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易挥发的剧毒氯代烃有机物1,2-二氯乙烷(1,2-dichloroethane,简称1,2-DCA)具有致癌、致畸、致突变效应,是土壤和地下水环境中常见有机污染物之一[1]。因其溶解性高、性质稳定,导致其在土壤和地下水中环境的降解难度大。因此,研究和探讨1,2-二氯乙烷在地下水中的降解具有重要意义。
地下水有机污染的主要修复方法包括抽出处理[2-3]、气相抽提[4]、可渗透反应墙[5]以及生物修复[6]等,但这些方法在处理成本、去除率及运行周期等方面尚存在不足之处。原位化学氧化技术虽然在污染地下水修复方面还处于研究发展阶段,但已表现出良好的处理效果[7-8]。碱活化过硫酸盐原位修复地下水是其中一种被广泛应用的技术。有研究[9]表明,过硫酸盐氧化体系中存在硫酸盐自由基(
$ {\rm{SO}}_4^ {-\cdot}$ )和羟基自由基(·OH),其对有机污染物的降解效果随pH变化而不同。在pH>8.5的条件下,$ {\rm{SO}}_4^ {-\cdot}$ 能与OH−反应并促进体系中·OH的生成,体系中的部分有机污染物可由·OH氧化降解[10-11]。MA等[12]选择活化过硫酸盐氧化苯酚作为研究对象,在碱性条件下苯酚的氧化速率有所增加,pH升高可显著降低化学反应活化能,降解苯酚时过硫酸盐的有效碱性活化pH阈值最小约为11。增大修复药剂在地下水含水层中的有效影响半径是地下水原位修复技术工程化应用的关键之一。修复药剂在含水层的运移受含水层自身水文地质条件和地下水渗流场影响较大。水动力控制法是利用井群系统,通过抽水或向含水层注水,人为地改变地下水的水力梯度,进而影响含水层的地下水渗流特征。在进行原位化学氧化修复时,通过水动力调控可以影响修复药剂的扩散和运移,从而间接影响地下水中污染物降解效果。
目前,针对氯代烃污染地下水原位化学修复的研究主要是室内氧化批实验以及土柱或砂箱模拟实验,因其存在尺度效应而影响了该技术的推广应用。本研究中,以某有机污染场地污染含水层为实验对象,采用水动力控制法强化原位化学氧化技术修复受1,2-二氯乙烷污染含水层,分析了碱活化过硫酸盐降解目标污染物的效果,探讨实验过程中目标污染物及地下水参数的变化规律,以期为该技术修复污染地下水的工程化应用提供参考。
水动力控制强化碱活化过硫酸盐原位修复1,2-二氯乙烷污染地下水
Hydrodynamic control-enhanced alkali activated persulfate for in situ remediation of 1,2-dichloroethane contaminated groundwater
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摘要: 针对某受1,2-二氯乙烷污染场地,开展水文地质实验并求解水文地质参数,采用水动力控制强化原位化学氧化技术修复了地下水含水层中受污染的地下水,探究了碱活化过硫酸盐对地下水中目标污染物去除效果,并对地下水水化学因子进行了长期监测。结果表明,实验区含水层渗透系数为7.89 m·d−1,导水系数为101 m2·d−1,在一维稳定流场中二维弥散条件下,含水层纵、横向弥散度αL和αT分别为0.89 m和0.089 m,地下水流速为3.85 m·d−1,水动力条件明显优于自然状态,通过水动力控制法干扰地下水流场可有效控制修复药剂在含水层中的扩散速度和影响范围。注药后实验区污染物浓度整体呈下降趋势,在第14天,注药井4 m以内1,2-二氯乙烷浓度低于检出限,药剂修复效果在含水层中可保持28 d。碱活化过硫酸盐降解1,2-二氯乙烷的反应速率常数为0.022 d−1,半衰期为29 d。实验期间地下水中硫酸盐浓度先上升后下降,140 d后恢复至原浓度水平,对实验场地二次污染影响较小。碱活化过硫酸盐在氯代烃类污染场地修复中将有广阔的应用前景。Abstract: In this study, the hydrological tests were conducted to solve the hydrological parameters of a 1,2-dichloroethane contaminated site. The hydrodynamic control-enhanced in-situ chemical oxidation was used to remediate the 1,2-dichloroethane contaminated groundwater in aquifer. The removal effect of target pollutant in groundwater by alkali activated persulfate (PS) was tested. A long term monitoring for the water chemical factors of groundwater was performed. The results showed that the permeability coefficient and the hydraulic conductivity of the studied aquifer were 7.89 m·d−1 and 101 m2·d−1, respectively. Under the condition of two-dimensional dispersion in one-dimensional steady flow field, the calculated groundwater velocity was 3.85 m·d−1 according to the advection-dispersion-reaction equation, and the longitudinal coefficient αL and lateral dispersion coefficient αT were 0.89 m and 0.089 m, respectively. The corresponding hydrodynamic conditions were significantly superior to natural conditions. The diffusion rate and influence range of remediation chemicals in aquifer could be effectively controlled by the disturbance of groundwater flow field with the hydrodynamic control method. After injecting the oxidation agents, the concentration of 1,2-dichloroethane in the studied area decreased generally, and the effective radius of the injection well was around 4 m. On the 14th day, the concentration of 1,2-dichloroethane around the injection well was below the detection limit, and the remediation effect of agents has maintained until 28 days. During this pollutant-removal period, the reaction rate constant of 1,2-dichloroethane degradation by alkali activated persulfate was 0.022 d−1, and the half-life was 29 d. Although the concentration of sulfate in the groundwater experienced an increase after 56 days, it returned to the original level before the injection on the 140 day. It indicated that the integrated technique applied in this study had less impact on the studied area. This alkali activated persulfate will have broad application prospects in chlorinated hydrocarbons contaminated sites.
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Key words:
- hydrodynamic control /
- activated persulfate /
- in-situ remediation /
- 1,2-dichloroethane /
- sulfate
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