ANALYSIS OF PREFERENTIAL FLOW AND DIFFUSION DISTANCE OF POLLUTANTS IN AIR-SPARGING

在地下水修复中，如土壤蒸汽提取、空气喷射等，我们通常会观察到“拖尾现象，即回收的污染物浓度下降得非常缓慢。了解尾矿很重要，因为它控制着清理污染场地所需的时间。研究人员将这种现象归因于污染物从土壤材料的微孔中缓慢洗脱。然而，我们提出了另一种假设，即这些修复系统中的空气和水的配置可能会导致尾矿。在本研究中，制备了内径为30 cm，内高为50 cm的不锈钢柱。将来自Tedori河的砂（从当地建造者获得）风干并过筛，然后将其0.5 - 2.0mm部分填充到柱中直至50 cm的高度。该柱连接到蓄水池，以便能够控制砂层中的地下水位。气体注入口设置在柱底部上方10 cm处。气体注入口通过质量流量控制器连接到氮气、氦气和二氧化碳气瓶。将二氧化碳溶解在柱中的水中，然后，供应氮气并测量流出气体中的二氧化碳浓度。结果，我们观察到明显的“拖尾”，时间-浓度关系在双对数图中几乎呈线性。由于我们的砂介质中微孔很少，我们认为“拖尾”不是由微孔扩散引起的。借助最近的分析拖尾的理论，在这一点上，我们认为拖尾是由在水相中的“扩散距离”a的分布引起的，并且该分布服从幂律分布：f（a）&lt;$a^<1.15>。

In groundwater remediation such as soil vapor extraction, air-sparging etc., we usually observe "tailing," the phenomenon that the concentration of the recovered pollutants decreases very slowly. Understanding the tailing is important because it controls the time required for the clean-up of polluted sites. Researchers have ascribed this phenomenon to the slow elution of pollutants from the micro-pores of the soil material. However, we came up with another hypothesis that the tailing can be caused from the configuration of the air and water in these remediation systems.In this research, a stainless column of 30 cm in inner diameter and 50 cm in inner height was prepared. Sand from Tedori river (obtained from a local constructor) was air-dried and sieved, and then 0.5 - 2.0 mm fraction of it was packed into the column up to the height of 50 cm. The column was connected to the water reservoir to enable to control the water table in the sand layer. Gas injection port was set 10 cm above the bottom of the column. The gas injection port were connected to nitrogen, helium and carbon dioxide cylinders via mass flow controllers. Carbon dioxide was dissolved into the water in the column, and then, nitrogen was supplied and the concentration of carbon dioxide in the effluent gas was measured. As the results, we observed an apparent "tailing," the time-concentration relationship was practically linear in double-log plots. As our sand medium has little micro-pores, we concluded that the "tailing" was caused not by the micro-pore diffusion. With the help of recent theory of analyzing the tailing, at this point, we consider that the tailing was caused by the distribution of the "diffusion distance" in the water phase, a, and the distribution obeys the power law distribution: f(a)〜a^<1.15>.