Page 168 - Industrial Wastewater Treatment, Recycling and Reuse

142 Industrial Wastewater Treatment, Recycling, and Reuse

In the last two decades a lot of research work has been carried out for the
development of new technologies, especially in the area of advanced oxida-
tion processes (AOPs) for the degradation of complex biorefractory pollut-
ants for complete mineralization or as a pretreatment (Babuponnusami and
Muthukumar, 2012; Gogate and Pandit, 2004a,b; Kusvuran and Erbatur,
2004; Pang et al., 2011; Thiruvenkatachari et al., 2007). AOPs are defined
as processes that involve the generation and use of the hydroxyl radical
•
( OH) as a strong oxidant to destroy (oxidize) compounds that cannot be
oxidized by conventional oxidants such as gaseous oxygen, ozone, and chlo-
rine. The hydroxyl radical reacts with the dissolved constituents, initiating a
series of oxidation reactions until the constituents are completely mineral-
ized to CO 2 and H 2 O.
Different AOPs have been developed and tested for the degradation
of different pollutants (inorganic and organic compounds) present in the
wastewater. These processes include cavitation (generated either by means
ofultrasonicirradiationorusingconstrictionssuchasvalves,orifices,andven-
turi in hydraulic devices) (Adewuyi, 2001; Hua and Hoffmann, 1997; Joshi
and Gogate, 2012; Saharan et al., 2011; Sivakumar and Pandit, 2002; Wang
et al., 2008; Weavers et al., 1998), photocatalytic oxidation (using ultraviolet
radiation/near UV light/sunlight in the presence of a semiconductor catalyst)
(Adewuyi, 2005; Cao et al., 2006; Konstantinou and Albanis, 2004; Lin et al.,
2012), and Fenton chemistry (using the reaction between Ferrous sulphate
and hydrogen peroxide (H 2 O 2 ), i.e., Fenton’s reagent) (Karci et al., 2012;
Kusic et al., 2006; Xue et al., 2009). These AOPs can also be used in com-
binations termed as hybrid methods such as Ultrasound assisted Fenton, sono-
photocatalytic, Photo-Fenton, and ozone/hydrogen peroxide to get the
enhanced oxidation efficiency and overcome the limitations and difficulties
of individual AOPs toward some specific pollutants (Adewuyi, 2005; Gogate
and Pandit, 2004b; Pang et al., 2011). In this chapter, we review these AOPs
and their combinations. The total or partial success of these AOPs in relation
to some specific biorefractory pollutants is discussed and recommendations
are made to arrive at an optimized treatment methodology/flow sheet.

3.2 CAVITATION

Cavitation is defined as the phenomenon of the formation, growth, and sub-
sequent collapse of microbubbles or cavities occurring in an extremely small
interval of time (microseconds) and at multiple locations in the reactor,
releasing large magnitudes of energy. As a result of cavity collapse, hot spots