UF薄膜處理單元矽酸積垢清洗策略研究

Abstract

半導體及光電與平面顯示器產業廢水回收在法令規範回收率的壓力及自然資源保護的觀念提升之下被日漸重視，其中含高單位濁度及複雜組成的化學機械研磨廢水回收技術也持續進步中。但礙於廢水特性使得回收水處理單元常因堵塞而降低回收效率，其中又以溶解矽因為分子量小且存在廢水中的化學性質穩定，即使以混凝沉澱技術亦不易將之去除而使得回收水系統中的薄膜單元發生結垢或積垢。 本研究針對已被矽酸積垢的超過濾薄膜設計不同時間、藥劑pH條件及溫度加以清洗，以計算清洗後薄膜通量恢復率及藉由電子顯微鏡拍攝薄膜表面狀態評估積垢清洗效果。研究結果發現以鹼液( pH11)、60分鐘及50℃的條件下清洗效果最好。三種不同清洗條件中又以溫度提升的效應最明顯。由於實驗初期即以實廠可以應用的條件為設計參考，針對實廠實際狀況稍微調整後即可以直接投入清洗。另實驗過程中觀察到薄膜孔隙會因為積垢堆積而被撐大，或因化學清洗造成薄膜損傷，適度縮短清洗週期避免積垢過度累積或是調整清洗條件都是可以避免清洗後薄膜過濾效能下降的方法。

In recent years, the recycle of wastewater has increasing gained the traction in the industry of Semiconductor and Photonics. The value of wafer recycling is not only supported by government regulations but also the fashion of environmental friendly industry. The recycle techniques for the high turbidity and complex-compositon CMP wastewater continue to improve; however, the recycle efficiency is low due to the nature of sewage that easy to cause fouling and scaling during the recycling process. The dissolved silica will enhance fouling and scaling on the membrane unit due to it is not easy to be removed from the wastewater via the coagulation precipitation because of the small molecular weight and stable chemical property.

This study investigated the cleaning strategies for the Silica fouling on ultrafiltration membrane by taking into account variables of time, pH of chemical solutions and temperature for cleaning. The cleaning efficiency was evaluated by the recovery rate of the flux as well as the surface condition of the membrane under electron microscope. The experimental data showed that the best cleaning efficiency can be received under the condition of 60 minutes cleaning time and the temperature of 50℃ with pH11 alkali solution. Among the three variables in this experiment, the elevation of temperature resulted the most positive effect to the cleaning efficiency. The experiment was virtually designed to meet the condition in a real fab; with minor modifications, the data is applicable on-the-spot to the fab. The experiment also observed membrane pore enlargement that maybe incurred by fouling pile-up or over cleaning. Ways to avoid the degrading filter efficiency of the membrane include shortening clean cycle to eliminate fouling pile-up and adjusting cleaning conditions.