Biosorption of cadmium ions by Actinomycetes and separation by flotation

Among the most important parameters which have to be examined, when treated waste waters are going to be recycled, is their content of toxic metals, d ue to ever decreasing metal disposal limits. For this reason, the examinati on of effective and innovate waste water treatment methods becomes an impor tant need. The removal of cadmium, a toxic metal of high environmental prio rity due to its toxicity, from dilute aqueous solutions has been studied in the present work, applying microorganisms and using living, as well as non -living bacterial biomass of two specially isolated Actinomycetes strains, AK61 and JL322. The main parameters influencing this treatment process, nam ely contact time, pH of the solution, temperature and toxic metal and bioma ss concentrations have been examined and Langmuir isotherms have been depic ted. Dispersed-air flotation was applied as the subsequent separation metho d for harvesting the suspended metal-laden microorganisms, following the bi osorption of cadmium. The investigated parameters (in batch mode, laborator y scale) were in this case the dispersion pH, the flotation time, the air f lowrate and the surfactant concentration. Electrokinetic measurements have been also performed for the biomass dispersions, under similar conditions w ith biosorption, providing useful information for the process mechanisms. A pplying the optimum defined conditions, over 95% removal of cadmium has bee n achieved in one stage and simultaneously, quantitative separation of the used (metal-loaded) biomass has been obtained. (C) 1999 Elsevier Science Lt d. All rights reserved.