The Effect Of Co-existed Transition Metal Ions On The Adsorption Of Cr By The Self-flocculating Yeast

In recent years, due to industrialization and urbanization accelerating, a large number of industrial and municipal wastewater was discharged into rivers, leading to deterioration of the aquatic environment and an increasing amount of toxic heavy metals in biogeochemical cycles. Successively, heavy metals penetrate into the aquatic and terrestrial ecosystems. Through the food chain transferring, it becomes a serious threat to aquatic life and human health. Cr is a typical heavy metal pollutant. Trivalent and hexavalent Cr compounds are the major forms of Cr in environment, usually in the form of Cr3+, CrO2-, CrO42- and Cr2O72-. Toxicity of Cr depended on its valence state; the toxicity of Cr(VI) is 100 times more than Cr (III). Electroplating industry is a typical industry emitting wastwater with heavy metal pollution, of which Cr(VI) wastewater is the main source.In a binary system, the coexistence of Ni2+or Zn2+ can inhibit the reduction of Cr(VI) by flocculating yeast SPSC01. And with increasing ion concentration, the impact of inhibition becomes more significant. Comparsion results indicated the effects of Zn2+ on the reduction of Cr(VI) are more significant than Ni2+. Coexistence of Cu2+ stimulates the reduction of Cr(VI) in low concentration (25 mg/L) by flocculating yeast SPSC01, completely shorten the reduction time from 12 h in Cr(VI) single system to 8 h. The coexistence of Ni2+ or Zn2+ decreases the removal efficiency of total Cr; inversely, the coexistence of Cu2+ exhibited a different result. The results determined on total Cr concentration of different parts of yeast cell through disrupting cell verified the promoting effect of Cu2+ on the removal of total Cr. By measuring flocculating ability of yeast after adsorption equilibrium, results indicate yeast SPSC01 which indeed absorbs heavy metals in different systems, the sedimentation rate reach almost 95%. The ORP of systems was monitored and Fourier transform infrared spectroscopy (FTIR) was analyzed, which showed coexistence of ions not only influence the changes of ORP in systems, but also influence interactions between different ions and absorption sites on cell surface. All in all, in a binary system, the coexistence of Ni2+, Zn2+ or Cu2+inhibit the adsorption of Cr(III) by flocculating yeast SPSC01. Because of different ion properties, the strength of the interactions between ions diversified. Isolating each component of cell proved that the presence of co-existed ions also affect Cr(III) adsorption ability of different cell components. After Fourier transform infrared spectroscopy (FTIR) analyzed, the results showed that the presence of co-existed ions affects surface functional adsorption sites of yeast cell. In the study on desorption and recycling of yeast, the results indicated that 0.5M NaHCO3, in room temperature (25℃), generates a very positive desorption, after five rotation of the yeast SPSC01 recycling, the removal rate of Cr(Ⅵ) could still reach above 90%, this indicates its high regenerating performance and recycling value.