**5.3 The difference between the performance of the living and non-living microalgae in the absorption of heavy metals**

Although living microalgae have shown promising capabilities in the process of removing heavy metals from various types of wastewater, the ability to treat wastewater depends on their growth rate, biomass concentration, absorption capacity, and their use by various factors that affect their growth. The pH of wastewater, the concentration of heavy metals in wastewater, etc., is limited and can severely affect the efficiency of the treatment process. Therefore, non-living microalgae are more economical for industrial applications for the following reasons:


In general, there are few reports of the use of live algae because the life of algae is very much affected by environmental conditions. Absorption of heavy ions in living species is more complicated because absorption occurs in the growth phase and is intracellular. On the other hand, non-living algae absorb ions on their surface and it is considered an extracellular process that is easier to control and optimize.

A great advantage of non-living algae is the possibility of reusing biomass, which can be used in deionized water while living algae have little resistance to regeneration. Another advantage of non-living algae is the ease of use in physical and chemical modification and no need to add nutrients to the environment. Due to the growth of live algae, substances resulting from its metabolism may interfere with the absorption process. The only advantage of living algae is higher absorption power and absorption of a wide range of elements [12, 16].
