treatment and this is where bioremediation becomes relevant providing several
techniques for cleaning up pollutants by means of biological tools (Shetty 2006).
Biological tools include living and nonliving microorganisms for removal or
recovery of toxic substances from wastewater. The natural affinity of biological
compounds for metallic elements could contribute to the purification of wastewater
polluted with metals (S ßahin and Öztürk 2005). The biosorption process is a feasible
option as it is efficient and cheap. Compared with conventional methods for
removing toxic metals from effluents, the biosorption process has the advantages of
low-operating cost, minimization of volume of chemicals and biological sludge to
be disposed of, and high efficiency in detoxifying very dilute effluents (Shetty 2006).
There are many different types of biosorbents like (i) Active biomass belonging
to algae, bacteria, or fungi; (ii) Nonactive kind of biosorbent which is essentially a
waste product or a by-product of a fermentation process; and (iii) Abundant natural
materials or polymers.
There is a small degree of selectivity, in solution, from numerous biosorbents in
the collection of heavy metals. The mechanism of metal sequestration can occur by
processes such as complexation, chelation, ion-exchange or coordination; or
physical mechanisms like adsorption or precipitation. However, since biomaterials
used for sorption are complex, a number of these mechanisms could be occurring
simultaneously. Biomaterials have several chemical groups: acetamide groups in
chitin, amino and phosphate groups in nucleic acids, amino, amide, sulfhydryl and
carboxyl groups in proteins, and hydroxyls in polysaccharides, which could
potentially attract and sequester metal ions. The efficiency of a biosorption process
depends not only on the binding properties of the biosorbents, but also on the
composition of the wastewater that will be used for treating (S ßahin and Öztürk
2005; Volesky and Holan 1995; Krishnani and Ayyappan 2006; Barros et al. 2006).
Polymers are used like biosorbents because they have different properties that
should be considered, such as degradation, hydrolysis and mechanical shearing,
and chemical and mechanical stability. Some polymers possess a flexible structure
and at certain hydrodynamic conditions the shape of such polymers can change so
that they will pass through the membrane even though their mass is more than the
molecular weight cut-off (MWCO) of the membrane (Shetty 2006; Geckeler and
Volchek 1996).
Among the many other low-cost absorbents identified, chitosan has the highest
sorption capacity for several metal ions (Chauhan et al. 2012; Juang and Shiau
2000; Laus et al. 2007; Liu et al. 2011; Sankararamakrishnan et al. 2007; Sobahi
et al. 2010). Chitosan ([b-(1?4)-2-amine-2-desoxy-D-glucose]) is a natural
polysaccharide that is formed by altering the N-deacetylation of its precursor,
Chitin. Chitin is the second most abundant natural polymer, and is widely distributed in nature, especially in the exoskeletons of marine invertebrates such as
prawn, crab, and lobster.
The difference between chitin and chitosan is essentially related to the possibility to solubilize the polymer in dilute acidic media. Therefore the degree of
acetylation (DA), which is related to the population balance of acetylated and
deacetylated (100-DA) groups, is essential to define these two terms. When chitin
82
L. Pérez-Sánchez et al.
techniques for cleaning up pollutants by means of biological tools (Shetty 2006).
Biological tools include living and nonliving microorganisms for removal or
recovery of toxic substances from wastewater. The natural affinity of biological
compounds for metallic elements could contribute to the purification of wastewater
polluted with metals (S ßahin and Öztürk 2005). The biosorption process is a feasible
option as it is efficient and cheap. Compared with conventional methods for
removing toxic metals from effluents, the biosorption process has the advantages of
low-operating cost, minimization of volume of chemicals and biological sludge to
be disposed of, and high efficiency in detoxifying very dilute effluents (Shetty 2006).
There are many different types of biosorbents like (i) Active biomass belonging
to algae, bacteria, or fungi; (ii) Nonactive kind of biosorbent which is essentially a
waste product or a by-product of a fermentation process; and (iii) Abundant natural
materials or polymers.
There is a small degree of selectivity, in solution, from numerous biosorbents in
the collection of heavy metals. The mechanism of metal sequestration can occur by
processes such as complexation, chelation, ion-exchange or coordination; or
physical mechanisms like adsorption or precipitation. However, since biomaterials
used for sorption are complex, a number of these mechanisms could be occurring
simultaneously. Biomaterials have several chemical groups: acetamide groups in
chitin, amino and phosphate groups in nucleic acids, amino, amide, sulfhydryl and
carboxyl groups in proteins, and hydroxyls in polysaccharides, which could
potentially attract and sequester metal ions. The efficiency of a biosorption process
depends not only on the binding properties of the biosorbents, but also on the
composition of the wastewater that will be used for treating (S ßahin and Öztürk
2005; Volesky and Holan 1995; Krishnani and Ayyappan 2006; Barros et al. 2006).
Polymers are used like biosorbents because they have different properties that
should be considered, such as degradation, hydrolysis and mechanical shearing,
and chemical and mechanical stability. Some polymers possess a flexible structure
and at certain hydrodynamic conditions the shape of such polymers can change so
that they will pass through the membrane even though their mass is more than the
molecular weight cut-off (MWCO) of the membrane (Shetty 2006; Geckeler and
Volchek 1996).
Among the many other low-cost absorbents identified, chitosan has the highest
sorption capacity for several metal ions (Chauhan et al. 2012; Juang and Shiau
2000; Laus et al. 2007; Liu et al. 2011; Sankararamakrishnan et al. 2007; Sobahi
et al. 2010). Chitosan ([b-(1?4)-2-amine-2-desoxy-D-glucose]) is a natural
polysaccharide that is formed by altering the N-deacetylation of its precursor,
Chitin. Chitin is the second most abundant natural polymer, and is widely distributed in nature, especially in the exoskeletons of marine invertebrates such as
prawn, crab, and lobster.
The difference between chitin and chitosan is essentially related to the possibility to solubilize the polymer in dilute acidic media. Therefore the degree of
acetylation (DA), which is related to the population balance of acetylated and
deacetylated (100-DA) groups, is essential to define these two terms. When chitin
82
L. Pérez-Sánchez et al.