**2.4.2 Thin film fixed bed reactor (TFFBR)**

Thin film fixed bed reactor (TFFBR) is one of the very first solar reactor which does not utilize a solar concentrating system. It implies that the TFFBR can utilize the diffuse as well as the direct portion of the solar UV-A illumination for the photocatalytic process. A TFFBR installed at PSA is depicted in Fig. 2 (Bockelmann et al., 1995; Goslich et al., 1997; Hilgendorff et al., 1993). The most important aspect in the TFFBR is the slopping plate coated with photocatalyst like Degussa P25 (Bockelmann, 1993) and rinsed with contaminated water in a very thin film (~100µm). The flowrate was controlled by a cassette peristaltic pump and ranges from 1–6.5Lh-1 (Bockelmann et al., 1995).

Heterogeneous Photocatalytic Oxidation an Effective Tool for Wastewater Treatment – A Review 227

positioned along the focal line. Subsequently only parallel light which enters the parabolic through can be concentrated on the pipe. The reflector of a CPCR generally made up of two half circle profiles side by side. The focal line is situated just above the connections of the two circles. Thus light entering from almost any angle can be reflected to the focal line of the

The double skin sheet reactor is a new kind of reactor which does not have a light concentrating properties. It is a flat and transparent structured box made of PLEXIGLAS® (Van Well et al., 1997). PLEXIGLAS® is a trademark of a commercialized Poly(methyl methacrylate) (PMMA) which is a transparent thermoplastic. The inner structure of the DSSR is depicted in Fig. 4. The suspension of the model pollutant and the photocatalyst is allowed to flow through these channels. The DSSR can use both the diffuse and direct

Many studies had been carried out to alter the characteristics of the titanium dioxide (TiO2) in order to improve the practical and commercial values of titanium dioxide (TiO2) as a photocatalyst. For most of the cases, doping was carried out to improve the photocatalytic activity, the absorption of visible region of the solar spectrum, and to impart separable

Ao et al. (2009) reported the degradation of a dye (Red X-3B) under sunlight using N-doped titania-coated g-Fe2O3 magnetic activated carbon (NT-MAC). The titanium dioxide (TiO2) was doped with nitrogen to improve the visible light absorption while the g-Fe2O3 magnetic activated carbon was coated to impart the magnetic properties. The preparations were carried out under low temperature and ambient pressure. It is reported that the photocatalytic of the NT-MAC was approximately three times than that of Degussa P25. The separation can be done easily using an external magnetic field. Furthermore, the prepared NT-MAC can be recycled and reused without any mass losing and the degradation of the X-

CPCR. Fig. 3 shows the schematic view of the reflector of a CPCR.

Fig. 4. A schematic view of the inner structure of a DSSR

3B remains higher than 85% after six cycles (Ao et al., 2009).

**2.5 Synthesis and doping method** 

property.

**2.4.4 Double skin sheet reactor (DSSR)** 

portion of the sunlight.

Fig. 2. A TFFBR installed at the PSA in Spain (Bockelmann et al., 1995)

The TFFBR was tested during its operation at the PSA. The efficiency of the performance of the TFFBR was found to be higher than that of the PTR during several test campaigns utilizing both model pollutants dissolved in pure water and real wastewater samples collected from a variety of industrial companies (Bahnemann, 2004).
