The Effect of Algae on Coagulation in Turbid Water
|摘要:||科技發達之今日，水質日趨惡化，尤其國內水體受到污染造成富含藻類之優養化水體，影響淨水程序之混沈效果，而藻類存在對混沈效果之影響程度一直未深入探討，因此本研究以單純顆粒及藻類為對象，在控制條件下進行混凝沈澱試驗，期能清楚區分混凝劑在兩顆粒共存下之分配比率。本研究以純種單細胞綠藻-小球藻（Chlorella vulgaris）作為水中生物顆粒之來源，以高嶺土為水中之無機顆粒，並調整高嶺土與藻類之混合比例，模擬自然原水中無機顆粒與藻類共存及藻類含量不一的情況，而研究中主要使用的混凝劑為多元氯化鋁(PACl)及硫酸鋁(Alum) 。
Raw water quality is deteriorating because of the excessive development of industries. Industrial pollution has caused eutrophication in surface water. It is speculated that algae may affect the coagulation and sedimentation processes in water treatment. The purpose of this study was to separate the coagulation between the simple inorganic particle and algae. Kaolin was the inorganic particle and Chlorella vulgaris was the biological particle used in this study. Synthetic water was prepared by mixing these two particles in different ratio to simulate the natural water. The coagulants used were aluminum sulfate (Alum) and polyaluminum chlorides (PACl). The result shows that kaolin consumes more coagulant than Chlorella, which also yields higher residual turbidity. For both particles, better coagulation results and less dosage were associated with the charge neutralization mechanism. The test in which equal turbidity of kaolin and algae was used showed that PACl was the most effective coagulant, followed by PFS, with Alum being the least. At the same time, the coagulation characteristic of the mixed water was between those of the pure kaolin and Chlorella, but Chlorella is predominant. Results also showed that kaolin removal increased with the ratio of algae rose, which suggested that the presence of algae promoted the kaolin removal. The floc size from kaolin coagulation was small, therefore the flocs settled slowly and denser. The flocs of algae were bigger, settled faster but much looser. As the ratio of algae increased, the size of the floc and the settling velocity increased but the density decreased.