Generalities
32
Microalgae eliminate heavy metals with two mechanisms:
• Adsorption: A process by which heavy metal ions are attracted and bind to the surface
of microalgae cells, forming a complex. This mechanism is generally driven by
electrostatic forces. Heavy metals adsorbed on microalgae can be removed by physical
separation techniques such as filtration or centrifugation. (Lau et al., 1999).
• Uptake: A process by which heavy metals are stored inside microalgae cells. This
mechanism is driven by transporters or channels allowing heavy metal ions to enter the
cell. Once the heavy metals have been taken up by the microalgae, they can be removed
by harvesting the biomass (Yang et al., 2020).
The removal efficiencies of several metals by selected microalgae are listed in Table 9.
Table 9: Microalgal removal of metals from wastewater.
Metals
Strain
Operating Condition
Initial consentration pH
Temperature (°C)
Time (Hour)
(mg /L)
Removal
Efficiency
(%)
Reference
Cadmium
Chlorella vulgaris
5
6,2
25
24
66
(Travieso et
al.,1999)
Nickel
Scenedesmus sp.
30
6
-
5
97
(Chong et al.
,2000)
Zinc
Synechocystis sp
30
6
-
5
40
(Chong et
al.,2000)
Copper
Spirulina platensis
56,6
7,96
28
240
94,9
(Chan et al.,
2013)
1.2.2.1.4.3. Symbiotic Relationship
Microalgae could also participate in a symbiotic relationship with bacteria (Figure 15), to
degrade organic matter (Subashchandrabose et al., 2011).
As a by-product of the photosynthesis process, microalgae produce oxygen, which could be
used by aerobic bacteria to mineralize organic matter into carbon dioxide and supply it to
microalgae as well as growth-promoting factors and vitamins (B12, B1 and B7) that stimulate
microalgae growth, and the process would be repeated when finally treating wastewater
(Ramanan et al., 2015).
32
Microalgae eliminate heavy metals with two mechanisms:
• Adsorption: A process by which heavy metal ions are attracted and bind to the surface
of microalgae cells, forming a complex. This mechanism is generally driven by
electrostatic forces. Heavy metals adsorbed on microalgae can be removed by physical
separation techniques such as filtration or centrifugation. (Lau et al., 1999).
• Uptake: A process by which heavy metals are stored inside microalgae cells. This
mechanism is driven by transporters or channels allowing heavy metal ions to enter the
cell. Once the heavy metals have been taken up by the microalgae, they can be removed
by harvesting the biomass (Yang et al., 2020).
The removal efficiencies of several metals by selected microalgae are listed in Table 9.
Table 9: Microalgal removal of metals from wastewater.
Metals
Strain
Operating Condition
Initial consentration pH
Temperature (°C)
Time (Hour)
(mg /L)
Removal
Efficiency
(%)
Reference
Cadmium
Chlorella vulgaris
5
6,2
25
24
66
(Travieso et
al.,1999)
Nickel
Scenedesmus sp.
30
6
-
5
97
(Chong et al.
,2000)
Zinc
Synechocystis sp
30
6
-
5
40
(Chong et
al.,2000)
Copper
Spirulina platensis
56,6
7,96
28
240
94,9
(Chan et al.,
2013)
1.2.2.1.4.3. Symbiotic Relationship
Microalgae could also participate in a symbiotic relationship with bacteria (Figure 15), to
degrade organic matter (Subashchandrabose et al., 2011).
As a by-product of the photosynthesis process, microalgae produce oxygen, which could be
used by aerobic bacteria to mineralize organic matter into carbon dioxide and supply it to
microalgae as well as growth-promoting factors and vitamins (B12, B1 and B7) that stimulate
microalgae growth, and the process would be repeated when finally treating wastewater
(Ramanan et al., 2015).