4.9.1 Removing Heavy Metals From Polluted and Leached Soils
Contaminated with the Help of Cyanobacteria
Of the 35 metals considered dangerous for human health, 23 have been classified as
HMs: Ag, As, Au, Bi, Cd, Ce, Co, Cr, Cu, Fe, Ga, Hg, Mn, Ni, Pb, Pt, Sb, Sn, Te,
Tl, U, V, and Zn. The most dangerous substances for health are Pb, Cd, Hg, and As.
Exposure to high concentrations of these metals can lead to poisoning, with
severe effects on the nervous system or on internal organs, such as the lungs, liver,
kidneys, and others. In recent years, many techniques have been developed to
remove HMs from wastewater in order to reduce the amount of metal-containing
wastewater resulting from industrial activities and to improve the quality of
effluents.
Numerous treatments, such as chemical precipitation, coagulation–flocculation,
flotation, ion exchange, or membrane filtration, can be used to remove HMs from
contaminated wastewater, each method having certain advantages and limitations. A
way to remove HMs by using cyanobacterial microorganisms is particularly wellresearched.
Use of Microorganisms for Removing Heavy Metals Biosorption is the property
of nontoxic microbial biomass to accumulate heavy metal ions, a metabolically
unsustainable process. In contrast, the term bioaccumulation describes an active
process in which HMs are removed by metabolic activity of living organisms. In
recent years, research has focused on biosorption mechanisms because biomass can
be successfully used to remove HMs from industrial effluents as well as to recover
precious metals from processing solutions (Thakare et al. 2021).
Microbial cells are excellent biosorbents due to their high surface area/volume
ratio due to a large number of potentially active chemosorption sites. Researches in
the field of heavy metal biosorption have led to the identification of several types of
microbial biomass efficient in the concentration of these metals.
Some types of biomass are waste resulting from industrial fermentation (e.g.,
Bacillus subtilis bacteria). Other types of microbes that can bind metals can be
harvested from specific environments such as lakes or seas (certain types of
cyanobacteria). They can accumulate considerable amounts of HMs, such as Cd,
Cr, Cu, Pb, U, Zn, or others (Pan et al. 2017).
General Characteristics of Cyanobacteria Cyanobacteria represent a large group
of Gram-negative bacteria, phototrophic prokaryotes characterized by the ability to
achieve photosynthesis in the presence of oxygen and autotrophy as the main source
of nutrition. It has been observed that certain cyanobacteria can grow in the dark on
some organic substrates or under anaerobic conditions, performing photosynthesis in
the absence of oxygen, using sulfides as electron donors. This trophic independence,
along with the ease of their cultivation, recommends cyanobacteria in decontamination processes.
4 Advanced Technologies for Ecological Reconstruction and Bioremediation of. . .
107
Contaminated with the Help of Cyanobacteria
Of the 35 metals considered dangerous for human health, 23 have been classified as
HMs: Ag, As, Au, Bi, Cd, Ce, Co, Cr, Cu, Fe, Ga, Hg, Mn, Ni, Pb, Pt, Sb, Sn, Te,
Tl, U, V, and Zn. The most dangerous substances for health are Pb, Cd, Hg, and As.
Exposure to high concentrations of these metals can lead to poisoning, with
severe effects on the nervous system or on internal organs, such as the lungs, liver,
kidneys, and others. In recent years, many techniques have been developed to
remove HMs from wastewater in order to reduce the amount of metal-containing
wastewater resulting from industrial activities and to improve the quality of
effluents.
Numerous treatments, such as chemical precipitation, coagulation–flocculation,
flotation, ion exchange, or membrane filtration, can be used to remove HMs from
contaminated wastewater, each method having certain advantages and limitations. A
way to remove HMs by using cyanobacterial microorganisms is particularly wellresearched.
Use of Microorganisms for Removing Heavy Metals Biosorption is the property
of nontoxic microbial biomass to accumulate heavy metal ions, a metabolically
unsustainable process. In contrast, the term bioaccumulation describes an active
process in which HMs are removed by metabolic activity of living organisms. In
recent years, research has focused on biosorption mechanisms because biomass can
be successfully used to remove HMs from industrial effluents as well as to recover
precious metals from processing solutions (Thakare et al. 2021).
Microbial cells are excellent biosorbents due to their high surface area/volume
ratio due to a large number of potentially active chemosorption sites. Researches in
the field of heavy metal biosorption have led to the identification of several types of
microbial biomass efficient in the concentration of these metals.
Some types of biomass are waste resulting from industrial fermentation (e.g.,
Bacillus subtilis bacteria). Other types of microbes that can bind metals can be
harvested from specific environments such as lakes or seas (certain types of
cyanobacteria). They can accumulate considerable amounts of HMs, such as Cd,
Cr, Cu, Pb, U, Zn, or others (Pan et al. 2017).
General Characteristics of Cyanobacteria Cyanobacteria represent a large group
of Gram-negative bacteria, phototrophic prokaryotes characterized by the ability to
achieve photosynthesis in the presence of oxygen and autotrophy as the main source
of nutrition. It has been observed that certain cyanobacteria can grow in the dark on
some organic substrates or under anaerobic conditions, performing photosynthesis in
the absence of oxygen, using sulfides as electron donors. This trophic independence,
along with the ease of their cultivation, recommends cyanobacteria in decontamination processes.
4 Advanced Technologies for Ecological Reconstruction and Bioremediation of. . .
107