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

12.6.2

Parameters

The decayable wastes produced from the waste/used/overripe vegetables and fruits

in the type of shells, epicarps, seeds, cobs, coats, peels, trimmings, stones, bagasse,

etc. were having different adsorption potentials. The capacity of adsorption of dyes

and metals via these agriculture wastes varies by various factors such as the host,

adsorbent structural characters, adsorbate initial concentration, modification in the

surface, size of the adsorbent particle, solution pH, temperature, dosage of the adsor-

bent, and concentration of the pollutant. The adsorbents of the small size represent

the high affinity for the removal of metal. The ionization degree and the density

of surface charge get affected by the pH of the solution because of the competition

between metal and hydrogen ions for binding to sites. Thus, along with sorbent treat-

ment measures, optimization is also important.

12.6.3

Recovery

Through chemical and physical treatment, recovery can be achieved of loaded dyes

and metals. Physical treatment can be done in two ways, i.e. heating and microwav-

ing. The chemical processes use the organic solvent, alkali, and acid. Generally, vari-

ous chemicals are being used for the desorption process; some are sodium hydroxide,

potassium hydroxide, sulfuric acid, hydrochloric acid, sodium nitrate, nitric acid,

EDTA, etc. Some metals have been recovered in traces amount such as cupric ion,

chromium ion, cadmium(II) ion, and nickel(II) ion after optimizing the parameters

and protocol. By using the improved method of striping, which involves the treat-

ment of alkali, gold can be recovered from biosorbents [13]. After metal elution,

adsorbent regeneration is cheaper and easier because of the presence of numerous

carboxyl and hydroxyl groups on the adsorbent surface.

12.7

Immobilization of Biosorbent

For the biosorption process, the liquid- and solid-phase separation step is an impor-

tant consideration. The commonly used techniques used in the separation are filtra-

tion and centrifugation, but at the industrial level, these methods are not suggested.

The suitable bed attached to biosorbent is referred to as a continuous system that is

advantageous [19]. In this system, using biosorbents as free microbial cells causes

many disadvantages, for example, biosorbent loss after regeneration, low rigidity

and strength, and difficulty in biomass separation [14]. By using the polymeric/

biopolymeric matrix, immobilization of microbial biomass can be done. It is a key

element that enhances the biosorbent performance after improving the capacity and

mechanical resistant and facilitates biomass separation from pollutants [15]. For the