地下水人工补给过程中流速对多孔介质胶体堵塞的影响机理

Mechanism of influence of flow velocity on colloid blockage in porous media during artificial groundwater recharge

通过一系列室内砂柱模拟实验,研究了流速对胶体在饱和多孔介质中滞留-迁移行为的影响;运用COMSOL软件模拟,拟合实验数据后得到表征胶体沉积的关键参数。结果表明:流速增大缩短了胶体在多孔介质中的滞留时间,并增强水动力拖拽力,导致介质对胶体的吸附量减少,有利于胶体的迁移;回灌时间的延续造成的多孔介质渗透系数降低,可通过瞬间增大流速使渗透系数在较短时间内恢复,然而随后形成新的吸附渗透性仍会降低。水源离子强度、介质粗糙度等因素会影响胶体迁移的流速效应。在相同条件下,吸附系数随着离子强度的增大而增加,随着流速的增大而增加。综合来看,离子强度的增加可抵消一部分水动力拖拽力的影响,提高胶体在多孔介质中滞留的概率;介质表面粗糙度的增加,可削弱水动力拖拽力作用,同时增加胶体与介质的吸附、沉积点位和接触面积,导致胶体易于在多孔介质中发生滞留并可能进一步导致介质堵塞。

Through a series of indoor sand column simulation experiments,the effect of flow velocity on the retention-migration behavior of colloids in saturated porous media was studied.The COMSOL software was used to simulate and fit the experimental data to obtain the key parameters that characterize colloid deposition.The experimental results show that the increase of the flow rate shortens the residence time of the colloid in the porous medium,and enhances the hydrodynamic drag force,resulting in a decrease in the adsorption capacity of the medium to the colloid,which is beneficial to the migration of the colloid.The continuation of the recharge time causes the permeability coefficient of porous media to decrease,and the permeability coefficient can be restored in a short time by increasing the flow velocity instantaneously.However,the permeability of the subsequent formation of new adsorption will still decrease.Factors such as water source ionic strength and medium roughness will affect the flow rate effect of colloid migration.The simulation results show that under the same conditions,the adsorption coefficient increases with the increase of ionic strength and increases with the increase of flow rate.On the whole,the increase in ionic strength can offset part of the influence of hydrodynamic drag and increase the probability of colloid retention in porous media.From glass beads to quartz sand,the increase in the surface roughness of the medium can also weaken the hydrodynamic drag.At the same time,the drag force increases the adsorption,deposition point and contact area of the colloid and the medium,which causes the colloid to easily stagnate in the porous medium and may further cause the medium to block.