• Due to their relatively larger size, separation is much easier than other microbial
biomass.
• Biomass production is larger.
• Production of extracellular polysaccharides helps in binding of metal ions.
Cyanobacteria can be used in live and immobilized form for the removal of dyes
and heavy metals. Various techniques are available for biomass immobilization like
adsorption on surfaces, flocculation, cross-linking of cells, encapsulation in a polymer gel, covalent bonding to carriers, and entrapment in a polymeric matrix.
Among the different technologies available for the treatment of wastewater
contaminated with heavy metals, bioremediation has proved to be cost-effective
and eco-friendly, which involves the use of biological materials for the treatment.
Different microorganisms like bacteria, fungi, yeast, and algae have been studied for
their dye/metal removal capabilities because of their continuous growing nature.
Both live and dead cells of alga are used for heavy metal and dye removal as
biosorbent (Aksu 2002; Hashim and Chu 2001; Wong et al. 2000; Donmez et al.
1999; Sandau et al. 1966; Crist et al. 1981; Tam et al. 1998; Aravindhan et al. 2007;
Robinson et al. 2001; Aksu 2005; Ozer et al. 2005). Due to easy availability, high
surface area, and high binding affinity, algae are considered as suitable biosorbents
(Darnall et al. 1986; Smith et al. 1994, Robinson et al. 2001; Aksu 2005).
Ahuja et al. (1999) reported the copper adsorption capacity of a freshwater
cyanobacterium Oscillatoria angustissima. Metal-removing capability has also
been reported for the green microalgae, Chlorella vulgaris (Harris and Ramelow
1990; Aksu et al. 1992; Cho et al. 1994). Metal binding is, however, found to vary in
different algal species (Wilde and Benmann 1993). Mohamed (2001) demonstrated
the ability of both live and dry cells of Gloeothece magna, a nontoxic freshwater
cyanobacterium, for the adsorption of cadmium and manganese. Corder and Reeves
(1994) reported the accumulation of nickel by live Cylindrica, Anabaena flos-aquae,
and Nostoc sp. The toxicity and uptake of iron, zinc, and copper have been studied
for Oscillatoria perornata var. altenate and Scenedesmus quadricauda var.
longispina by Mittal et al. (1992).
Marine algae have also been found to adsorb heavy metals. Matheickal and Yu
(1999) presented the uptake properties of two biosorbents (DP95Ca and ER95 Ca)
that were developed by chemically modifying the marine algae Durvillaea
potatorum and Ecklonia radiata for the lead and copper. There are certain other
reports for feasibility of using cheaply available marine or freshwater algae for heavy
metal removal (Darnall et al. 1986; Holan et al. 1993). The binding of single metals
individually to the green alga, Chlorella vulgaris, and their dependence on pH, mass,
and time have been studied by Darnall et al. (1986) and Kubiak et al. (1989).
Removal of Cr
6+ by Halimeda tuna, Sargassum vulgare, Pterocladia capillacea,
Hypnea musciformis, and Laurencia papillosa has been studied with varying pH,
initial metal ion concentration, and agitation time, and maximum sorption capacities
of 2.3, 3.3, 6.6, 4.7, and 5.3 mg/g were observed, respectively (Baran et al. 2005).
Gupta et al. (2001) have studied the biosorption of chromium VI from aqueous
solution by a filamentous green algae Spirogyra sp. and found the maximum
removal of 14.7 X 10
3 mg metal/kg of dry weight biomass at a pH of 2.0.
398
S. Mona et al.
biomass.
• Biomass production is larger.
• Production of extracellular polysaccharides helps in binding of metal ions.
Cyanobacteria can be used in live and immobilized form for the removal of dyes
and heavy metals. Various techniques are available for biomass immobilization like
adsorption on surfaces, flocculation, cross-linking of cells, encapsulation in a polymer gel, covalent bonding to carriers, and entrapment in a polymeric matrix.
Among the different technologies available for the treatment of wastewater
contaminated with heavy metals, bioremediation has proved to be cost-effective
and eco-friendly, which involves the use of biological materials for the treatment.
Different microorganisms like bacteria, fungi, yeast, and algae have been studied for
their dye/metal removal capabilities because of their continuous growing nature.
Both live and dead cells of alga are used for heavy metal and dye removal as
biosorbent (Aksu 2002; Hashim and Chu 2001; Wong et al. 2000; Donmez et al.
1999; Sandau et al. 1966; Crist et al. 1981; Tam et al. 1998; Aravindhan et al. 2007;
Robinson et al. 2001; Aksu 2005; Ozer et al. 2005). Due to easy availability, high
surface area, and high binding affinity, algae are considered as suitable biosorbents
(Darnall et al. 1986; Smith et al. 1994, Robinson et al. 2001; Aksu 2005).
Ahuja et al. (1999) reported the copper adsorption capacity of a freshwater
cyanobacterium Oscillatoria angustissima. Metal-removing capability has also
been reported for the green microalgae, Chlorella vulgaris (Harris and Ramelow
1990; Aksu et al. 1992; Cho et al. 1994). Metal binding is, however, found to vary in
different algal species (Wilde and Benmann 1993). Mohamed (2001) demonstrated
the ability of both live and dry cells of Gloeothece magna, a nontoxic freshwater
cyanobacterium, for the adsorption of cadmium and manganese. Corder and Reeves
(1994) reported the accumulation of nickel by live Cylindrica, Anabaena flos-aquae,
and Nostoc sp. The toxicity and uptake of iron, zinc, and copper have been studied
for Oscillatoria perornata var. altenate and Scenedesmus quadricauda var.
longispina by Mittal et al. (1992).
Marine algae have also been found to adsorb heavy metals. Matheickal and Yu
(1999) presented the uptake properties of two biosorbents (DP95Ca and ER95 Ca)
that were developed by chemically modifying the marine algae Durvillaea
potatorum and Ecklonia radiata for the lead and copper. There are certain other
reports for feasibility of using cheaply available marine or freshwater algae for heavy
metal removal (Darnall et al. 1986; Holan et al. 1993). The binding of single metals
individually to the green alga, Chlorella vulgaris, and their dependence on pH, mass,
and time have been studied by Darnall et al. (1986) and Kubiak et al. (1989).
Removal of Cr
6+ by Halimeda tuna, Sargassum vulgare, Pterocladia capillacea,
Hypnea musciformis, and Laurencia papillosa has been studied with varying pH,
initial metal ion concentration, and agitation time, and maximum sorption capacities
of 2.3, 3.3, 6.6, 4.7, and 5.3 mg/g were observed, respectively (Baran et al. 2005).
Gupta et al. (2001) have studied the biosorption of chromium VI from aqueous
solution by a filamentous green algae Spirogyra sp. and found the maximum
removal of 14.7 X 10
3 mg metal/kg of dry weight biomass at a pH of 2.0.
398
S. Mona et al.