Department of Civil and Environmental Engineering, Arizona State University, Tempe, Arizona, USA.
Water Environ Res. 2009 Nov;81(11):2337-43. doi: 10.2175/106143009x425960.
Soil aquifer treatment (SAT) and bank filtration use natural attenuation processes to purify water for subsequent use. Soil aquifer treatment may constitute both unsaturated and saturated flow conditions, while bank filtration systems are primarily saturated flow. This analysis focuses on the saturated zone, where the majority of residence time occurs, in both SAT and bank filtration systems. Sustainable removal mechanisms during subsurface flow are primarily surface-mediated and therefore depend on surface area. By analyzing saturated subsurface flow hydraulics in granular media, a relationship between surface area and travel time was developed. For saturated subsurface flow, the ratio of surface area-to-travel time varied by approximately a factor of 3, for common aquifer materials subject to identical hydraulic gradients. Because travel time criteria often are used to regulate SAT and bank filtration systems, these criteria also may determine the surface area and associated surface-mediated reactions for water purification. The ratio of surface area-to-travel time increases with increasing hydraulic gradient, implying that surface area is relatively constant for specific travel times, even if the hydraulic gradient changes; however, the increasing hydraulic gradient will increase the distance from the recharge zone to the recovery well. Therefore, travel time assessments based on maximum possible hydraulic gradients increase surface area and could provide a conservative limit for surface-mediated reactions. This analysis demonstrates that travel time criteria for SAT and bank filtration systems indirectly provide a minimum surface area that may support sustainable removal mechanisms.
土壤含水层处理 (SAT) 和滨岸过滤利用自然衰减过程来净化水，以供后续使用。土壤含水层处理可能包括非饱和流和饱和流条件，而滨岸过滤系统主要是饱和流。本分析侧重于 SAT 和滨岸过滤系统中的饱和带，大部分停留时间都发生在该带。在地下水流中，可持续去除机制主要是表面介导的，因此取决于表面积。通过分析颗粒介质中的饱和地下水流动力学，得出了表面积与停留时间之间的关系。对于饱和地下水流，表面积与停留时间的比值在常见的含水层材料中，在相同的水力梯度下变化约 3 倍。由于停留时间标准常用于调节 SAT 和滨岸过滤系统，这些标准也可能决定水净化的表面积和相关的表面介导反应。表面积与停留时间的比值随水力梯度的增加而增加，这意味着对于特定的停留时间，表面积相对恒定，即使水力梯度发生变化；然而，增加的水力梯度会增加从补给区到回收井的距离。因此，基于最大可能水力梯度的停留时间评估会增加表面积，并为表面介导反应提供保守限制。本分析表明，SAT 和滨岸过滤系统的停留时间标准间接提供了可能支持可持续去除机制的最小表面积。
