dye treatment process. Nevertheless, selection of these combinations is still an
intricate task as many factors are responsible, which is discussed in the next section.
13.7 Selection Criteria for Coagulants
Selection of any specific coagulant used for the treatment of any target pollutants
solely depends upon the characteristics of the coagulants, their hydrolysing properties, working pH range and several other factors. Thus, the factors responsible for
coagulant selection are as follows.
13.7.1 Properties of the Coagulants
These properties include the hydrolysing characteristics of the coagulant and their
flocs formation capacity in specific working pH. For example, alum, iron-based
coagulant and zirconium oxychloride were more preferably used in coagulation/
flocculation process over divalent metallic salts as they follow the Schulze-Hardy
rule that says the higher the valence state of metal-based counter ions, higher will be
the hydrolysis products, and more efficient will be destabilization of colloidal
particles (Jarvis et al. 2012; Sonal et al. 2018).
13.7.2 Concentration and Type of Colloidal Particles
The presence of hydrophilic colloidal particles in water is found to be more challenging to precipitate as compared to that of hydrophobic particles. Hydrophilic
particles form hydrogen bonding with the water molecules resulting in more dose
requirement. The presence of turbidity sometimes plays a decisive role in the
coagulation of colloidal particles (Peavy et al. 1985). Sufficient amount of colloidal
particles promotes entrapment of particles in the precipitate during the coagulation
process.
13.7.3 Quality of the Polluted Water
Pollutant quality also decides the coagulant and dose of the coagulant. The effluent
characteristics such as pH, alkalinity, turbidity, presence of organic matters, etc. play
an essential role in coagulant selection. For example, effective pH for alum is 6.5 to
8.5 only; beyond this pH, there must be an addition of external alkalis salts, thus
rendering the overall cost of treatment. Similarly, the effective pH for ferric sulphate
13 Role of Coagulation/Flocculation Technology for the Treatment of Dye. . .
319
intricate task as many factors are responsible, which is discussed in the next section.
13.7 Selection Criteria for Coagulants
Selection of any specific coagulant used for the treatment of any target pollutants
solely depends upon the characteristics of the coagulants, their hydrolysing properties, working pH range and several other factors. Thus, the factors responsible for
coagulant selection are as follows.
13.7.1 Properties of the Coagulants
These properties include the hydrolysing characteristics of the coagulant and their
flocs formation capacity in specific working pH. For example, alum, iron-based
coagulant and zirconium oxychloride were more preferably used in coagulation/
flocculation process over divalent metallic salts as they follow the Schulze-Hardy
rule that says the higher the valence state of metal-based counter ions, higher will be
the hydrolysis products, and more efficient will be destabilization of colloidal
particles (Jarvis et al. 2012; Sonal et al. 2018).
13.7.2 Concentration and Type of Colloidal Particles
The presence of hydrophilic colloidal particles in water is found to be more challenging to precipitate as compared to that of hydrophobic particles. Hydrophilic
particles form hydrogen bonding with the water molecules resulting in more dose
requirement. The presence of turbidity sometimes plays a decisive role in the
coagulation of colloidal particles (Peavy et al. 1985). Sufficient amount of colloidal
particles promotes entrapment of particles in the precipitate during the coagulation
process.
13.7.3 Quality of the Polluted Water
Pollutant quality also decides the coagulant and dose of the coagulant. The effluent
characteristics such as pH, alkalinity, turbidity, presence of organic matters, etc. play
an essential role in coagulant selection. For example, effective pH for alum is 6.5 to
8.5 only; beyond this pH, there must be an addition of external alkalis salts, thus
rendering the overall cost of treatment. Similarly, the effective pH for ferric sulphate
13 Role of Coagulation/Flocculation Technology for the Treatment of Dye. . .
319