EGI OpenIR
细菌生成纳米 Se 修复 Hg0污染环境
Alternative TitleRemediation of Hg0 contaminated environment using selenium nanoparticles synthesiszed by bacteria
王潇男
Subtype博士
Thesis Advisor潘响亮
2019-06-30
Degree Grantor中国科学院大学
Place of Conferral北京
Degree Discipline理学博士
Keyword生物纳米硒 元素汞 固定 稳定性 移动性 Biogenic Selenium Nanoparticles Elemental Mercury Immobilization Stability Transport
Abstract本研究选取一株柠檬酸杆菌,它可以在好氧和厌氧环境下将亚硒酸盐还原为无定型态的生物纳米硒颗粒,进而固定土壤和水体中的元素汞。本研究初步探究了亚硒酸盐好氧还原的机理,主要是超氧自由基在好氧亚硒酸盐还原过程中的调控作用。同时, 评估了主要环境因素例如胞外聚合物、矿物胶体、 溶解性有机质、颗粒态有机质、盐度、生物膜等对生物纳米硒稳定性、移动性及其固定元素汞效果的影响。 本文的主要结论如下:(1)筛选得到的柠檬酸杆菌(Citrobacter freundii Y9)在厌氧和好氧条件下均可将亚硒酸盐还原为被胞外聚合物包裹的无定型态的生物纳米硒颗粒。细菌胞外产生的超氧自由基可以调控好氧亚硒酸盐的还原。(2)在厌氧和好氧条件下, 4 mM 未纯化处理的生物纳米硒可以将菜园土中45.8-57.1%和 39.1-48.6%的元素汞转化为硒化汞这一残渣态汞的形式。 此外, 50mg L-1 纯化处理的生物纳米硒颗粒可以将黑土,黄壤、红壤、盐碱土等典型土壤中 72.2-87.1%的元素汞转化为硒化汞。(3)柠檬酸杆菌(Citrobacter freundii Y9)自身分泌的胞外聚合物中的酪氨酸、色氨酸、 芳香族Ⅰ和Ⅱ类蛋白等物质和纳米硒颗粒具有较强的结合能力, 是纳米颗粒的一种天然分散剂。带负电荷更多的胞外聚合物在纳米硒颗粒上的吸附使得颗粒表面的负电荷显著增加, 并通过静电斥力、空间位阻等使纳米硒颗粒的稳定性增强, 从而促进纳米硒颗粒对元素汞的固定效果。(4)矿物胶体和生物纳米硒颗粒间的异质聚集明显强于矿物胶体和生物纳米硒各自的同质聚集,它们之间的的异质聚集抑制了生物纳米硒对元素汞的固定效率。然而, 胞外聚合物的添加却可以抑制生物纳米硒的同质聚集以及生物纳米硒和矿物胶体之间的异质聚集,从而提高生物纳米硒的稳定性进而提高生物纳米硒对元素汞的固定效果。(5)研究发现, 不同分子量溶解性有机质和纳米硒颗粒间的结合能力为:3500-10000 道尔顿 > 1000-3500 道尔顿 > 100-1000 道尔顿 > 10000 道尔顿以上溶解性有机质。 一般情况下, 小分子量的溶解性有机物由于扩散迅速更容易和纳米颗粒结合,但是小分子量的溶解性有机质在较长时间内容易被大分子量的溶解性有机质替代。 然而, 溶解性有机质吸附引入的静电势垒可以抑制大分子量溶解性有机质对小分子量有机质的替换,从而使得中分子量的溶解性有机质比大分子量的溶解性有机质更容易吸附到硒颗粒表面。不同分子量溶解性有机质和硒颗粒表面的结合增强了硒颗粒的稳定性,从而促进了硒颗粒对元素汞的固定效果。(6)研究发现, 0-60 mg L-1 带更多负电荷的颗粒态有机质可以通过静电斥力抑制生物纳米硒颗粒间的同质聚集以及生物纳米硒颗粒和颗粒态有机质间的异质聚集。 80-100 mg L-1 的颗粒态有机质容易使生物纳米硒颗粒和元素汞附着,因为高浓度颗粒间更容易发生碰撞。颗粒态有机质并未对生物纳米硒固定元素汞产生显著影响。(7)随着盐度的升高生物纳米硒颗粒间的同质聚集和沉降显著增加。 一是因为盐度的增加使得生物纳米硒颗粒的双电层结构压缩,导致范德华引力占据主导地位。 二是, 盐度提高引入了更多的二价阳离子, 它们对生物纳米硒颗粒表面电荷的中和以及钙离子通过钙桥对生物纳米硒颗粒表面官能团和纳米硒颗粒间的桥联作用也促进了生物纳米硒颗粒的同质聚集。盐度升高导致的生物纳米硒颗粒间的聚集,抑制了生物纳米硒在土壤和盐溶液中对元素汞的固定。(8)细菌生物膜可以通过双电层作用、氢键、疏水性作用、 空间位阻以及桥联作用将生物纳米硒颗粒截留。此外,生物膜包裹导致的表面粗糙度增加、 孔隙堵塞、 孔隙筛分以及包封效应也都促进了生物纳米硒颗粒的沉积。 生物膜中的硫醇物质在一定程度上促进了元素汞的固定, 这可能是在生物纳米硒固定元素汞的过程中, 生物膜中的硫醇和元素汞生成了硫醇与汞的络合物。综上所述, 柠檬酸杆菌(Citrobacter freundii Y9)可以在厌氧和好氧条件下将亚硒酸根还原为无定型态的生物纳米硒颗粒,超氧自由基在好氧亚硒酸根还原过程中起着重要的调控作用。 该生物纳米硒对汞具有极强的结合能力,可以用于固定土壤和水体中的元素汞。 包括胞外聚合物、矿物胶体、溶解性有机物、颗粒态有机物、盐度、生物膜在内的主要环境因素可以影响生物纳米硒颗粒在环境中的聚集和迁移,进而影响生物纳米硒对元素汞的固定效果。本研究为全面、 准确评价环境中纳米颗粒的环境化学行为及其在汞污染修复中的应用提供了理论依据。
Other AbstractIn this study, a Citrobacter sp. strain was isolated from the environment, whichcan reduce selenite with formation of BiSeNPs under both aerobic and anaerobicconditions, and Hg0 can be immobilized by synthesized BioSeNPs. The selenitereducing mechanism including the mediation of superoxide free radical wasinvestigated in the present work. Furthermore, the effects of main environmentalfactors such as extracellular polymeric substances (EPS), clay minerals, dissolvedorganic matter (DOM), particulate organic matter (POM), salinity and biofilm onBioSeNPs and consequences for Hg0 immobilization were investigated. The mainconclusions of this study are listed as the follows:(1)The isolated Citrobacter freundii Y9 can bioreduce selenite with formation ofamorphous BioSeNPs which covered by EPS under both aerobic and anaerobicconditions. Superoxide free radical was found to mediate selenite reduction underaerobic condition.(2)It was found that 45.8-57.1% and 39.1-48.6% of Hg0 in vegetable garden soilwas transformed to Hg-HgSe in the presence of 4 mM unpurified BioSeNPs underanaerobic and aerobic conditions, respectively. The Hg0 immobilization performancewas also examined in black soil, red soil, yellow soil and saline soil, it was found that72.2-87.1% of Hg0 was transformed to HgSe in the presence of 50 mg L-1 purifiedBioSeNPs.(3)The tryptophan, tyrosine, and protein-like substances (aromatic I and IIproteins) in EPS secreted by Citrobacter freundii Y9 has a strong binding ability withselenium nanoparticles (SeNPs), which is a kind of natural dispersant fornanoparticles (NPs). Adsorption of more negative charged EPS significantly madeSeNPs more negatively charged, which can provide colloidal stability to SeNPs byeither electrostatic, steric or electrosteric mechanisms. EPS can therefore enhance theremediation efficiency using SeNPs in soil solution and groundwater contaminated with Hg0.(4)Heteroaggregation of BioSeNPs with colloidal minerals in groundwater wasstronger than homoaggregation of BioSeNPs or colloidal minerals. Hg0 remediationusing BioSeNPs was significantly inhibited by heteroaggregation of BioSeNPs withcolloidal minerals. However, the addition of EPS decreased the homoaggregation ofBioSeNPs and heteroaggregation of BioSeNPs with colloidal minerals, the stability ofBioSeNPs was enhanced as a consequence, which therefore promoted Hg0immobilization efficiency using BioSeNPs.(5)In the present study, the binding ability of MW dependent DOM with SeNPswas in the order: DOM (3500–10000 Da) > DOM (1000–3500 Da) > DOM(100–1000 Da) > DOM (above 10000 Da). Generally, low MW DOM was expectedto adsorb initially due to faster diffusion and these compounds would be displaced byhigh MW DOM over longer time period. However, the electrostatic barrier impartedby adsorbed DOM limited such displacement, leading to preferential adsorption of theintermediate MW fraction over the high MW fraction. Adsorbed DOM fractions,especially intermediate MW, enhanced the stability of SeNPs which favouredimmobilization of Hg0.(6)It was found that more negatively charged POM (0-60 mg L-1) inhibitedhomoaggregation as well as heteroaggregation with SeNPs which had a lowernegative charge through electrostatic repulsion. In the presence of POM (80-100 mgL-1), SeNPs were more likely to attach to POM with more Hg0 remaining in the POMsince a larger concentration of nanoparticles would lead to more effective collisions.However, Hg0 immobilization efficiency using SeNPs was not significantlyinfluenced by POM.(7)It was found that homoaggregation and sedimentation of BioSeNPs wereenhanced significantly with increasing salinity. Compression of the electric doublelayers of BioSeNPs at high ionic strengths resulted in attractive van der Waals forcesdominating and leading to enhanced aggregation. Moreover, neutralization of thesurface negative charge of BioSeNPs by divalent cations and the bridging ofBioSeNPs via calcium binding to surface functional groups were also associated with enhanced aggregation. Such enhanced aggregation exerted inhibition of Hg0immobilization in soil solutions/soils of varying salinity.(8)BioSeNPs were significantly retained in the presence of a bacterial biofilmthrough electrical double layer effects, hydrogen bonding, and hydrophobic, steric andbridging interactions. The retention of BioSeNPs in biofilm-coated quartz sand was~1.9 times higher than that for clean quartz sand during the period of BioSeNPsinjection. Moreover, enhanced surface roughness, pore clogging and sieving andentrapment effects mediated by the biofilm also contributed to deposition ofBioSeNPs. Thiol groups associated with the surface of the biofilm appeared toenhance the capture of Hg0 due to the reaction between Hg0 and thiol compoundsresulting in the formation of Hg2+-thiol complexes during the binding of Hg0 withBioSeNPs.In conclusion, Citrobacter freundii Y9 can reduce selenite to amorphousBioSeNPs under both anaerobic and aerobic conditions, and superoxide free radicalplays an important role in mediating reduction of selenite. The formed BioSeNPshave strong affinity to Hg which can be used in immobilization of Hg0 in water andsoil. The main environmental factors such as EPS, clay minerals, DOM, POM,salinity and biofilm have significant influence on BioSeNPs and its application in Hg0immobilization. The present study provides theoretical basis for fully understandingthe environmental fate of NPs and their application in environmental remediation.
Subject Area生态学
Language中文
Document Type学位论文
Identifierhttp://ir.xjlas.org/handle/365004/15360
Collection中国科学院新疆生态与地理研究所
研究系统
Affiliation中国科学院新疆生态与地理研究所
First Author Affilication中国科学院新疆生态与地理研究所
Recommended Citation
GB/T 7714
王潇男. 细菌生成纳米 Se 修复 Hg0污染环境[D]. 北京. 中国科学院大学,2019.
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