Page 151 - Industrial Wastewater Treatment, Recycling and Reuse

Advanced Physico-chemical Methods of Treatment for Industrial Wastewaters 125

acoustic cavitation using our experimental investigations is shown in
Figures 2.16–2.18 (Hiremath et al., 2012). The performance of the process
was evaluated using the results on the extent of reduction in the chemical
oxygen demand and in color. Three different dyes, i.e., methyl red, congo
red, and reactive red were used to see if the nature of the dye has any effect.
It is evident that, in all the cases, hydrodynamic cavitation using the vor-
tex diode performs far better compared to acoustic cavitation, both in terms
of COD removal and color removal. In the case of methyl red dye (initial
COD of 100 mg/L), the COD removal is above 61% as against 19% with
acoustic, and color removal is close to 40% as against 16%, more than double.
Similarly, for congo red dye (initial COD of 286 mg/L), these figures are
62% and 52% for COD and color using hydrodynamic cavitation, again
more than double that observed with acoustic cavitation. Reactive dyes
are considered to be refractory pollutants that are difficult to treat, and here,
too, the results with hydrodynamic cavitation are far superior with more
than 70% reduction in the COD of the wastewaters (initial COD of
456 mg/L). The consistency in obtaining better results using hydrodynamic
cavitation with the vortex diode clearly highlights the utility of such new
devices in treating industrial wastewater.

Figure 2.16 Comparison of hydrodynamic and acoustic cavitation: Methyl red dye.