【作者】 张坤；

【导师】 王道增；

【作者基本信息】 上海大学 ， 流体力学， 2011， 博士

【摘要】 本文的研究对象为污染底泥泥沙对上覆水体水质的影响。在河流湖泊污染治理过程中,底泥污染整治是主要的难点之一,也是目前较为普遍存在的环境问题。污染物进入水体中后,有一部分会积聚在底泥中。在一定的条件下,累积于底泥中的各种有机和无机污染物通过与上覆水体间的物理、化学、生物交换作用,重新进入到上覆水体中,成为影响水体水质的二次污染源。因此了解和掌握底泥中污染物的释放、扩散规律及释放机制对水体水质的改善有重要意义。本文采用实验和数值研究相结合的方法对污染底泥泥沙中污染物的扩散问题进行了较为细致的研究。本文选用泥沙对其具有吸附性的物质磷酸二氢钾和非吸附性的物质氯化钠这两种代表性物质,通过实验室循环水槽进行水力试验,对污染底泥中污染物的释放机制进行了较为详细的研究。实验主要包括底泥泥沙静态时泥沙-水界面释放和底泥泥沙起动时泥沙再悬浮动态释放,其中底泥泥沙静态释放又分为静水静态释放(上覆水体无流动)和静水动态释放(上覆水体有流动)两种。由此本文提出河流湖泊受污染底泥中污染物释放主要有三种机制,即底泥静止时泥沙-水界面的污染物扩散释放,泥沙起动再悬浮时随泥沙颗粒一起进入到上覆水体中含有污染物质的孔隙水与上覆水体混掺释放和泥沙再悬浮时悬浮泥沙颗粒的解吸释放。即底泥静止状态时,底泥中污染物的释放主要来自于底泥-水界面的扩散释放,其中包括分子扩散释放和含有污染物质的孔隙水扩散释放等。而再悬浮释放时底泥中污染物的释放主要来自于含有污染物质的孔隙水(该孔隙水主要是指底泥起动再悬浮时与底泥泥沙一起进入到上覆水体中底泥里所含有的孔隙水)与上覆水体的混掺释放以及吸附有污染物质的再悬浮泥沙颗粒的解吸释放。在河流湖泊中泥沙的吸附解吸作用对水体污染物输移转化产生重要影响,因此本文分析研究了泥沙颗粒对污染物的吸附与解吸特性,并对两种类型的泥沙即粘性泥沙和非粘性泥沙在吸附特性方面的异同进行了实验研究,选取磷作为吸附剂,结果表明Langmuir吸附等温式能较好地描述粘性泥沙和非粘性泥沙对磷吸附实验中水相磷平衡浓度与磷平衡吸附量的关系,且粘性泥沙由于其表面孔隙较多,对磷的吸附量要远远大于非粘性泥沙。同一含沙量条件下,相同粒径、性质的泥沙对磷的平衡吸附量随着水相磷初始浓度的增加而增大,但水相初始浓度增大到一定程度之后,泥沙平衡吸附量增加缓慢,最终达到饱和吸附量。将水体、泥沙和污染物作为一个完整的水环境系统考虑,能够更好地研究它们之间相互作用机制及动态耦合效应,本文据此对污染物在水体与底泥界面上的扩散迁移问题建立了流场-浓度场耦合模型并进行了数值模拟。为验证计算结果的合理性,将数值模拟结果与实验数据进行了比较,两者吻合较好,验证计算结果的合理性。最后利用该模型对不同流速下底泥中污染物的释放进行了研究,得到流速与上覆水体中污染物(磷)浓度的关系。更多还原

【Abstract】 The research of Polluted sediment impact on the water quality is carried out in this dissertation. Comprehensive treatment and pollution prevention of sediment, resolving this ubiquitous and significant environmental issue in the world, is one of the biggest challenges in lake treatment. Most pollutants entering water system may be stored in sediment resulting in a sediment-containing contaminant layer. A variety of inorganic and organic pollutants in the sediment, under certain circumstance, will release to aquatic environment through chemical react, and physical and biological exchange with water above, which may be the major contamination source of upper water. It is very important to know the laws of release and diffusion of bottom sediment to improve the water quality. Both experimental investigation and numerical simulation are conducted to investigate diffuse of phosphorus from polluted sediment in details.A conservative and a reactive tracer (NaCl and KH2PO4) are respectively used as the contaminant in bed sediment in a laboratory flume. The release mechanism of polluted sediment is studied in detail. The experiment studies the mechanism of pollutants release from sediment in the form of two processes: the static release at the sediment-water interface, and the dynamic release of re-suspension of sediment release. The static release divides into two paths, flow water and still water which the sediment keep rest. In this paper here are three mechanisms in the pollutant release: molecular diffusion at the sediment-water interface, release from pore water release and re-suspended particles. When the sediment is static, only molecular diffusion on sediment-water interface was considered. When the sediment re-suspension occurred, the re-suspend pore water and the re-suspend particle play the most important role.The different effects of cohesive sediment and non-cohesive sediment on the pollutant releasing flux are also studied. The study performed some laboratory experiments using KH2PO4 solution as the adsorbent. The data of isothermal adsorption experiments are analyzed by isothermal adsorption equations. The analyzed results indicate that the adsorption of phosphorous by suspended sediment is in agreement with Langmuir equation. The cohesive sediment adsorbed amount is greater than non-cohesive sediment because of the surface structure of cohesive presents more micro pore. In water body with the same concentration of sediment the amount of phosphorous adsorbed by suspended sediment increases with its initial concentration in water phase. When the initial concentration rose to a certain extent, the equilibrium adsorption capacity growing more slowly, and then reaches the saturation adsorption quantity.In order to study the release of sediment better, a model for contaminant release at sediment-water interface is established in this paper. Distribution of flow field and concentration field are obtained through numerically coupling the flow and concentration fields which is in a good agreement with experimental data. The model is used to study the influences of fluid velocity on release quantity, and the relationship between the amount of release and different flow velocity are obtained.更多还原