The Use of Cyanobacteria in Removing Heavy Metals In recent years, the ability
of MOs to accumulate and remove HMs in water has been tested. These processes
can be classified as active, metabolic processes or passive, nonmetabolic processes.
In active processes, adsorption, called bioaccumulation, is due to metal transport
through the cell membrane, followed by intracellular accumulation depending on
cellular metabolism.
In physicochemical interactions between the metal and the functional groups
present on the cell surface (based on physical adsorption, ion exchange, and complexation), the sorption process does not depend on metabolism. The cell wall,
composed of polysaccharides, proteins, and lipids, can provide sites for metal
bonding. Cyanobacteria have a cell wall that allows the passive adsorption of large
quantities of dissolved metals. On the surface of the cell wall, there are in fact
functional groups, such as carboxylate, hydroxyl, sulfate, phosphate, or amino
groups.
Metallic cations can be taken from the environment by the following:
Negatively charged groups on the cell wall, with the negative charge present on the
polysaccharide layers surrounding the cell wall or the negative charges of
polysaccharides released into the environment (water)
Interaction of metal cations with negative charges on the cell surface
Interaction of metal cations with negative charges on exocellular polysaccharide
layers
Interaction of metal cations with negative polysaccharide releases released into the
environment (water).
A large number of types of cyanobacteria have been tested in connection with their
ability to remove HMs (especially Cd, Hg, Ni, Zn, or Pb) from metallic solutions
(Garlapati et al. 2019).
For example, Tolypothrix tenuis and Calothrix parietina have removed high
amounts of Hg; Scytonema schmidlei, Anabaena cylindrica, and A. torulosa have
removed 96–98% from Cd found in a solution of Cd with concentration 1 mg/L.;
Gloeocapsa sp., Nostoc paludosum, N. piscinale, N. punctiforme, N. commune,
Oscillatoria agardhii, Phormidium molle, and Tolypothrix have removed 90–96%
Pb from a Pb solution with concentration 1 mg/L. The metal bonding process takes
place by complexing the metal ions with the polysaccharide, mucilaginous material
that covers the cell wall or is released from the cell surface.
The Ecological and Economic Efficiency of the Method As a result of numerous
studies on various cyanobacteria used to remove HMs from aqueous solutions,
promising results have been obtained with regard to the use of the tested species.
However, this type of biomass is far from being used on an industrial scale in the
treatment of HMs contaminated waste for two reasons: the biomass production costs,
which are still too high for industrial applications, and the lack of sufficient research
into the use of cyanobacteria to achieve some industrial lines that lead to the removal
of metals by means of these.
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of MOs to accumulate and remove HMs in water has been tested. These processes
can be classified as active, metabolic processes or passive, nonmetabolic processes.
In active processes, adsorption, called bioaccumulation, is due to metal transport
through the cell membrane, followed by intracellular accumulation depending on
cellular metabolism.
In physicochemical interactions between the metal and the functional groups
present on the cell surface (based on physical adsorption, ion exchange, and complexation), the sorption process does not depend on metabolism. The cell wall,
composed of polysaccharides, proteins, and lipids, can provide sites for metal
bonding. Cyanobacteria have a cell wall that allows the passive adsorption of large
quantities of dissolved metals. On the surface of the cell wall, there are in fact
functional groups, such as carboxylate, hydroxyl, sulfate, phosphate, or amino
groups.
Metallic cations can be taken from the environment by the following:
Negatively charged groups on the cell wall, with the negative charge present on the
polysaccharide layers surrounding the cell wall or the negative charges of
polysaccharides released into the environment (water)
Interaction of metal cations with negative charges on the cell surface
Interaction of metal cations with negative charges on exocellular polysaccharide
layers
Interaction of metal cations with negative polysaccharide releases released into the
environment (water).
A large number of types of cyanobacteria have been tested in connection with their
ability to remove HMs (especially Cd, Hg, Ni, Zn, or Pb) from metallic solutions
(Garlapati et al. 2019).
For example, Tolypothrix tenuis and Calothrix parietina have removed high
amounts of Hg; Scytonema schmidlei, Anabaena cylindrica, and A. torulosa have
removed 96–98% from Cd found in a solution of Cd with concentration 1 mg/L.;
Gloeocapsa sp., Nostoc paludosum, N. piscinale, N. punctiforme, N. commune,
Oscillatoria agardhii, Phormidium molle, and Tolypothrix have removed 90–96%
Pb from a Pb solution with concentration 1 mg/L. The metal bonding process takes
place by complexing the metal ions with the polysaccharide, mucilaginous material
that covers the cell wall or is released from the cell surface.
The Ecological and Economic Efficiency of the Method As a result of numerous
studies on various cyanobacteria used to remove HMs from aqueous solutions,
promising results have been obtained with regard to the use of the tested species.
However, this type of biomass is far from being used on an industrial scale in the
treatment of HMs contaminated waste for two reasons: the biomass production costs,
which are still too high for industrial applications, and the lack of sufficient research
into the use of cyanobacteria to achieve some industrial lines that lead to the removal
of metals by means of these.
108
M. Butu et al.