天然濁水混凝最適加藥量與顆粒表面界達電位之關係研究

Abstract

在水處理單元中，混凝後顆粒的界達電位常被使用來做為衡量混凝劑之最適加藥量的指標，然而淨水廠中採集自地表水的原水，其水質條件變化幅度相當大，導致不同天然原水達到最適加藥時的界達電位範圍亦有所不同，故以界達電位作為最適加藥量決定之指標仍存有許多爭議。本論文之目的為研究天然原水的混凝過程中，最適加藥量與混凝加藥後顆粒的界達電位之間的關係；本研究之天然原水採集自新竹給水廠，使用之混凝劑為PACl，藉由瓶杯試驗求得最適混凝加藥量及利用界達電位儀量測快混後水樣之界達電位，同時量測此時混沉後之殘餘濁度；另外，個別分析原水的水質項目以探討其對混凝最適加藥量之影響。 研究結果顯示，原水的濁度及鹼度影響最適加藥量及界達電位最甚，而最適加藥量幾乎都出現在中性pH 時，且最適混凝劑量隨濁度升高而增加，此時顆粒的界達電位偏正電荷。此外，原水濁度影響原水鹼度與最適加藥量之間的關係相當顯著；在低濁度(0~50 NTU)時，最適混凝加藥量隨鹼度升高而增加，但在高濁度(300~2700 NTU)時，最適混凝加藥量隨鹼度升高而減少。

The zeta potential of coagulated particles is commonly used as an index to evaluate the optimal dosage of coagulation in water treatment. However, the qualities of raw water taken from surface turbid water by water treatment plant (WTP) fluctuates immensely, resulting in variation of optimal zeta potential zone for coagulation of different natural turbid water. Therefore, there are still many debates on determination of the optimal dosage through the indication of zeta potential. The goal of this study is to investigate the relationship between optimal dosage and zeta potential of coagulated particles for coagulation of natural turbid water. Various natural turbid water samples were collected from HsinChu WTP, and then each coagulation test was conducted by PACl coagulant through jar test to determine the optimal coagulant dosage and corresponding zeta potential by a zeta meter, in which the residual turbidity of supernatant after sedimentation was measured. Various parameters of raw water quality were further measured independently to study their effect on determination of the optimal dosage. The results showed that turbidity and alkalinity of raw water governs the optimal dosage and corresponding zeta potential. The optimal dosage almost occurred at neutral pH and increases with increase in turbidity of raw water, in which the optimal zeta potential for turbidity removal was rather positive. Furthermore, the relationship between alkalinity of raw water and the optimal dosage is strongly affected by turbidity of raw water. The optimal dosage increases with increase in alkalinity for coagulation of low turbidity water (0~50 NTU). By contrast, the optimal dosage decreases with increasing alkalinity for coagulation of high turbidity water (300~2700 NTU).