TFT-LCD業鋁蝕刻製程含磷廢水最佳可行控制技術評估

Abstract

國內光電業中TFT-LCD業之含磷廢水，其最大來源為鋁蝕刻製程，為維護水體環境品質及減少優養化問題，環保署針對光電業之氮、磷廢水排放，擬制定嚴格法令管制，藉以削減磷營養鹽排放，達到消除污染及維持下游水體環境品質之目的。 本研究使用美國環保署空氣污染防制最佳可行控制技術評估步驟，探討本案例廠TFT-LCD業鋁蝕刻製程含磷廢水處理系統最佳可行控制技術評估，冀能獲得最佳可行控制技術及操作條件。研究結果顯示：1.從製程端實施含磷廢水濃度高、低分流處理措施及進行蝕刻機台風刀材質與流動模式改善，均能有效控制並降低含磷廢水排放量。2.以氯化鈣及氫氧化鈣化學加藥方式進行化學沈澱瓶杯試驗並輔以反應曲面法實驗設計，結果發現廢水中之氟離子會與磷酸根離子一同競爭鈣鹽，造成系統除磷效率降低。此外，當廢水中之除磷效率達到一定水準狀態後，即使增加鈣鹽濃度，對於降低廢水中之磷濃度有限。3.依反應曲面等高線圖發現pH對磷的去除改變敏感度遠高於化學沈澱藥劑添加量。4.使用望想函數之概念，獲得含磷廢水處理總有利條件 (Overall Desirability) D=1之最佳解，以氯化鈣藥劑而言，當Ca/P莫耳比達1.46、pH 8以上時，可使混凝、膠凝化學處理單元之除磷效率達目標值80 %以上，而當pH調升至8.5以上，此時Ca/P莫耳比可微幅調降至1.21左右，同樣具有相同之處理效果。研究結果證明，依此操作條件下，可使無機廢水處理單元出流水含磷濃度降至26 mg/L以下，達到總放流水含磷濃度降至10 mg/L以下最終目標，有效降低對環境所造成之衝擊。

The phosphorus-containing wastewater of electro-optical industry mostly come from Al-etching process in TFT-LCD industry. To avoid the effects of eutrophication, the EPA of Taiwan will propose a strict Environmental Decree to control the effluent of nitrogen and phosphorus-containing wastewater from electro-optical industry in order to minimize the impact of pollution at the down stream. The Best Available Control Technology（BACT）evaluation were used in this study to perform BACT evaluation of the phosphorus-containing wastewater treatment system of Al-etching process in TFT-LCD industry based on the Air Pollution Source Control of U.S. EPA. The purpose of this research is to study BACT and to optimize the operation conditions. The result of this study are listed as below. 1. It can be seen from the evaluation result that the high and low diffluence measures of phosphorus-containing wastewater concentration implemented in the process and the improvement of air knife material and airflow mode at the etching machine can be controlled effectively and reduce the amounts of phosphorus-containing wastewater. 2. In addition, chemical reagent, such as CaCl2 and Ca(OH)2 were added to perform chemical precipitation jar test; the design of experiment of Response Surface Methodology is also used. Furthermore, it can be obtained that whether the existence of F ion in the wastewater or not will indeed affect the phosphorus removal efficiency of the entire system; this is owing to F ion will compete with phosphate ion for calcium salt, and the decrease of phosphorus removal efficiency was therefore observed. When the phosphorus removal efficiency in the wastewater reached to certain level, the increase of calcium salt concentration in the wastewater will have minor effect on the reduction of the phosphorus concentration in wastewater. 3. It can be eveluated from Response Surface that the change of pH value is more sensitive than the addition of chemical precipitation reagents on the phosphorus removal efficiency. 4. This study use the concept of Desirability Function to acquire the optimized solution of phosphorus-containing wastewater treatment at（Overall Desirability）D=1. For CaCl2 reagent,80% removal was achieved when the Ca/P molar ratio was greater than 1.46 at pH 8; Ca/P molar ratio can be decreased to 1.21 when at pH 8.5. Besides, the phosphorus concentration in the inorganic wastewater effluent can be reduced to less than 26 mg/L. The phosphorus concentration of total effluent of this study can be reduced to 10 mg/L to meet the requirement of effluent standard. And finally, the impact to the environment can be reduced effectively.