28
A. A. Inyinbor et al.
solution phases; purification of impurities from the pharmaceutical and chemical
products; removal of metals in its ionic form from solution; purification of the process
effluent for the control of water pollution; removal of odor, taste, and color from
municipal water supplies and removal of impurities from oil, dry-cleaning solvents
[129–131]. Its simplicity and easy operations have given it much attraction [132].
On the basis of the types of the interface between the adsorbate and adsorbents,
it can be classified into physisorption and chemisorption. Physisorption involves
heterogeneous and reversible adsorption mechanism characterized by weak van der
Waal interphase physical forces, a non-specific multilayered process taking place
all over the adsorbent and it is dependent on the surface area, temperature pressure
and adsorbate nature with a lower energy of activation between 20 and 40 kJ mol
−1 .
Whereas chemisorption is a homogeneous and irreversible adsorption mechanism
characterized by strong chemical forces between adsorbate-adsorbent interphase,
monolayer in nature with high specificity process occurring at the center of the
adsorbent and high activation energy between 40–400 kJ mol
−1 . Chemisorption is
also influenced by the nature of the adsorbate, temperature, and surface area [133–
135]. Two major types of adsorption techniques are batch and dynamics (Column).
Patel [136] reported five types of adsorption techniques employed for contaminants
removal. The first is batch in nature and the remaining four are dynamics involving the
use of column. They are also generally referred to as continuous fixed bed, moving
bed, fluidized, and pulsed bed. Of all these five techniques, the most explored by
researchers based on ease of operation, cost effectiveness, efficiency and amount
of adsorbent used is batch technique [136]. There are seven generally operational
factors influencing adsorption, namely pH, concentration, contact time, temperature,
adsorbent dosage, stirring speed and ionic strength.
A number of researchers have worked on various categories of adsorbents classified as (i) natural adsorbents e.g., agro wastes, plant residues, biological adsorbents and other eco-friendly materials used directly with modification (ii) synthetic
adsorbents, such as porous materials like nanomaterials, metal-organic frameworks
(MOFs), and other artificial adsorbents that are polymeric in nature, (iii) semisynthetic adsorbents: these are prepared by modification of natural adsorbents and
incorporation of functional materials to enhance their performances [137, 138].
Adsorption is found very effective for the removal of categories of pollutants,
such as heavy metals, dyes, pharmaceuticals and other organic pollutants [139–144].
The expensive commercial activated carbon has however made adsorption techniques
economically unfriendly. Focus on economically friendly adsorbents as an alternative
to commercial activated carbon has been explored in recent times [145–151].
7 Conventional Wastewater Treatment Processes
Many wastewater treatments basically use a combination of biological, chemical,
and physical, processes. In addition, the removal of solid wastes, such as inorganic and organic solids and sometimes essential element from wastewater may
A. A. Inyinbor et al.
solution phases; purification of impurities from the pharmaceutical and chemical
products; removal of metals in its ionic form from solution; purification of the process
effluent for the control of water pollution; removal of odor, taste, and color from
municipal water supplies and removal of impurities from oil, dry-cleaning solvents
[129–131]. Its simplicity and easy operations have given it much attraction [132].
On the basis of the types of the interface between the adsorbate and adsorbents,
it can be classified into physisorption and chemisorption. Physisorption involves
heterogeneous and reversible adsorption mechanism characterized by weak van der
Waal interphase physical forces, a non-specific multilayered process taking place
all over the adsorbent and it is dependent on the surface area, temperature pressure
and adsorbate nature with a lower energy of activation between 20 and 40 kJ mol
−1 .
Whereas chemisorption is a homogeneous and irreversible adsorption mechanism
characterized by strong chemical forces between adsorbate-adsorbent interphase,
monolayer in nature with high specificity process occurring at the center of the
adsorbent and high activation energy between 40–400 kJ mol
−1 . Chemisorption is
also influenced by the nature of the adsorbate, temperature, and surface area [133–
135]. Two major types of adsorption techniques are batch and dynamics (Column).
Patel [136] reported five types of adsorption techniques employed for contaminants
removal. The first is batch in nature and the remaining four are dynamics involving the
use of column. They are also generally referred to as continuous fixed bed, moving
bed, fluidized, and pulsed bed. Of all these five techniques, the most explored by
researchers based on ease of operation, cost effectiveness, efficiency and amount
of adsorbent used is batch technique [136]. There are seven generally operational
factors influencing adsorption, namely pH, concentration, contact time, temperature,
adsorbent dosage, stirring speed and ionic strength.
A number of researchers have worked on various categories of adsorbents classified as (i) natural adsorbents e.g., agro wastes, plant residues, biological adsorbents and other eco-friendly materials used directly with modification (ii) synthetic
adsorbents, such as porous materials like nanomaterials, metal-organic frameworks
(MOFs), and other artificial adsorbents that are polymeric in nature, (iii) semisynthetic adsorbents: these are prepared by modification of natural adsorbents and
incorporation of functional materials to enhance their performances [137, 138].
Adsorption is found very effective for the removal of categories of pollutants,
such as heavy metals, dyes, pharmaceuticals and other organic pollutants [139–144].
The expensive commercial activated carbon has however made adsorption techniques
economically unfriendly. Focus on economically friendly adsorbents as an alternative
to commercial activated carbon has been explored in recent times [145–151].
7 Conventional Wastewater Treatment Processes
Many wastewater treatments basically use a combination of biological, chemical,
and physical, processes. In addition, the removal of solid wastes, such as inorganic and organic solids and sometimes essential element from wastewater may