12.6 Modification, Parameter Optimization, and Recovery

181

The complex interactions between the interfaces of liquid, solid, and air result in

the hydrophobicity [15]. During the study of the pH range, the zeta potential value

gradually decreases negatively. The pH value of fungal biomass and Streptomyces was

determined to be around three and zero, respectively, whereas, for yeast, it happened

at a low value of pH. It was observed that the zeta potential changes its value toward

less negative in the presence of surfactant, i.e. flotation collector and metals. The

neutralization of surface charge and reversal to positive value was also perceived

after the addition of the cationic polyelectrolyte [12].

The biosorption fixed-bed column process model is similar to the normal adsorp-

tion [14]. At the mines of the US Bureau, similar work was carried out with the

biomass of sphagnum peat. The separation at the solid or liquid stage was found to

be difficult during biosorption, and the possible reason for this might be due to the

low biomass mechanical resistance and stability [9].

12.6.1

Modification

The application of the agriculture waste as biosorbents needs modifications as

they cause the increment in the chemical oxygen demand and biochemical oxygen

demand due to the organic soluble compounds release from the waste of plants. It

leads to oxygen depletion in the water. The additive selection plays a vital role in the

adsorbent modification to ensure the best usability and good efficiency. This can

be enhanced by improving chemical and physical modalities. The adsorbent size

comes under physical modification which can be achieved by grinding or chopping,

freeze-drying, thermal treatment, stirring, and ultrasonic irradiation. The adsorbent

of small size provides the high surface area, which is suitable for the batch process

as compared to the column process of adsorption as it causes the clogging of the

column. The biosorbent’s physical structure might be damaged due to a high

temperature, but heating increases the efficiency of biosorption by increasing the

adsorbate kinetic energy and surface activity. By decreasing the resistance of mass

transfer of the pollutant, the agitation process can enhance the biosorption process.

Whereas chemical modifications in different types of chemicals including salicylic

acid, sodium hydroxide, methanol, carbon tetrachloride, hydrochloric acid, sodium

chloride, sodium carbonate, calcium chloride, phosphoric acid, epichlorohydrin,

ammonium hydroxide, citric acid, nitric acid, tartaric acid, acetone, toluene, forma-

lin, ethylenediaminetetraacetic acid (EDTA), iso-butanol, benzene, formaldehyde,

etc. include the adsorbents, chemical treatment for washing, co-polymerization of

graft enhances the binding group and eliminates the inhibition groups [7, 12] The

binding group enhancement includes the addition of ester group saponification,

hydroxyl group amination, phosphorylation, thiolation, oxidation, amine group

carboxylation, halogenation, xanthanation, and sulfonation. The inhibition group

removal is achieved by deamination and decarboxylation, while polymerization

of graft involves grafting by chemical initiation, photochemical, and high energy

radiation. Hence, it is recommended for having surface modification before using

the low-cost agri-waste-derived adsorbents.