Biosorption of Zn2+, Ni2+ and Co2+ from water samples onto Yarrowia lipolytica ISF7 using a response surface methodology, and analyzed by inductively coupled plasma optical emission spectrometry (ICP-OES)

Abstract

A response surface methodology (RSM) based on a central composite design with five variables and five levels was employed to interpret the biosorption efficiency of Zn²⁺, Ni²⁺ and Co²⁺ ions onto Yarrowia lipolytica ISF7. Independent variables, viz. pH, temperature, and Zn²⁺, Ni²⁺ and Co²⁺ ion concentrations were transformed into coded values and a quadratic model was built to predict the responses. Analysis of variance (ANOVA) and t-test statistics were used to test the significance of the independent variables and their interactions. The predicted maximum biosorption efficiencies (99.65, 99.30 and 98.78% for Zn²⁺, Ni²⁺ and Co²⁺ ions, respectively) under the optimum recommended conditions (pH 6.0, 25 °C, 30, 25 and 30 mg L⁻¹ of Zn²⁺, Ni²⁺ and Co²⁺ ions) following 24 h mixing were very close to the experimental values (99.65, 99.30 and 98.78% for Zn²⁺, Ni²⁺ and Co²⁺ ions, respectively). The equilibrium equation was extensively investigated and found to be efficiently represented by a Langmuir model with maximum monolayer biosorption capacities of 31.96, 24.40 and 25.77 mg g⁻¹ for Zn²⁺, Ni²⁺ and Co²⁺, respectively. The biosorption data trend closely followed a pseudo-second-order kinetic model. FTIR and scanning electron microscopy coupled with X-ray energy dispersed analysis (SEM-EDX) provided proof of progress of ion biosorption on the yeast surfaces.