Study of the degradation mechanism of TFT-LCD organic wastewater under aerobic, anoxic and anaerobic conditions

• Main Authors: Chin-Nang Lei, 李展能
• Other Authors: Liang-Ming Whang
• Format: Others
• Language: en_US
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/12009829216828330719

碩士 === 國立成功大學 === 環境工程學系碩博士班 === 96 === The amount of pollutants produced in manufacturing processes of TFT-LCD (Thin-film transistor liquid crystal display) substantially increases due to an increasing production of the opto-electronic industry in Taiwan. The total amount of wastewater from TFT-LCD manufacturing plants is expected to exceed 200,000 CMD in the near future. Typically, organic solvents used for TFT-LCD manufacturing processes account for more than 33% of the total TFT-LCD wastewater. The main components of these organic solvents are composed of the stripper (dimethyl sulphoxide (DMSO) and monoethanolamine (MEA)), developer tetra-methyl ammonium hydroxide (TMAH) and chelating agents. These compounds are recognized as non- or slow-biodegradable organic compounds and little information is available regarding their biodegradability. In this study, the performance of an anoxic-oxic sequencing batch reactor (A/O SBR) and an aerobic SBR treating synthetic TFT-LCD organic wastewater was evaluated. Long-term experimental results showed that both SBRs were able to achieve stable and satisfactory removal performance for DMSO, MEA, and TMAH. The removal efficiency for all three compounds was as high as 99%. In addition, batch tests were conducted to study the degradation kinetics and mechanism of DMSO, MEA, and TMAH under aerobic, anoxic and anaerobic conditions at different initial substrate concentration. Results showed that DMSO had the highest degradation rate under anaerobic condition, with the value of about 34 mg DMSO/g VSS-hr. MEA and TMAH had higher degradation rate under aerobic condition. MEA can be degraded under all conditions without any difficulties. The highest specific MEA degradation rate, about 121 mg MEA/g VSS-hr, was obtained under aerobic condition. Ammonia seemed to be the end product of MEA degradation under all three conditions. TMAH degradation seemed to be inhibited under anaerobic condition. Only little TMAH degradation was observed. The highest specific TMAH degradation rate, about 8 mg TMAH/g VSS-hr was obtained under aerobic condition. The end product of TMAH degradation was also seemed to be ammonia. In the previous tests, the intermediates or products formed in DMSO degradation was not known. Therefore, we have also conducted a few tests to study the degradation mechanism of DMSO degradation under aerobic, anoxic and anaerobic conditions. Results showed that under aerobic condition, almost all DMSO was converted into sulfate, with little amount of DMS observed during the period of investigation. The final product of DMSO degradation under both anoxic and anaerobic condition was DMS, which may cause the odor problem. The performance of a full-scale TFT-LCD wastewater treatment plant (plant G), comprised a UASB and an aerobic tank, was also investigated in this study. TMAH was the main component of plant influent. Results showed that plant G achieved good removal performance for TMAH. The removal efficiency of TMAH was 99% at an average 625 mg/L of TMAH. Batches were conducted to study the TMAH tolerance of UASB and aerobic tank sludge. In this study, 2,000 mg/L TMAH was degraded in 10 hours by UASB sludge. Methane and ammonia were produced during TMAH degradation. For aerobic tank sludge, 550 mg/L TMAH can be degraded gradually in 48 hours. This study showed that biological treatment of TFT-LCD organic wastewater was feasible. But further study should be done to investigate the optimum condition for the processes.