Prediction of Equillibrium Sorption Isotherm for Cadmium Biosorption by Microorganisms: Comparison of Linear and Nonlinear Methods

Modeling of experimental biosorption isotherm data is a fundamental step in the screening of the biosorption process and provides useful information about the mechanisms involved and the ability of biosorbents to remove the heavy metals ions. This paper focuses on modeling $Cd^{2+}$ biosorption by dead biomass of B. megaterium and Rhodotorula sp. by applying non-linear and linear forms of Langmuir, Freundlich, Jovanovic and Hill isotherm models. In order to determine the best fit isotherm model for each biosorbent, the results of linear methods have been compared with the results of nonlinear analysis. For both biosorbents, the non-linear forms of isotherms fit well with the experimental data, the regression coefficients (R²) being over 0.85. $Cd^{2+}$ biosorption by B. megaterium is described better by the non-linear Hill model, while the non-linear Langmuir model fits better with experimental data of Rhodotorula sp. biosorption. The maximum biosorption capacities calculated by these models are 15.59 mg/g for B. megaterium and 10.94 mg/g for Rhodotorula sp. These models also confirm that the surfaces of the biosorbents are homogeneous.