Reductive dechlorination of chlorophenols by hydrogenotrophic membrane bioreactors

• Main Authors: Chao-Chien Chang, 張朝謙
• Other Authors: 曾四恭
• Format: Others
• Language: zh-TW
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/00014759635957576755

博士 === 國立臺灣大學 === 環境工程學研究所 === 93 === 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.