| 研究生: |
劉嘉宏 Liou, Jia-Hong |
|---|---|
| 論文名稱: |
混凝劑種類對低濁度原水混凝影響之研究 Effect of Coagulant Type on the Coagulation of Low-Turbidity Source Water |
| 指導教授: |
葉宣顯
Yeh, Hsuan-hsien |
| 學位類別: |
碩士 Master |
| 系所名稱: |
工學院 - 環境工程學系 Department of Environmental Engineering |
| 論文出版年: | 2007 |
| 畢業學年度: | 95 |
| 語文別: | 中文 |
| 論文頁數: | 116 |
| 中文關鍵詞: | 膠羽密度 、碎形維度 、硫酸鋁 、氯化鐵 |
| 外文關鍵詞: | floc density, fractal dimension, ferric chloride, aluminum sulfate |
| 相關次數: | 點閱:117 下載:13 |
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烏山頭淨水場之處理程序為傳統之混凝、沉澱、快砂濾。其原水特性為低濁度(< 10 NTU)及高pH值(約8)。實場採樣分析結果發現,若明礬混凝劑加量隨原水濁度之降低而減少,會導致混凝效果不佳,甚至出現沉澱池出水濁度,反而高於進流水之情形。而該廠常碰到的另一問題為沉澱池傾斜板上方累積一層膠羽,當厚度太高時,可能將膠羽帶出至砂濾池,而影響出水濁度,此時需停止操作,以人工加以清洗,懷疑係因膠羽特性所引起。本研究,乃針對上述實場之現象進行探討,同時在實驗室做進一步之試驗,比較不同混凝劑對烏山頭原水之適用性。
根據實場研究結果,推論上述現象係因廠方以原水濁度之高低為明礬加藥量之指標,故當原水濁度降低時,混凝劑加量亦隨著降低。再加上該原水pH值偏高,在此情況下混凝劑加量與pH值,偏離氫氧化鋁膠羽較佳生成之範圍,致所加入之鋁鹽以單體狀溶解性鋁存在。即使生成膠羽,亦因密度或緻密性偏低,無法在傾斜板沉澱池中順利沉降,反而被水流帶出至傾斜板上端。實場之研究亦顯示膠羽之性質與去除效率,受膠羽池停留時間與沉澱池溢流率有很大之影響。
實驗室試驗比較硫酸鋁和氯化鐵兩種混凝劑之作用,結果發現鐵鹽,所產生之膠羽密度比鋁鹽大,且膠羽之緻密性(碎形維度大)也較高。而烏山頭原水之膠羽平均密度、碎形維度和平均沉降速度均比人工原水小,推測可能由於原水中顆粒性質之不同所導致。而就不同混凝機制而言,不管以鋁鹽或鐵鹽為混凝劑時,以沉澱掃曳機制存在之濁度去除效果較吸附及去穩定佳。就烏山頭原水而言,鐵鹽所需之最佳劑量比鋁鹽低,且在相同劑量時,殘餘濁度也較低。至於以氯化鐵為混凝劑時,處理水可能殘餘色度之問題,發現只要混凝劑加量與pH值控制在適宜氫氧化鐵膠羽生成之區域內,則無真色度之問題。
The treatment process of Wu San Tou Water Works is the conventional coagulation, sedimentation and filtration process. Its raw water is characterized by low turbidity (< 10 NTU) and high pH value (about 8). Alum was used as the coagulant, and its dosage was reduced with the decreasing of the turbidity of the raw water. However, under this operation strategy, field sampling found that sometimes the turbidity of effluent from sedimentation basin was higher that of the influent. Other problem encountered by the plant was the accumulation of sludge mat on the surface of the inclined plate in the sedimentation basin. When the thickness of sludge mat was excessive, the sludge may be carried by the water flow into the following sand filter, and causing premature turbidity breakthrough. As this happened, the operation needs to be interrupted, and the basin cleaned manually. Therefore, it reduced productivity and also was quite a burden to the operators. The research is aimed at solving the above-mentioned problems by both field investigation and lab-scale studies. The latter is mainly to compare the suitability of aluminum and iron salts as coagulants for Wu San Tou raw water.
Based on the results from field investigation, it is realized that the problems encountered by the treatment plant was due to the lower than optimum alum dosage used by the plant, when the raw water turbidity was low. The insufficient alum dosage coupled with high pH value of the raw water prevented the formation of aluminum hydroxide floc. This also means that, under this condition, most of the alum added existed as soluble Al species in the water. Therefore, the coagulation performance were poor.
In the lab-scale studies, the effect of aluminum sulfate and ferric chloride on the coagulation of both the raw water from Wu San Tou and artificial raw water, made up mainly from kaolin clay particles, were investigated. The results show that the floc generated from iron salt have higher density and higher fractal dimension than those from aluminum salt. This means iron floc is heavier and structurally more compact than aluminum floc. Floc from Wu San Tou raw water generally have lower density, fractal dimension and settling velocity than those from artificial raw water. This probably is due to the more complex constituents in the nature raw water, which contains algae cell and NOM, besides inorganic particles. Further, no matter which coagulants were used, those with sweep coagulation mechanism have higher turbidity removal than those with adsorption - destabilization mechanism.
For Wu San Tou raw water, iron salt coagulant required lower dosage than that of aluminum salt. Under same coagulant dosage, the treated water from iron salt also have lower residue turbidity than those from aluminum salt. Further, the residue color problem from iron salt can be avoided, if the dosage and pH value are located in the region appropriate for solid ferric hydroxide formation.
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