But free cells are not suitable for column packing. They can provide valuable
information in laboratory experimentation only (Ross and Townsley 1986). Free
cells have low mechanical strength and small particle size. Cell immobilization can
avoid the biomass-liquid separation requirement. Cell immobilization involves the
different forms of cell attachment or entrapment (Lopez et al. 1997). Several
techniques are used for immobilization like adsorption on surfaces, flocculation,
cross-linking of cells, encapsulation in a polymer gel, and entrapment in a polymeric
matrix. Entrapment inside a polymeric matrix, made as beads with optimum rigidity,
mechanical strength, and porosity, is the most popular technique (Lu and Wilkins,
1995; Annadurai et al. 2000). Both natural polymers (alginate, agar, carrageenan,
polysaccharides) and synthetic polymers are in use as gel-forming agents (Lozinsky
and Plieva 1998). Use of silica gel for cell entrapment is called as sol-gel technique
(Weller 2000). Rangsayatorn et al. (2004) studied the biosorption of cadmium by
alginate and silica gel immobilized cells of Spirulina platensis TISTR 8217 with
max biosorption capacities of 70.9 and 36.6 mg Cd/g biomass. There are several
other reports on use of polymers such as polyacrylamide (Macaskie et al. 1987;
Michel 1986; Sakaguchi and Nakajima 1991; Wong and Kwok 1992), polysulfone
(Jeffers 1991 Bai and Abraham 2003), and calcium alginate (Babu 1993; Costa and
Leite 1991; Peng and Koon 1993; Bayramoglu et al. 2002).
Abu Al-Rub et al. (2004) have investigated the technical feasibility of using blank
alginate beads and free and immobilized cells for nickel removal from aqueous
solution and also found the effect of pH, shaking time, and initial metal ion
concentration on adsorption capacity. Removal of copper by alginate beads of
algae has been studied by Tam et al. (1998). Fungal biomass can also be used for
metal removal. Kiff and Little (1986) utilized the immobilized fungal biomass for
biosorption of heavy metals.
Dong (2004) has compared the biosorption capacity of alginate beads and both
live and inactivated spores of Cladosporium sp. for copper II from aqueous solution.
The order for maximum biosorption capacity was found as:
Immobilized live biomass > immobilized inactivated biomass > blank calcium
alginate beads.
All the biosorbents were regenerated by acid treatment and were reused in three
biosorption and desorption cycles. Green algae Microcystis in gel has also been
found to remove copper and cobalt ions by Jhang et al. (1991). Macaskie and Dean
(1986) have used polyacrylamide gel for immobilization of Citrobacter sp., which
then help in removal of large quantities of cadmium. Darnall et al. (1986) found that
the biosorption of uranyl ions by Chlorella immobilized in polyacrylamide gel was
independent of changes in pH in the range of 4–9. There are certain other reports
indicating increase in removal of copper, zinc, cobalt, manganese, and mercury by
algae when it is in an immobilized form (Singh et al. 1989; Wilkinson et al. 1990).
Biodegradation of synthetic textile dyes by algae had been reported in a few
studies. The biodegradation pathway was thought to involve reductive cleavage of
the azo linkage followed by further degradation of the formed aromatic amines.
Several species of green microalgae were capable of decolorizing azo and triphenylmethane dyes to simpler organic compounds or CO 2 (Jinqi and Houtian 1992;
16 Cyanobacteria: The Eco-Friendly Tool for the Treatment of Industrial Wastewaters
399
information in laboratory experimentation only (Ross and Townsley 1986). Free
cells have low mechanical strength and small particle size. Cell immobilization can
avoid the biomass-liquid separation requirement. Cell immobilization involves the
different forms of cell attachment or entrapment (Lopez et al. 1997). Several
techniques are used for immobilization like adsorption on surfaces, flocculation,
cross-linking of cells, encapsulation in a polymer gel, and entrapment in a polymeric
matrix. Entrapment inside a polymeric matrix, made as beads with optimum rigidity,
mechanical strength, and porosity, is the most popular technique (Lu and Wilkins,
1995; Annadurai et al. 2000). Both natural polymers (alginate, agar, carrageenan,
polysaccharides) and synthetic polymers are in use as gel-forming agents (Lozinsky
and Plieva 1998). Use of silica gel for cell entrapment is called as sol-gel technique
(Weller 2000). Rangsayatorn et al. (2004) studied the biosorption of cadmium by
alginate and silica gel immobilized cells of Spirulina platensis TISTR 8217 with
max biosorption capacities of 70.9 and 36.6 mg Cd/g biomass. There are several
other reports on use of polymers such as polyacrylamide (Macaskie et al. 1987;
Michel 1986; Sakaguchi and Nakajima 1991; Wong and Kwok 1992), polysulfone
(Jeffers 1991 Bai and Abraham 2003), and calcium alginate (Babu 1993; Costa and
Leite 1991; Peng and Koon 1993; Bayramoglu et al. 2002).
Abu Al-Rub et al. (2004) have investigated the technical feasibility of using blank
alginate beads and free and immobilized cells for nickel removal from aqueous
solution and also found the effect of pH, shaking time, and initial metal ion
concentration on adsorption capacity. Removal of copper by alginate beads of
algae has been studied by Tam et al. (1998). Fungal biomass can also be used for
metal removal. Kiff and Little (1986) utilized the immobilized fungal biomass for
biosorption of heavy metals.
Dong (2004) has compared the biosorption capacity of alginate beads and both
live and inactivated spores of Cladosporium sp. for copper II from aqueous solution.
The order for maximum biosorption capacity was found as:
Immobilized live biomass > immobilized inactivated biomass > blank calcium
alginate beads.
All the biosorbents were regenerated by acid treatment and were reused in three
biosorption and desorption cycles. Green algae Microcystis in gel has also been
found to remove copper and cobalt ions by Jhang et al. (1991). Macaskie and Dean
(1986) have used polyacrylamide gel for immobilization of Citrobacter sp., which
then help in removal of large quantities of cadmium. Darnall et al. (1986) found that
the biosorption of uranyl ions by Chlorella immobilized in polyacrylamide gel was
independent of changes in pH in the range of 4–9. There are certain other reports
indicating increase in removal of copper, zinc, cobalt, manganese, and mercury by
algae when it is in an immobilized form (Singh et al. 1989; Wilkinson et al. 1990).
Biodegradation of synthetic textile dyes by algae had been reported in a few
studies. The biodegradation pathway was thought to involve reductive cleavage of
the azo linkage followed by further degradation of the formed aromatic amines.
Several species of green microalgae were capable of decolorizing azo and triphenylmethane dyes to simpler organic compounds or CO 2 (Jinqi and Houtian 1992;
16 Cyanobacteria: The Eco-Friendly Tool for the Treatment of Industrial Wastewaters
399