The optimization of a hydrofluoric acid wastewater recycles reverse osmosis process

• Main Authors: Chih-Ping Peng, 彭智平
• Other Authors: 洪俊雄
• Format: Others
• Language: zh-TW
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/83587266329327332433

碩士 === 國立中興大學 === 環境工程學系所 === 96 === As a result of the complicated process of the semiconductor industry, there are various types of wastewater and chemical pollution produced during the process. According to the elements and characters of the wastewater, we can divide them into two main groups: acid/alkali-containing wastewater and fluoride-containing wastewater. Very little of the hydrofluoric acid would dissipate during the etching process. Most of them would be drained out along with the cleaning water into the wastewater collecting system. The Effluent Standard on Fluoride (exclude Mixed Ionic) is 15.0 mg/1, announced on Sep. 3rd 2005 by Environmental Protection Administration Executive Yuan. Semiconductor process needs gallons of water; there would be lots of wastewater. In order to meet the standard, those factories start to use RO to retrieve the fluoride-containing wastewater. However, the results are not good enough. The condition and water quality of the Raw Water in this research are as listed：（1）Raw Water Temperature：25℃；（2）pH＝8.4；（3）Calcium ion Ca2+＝59.5 ppm as CaCO3；（4）Magnesium ion Mg2+＝4.14 ppm as CaCO3；（5）Conductivity＝356μS/cm；（6） Sulfate SO42-＝68.2 ppm；（7） Chloride Cl-＝6.75 ppm；（8） Fluoride F-＝5.77 ppm；（9） Nitrate NO3-＝1.79 ppm；（10）K-+ Na-＝20 ppm。 This research is based on the Taguchi Method to simulate the real factory condition and to improve the recycling efficiency in practice. The optimum operating condition would be: （1）MMF inflow = 42M3/hr；（2）NaOCl Amout ＝ 3 ppm；（3）NaOH Amout =10 ppm ；（4）RO inflow pH =11 ；（5）RO inflow Pressure = 8kg/cm2 .In this condition, we can maintain a better and stable wastewater recycling efficiency within 79.96% after the experimental simulation. Before having the optimum operating condition, the efficiency of the wastewater recycling would only be 64.15%. With the factors in this research, we continuously got 72.28% efficiency in average during one week, and even up more. Therefore we proved the operating condition is steadily and continuously effective.