algae. In acidic pH, the positive metal ions that can able to bind with negatively
charged algal biomass and increase the adsorption between the sorbents and the
sorbate. It is worth to mention that, in case of more acidic pH (<3), the excess H+
ions neutralize the negatively charged biosorbent surface, and thereby, reduce the
adsorption of metal ions (Kumar et al. 2008) therefore moderate acidic pH (3–5) is
preferred and suggested. In the case of alkaline pH (>8), a decrease in biosorption
may be due to the formation of soluble hydroxylated complexes of the metal ions
and their competition with the active sites, and eventually, the biosorption would
decrease (Saurav and Kannabiran 2011). Matheickal and Yu (1999) proposed
another concept, that was precipitation reaction occurs in alkaline pH, and the
formation of insoluble hydroxides of metal ion might reduce the concentration of
free sorbate ion available for biosorption. In contrast to the above concept, Sen et al.
(2018) reported that the alkaline pH of 11 was maximized the biosorption of
chromium when compare with acidic pH of 5 in cyanobacterial biomass. Believed
that the net negative charge present in the cyanobacterial biomass was comparatively
higher in alkaline pH, that facilitates the binding of positive hexavalent Cr ion onto
the cell surface. Therefore, it is clear that metal ion uptake is depended on the pH of
the solution, and the behavior of many different functional groups present in the
surface of algal cells as well as to complex formation constants (Zeraatkar et al.
2016).
9.2 Influence of Metal Concentration
Biosorption of heavy metals using algal biomass is largely dependent on the initial
concentration of the metal ions in the solution phase. Originally, biosorption
increases as the initial concentration of metal ion increases. Subsequently, no
significant increase in metal sorption was observed by a tandem increase in the
concentration of metal ions (Zeraatkar et al. 2016). For instance, the chromium
uptake increased from 0.2234 to 4.2172 mg/g, as the initial chromium concentration
increased from 5 to 150 mg/L. Meantime the percentage biosorption of chromium
decreased from 89.37% to 56.23% as the initial chromium concentration increased
from 5 to 150 mg/L (Kavitha et al. 2016). The decrease in percentage biosorption
possibly attributed due to a lack of sufficient surface area to accumulate much more
metal available in the solution (Ucun et al. 2002).
9.3 Influence of Biosorbent Concentration and Its Size
The increase in the dosage of biosorbent will increases the biosorption of metal ions
due to the larger surface area that in effect increases the number of available binding
sites. At lower concentrations of the biosorbent the amount of biosorbed metal per
unit weight of the biosorbent is high (Kanamarlapudi et al. 2018). For example, Fe
13 Phycoremediation of Heavy Metals, Factors Involved and Mechanisms Related. . .
277
charged algal biomass and increase the adsorption between the sorbents and the
sorbate. It is worth to mention that, in case of more acidic pH (<3), the excess H+
ions neutralize the negatively charged biosorbent surface, and thereby, reduce the
adsorption of metal ions (Kumar et al. 2008) therefore moderate acidic pH (3–5) is
preferred and suggested. In the case of alkaline pH (>8), a decrease in biosorption
may be due to the formation of soluble hydroxylated complexes of the metal ions
and their competition with the active sites, and eventually, the biosorption would
decrease (Saurav and Kannabiran 2011). Matheickal and Yu (1999) proposed
another concept, that was precipitation reaction occurs in alkaline pH, and the
formation of insoluble hydroxides of metal ion might reduce the concentration of
free sorbate ion available for biosorption. In contrast to the above concept, Sen et al.
(2018) reported that the alkaline pH of 11 was maximized the biosorption of
chromium when compare with acidic pH of 5 in cyanobacterial biomass. Believed
that the net negative charge present in the cyanobacterial biomass was comparatively
higher in alkaline pH, that facilitates the binding of positive hexavalent Cr ion onto
the cell surface. Therefore, it is clear that metal ion uptake is depended on the pH of
the solution, and the behavior of many different functional groups present in the
surface of algal cells as well as to complex formation constants (Zeraatkar et al.
2016).
9.2 Influence of Metal Concentration
Biosorption of heavy metals using algal biomass is largely dependent on the initial
concentration of the metal ions in the solution phase. Originally, biosorption
increases as the initial concentration of metal ion increases. Subsequently, no
significant increase in metal sorption was observed by a tandem increase in the
concentration of metal ions (Zeraatkar et al. 2016). For instance, the chromium
uptake increased from 0.2234 to 4.2172 mg/g, as the initial chromium concentration
increased from 5 to 150 mg/L. Meantime the percentage biosorption of chromium
decreased from 89.37% to 56.23% as the initial chromium concentration increased
from 5 to 150 mg/L (Kavitha et al. 2016). The decrease in percentage biosorption
possibly attributed due to a lack of sufficient surface area to accumulate much more
metal available in the solution (Ucun et al. 2002).
9.3 Influence of Biosorbent Concentration and Its Size
The increase in the dosage of biosorbent will increases the biosorption of metal ions
due to the larger surface area that in effect increases the number of available binding
sites. At lower concentrations of the biosorbent the amount of biosorbed metal per
unit weight of the biosorbent is high (Kanamarlapudi et al. 2018). For example, Fe
13 Phycoremediation of Heavy Metals, Factors Involved and Mechanisms Related. . .
277