Part D | 25.5
628 Part D Marine Algal Biotechnology
Therefore, the choice of the best solution flow rate
values should be a compromise between these two opposite situations [25.124]. Several such compromise
values of solution flow rate, used for the removal of
some heavy metal ions onto marine algae biomass in
dynamic continuous-flow conditions, are presented in
Table 25.6.
It should also be noted that a too little solution
flow rate has two undesirable consequences, from the
applicative point of view: (i) the saturation point not
reached, which means that the obtained breakthrough
curves cannot be modeled and characteristic parameters cannot be calculated, and (ii) the reach of the
saturation point is so slow and the metal ions concentration in the effluent becomes early high for that the
removal process is considered to be efficient, even if the
biosorbent is not exhausted. Under these conditions, the
biosorption process becomes unfeasible from economical considerations.
Effect of Initial Heavy Metal Ions Concentration
The variation of initial heavy metal ions concentration
changes the shape of breakthrough curves. An increase
in the initial concentration of heavy metal ions, when
other experimental parameters are kept constant, significantly affects the breakthrough curves, as is illustrated
in Fig. 25.9.
In all the studied biosorption systems that use marine algae biomass as biosorbent, the increase of the
initial heavy metal ions concentration caused a faster
breakthrough as expected. In addition, at a high initial heavy metal ions concentration, the breakthrough
curves were steeper in comparison with those at a low
initial heavy metal ions concentration, with a shorter
0.34 mmol/l
0.68 mmol/l
0.95 mmol/l
0
500
1000
1500
c/c 0
V (ml)
1
0.8
0.6
0.4
0.2
0
Fig. 25.9 Breakthrough curves for biosorption of Pb(II)
by biosorbent mixture-bed column (Ulva lactuca: Purolite A-100 D 1 W 2), at different initial metal ions concentrations (pH D 5:0; flow rate D 3:5 ml=min; H D 2:5 cm;
temperature D 20
ı C) [25.42]
mass transfer zone (MTZ). The steepness of the curve
(dc=dt) is a measure of the efficiency of the column to
reach the saturation, and a high value of this parameter
is better for the column performances [25.65].
The experimental results demonstrate that an increase in the initial heavy metal ions concentration
changes the biosorption rate through the packed bed and
increases the biosorbent-bed capacity. Thus, biosorption of heavy metal ions at breakthrough and saturation
was greater at high initial heavy metal ions concentration, because higher metal concentration provides better
driving force to the metal biosorption process during
continuous column run [25.42].
25.5 Modeling of Biosorption Process in Batch Conditions:
Isotherm and Kinetic Models
Biosorption of heavy metal ions is a passive nonmetabolically mediated process of metal ions binding by biosorbent. Many kinds of marine algae or
marine algae waste biomass can be used as biosorbents for the removal of heavy metal ions from
aqueous solution. Biosorption can also be defined as
a number of passive accumulation processes, which
may include, in any particular cases, ion exchange,
coordination, complexation, adsorption, and microprecipitation [25.18]. For this reason, biosorption is
considered to be a fast physical/chemical process,
and its rate is determined by the type of elementary
interactions.
Proper analysis and design of biosorption removal
processes requires relevant equilibrium and kinetic
data, as the vital information. In equilibrium, a certain
relationship prevails between heavy metal ions concentration from aqueous solution and biosorbent state. So,
it is both fundamentally and economically important
to correlate the equilibrium and kinetic data between
various heavy metal ions and biosorbents, in order to
asses the biosorption capacity for different heavy metal
628 Part D Marine Algal Biotechnology
Therefore, the choice of the best solution flow rate
values should be a compromise between these two opposite situations [25.124]. Several such compromise
values of solution flow rate, used for the removal of
some heavy metal ions onto marine algae biomass in
dynamic continuous-flow conditions, are presented in
Table 25.6.
It should also be noted that a too little solution
flow rate has two undesirable consequences, from the
applicative point of view: (i) the saturation point not
reached, which means that the obtained breakthrough
curves cannot be modeled and characteristic parameters cannot be calculated, and (ii) the reach of the
saturation point is so slow and the metal ions concentration in the effluent becomes early high for that the
removal process is considered to be efficient, even if the
biosorbent is not exhausted. Under these conditions, the
biosorption process becomes unfeasible from economical considerations.
Effect of Initial Heavy Metal Ions Concentration
The variation of initial heavy metal ions concentration
changes the shape of breakthrough curves. An increase
in the initial concentration of heavy metal ions, when
other experimental parameters are kept constant, significantly affects the breakthrough curves, as is illustrated
in Fig. 25.9.
In all the studied biosorption systems that use marine algae biomass as biosorbent, the increase of the
initial heavy metal ions concentration caused a faster
breakthrough as expected. In addition, at a high initial heavy metal ions concentration, the breakthrough
curves were steeper in comparison with those at a low
initial heavy metal ions concentration, with a shorter
0.34 mmol/l
0.68 mmol/l
0.95 mmol/l
0
500
1000
1500
c/c 0
V (ml)
1
0.8
0.6
0.4
0.2
0
Fig. 25.9 Breakthrough curves for biosorption of Pb(II)
by biosorbent mixture-bed column (Ulva lactuca: Purolite A-100 D 1 W 2), at different initial metal ions concentrations (pH D 5:0; flow rate D 3:5 ml=min; H D 2:5 cm;
temperature D 20
ı C) [25.42]
mass transfer zone (MTZ). The steepness of the curve
(dc=dt) is a measure of the efficiency of the column to
reach the saturation, and a high value of this parameter
is better for the column performances [25.65].
The experimental results demonstrate that an increase in the initial heavy metal ions concentration
changes the biosorption rate through the packed bed and
increases the biosorbent-bed capacity. Thus, biosorption of heavy metal ions at breakthrough and saturation
was greater at high initial heavy metal ions concentration, because higher metal concentration provides better
driving force to the metal biosorption process during
continuous column run [25.42].
25.5 Modeling of Biosorption Process in Batch Conditions:
Isotherm and Kinetic Models
Biosorption of heavy metal ions is a passive nonmetabolically mediated process of metal ions binding by biosorbent. Many kinds of marine algae or
marine algae waste biomass can be used as biosorbents for the removal of heavy metal ions from
aqueous solution. Biosorption can also be defined as
a number of passive accumulation processes, which
may include, in any particular cases, ion exchange,
coordination, complexation, adsorption, and microprecipitation [25.18]. For this reason, biosorption is
considered to be a fast physical/chemical process,
and its rate is determined by the type of elementary
interactions.
Proper analysis and design of biosorption removal
processes requires relevant equilibrium and kinetic
data, as the vital information. In equilibrium, a certain
relationship prevails between heavy metal ions concentration from aqueous solution and biosorbent state. So,
it is both fundamentally and economically important
to correlate the equilibrium and kinetic data between
various heavy metal ions and biosorbents, in order to
asses the biosorption capacity for different heavy metal