膠體與污染物於地下水中傳輸模式之發展與應用

Abstract

地下水中若有膠體存在，會提高污染物在含水層中之移動性。污染物與膠體在多孔介質表面的吸附脫附關係，可由平衡吸附公式或動能吸附公式來描述。地下水中膠體顆粒與污染物傳輸的方程式，若分別結合平衡吸附或動能吸附公式，構成以膠體於固相和液相濃度及污染物於固相、液相及膠體相為未知的聯立偏微分方程式，即為膠體及污染物傳輸之平衡及動能數學模式。 本論文採用有限差分法，發展膠體傳輸與污染物傳輸之數值模式，並將膠體傳輸之數值模式與解析解作分析比較，以驗證數值模式。此外，對三種膠體：高嶺土、藻類及溶解性有機物的管柱實驗，應用平衡與動能的數值模式，做模擬分析，經參數校正後，模擬結果顯示，動能模式較平衡模式有較佳的模擬結果。 於地下水污染物的傳輸方面，若忽略吸附於移動性膠體表面的污染物，對污染物傳輸的影響，則模擬污染物在地下水中遷移結果，不但會產生嚴重的誤差，而且不符合物化現象，本論文將該因素納入考慮，即得到良好的模擬結果。由模擬的結果可知，一般膠體與土壤介質間的吸附關係，以動能吸附來描述較為合適，而污染物在膠體及土壤介質表面之吸附關係，則平衡及動能模式皆可描述，但以平衡模式為較簡便的方法。此外，由模式模擬分析的結果可知，污染物有相當大的部份是吸附於移動性膠體上，因此，若地下水中有膠體時，對於污染物的模擬分析時，不可以忽略移動性膠體的存在。

Recent researches indicated that the presence of colloid in groundwater aquifer may increase the mobility of contaminant. Two mathematical models, the equilibrium model and the kinetic model, was developed to investigate the behavior of the colloid and contaminant transports and the adsorption process in porous media. These two models are composed of the transport equation and the adsorption equations. The equilibrium model was formed with one of the equilibrium adsorption equation and the kinetic model was formed with the kinetic equation. Numerical models were obtained by finite difference approximation using the central difference scheme and verified with the available solutions of the mathematical models. Compared with experimental data of colloid such as kaolin, algae and dissolved organic matter (DOM) in a column test, the simulated results indicate that the kinetic model yields better results than those of the equilibrium model. A significantly error was incurred in the simulation results of the contaminant transport model when neglecting the effect of contaminant adsorbed on mobile colloid. Good simulation results were obtained when the effect of the mobile colloid was considered in the contaminant transport models. The models are basically composed of both the kinetic and equilibrium adsorption, the kinetic adsorption is used to describe the relationship between the colloid and the solid matrix and the equilibrium adsorption is used to depict the relationship of the contaminant with the colloid and solid matrix. The simulation results indicate that a considerably amount of contaminant are adsorbed on the mobile colloid. Accordingly, it is more realistic to include the presence of mobile colloid when simulating the contaminant transport in groundwater.