2.2 Chemical Characteristics
The surface of the biosorbents consists of functional groups such as amino, carboxyl,
amide, carboxylate, thio-ether, thiols, sulphhydryl, imidazole, phenolic, phosphate
and hydroxide from the biomolecules on the cell wall. These functional groups react
with the pollutant and form covalent bond with them thus adsorbing them on the
surface of the biosorbents.
Polyelectrolytic components of algal cell walls consist of peptidoglycan and
teichuronic acid have specific charged groups with them. The pollutants in the
aqueous solution will have ionic interaction with these charged groups and adsorb
onto the cell surface [5].
3 Processing of Biosorbents
Pre-treatment of biomass to be used as adsorbents can involve physical treatments
like grinding and chemical treatments such as alkali treatment, acid treatment,
detergent treatment and treatment by organic solvents. These treatments increase
the pore size, making functional groups available for adsorption.
When biomass is used as biosorbent, the cells are collected, dried and powdered
and used as such. When live cells are used for biosorption, they can be used as such
or can be immobilized on solid surfaces. This helps in creating adsorbent with
properties necessary for the unit operations.
Burning of waste material in high temperatures decreases the oxygen and hydrogen contents and decreases the H/C and O/C ratio of the biochar. This increases the
capacity of adsorption of aqueous contaminants. Also increasing temperatures leads
to the increase in the surface area of the biochar [7]. Carbonized biomaterials by
heating them in a furnace (up to 600
C) in the presence of nitrogen can also be used
as biosorbents. This leads to the enrichment of carbon by decreasing the oxygen and
nitrogen composition. Carbonization is also effective in opening the pores as a result
of elimination of oxygen and nitrogen, thus increasing the surface area of the
adsorbent [14].
Fe 3 O 4 nanoparticles are incorporated into biosorbents to produce magnetic
biosorbents which can help in the easier phase separation process. Chelating groups
such as ethylenediaminetetraacetic acid (EDTA), diethylenetriamine (DETA),
polyamidoamine (PAMAM) and diglycolic amic acid (DGAA) offer strong binding
sites for metal ions when incorporated into the biosorbents by chemical
processes [19].
Different biosorbents used in water treatment and their pre-treatments are listed in
Table 1.
Another most important pre-treatment in the processing of biosorbents is the
immobilization of biosorbents. Also, immobilization of biosorbents has an advantage of increasing the reusability of biosorbent. Immobilization is done by mixing
the biosorbents with alginate or agar and forming small beads with them.
246
K. J. Samuel P N et al.
The surface of the biosorbents consists of functional groups such as amino, carboxyl,
amide, carboxylate, thio-ether, thiols, sulphhydryl, imidazole, phenolic, phosphate
and hydroxide from the biomolecules on the cell wall. These functional groups react
with the pollutant and form covalent bond with them thus adsorbing them on the
surface of the biosorbents.
Polyelectrolytic components of algal cell walls consist of peptidoglycan and
teichuronic acid have specific charged groups with them. The pollutants in the
aqueous solution will have ionic interaction with these charged groups and adsorb
onto the cell surface [5].
3 Processing of Biosorbents
Pre-treatment of biomass to be used as adsorbents can involve physical treatments
like grinding and chemical treatments such as alkali treatment, acid treatment,
detergent treatment and treatment by organic solvents. These treatments increase
the pore size, making functional groups available for adsorption.
When biomass is used as biosorbent, the cells are collected, dried and powdered
and used as such. When live cells are used for biosorption, they can be used as such
or can be immobilized on solid surfaces. This helps in creating adsorbent with
properties necessary for the unit operations.
Burning of waste material in high temperatures decreases the oxygen and hydrogen contents and decreases the H/C and O/C ratio of the biochar. This increases the
capacity of adsorption of aqueous contaminants. Also increasing temperatures leads
to the increase in the surface area of the biochar [7]. Carbonized biomaterials by
heating them in a furnace (up to 600
C) in the presence of nitrogen can also be used
as biosorbents. This leads to the enrichment of carbon by decreasing the oxygen and
nitrogen composition. Carbonization is also effective in opening the pores as a result
of elimination of oxygen and nitrogen, thus increasing the surface area of the
adsorbent [14].
Fe 3 O 4 nanoparticles are incorporated into biosorbents to produce magnetic
biosorbents which can help in the easier phase separation process. Chelating groups
such as ethylenediaminetetraacetic acid (EDTA), diethylenetriamine (DETA),
polyamidoamine (PAMAM) and diglycolic amic acid (DGAA) offer strong binding
sites for metal ions when incorporated into the biosorbents by chemical
processes [19].
Different biosorbents used in water treatment and their pre-treatments are listed in
Table 1.
Another most important pre-treatment in the processing of biosorbents is the
immobilization of biosorbents. Also, immobilization of biosorbents has an advantage of increasing the reusability of biosorbent. Immobilization is done by mixing
the biosorbents with alginate or agar and forming small beads with them.
246
K. J. Samuel P N et al.