removal efficiency increased as the Chlorella coloniales dose increased at all applied
initial Chromium concentrations, reaching their maximum values of 86.7% in 2.6 g/
L of algae dose (Jaafari and Yaghmaeian 2019). At lower concentrations of the
biosorbent, the Kavitha et al. (2016) study showed that the percentage biosorption of
chromium was increased from 70.09% (1.7522 mg/g) to 75.59% (1.8897 mg/g) as
the biosorbent size decreases from 104 to 44 μm with an increase in biosorbent
dosage from 10 g/L to 25 g/L, at 303 K for 50 mg/L of chromium initial concentration of Gracilaria corticata biomass. While decrease in biosorbent sizes, the surface
area of the biosorbent increases, thereby the number of active sites available on the
biosorbent is better exposed to the sorbate. Similar results were noticed by other
researchers.
9.4 Influence of Contact Time
Algae adsorbent adsorbs heavy metals passively on the surface of the cell wall
quickly within a few minutes and reaches saturation at a maximum of 30 min,
making biosorption highly dependent on contact time (Zeraatkar et al. 2016). As
time increases, the rate of biosorption decreases due to an increase in the percentage
of saturation of metal ions remaining in the solution (Kanamarlapudi et al. 2018;
Jaafari and Yaghmaeian 2019). The rapid initial adsorption perhaps attributed to the
accumulation of metals on to the surface of biosorbent, due to its large surface area
and later the process becomes slower. For instance, Sbihi et al. (2012) observed that
93.45 mg Cr g
À1 in 30 min of contact time in the microalgae of Diatoms sorbent and
stated that the live biomass was taking more than a day to reach 60% removal. The
same was evidenced by Das et al. (2018) found 20 days to remove >50% of total
dissolved solids in tannery effluent using live microalgae. Moreover, suggested that
the desorption process is starts when the contact time is raised. By this fact, the
previous researchers have also reported that less time was preferred when using more
biosorbents and stated that the biosorption process took place in two stages. The first
stage was rapid and achieved the equilibrium and the second stage represented
slower progressive adsorption and later the desorption progress (Kavitha et al.
2016; Sbihi et al. 2012; Tüzün et al. 2005). Besides, Sen et al. (2018), recently
stated that the wide variation in incubation time was not that important factor since
equilibrium was obtain within 5 min and did not consider as input variables.
9.5 Influence of Temperature
Adsorption is an exothermic process and therefore, by the Le Chatelier’s principles,
the amount of adsorption should increase with a decrease in the temperature of the
physical adsorption. Whereas, chemical adsorption first increases with an increase in
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A. Ayele et al.
initial Chromium concentrations, reaching their maximum values of 86.7% in 2.6 g/
L of algae dose (Jaafari and Yaghmaeian 2019). At lower concentrations of the
biosorbent, the Kavitha et al. (2016) study showed that the percentage biosorption of
chromium was increased from 70.09% (1.7522 mg/g) to 75.59% (1.8897 mg/g) as
the biosorbent size decreases from 104 to 44 μm with an increase in biosorbent
dosage from 10 g/L to 25 g/L, at 303 K for 50 mg/L of chromium initial concentration of Gracilaria corticata biomass. While decrease in biosorbent sizes, the surface
area of the biosorbent increases, thereby the number of active sites available on the
biosorbent is better exposed to the sorbate. Similar results were noticed by other
researchers.
9.4 Influence of Contact Time
Algae adsorbent adsorbs heavy metals passively on the surface of the cell wall
quickly within a few minutes and reaches saturation at a maximum of 30 min,
making biosorption highly dependent on contact time (Zeraatkar et al. 2016). As
time increases, the rate of biosorption decreases due to an increase in the percentage
of saturation of metal ions remaining in the solution (Kanamarlapudi et al. 2018;
Jaafari and Yaghmaeian 2019). The rapid initial adsorption perhaps attributed to the
accumulation of metals on to the surface of biosorbent, due to its large surface area
and later the process becomes slower. For instance, Sbihi et al. (2012) observed that
93.45 mg Cr g
À1 in 30 min of contact time in the microalgae of Diatoms sorbent and
stated that the live biomass was taking more than a day to reach 60% removal. The
same was evidenced by Das et al. (2018) found 20 days to remove >50% of total
dissolved solids in tannery effluent using live microalgae. Moreover, suggested that
the desorption process is starts when the contact time is raised. By this fact, the
previous researchers have also reported that less time was preferred when using more
biosorbents and stated that the biosorption process took place in two stages. The first
stage was rapid and achieved the equilibrium and the second stage represented
slower progressive adsorption and later the desorption progress (Kavitha et al.
2016; Sbihi et al. 2012; Tüzün et al. 2005). Besides, Sen et al. (2018), recently
stated that the wide variation in incubation time was not that important factor since
equilibrium was obtain within 5 min and did not consider as input variables.
9.5 Influence of Temperature
Adsorption is an exothermic process and therefore, by the Le Chatelier’s principles,
the amount of adsorption should increase with a decrease in the temperature of the
physical adsorption. Whereas, chemical adsorption first increases with an increase in
278
A. Ayele et al.