Solar driven advanced oxidation processes for water decontamination and disinfection - Solar Energy Sciences and Engineering Applications - page 400

or Fe 3 + , affecting iron species reactivity and distribution; precipitation reactions lead-
ing to a decrease of the active dissolved Fe 3 + ; or scavenging of hydroxyl radicals and
oxidation reactions involving these inorganic radicals. It has been well documented
that, for example, chloride ions show an inhibitory effect for oxidation reactions of
phenols (Tang and Huang, 1996), dichlorvos (Lu et al., 1997), and atrazine (De Laat
et al., 2004).
13.3.1.2 Dye degradation
Textile wastewater is considered highly polluting because of its high organic loads and
the presence of color. Colored wastewater is not usually considered as toxic, how-
ever it has been well documented that it may cause serious impact once release to
the environment (Orozco et al., 2008). Removal of waste products resulting from the
textile industry, specifically dyes, is probably one of the most successful applications
of solar driven Fenton-like processes. A wide variety of dyes and pigments have been
remediated with good results such as azo-dyes (Chacón et al., 2006; Orozco et al.,
2008) and benzidine-based dyes (Bandala et al., 2008c), as well as dye mixtures in real
textile wastewater (Bandala et al., 2008c). As with pesticide degradation, several vari-
ables affecting dye degradation have being identified related with iron salt counterions,
reaction pH, and reagent concentration, among many others (Orozco et al., 2008).
13.3.1.3 Surfactants degradation
Surfactants (surface active agents) are molecules which include in their chemical struc-
ture a hydrophilic head and a hydrophobic tail. This structure allows surfactants to
increase the aqueous solubility of hydrophobic compounds by solubilization. Surfac-
tants are frequently used in soap and as active ingredients in detergent formulations
like shampoos and dishwashing liquids. They play an important role in the paper,
food, polymers, cosmetics, food, pharmaceuticals, and oil recovery industries (Bandala
et al., 2008a). Besides their environmentally undesirable characteristics, surfactants
produce aesthetic effects after being released into the natural water courses, inhibit
gas transference between the water and the atmosphere, and consume dissolved oxy-
gen. Removal of up to 99% of surfactants from wastewater has been also successfully
carried out using SDPAF and Fenton-like processes in short reaction time (Bandala
et al., 2008b; Lin et al., 1999; Amat et al., 2004). This process has been applied to the
treatment of real wastewater from the surfactant enhanced soil washing (SESW) pro-
cess commonly applied to the restoration of oil polluted sites (Bandala et al., 2008a).
Results obtained in this case were also very interesting since the SDPAF and Fenton-like
processes tested were capable not only to completely remove the surfactant but also
eliminate 69% of the TPHs and other pollutants in the influent, measured as chemical
oxygen demand (COD). The resulting effluent has a high potential to be further treated
with conventional, i.e. biological, wastewater treatments.
13.3.2 Microorganisms inactivation by solar driven
photo-Fenton processes
Despite several different examples of the application of SDPAF for organic pollutant
remediation, relatively little work have been done on its application for inactivation of