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Bioremediation for Sustainable Environmental Cleanup

Biomineralization,

sulfite,

Figure 13.3. Metals and fungal interactions in bioremediation.

13.3.3 Algal Bioremediation

Microorganisms such as fungi, yeast, bacteria and microalgae can be used for the bioremediation

of metals. Microalgae have been widely used due to their various properties viz. simple structure

and high photosynthetic capacity. Microalgae can grow well in any given environment. Microalgae

can be used in the phycoremediation of poisonous heavy metals (Cameron et al. 2018). The dead

and living cells of microalgae can be used as biosorbents which is an eco-friendly process. The

microalgae can be used for the recovery of gold and silver (Birungi and Chirwa 2015, Jaafari and

Yaghmaeian 2019).

Mechanisms of Heavy Metal Removal by Microalgae

Heavy metals including manganese (Mn), zinc (Zn), Boron (B), Cobalt (Co), copper (Cu), iron (Fe)

and Molybdenum (Mo) can be used by microalgae. These can be consumed for cell and enzymatic

metabolism (Figure 13.4). Metals like lead, chromium, cadmium and arsenic are poisonous to

microalgae. Some cyanobacteria including Phormidium, Spirogyra, Anabaena and Oscillatoria can

grow in environments where heavy metals are present. These species have a tolerance ability to

metals stress (Balaji et al. 2016).

Microalgae have adopted different techniques for their protection from heavy metals toxicity

including gene regulation, exclusion, chelation and immobilization (Gómez-Jacinto et al. 2015).

They can form complexes of heavy metals and proteins without altering their activity (Priatni et al.

2017).

The elimination of heavy metals by using microalgae is acquired by two processes. Biosorption

(extracellular passive adsorption) is the first stage and bioaccumulation (intracellular positive

diffusion and accumulation) is the second stage. The first stage is rapid while the second stage is

slow. The microalgae cell wall contains lipids, proteins and polysaccharides. The polysaccharides