Effect of pretreatment on Cd(II) and Pb(II) biosorption by Nannochloropsis oculata microalgae biomass.

Microalgal biomass has proven to be highly effective in the removal of heavy metals such as Pb2+ and Cd2+. Moreover, there are treatments available to enhance the heavy metal removal capabilities. This study investigates the impact of alkaline pretreatment on Nannochloropsis oculata biomass on the biosorption of Pb2+ and Cd2+. Nannochloropsis oculata was cultured in fed-batch reactors at 25 °C, with 166 μmol photons m-2 s-1 light intensity, in f/2 Guillard medium for 21 days. The biomass was treated with 0.2 M CaCl2 and 0.2 M NaOH for 24 h with slow stirring. FTIR studies indicated that carboxyl functional groups were mainly responsible for binding Pb2+ and Cd2+ during biosorption. The maximum biosorption capacity of Pb2+ was 227.86 mg g-1 and 57.17 mg g-1 for Cd2+ in the untreated biomass. The treatment with CaCl2 (Bs1) was more effective in the removal of Pb2+ than NaOH treatment (Bs2), otherwise NaOH treatment (Bs2) was better in the absorption of Cd2+ than CaCl2 treatment (Bs1). The experimental results and biosorption isotherms suggest that the microalgae showed a greater affinity for the removal of Pb2+ than for Cd2+ in all of the experiments. Both biomass treatments had a negative effect on Pb2+ and Cd2+ biosorption. Furthermore, the equilibrium data align well with the Sips isotherm model in the Langmuir derivation, suggesting a complex monolayer biosorption process. [ABSTRACT FROM AUTHOR]