分层表流湿地中溶质输运过程的实验模拟与理论分析

Solute transport process in layered wetlands is of fundamental significance for wetlands ecological restoration, constructed wetlands wastewater disposal engineering and environmental risk assessment. By the method of experimental observation and theoretical analysis, this project focuses on solute dispersion in typical layered surface flow wetlands. In the theoretical analysis, the phase-average method is used to establish a solute transport model based on the transport equation of flows through porous media. By extension of the classic Taylor dispersion theory, Aris's concentration moment method and singular perturbation method, the multi-scale evolution mechanism and steady-state characteristics of solute transport in multi-layer wetland flow are analyzed. Furthermore, considering physicochemical effects such as adsorption and desorption, basic characteristics under various reaction conditions are obtained. Experimentally, an integrated experimental facility simulating the dispersion process of solute transport in a three-layer structure wetland was constructed. The basic parameters of the superficial solute transport equations and characteristics obtained by theoretical analysis were tested by PIV, UVP and PLIF measurement techniques. The results can provide the basis for engineering design of constructed wetland.

湿地中的溶质输运规律对于湿地生态修复、人工湿地污水处理和湿地污染环境风险评估等具有重要的研究价值。本项目将结合理论分析和实验测量，系统研究具有典型分层结构的表流湿地中溶质输运过程的模型机理。理论分析将采用相平均方法，建立以多孔介质流动输运方程为基础的多层结构湿地的溶质环境输运模型，推广Taylor弥散理论、Aris浓度矩法及奇异摄动法等经典方法，分析多层结构湿地流动中溶质输运的多尺度演化机理和稳态特征，并进一步确定吸附、解吸等多种生物理化反应组合条件下的弥散特征。实验方面，将搭建模拟湿地多层流动溶质弥散过程的综合实验台架，利用PIV、UVP和PLIF测量技术，检验和厘定在理论分析中得到的溶质输运模型基本参量和特征参数。研究成果可为湿地环境规划管理和人工湿地工程设计提供技术支持。

依照国家自然科学基金项目计划书中制定的研究计划，针对分层表流湿地中溶质输运过程的的机理，本课题组进行了深入系统的研究工作。本项目结合理论分析和实验测量，系统研究了具有典型分层结构的表流湿地中溶质输运过程的模型机理。理论分析采用相平均方法，全面刻画了典型分层表流湿地中的溶质弥散规律和特征，推广了Taylor弥散理论、Aris浓度矩法及奇异摄动法等经典方法，确定了不同阶广义弥散模型的适用时间，获得了随时间演化的弥散特征系数（弥散度、偏度和峰度），探讨了截面平均浓度和二维浓度分布的时空演化规律。实验方面，搭建了模拟湿地多层流动溶质弥散过程的综合实验台架，开发了分层表流湿地中溶质输运过程表观浓度的高分辨率模拟测量技术，测定了典型的天然湿地、人工湿地以及分层人工湿地溶质输运方程的基本参数，有望为湿地模拟与人工湿地工程设计提供基本依据。