Investigation of Low Temperature Thermal Desorption on Soils Contaminated by Organochlorine Pesticides with Thermogravimetric Analysis

[[abstract]]中文摘要 對於熱脫附處理技術而言，升溫程序與脫附溫度的設定為最重要參數設定之一，而利用熱重分析法決定熱脫附參數條件具有極高潛力，因為熱重分析儀具有偵測靈敏度高、樣品量小且可以快速解析並連續觀察污染土壤之失重溫度區段的優點。本研究以熱重分析法進行農藥污染土壤熱脫附處理實驗，來觀察農藥污染土壤在溫度程序控制下之連續失重情形，其操作參數有土壤種類、升溫速率、污染物濃度及脫附平衡溫度。藉由熱重分析儀所得之參數，進行實驗室規模土壤熱脫附處理實驗，並搭配氣相層析儀（GC-ECD）來連續觀察污染土壤脫附效果，以評估應用熱重分析儀解析污染土壤熱脫附之可行性與有效性。 實驗中選取老埤（Lp）與長濱（Cp）土系混合1，4，及8%之有機氯農藥（四氯異苯腈）製備成農藥污染土壤，以進行熱重分析儀之熱脫附實驗與實驗室規模土壤熱脫附實驗。研究結果得知在熱重分析儀之污染土壤熱脫附處理中，污染土壤失重主要可區分為四個階段，（1）溫度區段約室溫至120℃時，為水分的損失，即為脫水作用；（2）溫度區段約120-250℃時為主要四氯異苯腈揮發失重區段；（3）溫度區段約250-350℃時，有少部分四氯異苯腈被土壤吸持後因受熱而脫附；（4）溫度區段為350℃以上，大都為土壤本身物質的重量損失如：有機質或脫氫等。另外在實驗室規模之管柱土壤熱脫附處理實驗中，不同升溫速率、脫附溫度設定350℃下，皆在250-300℃時於GC-ECD系統中，可測得第一點濃度值。而老埤土系之污染土壤進行熱脫附處理時，去除率可達99％；長濱土系之污染土壤進行熱脫附處理時，去除率可達90％以上。由本研究可知，藉由熱重分析儀能快速且不需任何化學分析即可解析低溫熱脫附處理程序所需升溫程序。[[abstract]]For application of low-temperature thermal desorption on contaminated soils, the selection of a proper temperature program and desorption temperatures is critical. Thermogravimetric analysis (TGA) possess the advantages of high sensitivity, small sample quantity, quickness, and soil mass measurements under the temperature program of time-wise continuous record. The TGA technique is therefore highly effective to determine the thermal desorption parameters for soil decontamination. This study used TGA to perform thermal desorption experiments for soils contaminated with semi-voltile pesticides. The operating parameters included the types of soil, heating rates, concentrations of pollutants, and equilibrium desorption temperatures. By means of the parameters obtained from TGA, the effectiveness of low-temperature thermal desorption was further evaluated with a bench-scale column thermal desorption apparatus followed by a gas chromatography coupled with an electron capture detector (GC-ECD). Soil samples (Cp and Lp) were artificially contaminated with organochlorine pesticides (chlorothalonil) of 1, 4, and 8 wt% for the thermal desorption with TGA. Results showed that four mass-loss regions of contaminated soil were found: (1) region with temperatures between room temperature and 120℃, attributed to dehydration; (2) region with temperatures between 120 and 250℃, attributed to evaporation of the majority of chlorothonil; (3) region with temperatures between 250 and 350℃, attributed to the desorption of a minor potion of chlorothonil adsorbed by soil; (4) region with temperatures higher than 350℃, attributed to the mass loss of soil materials by organic matter destruction and dehydroxylation. For bench-scale thermal desorption with GC/ECD system, the first signal was detected at 250-300℃ for various heat rates and an equilibrium desorption temperature of 350℃. Furthermore, the LP soil can be decontaminated to up to 99% removal. The Cp soil can also be decontaminated to > 90% removal in the column desorption test. These results indicated that the desorption conditions (e.g., temperature programs and equilibrium desorption temperatures) obtained from TGA can be successfully applied to other larger-scale operations, without additional chemical analyses