7.2 pH
Biosorbents are rich in carboxylic, amine, hydroxyl and thiol groups. These groups
contribute to the characteristic acid–base property of the biosorbent. Hence, pH of
the solution can alter the chemical nature of the functional groups present in the
biosorbent and also the affinity of these groups towards metal ions. Some
biosorbents and adsorbates have a buffering effect which can neutralize the effect
of pH changes in the system [7, 17]. In many occasions, the change in pH alters the
equilibrium of the biosorption process.
7.3 Biomass State and Concentration
The concentration of biomass in the solution directly constitutes the amount of
surface area and functional groups available for the adsorption of the pollutants.
Also, the state of biosorbent whether dead or alive also influences the rate of
adsorption. At lower concentrations, the amount of adsorption doesn’t seem to be
affected, while in higher concentrations, the dead biomass adsorbs more than the live
biomass [2].
7.4 Coexisting Ions
When biosorption is applied to treat waste water, the waste water may contain more
than one ion in the solution. Presence of other coexisting ions can also influence the
rate of biosorption. Fe
2+ and Zn
2+ can affect the adsorption of heavy metals by
microorganisms. The microorganisms that uptake heavy metals such as uranium and
thorium are found to be not affected by the presence of coexisting ions, while the
presence of uranium and thorium might affect the adsorption of other metals [42].
7.5 Contact Time with the Adsorbent
The rate of adsorption also depends on the contact time for adsorbate and the
biosorbent. Increase in contact time leads to the increase in the percentage removal
of the biosorbent. However, the adsorption rate will be maximum initially and then
slows down and reaches the equilibrium. This is due to the presence of more vacant
sites for adsorption at the start than at the end of adsorption.
252
K. J. Samuel P N et al.
Biosorbents are rich in carboxylic, amine, hydroxyl and thiol groups. These groups
contribute to the characteristic acid–base property of the biosorbent. Hence, pH of
the solution can alter the chemical nature of the functional groups present in the
biosorbent and also the affinity of these groups towards metal ions. Some
biosorbents and adsorbates have a buffering effect which can neutralize the effect
of pH changes in the system [7, 17]. In many occasions, the change in pH alters the
equilibrium of the biosorption process.
7.3 Biomass State and Concentration
The concentration of biomass in the solution directly constitutes the amount of
surface area and functional groups available for the adsorption of the pollutants.
Also, the state of biosorbent whether dead or alive also influences the rate of
adsorption. At lower concentrations, the amount of adsorption doesn’t seem to be
affected, while in higher concentrations, the dead biomass adsorbs more than the live
biomass [2].
7.4 Coexisting Ions
When biosorption is applied to treat waste water, the waste water may contain more
than one ion in the solution. Presence of other coexisting ions can also influence the
rate of biosorption. Fe
2+ and Zn
2+ can affect the adsorption of heavy metals by
microorganisms. The microorganisms that uptake heavy metals such as uranium and
thorium are found to be not affected by the presence of coexisting ions, while the
presence of uranium and thorium might affect the adsorption of other metals [42].
7.5 Contact Time with the Adsorbent
The rate of adsorption also depends on the contact time for adsorbate and the
biosorbent. Increase in contact time leads to the increase in the percentage removal
of the biosorbent. However, the adsorption rate will be maximum initially and then
slows down and reaches the equilibrium. This is due to the presence of more vacant
sites for adsorption at the start than at the end of adsorption.
252
K. J. Samuel P N et al.