Environmental Engineering Reference
In-Depth Information
where
F
i(DOM)
is the contribution percentage to the normalised net H
2
O
2
production rate in the water (%) by each identified fluorescent DOM compo-
nent,
r
Fi
(DOM)
is the normalised H
2
O
2
production rate generated by each identi-
fied DOM component, and
r
net
(
DOM
)
is the whole, normalised net H
2
O
2
production
rate in the water samples. The percent contributions of unknown sources of H
2
O
2
in the water samples are estimated using a simple formula:
F
unknown
=
100—
(
F
FA
+
F
TRYP
+
F
OTHERS
). In the formula, the sum of the normalized H
2
O
2
pro-
duction rate of FA-like substances (
F
FA
), tryptophan-like substances (
F
TRYP
), and
other organic substances if any (
F
OTHER
S
) is subtracted from the normalised, net
H
2
O
2
production rate that is assumed as 100 %.
2.3 Advanced Analytical Method for H
2
O
2
Determination
in Natural Waters
Theory
: This method is based on the Fenton reaction, where H
2
O
2
reacts with
Fe
2
+
in acidic solution to yield HO
•
. The latter is scavenged by an aromatic com-
pound (e.g. benzene) to produce the respective phenolic compound (e.g. phenol)
according to the following reactions (Eqs.
2.6
,
2.7
) (Olasehinde et al.
2008
; Lee
et al.
1994
; Liu et al.
2003
):
H
2
O
2
+
Fe
2
+
→
Fe
3
+
+
HO
•
+
OH
−
(2.6)
HO
•
+
C
6
H
6
→
C
6
H
5
OH
(2.7)
where the rate constant of the first reaction (Eq.
2.6
) is
k
=
63 at pH 3, 1.2
×
10
2
at pH 4 and 5.7
×
10
2
M
−
1
s
−
1
at pH 5, respectively (Kwan and Voelker
2002
).
Phenol produced by the second reaction (Eq.
2.7
) is determined by high perfor-
mance liquid chromatography (HPLC) with fluorescence detector (Olasehinde et
al.
2008
). The amount of phenol produced is directly proportional to the H
2
O
2
concentration present in the sample solution.
Based on this theoretical framework, Olasehinde and his co-workers
(Olasehinde et al.
2008
) developed a new method for the measurement of H
2
O
2
in
the aqueous solution, which is highly sensitive and simpler than any other enzy-
matic process applied earlier to natural waters. The chemicals preparation, ana-
lytical procedure and HPLC instrumentation for this method are depicted below
(Olasehinde et al.
2008
):
Chemicals preparation
Benzene stock solution
: 2
×
10
−
2
M benzene solution is prepared by adding
88.8
μ
L of 99.7 % benzene in 50 mL of ultrapure water.
Fe
2
+
solution
: A 0.1 M Fe
2
+
solution is prepared by dissolving 1.39 g ferrous
sulphate pentahydrate into 50 mL of 0.07 M H
2
SO
4
solution.
H
2
SO
4
solution
: A 3.0 M sulphuric acid stock solution is prepared by diluting
16.3 mL of 98 % H
2
SO
4
to 100 mL with ultrapure water.
