https://scholars.lib.ntu.edu.tw/handle/123456789/77154
Title: | 土壤之物理及化學不均質性對有機污染復育成效之影響及模擬(3/3) Modeling the influence of physical and chemical heterogeneity on the performance of soil remediation for organic contaminants |
Authors: | 吳先琪 | Keywords: | 不均質性 | Issue Date: | 31-Jul-2003 | Publisher: | 臺北市:國立臺灣大學環境工程學研究所 | Abstract: | 由於土壤存在物理及化學不均質性,導致在規劃土壤復育工作時,模擬預測污染物行為發生困難。物理的不均質性導致土壤中流體傳輸速度有很大差異而產生流體流動區域及靜止區域。雖然數學的計算能力可以處理不均質的地下水文模式,但是因為地質水文調查的限制,無法提供模式所需要之空間參數,所以必須以統計的方法來處理物理不均質的問題。本研究以對數常態分布的一組質傳係數來描述移動相與靜止相間污染物趨向平衡的速度。模擬的結果與實驗數據相當吻合,顯示當傳輸尺度大於實驗室的土柱時,不平衡的分配或是貫穿曲線脫尾的現象主要是源於污染物在靜止相內受到質傳限制的移動所導致。而此組質傳係數之分布與土壤質地、水分含量及系統之尺度有關,這些性質均是可以很容易測量到的。此外土壤影像擷取系統可以快速及經濟的提供土壤質地之剖面分布,將有助於土壤復育之調查評估及預測工作。 The distributed mass-transfer coefficient approach is used to model the transport of pollutants where there is heterogeneous soil texture and mass-transfer limited partition kinetics. The experimental and simulation results indicate that in a length scale larger than that of a laboratory soil column the phenomenon of non-equilibrium transport or tailing is resulted mainly from the mass-transfer limited migration of the sorbate into the stagnant region inside the immobile phases. The problem of modeling each of these immobile phases due to the lack of geological information can be improved by using a distributed mass-transfer coefficient set, which is related to some of the easily obtained soil properties such as the length scale of the system of concerned, the moisture content and the heterogeneity of the soil texture profile. Also the soil video imaging system can be used to identify and locate the layers with high hydraulic conductivity and layers with low hydraulic conductivity, or say the heterogeneity of the soil column with quite low cost and in short time, which will be a promising tool to help on the characterizing, modeling and remediation of a contaminated site. Three VOCs were used to study the interaction between humin and organic contaminants. Higher sorbing capacity of humin for more polar VOCs and the C13-NMR data of humin indicate that humin was more hydrophilic than Aldrich humic acid. The apparent diffusivity of acetone, toluene, and hexane in the disks ranged from 10-8 to 10-10 cm2/s. The sorbed toluene in humin does not seem persistent to desorption; however, acetone and hexane, either a polar or a linear compound, show persistence against desorption. On the completion of the desorption experiments, there were approximately 35% and 20% sorbate residue for acetone and hexane, respectively. The sorption kinetics of toluene in dry and humid clay films was investigated by tracking the change of the IR absorbance. Under humid condition, similar toluene sorbed intensities are found on Ca -and Cu– montmorillonites. However, higher intensities of toluene sorbed were found on Cu-form under dry condition, which indicates stronger interaction occurring. On Ca- and Cu-montmorillonite, some portion of toluene is desorbed at an extremely slow rate under dry conditions. Either some original toluene peaks or some new peaks are persistent against desorption from montmorillonites, also suggesting the existence of irreversibly sorbed species. Theremay be some transformation of VOCs in clay systems. Although the persistence was not observed under high humidity conditions by spectroscopic method, the clay minerals could be a controlling factor of slow desorption in soil. The sorption and desorption of trichloroethylene (TCE) in humic acid and humin disks was investigated by microbalance. The apparent diffusivity of TCE in these two humic substances was in the 10-8 to 10-9 cm2/s magnitude. There are no residual sorbed TCE observed via a microbalance. The intrinsic sorption/desorption time scale of TCE on two cation exchanged montmorillonites was only few minutes by thin film/FTIR method. Molecular dynamic simulations were also used to study the sorption of organic contaminants in soil organic matter. The simulation results of the sorption kinetics and thermodynamics of toluene in humic acid are in good agreement with the experimental data. We believe that this technique will become a powerful tool not only to facilitate the solving of the problems of contaminated soil clean-up but also to be applied to a wider range of environmental problems. After studying soil chemical heterogeneity, we found the intrinsic sorption is fast for VOCs into humin, humic acid, and montmorillonite. So they do not contribute to the sequestration process in soils. The mass transfer of contaminants into soil plays the important role on the slow sorption/desorption in soils. |
URI: | http://ntur.lib.ntu.edu.tw//handle/246246/22117 | Other Identifiers: | 912211E002062 | Rights: | 國立臺灣大學環境工程學研究所 |
Appears in Collections: | 環境工程學研究所 |
File | Description | Size | Format | |
---|---|---|---|---|
912211E002062.pdf | 2.55 MB | Adobe PDF | View/Open |
Items in DSpace are protected by copyright, with all rights reserved, unless otherwise indicated.