Cadmium adsorption by a bacterial biofilm supported on clinoptilolite from aqueous solution

Heavy metals pollution represents a serious problem for human health and for life in general and bacterial biofilms are able to adsorb heavy metals from dilute aqueous solutions and accumulate them within their cell structure. The aim of this study was to investigate the ability of Escherichia coli biofilm (an effective agent for metal adsorption) supported on clinoptilolite for the removal of cadmium from aqueous solutions. Adsorption experiments were carried out in a laboratory-scale batch model with clinoptilolite alone and clinoptilolite covered by a bacterial biofilm. The effects of initial heavy metal concentrations, pH, and agitation time on the removal efficiency were studied. Finally, experimental results were analyzed using isotherm equations. The results of this study revealed that cadmium adsorption to clinoptilolite was lower than that of clinoptilolite covered by biofilm and adsorption of the cadmium was influenced by several parameters such as initial concentration of cadmium, biosorption time and solution pH. The uptake values for clinoptilolite and for clinoptilolite covered by biofilm were 6.8 mg/g and 9.6 mg/g respectively in the batch model, for initial cadmium concentrations of 25 and 100 mg/L. It was also observed that as the initial cadmium concentration increased, the uptake increased, but the removal rate decreased. Maximum adsorption efficiency was achieved at pH value of 6. The biosorption equilibrium for cadmium was best described by the Freundlich and Longmuir models. It is concluded that the presence of biofilm increased the uptake efficiency of clinoptilolite and the biofilm tested in our study seems very promising for the removal of cadmium from aqueous solution.