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13 Biosorption of Heavy Metals and Metal-Complexed Dyes Under the Influence

the biosorbents will get attached with hydronium ion, thereby shielding the metal

ions from adsorbing onto the biomass [12].

13.4

Chemistry of Metal-Complexed Dyes

The MCDs and acid dyes comprise of chelating active sites for the coordination of

metal ions along with the dyes, and these dyes are particularly used for the col-

oration of wool, silk, and nylon. These complex dyes are classified into two different

kinds such as mordant and premetallized dyes. Generally, the metal-complexed dyes

are having less solubility in the water system. The solubility of metal complexes

decreases to twofold than the mono-azo-type dyes which are chelated before with the

metal ions by carboxyl, hydroxyl, and amine functional groups. In case of divalent

Cu²⁺ ions, it has a coordination number of 4 and it can complex with two bidentate

ligands in the acid dye. Hannemann [13] stated that the major metals such as Cu²⁺,

Co²⁺, Ni²⁺, and Cr³⁺ used for the complexation of acid dyes. These 1 : 1 complexed

premetallized dyes are the source for the moderate dye used for wool and silk fibers.

In the dying process, the acidic MCDs should be maintained between the pH 2.7 and

4 which helps to increase the rate of dying. At the same time, the fastness property

on nylon 6,6 has improved by 1 : 2 MCDs.

13.5

Microbial Species Used for the Removal of Metals

and Metal-Complexed Dyes

Biosorption is a process mainly used for detoxifying the heavy metals and metal acid

dye solutions using bacteria, algae, and fungi. Different types of microorganisms play

an important role in the elimination of toxic metallics and dye contaminants by dif-

ferent mechanisms. The microbial consortium used for the removal of metal and

metal-complexed dyes is discussed in Sections 13.7–13.9.

13.5.1

Biosorption of Zinc Using Bacteria

There are various bacterial species having different capability of accumulating

metal ions present in aqueous solutions. Bacillus species have been identified

as the most potential bacterial species for metal sequestration and thus used in

commercial biosorbent applications [14]. The sulfate-reducing bacteria, Desulfo-

tomaculum nigrificans, was used to bioremediate higher concentration of zinc that

resulted in achieving maximum percentage of biosorption (60–70%) [15]. Certain

bacterial species such as Klebsiella oxytoca (P2), Pseudomonas veronii (2E), Ralstonia

taiwanensis (M2), Klebsiella ornithinolytica (1P), and Delftia acidovorans have the

capability to remediate heavy metals such as zinc, copper, and cadmium by different

processes such as biosorption, bioaccumulation, and bioprecipitation. Chen et al.

[16] studied the metal uptake by both live cell and nonliving Pseudomonas putida

CZ1 bacterial cells. The adsorption capacity of live P. putida CZ1 was found to be