Role of bacterial extracellular polymers in metal uptake in pure bacterial culture and activated sludge—I. Effects of metal concentration

Abstract

A gel filtration technique afforded a good separation between metal complexed with bacterial extracellular polymers and free metal ions. The complexation of polymers extracted from cultures of Klehsiella aerogenes and activated sludge with cadmium, nickel, manganese and cobalt was demonstrated. The extraction of extracellular polymers from cultures of K. aerogenes and activated sludge reduced the capacity of the cells and flocs to adsorb metal. Adsorption and complexation of metals by cells of K. aerogenes and extracellular polymers extracted from activated sludge were fitted to Freundlich equilibrium isotherms. Saturation of activated sludge polymer binding sites occurred at 10 mg 1 −1 metal additions for all the metals studied except manganese which was complexed to a very limited extent. Cells of K. aerogenes exhibited no saturation effects in the range of metal concentrations studied. Precipitation of metals below a concentration of 1 mg 1 −1 was minimal, with the exception of cadmium precipitation. At a concentration of 10 mg 1 −1, precipitation of cadmium, cobalt and manganese may have been the major mechanism of metal removal. The more soluble metals generally displayed the lowest removals. Concentrations of extracellular polymers and soluble chelating agents may be important in controlling removals of metals which are largely soluble in activated sludge.