Single and Hybrid Applications of Ultrasound for Decolorization and Degradation of Textile Dye Residuals in Water - Green Chemistry for Dyes Removal from Wastewater - page 286

consumed throughout the globe, but exert toxic effects in water via their
low biodegradability and transformation to carcinogenic amines under
anaerobic conditions.
The first part of the chapter has highlighted some fundamental concepts
of sonochemistry that are essential in understanding the mechanism of dye
degradation under ultrasonic irradiation, with sufficient amount of data to
support the viability of sonochemistry as a “green process” for decolorizing
and degrading dyeing process effluents and/or dye residuals. The second
part was devoted to hybrid processes such as US/O 3 , US/UV, US/Fenton,
US/persulfate and US/solids, the latter with nanoparticles such as tita-
nium dioxide, or reactive metals such as zero-valent iron and manganese
dioxide. The efficiency of all hybrid processes for enhancing decolorization
and mineralization of the test dyes was attributed to the synergy arising
from the turbulent flow conditions of ultrasonication that accelerate rates
of mass transfer (of solutes and chemical reagents) and radical formation
reactions while enlarging and cleaning the solid surfaces enriched with
reactive species and active sites, where dye molecules and their reaction
intermediates undergo oxidative and reductive decomposition. Finally, it
was noted that the power of hybrid processes also lied on ultrasonic activa-
tion of the additives or the solid surfaces to generate excess reactive species
such as HO , Fe 2+ /Fe 3+ , SO 4 - , and the sonoluminescence of bubble col-
lapse that provided sufficient energy for the formation and separation of
electron-hole pairs in semiconductors and their composites, respectively.
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