Langmuir adsorption isotherm model was applied based on Tsui et al. [24] in this study, and the model assumes monolayer sorption onto a surface and is given as below.

q = (qe x Cf) /(Л_1 + Cf) (3)

where qe = maximum metal uptake (mmol-g-1) (i. e., the maximum attainable binding capacity); and A = affinity constant (1 mmol-1) (i. e., the affinity of the metal ion toward the biomass).

The Freundlich equation is widely used in the field of environmental engineering, and was applied based on based Dahiya et al. [10-11]. Freundlich isotherm can also be used to explain adsorption phenomenon as given below.

l°gwqe = log10KF +(1/ n)log10Cf (4)

where KF and n are constants incorporating all factors affecting the adsorption capacity and an indication of the favorability of metal ion adsorption onto biosorbent, respectively. It is shown that 1/n values between 0.1 and 1.0 correspond to beneficial adsorption. That is, qe versus Cf in log scale can be plotted to determine values of 1/n and Kf.