中试尺度下连续式可渗透反应墙修复Cr（Ⅵ）污染地下水效果评估

以Cr(Ⅵ)污染地下水场地为例,基于室内模拟实验确定的PRB墙体尺寸及反应介质,建设了国内首座连续式PRB装置,自墙体建成后运行10个月内,对墙体内外监测井水位、水环境指标进行了4次监测。结果表明:PRB墙体内地下水流速>周边含水层中地下水流速,地下水流向虽局部有所改变,但总体上仍垂直穿过PRB墙体,未出现绕流现象;连续4期监测数据显示墙体内部均无Cr(Ⅵ)检出,受丰水期影响第4期墙体上下游C(Ⅵ)浓度明显高于其他期;墙体上、下游地下水pH在6.5~8.5,符合GB 5749—2006《生活饮用水卫生标准》,由于墙体内部铁的腐蚀作用pH快速增大,pH值在9~10.5,明显高于墙体上、下游;墙体内部发生强烈的氧化还原反应,连续3期监测的ORP值均为负值(-260~-140 mV),处于强还原性环境;墙体内Fe(Ⅱ)浓度高于墙体外,分布不均匀,其中G3-2井处浓度最高为3.52 mg/L;墙体内Cr(Ⅵ)的去除与Ca2+、Mg2+、HCO₃-、SO₄2-的去除同时进行,Mg2+和SO₄2-是Cr(Ⅵ)去除的主要影响因素。 综上,中试尺度下可渗透反应墙修复 Cr( Ⅵ ) 污染地下水案例中,在运行 10 个月监测周期内墙体内处于强还原、碱性环境,反应材料活性高,Cr( Ⅵ )修复效果明显。

EFFECT EVALUATION OF Cr（Ⅵ） CONTAMINATED GROUNDWATER REMEDIATION BY PERMEABLE REACTIVE WALL IN PILOT SCALE

In this paper, taking Cr(Ⅵ) contaminated groundwater site as an example, based on the size and reaction medium of PRB wall determined by indoor simulation experiment, the water level and water environment indexes of the monitoring well inside and outside the wall were monitored for four times in 10 months after the completion of the PRB wall. The results showed that the groundwater velocity in the PRB wall was greater than that in the surrounding aquifer. Although the groundwater flow direction changed locally, it still passed through the PRB wall vertically and no flow around was found. The monitoring data of four consecutive periods showed that no Cr(Ⅵ) was detected inside the wall, affected by the wet season, and the concentration of Cr(Ⅵ) in the upper and lower reaches of the wall in the fourth period was significantly higher than that in other periods. The pH value of groundwater in the upstream and downstream of the wall was between 6.5 and 8.5, meeting the requirements of China's national drinking water standard. Due to the corrosion of iron in the wall, the pH value increased rapidly and ranged in 9~10.5, which was significantly higher than that in the upstream and downstream of the wall. There was a strong oxidation-reduction reaction in the wall, and the ORP values monitored in three consecutive periods were negative(-260~-140 mV), indicating a strong reducing environment. Fe(Ⅱ) concentration in the wall was higher than that outside the wall, its distribution was uneven, and the concentration in Well G3-2 was the highest, with a value of 3.52 mg/L; the removal of Cr(Ⅵ) in the wall was carried out simultaneously with the removal of Ca2+, Mg2+, HCO₃- and SO₄-, and Mg2+ and SO₄- were the main influencing factors of Cr(Ⅵ) removal. To sum up, in the case of remediation of Cr(Ⅵ) contaminated groundwater by permeable reaction wall at pilot scale, the wall was in a strong reducing and alkaline environment during the monitoring period of 10 months, the reactive material was highly active, and the remediation effect of hexavalent chromium was obvious.