Environmental Engineering Reference
In-Depth Information
The AOPs are generally classified in terms of whether UV source is used in
the process: Nonphotochemical Processes and Photochemical Processes.
The most common AOPs are ozonation, photocatalytic degradation,
Fenton's reagent (H
2
O
2
/Fe
2+
), photo-Fenton, and wet air oxidation (WAO).
The objective of this chapter is to provide the readers with knowledge
about AOPs.
In view of the importance of the removal of dyes from aqueous media,
it is the purpose of this chapter:
t to present an overview of AOPs by investigating them in two
categories such as nonphotochemical and photochemical
processes;
t to introduce the most important aspects of various AOPs
such as ozonation, Fenton's reagent oxidation, wet air oxida-
tion and photocatalytic degradation processes;
t to discuss the key factors inluencing the AOPs' eiciency;
and
t to present a perspective to the readers on the research per-
formed on the removal of dyes from aqueous media by AOPs
which is found in literature.
3.2
Advanced Oxidation Processes
Advanced oxidation processes (AOPs) are defined as a set of chemical
treatment processes designed to remove organic compounds in wastewater
by several oxidation reactions.
In order to generate highly reactive intermediates, OH radicals, the
AOPs may proceed along one of the two routes given below [12]:
t Use of high energy oxidants such as ozone and H
2
O
2
and/
or photons. The generation of hydroxyl radical might possi-
bly be by the use of UV, UV/O
3
, UV/H
2
O
2
, Fe
+2
/H
2
O
2
, TiO
2
/
H
2
O
2
and a number of other processes [13].
t Use of O
2
in temperature ranges between ambient conditions
and those found in incinerators, such as in wet air oxidation
(WAO) processes in the region of 1-20 MPa and 200-300 C.
They are mainly all characterized by the same chemical feature, which is
the generation of powerful non-selective oxidizing agent, hydroxyl radicals
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