Application of an E. coli biofilm supported on Kaolin to the removal of Cd(II), Cr(VI), Fe(III) and Ni(II) from aqueous solutions

Abstract

The pollution caused by heavy metals is one the major environmental problems that is imperative to be solved. New technologies, easy to implement and to adapt to any system, deserve special attention and are the focus of this presentation. This paper aims to investigate the biosorption behaviour of a biofilm of E. coli supported on kaolin clay for the treatment of cadmium, iron, nickel and chromium aqueous solutions. The effect of metals initial concentrations were studied and the relationship between pH and removal efficiency were analysed. Adsorption characteristics of a biosorbent can be depicted by an adsorption isotherm. Langmuir, Redlich-Peterson and Sips are commonly used for the description of adsorption data and were applied to the experimental results described by this report. The presence of functional groups in the suspended biomass that may have a role in biosorption process was confirmed by FTIR. It was demonstrated that a biofilm of E. coli supported on kaolin is able to remove Cr (VI), Cd (II), Ni (II) and Fe (III) from aqueous solutions. The isotherms were fitted and the best fit for chromium and nickel was obtained with the Redlich-Peterson model isotherm and for cadmium the best fit was the obtained with the Sips model. In terms of removal percentage, the results showed 100% of removal for iron for the whole range of concentrations tested. For cadmium, the removal percentage remains around 70% for all the initial concentrations tested (between 67.1% and 78.9%) and is higher than the obtained for nickel and chromium. The analyses by FTIR showed that functional groups on the biomass, such as hydroxyl, carboxyl and phosphate groups, may be the main binding sites for biosorption of the studied heavy metals by E. coli. Finally, the metal affinity to the biofilm was found to follow the sequence Fe > Cd > Ni > Cr and the preference of a sorbent for a metal may be explained on the basis of electronegativity of the metal ions and on the basis of the cation/anion state.Fundação para a Ciência e a Tecnologia (FCT)FEDERMinas de Barqueiros, S.A