photodegradation. Camera-Roda et al. have also reported a process combining
pervaporation and photocatalysis (Camera-Roda and Santarelli 2005). They reported
that the integration of photocatalysis to the pervaporation process improved its
efficiency. However, in the process presented, the photocatalyst remains in the
treated wastewater. Finally, direct contact membrane distillation coupled with
photocatalysis process was implemented for the removal of dyes (Mozia et al.
2005, 2007a, b, c; Mozia and Morawski 2006, 2009) as well as for other pollutants
(Mozia et al. 2014). In such process, the feed flows through the membrane under gas
phase. In this case, the process is driven by the vapor pressure difference between the
two sides of the membrane. The main advantage of this technology is that membrane
fouling does not occur, even after 180 h of stream and independently of the TiO 2
source (Mozia 2010). Another advantage is that, theoretically, 100% of the nonvolatile compounds such as salts, dyes, or other large organic molecules are separated
(Tomaszewska et al. 1998; Curcio et al. 2010). As a result, permeate was found to be
of high quality. However, such process suffers from several drawbacks among
which high-energy consumption and a low flux as compared to pressure-driven
processes.
Several studies report dye treatment using TiO 2 particles in suspension in the
reaction mixture (Molinari et al. 2002a, b, 2004; Ryu et al. 2005; Cui et al. 2006;
Jiang et al. 2010; Damodar et al. 2010). For example, Molinari et al. reported the
removal of Congo red and patent blue from wastewater through a pressure-driven
membrane process using the reference TiO 2 Degussa P25 catalyst in suspension in
the feed (Molinari et al. 2004). A comparison between suspended and entrapped
TiO 2 as well as the influence of different parameters such as system configuration,
irradiating source and its position, the pressure in the membrane cell and the initial
concentration of the substrates, and the recirculation rate were studied. It was found
that the photodegradation rate of Congo red was 50 times higher with the immersed
UV lamp than that found with the external lamp. Also, as discussed above, the use of
the photocatalyst in suspended form was more efficient than TiO 2 entrapped in a
polymeric membrane. Damodar et al. developed a process coupling a
polytetrafluoroethylene membrane with a TiO 2 /UV slurry reactor that was
implemented for the degradation of reactive black 5 (Damodar et al. 2010). Such a
system was found capable of removing 75–82% TOC, operating efficiently for long
periods with high removal efficiency, as well as efficiently recycling of the catalyst.
Jiang et al. reported the photocatalytic degradation of acid Red B in a slurry
photocatalytic membrane reactor (Jiang et al. 2010). It was observed that the TiO 2
loading and the initial dye concentration strongly influence the reaction rate.
Cui et al. studied the performances of a slurry photocatalytic reactor coupled with
a membrane for the photodegradation of methyl orange (Cui et al. 2006). They found
that the degradation rate is higher as compared to a cylindrical reactor, and the
rejection rate of the TiO 2 photocatalyst particles reaches 99.9%.
Additionally to the dyes, numerous pollutants such as sodium dodecylbenzene
sulfonate (H. Zhang et al. 2006b), trichloroethylene (Choo et al. 2008a, b) biologically treated sewage effluent (Shon et al. 2008), fulvic acids (Fu et al. 2006a, b),
para-chlorobenzoate (Huang et al. 2007), bisphenol A (Chin et al. 2007a, b),
2 Dyes Depollution of Water Using Porous TiO 2 -Based Photocatalysts
71
pervaporation and photocatalysis (Camera-Roda and Santarelli 2005). They reported
that the integration of photocatalysis to the pervaporation process improved its
efficiency. However, in the process presented, the photocatalyst remains in the
treated wastewater. Finally, direct contact membrane distillation coupled with
photocatalysis process was implemented for the removal of dyes (Mozia et al.
2005, 2007a, b, c; Mozia and Morawski 2006, 2009) as well as for other pollutants
(Mozia et al. 2014). In such process, the feed flows through the membrane under gas
phase. In this case, the process is driven by the vapor pressure difference between the
two sides of the membrane. The main advantage of this technology is that membrane
fouling does not occur, even after 180 h of stream and independently of the TiO 2
source (Mozia 2010). Another advantage is that, theoretically, 100% of the nonvolatile compounds such as salts, dyes, or other large organic molecules are separated
(Tomaszewska et al. 1998; Curcio et al. 2010). As a result, permeate was found to be
of high quality. However, such process suffers from several drawbacks among
which high-energy consumption and a low flux as compared to pressure-driven
processes.
Several studies report dye treatment using TiO 2 particles in suspension in the
reaction mixture (Molinari et al. 2002a, b, 2004; Ryu et al. 2005; Cui et al. 2006;
Jiang et al. 2010; Damodar et al. 2010). For example, Molinari et al. reported the
removal of Congo red and patent blue from wastewater through a pressure-driven
membrane process using the reference TiO 2 Degussa P25 catalyst in suspension in
the feed (Molinari et al. 2004). A comparison between suspended and entrapped
TiO 2 as well as the influence of different parameters such as system configuration,
irradiating source and its position, the pressure in the membrane cell and the initial
concentration of the substrates, and the recirculation rate were studied. It was found
that the photodegradation rate of Congo red was 50 times higher with the immersed
UV lamp than that found with the external lamp. Also, as discussed above, the use of
the photocatalyst in suspended form was more efficient than TiO 2 entrapped in a
polymeric membrane. Damodar et al. developed a process coupling a
polytetrafluoroethylene membrane with a TiO 2 /UV slurry reactor that was
implemented for the degradation of reactive black 5 (Damodar et al. 2010). Such a
system was found capable of removing 75–82% TOC, operating efficiently for long
periods with high removal efficiency, as well as efficiently recycling of the catalyst.
Jiang et al. reported the photocatalytic degradation of acid Red B in a slurry
photocatalytic membrane reactor (Jiang et al. 2010). It was observed that the TiO 2
loading and the initial dye concentration strongly influence the reaction rate.
Cui et al. studied the performances of a slurry photocatalytic reactor coupled with
a membrane for the photodegradation of methyl orange (Cui et al. 2006). They found
that the degradation rate is higher as compared to a cylindrical reactor, and the
rejection rate of the TiO 2 photocatalyst particles reaches 99.9%.
Additionally to the dyes, numerous pollutants such as sodium dodecylbenzene
sulfonate (H. Zhang et al. 2006b), trichloroethylene (Choo et al. 2008a, b) biologically treated sewage effluent (Shon et al. 2008), fulvic acids (Fu et al. 2006a, b),
para-chlorobenzoate (Huang et al. 2007), bisphenol A (Chin et al. 2007a, b),
2 Dyes Depollution of Water Using Porous TiO 2 -Based Photocatalysts
71