- 學位論文
零價鐵對微生物分解1,2-二氯乙烷之影響
Influence of zero-valent iron on the biodegradation of 1,2-dichloroethane
摘要
1,2-二氯乙烷 (1,2-dichloroethane)是重要之含氯脂肪族碳氫化合物製造過程之中間產物，具有毒性、腐蝕性、易燃性，對人體有致癌之風險，非生物性水解反應半生期很慢約5.8年。大部分含氯有機物可以還原態鐵之方法將其還原脫氯去除，然而1,2-DCA卻不易被鐵脫氯還原。因此本研究以添加不同之微生物及不同基質之實驗條件下，探討零價鐵是否有助於生物復育分解地下水中之1,2-DCA。 本研究首先將現地採回來之地下水及土樣，以不馴養之情況下直接在無零價鐵及有零價鐵之生物分解實驗中當做植種，實驗結果顯示1,2-DCA無分解之現象。另外亦進行微生物植種在厭氧及好氧下馴養。實驗結果顯示，厭氧批次馴養實驗之1,2-DCA濃度下降達60％-70％；而好氧馴養實驗部分，不同菌源有不同之結果，以醉月湖底泥做為植種，1,2-DCA並無分解反應作用，以生活污水污泥為植種，反應時間約40天，1,2-DCA去除率達70％。以食品工廠污泥為植種，反應時間40天，1,2-DCA去除率約60％。本研究還進行曝氫氣之連續流厭氧馴養實驗。連續流系統結果顯示不到10天1,2-DCA濃度便開始下降，可將1,2-DCA生物分解幾乎完全去除 (20 mg/L降至15 μg/L)。推測管柱中微生物分解1,2-DCA之反應機制主要為呼吸脫氯，優勢菌群可能為脫鹵菌群。以馴養所得之微生物做為植種進行不同實驗條件之批次實驗顯示，因鐵氧化釋出氫氣較緩慢，不會刺激甲烷生成菌生長，故不會與脫鹵菌競爭氫氣。因此以連續流馴養微生物植種之批次實驗中，以只有加入醋酸鹽與零價鐵之批次，其脫氯分解1,2-DCA之反應效果最好。 本研究亦於管柱連續流中灌入零價鐵，並停止曝入氫氣。實驗結果顯示，以零價鐵代替連續直接曝氫氣之方式，亦可達到將1,2-DCA脫氯分解之目的。灌入零價鐵之實驗中，管柱出流口中1.2-DCA濃度於第12天已降解至15 μg/L，達到中華民國法規容許之地下水污染物第二類管制標準值，且曝入氫氣及灌入零價鐵方式之速率常數值，分別為0.24 day-1及2.50 day-1，顯示灌入零價鐵緩慢持續釋氫氣之方式，較直接曝入氫氣之方式有助於脫鹵菌將1,2-DCA脫氯去除。若直接以曝氫氣之方式處理受1,2-DCA污染之現地，產生之氫氣難溶於水且易阻塞於土壤孔徑中，故灌入零價鐵之方式在現地生物復育分解1,2-DCA之工程上具有可行性。最後，管柱連續流系統改以碳酸鹽做為脫鹵菌之碳源，結果顯示1,2-DCA無明顯之降解現象。由此得知，有機物代謝產生的電子會參與脫鹵菌進行1,2-DCA之脫鹵反應，因此脫鹵菌必須要在含有有機物之環境下才有利於將1,2-DCA分解。
並列摘要
1,2-dichloroethane (1,2-DCA) is an important chemical intermediate during the manufacturing reaction of chlorinated aliphatic hydrocarbons. 1,2-DCA affects human and environmental health owing to its toxicity and carcinogenicity. The half-life of 1,2-DCA under abiotic hydrolysis reaction is about 5.8 years. A popular method for degrading chlorinated organics is to place a permeable reactive barrier consisting of a reductant such as zero-valent iron (ZVI) in the path of a contaminant plume. However, 1,2-DCA is resistant to degradation processes only by using ZVI. Therefore, this study was aimed to investigate the influence of zero-valent iron on the biodegradation of 1,2-dichloroethane and whether ZVI was practicable for the bioremediation of 1,2-DCA. The batch experiments were conducted in microcosms spiked with groundwater and aquifer material from a contaminated site either with ZVI or without ZVI. However, no 1,2-DCA transformation was observed in any conditions. Other batch experiments under anaerobic or aerobic conditions were performed with inocula from enriched microbial cultures. The results show that 1,2-DCA was degraded about 60％-70％ within 127 days under anaerobic condition with enriched culture originally from the site or under aerobic condition. 1,2-DCA was degraded about 70％ within 40 days in microcosms with sludge from sewage, and 60％ within 40 days with sludge from industrial wastewater. But 1,2-DCA was not degraded in microcosms spiked with Drunken Moon Lake sediment. In addition, 1,2-DCA was biodegraded in a plug-flow column which was fed with medium equilibrated with H2. The result shows that the concentration of 1,2-DCA was initially 20 mg/L and disappeared within 20 days of incubation. It suggests that 1,2-DCA has been reduced with an anoxic respiratory process. ZVI provides a slow and steady source of low cocwntration of H2, under which dechlorination may be favored over competing methanogenesis. It is concluded that 1,2-DCA can be biodegradated in porous medium under anaerobic condition with ZVI added to stimulate dechlorination. The first-order rate constant of 1,2-DCA disappearance was 0.24 day-1 with addition of H2 and was 2.5 day-1 by replacing H2 with ZVI. The results suggest that addition of ZVI favors biodegradation of 1,2-DCA and is a promising technology for 1,2-DCA bioremediation. Finally, Carbonate was not able to replaced acetate as the carbon source of bacterial while ZVI is the electron donor. Organic substrate are required for the anaerobic dehalogenation of 1,2-DCA.