900 JST) after sunset (Fig.
8
b) (Mostofa KMG and Sakugawa H
unpublished data). The pH varied from 7.0 to 7.3 (Mostofa and Sakugawa
2009
).
The production of Fe(II) was the highest at noon, and it was almost the same in
clean upstream river (3.8
μ
M, 7.3 % of the total Fe) and polluted river waters
(4.0
μ
M, 1.9 % of the total Fe). In a similar way, the H
2
O
2
production was also
maximum at noon and reached 40 and 63 nM, respectively (Fig.
8
,
“
Photoinduced
to reach up to 0.9 nM in a Swiss Lake at pH 8.0-8.5; 15 nM in a low-land lake
in the United Kingdom at pH 7.0-7.5; and approximately 0-145
μ
M in a salt
marsh at Skidaway Island in the USA (Viollier et al.
2000
; Aldrich et al.
2001
;
Emmenegger et al.
2001
). The peak concentration of Fe(II) ranged from 4 to 8 %
of the total iron concentration at pH 8 in waters of Narragansett Bay. It was also
observed an increase of Fe(II) concentration by lowering the pH over the entire
