Kamolpornwijit W, Liang L, West O R, Moline G R, Sullivan A B
Environmental Sciences Division, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37830-6036, USA.
J Contam Hydrol. 2003 Nov;66(3-4):161-78. doi: 10.1016/S0169-7722(03)00031-7.
The operating life of an Fe(0)-based permeable reactive barrier (PRB) is limited due to chemical reactions of Fe(0) in groundwater. The relative contributions from mineral precipitation, gas production, and microbial activity to the degradation of PRB performance have been uncertain. In this controlled field study, nitrate-rich, site groundwater was treated by Fe(0) in large-volume, flow-through columns to monitor the changes in chemical and hydraulic parameters over time. Tracer tests showed a close relationship between hydraulic residence time and pH measurements. The ionic profiles suggest that mineral precipitation and accumulation is the primary mechanism for pore clogging around the inlet of the column. Accumulated N(2) gas generated by biotic processes also affected the hydraulics although the effects were secondary to that of mineral precipitation. Quantitative estimates indicate a porosity reduction of up to 45.3% near the column inlet over 72 days of operation under accelerated flow conditions. According to this study, preferential flow through a PRB at a site with similar groundwater chemistry should be detected over approximately 1 year of operation. During the early operation of a PRB, pH is a key indicator for monitoring the change in hydraulic residence time resulting from heterogeneity development. If the surrounding native material is more conductive than the clogged Fe-media, groundwater bypass may render the PRB ineffective for treating contaminated groundwater.
由于地下水中零价铁（Fe(0)）的化学反应，基于零价铁的可渗透反应屏障（PRB）的使用寿命有限。矿物沉淀、气体产生和微生物活动对PRB性能退化的相对贡献尚不确定。在这项受控的现场研究中，通过在大容量、流通式柱中用零价铁处理富含硝酸盐的现场地下水，来监测化学和水力参数随时间的变化。示踪剂测试表明水力停留时间与pH测量值之间存在密切关系。离子分布表明矿物沉淀和积累是柱入口周围孔隙堵塞的主要机制。生物过程产生的累积氮气也影响了水力状况，尽管其影响仅次于矿物沉淀。定量估计表明，在加速流动条件下运行72天后，柱入口附近的孔隙率降低高达45.3%。根据这项研究，在具有相似地下水化学性质的场地，通过PRB的优先流应在大约1年的运行时间内被检测到。在PRB的早期运行期间，pH是监测由非均质性发展导致的水力停留时间变化的关键指标。如果周围的天然物质比堵塞的铁介质更具传导性，地下水绕过可能会使PRB对处理受污染的地下水无效。
