Study Of Cr(VI) Biosorption By Flocculating Yeast SPSC01

Heavy metal pollution has been the very serious world environmental problems. Chromium in this article is a typical heavy metal with higher toxicity. Trivalent and hexavalent compounds (Cr3+, CrO2-, CrO42-, Cr2O72-) are the major compounds of Chromium in waters. Traditional treatment methods of Cr(VI) includes ion exchange, chemical precipitation, activated carbon adsorption, etc. It is suitable for high concentration wastewater treatment. When the Cr(VI) concentration is low (<100 mg/L), the removal efficiency is low, and the cost is high.Biosorption of heavy metal have higher advantages than physical and chemical methods, particularly in the treatment of low concentrations of heavy metals in wastewater. The normal biosorbents includes bacteria, fungi, yeast and algae. Biological materials have wide variety of sources and those costs are low. However, Biosorption is limited because of small scale, low density, solid-liquid separation in the application of heavy metals in wastewater treatment.The flocculating yeast SPSC01 in this article with good flocculation characteristics has been put into the industrial production of fuel ethanol. The mechanism of Cr(VI) biosorption by flocculating yeast SPSC01 has been studied. The results showed that, pH was the most significant parameter on the process of Cr(VI) reduction-adsorption. In the certain range, Cr(VI) was more favorable reduced to Cr (Ⅲ) with the lower pH, and the process was reached equilibrium much earlier. Cr(III) was more favorable adsorbed on biosorbents with the higher pH, and the total chromium removal rate was higher. pH 2 was the optimal pH, considering all the factors. It was found that the Cr adsored to SPSC01 was Cr(III), by digesting SPSC01 after adsorption. SPSC01 was approached by chemical modification, and SPSC01 was compared with the different biosorbents on Cr(VI) adsorption.The results indicated that the major functional groups (amino, carboxyl and amide) may contribute to the absorption of Cr(VI). FTIR results also proved this result. Most of the Cr was absorbed on the cell wall, from the result of TEM and Cr composition on the components of SPSC01 after separation. Cell wall prevented the entry of lots of Cr ions, reducing the toxicity of Cr. When the Cr(VI) adsorption process reached equilibrium, SPSC01 still has biological activity, so could be adsorbed after desorption, and improved efficiency. The method of 1 mol/L HNO3 at 35℃was a good desorption method. SPSC01 could be recycled under this way, and the method was a favorable way for recovery of Cr.