Study of Biodegradation Mechanism and Microbial Ecology of TFT-LCD Wastewater Treatment

• Main Authors: Po-ChunChen, 陳柏均
• Other Authors: Liang-Ming Whang
• Format: Others
• Language: en_US
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/77538332167032213286

碩士 === 國立成功大學 === 環境工程學系碩博士班 === 98 === Thin-film transistor liquid crystal display (TFT-LCD) is one of the most promising industries in Taiwan in the 21st century. Along with the increasing production of TFT-LCD, more and more wastewater from the manufacturing processes is also produced. The total amount of TFT-LCD wastewater in Taiwan is expected to be as high as 200,000 CMD in the future. Nearly one third of the TFT-LCD wastewater is organic, mainly comprises of dimethylsulfoxide (DMSO), monoethanolamine (MEA), and tetramethylammonium hydroxide (TMAH). These compounds were considered to be slow- or non-biodigradable. In this study, two lab-scale sequencing batch reactors (SBRs) were established to study the biodegradability of TFT-LCD wastewater. These two SBRs were operated as anoxic/oxic and aerobic respectively, with synthetic TFT-LCD wastewater (containing DMSO, MEA, and TMAH) as substrate. From the long-term monitoring, the removal efficiency of DMSO, MEA, and TMAH was as high as 99%. This implies that biodegradation of this kind of wastewater is feasible. Because MEA and TMAH are organic nitrogen compounds, ammonia was produced during their biodegradation and further be nitrified to nitrate. Though with high removal efficiency, the intermediates produced during biodegradation of TFT-LCD were still unknown. Therefore, the mechanism of the degradation of DMSO, MEA, and TMAH under different conditions was also studied. No specific intermediate besides ammonia was detected during MEA and TMAH degradation. However, for DMSO, large amount of odorous dimthylsulfide (DMS) was produced under anaerobic condition. DMS was also found out to be an inhibitor of nitrification in this study. This implies that the presence of DMS is a major problem of TFT-LCD wastewater treatment. From the results of 16S rDNA cloning sequencing, Hyphomicrobium and Thiobacillus were the dominant DMSO-degrading communities in our systems. This result was also verified by fluorescence in-situ hybridization (FISH). Terminal restriction fragment length polymorphism (T-RFLP) was also used to study the community of the two SBRs. In aerobic SBR, Hyphomicrobium was found to be the dominant community and both Hyphomicrobium and Thiobacillus were found in A/O SBR. We also used the T-RFLP method to study the communities of ammonia oxidizing bacteria (AOB) in our system. The main AOB communities in aerobic SBR were Nitrosospira sp. and Nitrosomonas europaea. For A/O SBR, Nitrosomonas europaea and TF491 were the dominant communities. In the batch tests, we observed that TF491 was suppressed with the presence of DMS. This might make the communities of AOB less diverse in TFT-LCD wastewater treatment processes. A full-scale anoxic/oxic membrane bioreactor (A/O MBR) treating TFT-LCD wastewater was also investigated in this study. From the long-term monitoring results, more than 99% of DMSO, MEA, and TMAH were removed in this process. However, the conversion rate of DMSO to sulfate was only 77%, about 23% was emitted to the atmosphere as organic sulfur compounds, like DMS. Therefore, reducing the production of such kind of volatile sulfur compounds is crucial for TFT-LCD wastewater treatment. In summary of this study, aerobic treatment without production of intermediates was feasible. But further studies are needed to obtain the optimum process for treating carbon, nitrogen, and sulfur simultaneously.