【作者】 徐娟；

【导师】 盛国平；

【作者基本信息】 中国科学技术大学 ， 环境工程， 2013， 博士

【摘要】 城市生活污水中的痕量有毒物质(如重金属和抗生素)的污染问题日趋严重。由于它们对微生物具有抑制效应,常规的活性污泥法对其去除效果非常有限,导致它们在污水厂出水中有残留,可能会诱发环境风险。活性污泥在降解废水基质的同时,会产生一类大分子物质-胞外聚合物(Extracellular polymeric substances,EPS)覆盖在微生物细胞表面及填充在污泥絮体内部空隙中。EPS具有大量的活性官能团和疏水区域,有很强的吸附和络合污染物的能力。重金属和抗生素类痕量污染物进入废水生物处理反应器中,将首先和微生物EPS发生吸附或络合等相互作用,进而影响这些物质在反应器中的迁移和去除行为。然而目前对EPS在这些痕量污染物去除中的内在作用机制并不清楚。本论文基于先进的分析技术,,建立表征微生物EPS与痕量有毒污染物之间相互作用的灵敏分析方法,深入探讨EPS和污染物的相互作用机制,明晰EPS在污染物迁移和去除过程中所起的作用,为强化痕量有毒污染物在活性污泥系统中的去除提供理论依据和技术指导。主要研究内容和研究结果如下：1.集成应用等温滴定微量热、三维荧光光谱、X射线精细结构吸收光谱及红外光谱等多种分析方法,探索了活性污泥EPS结合水体中的重金属离子(以铜离子为例)的热力学特性和机制。研究结果表明：EPS中的蛋白及腐殖质组分对重金属均有很强的结合能力。EPS对铜离子的结合容量、结合常数及结合焓变分别为5.74×102mmol/g,2.18×105L/mol和11.30kJ/mol,是一个典型的放热过程,并且在热力学上是有利的。铜离子的加入导致了EPS结构的无序度增加,且结构的熵增是整个结合作用的主要驱动力。X射线精细结构吸收光谱显示铜离子可能与EPS分子中羧基官能团中的氧原子发生结合。2.探索了活性污泥EPS与典型磺胺类抗生素一磺胺二甲嘧啶(sulfamethazine, SMZ)的相互作用机制。研究结果表明：SMZ主要与EPS中的蛋白相结合,SMZ中的苯环结构与EPS发生了明显的π-π相互作用,较高的结合常数表明SMZ能够被活性污泥EPS有效富集,进而影响其后续生物降解过程。等温滴定微量热结果表明该相互作用在热力学上可自发进行,且主要由疏水作用驱动。光散射和凝胶渗透色谱结果表明发生结合后EPS的结构膨胀,变的更加疏松,有利于污染物在活性污泥絮体中的传质和对污染物的富集。3.发展了表面等离子共振结合等温滴定微量热方法用于解析腐殖质(腐殖酸和富里酸)与SMZ相互作用的微观动力学及热力学。结果表明SMZ与腐殖酸的结合受溶液化学环境影响明显,随离子强度增加而增强,随温度升高而减弱。同时,随着温度的上升,相互作用由焓驱动为主转为熵焓协同驱动,疏水作用逐渐强化；而SMZ与富里酸的相互作用受pH影响很大,富里酸主要和阴离子态和中性态SMZ发生相互作用；核磁滴定结果表明SMZ芳环上的氢核与富里酸的相互作用较强,存在明显的π-π作用；该过程主要由熵驱动主导。4.分别研究了磺胺类抗生素在间歇和连续流生物处理反应器中的去除状况,探索了活性污泥EPS在抗生素迁移转化中的作用机制。研究结果表明：活性污泥EPS对磺胺类抗生素有明显的吸附和富集能力。磺胺的降解可以分为两个阶段：生物吸附和生物降解。EPS通过生物吸附将SMZ从水相富集去除,便于后续的生物降解,对SMZ的去除起着重要作用。同时,当生物处理反应器中微生物受到SMZ冲击时,会产生更多的EPS抵御侵害,进而将SMZ吸附去除。随着微生物对SMZ的耐受能力的提升,EPS对SMZ的吸附效果也会强化。5.针对处理有机废水的微生物燃料电池(microbial fuel cell, MFC)反应器,采用实验分析结合数学模拟的方法研究了该反应器中质子交换膜(proton exchange membrane, PEM)污染问题。研究结果表明：在长期的MFC运行中,质子交换膜被微生物、EPS及无机盐污染,导致MFC性能的下降。一方面,阳离子传质的物理阻碍直接导致电流衰减,另一方面,质子传质受限引起的pH梯度导致电势损失加剧。膜污染导致的MFC性能的恶化主要由扩散系数下降导致的阳离子传质受限和加剧的阴极电势损失共同引起。更多还原

【Abstract】 The occruences of plenty of trace toxic contaminants (such as heavy metals, antibiotics) in the municipal wastewater have attracted more and more attention. As the activity of the microbes can be inhibited by the contaminats, the removals of these pollutants are limited in the conventional activated sludge processes. The redidues of the contaminats in the effluence from wasteater treatment plants will cause serious environmental risks. Extracellular polymeric substances (EPS) are produced by the microbes when organics in wastewater are consumed in wastewater treatment bioreactors. EPS are a major component of microbial aggregates, and present both outside of cells and interior microbial aggregates. They have huge abilities of adsorption and complex for trace toxic contaminants, due to the presence of many functional groups and hydrophobic regions in EPS. The trace toxic contaminants in wastewater will interact with EPS at initial, and thus.their migration and removal in the wastewater treatment bioreactor would be greatly influenced. However, the crucial roles of EPS on the migration and removal of trace toxic contaminants are not clear. In this work, sensitive methods for characterizing the interaction between EPS and trace toxic contaminants were developed. The roles of EPS on the migration and removal of trace toxic contaminants in wastewater treatment bioreactors were also explored. This work provided theroritical basis and technical supporting for enhancing the removal of trace toxic contaminants in activated sludge system. The main contents and results are listed below:1. The thermodynamic characteristics of the binding between aqueous metals (with copper ion as an example) and sludge EPS were investigated combinding isothermal titration calorimetry (ITC), three-dimensional excitation-emission matrix (EEM) fluorescence spectroscopy, X-ray absorption fine structure (XAFS) and Fourier transform infrared spectroscopy (FTIR) analysis. The results show that the proteins and humic substances in EPS were both strong ligands for Cu2+. The binding capacity, binding constant, binding enthalpy were calculated as5.74×102mmol/g,2.18×105L/mol and11.30kJ/mol, respectively, implying that such a binding process was exothermic and thermodynamically favorable. The disorder degree of EPS increased with the addition of Cu2+and the binding process was found to be driven mainly by the entropy change. A further investigation shows that Cu2+was bound with the oxygen atom in the carboxyl groups in the sludge EPS molecules.2. The interaction mechanism between sludge EPS and a typical sulfonamide antibiotic, sulfamethazine (SMZ) was explored. Results show that SMZ interacted mainly with the protein-like substances in EPS, and the π-π interaction occurred between EPS and aromatic ring in SMZ molecules. The relatively high binding constant indicated the effective enrichment of SMZ by EPS, which would influence the following degradation process of SMZ by activated sludge. The binding process proceeded spontaneously, and the driving force was mainly from the typical hydrophobic interaction. After binding with SMZ, the conformation of EPS was expanded and their structure became loose, which was favored for the mass transfer and pollution capture in sludge.3. SPR combined with ITC method was developed to investigate the microscopic kinetics and thermodynamics of interaction between SMZ and humic substances. Results indicated that the interaction between SMZ and humic acids (HA) was greatly influenced by the aquatic ionic strength, temperature, pH etc.. It could be enhanced with increasing ionic strength and be depressed with increasing temperature. Simultaneously, the transformed to be entropy-driven collaboration with enthalpy-driven from entropy-driven as temperature raised. The hydrophobic interaction between SMZ and HA was enhanced at a high temperature. Interaction between SMZ and fulvic acids (FA) was also greatly influenced by the pH of solution. The π-π interaction occurred between FA and aromatic ring in SMZ, and the interaction was mainly entropy-driving.4. The removal of sulfonamides was explored in the wastewater treatmetn bioreactor with batch and continuous modes respectively, and the crucial roles of EPS in the migration and transformation of sulfonamide were investigated. Results show the removal of SMZ could be regarded as two stages:bioabsorption and biodegradation. SMZ could be absorbed and enriched by the sludge EPS, EPS played an important role in SMZ removal at the adsorption stage, which was benefited for the subsequence biodegration of SMZ by activated sludge. Furthermore, more EPS could be produced by the actived sludge in response to the shocking of SMZ to the wastewater treatment bioreactor, which also enhanced the biosorption of SMZ by EPS. The adsorption quantity of EPS enlarged with the increasing tolerance of microbes to SMZ.5. Proton exchange membrane (PEM) fouling in microbial fuel cell is investigated by experimental analysis and mathematical simulation. Results show that PEM is readily fouled by the microorganisms, EPS and inorganic salts during the long-term operation of MFC. This would decrease the conductivity, cation diffusion of the PEM, and thus deteriorate the MFC performance. The physical blockage of cations transfer directly caused the decay of current. Furthermore, the potential loss caused by the pH-gradient was enhanced attributed to proton transfer limitation. The transfer limitation of cations because of the decreasing diffusion coefficients and the heightened cathodic potential loss after PEM fouling were proven to be the mainly reasons for the deterioration of MFC performance.更多还原