polyaluminium chloride (PAC) or polyferric sulphate (PFS)] have also been assessed
as a coagulant aid to assist the conventional coagulants and to overcome their
residual toxicity and dose requirement (Huang et al. 2015; Rong et al. 2014). The
pre-hydrolysed salts assist the traditional additives as they get hydrolysed during the
coagulant preparation, thus resulting into more control experimental conditions and
very less impact on pH of the treated water (Renault et al. 2009). They also help in
the formation of larger flocs as compared to alum (Huang et al. 2015). Despite this,
their mode of action of floc formation, mechanism of targeting dye molecules, health
and environmental safety of effluent are still lacking (Jeon et al. 2009). Unlike
pre-hydrolysed salts, organic polymers are categorized as natural and synthetic
polymers, having a large number of similar chemical units bonded together by
covalent bonds. Natural polymers have advantages of non-toxicity and biodegradability but are not that effective as synthetic polymers (Zahrim et al. 2011). Also,
their biodegradability influences their long storage life hence confined their applications (Dragan and Dinu 2008).
In contrast, synthetic polymers own more controlling specific properties of
molecular weight and charge functionalities (Bratby 2006). Cationic polymers are
found to be more effective for dye removal than anionic and non-ionic polymers
(Salamone 1998). Despite this, these polymers are not found more effective in the
removal of more diverse class of dyes, thus limiting their use (Table 13.2). Also, it
was found in a study that the non-reactive monomers, such as acrylamide of
synthetic polymers, are toxic and have carcinogenic potentials (Bratby 2006).
Surmounting toxicity of chemical coagulants, natural coagulants (including plantand animal-based coagulant) such as Moringa seeds (Tie et al. 2015), chitosan
(Szyguła et al. 2008), okra mucilage (Freitas et al. 2015) and several other naturally
derived polymers were also used for dye wastewater treatment, because of their
advantages of no toxicity and bioavailability, over other chemical coagulants or
polymers. Nevertheless, their use in practical treatment technology is still restricted
because of short self-storage life (Dragan and Dinu 2008) and limited working pH
range (Renault et al. 2009). Also, the extraction process of these natural coagulants
varies because of their properties and thereby affects the coagulation/flocculation
process (Renault et al. 2009; Guibal 2004) and rebuts their uses in industries.
Moreover, one microorganism derived-coagulant named xanthan gum has been
also observed. It is a high molecular weight polysaccharide derived from
Xanthomonas campestris bacterial coat. But its use in the textile industry’s wastewater has not been reported yet in the literature (Davidson 1980; Cohan 2010), might
be because of its complex structure and higher molecular weight as compared to guar
gum (Verma et al. 2011).
The current trends for the dye wastewater treatment clearly remark about the
subsequent advancement in the use of metallic, inorganic and natural coagulants in
the treatment process. It has been observed that initially alum and iron-based
coagulants were extensively used, but as the dye developed, new coagulants have
been introduced to overcome the limitations of the existing one. Different coagulant
combinations and various coagulant aids have also been used for amelioration of the
318
S. Sonal and B. K. Mishra
as a coagulant aid to assist the conventional coagulants and to overcome their
residual toxicity and dose requirement (Huang et al. 2015; Rong et al. 2014). The
pre-hydrolysed salts assist the traditional additives as they get hydrolysed during the
coagulant preparation, thus resulting into more control experimental conditions and
very less impact on pH of the treated water (Renault et al. 2009). They also help in
the formation of larger flocs as compared to alum (Huang et al. 2015). Despite this,
their mode of action of floc formation, mechanism of targeting dye molecules, health
and environmental safety of effluent are still lacking (Jeon et al. 2009). Unlike
pre-hydrolysed salts, organic polymers are categorized as natural and synthetic
polymers, having a large number of similar chemical units bonded together by
covalent bonds. Natural polymers have advantages of non-toxicity and biodegradability but are not that effective as synthetic polymers (Zahrim et al. 2011). Also,
their biodegradability influences their long storage life hence confined their applications (Dragan and Dinu 2008).
In contrast, synthetic polymers own more controlling specific properties of
molecular weight and charge functionalities (Bratby 2006). Cationic polymers are
found to be more effective for dye removal than anionic and non-ionic polymers
(Salamone 1998). Despite this, these polymers are not found more effective in the
removal of more diverse class of dyes, thus limiting their use (Table 13.2). Also, it
was found in a study that the non-reactive monomers, such as acrylamide of
synthetic polymers, are toxic and have carcinogenic potentials (Bratby 2006).
Surmounting toxicity of chemical coagulants, natural coagulants (including plantand animal-based coagulant) such as Moringa seeds (Tie et al. 2015), chitosan
(Szyguła et al. 2008), okra mucilage (Freitas et al. 2015) and several other naturally
derived polymers were also used for dye wastewater treatment, because of their
advantages of no toxicity and bioavailability, over other chemical coagulants or
polymers. Nevertheless, their use in practical treatment technology is still restricted
because of short self-storage life (Dragan and Dinu 2008) and limited working pH
range (Renault et al. 2009). Also, the extraction process of these natural coagulants
varies because of their properties and thereby affects the coagulation/flocculation
process (Renault et al. 2009; Guibal 2004) and rebuts their uses in industries.
Moreover, one microorganism derived-coagulant named xanthan gum has been
also observed. It is a high molecular weight polysaccharide derived from
Xanthomonas campestris bacterial coat. But its use in the textile industry’s wastewater has not been reported yet in the literature (Davidson 1980; Cohan 2010), might
be because of its complex structure and higher molecular weight as compared to guar
gum (Verma et al. 2011).
The current trends for the dye wastewater treatment clearly remark about the
subsequent advancement in the use of metallic, inorganic and natural coagulants in
the treatment process. It has been observed that initially alum and iron-based
coagulants were extensively used, but as the dye developed, new coagulants have
been introduced to overcome the limitations of the existing one. Different coagulant
combinations and various coagulant aids have also been used for amelioration of the
318
S. Sonal and B. K. Mishra