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, due to ever decreasing metal disposal limits. For this reason, the examination of effective and innovate waste water treatment methods becomes an important need. The removal of cadmium, a toxic metal of high environmental priority 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, namely contact time, pH of the solution, temperature and toxic metal and biomass concentrations have been examined and Langmuir isotherms have been depicted. Dispersed-air flotation was applied as the subsequent separation method for harvesting the suspended metal-laden microorganisms, following the biosorption of cadmium. The investigated parameters (in batch mode, laboratory scale) were in this case the dispersion pH, the flotation time, the air flowrate and the surfactant concentration. Electrokinetic measurements have been also performed for the biomass dispersions, under similar conditions with biosorption, providing useful information for the process mechanisms. Applying the optimum defined conditions, over 95% removal of cadmium has been achieved in one stage and simultaneously, quantitative separation of the used (metal-loaded) biomass has been obtained. (C) 1999 Elsevier Science Ltd. All rights reserved.