Adsorption isotherm
NR5 was raised in 100 ml nutrient broth medium (pH 7.0) with 100mg of
arsenic (V), and flask without bacteria served as control. All the
flasks were incubated at 30℃ for 48 h and 250rpm. Subsequently,
bacterial culture was harvested at different time interval of 6h and
bacterial pellet and liquid phase stored for arsenic content estimation
using ICP-OES. The equilibrium arsenic concentration was plotted against
arsenic content adsorbed on bacterial cell (mg/g), and calculated by
using control. In order to understand adsorption behaviours and
mechanism of arsenic removal by NR5, adsorption isotherm with
consideration of Langmuir (Langmuir 1918) and Freundlich (Freundlich
1906) was studied. Langmuir described the monolayer adsorption pattern
and hypothesized that numerous binding sites on the surface of
biosorbent are available equally for metal sorption, calculated by using
equation 2.
\begin{equation}
\frac{C_{\text{eq}}}{q_{\text{eq}}}=\frac{1}{q_{\max}b}+\frac{C_{\text{eq}}}{q_{\max}}\nonumber \\
\end{equation}where, Ceq is the arsenic content remained in liquid
phase, qeq is the amount of arsenic per unit mass of
NR5, and the 1max is the maximum capacity of NR5. Here, b represents
Langmuir constant (mgL-1).
On the other hand, Freundlich isotherm represents multilayer sorption,
summarize in equation 3 shows an empirical relation suggest non-liner
relationship of arsenic concentration and amount.
\begin{equation}
q_{\text{eq}}=K_{f}C_{\text{eq}}\frac{1}{n}\nonumber \\
\end{equation}where, qeq is the amount of arsenic per unit mass of
NR5. Kf is the Freundlich constant coefficient (mg/g), while n is the
arsenic adsorption intensity (mg/g). In order to determine the rate of
metal sorption, adsorption kinetic was investigated using following
kinetic models Lagergren pseudo-first, Lagergren pseudo second-order,
and Elovich. Table 1 demonstrating, arsenic adsorption capacity (qt) at
equilibrium, k1, k2 as are rate constant for first- and second-order
reactions.