13.8.6 The Affinity of Colloids for Water
In turbid water usually, a mixture of hydrophilic-hydrophobic colloidal particles is
present. Hydrophilic (water-loving) colloids seem very stable as their hydration shell
prevents chemicals to readily replace the sorbed water molecules, thus inhibiting
their destabilization from the suspension. The stability of hydrophilic colloidal
particles mainly depends on their strong interaction with the water molecules than
on their electrostatic charge (Hammer 1986). Dye molecules primarily are reactive,
and soluble dyes have more affinity with the water molecules, thus rendering
difficulties in the destabilization of the molecules (Patel and Vashi 2015). To settle
down such particles, usually 10–20 times more coagulant dose has been required.
Contrarily, hydrophobic (e.g. metal oxides) particles can be easily destabilized and
coagulated.
13.8.7 Temperature
Lower temperature adversely affects the process of coagulation by altering the
coagulant solubility. The lower temperature also increases the water viscosity,
thereby hindering the kinetics of hydrolysis reactions and particle flocculation
(Morris and Knocke 1984) and, thus, affects the sedimentation process. In contrast,
higher temperature increases the rate and effectiveness of the process, (i) by increasing the kinetic energy of the molecules and rate of chemical reactions and (ii) by
decreasing viscosity of water and altering the structure of the flocs, resulting in larger
agglomerations.
13.8.8 Ionic Concentration and Composition (Cations
and Anions in Solution)
The presence of higher ionic strength in the solution will enhance the destabilization
behaviour of the colloidal particles. The presence of anions such as sulphate, silicate
and phosphate suppressed the occurrence of charge reversal and re-stabilization of
colloids (Boisvert et al. 1997). And the presence of divalent cations such as Ca
2+ and
Mg
2+ also plays beneficial effects on coagulation of negatively charged particles by
compressing the colloidal double layer and minimizing the repulsive potential
(Black et al. 1965).
13 Role of Coagulation/Flocculation Technology for the Treatment of Dye. . .
323
In turbid water usually, a mixture of hydrophilic-hydrophobic colloidal particles is
present. Hydrophilic (water-loving) colloids seem very stable as their hydration shell
prevents chemicals to readily replace the sorbed water molecules, thus inhibiting
their destabilization from the suspension. The stability of hydrophilic colloidal
particles mainly depends on their strong interaction with the water molecules than
on their electrostatic charge (Hammer 1986). Dye molecules primarily are reactive,
and soluble dyes have more affinity with the water molecules, thus rendering
difficulties in the destabilization of the molecules (Patel and Vashi 2015). To settle
down such particles, usually 10–20 times more coagulant dose has been required.
Contrarily, hydrophobic (e.g. metal oxides) particles can be easily destabilized and
coagulated.
13.8.7 Temperature
Lower temperature adversely affects the process of coagulation by altering the
coagulant solubility. The lower temperature also increases the water viscosity,
thereby hindering the kinetics of hydrolysis reactions and particle flocculation
(Morris and Knocke 1984) and, thus, affects the sedimentation process. In contrast,
higher temperature increases the rate and effectiveness of the process, (i) by increasing the kinetic energy of the molecules and rate of chemical reactions and (ii) by
decreasing viscosity of water and altering the structure of the flocs, resulting in larger
agglomerations.
13.8.8 Ionic Concentration and Composition (Cations
and Anions in Solution)
The presence of higher ionic strength in the solution will enhance the destabilization
behaviour of the colloidal particles. The presence of anions such as sulphate, silicate
and phosphate suppressed the occurrence of charge reversal and re-stabilization of
colloids (Boisvert et al. 1997). And the presence of divalent cations such as Ca
2+ and
Mg
2+ also plays beneficial effects on coagulation of negatively charged particles by
compressing the colloidal double layer and minimizing the repulsive potential
(Black et al. 1965).
13 Role of Coagulation/Flocculation Technology for the Treatment of Dye. . .
323