reactions and the important factors influencing the efficiency of these processes in
applications to wastewater treatment. An effort is made here to inform the reader on
the current state of the art, the remaining challenges for the development of these
processes.
11.1 Homogeneous Photo-Fenton Reaction
Polychromic UV light was first utilized to assist Fenton process (FeCl 2 /H 2 O 2 ),
where the photolysis of H 2 O 2 in the absence of Fe 2 Cl was used as a control
[3]. Decomposition of 4-nitrophenol was observed in both cases, and the better
result was obtained from UV light-assisted Fenton system, which was ascribed to the
photo-triggered reduction of Fe
3+ to Fe
2+ . The concept of “photo-Fenton reactions”
was formally proposed in 1992 [4], where the yield of HO
• formed per Fe
2+ oxidized
by H 2 O 2 was determined as a function of pH. In this case, Fe
2+ was produced from
the photoreduction of Fe
3+ (λ ¼ 436 nm) in order to avoid artifacts that can result
from locally high concentrations of the reagents that are inherent in the initial stages
of the mixing process. The photo-generated Fe
2+ and its oxalate, citrate, and
phosphate complexes react with H 2 O 2 efficiently, producing HO
• in aqueous solutions with pH ranging from 3 to 8.
The study on the oxidation of reactive black 5 (RB5) in aqueous solution
demonstrated that both Fenton (H 2 O 2 /Fe
2+ ) and photo-Fenton (H 2 O 2 /Fe
2+ /UV)
processes can effectively decolorize RB5 with a little difference between them
[5]. In contrast, there is a significant increment for TOC removal through photoFenton process (46.4%) compared to Fenton process (21.6%). This fact indicates
that although UV low-pressure mercury lamp has little effect on dye decolorization,
it is particularly important in dye mineralization.
The cost associated with the use of artificial irradiation sources has hindered the
industrial application of the photo-Fenton process using Fe
2+ , H 2 O 2 , and UV
irradiation as a source of HO
• for the oxidation of organics. Solar radiation for the
photodegradation of raw gasoline in water has been studied to reduce the cost. The
photo-Fenton process was also applied to a real effluent, i.e., oil field-produced
water, and the experimental results demonstrate the feasibility of employing solar
irradiation to degrade this complex saturated-hydrocarbon-containing system [6].
Besides organics, the inactivation of the coliphage MS2 (a human virus indicator)
by solar photo-Fenton was evaluated at near-neutral pH in carbonate buffer solution
matrix. The effects of reactant concentration (H 2 O 2 , Fe
2+ , Fe
3+ ) and solar irradiance
on the photo-Fenton process were studied. Specifically, the solar exposure/Fe
3+
treatment showed a strong dependence on the iron concentration and solar irradiance
intensity. The MS2 inactivation observed with the photo-Fenton process (solar
exposure/H 2 O 2 /Fe
2+ /
3+ ) carried out with Fe
3+ was faster than with Fe
2+ (detection
limit achieved at 20 min and 50 min, respectively). Moreover, virus inactivation by
photo-Fenton under different solar irradiance values (15, 30, and 45 W m
À2 ), H 2 O 2
and Fe
3+ concentrations (0.1, 0.5, and 1 mg L
À1 ), and different pH values (6, 7, and 8)
260
11 Photo-Fenton Reaction
applications to wastewater treatment. An effort is made here to inform the reader on
the current state of the art, the remaining challenges for the development of these
processes.
11.1 Homogeneous Photo-Fenton Reaction
Polychromic UV light was first utilized to assist Fenton process (FeCl 2 /H 2 O 2 ),
where the photolysis of H 2 O 2 in the absence of Fe 2 Cl was used as a control
[3]. Decomposition of 4-nitrophenol was observed in both cases, and the better
result was obtained from UV light-assisted Fenton system, which was ascribed to the
photo-triggered reduction of Fe
3+ to Fe
2+ . The concept of “photo-Fenton reactions”
was formally proposed in 1992 [4], where the yield of HO
• formed per Fe
2+ oxidized
by H 2 O 2 was determined as a function of pH. In this case, Fe
2+ was produced from
the photoreduction of Fe
3+ (λ ¼ 436 nm) in order to avoid artifacts that can result
from locally high concentrations of the reagents that are inherent in the initial stages
of the mixing process. The photo-generated Fe
2+ and its oxalate, citrate, and
phosphate complexes react with H 2 O 2 efficiently, producing HO
• in aqueous solutions with pH ranging from 3 to 8.
The study on the oxidation of reactive black 5 (RB5) in aqueous solution
demonstrated that both Fenton (H 2 O 2 /Fe
2+ ) and photo-Fenton (H 2 O 2 /Fe
2+ /UV)
processes can effectively decolorize RB5 with a little difference between them
[5]. In contrast, there is a significant increment for TOC removal through photoFenton process (46.4%) compared to Fenton process (21.6%). This fact indicates
that although UV low-pressure mercury lamp has little effect on dye decolorization,
it is particularly important in dye mineralization.
The cost associated with the use of artificial irradiation sources has hindered the
industrial application of the photo-Fenton process using Fe
2+ , H 2 O 2 , and UV
irradiation as a source of HO
• for the oxidation of organics. Solar radiation for the
photodegradation of raw gasoline in water has been studied to reduce the cost. The
photo-Fenton process was also applied to a real effluent, i.e., oil field-produced
water, and the experimental results demonstrate the feasibility of employing solar
irradiation to degrade this complex saturated-hydrocarbon-containing system [6].
Besides organics, the inactivation of the coliphage MS2 (a human virus indicator)
by solar photo-Fenton was evaluated at near-neutral pH in carbonate buffer solution
matrix. The effects of reactant concentration (H 2 O 2 , Fe
2+ , Fe
3+ ) and solar irradiance
on the photo-Fenton process were studied. Specifically, the solar exposure/Fe
3+
treatment showed a strong dependence on the iron concentration and solar irradiance
intensity. The MS2 inactivation observed with the photo-Fenton process (solar
exposure/H 2 O 2 /Fe
2+ /
3+ ) carried out with Fe
3+ was faster than with Fe
2+ (detection
limit achieved at 20 min and 50 min, respectively). Moreover, virus inactivation by
photo-Fenton under different solar irradiance values (15, 30, and 45 W m
À2 ), H 2 O 2
and Fe
3+ concentrations (0.1, 0.5, and 1 mg L
À1 ), and different pH values (6, 7, and 8)
260
11 Photo-Fenton Reaction