rate of the formation of reactive species increases compared with the respective
individual processes, sometimes with synergistic changes. Sequential application of
various AOPs is another way to enhance selectivity. A separation treatment prior to
the application of an AOP can be designed—transferring pollutants from the liquid
to another phase so that they can be treated more easily. Effluents containing volatile
organics or solids may be first subjected respectively to stripping or coagulation,
flocculation, sedimentation, and filtration in order to remove these compounds from
the effluent prior to the AOP treatment. AOPs can be applied as a pretreatment stage
to enhance the biodegradability and reduce the toxicity, followed by a biological
posttreatment (Comninellis et al. 2008).
AOTs have actually a variable development and commercialization degree, in
constant change as technological advances take place. Currently, UV/H 2 O 2 , UV/O 3 ,
UV/H 2 O 2 /O 3 , UV/Fenton, and UV/TiO 2 are totally or partially commercialized.
In what follows, permanganate, Fenton, ozonation, ferrate, radical reactions, and
photooxidation will be briefly described. Since there is a large amount of references
to the subject, only the most important and recent papers have been included,
together with review papers to be consulted.
7.2 Non-photochemical Oxidative Methods
7.2.1 Permanganate
Permanganate is one of the most well-recognized chemical oxidants within the
environmental industry and has been widely used for treatment of pollutants in
drinking water and wastewater applications for over 50 years. The use of permanganate in groundwater treatment applications (in situ chemical oxidation—ISCO) is
also a proven, well-documented technology.
Permanganate is traditionally available as sodium or potassium salt. The initial
oxidation reactions are independent of pH, but sometimes the pH influences the type
of intermediate products (Yan and Schwartz 2000), and the conversion of intermediate oxidation products to CO 2 occurs more rapidly under acidic pH conditions. The
main advantage is that final benign reaction products such as carbon dioxide, water,
and inorganic salts (e.g., chlorides) are produced via direct electron exchange
processes.
Potassium permanganate has an affinity for organic compounds containing
carbon–carbon double bonds, aldehyde groups, and hydroxyl groups. The permanganate ion takes electron density from the π bonds in chlorinated alkenes, creating a
bridged oxygen compound known as the cyclic hypomanganate ester (Yan and
Schwartz 2000). This intermediate ester is unstable and further reacts by a number
of mechanisms including hydroxylation, hydrolysis, or cleavage. Under normal pH
and temperature conditions, the primary oxidation reactions involve spontaneous
cleavage of the carbon–carbon bond. Once the double bond is broken, the highly
7 Introduction to Oxidative Technologies for Water Treatment
123
individual processes, sometimes with synergistic changes. Sequential application of
various AOPs is another way to enhance selectivity. A separation treatment prior to
the application of an AOP can be designed—transferring pollutants from the liquid
to another phase so that they can be treated more easily. Effluents containing volatile
organics or solids may be first subjected respectively to stripping or coagulation,
flocculation, sedimentation, and filtration in order to remove these compounds from
the effluent prior to the AOP treatment. AOPs can be applied as a pretreatment stage
to enhance the biodegradability and reduce the toxicity, followed by a biological
posttreatment (Comninellis et al. 2008).
AOTs have actually a variable development and commercialization degree, in
constant change as technological advances take place. Currently, UV/H 2 O 2 , UV/O 3 ,
UV/H 2 O 2 /O 3 , UV/Fenton, and UV/TiO 2 are totally or partially commercialized.
In what follows, permanganate, Fenton, ozonation, ferrate, radical reactions, and
photooxidation will be briefly described. Since there is a large amount of references
to the subject, only the most important and recent papers have been included,
together with review papers to be consulted.
7.2 Non-photochemical Oxidative Methods
7.2.1 Permanganate
Permanganate is one of the most well-recognized chemical oxidants within the
environmental industry and has been widely used for treatment of pollutants in
drinking water and wastewater applications for over 50 years. The use of permanganate in groundwater treatment applications (in situ chemical oxidation—ISCO) is
also a proven, well-documented technology.
Permanganate is traditionally available as sodium or potassium salt. The initial
oxidation reactions are independent of pH, but sometimes the pH influences the type
of intermediate products (Yan and Schwartz 2000), and the conversion of intermediate oxidation products to CO 2 occurs more rapidly under acidic pH conditions. The
main advantage is that final benign reaction products such as carbon dioxide, water,
and inorganic salts (e.g., chlorides) are produced via direct electron exchange
processes.
Potassium permanganate has an affinity for organic compounds containing
carbon–carbon double bonds, aldehyde groups, and hydroxyl groups. The permanganate ion takes electron density from the π bonds in chlorinated alkenes, creating a
bridged oxygen compound known as the cyclic hypomanganate ester (Yan and
Schwartz 2000). This intermediate ester is unstable and further reacts by a number
of mechanisms including hydroxylation, hydrolysis, or cleavage. Under normal pH
and temperature conditions, the primary oxidation reactions involve spontaneous
cleavage of the carbon–carbon bond. Once the double bond is broken, the highly
7 Introduction to Oxidative Technologies for Water Treatment
123