Bioaccumulation and Biosorption: The Prospects and Future Applications 59

Figure 4.1. Biological methods for removal of heavy metals.

metal removal requires metabolic activity, bioaccumulation occurs only when microbial cells are

alive. Biosorption is a technique that involves the utilization of dead biomass. Materials utilized in

biological processes to remove metals include wasted biomass and organisms found naturally in the

environment. This lowers the cost of biological approaches, making them more accessible to a wider

range of applications (Garg et al. 2012).

4.4 Biosorption

The removal of heavy metals using live microbes is complicated. Heavy metals have a harmful

influence on living organisms’ cells, which is the main issue. Advanced research, on the other hand,

revealed that dead cells could attach metal ions through a variety of physicochemical methods

(Gerber et al. 2018). Biosorption and biosorbents of various origins have received a lot of interest as

a result of this new finding. Several studies in this field have contributed to the spread of biosorption

knowledge (Hansda et al. 2016). As a result, the number of new potential applications has increased.

This process is known to be influenced not only by the kind and chemical composition of the

biomass but also by external physicochemical factors. The processes behind the biosorption process

have also been identified and elucidated. Many research centres across the world are working to

better understand biosorption (Hlihor et al. 2015). Furthermore, the potential of various biological

materials found in nature is being researched in order to improve their properties for heavy metal

removal, learn about binding mechanisms and develop the most effective biosorbents for the

removal of contaminants, including heavy metals (Ibuot et al. 2020). Metal ions (typically in the

form of cations) are bound by cell membranes in a physicochemical procedure termed biosorption,

i.e., by negatively charged substances present in cell membranes. Understanding the biosorption

mechanisms that allow heavy metals to be removed is critical for process optimization (Irshad

et al. 2021). During sorption, numerous distinct mechanisms take place. Due to the complexity of

biological materials, several mechanisms may occur at different rates simultaneously. The following

mechanisms are covered by biosorption:

• Ion exchange is a reversible chemical reaction that occurs on materials containing relevant

functional groups and involves exchanging mobile ions for other ions of the same charge.

• Heavy metal ions bind to the cell membrane with functional elements, resulting in complexation.

• Physical adsorption is triggered by van der Waals forces, which are intermolecular interactions.

There is no chemical bonding in the case of physisorption.

Heavy metals are bound by cells that have ceased to function metabolically, which is the major

benefit of biosorption. As feeding living biomass necessitates an additional source of nutrients and

energy, contaminants can be removed by dead organisms, simplifying and lowering the cost of the

process (Jin et al. 2020). In this process, cell membranes play a crucial role. Before accessing the cell

membrane and cytoplasm, all metal ions pass through the cell wall. As a cell wall’s structure is made

up of diverse polysaccharides and proteins, there are several active places for metal ion binding.

Like commercially available resins, a cell wall can be treated as a complicated ion exchanger (Joshi

et al. 2011). Different microbial cell wall compositions and intercellular changes have a major impact