Environmental Engineering Reference
In-Depth Information
(CH
3
OOOH) is reported in earlier studies (Fig.
8
). For ROOH measurement,
50,000 units mL
−
1
catalase solution was used to decompose nearly all of the
ROOH in the samples during the same six minute reaction. In this way it is possi-
ble to provide only the signal of the background DOM or water fluorescence. The
fluorescence-developing reagent is peroxidase mixed with
p
-hydroxyphenylacetic
acid also in this case. The difference between the fluorescence measurements
using 500 and 50,000 units mL
−
1
of catalase (decomposition of H
2
O
2
alone and
of H
2
O
2
and ROOH, respectively) provides an estimate of the ROOH concentra-
tions in the samples. Also in this case it is possible to use the external standards
for calibration (Fig.
8
b).
The production of H
2
O
2
and ROOH in water samples is normalized as a function
of natural sunlight using the following (Eq.
2.3
) (Mostofa and Sakugawa
2009
):
D
(
2
−
NB
,
Is
)
×
r
(
H
2
O
2
,
Ixe
)
D
(
2
−
NB
,
Ixe
)
r
(
H
2
O
2
,
Is
)
=
(2.3)
where
r
(
H
2
O
2
,
Is
)
is the rate of H
2
O
2
production, corrected for the intensity of nat-
ural sunlight (at noon under clear-sky conditions, on 6 July 2004 at Hiroshima
University Campus), in natural water samples and standard DOM materials,
D
(
2
-
NB,Is
)
and
D
(
2
-
NB,Ixe
)
are the degradation rates of 2-NB (2-nitro-benzalde-
hyde) estimated using the intensity of natural sunlight and the adopted irradiation
device, respectively, and
r
(
H
2
O
2
,
Ixe
)
is the observed H
2
O
2
production rate under the
adopted irradiation device.
The production rate of H
2
O
2
in irradiated water samples can be determined
from the net production of H
2
O
2
(final concentration minus initial concentration)
measured for the initial 60 min of the irradiation period. The rate of H
2
O
2
gen-
eration is then normalised to sunlight intensity with (Eq.
2.3
). The normalised
rate of H
2
O
2
production of a specific fluorescent DOM component (identified by
parallel factor modeling on DOM) is estimated on the basis of its fluorescence
intensity observed in waters and can be determined using (Eq.
2.4
) (Mostofa and
Sakugawa
2009
):
FI
Fi
(
DOM
)
×
r
RS
FI
RS
r
Fi
(
DOM
)
=
(2.4)
where r
Fi (DOM)
is the normalised production rate of H
2
O
2
of an identified fluo-
rescent DOM component in natural waters, FI
Fi(DOM)
is the fluorescence intensity
of the identified fluorescent DOM component in natural waters, FI
RS
is the fluo-
rescence intensity of the relevant standard substance in the aqueous solution, and
r
RS
is the normalised production rate of H
2
O
2
of the relevant standard substance
in solution. Finally, percentages of each identified DOM component contribut-
ing to the rate of production of H
2
O
2
are calculated using the following (Eq.
2.5
)
(Mostofa and Sakugawa
2009
):
F
i
(
DOM
)
=
r
Fi
(
DOM
)
×
100
r
net
(
DOM
)
(2.5)
