Photocatalytic Processes for the Removal of Dye - Green Chemistry for Dyes Removal from Wastewater - page 128

In solar photoreactors, solar radiation is collected and distributed
inside the photoreactor in such a way that maximizes photocatalytic effi-
ciency. The collectors are of two types: i) non-concentrating collectors, and
ii) concentrating collectors. Non-concentrating collectors are capable of
using both direct and diffuse radiation and provide high optical and quan-
tum efficiency. However, their limitations are low mass transfer, reactant
contamination, reactant vaporization, etc. On the contrary, concentrating
collectors have certain advantages such as providing excellent mass trans-
fer, zero vaporization of the reactant, and small reactor tube area. But they
experience difficulties in using diffuse solar radiation and thus have low
quantum and optical efficiencies [21].

4.5 Solar Photoreactor for Degradation of

Different Dyes

This section discusses three different types of solar photoreactors which
have been utilized for photodegradation of several dyes. Compound
parabolic collector (CPC) allows both direct and diffuse sun light for
reflection onto the absorber surface, increasing the number of photons
available and making the setup active on an overcast day in the absence
of direct sunlight [22].
Augugliaro et al. [23] have installed CPCs at Plataforma Solar de Almeria
(PSA, Spain) for the photodegradation of two azo-dyes (methyl-orange
and orange II) with aqueous suspension of polycrystalline TiO 2 . Two pho-
toreactors with three CPC modules were used in series which provided
3.08 m 2 of irradiation surface. Solar radiation was useful in degrading both
dyes, although the mineralization process was slow with the formation of
NO 3 - , SO 4 2- and carbon dioxide. In another study, Augugliaro et al. [24]
applied solar photo-oxidation reaction in combination with membrane
technology for the degradation of lincomycin and separation of photocata-
lyst particles. Montano et al. [25] used photo-Fenton oxidation with a CPC
solar photoreactor for the degradation of two reactive dyes (Procion Red
H-E7B and Cibacron Red FN-R) in both bench scale and pilot scale. Here,
the photo-oxidation method was also used as a pretreatment method along
with an anaerobic biological treatment in an immobilized biomass reac-
tor. The combination of photo-oxidation and biological processes worked
more efficiently than individual processes in bench scale.
The CPC photoreactor follows a similar principle as that of the solar
thermal process, which is deficient in a few areas such as photocatalyst
handling, effective photocatalyst illumination, and mass transfer between