水动力作用对污染物在河流水沙两相中分配的影响研究进展

通过总结近年来有关水动力作用对河流中泥沙吸附/释放重金属、磷等污染物影响研究成果,分析了水流紊动强度和流速对污染物在河流水沙两相中分配的影响规律。当水流紊动强度较低时,泥沙主要以床沙形式存在,泥沙对污染物的吸附/释放速率和强度较低;随着紊动强度增大,水沙界面切应力随之增大并促使泥沙悬浮,污染物与悬浮泥沙颗粒接触面积增大,使得泥沙对污染物的吸附/释放速率和强度显著增加。流速对污染物在水沙两相间分配的影响较为复杂。泥沙静止时,流速的增大会减小边界层厚度,增大水体溶解氧含量、氧化还原电位等参数,并使污染物在水体里的扩散由分子扩散转变为以紊动扩散为主,增强污染物在水-沙界面的交换通量,对污染物在水沙两相间的分配产生影响;随着流速进一步增大,床沙逐渐起动、悬浮,此时除上述因素外,泥沙运动状态、悬浮颗粒间碰撞强度、悬浮物的絮凝等均会对泥沙吸附/释放污染物产生影响,由于影响因素较多,作用机制复杂,目前关于泥沙运动对污染物在水沙两相间分配的影响所得结论仍存在分歧。相应的机理研究及数学模型的建立均做了较大简化。综观当前的研究成果,水沙运动及其化学生物过程等对污染物在河流水沙两相中的分配作用机理和耗氧有机物、有毒有机物等污染物与泥沙的作用机理是这一领域的未来研究重点。

Review of influence of hydrodynamic action on distribution of pollutants in water and sediment in river

Through a review of recent investigations into the effects of hydrodynamic action on the adsorption/release of pollutants(heavy metals, phosphorus, etc. )by sediments, the influence of water turbulence intensity and velocity on the distribution of pollutants in water and sediment in rivers was analyzed. The results show that, when the turbulence intensity is low, sediments occur in a form close to bed sediment, and the rate and extent of adsorption/release of pollutants by sediments are low. As the turbulence intensity increases, the shear stress at the water-sediment interface increases, sediment suspension is promoted, and the contact area between pollutants and suspended sediment particles increases, leading to a significant increase in the rate and extent of adsorption/release of pollutants by sediments. The effect of the water velocity on the distribution of pollutants in water and sediment is complex. When the sediment is stationary, with the increase of the velocity, the boundary layer thickness decreases, the dissolved oxygen content in water and redox potential increase, the diffusion of pollutants in the water body changes from molecular diffusion to turbulent diffusion, and the pollutant exchange flux at the water-sediment interface increases. With further increase of the velocity, the bed sediment gradually moves and is suspended. At this moment, the state of sediment movement, intensity of collision between suspended matters, and flocculation of sediments also have effects on the adsorption/release of pollutants by sediments. Because of the extensive factors and the complexity of the functional mechanism, there is a disagreement between results regarding the influence of sediment movement on the adsorption/release of pollutants by sediments reported by different researchers, and simplification is carried out through mechanism studies and establishment of mathematical models. It is pointed out that future studies should focus on the mechanism of the influence of the water and sediment movement as well as chemical and biological processes on the distribution of pollutants in water and sediment in rivers and the interaction of oxygen consumption organics and nocuous organics with sediments.