- 學位論文
過硫酸鹽氧化應用於土壤及地下水污染整治之研究
Application of Persulfate Oxidation to Remediation of Contaminated Soil and Groundwater
摘要
本研究之目的在探討澎湖地區過硫酸鹽氧化法對遭受石油碳氫化合物污染之土壤及地下水，其復育所用方法之使用性及適當性。本研究工作分三個工作階段，其中包含實驗室試驗和現地模場試驗。場址土壤重金屬之含量於氧化試驗前即先進行評估，並進行實驗室規模之化學氧化試驗。 於研究場址試驗(加油站整治)中顯示，當pH值小於4時，曾造成地下水中鎳溶出量高達1.19 mg/L，超過地下水管制標準(1 mg/L)，pH值上升至6以後，鎳濃度降為0.719 mg/L，隨著pH值上升鎳濃度逐漸下降，此說明因化學反應造成pH值偏酸性為鎳溶出之主因。 在模場試驗(發電廠模場整治)中，由實驗室及現場模場試驗結果得知氧化劑過硫酸鹽的化性比過氧化氫穩定，其中間產物SO4-．亦較OH．穩定。過硫酸鹽受到土壤中CO32-、HCO3-、Cl-等自由基捕捉劑及有機質影響較過氧化氫為小，故其土壤氧化劑的需求量較低。實驗室試驗結果顯示過硫酸鹽氧化提供較佳去除效率，過硫酸鹽氧化法於72小時內之TPHd去除效率高達90%，而Fenton-like氧化法之TPHd去除效率僅達41%。模場試驗證實過硫酸鹽氧化法不論以亞鐵和過氧化氫或僅以過氧化氫做為啟動劑，其對TPHd的移除率均可視為有效的整治方法。氧化過程中所產生的熱、低pH、氣體皆有助於污染物的脫附以供回收，並提升污染物之溶解度以利氧化分解。污染物溶解度的提升可由實驗室試驗結果顯示氧化作用期間污染物在容易中的濃度高達289 mg/L，相對於地下水中相同的污染物濃度1.34 mg/L高出甚多。模場試驗數據分析結果顯示，71.7%的TPHd被過硫酸鹽氧化分解，23.5%的TPHd以自由相被回收，僅<5%的TPHd殘留在土壤中。 因土壤母質中鎳含量高，且土壤對其吸附選擇性較其他重金屬低，因此在氧化處理過程所導致pH下降時，鎳容易呈游離狀態，而地下水環境在反應過程必與土壤基質接觸，化學氧化劑與土壤所含物質反應可能導致地下水鎳濃度超過管制標準，故在施作前宜進行可行性評估，避免可能導致之負面效應。
並列摘要
The purposes of this study are to explore the applicability and relevance to implement persulfate oxidation as a remedial means for soil and groundwater contaminated by petroleum hydrocarbons in Penghu area. This study consisted of three main work tasks including two laboratory and one pilot-scale demonstrations. Prior to oxidation testings, priority heavy metals content of the testing soils collected from the project area was evaluated through bench-scale chemical oxidation experiments. As in the tests for the the study site, a gasoline service station, it was observed that at pH of groundwater less than 4.0, heavy metal as nickel was detected at a concentration of 1.19 mg/L in groundwater, exceeding the regulatory standard of 1.0 mg/L. When pH elevated to a level above 6.0, nickel concentration was declined to a concentration of 0.719 mg/L. It appeared that decrease in nickel concentration was attributed to the pH increases in groundwater; therefore, it appeared that decrease in pH in groundwater during oxidation treatment process was the main cause to trigger the increase of nickel concentration. As in the field pilot tests for power plant remediation, Results obtained from the bench- and pilot-scale tests reveal that persulfate is a more persistent oxidant than hydrogen peroxide and sulfate radical (SO4-•) has longer reaction time than hydroxyl radical (OH-•). Furthermore, it was observed that persulfate was subject to less impact by radical scavengers as CO32-, HCO3-, and Cl- than was hydrogen peroxide, and it thereby, had less soil oxidant demand in the aqueous system onsite. Data obtained from bench-scale experiments showed that persulfate oxidation provided better removal efficiency for petroleum hydrocarbons than Fenton-like reaction. Results of bench experiments revealed that nearly 90% of total petroleum hydrocarbons (TPHd) in the soil matrix was reduced through persulfate oxidation, as opposed to 41% through Fenton-like reaction. The subsequent pilot-scale testing showed that persulfate activated by either ferrous ion or hydrogen peroxide could effectively reduce TPHd concentration to below the regulatory standard within two weeks of testing period. In the course chemical oxidation, heat, low pH, and gas generated during oxidation process would not only enhance desorption of the contaminants but also elevate the solubility of the chemicals of concern. Persulfate oxidation in the pilot test was observed to elevate the solubility of TPHd by two orders of magnitude, from 1.34 mg/L in groundwater to 289 mg/L in leachate collected from the soil treatment cells. Statistical analysis of the pilot testing performed at a power-plant indicated that 71.7% of diesel fuel was reduced through persulfate oxidation, 23.5% of diesel fuel was recovered from leachate as free product, and less than 5% of diesel fuel remained in the soil. Nickel has poor sorption selectivity to soil as compared to other divalent metals and has strong tendency to dissolve in groundwater as pH declines, causing secondary site contamination, particularly in the area where the aquifer consists of nickel-rich soil. Therefore, treatability of chemical oxidation for groundwater remediation should be carefully evaluated and planned prior to implementation to prevent from adverse site impact.