【作者】 孙凤；

【导师】 裴海燕；

【作者基本信息】 山东大学 ， 环境工程， 2013， 博士

【摘要】 蓝藻水华引发的微囊藻毒素(Microcystins, MCs)次生污染已成为全球关注的热点环境问题。MCs是水华藻类的次生代谢产物,属于环状多肽,细胞死亡或解体后大量释放到水体中,危害水质安全。MCs具有极高的细胞选择性和专一生物毒性,机体摄入后可经多种途径转移到肝脏等靶器官。毒素暴露后,肝细胞的氧化应激水平显著提高,同时伴生有DNA损伤、细胞骨架破坏、细胞凋亡现象。鉴于MCs对水环境安全及人类健康的危害,控制水体蓝藻水华和MCs浓度水平,确保饮用水安全供给已经成为科学工作者重点关注的环境问题。原水除藻(物理、化学、生物方式)、化学混凝、沉淀、过滤、消毒、活性炭吸附、生物降解等工艺陆续应用于MCs的调控并且获得了明显的成效。但是由于技术限制和认识不足,上述各类工艺尚难以从根本上调控MCs的产生、释放和毒性风险问题,仍然需要对受MCs污染的原水层层设防,逐级调控。本论文从蓝藻细胞低破损去除、含藻给水污泥减量化处理、MCs消毒副产物鉴定与毒性评价方面,优化了受蓝藻水华污染饮用水的处理工艺,为MCs的有效调控提供新的技术支持。论文主要包括以下五部分：论文第一章阐述了微囊藻毒素的理化特性、生成机制与污染现状；归纳了微囊藻毒素典型的生物毒性、作用机制、水质标准与检测方法；详细介绍了针对营养物质、针对水源地藻细胞/MCs和针对给水常规/深度处理中MCs调控策略与工艺进展。在文献综述的基础上分析了目前相关研究存在的问题,提出了基于蓝藻细胞低破损去除、含藻给水污泥减量化处理、MCs消毒副产物鉴定与毒性评价研究的饮用水微囊藻毒素污染调控技术。论文第二章针对混凝沉淀工艺过程中蓝藻细胞的破损与胞内毒素释放问题,通过模拟混凝沉淀工艺,评价了混凝药剂和工艺运行条件(搅拌速度、时间、静沉时间等)对蓝藻细胞及其代谢产物的去除效果,在此基础上考察蓝藻细胞代谢产物的释放规律,阐明蓝藻细胞的破损机理；并对混凝剂剂量、搅拌操作及絮体堆积时间等条件进行了优化。在优化后的混凝条件下(对AlCl3而言最优条件为15mg/L,快搅250r/min、1min,慢搅20r/min、20min;对PACl而言最优条件为4mg/L,快搅150r/min、2min,慢搅40r/min、30min),几乎所有铜绿微囊藻细胞都可通过表面电中和被完整去除,混凝剂的投加和搅拌条件并没有导致MCs的额外释放。AlCl3混凝絮体中,藻细胞表面能够形成一种有效保护层,一定程度上减弱了藻细胞的溶解。与AlCl3不同,PACl能够打破藻细胞外的保护层,显著加剧藻细胞的破损,使其在絮体堆置2天后即发生溶解。本研究不仅对传统饮用水混凝沉淀处理工艺中有效去除藻细胞具有重要意义,对于沉淀污泥处理过程中水资源的循环利用和二次污染防治同样具有重要的指导意义。论文第三章在混凝沉淀净化处理含藻原水工艺优化的基础上,进一步考察了含藻给水污泥真空过滤脱水过程中机械作用和理化作用对蓝藻细胞稳定性与MCs释放特性的影响。基于不同操作条件下过滤效率(过滤时间、平均滤速)、滤液浊度、MCs浓度的变化,明确了机械作用和理化作用对藻细胞完整性的具体影响,并据此对过滤操作条件进行优化。研究发现载样量对污泥脱水特性影响显著,污泥在过滤介质表面逐渐堆积,不仅降低滤速且对藻细胞具有明显的挤压破坏,实际操作中应避免污泥层的形成,以提高滤速同时减少MCs释放。含藻给水污泥过滤脱水时应选择亲水性过滤介质,在保证较高过滤效率的条件下尽可能降低介质孔度。尽管正压过滤效率略有提高,却会造成絮体和藻细胞破损,从减少MCs释放的角度来讲,应选择低破坏性的真空过滤技术。在合适的推动力作用下(高真空度),含藻给水污泥过滤效率较高且未增加滤液MCs浓度和浊度,应优先选择。污泥堆存时间的延长虽有利于提高污泥脱水效率,却显著提高了滤液MCs浓度和浊度。在实际给水厂含藻给水污泥减量化处理时,应控制严苛的堆存时间(AlCl3给水污泥要求堆存时间不超过4d, PACl给水污泥要求堆存时间不超过2d)。本研究完善了对蓝藻细胞胞内MCs的归趋方式的认识,同时具体研究结果能够为实际给水厂含藻给水污泥的减量化处理和含泥水资源化利用提供借鉴和参考。论文第四章以典型毒素MCLR和MCRR作为饮用水中微囊藻毒素调控研究的契入点,通过模拟常规氯消毒工艺条件,在实现MCs氧化去除的同时借鉴微囊藻毒素的传统制备工艺,实现MCs消毒副产物(MC-DBPs)的分离纯化,并利用液相色谱-质谱(LC/MS)、质谱-质谱联用(MS/MS)等技术对MCs及MC-DBPs进行结构对比解析,进而确定主要MC-DBPs的结构特性与生成机制；同时在色谱制备的基础上利用蛋白磷酸酶抑制毒性实验建立和完善MC-DBPs环境风险的评价方法。研究表明在不同消毒模式下,MCs能够稳定消减至WHO规定的限值(1.0μg/L)以下,但同时氧化生成多种MC-DBPs。典型DBPs产物类型与分布受MCs类型和消毒剂量的影响与制约。综合分析MC-DBPs的生成机制,不难发现MC主要经历Adda共轭二烯双键加成反应和部分初级产物的脱水反应。蛋白磷酸酶PP1的毒性抑制实验均证实多数MC-DBPs的生物毒性较原毒素有明显下降,但残余的生物毒性依然不能忽视。尽管消毒处理可有效调控MCs的浓度水平,但综合考虑MC-DBPs的含量变化和潜在生物毒性,MC-DBPs对饮用水的二次污染同样值得关注。本研究建立的针对MC-DBPs毒性分析评价技术并不局限于MCLR和MCRR,依据原水中MCs的分布特征,同样适用于其它类型毒素消毒副产物毒性的评价与调控。本研究有助于综合认识MCs的危害及其调控策略和提高饮用水质量,因而具有重要实际意义和应用价值。论文第五章对各研究部分进行了总结,并分析了“饮用水处理工艺中微囊藻毒素污染调控技术的优化研究”的优势与不足之处,展望了该领域的发展方向。本论文优化和改进了微囊藻毒素污染原水的常规处理工艺,为MCs的有效调控提供新的技术支持与参考。更多还原

【Abstract】 The increasing frequency and intensity of cyanobacterial blooms is a growing environmental and human health concern. The most common toxins produced by cyanobacteria are microcystins (MCs), a class of hepatotoxic monocyclic heptapeptides. MCs have been the cause of several poisonings of livestock and wildlife around the world, and they also posed a health hazard for humans through the use of drinking water. When orally ingested MCs, they are actively absorbed to hepatic cells, irreversibly inhibit protein phosphatase1, subsequently leading to disruption of cell structures, intrahepatic hemorrhage and death. Since MCs are potent hepatotoxins, controlling of their levels in drinking water became a great important issue. Previous studies have suggested various techniques for the control of MCs in drinking water, such as coagulation, flocculation, filtration, activated carbon adsorption and disinfection. These treatment processes were efficient in removing cyanobacteria cells and internal MCs, but were unreliable for dissolved MCs due to the fragility of cyanobacteria cells (inappropriate operations probabily lead to secondary pollution). Consequently, it is still necessary for new or modified water treatment methods to eliminate these toxins. In this research, we focused on the "the optimization of the removal technology for MCs pollution in drinking water treatment processes", including the lysis of Microcystis aeruginosa in coagulation and sedimentation, the dewatering of algae containing sludge and MC-DBPs formation and toxicity in disinfection.This study has five chapters, just as follows:In chapter one, we described the physical and chemical characteristics, the generation mechanisms and the current pollution status of MCs; summarized the typical biotoxicities and mechanisms, the related water quality standards and detection methods of MCs; we also introduced the control strategies and technologies directed against nutrients, algae cells/microcystins in raw water, in conventional/deep treatments of drinking water. Based on literature review, we proposed the researching aims, meanings, methods and contents of our work.In chapter two, we simulated the coagulation-sedimentation process and assessed the effects of coagulant dose, shear, and floc storage time on the integrity of Microcystis aeruginosa FACHB-905, to effective control cyanobacteria lysis both in coagulation and floc storage processes. On this basis, we investigated the release of intracellular MCs, clarified the breakage mechanism of cyanobacteria cells, and optimized coagulant dosage, stirring parameters and floc deposition time. Under the optimum coagulation conditions for cyanobacterial cells removal (for AICl3, coagulant dose15mg/L, rapid mix250r/min for1min, slow mix20r/min for20min; for PACl, coagulant dose4mg/L, rapid mix150r/min for2min, slow mix40r/min for30min), all cells were removed intactly by the surface charge neutralization with AlCl3/PACl and there was no additional release of MCs into the treated water. The formation of AICl3flocs brought a protection for cyanobacterial cells and reduced their breakage in a certain degree, however, they should also be treated or disposed within6days to avoid the lysis of cells and additional release of MCs. While in the PACl coagulation-sedimentation process, PACl could destroy the protective effects of EPSs produced by M. aeruginosa cells, inducing obvious damage to the cells and leading to a large amount of MCs release above background concentration. This study is not only significant for the effective removal of cyanobacterial cells in natural blooms, but also instructive for the safe treatment of coagulation flocs (secondary pollution) in drinking water treatment plants.In chapter three, we further investigated the characteristics of algae lysis and microcystin release in the filtration of algae containing sludge formed in coagulation treatment. By evaluating filtration efficiency (time and average rate), turbidity and MCs concentration in different operating conditions, the influences of mechanical action and physical/chemical effects on algal cell integrity were explicated, and the operation conditions were also optimized for vacuum filtration. Experiments showed that sample loading volume had significant influence on sludge dewatering characteristics, sludge would gradually accumulated on the surface of filtration media, resulting in reduced filtration rate and algae lysis. In actual operation, the formation of sludge layer should be avoided. Hydrophilic filtration media with lower porosity should be choosen to enhance filtration efficiency and remove solid insoluble matter. Despite positive pressure filtration had a higher efficiency, it could induce the damage of the flocs and algae cells. In consideration of MCs release, vacuum filtration with low-destructibility should be choosen. With appropriate driving force (higher vacuum), algae containing sludge had higher filtration efficiency and stable MCs concentration and turbidity levels. Prolonging the storage time of sludge was conducive to improving the efficiency of sludge dewatering, but also enhanced MCs concentration and turbidity. For this reason, the storage time of algae containing sludge should be severely restricted in actual water supply factories (the storage times for PACl and AlCl3should not be more than2d and4d, respectively). This work gave deeper knowledge on the fate of intracellular MCs in the process of sludge dewatering, while concrete experimental results provided valuable references for algae containing sludge treatment and the re-utilization of sludge resource.The principal objective of chapter four was to provide an evaluation of the generative mechanism and biological toxicity of MC-DBPs involved in disinfection. The widespread and dangerous MCs, MCLR and MCRR, were selected as the target of disinfection treatment and its primary DBPs were identified by mass spectrometry, liquid chromatography/mass spectrometry and tandem mass spectrometry. In addition to the generative mechanism studies, the biological toxicity of MC-DBPs on protein phosphatasel (PP1) was evaluated by molecular toxicity experiments. Subject to disinfection, MCs could be reduced to the limit value (1.0μg/L) of WHO, but could also be oxidized to a variety of MC-DBPs. The types and distributions of DBPs were under the influence and restriction of MCs type, disinfectant dose and reaction time. With a comprehensive analysis of MC-DBP formation mechanism, it was not difficult to find MCs mainly subjected to the the addition reaction of Adda conjugated diene and dehydration reaction of some secondary products. Though most MC-DBPs had lower toxicity on protein phosphatase1than MCs, they still possessed certain biological toxicity. From the perspective of the drinking water safety, disinfection was valid regulate method for MCs, but the secondary pollution of MC-DBPs also deserved further attention. The evaluation technology on MC-DBPs established in this work was not limit to MCLR and MCRR, it also could be applied to other toxin types according to their distribution characteristics in raw water. This study offers valid technique support for MC-DBPs identifiation, contributes to a comprehensive cognition on their hazard, and thus has great significance to prevent and control the environmental risk induced by MCs.Finally, we summarized the research findings of above parts and discussed the future developments of the removal technologies on microcystin pollution in drinking water treatment processes. This study has enriched the research on the optimization for removal technology on MCs pollution in drinking water treatment processes, and provided some reference gists for the control of MCs and their potential biotoxicity.更多还原