**5.4 The functional potential of stabilized microalgae in the absorption of heavy metals**

The methods of flocculation, surface absorption, creating covalent bonds with carriers, transverse bands of algae, and trapping algae in a polymer network are among the methods of immobilization or stabilization of algae. Natural biopolymers such as agar and alginate or synthesized materials such as silica gel and polyacrylamide can be used as base materials. Natural polymers such as calcium alginate are widely used to create a stationary substrate for algae due to their non-toxicity. Among the synthetic polymers, polyacrylamide is the most used because it has good resistance and does not create a toxic environment, and is relatively cheaper [40].

Ashfaq Ahmad et al. studied the biosorption of Fe2+, Mg2+, and Zn2+ ions from aqueous solutions by free and stabilized *C. vulgaris* microalgae biomass on calcium alginate and the factors affecting this process in a laboratory manner. The results of their investigations showed that the biological absorption of all tested metal ions by cells fixed on calcium alginate is economical and with higher efficiency [41].
