2 Natural Coagulates for Wastewater Treatment …
21
organic matters, dyes, and other wastes in water and wastewater. Many researches
have been conducted to assess the performance of natural coagulants comparing to
the chemical coagulants. Previous literature has indicated that the efficacy of natural
coagulants is approximately equal to that of chemical coagulants, where according
to the comparison between the performance of the natural and chemical coagulants
in Table 2.1.
The natural coagulation of chitosan has recorded a higher removal ratio of COD
comparing with the alum in the textile wastewater which estimated by 70.5 versus
36%, and with the ferric chloride by 70.5 versus 68.75% (Nechita 2017; Naghan
et al. 2015). Moreover, natural coagulants have overcome chemical coagulants in the
removal efficiency of total suspended solids (TSS), while previous studies showed
that there is a convergence between natural and chemical coagulants in the highperformance removal of oils and greases from wastewater (Hosny et al. 2016; Sun
et al. 2017). The increase in coagulants may lead to an increase in the efficacy of
water and wastewater treatment, but chemical coagulants cannot be used excessively
to avoid secondary pollution and the hazards that can be resulted from this excessive
utilization, in contrast to using a high dose of natural coagulants which is safe and
highly efficient. A previous study has been performed by Shan et al. (2017), showed
that the high dosage of natural coagulants have the high potential to remove heavy
metals from wastewater.
2.4 Coagulants/Flocculants Mechanism
The coagulation and flocculation mechanisms differ according to the coagulants
type, as there are four types of coagulation/flocculation processes including charge
neutralization, sweep coagulation, bridging and patch flocculation (Amran et al.
2018) (Fig. 2.2). The stabilized colloidal dispersion undergoes to high concentrations
of simple salts in the coagulation process, the added counter-ions permeate to the
diffuse double layer, and this process compresses the double layer and lead to the
reduction of the repulsion among colloids which allow the aggregation by van der
Waals forces (Liu et al. 2015). According to Schulze-Hardy rule, the effect of this
phenomenon can be stronger by the increase of the counter ions charge where the
previous literature showed the vary of the relative power of Al
3+ , Mg
2+ , and Na
+ for
the coagulation of negative colloids estimated in the ratio of 1000:30:1 (Ghernaout
et al. 2011; Trefalt et al. 2017). Charge neutralization mechanisms usually employ
the ionisable polymer (polyelectrolytes) coagulants in the stabilization process of
colloidal particles. The colloidal particles are negatively charged particles due to the
repulse process between them. The added coagulants with a high positive charge take
advantage of the surfaces of negatively charged colloids to be stick on them (Surface
absorption) in the coagulation/flocculation processes which leads to the coagulants
penetration phase to the diffuse double layers surrounding by the particles rendering
them heavier and smaller in volume due to the closer distance between the particles
and end to the accumulation (Kristianto 2017). The coagulants with high charge
21
organic matters, dyes, and other wastes in water and wastewater. Many researches
have been conducted to assess the performance of natural coagulants comparing to
the chemical coagulants. Previous literature has indicated that the efficacy of natural
coagulants is approximately equal to that of chemical coagulants, where according
to the comparison between the performance of the natural and chemical coagulants
in Table 2.1.
The natural coagulation of chitosan has recorded a higher removal ratio of COD
comparing with the alum in the textile wastewater which estimated by 70.5 versus
36%, and with the ferric chloride by 70.5 versus 68.75% (Nechita 2017; Naghan
et al. 2015). Moreover, natural coagulants have overcome chemical coagulants in the
removal efficiency of total suspended solids (TSS), while previous studies showed
that there is a convergence between natural and chemical coagulants in the highperformance removal of oils and greases from wastewater (Hosny et al. 2016; Sun
et al. 2017). The increase in coagulants may lead to an increase in the efficacy of
water and wastewater treatment, but chemical coagulants cannot be used excessively
to avoid secondary pollution and the hazards that can be resulted from this excessive
utilization, in contrast to using a high dose of natural coagulants which is safe and
highly efficient. A previous study has been performed by Shan et al. (2017), showed
that the high dosage of natural coagulants have the high potential to remove heavy
metals from wastewater.
2.4 Coagulants/Flocculants Mechanism
The coagulation and flocculation mechanisms differ according to the coagulants
type, as there are four types of coagulation/flocculation processes including charge
neutralization, sweep coagulation, bridging and patch flocculation (Amran et al.
2018) (Fig. 2.2). The stabilized colloidal dispersion undergoes to high concentrations
of simple salts in the coagulation process, the added counter-ions permeate to the
diffuse double layer, and this process compresses the double layer and lead to the
reduction of the repulsion among colloids which allow the aggregation by van der
Waals forces (Liu et al. 2015). According to Schulze-Hardy rule, the effect of this
phenomenon can be stronger by the increase of the counter ions charge where the
previous literature showed the vary of the relative power of Al
3+ , Mg
2+ , and Na
+ for
the coagulation of negative colloids estimated in the ratio of 1000:30:1 (Ghernaout
et al. 2011; Trefalt et al. 2017). Charge neutralization mechanisms usually employ
the ionisable polymer (polyelectrolytes) coagulants in the stabilization process of
colloidal particles. The colloidal particles are negatively charged particles due to the
repulse process between them. The added coagulants with a high positive charge take
advantage of the surfaces of negatively charged colloids to be stick on them (Surface
absorption) in the coagulation/flocculation processes which leads to the coagulants
penetration phase to the diffuse double layers surrounding by the particles rendering
them heavier and smaller in volume due to the closer distance between the particles
and end to the accumulation (Kristianto 2017). The coagulants with high charge