半導體廠含氟廢水加藥效能評估

Abstract

本研究模擬某半導體廠含氟廢水處理之化學混凝沉澱程序，探討氯化鈣加藥比例與水中氟離子反應形成氟化鈣顆粒之效率，及聚氯化鋁及高分子凝集劑對水中氟化鈣顆粒沉降之影響。 該廠含氟廢水氟離子濃度約為400 mg/L至1500 mg/L，導電度為2500~5000 μS/cm，pH約2.78~3.46，水質偏酸性。以瓶杯試驗模擬該廠含氟廢水之加藥程序得知，氯化鈣加藥反應前將pH值調整為5.5對後續氯化鈣與水中氟離子反應效率會更好。 而氯化鈣加藥反應後，添加聚氯化鋁及高分子凝集劑沉降水中氟化鈣顆粒時，其不同氟離子濃度廢水之氯化鈣加藥量為鈣氟比 1.6時，降低水中氟離子濃度之效率可達97 %以上。再者，氯化鈣加藥反應後，運用溶液飽和原理及靜置沉降原理操作水中氟化鈣顆粒沉降，氯化鈣加藥量為鈣氟比 1.7時，降低水中氟離子濃度之效率，可達95 %以上。 最後將批次加藥參數，套用於半導體廠含氟廢水自動加藥系統參數中，觀察當氯化鈣加藥鈣氟比為1.6時，其原系統設計之水中殘餘氟離子濃度震盪曲線自較大震盪區間降為較穩定狀態。針對過量之氯化鈣給予適當控制，用藥成本可節省新台幣602,914元。

This study explores the effect of calcium chloride (CaCl2) dosage on the outflow fluoride ion (F-) concentration of a wastewater treatment process in a semiconductor plant. The wastewater of this semiconductor plant contains F- concentration of approximately 400 mg/L to 1500 mg/L, conductivity of 2500~5000 μS/cm and pH of 2.78 to 3.46.

The jar simulation test results indicated that the pH value should be adjusted to pH5.5 before adding calcium chloride (CaCl2), which can result in better coagulation efficiency. When adding a polymer coagulant, it can promote particle coagulation and sedimentation. The best calcium to fluoride ratio (Ca/F) is 1.6, which has the high F- removal efficiency of over 97%. But if polymer coagulant was not added then the best calcium to fluoride ratio (Ca/F) is 1.7, which has the high F- removal efficiency of over 95%.

Finally the results of the jar test was applied to the wastewater plant of the semiconductor factory using the calcium chloride (CaCl2) dosage of Ca/F=1.6. It reveals that compared to the original design where the treated water was experiencing high fluctuation of F- concentration, the adequate control of calcium chloride (CaCl2) dosage led to stable and low residual F- concentration in the treated wastewater. This can effectively reduce the cost by up to 602,914 NT.