Part D | 24.5
606 Part D Marine Algal Biotechnology
24.4 Biosorption Experiments: Procedure
24.4.1 Biosorption: Kinetic Curves
The kinetic curves of adsorption describe the time evolution of the concentration of metal in solution, in the
presence of the adsorbent biomaterial. A stock solution
containing a known amount of metal salts is prepared
to test the ability of the adsorbent macrophytes. Dried
biomass of the macrophytesis is suitably fragmented
to increase the adsorbing surface area and is placed
in a beaker with deionized water. The pH of the solution is adjusted using solutions of NaOH and HCl (in
general, 0:1 M) according to the experimental plan followed. Indeed, pH check control is important to avoid
metal precipitation in solution. Subsequently, a stock
solution with metals is added according to experimental
conditions. Aliquot amounts of solution are then periodically sampled to determine the concentration of metal.
In general, the kinetic curves are set for investigation of
different pH values.
24.4.2 The Langmuir Adsorption Isotherm
The equilibrium isotherms represent the concentration
of the metal on the solid (q, mg=g) as a function of
the respective concentration in solution at equilibrium
(C eq , mg=L). The determination of isotherms is essential to define the capacity of the adsorption of metal ions
by the adsorbent material, such as dried macrophytes.
For the determination of curves, a known amount of
dried and fragmented biomass is added to a solution
of deionized water with varying concentrations of metals established from the experimental plan. The pH of
the solutions is adjusted to predetermined values with
solutions of NaOH (general 0:1 M) and HCl (general
0:1 M) [24.24, 38]. 1 mL aliquots of test solution are
sampled periodically and centrifuged for metal determination. Metal uptake, q (mg g
1 ), is calculated as the
difference in metal concentration in the aqueous phase
before and after sorption, according to (24.1)
q D
V
C i C eq
W
;
(24.1)
where V is the volume of metal solution (L), C i and C eq
are the initial and equilibrium concentration of metal in
solution (mg=L), respectively, and W is the mass of dry
macrophytes (g).
Through regression analysis, the Langmuir adsorption isotherm [24.84] given in (24.2) was adapted to the
experimental data
q D
q max bC eq
1 C bC eq
;
(24.2)
where q max (mg=g) and b (L=mg) are the Langmuir
constants, which represent the maximum adsorption
capacity and the affinity between the metal ion and adsorbent dried biomass, respectively.
24.5 Conclusions
Macrophytes represent particularly efficient biosorbents compared with other biomass types for the treatment of wastewater [24.24, 26, 37, 38, 45, 46]. Furthermore, due to their economic value in many food, cosmetic, and pharmaceutical applications, there is a large
bulk of information about their cell wall structure
and biochemical composition of the thalli [24.85–89].
Brown algae, in particular the orders Laminariales and
Fucales, are the most important algae with respect
to biosorption because of the abundance of their cell
wall matrix polysaccharides and extracellular polymers
(Table 24.1). Alginates and fucoidans (sulfated mucopolysaccharides) are mainly responsible for the natural
ion exchange ability of brown algae. In fact, previous studies support the possibility that the biosorption
process consists essentially of ion exchange, which involves the carboxyl group in the alginate polymer and
sulfonic acid in the fucoidan [24.24, 26, 38]. The cuticle
of seagrasses is also rich in carboxyl groups, which are
involved in the bond with the protonated metal, while
red and green algae have a lower capacity to immobilize protonated metals due of the presence of groups
other than carboxylic ones (Table 24.1). In general, it is
assumed that the number of binding sites identified decreases in the order brown algae > seagrasses > green
algae > red algae.
Moreover, recent literature confirms that the structure of the thallus affects the adsorption performance
of the algae [24.24–26, 38, 45]. Pennesi et al. [24.24]
concluded that the sorption abilities of the red algae
Porphyra and Polysiphonia might be related to the simple structure of the thallus (i. e., monostromatic blades
606 Part D Marine Algal Biotechnology
24.4 Biosorption Experiments: Procedure
24.4.1 Biosorption: Kinetic Curves
The kinetic curves of adsorption describe the time evolution of the concentration of metal in solution, in the
presence of the adsorbent biomaterial. A stock solution
containing a known amount of metal salts is prepared
to test the ability of the adsorbent macrophytes. Dried
biomass of the macrophytesis is suitably fragmented
to increase the adsorbing surface area and is placed
in a beaker with deionized water. The pH of the solution is adjusted using solutions of NaOH and HCl (in
general, 0:1 M) according to the experimental plan followed. Indeed, pH check control is important to avoid
metal precipitation in solution. Subsequently, a stock
solution with metals is added according to experimental
conditions. Aliquot amounts of solution are then periodically sampled to determine the concentration of metal.
In general, the kinetic curves are set for investigation of
different pH values.
24.4.2 The Langmuir Adsorption Isotherm
The equilibrium isotherms represent the concentration
of the metal on the solid (q, mg=g) as a function of
the respective concentration in solution at equilibrium
(C eq , mg=L). The determination of isotherms is essential to define the capacity of the adsorption of metal ions
by the adsorbent material, such as dried macrophytes.
For the determination of curves, a known amount of
dried and fragmented biomass is added to a solution
of deionized water with varying concentrations of metals established from the experimental plan. The pH of
the solutions is adjusted to predetermined values with
solutions of NaOH (general 0:1 M) and HCl (general
0:1 M) [24.24, 38]. 1 mL aliquots of test solution are
sampled periodically and centrifuged for metal determination. Metal uptake, q (mg g
1 ), is calculated as the
difference in metal concentration in the aqueous phase
before and after sorption, according to (24.1)
q D
V
C i C eq
W
;
(24.1)
where V is the volume of metal solution (L), C i and C eq
are the initial and equilibrium concentration of metal in
solution (mg=L), respectively, and W is the mass of dry
macrophytes (g).
Through regression analysis, the Langmuir adsorption isotherm [24.84] given in (24.2) was adapted to the
experimental data
q D
q max bC eq
1 C bC eq
;
(24.2)
where q max (mg=g) and b (L=mg) are the Langmuir
constants, which represent the maximum adsorption
capacity and the affinity between the metal ion and adsorbent dried biomass, respectively.
24.5 Conclusions
Macrophytes represent particularly efficient biosorbents compared with other biomass types for the treatment of wastewater [24.24, 26, 37, 38, 45, 46]. Furthermore, due to their economic value in many food, cosmetic, and pharmaceutical applications, there is a large
bulk of information about their cell wall structure
and biochemical composition of the thalli [24.85–89].
Brown algae, in particular the orders Laminariales and
Fucales, are the most important algae with respect
to biosorption because of the abundance of their cell
wall matrix polysaccharides and extracellular polymers
(Table 24.1). Alginates and fucoidans (sulfated mucopolysaccharides) are mainly responsible for the natural
ion exchange ability of brown algae. In fact, previous studies support the possibility that the biosorption
process consists essentially of ion exchange, which involves the carboxyl group in the alginate polymer and
sulfonic acid in the fucoidan [24.24, 26, 38]. The cuticle
of seagrasses is also rich in carboxyl groups, which are
involved in the bond with the protonated metal, while
red and green algae have a lower capacity to immobilize protonated metals due of the presence of groups
other than carboxylic ones (Table 24.1). In general, it is
assumed that the number of binding sites identified decreases in the order brown algae > seagrasses > green
algae > red algae.
Moreover, recent literature confirms that the structure of the thallus affects the adsorption performance
of the algae [24.24–26, 38, 45]. Pennesi et al. [24.24]
concluded that the sorption abilities of the red algae
Porphyra and Polysiphonia might be related to the simple structure of the thallus (i. e., monostromatic blades