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Advanced Physico-chemical Methods of Treatment for Industrial Wastewaters 93

the aluminum or iron anode in the electrochemical reactor releases requisite
3+ 2+
Al or Fe cations in the solution upon application of an electric field. At
the cathode, water cleavage takes place, generating hydroxyl ions that help
in precipitation through formation of hydroxides in solution. The process is
more complex when compared to conventional chemical process and is still
not widely accepted commercially. Newer developments in this area include
better electrodes, which dictate the coagulation process; improvements in
the kinetics; and newer electrochemical reactor configurations. There have
been some studies proving the efficiency of electro-coagulation for heavy
metal removal from wastewater and process integration using adsorption
and electro-coagulation for the removal of Cr(VI) of the order of 97% in
the pH range of 3–6 (Ait Ouaissa et al., 2013).
Cavigulation is a process that combines two physico-chemical opera-
tions, namely coagulation and cavitation. The first principles of cavigulation
are still not clearly understood. At present, the approach to cavigulation
appears to be rather empirical, where coagulation and cavitation in combi-
nation are believed to offer better conditions for degradation of pollutant
species through physical and chemical destruction.

2.2.4 Case Study: Dye Wastewater Treatment
The use of coagulants in dye wastewater treatment is a complex problem,
and no general solutions are yet available. Textile and dyeing industries
use many kinds of dyes, both reactive and non-reactive, and discharge large
amounts of highly colored wastewater. Such effluent must be treated prior to
discharge in order to comply with the environmental protection laws for the
receiving waters. The biological treatment processes that are frequently used
to treat textile effluents are generally efficient for meeting limits of BOD and
suspended solids removal. However, these methods are largely ineffective
for removing color from the wastewaters. Process design aspects of dye
wastewater treatment involving various physico-chemical methods have
been discussed in recent literature (Joo et al., 2007; Fung et al., 2012).
Application of the coagulation process can be accomplished in such cases
through the use of coagulant formulations that yield superior performance.
Coagulation has been effective in removing color especially from wastewa-
ters containing dissolved solids and charged matters. However, high chem-
ical dosages are usually required, and large volumes of sludge must be
disposed of, in general, for inorganic coagulants, resulting in a high cost
for sludge disposal. A near-zero production of sludge in the case of organic