Environmental Engineering Reference
In-Depth Information
5.2 Photo-Fenton Type Reaction for Decomposing
Organic Pollutants
One of the key applications of H
2
O
2
is its use in the degradation of organic pollut-
ants in the wastewater treatment industry by means of Fenton's reaction (Fe
2
+
and
H
2
O
2
), photo-Fenton reaction (UV/Visible-Fe
2
+
/H
2
O
2
,
< 580 nm), UV/Visible-
ferrioxalate/H
2
O
2
reaction and ozone with H
2
O
2
(Zepp et al.
1992
; Voelker et al.
1997
; Fenton
1894
; Safazadeh-Amiri et al.
1997
; Glaze and Kang
1989
; Tizaoui et
al.
2007
). Among many other applied technologies, these four are major commer-
tialized technologies.
λ
5.3 Indicators for Microbial Modification of Bulk DOM
ROOH compounds are significantly produced in natural waters under dark conditions
(Figs.
1
and
2
) and are more concentrated in deep seawater than in the surface layer
(Sakugawa et al.
2000
). Net ROOH formation (dark production minus dark con-
sumption) is observed in both filtered and unfiltered river waters (Fig.
2
). In contrast,
net H
2
O
2
formation is only observed in filtered waters. The microbial modification
of bulk DOM can yield ROOH compounds in natural waters. Microbially-induced
changes in the bulk DOM composition are in agreement with the observation of a red
shift of the fulvic acid-like fluorescence (peak C) with an increase in fluorescence in
deeper lake or seawaters (Hayase and Shinozuka
1995
; Mostofa et al.
2005
; Moran et
al.
2000
). Therefore, dark production of organic peroxides could be a useful indicator
for the microbial modification of bulk DOM in aquatic environments.
5.4 Function of H
2
O
2
as an Oxidizing-Reducing Agent
in Aqueous Solution
On the basis of the reduction potential V, the oxidizing agents in aqueous solution can
be classified according to the following order: Fluorine (V
=
3.0) > Hydroxyl radi-
cal (HO
•
) (V
=
2.8) > Ozone (V
=
2.1) > Peracetic acid (ROOH) (V
=
1.8) > H
2
O
2
(V
=
1.8) > Potassium permanganate (V
=
1.7) > Hypochlorite (V
=
1.5) > Chlorine
dioxide (V
=
1.5) > Chlorine (V
=
1.4) (Buettner
1993
).
H
2
O
2
and ROOH compounds act as intermediates in the reduction of oxygen in
natural waters. They can act as oxidants or reductants in their reactions with metal
ions (Moffett and Zika
1987a
,
b
). For example, H
2
O
2
and ROOH compounds can
oxidize Cu(I) and Fe(II) in natural waters (Moffett and Zika
1987a
,
b
), a process
that can be schematically generalized as follows:
M
n
+
+
R
′
OOH
→
M
(
n
+
1
)+
+
R
′
O
•
+
OH
−
(
R
′
=
H or R
)
(5.1)
