Bioremediation of Heavy Metals from Aquatic Environments 231
Figure 13.4. Mechanism of heavy metal removal by microalgae.
are alginate and cellulose. Its cell wall also provides various functional groups including imidazole,
phosphate, sulfonate, thiol, amino, carboxyl and hydroxyl. These functional groups can bind with
heavy metals (Priatni et al. 2017). They also contain a large amount of alcohol and carboxyl groups
that attract the cations and anions of heavy metals (Pradhan et al. 2019).
The spectroscopy including NMR (Nuclear Magnetic Resonance) and FTIR (Fourier transform
infrared) can be used to find out different functional groups of microalgae. Various methods can be
used for the adsorption of heavy metals on the outer surface of microalgae. These methods include
the ionic exchange of heavy metal ions with cell wall cation. The heavy metals are moved into the
cytoplasm by the process of diffusion (Ibuot et al. 2017, Pradhan et al. 2019).
Algal Bioremediation of a few metals
Arsenic (As) is a toxic heavy metal. Its pollution is caused by human activities including medical
use, smelting and mining (Arora et al. 2017, Singh et al. 2016). Microalgae are used to reduce the
pollution of arsenic by the complex formation with glutathione (Papry et al. 2019).
Cadmium (Cd) is poisonous heavy metal. It is released into the surroundings by human activities
including color pigments, tanning industries and pesticide use (Abinandan et al. 2019). The dead
microalgae can be used for bioremediation of Cd by surface binding mechanism.
Chromium (Cr) is used in ink, paint and dyes (Gupta and Rastogi 2008). Microalgae can be
used for the removal of chromium by using the mechanism of biosorption. Navicula pelliculosa and
Phaeodactylum tricornutum have been used for this purpose (Hedayatkhah et al. 2018).
13.3.4 Phytoremediation
The use of living plants to remove heavy metals and metalloids from water, soil and the air is called
phytoremediation. The types of phytoremediation are:
• Phytoextraction
• Phytostabilization