13.9 Biosorption of Metal-Complexed Dyes

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wall acts as a primary source for the removal of dyes. The fungal cell wall consists

of a huge amount of chitin and chitosan in addition to proteins, amino acids,

and lipids which has the functional groups of carboxylic and amine groups. But

the biosorption capacity of the cell wall reduces due to the presence of different

ionizable sites such as carboxy and phosphate present in the glucosamine. The ionic

strength of the solution affects directly the surface charge of the biomass as well

as the solubility of the dyes. The surface charge of the biomass can be evaluated

by measuring the zeta potential or isoelectric point to pH. The surface charge of

the ligands present on the cell wall becomes negative due to the deprotonation of

carboxyl, phosphate, and the amine groups or positive due to imidazole at lower

pH. These functional groups are responsible for the attachment of dyes on the

microbial surface. At lower pH, the positively charged functional groups will attract

the negatively charged MCDs due to the electrostatic interaction between the

ligands and dyes [37]. The biosorption of Yellow RL adsorbed on the cell surface

at the pH 2 is due to the presence of positively charged molecules. But the textile

and tanning industrial dyes contain both salt and dyes. The salt concentration in

the effluent directly changes the ionic strength and pH of the solution, and also it

resists the equilibrium uptake of dyes in the biosorption process. It [3] was observed

that the impact of ionic strength on the biosorption process is enhanced by the

ion exchange mechanism at acidic pH conditions. The higher ionic strength or pH

of the solution is favorable for the removal of dyes which is very stable or highly

solubilized at higher pH conditions. But there is a possibility of denaturation of

biosorbents. Muthezhilan et al. [38] isolated strains of Rhizopus, Mucor, Aspergillus,

Cladosporium, Fusarium, Penicillium, and Trichoderma from dye-containing indus-

trial effluents. The other isolated microbial species are Aspergillus flavus, Fusarium

oxysporum, Fusarium moniliforme, and Trichoderma from the soil samples around

the textile industries of Nanjanjud, Karnataka (India). They analyzed soil samples

from different textile dye industries in Mangalagiri. Mucor mucedo was found to

be predominant. Additionally, 13 terrestrial strains of fungi for the decolorization

and degradation of dyes in the soil were taken. They concluded that effective dye

degraders for the remediation of the environment contaminated with recalcitrant

dyes can be obtained from soils. The biosorption of chromium-complexed metal

dyes using Pseudomonas strains was carried out. The study was carried out using

the native and heat-treated Pseudomonas strain DY1. The results clearly showed

that the thermally modified bacteria displayed a significant adsorption capacity of

about 2.98 mmol/g of biomass which is 20-fold higher than the adsorption capacity

of live cells. Moreover, the adsorption capacity of the live and thermally modified

P. putida DTZ did not improved at the temperature of 4 and 30 ^∘C. The percentage of

biosorption significantly increased between 30 and 100 ^∘C [39]. Akar et al. observed

that the maximum amount of Acid Black 172 absorbed by the cones of macro-fungi,

Agaricus bisporus, and Thuja orientalis was around 0.18 mmol/g of biomass.

Moreover, the interaction efficacy of sawdust was analyzed by varying different

parameters such as pH, particle size, contact time, and initial metal concentration.

The amount of metal complex interacted on the sawdust increases with the increase

in the surface to volume ratio of the particles. The maximum amount of metal