Environmental Engineering Reference
In-Depth Information
According to Eq.
2.7
, the plot of 1/
r
P
versus 1/[
B
] should be straight line (Takeda
et al.
2004
) and
k
′
SC
/k
B
can be calculated from the slope and intercept of the plot.
Thus,
F
B,HO
can be calculated with Eq.
2.6
using the values of
k
′
SC
/k
B
and [
B
].
2.5 Levels of Photoinduced Generation of HO
•
in Natural Waters
•
The production rates of HO
that have been estimated in a variety of waters, in
the presence of standard chemical species (NO
2
-
, NO
3
-
and H
2
O
2
) or of stand-
ard organic substances under sunlight are summarized in Table
2
(Mopper and
Zhou
1990
; Takeda et al.
2004
; Zepp et al.
1987
; Haag and Hoigné
1985
; White
et al.
2003
; Arakaki and Faust
1998
; Nakatani et al.
2007
; Mostofa KMG and
Sakugawa H, unpublished data; Nakatani et al.
2004
; Qian et al.
2001
; Allen et
al.
1996
; Mabury
1993
; Grannas et al.
2006
; Anastasio and Newberg
2007
). The
rates are typically varied in a range from 10
-7
to 10
-10
M s
-1
in aqueous solu-
tion (Table
2
). Production rates in rivers are (0.6-7.5)
×
10
-11
M s
-1
in upstream
waters, (0.4-7.4)
×
10
-8
M s
-1
in upstream waters contaminated with AMD,
(1.0-2.9)
×
10
-11
M s
-1
in non-polluted river waters, 2.4
×
10
-11
M s
-1
in
Ogeechee River, (2.0-6.0)
×
10
-10
M s
-1
in Wetland on Lake Erie and Artificial
Agricultural wetland, 6.4
×
10
-11
M s
-1
in Rice field water, (2.0-17.0)
×
10
-
10
M s
-1
in Satilla River and Pine Barrens that have iron-rich waters (Table
2
). It is
noticeable that the production rates of HO
•
are higher by two to five orders of mag-
nitude in stream waters contaminated with AMD (Allen et al.
1996
) than in typical
river waters. Such an effect might be caused by the photo-Fenton reaction that is
considerably favored in the presence of elevated iron contents (Allen et al.
1996
;
McKnight et al.
1988
). Similarly, high production rates of HO
•
have been observed
in Satilla River water (White et al.
2003
), where more than 70 % of the total HO
•
production is accounted for by the photo-Fenton reaction. Therefore, the latter pro-
cess is expected to be the main contributor to HO
•
photo-production in iron-rich
waters. In contrast, upstream waters mainly contain DOM components (mostly ful-
vic and humic acids) that are the major contributors to HO
•
photo-production in
•
these systems. A possible pathway that yields HO
from DOM is the photoinduced
which could induce the photo-Fenton reaction in the presence of Fe or produce
HO
•
by direct photolysis (Nakatani et al.
2007
; Mostofa KMG and Sakugawa
H, unpublished data). An alternative explanation for the production of HO
•
from
DOM is the oxidation of water by the excited triplet states (
3
DOM*) (Brigante
et al.
2010
).
In lake water the production rates of HO
•
are very variable, ranging from
1.8
×
10
-13
to 4.6
×
10
-11
M s
-1
(Table
2
). The HO
•
photo-production depends
on the irradiation wavelength. For instance, the formation rate of HO
•
observed on
extracted lake DOM under sunlight is higher [(1.6-1.8)
×
10
-10
Ms
-1
at 308 nm]
