Chang (2011) found that Spirogyra has higher adsorption capacity for Pb(II) and Cu
(II) than Cladophora sp. Hence, capacity for bio-removal of metal in macro- and
microalgae, clear differences have been observed in accumulation.
4.2 Active Algal Biomass vs. Passive Algal Biomass
The difference of metal biosorption via AAB and PAB has been clearly explained in
the above sections. However, ion exchange is the common process found in both
biosorbents which has a large contribution in biosorption potential. Most of the
researchers preferred PAB for biosorption process due to its possibility to recycle
and reuse. In addition to this, PAB don’t require additional nutrient source, and its
application to remove heavy metal ions under extreme environmental conditions was
found feasible in comparison to the living algal biomass. PAB biomass can be
pretreated by physical and chemical methods to improve biosorption efficiency,
while in living algal cell, sorption potential is limited and depends on growth
capacity of algal strain. Acidic and alkaline condition of growth medium can affect
the growth rate of algae and causes metal ion precipitation, respectively. Table 3.5
summarizes the efforts of various researchers toward the algal-based metal
biosorption.
4.3 Immobilized Algae
Initially, immobilization of algal cells was proposed to deal with the challenges
associated with harvesting and dewatering of algal cells. However, immobilization
offers several advantages over the algal cells grown in free suspension such as
(1) immobilized algal cells occupy less surface area; (2) immobilized algal cell has
been found with increased photosynthetic activity, biosorption capacity, and bioactivity; and (3) immobilized algal cells are found to be resistant to harsh environmental condition and less exposure to toxicity. Immobilization increases the
applicability of entrapped algal cells for repetitive biosorption process (Eroglu
et al. 2015). Researchers have developed various techniques (adsorption on surface,
flocculation, liquid-liquid emulsion, covalent coupling, etc.) for entrapment of algal
cells, but application of synthetic polymer (poly acryl amide) or natural polymers
(agar, cellulose, and alginate) is the most preferred technique.
Immobilization of algal cell using polysaccharide gels has often been used for the
purpose of wastewater treatment (nutrient uptake and metal ion removal). Entrapment of algal cells in alginate has been found to have sufficient immobilization and
improved removal efficiencies from aqueous environment (Table 3.6). Maznah et al.
(2012) reported higher biosorption capacity (Cu, 33.4 mg/g; Zn, 28.5 mg/g) in algal
cells (Chlorella sp.) immobilized by sodium alginate than that of the free biomass.
Recently, it has been found that incorporation of polyethyleneimine in alginate algal
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S. Ahmad et al.
(II) than Cladophora sp. Hence, capacity for bio-removal of metal in macro- and
microalgae, clear differences have been observed in accumulation.
4.2 Active Algal Biomass vs. Passive Algal Biomass
The difference of metal biosorption via AAB and PAB has been clearly explained in
the above sections. However, ion exchange is the common process found in both
biosorbents which has a large contribution in biosorption potential. Most of the
researchers preferred PAB for biosorption process due to its possibility to recycle
and reuse. In addition to this, PAB don’t require additional nutrient source, and its
application to remove heavy metal ions under extreme environmental conditions was
found feasible in comparison to the living algal biomass. PAB biomass can be
pretreated by physical and chemical methods to improve biosorption efficiency,
while in living algal cell, sorption potential is limited and depends on growth
capacity of algal strain. Acidic and alkaline condition of growth medium can affect
the growth rate of algae and causes metal ion precipitation, respectively. Table 3.5
summarizes the efforts of various researchers toward the algal-based metal
biosorption.
4.3 Immobilized Algae
Initially, immobilization of algal cells was proposed to deal with the challenges
associated with harvesting and dewatering of algal cells. However, immobilization
offers several advantages over the algal cells grown in free suspension such as
(1) immobilized algal cells occupy less surface area; (2) immobilized algal cell has
been found with increased photosynthetic activity, biosorption capacity, and bioactivity; and (3) immobilized algal cells are found to be resistant to harsh environmental condition and less exposure to toxicity. Immobilization increases the
applicability of entrapped algal cells for repetitive biosorption process (Eroglu
et al. 2015). Researchers have developed various techniques (adsorption on surface,
flocculation, liquid-liquid emulsion, covalent coupling, etc.) for entrapment of algal
cells, but application of synthetic polymer (poly acryl amide) or natural polymers
(agar, cellulose, and alginate) is the most preferred technique.
Immobilization of algal cell using polysaccharide gels has often been used for the
purpose of wastewater treatment (nutrient uptake and metal ion removal). Entrapment of algal cells in alginate has been found to have sufficient immobilization and
improved removal efficiencies from aqueous environment (Table 3.6). Maznah et al.
(2012) reported higher biosorption capacity (Cu, 33.4 mg/g; Zn, 28.5 mg/g) in algal
cells (Chlorella sp.) immobilized by sodium alginate than that of the free biomass.
Recently, it has been found that incorporation of polyethyleneimine in alginate algal
66
S. Ahmad et al.