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E. Emekdar and U. K. ¸
Sahin
color concentrations and low cost [13]. Adsorbent materials and their details will be
discussed in the further part of this chapter.
2.2 Oxidative Refining Methods
Oxidative methods use generally oxidative chemicals, and this class can be known as
chemical methods. Different radicals are used to eliminate impurities by oxidizing
them. These methods can be applied easily; thus, they are the most commonly used
class. This class has two subtitles as advanced oxidative method (AOM) and chemical
oxidative methods.
The advanced oxidative method uses hydroxyl radicals which are very strong
oxidative, and the generated radicals eliminate organic and inorganic impurities.
This method is very useful for textile wastewater and fast [13]. This method can be
supported by ultrasonic or hydrodynamic cavitation. Also, photocatalytic oxidation
and Fenton reaction which is between Fe
3+ ions and H 2 O 2 can be in AOM-type
refining. In Fenton reaction, a Fe
2+ ion mixture which has pH 2–3 as the acid is
prepared, and H 2 O 2 is added to form hydroxyl radicals [14]. Other Fenton’s reagents
can be used, but iron salts are the most common ones. Mud formation is a disadvantage
of the Fenton method because reagent and dyestuff form a complex molecule and
produce floccules [13].
The chemical oxidative method is another method for oxidative methods. It uses
oxidative agents as ozone and hydrogen peroxide that attacks to the conjugated
double bonds and functional groups at chromophore region of dyestuffs. In this
method, effluent is taken into the tank, and the oxidant is added in the reactor,
and finally, caustic is added for pH adjustment. In the case of ozone that needs
good stabilization conditions as pH and temperature, it removes toxic ingredients,
hydrocarbons, phenols, etc., and decreases chemical oxygen demand (COD) of the
effluent. For hydrogen peroxide, pH, temperature, peroxidase usage, and strength are
parameters that must be paid attention to for suitable removal of dyestuff, especially
for acid dyes. To improve these methods, hydrogen peroxide and UV light are used
for oxygen. Another chemical is NaOCl thanks to its Cl
− component for breaking
amine bond. Also, coagulation is another option in chemical methods for wastewater
that cannot form floccules naturally by waiting as in the flocculation method. Particles
coagulate with coagulant chemicals, and coagulated particles are eliminated [14]. If
the coagulation occurs by using reaction with ions that are released as Al(OH) 3 and
Fe(OH) 3 from aluminum and iron electrodes, it is known as electrocoagulation [15].
2.3 Biological Refining Methods
Biological refining is eliminating impurities by decomposing them in a natural
cycle of microorganisms. These methods are very advantageous because they are
E. Emekdar and U. K. ¸
Sahin
color concentrations and low cost [13]. Adsorbent materials and their details will be
discussed in the further part of this chapter.
2.2 Oxidative Refining Methods
Oxidative methods use generally oxidative chemicals, and this class can be known as
chemical methods. Different radicals are used to eliminate impurities by oxidizing
them. These methods can be applied easily; thus, they are the most commonly used
class. This class has two subtitles as advanced oxidative method (AOM) and chemical
oxidative methods.
The advanced oxidative method uses hydroxyl radicals which are very strong
oxidative, and the generated radicals eliminate organic and inorganic impurities.
This method is very useful for textile wastewater and fast [13]. This method can be
supported by ultrasonic or hydrodynamic cavitation. Also, photocatalytic oxidation
and Fenton reaction which is between Fe
3+ ions and H 2 O 2 can be in AOM-type
refining. In Fenton reaction, a Fe
2+ ion mixture which has pH 2–3 as the acid is
prepared, and H 2 O 2 is added to form hydroxyl radicals [14]. Other Fenton’s reagents
can be used, but iron salts are the most common ones. Mud formation is a disadvantage
of the Fenton method because reagent and dyestuff form a complex molecule and
produce floccules [13].
The chemical oxidative method is another method for oxidative methods. It uses
oxidative agents as ozone and hydrogen peroxide that attacks to the conjugated
double bonds and functional groups at chromophore region of dyestuffs. In this
method, effluent is taken into the tank, and the oxidant is added in the reactor,
and finally, caustic is added for pH adjustment. In the case of ozone that needs
good stabilization conditions as pH and temperature, it removes toxic ingredients,
hydrocarbons, phenols, etc., and decreases chemical oxygen demand (COD) of the
effluent. For hydrogen peroxide, pH, temperature, peroxidase usage, and strength are
parameters that must be paid attention to for suitable removal of dyestuff, especially
for acid dyes. To improve these methods, hydrogen peroxide and UV light are used
for oxygen. Another chemical is NaOCl thanks to its Cl
− component for breaking
amine bond. Also, coagulation is another option in chemical methods for wastewater
that cannot form floccules naturally by waiting as in the flocculation method. Particles
coagulate with coagulant chemicals, and coagulated particles are eliminated [14]. If
the coagulation occurs by using reaction with ions that are released as Al(OH) 3 and
Fe(OH) 3 from aluminum and iron electrodes, it is known as electrocoagulation [15].
2.3 Biological Refining Methods
Biological refining is eliminating impurities by decomposing them in a natural
cycle of microorganisms. These methods are very advantageous because they are