Part D | 25.1
612 Part D Marine Algal Biotechnology
ral water ecosystems [25.4, 5], and water contaminated
by such pollutants remains an important problem with
serious ecological and human health consequences.
The presence of some heavy metals, such as copper,
zinc, cadmium, lead, mercury, cobalt, nickel, and others, has a potentially damaging effect on human health
and other biological systems, when the tolerance levels
are exceeded [25.6, 7]. In order to prevent the deterioration of environment quality, legislation governing the
levels of heavy metals, discharged from waste stream is
becoming progressively stricter [25.8].
Under these conditions, it is desirable for the benefit
of environment to eliminate the heavy metal ions from
industrial waste stream, and this could also be important
from economical considerations, due to the high value
of these metals. Together with pollution prevention and
detection, the elimination of a wide range of pollutants
from aqueous waste stream is an absolute requirement
for sustainable development [25.9].
The most widely employed methods for removing heavy metals from metal-bearing effluents include chemical precipitation, ion exchange, adsorption,
flocculation, solvent extraction, membrane-related processes, electrochemical and biological techniques, and
different combination of these [25.10–14]. Low efficiency performances, particularly when are used for
small concentrations of heavy metal ions, low selectivity, the necessity of using expensive chemicals in
some methods, and the generation of high amount of
toxic sludge or high energy consumption, are the main
drawbacks of these conventional methods [25.13, 15].
Therefore, the development of new methods for the removal of heavy metal ions from aqueous environments
that minimize these disadvantages is an actual scientific
issue, which has great applicative importance.
In regard to its simplicity and high-efficiency characteristics, the adsorption is looked upon as a better method that is recommended for the removal of
low concentrations of heavy metal ions in wastewater (1100 mg=l dissolved metal ions) [25.16], because
it is rapid, reversible, economical and environmental friendly in contrast with the mentioned conventional methods [25.17, 18]. Well-designed adsorption
processes have high efficiency, resulting in high-quality
effluents after treatment, which can be recycled.
The adsorption process, generally implies the presence of solid material, called adsorbent, that binds
metal ions from contaminated aqueous solutions by
physical attractive forces, ion exchange, or/and chemical binding. Cheap and efficient adsorbents are advisable for the treatment of aqueous effluents containing
heavy metal ions. Thus, natural materials available in
large quantities or waste products from industry or agriculture, generally designated low-cost adsorbents, have
been proved suitable for this purpose. This is due to
the fact that most such materials have high number
and variety of superficial functional groups (e.g., carboxyl, hydroxyl, amino, phosphate, etc.), which can
retain the metal ions through different kinds of mechanisms. Moreover, because such cost adsorbents are
cheap and easily regenerable, they are an attractive
alternative over commonly used adsorbing materials,
such as activated carbon, which is costly to use for the
removal of such dangerous chemicals from industrial
wastes [25.12, 19].
In the past few decades, biosorption using microorganism biomass as the adsorbent has emerged as
a potential alternative method in the removal of contaminants from aqueous effluents. The use of biological
materials, including living and nonliving microorganisms for the removal of heavy metals from industrial
wastewater, has gained important credibility in the
last few years, because of the good efficiency, minimization of secondary (chemical or biological) wastes,
and low cost of these materials [25.16, 18]. The microorganisms, such as bacteria, algae, fungi, or yeasts,
can uptake heavy metals from aqueous solutions, both
actively (metabolically mediated – bioaccumulation)
and passively (by physical–chemical pathways, named
biosorption) [25.20, 21].
Although in the beginning most studies have been
focused on heavy metal accumulation and concentration within living organisms [25.22, 23], upon noticing that dead biomass possesses high metal retention
capacity [25.24], the interest was shifted to biosorption [25.25, 26]. This is mainly due to the fact that the
nonliving biological materials are easier and cheaper
to obtain, and their utilization as biosorbents has been
shown to be an economical and effective method to remove the heavy metals from wastewater.
The term biosorption indicates a metabolismindependent binding of heavy metals by dead (nonliving) biological materials, and is defined as the ability
of these materials to bind the metal ions to the surface
of cellular walls or membrane, in the equilibrium process [25.21, 27, 28]. In the biosorption processes, the
nonliving biological materials (biomass) act as a chemical substrate of biologic origin and the main advantages
of their utilization are: (i) the variety of functional
groups from the biosorbent surface, (ii) relatively small
and uniform distribution of binding sites on biosorbent
surface, and (iii) the preference of alkali and alkali-
612 Part D Marine Algal Biotechnology
ral water ecosystems [25.4, 5], and water contaminated
by such pollutants remains an important problem with
serious ecological and human health consequences.
The presence of some heavy metals, such as copper,
zinc, cadmium, lead, mercury, cobalt, nickel, and others, has a potentially damaging effect on human health
and other biological systems, when the tolerance levels
are exceeded [25.6, 7]. In order to prevent the deterioration of environment quality, legislation governing the
levels of heavy metals, discharged from waste stream is
becoming progressively stricter [25.8].
Under these conditions, it is desirable for the benefit
of environment to eliminate the heavy metal ions from
industrial waste stream, and this could also be important
from economical considerations, due to the high value
of these metals. Together with pollution prevention and
detection, the elimination of a wide range of pollutants
from aqueous waste stream is an absolute requirement
for sustainable development [25.9].
The most widely employed methods for removing heavy metals from metal-bearing effluents include chemical precipitation, ion exchange, adsorption,
flocculation, solvent extraction, membrane-related processes, electrochemical and biological techniques, and
different combination of these [25.10–14]. Low efficiency performances, particularly when are used for
small concentrations of heavy metal ions, low selectivity, the necessity of using expensive chemicals in
some methods, and the generation of high amount of
toxic sludge or high energy consumption, are the main
drawbacks of these conventional methods [25.13, 15].
Therefore, the development of new methods for the removal of heavy metal ions from aqueous environments
that minimize these disadvantages is an actual scientific
issue, which has great applicative importance.
In regard to its simplicity and high-efficiency characteristics, the adsorption is looked upon as a better method that is recommended for the removal of
low concentrations of heavy metal ions in wastewater (1100 mg=l dissolved metal ions) [25.16], because
it is rapid, reversible, economical and environmental friendly in contrast with the mentioned conventional methods [25.17, 18]. Well-designed adsorption
processes have high efficiency, resulting in high-quality
effluents after treatment, which can be recycled.
The adsorption process, generally implies the presence of solid material, called adsorbent, that binds
metal ions from contaminated aqueous solutions by
physical attractive forces, ion exchange, or/and chemical binding. Cheap and efficient adsorbents are advisable for the treatment of aqueous effluents containing
heavy metal ions. Thus, natural materials available in
large quantities or waste products from industry or agriculture, generally designated low-cost adsorbents, have
been proved suitable for this purpose. This is due to
the fact that most such materials have high number
and variety of superficial functional groups (e.g., carboxyl, hydroxyl, amino, phosphate, etc.), which can
retain the metal ions through different kinds of mechanisms. Moreover, because such cost adsorbents are
cheap and easily regenerable, they are an attractive
alternative over commonly used adsorbing materials,
such as activated carbon, which is costly to use for the
removal of such dangerous chemicals from industrial
wastes [25.12, 19].
In the past few decades, biosorption using microorganism biomass as the adsorbent has emerged as
a potential alternative method in the removal of contaminants from aqueous effluents. The use of biological
materials, including living and nonliving microorganisms for the removal of heavy metals from industrial
wastewater, has gained important credibility in the
last few years, because of the good efficiency, minimization of secondary (chemical or biological) wastes,
and low cost of these materials [25.16, 18]. The microorganisms, such as bacteria, algae, fungi, or yeasts,
can uptake heavy metals from aqueous solutions, both
actively (metabolically mediated – bioaccumulation)
and passively (by physical–chemical pathways, named
biosorption) [25.20, 21].
Although in the beginning most studies have been
focused on heavy metal accumulation and concentration within living organisms [25.22, 23], upon noticing that dead biomass possesses high metal retention
capacity [25.24], the interest was shifted to biosorption [25.25, 26]. This is mainly due to the fact that the
nonliving biological materials are easier and cheaper
to obtain, and their utilization as biosorbents has been
shown to be an economical and effective method to remove the heavy metals from wastewater.
The term biosorption indicates a metabolismindependent binding of heavy metals by dead (nonliving) biological materials, and is defined as the ability
of these materials to bind the metal ions to the surface
of cellular walls or membrane, in the equilibrium process [25.21, 27, 28]. In the biosorption processes, the
nonliving biological materials (biomass) act as a chemical substrate of biologic origin and the main advantages
of their utilization are: (i) the variety of functional
groups from the biosorbent surface, (ii) relatively small
and uniform distribution of binding sites on biosorbent
surface, and (iii) the preference of alkali and alkali-