Page 212 - Industrial Wastewater Treatment, Recycling and Reuse

186 Industrial Wastewater Treatment, Recycling, and Reuse

leads to an enhanced generation of the hydroxyl radicals, which eventually
results in higher oxidation rates. The efficacy of the process and the extent
of synergism depend not only on the enhancement in the number of free rad-
icals but also on the alteration of reactor conditions, leading to a better contact
of the generated free radicals with the pollutant molecules and also better uti-
lization of the oxidants and catalytic activity.
The depiction of case study related to the degradation of imidacloprid
using the hybrid methods based on HC proves that the combination of
different AOPs gives higher extents of degradation per unit supplied
energy as compared to individual methods. Combining H 2 O 2 with
HC leads to better utilization of the oxidant and hence higher degrada-
tion rates due to the dissociation of H 2 O 2 under the action of cavitation.
The mass transfer resistance, which is a major limiting factor for the appli-
cation of ozone or H 2 O 2 alone, is also eliminated due to the enhanced
turbulence generated by cavitation. Further, the inclusion of ferrous ions
and UV light improves process efficiency. In the combined process of HC
and photocatalysis, it is important to run the processes of HC and UV
light simultaneously rather than sequentially. The major factor control-
ling the overall efficiency of destruction is, however, the stability of
the photocatalyst under the effect of cavitation. Efforts are required in
terms of new designs that will protect the catalyst but at the same time
yieldenhancedeffects.
Overall, it can be said that AOPs are an effective method for degrading
complex biorefractory pollutants. However, further research work needs to
be done in the direction of developing AOPs for the treatment of real indus-
trial effluents, and focus should be in the direction of solving scale-up prob-
lems such as challenges in the design and obtaining higher degradation
possibly at lower levels of energy requirements.

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