界面活性劑TX-100/萘微胞在砂土吸附性探討

界面活性劑淋洗常運用於土壤及地下水受疏水性有機污染物(Hydrophobic Organic Compounds, HOCs)污染的整治。界面活性劑可增加HOCs的溶解度及移動性以增加整治效率。雖然界面活性劑可以形成微胞幫助HOCs增溶移動，但當界面活性劑溶解包覆這些HOCs流經低污染或無污染區域時，也可能再度被土壤吸附，反而助長污染物的流佈，而使得HOCs擴散或吸附於原來未污染的土壤裡。本研究選用萘為HOCs的代表物，萘為煤焦油的煉製與加工過程，或是化石燃料燃燒時釋放。由於在全球大量使用與排放，被美國環保署列為優先控制的16種多環芳香烴(Polycyclic Aromatic Hydrocarbons, PAHs)之一。Triton-X-100(TX-100)為目前現地整治經常使用的非離子型界面活性劑，具有增溶性佳，在水中容易形成微胞的特性。試驗分為萘或TX-100分別在土壤上吸附，以及萘在TX-100溶液中形成TX-100/萘微胞後兩種物質在土壤上吸附的探討，提供之後現地整治參考使用。結果顯示，在兩種不同土水比下，萘在S:W=1:100有較完整的吸附曲線，以吸附等溫線迴歸後發現相關係數都超過0.95，兩種吸附模式可能都適用於萘在砂土上的吸附。TX-100在S:W=1:1時在土壤上的吸附曲線以相同方式迴歸後發現Langmuir之相關係數為0.9496，顯示TX-100在砂土上的吸附較為接近Langmuir吸附模式。以矽砂與砂土比較之後發現土壤有機質含量對萘或TX-100在土壤上的吸附量有高度正相關。另在TX-100/萘微胞吸附試驗發現TX-100被吸附到土壤表面時，萘隨之吸附至土壤的趨勢增大；而當土壤吸附TX-100的量達到飽和後，當TX-100在水溶液中微胞增多時，萘會維持在水相TX-100微胞中。而萘在固-液相的濃度對TX-100於固-液相濃度的分配並無顯著影響。土壤有機質本身會影響TX-100在土壤上的最大吸附量，而TX-100在固-液相的濃度分配又會影響萘在土壤上的吸附比例。影響污染物由界面活性劑微胞脫附再吸附至土壤中，最重要因子應為土壤有機質含量，其次為流佈至下游時水中的TX-100濃度。

關鍵字

Triton-X-100 ；萘；土壤有機質；吸附；等溫吸附模式

並列摘要

Surfactant enhanced aquifer remediation (SEAR) is commonly used in the remediation of soil and groundwater contaminated by hydrophobic organic compounds (HOCs). Surfactants can increase the solubility of HOCs to enhance the remediation efficiency. The inner core of surfactant micelles creates a hydrophobic zone to favor the HOCs moving into the micelle. However, during the SEAR, when the HOC-containing surfactant micelles flow through downstream low-pollution or non-pollution areas, the release of HOCs from the surfactant micelles and resorb and increase the HOCs concentration on the soil downstream might occur. In this study, naphthalene (Nap) was selected as the representative HOCs. Underground storage and transport units of oil refining and coal tar processing could release Nap in to the subsurface. Nap is listed as one of the 16 PAHs that are monitored by the USEPA. Triton-X-100 (TX-100) is a non-ionic surfactant commonly used in-situ SEAR remediation. It has the characteristics of good solubility enhancement and easy formation of micelles in water. The experiment in this research includes the sorption of naphthalene or TX-100 on the sandy soil, and the sorption of Nap containing TX-100 on the soil. A silica sand and an aquifer sand were tested. The results show that under two different soil-water ratios (S:W=1:1, 1:100), Nap exhibits a clear sorption isotherm at S:W=1:100. After regression with Freundlich and Langmuir sorption models, it was found that the correlation coefficients were greater than 0.95 for both models. The correlation coefficient of Langmuir adsorption model for TX-100 on the soil at S:W=1:1 is 0.9496, showing that the adsorption of TX-100 on sand is closer to Langmuir adsorption model. The content of soil organic matter had a high effect with the adsorption amount of Nap or TX-100 on the sand after comparing the sorption data for silica sand and sandy soil. The adsorption results of Nap-containingTX-100 micelles on soils found that when TX-100 was adsorbed to the soil surface, naphthalene is more easily moved out from TX-100 micelles and adsorbed on the soil. When the amount of TX-100 absorbed by the soil reaches saturation, TX-100 micelles increase in aqueous solution, Nap will remain in TX-100 micelle in aqueous phase. On the other hand, Nap has no significant effect on TX-100 sorption on soils. Soil organic matter will affect the maximum adsorption of TX-100 on the soil, and the concentration distribution of TX-100 in the soil-water phase will affect naphthalene adsorbed on soil. In short, the pollutants are desorbed from the micelles and then adsorbed to the soil if TX-100 in aqueous phase is low. The most important factor should be the soil organic matter content, and the second is the concentration of TX-100 in water when it flows downstream.