180

12 Microbes and Agri-Food Waste as Novel Sources of Biosorbents

Electrostatic interaction

Zn

Zn

HPO4

2–

Mg²⁺

Co²⁺

Cu²⁺

BH

B-Cu + H⁺

EPS + Cd²⁺

EPS-Cd

Mg-org

NiHPO4

Ion exchange

Active transport

Metal precipitation

Cell surface interaction

Intercellular interaction

Extracellular interaction

Complexation

Metal binding protein

Figure 12.1

Schematic representation of the different mechanisms of microbial (bacterial)

biosorption. Source: Based on Demirbas [12].

proved to be a promising candidate for the exclusion of methylene blue and mala-

chite green dyes. Leaves powder demonstrated more biosorption than stem powder,

and coarse exterior and functional groups made the potato wastes a better asset for

the biosorption [12].

12.6

Modification, Parameter Optimization,

and Recovery

The availability and number of the functional groups are mainly responsible for

the biosorption potential of biosorbents. These can be modified by changing their

surface characteristics through certain processes. Microbial-derived biosorbents

are responsive for modification to increase the available binding sites and enhance

the biosorption capacity leaving low residual metal concentration. Several methods

have been employed for surface modification of microbial biomass. Some param-

eters were studied on the kinetic model and isotherm of biosorption, which can

affect the selectivity [13]. It could be accomplished by using a molecular technique

in the synthesis known as molecular imprinting. Numerous parameters can affect

the microbes’ hydrophobicity. Some of these parameters are contact angle, surface

tension, and electrokinetics and have been studied for the toxic metals’ removal

from aqueous medium [14]. Also, the hydrophobicity and floatability were interre-

lated, and these physicochemical parameters were confirmed with the laboratory

measurements.