Study On The Baker's Yeast And Its Immobilization On Adsorbing And Removing Chromium Ion

Heavy metal is the pollutant which is extremely harmful to the ecological environment. It's easy to accumulate in living organism, and ultimately does harm to human health through the food chain due to its non-degradable feature. With the rapid development of chemical industry including electroplating, metallurgy, dyes, oil and batteries, heavy metal pollution on the ecological environment and human health has become increasingly serious, more and more attention about the treatments of wastewater containing heavy metal ions has been paid in recent years. In the large number of processing methods, such as electrolytic method, ion exchange method, electrodialysis method, etc. the biosorption attracts extensive attention, for which have many advantages, such as good effect on removing heavy metal ions, convenient operation, low cost and no secondary contamination. Immobilized microorganism technology can fix dominant bacteria, which are filtered out selectively, forming a wastewater treatment material that is efficient, fast and able to consecutively dealing with the wastewater. Moreover, immobilized microorganism technology can effectively reduce the secondary pollution and has good effect on removal of heavy metal. It has already shown its great potential and become a research focus in both home and abroad these years. This research mainly consists of the following two parts:The first part studies the biosorption of baker's yeasts for Cr(III,VI). All the influencing factors on adsorption, such as adsorption time, pH value, initial concentration of Cr(III,VI) and coexisting ions, were investigated and the results showed that the capacity of yeast's adsorption for Cr(III) was better than that for Cr(VI). In addition, all of these adsorbing processes fit very well with the model of the Langmuir isotherm. baker's yeasts were determined by infrared spectrometer, the investigations indicated that the active groups of baker's yeasts contains carboxyl, amido, hydroxyl, carbonyl, phosphoryl, etc. Under the conditions of pH 5.5, the zeta potential of the baker's yeasts was negatively charged, which made it's easier to combine with Cr(III) in the form of cations. Under the conditions of pH 1, the baker's yeasts was were positively charged, which made it's easier to combine with Cr(VI) in the form of anions.The second part studies the adsorption of the three kinds of adsorbents (chitosan, immobiled baker's yeasts with/without chitosan) for Cr(III). All the influencing factors on adsorption, such as adsorption time, pH value, initial concentration of Cr(III), coexisting ions and elution conditions, were studied and the results showed that the adsorbed mass of the immobiled baker's yeasts with chitosan was bigger than the sum of the two others', it is suggested that added chitosan enhanced the mass transfer performance of the immobilized baker's yeast, and finally improve the adsorption and desorption effects of the immobilized baker's yeast on Cr(III). In addition, all of these adsorbing processes fit very well with the model of the Langmuir isotherm. The elution experiment showed that both reversible and irreversible adsorption occurred simultaneously in the adsorption process and the reversible adsorption had a greater affect. And the effects of adsorption and desorption dynamically was better than statically. After examining by SEM and TEM, the results showed the baker's yeasts can adsorb Cr(III) when they were immobilized, and the chitosan strenghen the stability of immobilized medium. The results of the FTIR testing indicated that these active groups (carboxyl, amido, hydroxyl, phosphoryl, etc.) played a very important role in the process of removing Cr(III). XRD analysis showed that some chemical action happened between chitosan and sodium alginate when adding chitosan in the process of immobilization. In addition, the degeneration on diffraction of the adsorbents after they adsorbed Cr(III) showed that some interreaction happened between Cr(III) and the adsorbents, so their capability and effects of crystal formation were changed.