Effects of culture pH on cell surface properties and biosorption of Pb(II), Cd(II), Zn(II) of green alga Neochloris oleoabundans

Abstract

Microalgal biomass has been established as a promising biosorbent for heavy metal ion (HMI) removal from contaminated waters. In this study, the cell surface properties of green alga Neochloris oleoabundans grown at different culture pH, i.e., 7.5, 8.5, and 9.5, which are referred to as B-7.5, B-8.5, and B-9.5, respectively, were investigated. The biosorption of three HMIs, i.e., Pb(II), Cd(II) and Zn(II), were studied systematically by these three types of biomasses. The results of isothermal analysis indicate that the biosorption was monolayer surface adsorption. Based on the Sips model, which best fits the experimental data among the three tested isotherm models, the biosorption capacities of all the three tested HMI on different biomasses followed the order B-9.5 > B-8.5 > B-7.5. The algal biomass obtained at culture pH 9.5, i.e., B-9.5, exhibited the highest biosorption capacities of Pb(II), Cd(II), and Zn(II) at biosorption pH 6.0, which were 100.01, 43.92, and 32.43 mg/g, respectively, corresponding to 3.0, 3.3, and 2.3 folds of that exhibited by B-7.5. FTIR, SEM, EDS and XPS were employed for characterization of cell surface. The XPS analysis revealed higher content of carboxyl (COOH) group on the B-9.5 cell surface than B-7.5 and B-8.5, which might be responsible for the much higher biosorption capacity of HMI by B-9.5.