利用供氫之薄膜生物反應槽進行氯酚還原脫氯之研究

Abstract

氯酚化合物是常見的工業污染物，其污染型態常以水、空氣、土壤及地下水等方式存在於環境中，而在氯酚污染之處理技術中，生物處理方法是較為普遍而經濟的方法，其中又以厭氧生物方法為主流，主要是因為在厭氧環境下，氯酚可被微生物以還原脫氯途徑分解，在此途徑下，氯酚依序被脫氯產生單氯酚，然後再脫氯變成酚而破環分解，由於此代謝途徑會使氯酚之毒性持續降低，因此也較普遍被學者廣泛的研究。本研究利用供氫之薄膜生物反應槽進行氯酚脫氯反應之研究，利用氫氣當成電子供給者，而以氯酚為電子接受者進行還原脫氯反應，此反應途徑不需外加有機物質，因此可避免二次污染的問題。實驗結果顯示在2-CP三個月的馴養期間，已馴養出脫氯氫細菌，可利用氫氣為電子供給者進行2-CP之還原脫氯反應，中間產物為酚，而酚仍可被微生物繼續分解。反應槽在2-CP進流濃度為24.8 mg/L，以及HRT 15小時條件下 (負荷率0.72 g/m2 d)，2-CP之去除率為94 %，而TOC去除率為60 %。2-CP脫氯反應之最佳pH範圍為5.8 ~ 7.2之間，當pH≦5或≧8時，2-CP的去除率則大幅的下降至50 %以下。環境中的硝酸鹽及硫酸鹽均會取代2-CP之電子接受者的角色，因而對脫氯反應產生抑制作用，不過這兩者的抑制機制有些許的差異，主要差異在於硝酸鹽會立即取代2-CP之電子接受者的角色，而硫酸鹽則需經過ㄧ段時間才會完全抑制脫氯反應，其主要的原因可能是本系統之脫氯菌大部分也具有脫硝能力。本系統對於不同氯酚也都具有脫氯能力，其脫氯速率依序為2-CP > 2,4-DCP > 4-CP > 3-CP, 3,4-DCP > 2,4,5-TCP > 2,5-DCP，多氯酚之脫氯反應會依鄰位(ortho)、間位(meta)、對位(para)之順序將氯基脫去。由2-CP馴養反應槽之菌相鑑定與親缘分析結果顯示，大部分菌種屬於Proteobacteria/ β-proteobacteria，其中又以Ralstonia sp. 50為最主要菌種，此菌種可適應不同環境條件，並以不同的代謝途徑來分解各種氯酚。

Chlorophenols (CPs) are widely known as industrial pollutants. These chemicals have been recognized as organic pollutants of water, air, soil and groundwater. Commonly, biological methods are used for the remediation of these pollutants, especially the anaerobic biotechnology. By the anaerobic pathway, chlorine substituents are replaced by hydrogen and produces less-chlorinated compounds. This process is widely studied because less chlorinated CPs represent less toxic to the environment. This study utilized hydrogenotrophic membrane bioreactors to cultivate hydrogen bacteria for dechlorinating the CPs. The H2 was used as the electron donor and the CPs were used as the electron acceptors, thus the dechlorination was proceeded. This process needed not the external organics, so it could prevent the secondary pollution. Experimental results showed that the 2-CP dechlorinating bacteria were cultivated after three months acclimation. The 2-CP was dechlorinated to produce phenol, and the phenol could also be degraded. Under the condition of influent 2-CP 24.8 mg/L and HRT of 15 h (loading rate = 0.72 g/m2 d), the 2-CP and TOC removal efficiency was 94% and 60%, respectively. The suitable pH range was 5.8 ~ 7.2. When the pH value was below 5, or higher than 8, the 2-CP removal efficiency will drop to below 50%. Nitrate and sulfate could take the place of 2-CP as the electron acceptor, and thus inhibited the 2-CP dechlorination. However, their inhibition mechanisms were a little different. Nitrate will take the place of 2-CP immediately, while the sulfate take a period of time to reach completely inhibition. The reason might be because the dechlorinating bacteria also possess the denitrification ability. This system could also dechlorinate the other CPs, and their dechlorinating rate were 2-CP > 2,4-DCP > 4-CP > 3-CP, 3,4-DCP > 2,4,5-TCP > 2,5-DCP. The CPs will be dechlorinated by remove the ortho, meta and para chlorine substutes in sequence. From the microbial identification and phylogenetic analysis of the 2-CP bioreactors, the most dominant bacteria belonged to Proteobacteria/ β-proteobacteria. In which, the Ralstonia sp. 50 was the most dominant species and could adapt to different environmental conditions and degrade the CPs by different metabolic pathways.