网格絮凝去除黄河水中微污染物的絮凝效果及絮凝机理研究

The water supply of Lanzhou is mainly taken from the Yellow River, but there appear many harmful micropollutants in the source water with the quality being continuous deteriorating. These micro pollutants are mostly the hydrophobic compounds with lower solubility and concentration in water, extremely easy to transfer into the suspended sediment or adsorb on the surface of solid phase. It is a feasible way to remove the micropollutants from water by coagulants. So the proposals with enhanced coagulation process to separation the contaminants from raw water is enabled: use the blended efficient flocculants in the grid flocculating, then study the effect and the mechanism of flocculation comprehensively combined with the flow field detection. .There should have a comprehensive theoretical system as guidance to design, construction and operation, but the contribution of vortices to flocculation, which are commonly used as efficient coagulation equipment, is not clear, which require fully research. So the proposals with experiment as the main method will be used to measure the velocity vector of the vortices with particle image velocimetry (PIV) technique. At the same time, the vortices flocculation mechanism and the aggregation process of particles in vortices are detected, then the analysis, calculation and comparison will be made to reveal the real vortices flocculation mechanism of the micropollutants in the grid flocculating tank. It is the first time that PIV is applied to research the aggregation process of particles in various turbulence flow regimes in the grid flocculating tank. It will be very helpful to promote the technology development of the slightly polluted raw water treatment and to alleviate the water crisis of Lanzhou.

兰州城市供用水主要取自黄河水，而黄河水质不断恶化，水中出现了对人体有害的微污染物。这些微污染物大多为疏水性化合物，在水中的溶解度、浓度均很低；极易转移至沉积物中或吸附于固相物质表面，因而可用混凝的方法将其从水中分离除去。课题组提出用强化混凝工艺去除原水中的微污染物，将高效复配絮凝剂应用于网格絮凝池，结合流场检测，深入研究其去除微污染物的絮凝效果与原理。.高效的混凝方法需要有完善的理论体系进行设计、施工及运行指导，而目前常用的高效混凝设备，其涡絮凝机理仍然不甚明了，需要进行深入研究。课题组计划以实验为主要研究手段，将粒子图像速度场（PIV）应用于网格絮凝池涡流场的检测，同时对絮凝颗粒在网格涡流场中的聚集过程进行监测、分析、计算和比较，以揭示微污染物涡絮凝的真正絮凝原理。本研究第一次将PIV技术应用到网格絮凝池中研究涡流场对絮凝效果的影响，这将促进微污染原水处理技术的发展，缓解兰州供水压力。

在参阅大量资料的前提条件下，设计出两套实验模型，并对照Taylor-Couette反应器涡流场形态特征，研究网格反应器涡流场及其絮凝效果。采用粒子成像速度场仪（PIV）对Taylor-Couette和网格絮凝池涡流场进行测量，获得各转速下涡流场信息。基于PIV测量结果，应用Fluent计算流体力学软件(CFD)对Taylor-Couette和网格絮凝池涡流场进行数值模拟，从多个层面上验证同等条件下的涡流场形态以及其所对应的转速区间的划分范围，用不同视角寻找涡流场形态特征与涡流动机制（可用旋转雷诺数Re或内筒转速n反映）间的区别与联系，对涡的形态特征及其转速分区进行确认。同时应用Taylor-Couette反应器和网格絮凝池进行各种混凝试验，再用PIV测量混凝过程，对综合了化学条件和水动力学条件的混凝过程进行全方位的同步测量与表征，定量分析反应器内涡流场形态特征与混凝效果之间的关联关系。. 研究显示：可形成大絮体并不代表具有好的絮凝效果，只有粒径合适且分布均匀的混凝过程效果才最好。层流涡产生的絮体粒径最大，但浊度去除率不高；波状涡和调制波状涡产生的絮体粒径相对较大，也比较均匀, 浊度去除率较高；湍流涡没有大絮体产生，浊度去除率最低。说明水力条件是影响絮凝效果的重要影响因素。在以上四种涡形态中，波状涡絮凝效果最佳，层流涡混合效能不行，调制波状涡只有在药剂投加量比较大的情况下，才会有较好的絮凝效果，湍流涡条件下不适合进行絮凝反应。