固定化酿酒酵母处理含铀废水的特性及机理

Radioactive waste treatment in security ensures the sustainable development of the nuclear industry. Biotechnology,with the great application potentiality to treat low-level radioactive wastewater in large quanity,is an relative innovative method in comparison with the traditional physical and chemical treatment technologies.Biotechnology has not been applied yet in treating radioactive wastewater, due to the nature of organisms, and due to the limited understanding of radionuclide-microbe interactions,etc. In this project, uranium-containing wastewater treatment by the immobilized Saccharomyces cerevisae will be investigated. First, the innovative immobilization methods will be developed to produce the immobilized yeast cells of Saccharomyces cerevisiae with good mechanical performance, expected to be suitable for treating uranium-containing wastewater in real application. Then, removal of radionuclide uranium from aqueous solution onto the immobilized yeast cells of Saccharomyces cerevisiae will be studied, deeply and systemically. The effects of factors influencing uranium removal by the immobilized yeast cells such as initial solution pH, biomass dosage, contact time, temperature, initial uranium concentration,ionic strength, organic matter, co-existing cations and anions will be analyzed. Important factors such as pH on uranium removal will be discussed in detail. The kinetics, isotherms and thermodynamics of uranium sorption onto the immobilized cells will be explored.The performance of uranium removal from wastewater by the immobilized yeast cells will be evaluated. Based on the above macro-level study, the interactions between uranium and the immobilized Saccharomyces cerevisae at micro-level will be explored through the multidisciplinary knowledges and the complementary modern analysis technologies, such as atomic absorption spectrometry (AAS), inductively coupled plasma atomic emission spectroscopy (ICP-AES), infrared absorption spectroscopy or fourier transformed infrared spectroscopy (IR or FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), TEM-EDX (energy-dispersive X-ray), SEM-EDX, and X-ray photoelectron spectrum (XPS), X-ray absorption fine structure (XAFS), atomic-force microscopy (AFM) etc. At celluar/molecular/atomci level, Uranium speciation and location, the solid-liquid interface and the inside of the immobilized yeast cells of Saccharomyces cerevisae, as well as the aqueous solution system, will be characterized before and after uranium contact with the immobilized yeast cells of Saccharomyces cerevisiae in aqueous solution. The project is expected to offer valuable information for applying the biotechnologies in uranium-containing radioactive wastewater treatment.

放射性废物的安全处理处置是核工业可持续发展的保证。与传统物理化学方法比较，生物法是具有较大潜力治理大规模放射性废水的新方法。生物本身特性、对生物-放射性核素相互作用理解不足等因素，限制了生物法的应用。本项目拟以核工业的重要原料放射性核素铀为对象，以酿酒酵母为模式生物，研究固定化新技术、制备适于处理含铀废水、具有实用潜力的固定化酵母，系统、深入地研究固定化酵母处理含铀废水的特性及机理。考察多种影响因素以及动力学、热力学等过程，评价固定化酵母处理含铀废水的性能，获得固定化酵母处理含铀废水的特性。结合重要影响因素如pH的控制与分析，综合利用多种仪器分析手段（SEM-EDX,AFM,XPS,XAFS,FTIR等），在细胞/分子/原子微观尺度上,分析铀的去向与赋存形态、细胞固液界面反应机制与界面特征、细胞内部特征、水溶液体系变化特征等,揭示固定化酵母与铀的相互作用机理,为生物法治理含铀废水提供依据。

铀主要用作为原子能发电的核燃料或制备核武器的原材料。放射性废物的安全处理处置是核工业可持续发展的保证。生物法是具有较大潜力治理大规模放射性废水的新方法。生物本身特性、对生物-放射性核素相互作用理解不足等因素，限制了生物法的应用。固定化细胞技术是改善生物法工业化应用的重要技术手段。本项目以核工业的重要原料放射性核素铀为对象，以酿酒酵母为模式生物，探索比较了多种固定化细胞新技术，制备比较了不同包埋载体（海藻酸钠/聚乙烯醇/氧化石墨烯）、不同来源形式酵母细胞（工业废弃干酵母、商业高活性干酵母、新鲜培养湿酵母）、不同包埋方法（硼酸-氯化钙法、磷酸盐法、硫酸盐法、硝酸盐法、共培养方法）等制备的多种固定化酵母，对各类酵母进行了表征，探讨了新型固定化酵母吸附铀的特性及机理。综合利用聚乙烯醇-硼酸和或海藻酸-氯化钙两种制备容易且价格低廉的固定化包埋方法，通过添加新型碳材料氧化石墨烯修饰聚合物材料，获得了性能优良的新型固定化酵母。该方法降低了聚乙烯醇用量（从经验值7.5%~15%降低到5%），例如聚乙烯醇、海藻酸钠、氧化石墨烯分别为5%、1%、0.01%时制备的固定化废弃酵母颗粒，增强了酵母的机械性能、对酸碱盐溶液长期（10个月）浸泡处理具有更强化学抗性，具有较宽泛的pH值使用范围（3~9）、对铀吸附稳定，酸脱附效率达到90%以上。分析了多种影响因素如时间、铀浓度、pH值对固定化酵母吸附铀的影响，探讨了动力学等过程，表明一定反应条件下固定化酵母与自由细胞比较，吸附量从32 mg/g降低到21.4~27.4 mg/g，符合准二级动力学过程。包埋的活性干酵母具有较高活性，葡萄糖（初始浓度16.3 g/L）利用率达到98.5%以上，乙醇浓度达到6.7 g/L以上。研究证实本项目提供了一种利用氧化石墨烯修饰聚乙烯醇-海藻酸钠包埋固定化微生物处理含铀废水的新方法。结合各类现代仪器检测技术, SEM-EDS、FTIR、TEM-EDS、XPS、XAFS、ICP-MS、ICP-OES、UV-VIS等证明，固定化细胞中起主要吸附作用的是微生物酵母；吸附的铀不均匀分布于细胞表面以及细胞内部；细胞含氧含磷基团发挥了重要的铀吸附作用；固定化酵母不同程度释放K、Na、Ca、Mg离子；固定化酵母吸附铀的过程是静电吸引、离子交换、表面络合等多种机制共同发挥作用的结果。本研究为含铀废水治理提供了依据。