Environmental Engineering Reference
In-Depth Information
25.4.1 Fenton's Oxidation Process
It is a widely used process in which hydrogen peroxide is the oxidizer in the presence
of iron catalyst. It is simplest and economical and the reagents are easily available. This
method is used for the treatment of water and wastewater and hazardous wastes. Fenton's
process is known to remove many recalcitrant compounds in wastewater. In this process,
hydroxyl radicals are generated by the decomposition of H
2
O
2
in the presence of iron. The
reactions can be represented as follows.
Fe
2+
+ H
2
O
2
→ Fe
3+
+ OH
−
+
∙
OH
3
+
2
+
+
Fe
+ →+
HO
Fe
HO
+
H
22
2
3
+
+ +
+ →++
2
Fe
HO
Fe
OH
2
2
The radicals generated oxidize the organic components in water in the presence of iron. In
the case of the photo-Fenton process, the oxidation of Fe
2+
to Fe
3+
and the hydroxyl radical
generation takes place in the presence of a light source.
There are some disadvantages in this method. Residual iron present in water, in excess
amounts after the process, can be toxic to the microorganisms. This affects the perfor-
mance of the subsequent biological treatment. This process is dependent on the pH of the
water. Some studies reported that a pH range of 3-3.5 is optimum for the process. Hence,
the pH of the wastewater should be adjusted to achieve the optimum removal. Another
drawback is the sludge generation due to the precipitation of iron. As iron has coagulant
properties, sludge is generated after the treatment.
25.4.2 Photolysis
This process involves the use of natural or artiicial light to degrade pollutants. Photo-
chemical reactions take place, leading to the degradation of the target compound. One
example of this process is UV treatment. UV treatment is used for disinfection since it is
more eficient than chlorination and it does not produce any disinfection by-products. The
eficiency can be increased by using hydrogen peroxide along with UV radiation. This
method depends on the absorption spectra of the target compounds selected. This method
is expensive and cannot be a sustainable solution to the water and wastewater treatment.
25.4.3 Ozonation
Ozone is a strong oxidizing agent. It produces reactive oxygen species on reaction with
water. The performance of ozone can be increased if a catalyst such as hydrogen perox-
ide or iron is used. At high pH, more hydroxyl radicals are produced during ozonation.
Ozonation can be used for water and wastewater treatment. Cost is an important criterion
while adopting this method.
25.4.4 Electrochemical Oxidation
In this method, contaminants are degraded by anodic oxidation. Platinum, TiO
2
, PbO
2
,
etc., are used as anodes. Oxidants such as ozone, hydroxyl radicals, and hydrogen peroxide
