饱和砂质土壤中不同流速条件下1, 2-二氯乙烷的运移及模拟

采用室内土柱试验方法,研究了孔隙水流速对1,2-二氯乙烷(1,2-DCA)在饱和砂质土壤中运移行为的影响.借助CXTFIT模型,通过示踪剂(KBr)穿透试验,获取了土柱内部条件参数,包括弥散系数D和孔隙水流速v,以及可动水和不可动水的分配比例.应用示踪剂试验获取的参数,分别使用平衡模型和非平衡两点模型对1,2-DCA在不同孔隙水流速下的穿透曲线进行了拟合.结果表明,平衡模型不能很好地模拟本文试验条件下1,2-DCA的运移,而非平衡两点模型拟合精度较高.试验条件下,流速对1,2-DCA运移影响显著.孔隙水流速较高时穿透时间较短,穿透曲线峰值更高.土壤对1,2-DCA的吸附作用是影响穿透特征的主要因素,高流速条件下,吸附作用的影响较小.

Simulation of the transport of 1, 2-dichloroethane in saturated sandy soil under different flow rates

A soil column experiment was conducted to evaluate the effect of pore water velocity on transport of 1,2-dichloroethane (1,2-DCA) in saturated sandy soil. A nonlinear least-squares optimization approach (CXTFIT 2.1) was used to fit the breakthrough curves. Br^- was used as a tracer to obtain the parameters of the internal conditions of the soil column, including dispersion coefficient (D), pore water velocity (v), and the distribution proportion of movable and immovable water. Based on the fitted parameters, one dimensional convection-dispersion equation based on local equilibrium assumption model (LEA) and non-equilibrium assumption model (NEA) were applied to describe the transport characteristics of 1,2-DCA under different pore water velocities. The results showed that the breakthrough curves of 1,2-DCA could be simulated very well by the NEA model but poorly by the LEA model. Under the test conditions, pore water velocity had significant impact on the transport of 1,2-DCA. The faster the velocity of pore water was, the less the penetration time was needed, and the higher peak value of the breakthrough curves achieved. The transport of 1,2-DCA was mainly influenced by the adsorption effect of soil, and it seemed to be less impacted under higher pore water flow rate.