本研究案例廠為一TFT-LCD六代廠，該廠建置以高水回收率為目標；製程水回收率90 %、全廠水回收率85 %。也因高水回收率，致使稀釋效果不佳，放流水的磷濃度較同產業偏高。由案例廠含磷廢水流佈調查，含磷濃度較高的廢水主要來源共有二處：一為製程所直接排放之鋁蝕刻清洗廢水；另一為鋁蝕刻清洗廢水，經混合其他低濃度有機廢水收集後，再經生物處理系統(缺氧/好氧+MBR)及逆滲透過濾處理後，於逆滲透單元所產生的RO濃縮排出水(ROR)。本研究分別利用氯化鈣、氯化鋁、氯化亞鐵三種混凝劑，進行化學混凝瓶杯試驗操作，處理上述二股實廠廢水。實驗結果顯示，其除磷的最適操作條件分別為：(1)氯化鈣之最適pH值為8、Ca/P比為2.0、(2)氯化鋁之最適pH值為5、Al/P比為1.4、及(3)氯化亞鐵之最適pH值為6、Fe/P比為1.8。鋁鹽和鐵鹽之實驗結果與文獻相同，但氯化鈣在pH值高於9以上，磷的去除效率會減低，此與一般添加石灰在pH值10以上，可得較佳效果，明顯的不同。此外經整體評估比較藥劑成本及操作狀況，於案例廠除磷，以氯化鈣為較佳的混凝藥劑。比較化學混凝除磷單元於案例廠設置地點，不論設在二股實廠廢水源何處，其化學藥劑及污泥操作費用差異很小，但鋁蝕刻清洗廢水經直接化混後，其水質可能會阻塞後續RO膜，失去水回收效益，且鋁蝕刻清洗廢水之化混單元的工程施作費用較高，經評估水資源效益及工程費用後，將化混單元，設置於案例廠處理RO濃縮水中的磷，為較適之位置。The wastewater treatment system, installed at a 6th generation of TFT-LCD manufacturing plant, was designed to meet the goal of reaching 90 % process water recovery and 85 % total water recovery. The high percentage of water recovery resulted in losing the dilution efficiency, thus, the effluent phosphorous concentration was much higher compared with the effluent qualities discharged by similar industry.According to the investigation of phosphorous distribution in various sources of this case plant, it found that there are two major sources of phosphate containing wastewater. One is directly discharge from cleaning process of Al-etching. The other is RO reject (ROR) in which the RO system followed on the anoxic/aerobic coupled with membrane filtration (A/O MBR) process for treating the mixture of raw wastewater from cleaning process of Al-etching and low organic concentration wastewater from other manufacturing processes. This study intent to investigate the optimum operation conditions for removing the phosphate from the above two sources of wastewater by chemical coagulation jar test using calcium chloride, aluminum chloride, and ferrous chloride as coagulant, respectively. The experimental results revealed that the optimum operating conditions were: (1) pH value was 8 and Ca/P dosage ratio was 2 for calcium chloride; (2) pH value was 5 and Al/P dosage ratio was 1.4 for aluminum chloride; and (3) pH value was 6 and Fe/P dosage ratio was 1.8 for ferrous chloride. The optimum results obtained in this study were fully agreeing with the past studies for aluminum chloride and ferrous chloride as coagulant. However, the phosphate removal efficiency was decreased as the pH value was greater than 9 for calcium chloride as coagulant in this study. This result was completely disagreeing with using lime as common coagulant which the best phosphate removal efficiency generally occurs at pH was above 10. Based on the comparative evaluation of chemical cost and operating condition for the three coagulants, it suggests that calcium chloride is the proper coagulant for removing phosphate in the case plant.Comparing the chemical cost and waste sludge treatment cost for treating these two phosphate containing wastewater streams, there are insignificant differences for installing chemical coagulation process at either site of wastewater source. However, the wastewater from cleaning process of Al-etching after pretreatment by chemical coagulation, its water qualities may cause clogging of the RO membrane and decreasing the benefits for water recycle and reuse. Meanwhile, the construction cost of chemical coagulation process for phosphate removal from Al-etching wastewater was high. Consequently, the better location for phosphate removal by chemical coagulation process in this case plant should focus on ROR stream.
