temperature and then starts to decrease. Increased biosorption of heavy metal at
increasing temperature was attribute to bond rupture, which may increase the
number of active sites involved in metal sorption or increase the affinity of metal
sites at the initial rise (Mehta and Gaur 2005). At certain times, the temperature can
have a positive or negative effect on biosorption. An increase or decrease in
temperature induces a difference in the biosorption potential of the biosorbent
(Kanamarlapudi et al. 2018). For example, according to Soleymani et al. (2014),
temperature variation between 15 and 45
C slightly increases the Cu, metal uptake
capacity from 38.63 to 42.24 mg/g, respectively. The same effects were also
observed by Kavitha et al. (2016), where the percentage biosorption of Cr increased
from 79.31% to 91.44% as temperature increased from 283 to 323 K using a
microalgae (Gracillaria corticata) biosorbent.
9.6 Influence of Agitation Speed
Mixing the solution also has a considerable impact on biosorption. The increased
speed of agitation increases the biosorption ability of the biosorbent by decreasing its
resistance to mass transfer (Kanamarlapudi et al. 2018). For instance, Mahmoud
et al. (2017) found that the adsorption of Zn increased rapidly as the agitation speed
increased from 50 to 200 rpm and a stage of equilibrium was attained at this speed
with 76.7% and 90.5% removal efficiencies in case of both natural and modified
adsorbents, respectively.
10 Mechanism of Heavy Metal Uptake by Algae
The uptake of metals from wastewater by algae can be passive or active, or both.
Passive uptake is independent of cellular metabolisms and involves the binding of
metals into polyanionic cell wall or ion exchange between protons and heavy metal
ions at the binding site, adsorption by physical forces (van der Waals forces, covalent
bonding, redox interaction, biomineralization), electrostatic interactions, surface
complexation, micro-precipitation and bioaccumulation (Brinza et al. 2007). The
cell wall composition of algae is playing a major role in binding with metal ions,
which are either polysaccharides or different glycoproteins groups, specifically,
glycan, mannan, alginic acid, proteins, and xylans. Additionally, the cell wall of
cyanobacteria is composed of peptidoglycan, and produce sheaths with extracellular
polymeric substances, which are utilize for sorption (Zeraatkar et al. 2016). The cell
wall provides functional groups (carboxyl, phosphate, hydroxyl, amino, sulfur,
sulfide, and thiol), oxygen, and nitrogen-based moieties as well as form coordinate
bonds with heavy metal ions. Passive uptake is rapid, reaching maximum adsorption
13 Phycoremediation of Heavy Metals, Factors Involved and Mechanisms Related. . .
279
increasing temperature was attribute to bond rupture, which may increase the
number of active sites involved in metal sorption or increase the affinity of metal
sites at the initial rise (Mehta and Gaur 2005). At certain times, the temperature can
have a positive or negative effect on biosorption. An increase or decrease in
temperature induces a difference in the biosorption potential of the biosorbent
(Kanamarlapudi et al. 2018). For example, according to Soleymani et al. (2014),
temperature variation between 15 and 45
C slightly increases the Cu, metal uptake
capacity from 38.63 to 42.24 mg/g, respectively. The same effects were also
observed by Kavitha et al. (2016), where the percentage biosorption of Cr increased
from 79.31% to 91.44% as temperature increased from 283 to 323 K using a
microalgae (Gracillaria corticata) biosorbent.
9.6 Influence of Agitation Speed
Mixing the solution also has a considerable impact on biosorption. The increased
speed of agitation increases the biosorption ability of the biosorbent by decreasing its
resistance to mass transfer (Kanamarlapudi et al. 2018). For instance, Mahmoud
et al. (2017) found that the adsorption of Zn increased rapidly as the agitation speed
increased from 50 to 200 rpm and a stage of equilibrium was attained at this speed
with 76.7% and 90.5% removal efficiencies in case of both natural and modified
adsorbents, respectively.
10 Mechanism of Heavy Metal Uptake by Algae
The uptake of metals from wastewater by algae can be passive or active, or both.
Passive uptake is independent of cellular metabolisms and involves the binding of
metals into polyanionic cell wall or ion exchange between protons and heavy metal
ions at the binding site, adsorption by physical forces (van der Waals forces, covalent
bonding, redox interaction, biomineralization), electrostatic interactions, surface
complexation, micro-precipitation and bioaccumulation (Brinza et al. 2007). The
cell wall composition of algae is playing a major role in binding with metal ions,
which are either polysaccharides or different glycoproteins groups, specifically,
glycan, mannan, alginic acid, proteins, and xylans. Additionally, the cell wall of
cyanobacteria is composed of peptidoglycan, and produce sheaths with extracellular
polymeric substances, which are utilize for sorption (Zeraatkar et al. 2016). The cell
wall provides functional groups (carboxyl, phosphate, hydroxyl, amino, sulfur,
sulfide, and thiol), oxygen, and nitrogen-based moieties as well as form coordinate
bonds with heavy metal ions. Passive uptake is rapid, reaching maximum adsorption
13 Phycoremediation of Heavy Metals, Factors Involved and Mechanisms Related. . .
279