Advanced Oxidation Processes for Removal of Dyes from Aqueous Media - Green Chemistry for Dyes Removal from Wastewater - page 100

and so the degradation rate decreases. Thus, an increase in the number
of substrates being accommodated in the lattice of the catalyst inhibits
the action of the catalyst with oxygen, thereby decreasing the degrada-
tion efficiency [123]. Hence, it can be concluded that the oxidation process
requires more catalyst loading and longer reaction times for higher dye
concentrations [124].
Catalyst Loading
Catalyst is known to increase the applicability of the wet oxidation process
using dedicated catalysts, which potentially promote oxidation in a shorter
reaction period under milder operating conditions [125].
When the loading of the catalyst is increased, the number of dye
molecules adsorbed also increase. However, above a certain level, the dye
molecules available may not be sufficient for adsorption, hence the addi-
tional catalyst will not be involved in the catalysis activity [126].
Some studies on the WAO of dyes are summarized in Table 3.5. These
studies show that the removal of dyes has attracted a lot of interest by show-
ing good potential for dealing with dye wastewater. The following points
can be concluded:
t he WAO process is suitable for a wide range of dyes.
t A high degree of decolorization can be achieved.
t CWAO processes have proven to be extremely eicient in
TOC removal from wastewaters.
t he use of catalyst not only improves treatment eiciency,
but also reduces the severity of reaction conditions.
3.2.1.4 ElectrochemicalOxidation
Electrochemical oxidation is another method that belongs to the advanced
oxidation methods. The electrochemical oxidation method is considered
an environmentally friendly technology that is able to electrogenerate
in situ hydroxyl radicals [130-132]. One of the main advantages of the
method is that on the surface of electrodes only electrons are produced
and consumed.
Electrochemical methods oxidize and reduce pollutants in wastewa-
ter by means of electrode reactions. The electrodes needed are available
in various shapes (bar, plate, porous and fiber) and are made of vari-
ous materials; processes are influenced significantly by the anode mate-
rial. The requirements for an ideal anode material include acceptable
efficiency, cost-effectiveness and stability in severe conditions [133].