Single and Hybrid Applications of Ultrasound for Decolorization and Degradation of Textile Dye Residuals in Water - Green Chemistry for Dyes Removal from Wastewater - page 274

7.2.4 Reactors

There are two essential components in sonochemistry: the liquid and a source
of high-energy vibrations [66]. The former is necessary, because it is the only
medium for the formation of acoustic cavity bubbles; while the latter is the
transducer, which is a device capable of converting electrical to sound energy
[67]. The most common equipment for generating acoustic cavitation in the
laboratory are the bath, the probe and the plate-type reactors; but the for-
mation and ejection of radicals to the bulk solution are 20-25-fold higher
in plate-type reactors than in probe or bath systems at equivalent acoustic
powers [37]. Although in general all lab-scale systems are operated on con-
tinuous mode, pulse mode of irradiation is also common with the advantage
of more effective utilization of hydroxyl radicals via temperature control, i.e.,
the availability of a longer time for heat dissipation [50,68].
A selection of most commonly used lab-scale reactors for sonochemical
decolorization and mineralization of textile dyes is presented in Figure 7.4.
Note that the common feature of all reactors is that they are cooled by circu-
lating water to prevent excessive heating. The “horn” and “bath” are associ-
ated with low frequency emission and thus mechanical effects (e.g., cleaning,
dispersing) and thermal decomposition of volatile solutes, while the “plate”
is recognized as a source of high-frequency irradiation and thus aqueous-
phase sonochemistry. However, there is plenty of literature on the use of
short-frequency or “power” ultrasound with very effective decolorization.

7.3 Hybrid Processes with Ultrasound:

A Synergy of Combinations

In the previous sections, we have tried to demonstrate the power of ultra-
sound for decolorizing and decomposing a wide range of synthetic dyes,
pointing out, however, that ultrasound alone is ineffective for sufficient
mineralization of these compounds. The rest of this chapter, therefore, is
devoted to the description of the most commonly used hybrid processes
that employ combined application of ultrasound with an AOP or hetero-
geneous catalysis. A list of hybrid processes used in decolorization and
mineralization of dyestuff and dying effluents and their selected operation
parameters is presented in Table 7.5.

7.3.1 Sono-Ozonolysis (US/O 3 )
Decolorization/mineralization of synthetic dye solutions and simulated
dyebaths by US/O 3 process has been found considerably more effective