三峡库区黏性泥沙絮凝影响因素及其环境效应

The significant flocculation of cohesive sediment was observed in Three Gorges Reservoir, especially in the period of water-storing. However, the flocculation characteristics are still not well understood, such as the factors influencing the flocculation, flocculation dynamics or the environmental effect of cohesive sediment after flocculation. A flocculation-sedimentation column is designed, in which flocculation is induced by an oscillating grid, and the floc image analysis method and the laser particle analyzer technology are coupled to measured the floc size distribution during the flocculation process. The cohesive sediment will be sampled in Three Gorges Reservoir, and the influence of velocity gradient and sediment characterization (Zeta potential and organic matter content) on the flocculation of cohesive sediment will be analyzed. Base on the population balance model for flocculation dynamics, the relationship between the flocculation dynamic parameters and the factors influencing flocculation of cohesive sediment will be evaluated, and the floc size distributions resulting from the flocculation of cohesive sediment in different situations will be simulated. The effects of cohesive sediment on phosphate adsorption and desorption will be investigated when the flocculation of cohesive sediment occurred under turbulent condition, and the relationship between the Langmuir adsorption parameters and the characterization parameters of floc size distribution (D50 and D90/D10) or organic matter content will be evaluated. The results of this study are helpful to better understand the cohesive sediment movement and the transfer of pollutants in cohesive sediment, and able to provide a basic scientific and theoretical support to river regulation and environment protection in Three Gorges Reservoir.

三峡大坝蓄水后，库区出现了明显的黏性泥沙絮凝现象。目前，对于三峡库区黏性泥沙絮凝的影响因素，絮凝动力学特征以及黏性泥沙絮凝后对污染物的吸附效应知之甚少。本研究以三峡库区黏性泥沙为研究对象，设计絮凝沉降柱，采用絮体图像分析与激光粒度仪相结合的方法测量絮凝过程的絮体粒径分布，明确紊流条件（速度梯度）和泥沙特性（Zeta电位和有机物含量）对黏性泥沙絮凝的影响；应用群体平衡模型描述黏性泥沙絮凝动力学，构建絮凝动力学参数与絮凝影响因素之间的关系式，模拟计算三峡库区黏性泥沙在不同絮凝条件下的粒径分布规律；试验分析三峡库区黏性泥沙在紊流条件下絮凝后对磷的吸附解吸规律，揭示Langmuir吸附参数与粒径分布特征参数（D50、D90/D10）及有机物含量的关系。研究成果有助于更好地认识三峡库区黏性泥沙运动特性和污染物在泥沙中的迁移转化规律，能够为三峡库区河道整治和环境保护提供科学依据和理论支撑。

三峡库区蓄水以来，库区水体流速降低，泥沙发生絮凝沉降后导致较为严重的泥沙淤积问题。为深入认识三峡库区泥沙絮凝特性，课题组研发了专门的絮凝沉降装置及絮体图像采集系统，研究了三峡库区典型河段的泥沙在不同的流体剪切率等影响因素作用下的絮体粒径分布规律，明确了三峡库区泥沙絮凝临界剪切率约为20s-1左右，三峡库区上游（长寿）、中游（忠县）、下游（奉节）河段絮体最大粒径分别为130μm、126μm和114μm，并发现上游河段在泥沙浓度较高时更容易发生淤积，而中游河段泥沙在泥沙浓度较低时更容易发生絮凝淤积。同时，课题组开展了三峡库区不同河段的泥沙絮凝后对磷的吸附/释放研究，发现上游（长寿）、中游（忠县）、下游（奉节）河段的泥沙对磷的吸附动力学参数（最大吸附容量、平均吸附速率）都呈现递减的规律，考虑是由于泥沙颗粒粒径及表面特性、有机质含量的差异所致。综上所述，本课题研究了不同条件下三峡库区黏性泥沙絮凝特征及对磷的吸附/释放规律，有助于进一步提升对三峡库区泥沙淤积及水体污染的认识，可为河道治理及水环境防治等方面提供科学依据。