Part D | 25.4
624 Part D Marine Algal Biotechnology
gradual biosorption, near to the equilibrium (zone II).
In most of the biosorption studies using marine algae
or marine algae waste biomass as biosorbent, no further
significant biosorption is noted after 3 h [25.24].
By analyzing the experimental dependences obtained in the study of the influence of contact time on
the removal efficiency of heavy metal ions from aqueous solutions, the optimum value of this parameter can
be establish. In Table 25.4 are summarized the values
of contact time required for the efficient removal of
heavy metal ions from aqueous environments, in the
case of different types of marine algae and marine algae
waste biomass. No more than 120 min of contact time
is necessary in these biosorption processes. Such low
values of contact time required to attain the equilibrium
state indicate that the biosorption of heavy metal ions
onto marine algae biomass is mainly controlled by the
chemical (electrostatic) interactions between positively
charged metal ions and negatively charged functional
groups form biomass surface; the share of elementary
diffusion processes, especially the intraparticle type, is
much smaller [25.112].
Such two-steps adsorption behavior has been reported in most studies of metal ion retention in various low-cost materials [25.16, 18, 112–114], and is
mainly determined by the presence of sites with different binding affinities for metal ions on the adsorbent
surface, thereby yielding different binding sites. According to Qin and co-workers [25.25, 89], the rapid
initial biosorption step is generally the result of the
fast transfer of metal ions to the surface of the biosorbent particles, while the subsequent slow biosorption
process is a consequence of the slow diffusion on
metal ions into the pores of the biosorbent particles.
The very fast biosorption and settling of marine algae
biomass make these materials suitable for continuous
flow wastewater treatment systems.
Effect of Temperature
Temperature is also an important experimental parameter for the removal of heavy metal ions, dealing
with the thermodynamics of the biosorption process.
This parameter is directly related to the kinetic energy of the metal ions, and an increase or decrease
in temperature should cause a change in the amount
of heavy metal ions removed or retained by biosorbent [25.87].
In general, the temperature affects the removal efficiency of the heavy metal pollutants from aqueous
solution, but to a limited extent in a certain range
of temperature. In case of marine algae biomass the
most experimental studies were performed in the temperature range of 550
ı C, at a contact time lower
than 4 h. This is because in this temperature range,
the biosorbent materials do not suffer secondary processes of thermal degradation [25.16], and the low
value of contact time do not make the volume of aqueous solutions vary significantly, due to the evaporation
phenomena.
The effect of temperature on the heavy metal removal by biosorption onto marine algae biomass depends on the nature of the heavy metal ion and on
the nature of biomass used as biosorbent, and usually was observed in two stages. The biosorption
equilibrium occurs rapidly at lower heavy metal ion
concentrations, for all temperature values, and becomes relatively constant at higher concentrations.
Table 25.4 presents the values of temperature considered as optimum for the removal of some heavy
metal ions from aqueous solution, using different types
of marine algae and marine algae waste biomass as
biosorbents.
Such processes are normally exothermic, so
biosorption capacity increases with decrease of temperature, and indicate that the ion exchange interactions
exist in the biosorption process to some extent. The decrease of biosorption capacity of marine algae biomass
at higher temperatures may be due to the damage of
active binding sites in the biomass [25.115]. When the
temperature is too high, a distortion of some available
functional groups from the cell surface occurs, and in
consequence the efficiency of the biosorption process
decreases.
However, Gupta and Rastogi [25.102] have found
that the Pb(II) biosorption on Spirogyra sp. marine algae increases with increasing temperature, in the range
of 2545
ı C. They explained that higher temperature
would lead to higher affinity of sites for metal ions,
and the energy of the systems facilitates the binding of Pb(II) ions on the functional groups from cell
surface to some extent. Such behavior has been observed and for the other removal processes of heavy
metal ions using marine algae and marine algae waste
biomass [25.76, 110].
The variation of temperature does not always significantly change the biosorption capacities of marine
algae biomass. Bulgariu and Bulgariu [25.41] have
shown that temperature (in the 1040
ı C range) has
minor effect on the removal of the Pb(II), Cd(II), and
Co(II) ions from aqueous solution onto marine green
algae waste biomass. Thus, the increase of temperature with 30
ı C determined a decrease of biosorption
624 Part D Marine Algal Biotechnology
gradual biosorption, near to the equilibrium (zone II).
In most of the biosorption studies using marine algae
or marine algae waste biomass as biosorbent, no further
significant biosorption is noted after 3 h [25.24].
By analyzing the experimental dependences obtained in the study of the influence of contact time on
the removal efficiency of heavy metal ions from aqueous solutions, the optimum value of this parameter can
be establish. In Table 25.4 are summarized the values
of contact time required for the efficient removal of
heavy metal ions from aqueous environments, in the
case of different types of marine algae and marine algae
waste biomass. No more than 120 min of contact time
is necessary in these biosorption processes. Such low
values of contact time required to attain the equilibrium
state indicate that the biosorption of heavy metal ions
onto marine algae biomass is mainly controlled by the
chemical (electrostatic) interactions between positively
charged metal ions and negatively charged functional
groups form biomass surface; the share of elementary
diffusion processes, especially the intraparticle type, is
much smaller [25.112].
Such two-steps adsorption behavior has been reported in most studies of metal ion retention in various low-cost materials [25.16, 18, 112–114], and is
mainly determined by the presence of sites with different binding affinities for metal ions on the adsorbent
surface, thereby yielding different binding sites. According to Qin and co-workers [25.25, 89], the rapid
initial biosorption step is generally the result of the
fast transfer of metal ions to the surface of the biosorbent particles, while the subsequent slow biosorption
process is a consequence of the slow diffusion on
metal ions into the pores of the biosorbent particles.
The very fast biosorption and settling of marine algae
biomass make these materials suitable for continuous
flow wastewater treatment systems.
Effect of Temperature
Temperature is also an important experimental parameter for the removal of heavy metal ions, dealing
with the thermodynamics of the biosorption process.
This parameter is directly related to the kinetic energy of the metal ions, and an increase or decrease
in temperature should cause a change in the amount
of heavy metal ions removed or retained by biosorbent [25.87].
In general, the temperature affects the removal efficiency of the heavy metal pollutants from aqueous
solution, but to a limited extent in a certain range
of temperature. In case of marine algae biomass the
most experimental studies were performed in the temperature range of 550
ı C, at a contact time lower
than 4 h. This is because in this temperature range,
the biosorbent materials do not suffer secondary processes of thermal degradation [25.16], and the low
value of contact time do not make the volume of aqueous solutions vary significantly, due to the evaporation
phenomena.
The effect of temperature on the heavy metal removal by biosorption onto marine algae biomass depends on the nature of the heavy metal ion and on
the nature of biomass used as biosorbent, and usually was observed in two stages. The biosorption
equilibrium occurs rapidly at lower heavy metal ion
concentrations, for all temperature values, and becomes relatively constant at higher concentrations.
Table 25.4 presents the values of temperature considered as optimum for the removal of some heavy
metal ions from aqueous solution, using different types
of marine algae and marine algae waste biomass as
biosorbents.
Such processes are normally exothermic, so
biosorption capacity increases with decrease of temperature, and indicate that the ion exchange interactions
exist in the biosorption process to some extent. The decrease of biosorption capacity of marine algae biomass
at higher temperatures may be due to the damage of
active binding sites in the biomass [25.115]. When the
temperature is too high, a distortion of some available
functional groups from the cell surface occurs, and in
consequence the efficiency of the biosorption process
decreases.
However, Gupta and Rastogi [25.102] have found
that the Pb(II) biosorption on Spirogyra sp. marine algae increases with increasing temperature, in the range
of 2545
ı C. They explained that higher temperature
would lead to higher affinity of sites for metal ions,
and the energy of the systems facilitates the binding of Pb(II) ions on the functional groups from cell
surface to some extent. Such behavior has been observed and for the other removal processes of heavy
metal ions using marine algae and marine algae waste
biomass [25.76, 110].
The variation of temperature does not always significantly change the biosorption capacities of marine
algae biomass. Bulgariu and Bulgariu [25.41] have
shown that temperature (in the 1040
ı C range) has
minor effect on the removal of the Pb(II), Cd(II), and
Co(II) ions from aqueous solution onto marine green
algae waste biomass. Thus, the increase of temperature with 30
ı C determined a decrease of biosorption