Characterization of Pb2+ biosorption from aqueous solution by Rhodotorula glutinis

Abstract

The yeast Rhodotorula glutinis was examined for its ability to remove Pb 2+ from aqueous solution. Within 10 min of contact, Pb 2+ sorption reached nearly 80% of the total Pb 2+ sorption. The optimum initial pH value for removal of Pb 2+ was 4.5-5.0. The percentage sorption increased steeply with the biomass concentration up to 2 g/l and thereafter remained more or less constant. Temperature in the range 15-45°C did not show any significant difference in Pb 2+ sorption by R. glutinis. The light metal ions such as Na + , K + , Ca 2+ , and Mg 2+ did not significantly interfere with the binding. The Langmuir sorption model provided a good fit throughout the concentration range. The maximum Pb 2+ sorption capacity q max and Langmuir constant b were 73.5 mg/g of biomass and 0.02 l/mg, respectively. The mechanism of Pb 2+ removal by R. glutinis involved biosorption by direct biosorptive interaction with the biomass through ion exchange and precipitation by phosphate released from the biomass. IntroductionBecause of rapid industrialization, an alarming amount of toxic heavy metals has been released into the environment, endangering natural ecosystems and public health. From hundreds to thousands of tons of lead are discharged from electric battery manufacturing, lead smelting, internal combustion engines fueled with leaded petroleum, and mining activities. Lead acts on the central nervous system, on blood pressure and on reproduction [1].Conventional methods for heavy metal removal are precipitation, coagulation, reduction, ion exchange, evaporation and membrane processes. These methods have several disadvantages, such as less-effective removal of metal ions, high reagent requirements, high costs, the generation of toxic sludges, and the problem of the safe disposal of the materials [2]. Biosorption (biological metal removal) processes have distinct advantages over conventional methods; for example, they are highly selective, more efficient, easy to operate, and cost effective.The potential for using microorganisms in the treatment of metal-bearing wastewater has been studied intensively, and many microorganisms including bacteria, fungi, and algae have been found to remove metals from solutions [3,4]. The biosorption of heavy metal ions by microorganisms may be placed into two categories: metabolism-independent entrapment in the cellular structure and subsequent sorption onto the binding sites present in the cellular structure, and metabolism-dependent transport across the cell membrane through the cell metabolic cycle [5]. The metal-sorption mechanisms, including complexation, ion exchange, coordination, adsorption, chelation, and microprecipitation, are complex and are dependent on the chemistry of the metal ions, surface properties of the microorganisms, and cell physiology [6,7]. The biosorption process is affected by the physicochemical influence of the environment, such as pH, temperature, biomass concentration, initial metal concentration, and competing ions [8].Yeasts possess an acknowledged potential for the r...

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