藻類存在對濁度混沈去除之影響

Abstract

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) 。 結果發現不論是以PACl或是Alum為混凝劑時，高嶺土所耗用之混凝劑量均較藻類多，其最適加藥量下之殘餘濁度值也較高，而此兩者之混凝機制均顯示以電性中和為主時所需之劑量低且混凝效果良好。而高嶺土與藻類以等濁度混合之試驗中顯示以PACl混凝效果之最佳，PFS次之，而Alum則最差。同時也發現混合水樣之混凝特性介於純藻及純高嶺土之混凝特性間，而整體之混凝特性以藻類為主導。此外，在不同顆粒混合比例下之混凝試驗中顯示隨著含藻比例的增加，高嶺土的去除效率隨之增加，因此藻類的存在確實可提升高嶺土的去除。而在膠羽特性分析的結果則顯示高嶺土所形成之膠羽較小、沈降速度慢但卻較為緻密，藻類膠羽較鬆散，但由於藻類膠羽較大所以其沈降速度比高嶺土稍微快一些。而隨著藻類比例的增加，膠羽粒徑及沈降速度均逐漸增加，膠羽密度卻是呈相反的變化。

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.