Page 150 - Industrial Wastewater Treatment, Recycling and Reuse

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device such as orifice type, venturi type, or vortex diode. Further, they can
be used in isolation, in sequence, or in parallel. The process parameters that
need to be optimized include flow and pressure drop apart from the number
of passes that are required for effecting the desired reduction in the effluent
COD. Some other process parameters such as addition of an oxidizing agent,
a coagulant, in situ, or the form of a combination of processes can also be
evaluated. For practical applications, the cost of the technology is dictated
by the pressure drop across the device and the number of passes.
The working of the vortex diode in cavitation is significantly different
and is expected to yield cavities that are different from the other devices,
both in quality and quantity. This would be reflected in the extent and
nature of degradation of pollutants, not just for types of cavitation such as
acoustic and hydrodynamic but also among different cavitating devices.

2.5.2 Application of Cavitation in Dye Wastewater Treatment
Therearecertainorganicpollutants,especiallyindye/pigment/textilewaste-
waters, that are considered refractory compounds—difficult to remove/
degrade by using conventional methods of chemical/biological treatment.
For such pollutants, newer techniques have to be explored such as cavitation,
where extreme conditions of cavitation can break down pollutants and
organic molecules. Typically, hydrodynamic and sonochemical or acoustic
cavitationarefoundusefulinthedestructionoforganics.Cavitationgenerates
strong oxidizing conditions due to the production of hydroxyl radicals and
also hydrogen peroxide. Although significant work has been reported in
the area of sonochemical reactors and their application in wastewater treat-
ment, the implementation for actual industrial practice is still negligible
because of the high cost of treatment and operational difficulties, especially
in power dissipation. The impact of cavitation processes can be dramatically
increased by combining them with other oxidation processes employing cat-
alysts or additives. It has been reported that cavitation coupled with coagula-
tion, called cavigulation, can be effective in water treatment and pollutant
removal (http://bestotc.com/493/uncategorized/cavigulation-cavitation-
technologies-solution-to-the-water-crisis-refining-the-desalination-process;
Chakinala et al., 2009; Mishra and Gogate, 2010; Ranade et al., 2013; Saharan
etal.,2011,2013;Sawantetal.,2008;Wangetal.,2011;Xuetal.,2010).Thus,
process intensification can work wonders if cavitation and other suitable
methods are integrated, especially in treating wastewaters containing refrac-
tory pollutants and/or having unusually high COD.
A comparison of synthetic dye wastewater treatment for different types
of dyes with hydrodynamic cavitation (vortex diode as cavitating device) and