| Biosorption is a process that utilizes inexpensive biomaterials to sequester heavy metals and is particularly useful for the removal of contaminants from industrial effluents.Compared with conventional methods such as ion exchange and precipitation,Biosorption process offers the advantages of low operating cost,minimization of volume of chemical and biological sludge to be disposed of,high efficiency in detoxifying very dilute effluents.These advantages have served as the primary incentives for developing biosorption processes to clean up heavy-metal pollution.Biosorption of heavy metals by yeast cells has been studied extensively in the last decade for wastewater treatment.Although flocculating yeast cells can be separated from liquid phase easily,which is desirable for large scale processes,they have been rarely used in biosorption.In this study,a self-flocculating yeast strain,SPSC01,was utilized for the Cr(Ⅵ) removal. The ability of the self-flocculating yeast SPSC01 to remove Cr(Ⅵ) from aqueous solutions was investigated.Effect of initial pH,contact time,initial concentration of Cr(Ⅵ),initial concentration of biosorbent and temperature on the biosorption was determined and it was found that pH was a significant factor affecting not only the removal ability of Cr(Ⅵ) by the self-flocculating yeast but also the contact time required for the biosorption equilibrium,with an optimum of 2.0,while no significant impact of temperature from 30 to 40℃on the biosorption was observed.The fitness of the experimental data for the Freundlich and Langmuir adsorption models was further examined and good correlations with R2=0.9808 and 0.9836 were observed,indicating both monolayer biosorption and the presence of heterogeneous surface conditions.Since only Cr(Ⅲ) was detected in the solution after the self-flocculating yeast adsorbed with Cr(Ⅵ) was treated by HNO3 under high temperature,the mechanism of the biosorption was deduced to be the reduction of Cr(Ⅵ) into Cr(Ⅲ) on the surfaces of the self-flocculating yeast,and a pseudo second-order kinetic model was developed to describe the biosorption process.
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