**8. Immobilization of biosorbent**

A major consideration for any biosorption is the separation of solid and liquid phases. Centrifugation and filtration are the routinely used techniques but not recommended at the industrial level. A continuous system with the biosorbent attached to a suitable bed is advantageous [149]. The use of free microbial cells as a biosorbent in continuous system is associated with many disadvantages such as the difficulty in separation of biomass, loss of biosorbent after regeneration, low strength, and little rigidity [150]. Microbial biomass can be immobilized by using a biopolymeric or polymeric matrix. The technique of immobilization is a key element that improves the performance of the biosorbent by increasing the capacity, improving mechanical strength and resistance to chemicals, and facilitating easy separation of biomass from a solution containing pollutants [151]. The process of immobilization is well suited for non-destructive recovery. Immobilization of the biosorbent into suitable particles can be done by using techniques like entrapment (in a strong but permeable matrix) or encapsulation (within a membrane-like structure) [152]. A number of matrices have been employed for immobilization including sodium or calcium alginate, polyacrylamide, silica, polysulfone, and polyurethane. It is very important to use a suitable immobilization matrix since it determines the mechanical strength and chemical resistance of the biosorbent particle targeted for biosorption while the matrix should be cheap and feasible to operate [153]. The use of an immobilized biosorbent is also associated with some disadvantages like increase in the cost of the biosorbent and an adverse effect on the mass transfer kinetics. This is because immobilization reduces the number of binding sites that are accessible to metal ions as majority of the sites are embedded within the bead [154]. The live and heat-inactivated *Trametes versicolor* immobilized within carboxyl methylcellulose (CMC) beads were efficient in the removal of Cu (II), Pb (II), and Zn (II) from the aqueous solution. The biosorption capacity were found to be 1.51 and 1.84 mmol, 0.85 and 1.11 mmol, and 1.33 and 1.67 mmol for Cu, Pb and Zn of both live and heat-inactivated biosorbents, respectively. The study shows the best fit with the Langmuir isotherm model [155]. **Table 9** gives the examples of various immobilization matrices used for the biosorption of metal ions.

**9. Desorption and the regeneration of biosorbents**

*Trametes versicolor* Cd (II) Langmuir

**Table 9.** Various immobilization matrixes used with biomass for biosorption of metals.

**Type of biosorbent Metal** 

Silica *Aspergillus niger* Cr, Cu, Zn,

*chrysosporium*

*pseudomonas maltophilia*

*Corynebacterium glutamicum*

Polyurethane *Phanerochaete* 

**biosorbed**

Pb (II), Cu (II), Cd(II)

Reactive yellow 2

Cd

**Isotherm model**

Redlichpeterson

Polyacrylamide *Pseudomonas sp* U Freundlich [160]

Calcium alginate *Bacillus cereus* Pb (II) Freundlich [162]

Sepiolite *Aspergillus niger* Fe (II, III) [164]

and Freundlich

*Phaseous vulgaris* Ni (II) Langmuir C–O, –C–S [157]

**Functional groups involved**

Application of Biosorption for Removal of Heavy Metals from Wastewater

Au Langmuir [161]

**Mechanism Reference**

http://dx.doi.org/10.5772/intechopen.77315

Chemisorption [159]

[156]

87

[158]

[163]

the following requirements [112]

• non-damaging to the biomass; and • ensure intact metal-binding capacity.

The possible eluents are dilute mineral acids (HCl, H<sup>2</sup>

• environment friendly;

• low cost;

**Immobilized matrix**

In order to keep the process costs down and for recovery of valuable metal ions after the biosorption, it is crucial for regeneration of the biosorbent [152]. The primary objective of desorption is to retain the adsorption capacity of the biosorbent. The process of desorption should be such that the metal can be recovered in the concentrated form (in case of metals of economic value), and the biosorbent needs be restored to the original state with undiminished biosorption capacity for reuse [8]. Hence an appropriate eluent for desorption should meet

acetic and lactic acids), and complexing agents (EDTA, thiosulphate, etc.) for the recovery of the biosorbent and metal recovery. Desorption efficiency can be determined by the S/L ratio, that is, solid to liquid ratio. The solid represents the biosorbent and liquid represents the eluent (volume) applied. For complete elution and to make the process economical, high S/L values are desirable [3]. Although, desorption is considered advantageous, in some instances,

SO<sup>4</sup>

and HNO<sup>3</sup>

), organic acids (citric,


**Table 9.** Various immobilization matrixes used with biomass for biosorption of metals.
