叠加电场促进土壤过硫酸盐匀化传质机理及原位热活化增效研究

Efficient in-situ remediation of low permeability organic contaminated soil is one of the hotspots in the field of soil remediation technology research. Electrokinetic remediation technique (EK) is not affected by soil permeability and can enhance the soil mass transfer process. Therefore, can use as the reinforcement method of in situ chemical oxidation technique (ISCO) to enhance the migration and diffusion of oxidation reagents in low permeability soil. During the process of EK delivery of persulfate (PS) to remediate organic contaminated soil, it is difficult to quantify the process of reagent migration and space distribution, achieve uniform distribution in the remediate soil, the penetration extent is small and oxidation efficiency are limited, difficult to in-situ activation in remediate soil. In order to solve these problems, a novel approach of combining EK delivery of PS and low temperature electro-thermal activation technique is proposed in this study. The petroleum (TPH) is chosen as the target contaminant, base on the PS migration and space allocation quantized model under the symmetric electric field, to design a two-dimensional superimposed electric field, which can promote the uniform distribution of PS, and finally reveal the homogeneous mass transfer mechanism. Use the electrical heating method to activate the PS, the energy-heat conversion efficiency and soil heat transfer efficiency will investigate, and obtain the quantitative correspondence between soil temperatures, water contents, PS activation efficiencies and TPH removing efficiencies, clarify the synergistic mechanism. The results of this project will provide the theoretical and scientific basis for the application and technical innovation of EK-ISCO.

低渗透性有机污染土壤的高效原位修复是土壤修复技术研究领域的热点之一。电动技术（EK）不受土壤渗透性影响且可增强土壤传质过程，可作为原位化学氧化技术（ISCO）的强化手段，增强药剂在低渗透性土体内迁移扩散。本研究针对EK运送过硫酸盐（PS）技术存在的药剂迁移及空间分配过程难以量化、难以实现空间均布、运送量及氧化效率有限、原位活化难以实现等问题，开展电加热原位活化EK运送PS组合修复工艺研究。以石油（TPH）为目标污染物，以PS在对称电场下的迁移及空间分配量化模型研究为基础，设计可实现PS空间均匀分配的二维叠加电场，阐明匀化传质机理；采用原位电加热手段活化PS，探讨不同加热方式的电能-热能转换效率及土壤传热效率，研究土壤温度-水分-PS活化效率-TPH去除效率的量化对应关系，阐明原位热活化增效机制，为有机污染低渗透性土壤的EK-ISCO修复技术创新与应用提供科学依据和理论基础。

针对原位化学氧化技术（ISCO）应用于低渗透性有机污染土壤修复的技术瓶颈，包括药剂传质扩散受限、难以实现有效空间分配及高效活化等问题，基于电动技术（EK）和热传导过程不受土壤异质性与低渗透性影响等特点，开展叠加电场促进土壤过硫酸盐（PS）匀化传质机理及原位热活化增效研究。结果表明，一维单向电场和极性切换电场均不能实现PS的有效空间分配；普通二维对称电场（CEF）条件下土壤PS浓度与场强呈现显著正相关关系（R2=0.87-0.96），但与一维电场相比PS注入量并未显著提高；叠加电场（SEF）的场强集中于0.5-1.5 V/cm（占比90.7%），且与土壤PS浓度的相关性（R2=0.95-0.99）优于CEF。与CEF（CPS=48.4-78.9 mg/kg，Cave=63.96 mg/kg）相比，SEF的PS空间分布更为均匀（CPS=98-117.7 mg/kg），注入量（Cave=107.2 mg/kg）显著提高。电热传导加热（ECH）过程土壤温度变化趋势拟合结果表明，虽然饱水带导热系数k显著高于包气带，但随着土壤含水量降低土壤温度也随之下降。因此，保证ECH的土壤含水量是温度保持和PS有效活化的关键。基于上述研究结果，构建SEF/PS-ECH组合工艺，PS注入15 d后启动ECH（T=90℃），加热结束时土壤温度范围47.7-79.4 ℃，PS经有效活化产生大量硫酸根自由基或羟基自由基，土壤TPHs（C0=2857.3 mg/kg）残留量在640.7-763.8 mg/kg之间（Cave=701.5 mg/kg），显著低于《土壤环境质量 建设用地土壤污染风险管控标准（试行）》（GB36600—2018）第一类用地筛选值。综上，研究所构建的叠加电场运送PS+电热传导原位热活化阶段式组合工艺，可以为有机污染低渗透性土壤的EK-ISCO修复技术创新与应用提供科学依据和理论基础。