oxygen demand removal in ozonation, O 3 /H 2 O 2 , and O 3 /activated carbon processes
were 30, 80, and 100%, respectively (Parsa and Negahdar 2012).
Catalytic Ozonation
Several reports have suggested the use of catalyzed ozonation of dye for the
decolorization and chemical oxygen demand removal from industrial wastewater.
Catalyzed ozonation of Procion Red MX-5B was carried out at an ozone dose of
260 mg h
À1 and pH 11.0. The results revealed the successful removal of color,
chemical oxygen demand, and total organic carbon with maximum values in the
range of 75–97%. The presence of ionic and acidic species in the solution indicated
the mineralization caused by ozonation. Mn
2+ was considered to the best metal ion
for decolorization and chemical oxygen demand removal compared to the rest
(Pachhade et al. 2009).
The solution of an azo dye 23 was subjected to MgO nanocrystal-catalyzed
ozonation using a lab-scale batch reactor. At optimized pH of 8 and catalyst dosage
of 5 g/L, clear improvements in both reaction time and decolorization efficiency
were noticed. Complete decolorization of 200 mg/L dye solution was achieved in
9 min only, which may take up to half an hour without the addition of catalyst
(Moussavi and Mahmoudi 2009). Overall, catalytic ozonation was regarded as a
reasonable process for treating dye wastewater prior and later to the discharge.
17.3.2 Photocatalytic Treatment
A photocatalyst absorbs energy from light to produce electron-hole pairs which is
used to impart chemical transformations in the reaction participants (Natarajan et al.
2018; Davis et al. 1994). Ammonium oxalate fiber surface was modified with silver
nanoparticles of different sizes and shapes and tested for photodegradation of 8 in
aqueous solution. The study revealed successful degradation of 8, particularly under
sunlight, a capability that can be extended to dye removal from wastewater streams
under the normal sunlight conditions (Wu et al. 2010). A mesoporous-assembled
TiO 2 nanocrystal photocatalyst was used to remove acid yellow and acid black dyes
with mono and diazo groups. At photocatalyst dose of 10/L, initial pH of 4.5, and
acid yellow and acid black concentrations of 2.5 and 5 mg L
À1 , highest degradation
efficiency was achieved. Although water hardness hampered the degradation, pH
optimization can resolve the issue to resist a decrease in efficiency (Wongkalasin
et al. 2011).
3, 8, and methyl yellow were degraded to demonstrate the catalytic and magnetic
activity of palladium/hydroxyapatite/Fe 3 O 4 nanocatalyst. The effective degradation
of dyes by the novel catalyst was attributed to the formation of Pd hydroperoxide as a
result of a reaction between catalyst and dissolved oxygen under acidic condition
followed by oxidation of azo dyes under hydroxyapatite catalysis (Safavi and
17 Methods for the Treatment of Wastewaters Containing Dyes and Pigments
633
were 30, 80, and 100%, respectively (Parsa and Negahdar 2012).
Catalytic Ozonation
Several reports have suggested the use of catalyzed ozonation of dye for the
decolorization and chemical oxygen demand removal from industrial wastewater.
Catalyzed ozonation of Procion Red MX-5B was carried out at an ozone dose of
260 mg h
À1 and pH 11.0. The results revealed the successful removal of color,
chemical oxygen demand, and total organic carbon with maximum values in the
range of 75–97%. The presence of ionic and acidic species in the solution indicated
the mineralization caused by ozonation. Mn
2+ was considered to the best metal ion
for decolorization and chemical oxygen demand removal compared to the rest
(Pachhade et al. 2009).
The solution of an azo dye 23 was subjected to MgO nanocrystal-catalyzed
ozonation using a lab-scale batch reactor. At optimized pH of 8 and catalyst dosage
of 5 g/L, clear improvements in both reaction time and decolorization efficiency
were noticed. Complete decolorization of 200 mg/L dye solution was achieved in
9 min only, which may take up to half an hour without the addition of catalyst
(Moussavi and Mahmoudi 2009). Overall, catalytic ozonation was regarded as a
reasonable process for treating dye wastewater prior and later to the discharge.
17.3.2 Photocatalytic Treatment
A photocatalyst absorbs energy from light to produce electron-hole pairs which is
used to impart chemical transformations in the reaction participants (Natarajan et al.
2018; Davis et al. 1994). Ammonium oxalate fiber surface was modified with silver
nanoparticles of different sizes and shapes and tested for photodegradation of 8 in
aqueous solution. The study revealed successful degradation of 8, particularly under
sunlight, a capability that can be extended to dye removal from wastewater streams
under the normal sunlight conditions (Wu et al. 2010). A mesoporous-assembled
TiO 2 nanocrystal photocatalyst was used to remove acid yellow and acid black dyes
with mono and diazo groups. At photocatalyst dose of 10/L, initial pH of 4.5, and
acid yellow and acid black concentrations of 2.5 and 5 mg L
À1 , highest degradation
efficiency was achieved. Although water hardness hampered the degradation, pH
optimization can resolve the issue to resist a decrease in efficiency (Wongkalasin
et al. 2011).
3, 8, and methyl yellow were degraded to demonstrate the catalytic and magnetic
activity of palladium/hydroxyapatite/Fe 3 O 4 nanocatalyst. The effective degradation
of dyes by the novel catalyst was attributed to the formation of Pd hydroperoxide as a
result of a reaction between catalyst and dissolved oxygen under acidic condition
followed by oxidation of azo dyes under hydroxyapatite catalysis (Safavi and
17 Methods for the Treatment of Wastewaters Containing Dyes and Pigments
633