Biosorption of metals (Cd, Cu and Zn) by the freshwater diatom Planothidium lanceolatum: a laboratory study

Abstract

Biosorption, the naturally occurring physiochemical process which passively concentrates and binds contaminants to cellular structures, can be used in biological systems for the removal of metal ions from polluted waters. It also has the potential to achieve better performance at lower cost than conventional wastewater treatment technologies. The aim of this study was to characterize the ability of the freshwater diatom Planothidium lanceolatum (Brébisson) Lange-Bertalot to biosorb cadmium (Cd), copper (Cu) and zinc (Zn) from aqueous solutions. This diatom is one of the most dominant microalgae in the Tensift River, Marrakech region, Morocco, into which industrial wastewaters are often discharged directly, without pretreatment. As the water from this river is used for irrigation, it represents a potential risk to the environment and human health. The choice of these three heavy metals is based on their high concentrations in mining waste and industrial wastewaters. Our results indicate that the biosorption of metals by P. lanceolatum increased with the initial concentration of metal ions in the medium up to 100–130 mg L−1. The maximum biosorbed metal ion concentrations were 104, 81 and 41 mg per 16×108 diatom cells L−1 for Zn, Cu and Cd, respectively. The maximum uptake of metals was obtained at pH 6.0 for Cu and at pH 8.0 for Cd and Zn. An increase in the biosorption of P. lanceolatum was observed with an increase in temperature from 15 to 25†C. The biosorption of all three metal ions followed the Langmuir isotherm. Competitive biosorption of Cd, Cu and Zn ions was also achieved. Fourier transform infrared spectroscopy revealed the different metal-binding functional groups on the diatom surface that are able to react with metals in the medium. The results suggest that P. lanceolatum can be used as a biosorbent for the efficient removal of heavy metals from aqueous solutions at temperature and pH values close to average values in the Tensift River.