Study On Adsorption Mechanism Of Lead And Cadmium Wastewater Treated By Immobilized Yeast

Heavy metal wastewater pollution has plagued human society for years.The heavy metal has large toxic effects on the human body,which has damaged the ecological environment badly.The wastewater of lead and cadmium,which is mainly from electroplating or metallurgy and other industries,is a major cause of human bone pain and other diseases.Immobilized microorganism technology has advantages of high efficiency,no secondary pollution and so on when use it to treat heavy metal wastewater.It has good environmental and economical benefits.In this paper,sodium alginate,gelatin and polyvinyl alcohol were used as the materials to prepare the immobilized yeast according to the optimized proportion(sodium alginate 2%,gelatin 0.5%,polyvinyl alcohol 2%).The experiment showed that immobilized yeast had the strongest ability to deal with heavy metal ions compared to separate yeasts and carrier,implemented under the condition that Pb2+,Cd2+ initial concentration was 120mg/L,pH =5.0,temperature was 25 ? and rotational speed was 180r/min.And the result was showed that immobilization technique could improve the ability of yeast to absorb heavy metal ions.Immobilized yeast adsorption capacity of Pb2+ and Cd2+ was 9.5mg/g and 7.84mg/g,respectively.The analysis of experiment with 0.1mol/L HCl as desorption agent showed that the immobilized yeast pellets can be recycled at least 5 times,each time the adsorption rate of Pb2+ can reach above 70%,the desorption rate can reach more than 85%;each time the adsorption rate of Cd2+ can reach above 60%,the desorption rate can reach more than 80%.The above showed that the immobilized yeast had good stability and reproducibility.It was found that the SA-PVA-gelatin carrier's structure was beneficial to the adhesion and growth of yeast according to SEM technique.At the same time that immobilization techniquet had little impact on microorganism was proved by a large of yeast inside.The internal structure of immobilized yeast beca1e more loose after adsorpting Pbro and Cd2+,which was beneficial to further adsorption.It was found that the characteristic absorption peak of ester carbonyl was increased by FTIR,which indicated that the carboxyl group on the surface of yeast cells could react during adsorption.Changes of FTIR spectra between before and after treatment with immobilized yeast showed that the adsorption of Pb2+ was related to-OH,-COOH1 B-O or cyclic C-H groups,and there were groups of-OH,-COO,B-O or Cyclic C-H,carbonyl,-CH2-involved in adsorption reaction of Cd2+.It was proved that there were chemical adsorption in the adsorption process.It was showed that immobilized yeast had less adverse effect of oxidative injury than yeast by the content of MDA produced in the process of Pb2+ and Cd2+ coercion.And it was found that the extracellular complexation mechanism played an important role in the adsorption by using the method of adding HNO3,which reflecting the tolerance of immobilized yeasts resulting in alleviating the toxic effects of Pb2+ and Cd2.