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.