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研究生:陳維基
研究生(外文):Chen, Wei-Ji
論文名稱:土壤水分對土壤氣提法去除甲苯的影響
論文名稱(外文):Effect of soil moisture content on the removal of toluene by soil vapor extraction process
指導教授:吳先琪
指導教授(外文):Wu Shian-Chee
學位類別:碩士
校院名稱:國立臺灣大學
系所名稱:環境工程學研究所
學門:工程學門
學類:環境工程學類
論文種類:學術論文
論文出版年:1997
畢業學年度:85
語文別:中文
論文頁數:95
中文關鍵詞:土壤水分土壤氣提法
外文關鍵詞:soil moisture contentsoil vapor extraction
相關次數:
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在土壤不飽和層受到揮發性有機物污染時,土壤氣提法為一經濟有效
的處理方法,可以在污染場址現地(in-situ)以簡單的設備、較少的土
壤擾動以及地形地物的限制下施行而達到處理的效果。為了預測土壤氣提
法對污染物的去除效率,則必須了解氣提法在不飽和層中所造成的污染物
傳輸現象,以及在不飽和土層的土壤環境中,水分對傳輸現象所造成之影
響。
本研究是以新店溪岸沖積土作為研究對象,由批次實驗求得在不同含水率
下土壤對甲苯的等溫吸附曲線以及線性氣固相分配係數,研究結果顯示在
烘乾土時土壤對甲苯的吸附能力最大,而隨著土壤含水率的增加而吸附能
力降低,與過去的研究結果相似,主要應是土壤孔隙的礦物表面為水分佔
據所致。其次再以沖積土填充之土柱模擬不同含水率下之氣提實驗,以瞬
間脈衝方式輸入甲苯為污染物後發現,在風乾土(含水率為1.6%)的情況
下所造成的慢吸附現象最為明顯,對污染物的去除效率亦較差,僅
有16.74∼36.25%。在模擬含毛細水(含水率為14.09∼24.15%)與飽和含
水層(含水率為23.24%)之土柱中,水分佔據了土壤表面的吸附位址並阻
礙了甲苯分子在土壤孔隙中之擴散,抑制了慢吸附作用,因此甲苯貫穿土
柱的時間較短,並且對加入之甲苯的去除率較高,可達50.02∼58.54%。
以一維平衡傳輸模式模擬不同含水率之土壤管柱,以土壤氣提法處理其中
以瞬間脈衝方式輸入之甲苯時發現,由於土壤對甲苯的慢吸附作用,使出
流氣體中甲苯質量之實驗值較模擬值為低;並且在模擬水分含量較高之土
壤管柱中,不均勻的氣體流速與流經路線所造成氣體可流經之土柱截面積
較小之現象,導致了實驗中出流氣體的甲苯濃度峰值出現時間較模擬值為
早。此外,在比較不同含水率土壤管柱之模擬結果時亦發現水分含量高的
土柱均較風乾土柱之穿透時間短以及拖尾現象較不嚴重,顯示水分在此脈
衝輸入污染物的氣提過程中可阻礙污染物在傳輸途中之擴散,有助於氣提
之處理效果;但若在污染區呈現飽和含水之狀況下,則會由於相同的阻礙
效應而降低其處理效能。
Soil vapor extraction (SVE) is a cost-effective remediation
process for the soil of unsaturated zone contaminated with
volatile organic compounds (VOCs). This process can be applied
with simple basic equipment without the confinement of site
geographical features, and can be used in-situ for the purpose
of lowering the disturbance of the site. In order to predict and
evaluate the removal efficiency of the SVE process under humid
conditions, this study investigates the transport phenomena in
soil during SVE actices and find out how the VOCs removal will
be influenced by the soil moisture content.
The soil collected from the riverside of Hsin-Tien Hsi was used
in this study. From batch tests, the adsorption isotherm and
linear partition coefficients of toluene vapor to the soil were
obtained. The data revealed that the sorption capacity was the
highest for the oven-dried soil, and with the increase of soil
moisture content, the sorption capacity deceased. It may result
from the competition between water and toluene in the sorption
sites on the mineral surface. Same results have been reported in
the lerature. In the venting experiments,
toluene was induced into soil columns of various moisture
content by pulse inputs. The results revealed that the slow
sorption effect was most obvious in air-dried condition
(moisture content=1.6%). Also the removal efficiency in air-
dried condition was the lowest (16.74~36.25%). In the columns
simulating capillary zone and saturate zone, the breakthrough
time was quicker and removal efficiency was higher (50.02
~58.54%) than the air-dried column because water occupied the
sorpti sites and obstructed the diffusion of toluene into soil
pores. The one-dimension
advection-diffusion model weree contents. The results showed
that the model did not fit the data well due to the slow
equilibration equilibrium phenomena proven with the lower
toluene concentration peak and obvious tailings. In the columns
with higher moisture contents, the measured toluene
concentration peak moved faster than the model prediction
possibly due to the formation of stagnant saturated regions and
mo confined gas channels and flow path in soil columns. It
revealed that soil water will promote the removal efficiency in
this pulse input experiment by blocking the diffusion path for
toluene. But if the contaminant was originally spread into the
stagnant moistened zone, the same effect will decrease the
removal efficiency.
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