Nanotechnostructured Catalysts TiO Nanoparticles for Water Purification - Nanotechnologies for Water Environment Applications - page 60

treatment steps, usually sedimentation and filtration are necessary to remove the fine
particles from the suspension, which can be inconvenient, time-consuming and
expensive. A further challenge is the fouling of the surface of the light fixture due to
adsorption and decomposition of TiO 2 particles. Hence, large-scale applications of the
slurry photocatalytic reactor is quite problematic at the present time (Hoffmann et al.,
1995; Gogate and Pandit, 2004; Kwon et al., 2008).
Figure 3.8 Schematic representation of batch slurry photocatalytic reactors. (Redrawn
from Lizama et al., 2002).
3.4.1.2 Compound Parabolic Concentrator (CPC) System
To overcome the limitations of the slurry phase reactor, many other reactor
configurations have been developed over the last decade. Among them, CPC reactors
seem to be promising with huge commercial potential (Blanco et al., 1999; Krutzler et
al., 1999; Malato et al., 2002a; Parra et al., 2002; Robert and Malato 2002; Rodriguez et
al., 2005; Gernjak et al., 2006; Rincon and Pulgarin 2007). A typical CPC system is
illustrated in Figure 3.9 (Blanco et al., 1999). In a CPC system, the water flows through
a series of tubular reactors then is being collected at a sedimentation tank, which can
reclaim 99% of TiO 2 from the slurry (Blanco et al., 1999; Kositzi et al., 2004). A curved
reflective surface allows the capture of diffuse UV sunlight without solar tracking,
which, in turn, produce a 360 o illumination over the tubular reactor. Al reflective
surface with TiO 2 -SiO 2 multi-layer coating can achieve up to 95% usage efficiency of
UV range of the solar spectrum.