Page 211 - Industrial Wastewater Treatment, Recycling and Reuse

Advanced Oxidation Technologies for Wastewater Treatment: An Overview 185

there are many issues that need to be addressed for the successful implemen-
tation of these AOPs on an industrial scale. Economic considerations and
effectiveness of these processes in treating a real industrial complex effluent
on a larger scale are the major challenges to be overcome for the successful
implementation of these technologies. As in the case of acoustic cavitation,
the material and fabrication costs for the transducers are very high, making it
an uneconomical operation to be tried on industrial scale. In the case of
photocatalytic processes the engineering design and fabrication consider-
ations for providing uniform distribution of UV radiation throughout the
reactor adds to the total costs. In addition, the maintenance cost for catalyst
regeneration and UV lamp life makes this process even more expensive.
Similarly, for the Fenton process, the cost of chemical reagent (ferrous sul-
phate and H 2 O 2 ) is very high. Further, the separation of sludge formed dur-
ing the Fenton treatment also adds significant cost including that required for
effective disposal of sludge after separation. These problems associated with
Fenton process makes it an uneconomical process for large-scale operation.
Among all the AOPs studied, HC has the potential for application on a larger
scale because of its capability for generating hydroxyl radicals under ambient
conditions, its ease of scale-up, and its lower material costs, making it more
economically feasible. The biodegradability enhancement of distillery
wastewater using HC as reported in the case study proves that this method
can be used effectively as a pretreatment method in relation to existing
biological treatment such that the efficiency of a conventional process can
be improved many fold. Further efforts are required on the experimental
front as well as in terms of kinetic modeling to establish this method as an
effective pretreatment method for different industrial effluents with a high
degree of efficiency and lower treatment costs.
On the other hand, hybrid methods offer higher efficiency over individ-
ual AOPs. The similarity between the mechanism of destruction and
optimum operating conditions also points toward the synergism between
these methods. Indeed, combinations of these AOPs should give better results
when compared to individual techniques. Moreover, some of the drawbacks
of the individual techniques can be eliminated by the characteristics of other
techniques (e.g., mass transfer limitations and fouling of the catalyst in the case
of photocatalytic oxidation will be eliminated by the turbulence created by
cavitation). The expected synergism between different hybrid methods is
mainly due to an identical controlling reaction mechanism, i.e., the free radical
attack. Generally, the combination of two or more AOPs, such as cavitation/
ozone, cavitation/H 2 O 2 , cavitation/photocatalysis, and cavitation/Fenton,