2 Natural Coagulates for Wastewater Treatment …
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while the precipitate enmeshment is the mechanism where the colloidal particles are
physically enmeshed (entrapped) by metal precipitates when they are forming and
settling. These mechanisms have been elaborated by scientists in 1963 who proposed
to name the mechanism of double-layer compression by “coagulation” and the mechanism of precipitate enmeshment by “flocculation”. In 1980 systematic studies have
been conducted to improve the coagulation performance of natural organic materials
(AWWA Research Committee Report 1989), various surface waters have been used
during these studies and several variables were investigated, such as mechanical conditions of coagulation, pH, temperature and other factors. While the coagulation has
continued to develop using various methods to this day.
2.3 Natural and Chemical Coagulants
The coagulants are divided into chemical and natural coagulants as shown in Fig. 2.1.
The coagulation process is one of the most effective treatment processes for removing
total suspended solids (TSS), chemical oxygen demand (COD), organic materials,
and colours. However, the performance of the removal process depends on the type of
the coagulant used. The general concept of the coagulation process can be defined as
the neutralization of the suspended matters with the negative charge and agglomerate
the destabilized particles to form a heavy clumped mass of small particles that allow
them to precipitate (Yusoff et al. 2018).
Aluminum salts and poly-aluminium chloride (PAC) are the most used coagulants
in the treatment of water and wastewater all around the world, as they are considered
widely available chemical coagulants which have high efficiency of treatment. The
reason that led to involve it in most of the wastewater treatment processes recently
and dispensed with traditional treatment methods of the natural coagulants (Zhao
et al. 2015). However, recent studies performed by researchers have raised doubts
about the danger of introducing these substances into the environment, where alumbased coagulants leave a high level of aluminium residuals in the treated water under
the conditions of cold temperature or low pH levels which can damage the ecosystem
and cause health issues (Matilainen et al. 2010).
In addition to that, the long-term exposure to aluminium residuals may cause
bioaccumulation in the human brain, bones, and liver (Walton 2012). Furthermore,
low molecular weight Al species can pose a deadly threat to the organisms due to
the high solubility and zwitterion properties of these substances which enable them
to penetrate biological membranes (Trenfield et al. 2017; Yusoff et al. 2018).
On the other side, ferric salts and synthetic polymers coagulates have been
employed to replace the alum-based coagulates but the limitation of the availability
and the lack of environmental impacts studies about these coagulates in addition to
the high cost of them made their success limited (Ndabigengesere et al. 1995). In
view of the hazardous caused by the utilization of chemical coagulants, the return
to the natural coagulants application has become a desirable option (Verma et al.
2012). The applications of natural coagulants can be a suitable option for water
19
while the precipitate enmeshment is the mechanism where the colloidal particles are
physically enmeshed (entrapped) by metal precipitates when they are forming and
settling. These mechanisms have been elaborated by scientists in 1963 who proposed
to name the mechanism of double-layer compression by “coagulation” and the mechanism of precipitate enmeshment by “flocculation”. In 1980 systematic studies have
been conducted to improve the coagulation performance of natural organic materials
(AWWA Research Committee Report 1989), various surface waters have been used
during these studies and several variables were investigated, such as mechanical conditions of coagulation, pH, temperature and other factors. While the coagulation has
continued to develop using various methods to this day.
2.3 Natural and Chemical Coagulants
The coagulants are divided into chemical and natural coagulants as shown in Fig. 2.1.
The coagulation process is one of the most effective treatment processes for removing
total suspended solids (TSS), chemical oxygen demand (COD), organic materials,
and colours. However, the performance of the removal process depends on the type of
the coagulant used. The general concept of the coagulation process can be defined as
the neutralization of the suspended matters with the negative charge and agglomerate
the destabilized particles to form a heavy clumped mass of small particles that allow
them to precipitate (Yusoff et al. 2018).
Aluminum salts and poly-aluminium chloride (PAC) are the most used coagulants
in the treatment of water and wastewater all around the world, as they are considered
widely available chemical coagulants which have high efficiency of treatment. The
reason that led to involve it in most of the wastewater treatment processes recently
and dispensed with traditional treatment methods of the natural coagulants (Zhao
et al. 2015). However, recent studies performed by researchers have raised doubts
about the danger of introducing these substances into the environment, where alumbased coagulants leave a high level of aluminium residuals in the treated water under
the conditions of cold temperature or low pH levels which can damage the ecosystem
and cause health issues (Matilainen et al. 2010).
In addition to that, the long-term exposure to aluminium residuals may cause
bioaccumulation in the human brain, bones, and liver (Walton 2012). Furthermore,
low molecular weight Al species can pose a deadly threat to the organisms due to
the high solubility and zwitterion properties of these substances which enable them
to penetrate biological membranes (Trenfield et al. 2017; Yusoff et al. 2018).
On the other side, ferric salts and synthetic polymers coagulates have been
employed to replace the alum-based coagulates but the limitation of the availability
and the lack of environmental impacts studies about these coagulates in addition to
the high cost of them made their success limited (Ndabigengesere et al. 1995). In
view of the hazardous caused by the utilization of chemical coagulants, the return
to the natural coagulants application has become a desirable option (Verma et al.
2012). The applications of natural coagulants can be a suitable option for water