【作者】 杨晓南；

【导师】 崔福义；

【作者基本信息】 哈尔滨工业大学 ， 市政工程， 2013， 博士

【摘要】 纳米技术是世界发达国家最优先发展的科技领域之一，纳米材料已广泛应用于工业、农业和科技等领域。在创造产业利益的同时，纳米材料通过直接或间接方式被排放入环境，由此引发的环境风险问题受到广泛关注。水环境是纳米材料的主要归宿地之一，复杂的水环境会改变纳米颗粒在水中的环境行为与稳定性，与活性污泥的相互作用也会对污水处理效能和微生物特性产生抑制作用，最终危害水生环境安全。针对此问题，本文以应用最为广泛的纳米二氧化钛（纳米TiO₂）为研究对象，研究纳米TiO₂在水中的存在特性，分析TiO₂在天然水与污水中的粒度分布、稳定性及其影响因素。同时研究纳米TiO₂对污水生物处理系统中活性污泥絮体稳定性和表面特性的影响，确定纳米TiO₂对活性污泥絮体物理化学稳定性的影响机制。采用最新的焦磷酸测序技术解析纳米TiO₂对活性污泥絮体生物稳定性的作用行为，考察了微生物生理生化特性及群落生态结构对纳米TiO₂长期影响下的环境响应，为深入研究纳米材料对水环境的潜在危害提供理论基础。纳米TiO₂在水中的表面电荷、粒径范围和浓度是影响其在水环境中迁移转化的关键因素。在去离子水中，纳米TiO₂颗粒分布均匀，粒径大小差异较小，分散程度较好。纳米TiO₂的等电点为pH=6.50，当pH<6.50时，纳米TiO₂颗粒表面带正电荷，而溶液pH>6.50时带负电荷。纳米TiO₂与水中溶解性有机质（天然有机物DOM、污水中有机物）之间的相互作用形式主要为配位体交换和静电力作用，其中配位体交换作用主要为羧基和酚羟基官能团的相互作用。天然水环境条件下，当pH为7时，纳米TiO₂与低分子量DOM配位体反应程度较高，而静电排斥为高分子量DOM与纳米TiO₂的作用主导，导致水体颗粒聚集体稳定性增加。pH为5时，纳米TiO₂与DOM之间的相互作用由两种方式共同完成。与天然水环境相似，城市污水环境中低分子量有机物与纳米TiO₂相互作用主要以配位体交换反应为主，而静电斥力作用是高分子量有机物与纳米TiO₂作用的主导，因此城市污水环境中主要为小分子量有机物与纳米TiO₂的相互作用，这为有效去除进入进入城市污水处理厂后的纳米材料提供理论依据。通过扩展的DLVO理论的解析和热力学分析手段，应用开尔文显微镜原位检测活性污泥絮体表面电势的创新手段，考察了纳米TiO₂对活性污泥生物处理系统中活性污泥絮体物化稳定性的影响。理论分析与实验结果表明，长期暴露的纳米TiO₂使活性污泥絮体与纳米颗粒碰撞几率增加。由于活性污泥胞外聚合物（EPS）的作用使纳米TiO₂包裹于絮体表面。通过活性污泥絮体表面电势的表征，分析了纳米TiO₂对活性污泥絮体表面电势的影响。结果显示纳米TiO₂的存在导致系统内微生物胶体稳定性增加，降低了絮体沉淀性能，从而增加了活性污泥处理系统运行失效的风险。通过扩展的DLVO理论解析了纳米TiO₂存在的活性污泥微生物体系的稳定性。在范德华吸引作用、静电力作用和水合作用共同作用下，短程范围内活性污泥微生物体系中的纵斥力势垒不断增加，吸引作用和有效Hamaker值均呈下降趋势。在中程范围内静电力自由能对总位能的贡献呈现优势，而且随着纳米TiO₂浓度的增加呈增加趋势，导致活性污泥的稳定性增加、凝聚能力降低，直接降低泥水分离效果。采用序批式活性污泥工艺（SBR）模拟城市污水活性污泥生物处理系统，研究长期暴露下（30天）不同浓度纳米TiO₂对稳定运行状态下SBR系统处理效能和微生物生理生化与菌群群落生态的影响。实验结果表明，不同浓度纳米TiO₂对活性污泥系统有机物和NH3-N的去除能力具有显著的抑制作用，且随着投加量的增加抑制程度加强，而整个过程对PO43-去除没有影响。不同浓度纳米TiO₂对微生物数量和活性影响研究结果证实，微生物数量和活性受纳米TiO₂的影响结果与污水处理效能结果一致，在低浓度投加条件下，系统微生物浓度和活性并未受到较大影响，而当投加浓度提高后（25和100mg/L），由于活性污泥胞外聚合物（EPS）中的羧基和羰基与纳米TiO₂发生了配位体作用，导致系统MLVSS含量与未投加系统相比分别降低了18.4%和22.9%，以TTC-电子传递体系（TTC-ETS）表征的污泥活性分别降低了19.95%和44.77%，EPS中蛋白质和多糖含量均有不同程度的降低。应用焦磷酸测序技术深度分析了微生物对纳米TiO₂长期影响的群落结构响应，实验结果表明在纳米TiO₂长期存在下的活性污泥微生物群落结构与无纳米TiO₂存在时存在明显差异。活性污泥菌群Shannon指数随着纳米TiO₂投加浓度的提高逐渐降低，生物群落多样性受抑制于纳米TiO₂，导致菌群稳定性降低。微生物群落差异性分析结果显示，活性污泥系统中优势菌群结构对不同浓度的纳米TiO₂存在相应的菌落响应，且在聚类关系上存在差异。纳米TiO₂对微生物在门、纲、属水平均有一定程度的影响，以Nitrospirae门硝化细菌和Actinobacteria门异氧菌受抑制程度最高，而对Proteobacteria门除磷菌具有促进作用。更多还原

【Abstract】 Nanotechnology was of priority in the developed countries, and has been applied inthe areas of industry, farming and science and technology. In the meantime, it willinevitable cause the release of nanoparticles to the environment by direct or indirectways. Thus the corresponding environmental implications arise great concerns. Aquaticenvironment was the main receptor of nanoparticles, and the behavior and stability ofnanoparticles would change under the complicated water conditions. Also the inhibitionof wastewater treatment efficiency and organism’ property may also be inhibited for thereason of the interaction of activated sludge and nanoparticles, which will threaten thewater safety eventually. For these reasons, the nano TiO₂, one of the most commonnanomaterials was selected for the study of the surface characteristic in aquatic system.And the diameter distribution, stability and the effect factors of nano TiO₂in surfacewater and wastewater were analyzed. On the other hand, effects of nano TiO₂on thefloc stability and surface characteristic in biological wastewater treatment plant（WWTP）were studied to confirm the physical and chemical mechanism. Additional, the newpyrosequencing was employed to investigate the effects of nano TiO₂on the biologicalstability. The response of physiological/biochemical characteristics and microbialcommunity structures to nano TiO₂was evaluated. This research will provide theorybasis for the study of potential risks of nanoparticles to aquatic environment.The distribution of nano TiO₂was even and the differences of diamater wasneglectable, which resulted in acceptable distribution degree. The zero potential pointlocation was between the pH6and7, and the absolute value of potential increased asthe pH deviated from the isoelectric point. The results of the fourier transform infraredspectroscopy and three-dimensional fluorescence spectrum showed that the interactionof nano TiO₂and dissolved organic matters was the electrostatic repulsion and ligandexchange, in which the ligand exchange was dominated by the interaction of thefunctional group of carboxyl and phenol hydroxyl groups. The stronger reaction wasdrived by ligand exchange in the situation of smaller molecular weight of dissolvedorganic matters as the pH was7. However, the electrostatic repulsion dominated theinteraction of high molecular weight dissolved organic matters and nano TiO₂, whichresulted in more stability of particles’aggregators. On the contrary, at pH was5, theadsorption of nano TiO₂and dissolved organic matters was accompliced by both thesetwo effects, and the adsorption was greater in smaller molecular weight of dissolvedorganic matters and nano TiO₂. In consistent with the situation of natural aquaticenvironment, the dominated effect of nano TiO₂and dissolved organic carbon waselectrostatic repulsion and ligand exchange for bigger and smaller molecular weight of dissolved organic carbon respectively in wastewater environment, and the interactionwas principally achieved by smaller molecular weight of dissolved organic matters.These results would be a theory basis for the removal of nanoparticles in WWTP.The wide application of nanosized titanium dioxide （nano TiO₂） will result in highconcentrations of the molecule in the aquatic environment, especially in the influent ofWWTP. The present study focuses on the potential effect of nano TiO₂on thephysicochemical stability of activated sludge flocs after long-term exposure, on whichlimited information is currently available. Kelvin probe force microscopy （KPFM） wasinnovatively applied to assess the surface potential of the activated sludge in situ. Thephysicochemical characteristics of the bioflocs with and without long-term exposure tonano TiO₂were well elucidated by the thermodynamic approach. The results showedthat the repulsive force predominated the bioflocs system as the concentration of nanoTiO₂increased, owing to the corresponding increase in the density of the negativecharge. The bioflocs exposed to100ppm nano TiO₂presented the strongest stabilitycompared to the other two samples with low concentrations of nano TiO₂, which alsoindicated that the bioflocs with long-term exposure to nano TiO₂had a low settlementefficiency of the corresponding activated sludge. Further, the extended Derjaugin,Landau, Verwey, and Overbeek （XDLVO） theory was used to explore the flocculationstability of the bioflocs system. As the concentration of nano TiO₂increased, the van derWaals interaction and the effective Hamaker constant decreased, the electrostaticdouble-layers interaction increasingly contributed to the interfacial repulsion, the Lewisacid–base interaction also exhibited a repulsive contribution to the total interactionenergy and the total free energy of interaction exhibited a repulsive contribution. Theseresults are the keys for interpreting the adverse effects of nano TiO₂on the activatedsludge flocs of WWTP.The effects of long-term exposure of nano TiO₂at different concentration on thepollutions removal, physiological/biochemical characteristics and microbial communitystructures were evaluated in sequencing batch reactor. The results suggested that, theNH3-N and TOC removal was remarkable inhibited by nano TiO₂, and the inhibitionwas enhanced along with the increase dosage of nano TiO₂, whereas the biologicalphosphorus removal was unaffected. In accordance with the removal efficiency, theMLVSS and activities of microorganism were effected directly by the nanoTiO₂in theinfluent. For the reason of the ligand exchange, the MLVSS decreased to18.4%and22.9%, and the TTC-ETS decreased19.95%and44.77%as the dosage was25and100mg/L respectively, also the protein and carbohydrate in extracellular polymericsubstances were inhibited.The response of physiological/biochemical characteristics and microbial community structures to nano TiO₂were analyzed by pyrosequencing. The resultsillustrated that nano TiO₂obviously reduced the diversity of microbial community inactivated sludge. The Shannon index was highly decreased after long-term exposure tonano TiO₂, which resulted in the deterioration of activated sludge floc stability. Furtherstudy revealed that the predominance microbial community was changed afterlong-term exposure to nano TiO₂. The response of predominance microbial communitywere consistent with the observed influences of nano TiO₂on biological nitrogen andphosphorus removal, and the differences were found in cluster relation. The effects werefound on the levels at phylum, class and genus, especially on Actinobacteria andActinobacteria which were in charge of nitration and heterotrophism, and the proportionof Proteobacteria was increased.更多还原