7.6.2 Direct Oxidation
Direct oxidation is aprocess in which the organic pollutants can be removed when it
reaches the electrode surface and then the oxidation will take place on the surface
and finally return to the bulk of the solution (Barrera-díazn et al. 2014). Moreover,
they added that the movement of the pollutant to the electrode surface depends upon
the mass transfer activity such as migration, convection, and diffusion.
In this process, the degradation of the pollutant and the disinfection of the
microorganism depend upon the production of hydrogen and hydrogen peroxide
bubbles in the cathode and the intensity of the current applied, that is, if the
concentration of the bubbles is low, it enhanced the formation of hydrogen peroxide,
and this leads to the electro-disinfection of the wastewater. Furthermore, this hydrogen peroxide can react with the organic pollutants in the wastewater in the cathode to
form hydroxyl radicals (Lakshmi and Vasudevan 2013). However, their efficency to
degrade phenol in the electron–Fenton process shows the generation of hydrogen
peroxide in the cathode is indirect electro-oxidation because they are generated by
the reduction dissolved oxygen in the solution and it will depend upon the nature of
the electrode such as polyacrylonitrile-based carbon fiber brush (Xia et al. 2015).
Llanos et al. (2014) reported that their research treating urban wastewater using
electro-disinfection combined with the electro-coagulation process in which borondoped diamond is used as anode and stainless steel as the cathode and having
perforated iron plate as a bipolar electrode shows that they have the efficiency to
remove bacteria to about 99% from the solution. Recent study by Ghasemian et al.
(2017) to disinfect wastewater whiach has bacteria-laden water using electrodes of
antimony-doped tin–tungsten oxide shows that they disinfect the E.coli bacteria
entirely because of the electrodes containing high oxygen potential. This leads to
the production of hydroxyl radicals and oxidation of the pollutants present in the
wastewater. In general, using boron-doped diamond as an electrode to generate
oxygen potential in the disinfection of bacteria as well as complete mineralization
of organic pollutants when compared with other electrodes such as SnO 2 and PbO 2
because it has high oxygen evolution potential (Panizza and Cerisola 2009).
7.6.3 Indirect Electro-oxidation
This is another method of electro-oxidation in which it can disinfect or degrade the
wastewater using strong oxidants of disinfection agents such as carbonates, sulfates,
and chlorides which lead to the generation of free chlorine on the surface of the
electrode of anode; however, the generation of the free chlorine will depend upon the
applied current, duration of time, and pH of the solution. Moreover, it can also
degrade and disinfect the wastewater using oxidants such as ozone, peroxides, and
hydroxyl radicals that can be directly generated from the wastewater (Polcaro et al.
2007).
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T. G. Ambaye et al.
Direct oxidation is aprocess in which the organic pollutants can be removed when it
reaches the electrode surface and then the oxidation will take place on the surface
and finally return to the bulk of the solution (Barrera-díazn et al. 2014). Moreover,
they added that the movement of the pollutant to the electrode surface depends upon
the mass transfer activity such as migration, convection, and diffusion.
In this process, the degradation of the pollutant and the disinfection of the
microorganism depend upon the production of hydrogen and hydrogen peroxide
bubbles in the cathode and the intensity of the current applied, that is, if the
concentration of the bubbles is low, it enhanced the formation of hydrogen peroxide,
and this leads to the electro-disinfection of the wastewater. Furthermore, this hydrogen peroxide can react with the organic pollutants in the wastewater in the cathode to
form hydroxyl radicals (Lakshmi and Vasudevan 2013). However, their efficency to
degrade phenol in the electron–Fenton process shows the generation of hydrogen
peroxide in the cathode is indirect electro-oxidation because they are generated by
the reduction dissolved oxygen in the solution and it will depend upon the nature of
the electrode such as polyacrylonitrile-based carbon fiber brush (Xia et al. 2015).
Llanos et al. (2014) reported that their research treating urban wastewater using
electro-disinfection combined with the electro-coagulation process in which borondoped diamond is used as anode and stainless steel as the cathode and having
perforated iron plate as a bipolar electrode shows that they have the efficiency to
remove bacteria to about 99% from the solution. Recent study by Ghasemian et al.
(2017) to disinfect wastewater whiach has bacteria-laden water using electrodes of
antimony-doped tin–tungsten oxide shows that they disinfect the E.coli bacteria
entirely because of the electrodes containing high oxygen potential. This leads to
the production of hydroxyl radicals and oxidation of the pollutants present in the
wastewater. In general, using boron-doped diamond as an electrode to generate
oxygen potential in the disinfection of bacteria as well as complete mineralization
of organic pollutants when compared with other electrodes such as SnO 2 and PbO 2
because it has high oxygen evolution potential (Panizza and Cerisola 2009).
7.6.3 Indirect Electro-oxidation
This is another method of electro-oxidation in which it can disinfect or degrade the
wastewater using strong oxidants of disinfection agents such as carbonates, sulfates,
and chlorides which lead to the generation of free chlorine on the surface of the
electrode of anode; however, the generation of the free chlorine will depend upon the
applied current, duration of time, and pH of the solution. Moreover, it can also
degrade and disinfect the wastewater using oxidants such as ozone, peroxides, and
hydroxyl radicals that can be directly generated from the wastewater (Polcaro et al.
2007).
232
T. G. Ambaye et al.