12.2 Conventional Methods for Agri-Food Waste Treatment

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12.2

Conventional Methods for Agri-Food Waste

Treatment

Generally, the biological, chemical, and physical methods are used for the removal

of heavy metals. The conventional methods involved in removing the metal ions

are reverse osmosis, extraction of solvent, ion exchange, precipitation of chemical,

coagulation of chemical, membrane filtration, and adsorption from an aqueous

solution. Every technology has its disadvantages and advantages in the applica-

tion. Consequently, these traditional processes have certain limitations such as

the requirement of the high energy and reagent, toxic sludge/waste production,

and partial metal removal. If the concentration of the metal increases than the

permissible value (1 mg/l), then some of these approaches become uneconomical.

Microbial biomass nowadays becomes a sustainable option for developing

eco-friendly and cost-effective methods for the treatment of wastewater. For

removal and controlling the heavy metal pollution, much attention has been given

to biotechnological processes. The biosorption is an alternate method as it utilizes

different types of biological materials, for example, algae, bacteria, yeast, fungi,

etc. [2]. The capability of metal bioaccumulation via the uptake pathway from the

aqueous waste solution through biomaterials is regulated by physiochemical or

metabolically active processes, known as the biosorption. The absorbent binds with

heavy metals and separates them from the source. The biosorbents that have the

potential to absorb the metals include yeast, fungi, bacteria, and algae [5].

Biosorption has merits over conventional methods such as minimization of chem-

ical use, less expensive, highly efficient, and the possibility of biosorbent regenera-

tion. Both liquid and solid phases are involved in the process of biosorption along

with the sorbent species. The species of adsorbate adsorbent has a high affinity due to

which the latter is attracted and bounded using different ways. This process remains

continued to establish an equilibrium among the adsorbate species of solid bound

and their remaining substances in the solution. The distribution between the phases

of liquid and solid is determined by the adsorbent degree of affinity [4]. It can be

affected by the physicochemical properties and the bioavailability of the pollutant.

This process is passive, independent in metabolism between the physicochemical

interaction of microbial surfaces and heavy metal ions. The microorganism’s cell

wall contains several functional groups that provide the attraction forces to metal

ions and removes the pollutants with high efficiency [5]. It is a multistep process

that comprises four successive steps mentioned later [5]:

1. Solute transfer on the boundary liquid film

2. Solute transport to the particle surface

3. Transfer of solute to internal active binding sites

4. Solute interaction with binding sites

The biosorbent possesses various functional groups, namely, thioether, amide,

imine, carbonyl, phosphate, amine, sulfhydryl, imidazole, sulfonate, phenolic, and

phosphodiester groups, which sequesters and attracts the metal ions [8]. There are

several key factors to control or characterize the mechanism such as biosorbent