薄膜電晶體液晶顯示器（TFT-LCD）製程有機廢水處理與回收再利用之研究

Abstract

薄膜電晶體液晶顯示器(Thin Film Transistor Liquid Crystal Display, TFT-LCD)製造業為台灣近年來蓬勃發展之高科技產業。在大尺寸TFT-LCD產業方面，去年我國總產值居世界第三位，占有率23.3%(僅次於南韓和日本) 。預估今年將提升至36%，超越日本，逼近南韓，希望在2006年前再超越南韓，產值可達1.3兆元，成為全球第一大TFT-LCD顯示器供應國。其中製程使用大量之現像液（Developer）、剝離液（Stripper）及清洗溶劑（Rinse）等有機物質，由於其成分複雜，且含有高強度有機氮、硫類物質。面對台灣日益增加之TFT-LCD製造廠，估計未來每日所產生之有機廢水量將達到100,000噸。 由於其有機廢水量約佔總廢水量之三分之一以上，若以目前一般設廠環評要求，欲達成回收率80%以上目標，則有機廢水回收再利用將勢在必行，而回收再利用之技術應積極的研究與開發 。本研究為利用生物薄膜（MBR）處理程序配合逆滲透（RO）系統及臭氧（O3）、臭氧/雙氧水（O3/H2O2）程序之高級氧化單元，處理TFT-LCD製程有機廢水，比較各程序之處理水質與各用水標準間之差異。 於實驗試驗期間，經污泥馴養及控制適當微生物生長條件下，各槽中MLSS濃度可依進流廢水性質、流量或不同食微比條件下，控制各槽中MLSS 濃度於4560~7260mg/L間，而放流水中SS濃度則因薄膜單元之有效固液分離作用幾乎測不出任何SS濃度。於有機碳之去除上，因槽中MLSS 濃度較傳統處理程序為高，故COD之平均去除效率則可達98.5% ，放流水COD 濃度小於15 mg/L。對於TOC之去除上則可達到更佳之處理效率，平均去除效率分別為97.4%，放流水濃度小於6.73mg/L。至於有機氮之去除效能，生物薄膜程（MBR）序對於總氮及T K N 之去除效率可達74.1 %及88.6 %，但由放流水中氮類大部分為硝酸鹽氮及氨氮形式看出，薄膜單元有效控制污泥停留時間(>30天)，使好氧槽中可產生有效之硝化作用，轉化有機氮為硝酸鹽氮及氨氮，然而於整個試驗期間中，總氮之去除效率均可達76%，可看出生物薄膜程序於操作穩定性上及去除效率上，均較傳統生物程序為高。 目前經生物薄膜程序處理之有機廢水水質COD：13.2 mg/L、TOC：6.73 mg/L、NH3-N約16.8 mg/L，導電度約1979μs/cm。因已經UF過濾其SDI值小於3，其處理水可直接進入逆滲透系統處理。在進入逆滲透系統處理後，處理水COD低於偵測極限(<5mg/L)，TOC小於1.5 mg/L，導電度亦小於30.7μs/cm，其處理水相當不錯已接近自來水質，建議可回收至冷卻水塔補充水系統。 而再經由後段臭氧處理時，若單獨以臭氧對TOC進行催化降解時，TOC濃度由1.479 mg/L被降解0.92 mg/L，並不符合回收到製程用水之水質要求，TOC需小於0.8 mg/L之要求。於是便在臭氧系統中加入雙氧水，做為催化劑。實驗結果發現加入雙氧水後，可有效的降解水中TOC濃度至0.663 mg/L，符合回收到製程用水之水質要求，且在高級氧化程序過程中，經過臭氧（O3）、臭氧/雙氧水（O3/H2O2）程序後，水中導電度亦在60 μs/cm之內，因此可考慮回收至超純水用水水源。

Thin Film Transistor Liquid Crystal Display (TFT-LCD) manufacturing industry is a rising and flourishing technological industry in Taiwan recently. Regarding the large size TFT-LCD industry, Taiwan’s total yield is the third in world (only less than South Korea and Japan). It is expected that the yield will increase to 36% and be better than Japan and close to South Korea. It is hoped that it will be better than South Korea before 2006, and the yield will bring in 38 billion USD. Taiwan will supply the most TFT-LCD monitors in the world. During the process of manufacturing, a lot of organic matter is used in activities, such as developing, stripping, and rinsing. The organic matter’s composition is complex and includes strong organic nitrogen and sulfur. It is estimated that the organic wastewater from the process will be more than 100,000 tons per day. The quantity of organic wastewater is over one third of the total wastewater quantity for the industry. According to the requirements of environmental estimation, the ratio of recycling should be higher than 80%. It is necessary to recycle the organic wastewater and the technology of recycling should be researched and developed actively. The study is using the contra-osmotic system and a high-level oxidization process of ozone or ozone/hydrogen peroxide to treat TFT-LCD organic wastewater and to compare the different processes of treatment with the standard of water. In the experiment, via the growing of sludge and controlling the factors of growing appropriate microbes, we can control the concentration of MLSS between 4560 and 7260 mg/L according to the quality of in/out wastewater, flow capacity, and food/MLSS ratio. However, the concentration of SS in the effluent can almost not be measured because of the separating reaction of solids and liquids in the membrane. For removing organic carbon, the average effect of removing COD can be 99.5%, and the concentration of COD in the effluent is lower than 15 mg/L because the concentration of MLSS in our process is higher than in the traditional process. In our experiment, the TOC removal also has a good treatment effect, for example, the average level of removal is 97.4% and the concentration of the effluent is lower than 6.73 mg/L. For the effect of organic nitrogen removal, the level of removal for the membrane bioreactor can be as high as 74.1% for total nitrogen removal and 88.6% for TKN. Because the nitrogen in the effluent shows in the forms of nitrate and ammonia, and the effectively controlled remaining time of the membrane is longer than 30 days, the nitration changes the organic nitrogen to nitrate and ammonia in the aerobic tank. However, the effect of total nitrogen removal is able to reach 76% during the experiment. According to this data, the stability of the procedure and the effect of removal in the membrane bioreactor are all better than in a traditional bioreactor. At present, the qualities of organic wastewater treated via a membrane bioreactor are COD: 13.2 mg/L, TOC: 6.73 mg/L, NH3-N about 16.8 mg/L, and conductivity about 1,979 μs/cm. Because the water has been filtered from UF and the SDI value is smaller than 3, the water can flow into RO directly to be treated. After the treated water flows into RO, if the COD is too low to detect (< 5 mg/L), the TOC is lower than 1.5 mg/L, and the conductivity is also lower than 30.7 μs/cm. The qualities of treated water are similar to tap water. As a suggestion, we could recycle the water into a radiator system. Then, after the second ozone treatment, the TOC is lower than 0.663 mg/L, and the conductivity is within the required quality. The water is able to be considered to be recycled to a radiator water resupply system. If it is alone to catalyze the decreasing of TOC concentration via the second ozone treatment, it will not conform to the requirement of TOC being lower than 0.8 mg/L, according to the requirement of recycled water quality, because the concentration of TOC only will decrease to 0.92 mg/L from 1.479 mg/L. That is why hydrogen peroxide is added as a catalyst in the ozone system. It has been discovered from the experiment that the concentration of TOC can be decreased to 0.663 mg/L after adding hydrogen peroxide, which conforms to the requirement of recycled water quality. Also, during the high-level oxidization process, the conductivity is within 60 μs/cm after the process of ozone and ozone/hydrogen peroxide. It can even be considered to recycle the water to be reused in the first step of the TFT-LCD production process.