Marine Algae Biomass for Removal of Heavy Metal Ions 25.2 Chemical Characteristics of Marine Algae Biomass 613
Part D | 25.2
earth metal ions for the binding sites is less than in the
case of ion exchange resins [25.16].
The marine algae are available in large quantities in
many regions of the world, and are a kind of promising
biological resources [25.29]. Even, though the red and
brown algae have been the most used biosorbents for
the removal of heavy metals [25.30], their utilization
may cause serious secondary pollution due to organic
substances release, such as alginate dissolving from
biosorbents, during of the biosorption process. Another
problem of brown algae utilization is that the leaching
of some retained compounds may also lead to a loss
of biosorption capacity [25.31]. These secondary processes drastically limit their industrial application.
In the case of green algae, the effect of secondary
pollution is significantly lower, and many studies from
the literature [25.17, 32, 33] have shown that these
posses high metal binding capacities, due to the presence of polysaccharides, proteins, or lipids from the cell
walls surface. The marine green algae are mainly cellulose, and high percentages of the cell wall are proteins
bonded to polysaccharides to form glycoproteins. These
compounds contain several functional groups (amino,
carboxyl, sulfate, hydroxyl, etc.) which could play an
important role in the biosorption process [25.34–36]. In
addition, the marine green algae are particularly useful
in the biosorption process of heavy metals due to their
relatively simple structure, high surface area, and small
and uniform distribution of binding sites [25.37, 38].
However, the marine algae are frequently used for
the extraction of oil in the cosmetic industry and for
the production of biofuels [25.39, 40]. This utilization
is more economically efficient than the removal of
heavy metal ions from wastewater, and for this reason high quantities of marine algae are used for this
purpose. After the extraction process, the remained marine algae biomass is considered to be a waste and is
discharged or incinerated, becoming a serious problem for environmental protection. In order to avoid
this problem, the marine algae waste biomass can also
be used as biosorbent for the removal of heavy metals ions from wastewater. Recent studies performed
by Bulgariu and Bulgariu [25.41, 42] have shown that
the biosorption capacity of the marine green algae
waste biomass obtained after extraction of oils from
marine green algae (Ulva lactuca sp.) can be successfully used for the removal of heavy metal ions
from aqueous solution, and that the metal uptake capacity is not significantly affected by the extraction
step.
In this chapter, the biosorptive characteristics of
marine algae biomass (marine algae and marine algae
wastes) for different heavy metal ions from aqueous solution, as a function of the experimental procedure used
in the biosorption process and experimental conditions
(solution pH, biosorbent dose, contact time, temperature, etc.) are presented. The most important isotherm
and kinetic models used for the mathematical description of experimental biosorption data are also reviewed.
The biosorption mechanism has been found to be quite
complex, including adsorption, surface precipitation,
ion exchange, and complexation.
25.2 Chemical Characteristics of Marine Algae Biomass
Marine algae (or seaweeds) are relatively undifferentiated simple biological organisms that fall into the
general category of plants. Their size varies from
tiny microscopic unicellular forms (310 m) to large
macroscopic multicellular forms (up to 70 m long).
Most of the marine algae are photosynthetic biological organisms that have chlorophyll, but they also
contain additional pigments, that are the basis of
classification [25.43].
Even if they are considered the oldest member of
the plant kingdom (existing back many hundreds of millions of years), the marine algae do not form a homogeneous group. They are found throughout the world’s
oceans and seas, and are divided into several categories, namely: (i) brown algae (Phaeophyta division),
(ii) red algae (Rhodophyta division), and (iii) green algae (Chlorophyta division), as a function of the color of
additional pigments. The mixture of pigments in their
chloroplasts lends characteristic colors to the marine
algae, and many of their scientific names are based
on these colors [25.44]. The differences between these
types of marine algae are mainly in the structure of cell
walls, where the retention of heavy metal ions takes
place.
The cell walls of brown algae generally contain
three main components: cellulose (that is the structural support), alginic acid (a polymer of mannuronic
and guluronic acids, and the corresponding salts of
sodium, potassium, magnesium and calcium and represent 1440% of the dry weight of the biomass)
Part D | 25.2
earth metal ions for the binding sites is less than in the
case of ion exchange resins [25.16].
The marine algae are available in large quantities in
many regions of the world, and are a kind of promising
biological resources [25.29]. Even, though the red and
brown algae have been the most used biosorbents for
the removal of heavy metals [25.30], their utilization
may cause serious secondary pollution due to organic
substances release, such as alginate dissolving from
biosorbents, during of the biosorption process. Another
problem of brown algae utilization is that the leaching
of some retained compounds may also lead to a loss
of biosorption capacity [25.31]. These secondary processes drastically limit their industrial application.
In the case of green algae, the effect of secondary
pollution is significantly lower, and many studies from
the literature [25.17, 32, 33] have shown that these
posses high metal binding capacities, due to the presence of polysaccharides, proteins, or lipids from the cell
walls surface. The marine green algae are mainly cellulose, and high percentages of the cell wall are proteins
bonded to polysaccharides to form glycoproteins. These
compounds contain several functional groups (amino,
carboxyl, sulfate, hydroxyl, etc.) which could play an
important role in the biosorption process [25.34–36]. In
addition, the marine green algae are particularly useful
in the biosorption process of heavy metals due to their
relatively simple structure, high surface area, and small
and uniform distribution of binding sites [25.37, 38].
However, the marine algae are frequently used for
the extraction of oil in the cosmetic industry and for
the production of biofuels [25.39, 40]. This utilization
is more economically efficient than the removal of
heavy metal ions from wastewater, and for this reason high quantities of marine algae are used for this
purpose. After the extraction process, the remained marine algae biomass is considered to be a waste and is
discharged or incinerated, becoming a serious problem for environmental protection. In order to avoid
this problem, the marine algae waste biomass can also
be used as biosorbent for the removal of heavy metals ions from wastewater. Recent studies performed
by Bulgariu and Bulgariu [25.41, 42] have shown that
the biosorption capacity of the marine green algae
waste biomass obtained after extraction of oils from
marine green algae (Ulva lactuca sp.) can be successfully used for the removal of heavy metal ions
from aqueous solution, and that the metal uptake capacity is not significantly affected by the extraction
step.
In this chapter, the biosorptive characteristics of
marine algae biomass (marine algae and marine algae
wastes) for different heavy metal ions from aqueous solution, as a function of the experimental procedure used
in the biosorption process and experimental conditions
(solution pH, biosorbent dose, contact time, temperature, etc.) are presented. The most important isotherm
and kinetic models used for the mathematical description of experimental biosorption data are also reviewed.
The biosorption mechanism has been found to be quite
complex, including adsorption, surface precipitation,
ion exchange, and complexation.
25.2 Chemical Characteristics of Marine Algae Biomass
Marine algae (or seaweeds) are relatively undifferentiated simple biological organisms that fall into the
general category of plants. Their size varies from
tiny microscopic unicellular forms (310 m) to large
macroscopic multicellular forms (up to 70 m long).
Most of the marine algae are photosynthetic biological organisms that have chlorophyll, but they also
contain additional pigments, that are the basis of
classification [25.43].
Even if they are considered the oldest member of
the plant kingdom (existing back many hundreds of millions of years), the marine algae do not form a homogeneous group. They are found throughout the world’s
oceans and seas, and are divided into several categories, namely: (i) brown algae (Phaeophyta division),
(ii) red algae (Rhodophyta division), and (iii) green algae (Chlorophyta division), as a function of the color of
additional pigments. The mixture of pigments in their
chloroplasts lends characteristic colors to the marine
algae, and many of their scientific names are based
on these colors [25.44]. The differences between these
types of marine algae are mainly in the structure of cell
walls, where the retention of heavy metal ions takes
place.
The cell walls of brown algae generally contain
three main components: cellulose (that is the structural support), alginic acid (a polymer of mannuronic
and guluronic acids, and the corresponding salts of
sodium, potassium, magnesium and calcium and represent 1440% of the dry weight of the biomass)