- 學位論文
聚氯化鋁形態分佈對混凝膠羽釋出鋁之影響
Effect of polyaluminum chloride species distribution on the residual Al released from floc
摘要
國內淨水場通常使用聚氯化鋁(polyaluminum chloride, PACl)淨化民生飲用水水質，淨水場為了避免清水濁度超標而時常過量添加PACl，雖然使得顆粒態物質去除，但也增加了水中鋁殘留量增加，增加清水鋁超標風險(>0.2 mg/L as Al)，因此如何有效降低水中殘餘鋁成為現今國內自來水處理的重點議題。PACl混凝劑之鋁形態分佈會影響膠羽聚集、破碎及再生長程度，這些過程中會發生鋁水解物種的改變，同時關係到水中殘留鋁量。因此，本研究使用不同鋁形態分佈之PACl混凝劑進行30 NTU之無機(DOC:0 mg/L)及之有機(DOC:2 mg/L)顆粒水樣之膠羽聚集、破碎及再生長實驗，分別為實驗室製備PACl (PACl-H)、實場PACl (PACl-W)、中華化學PACl (PACl-C)，研究目的主要探討不同鋁形態PACl混凝劑所形成之膠羽在聚集、破碎及再生長等程序中膠羽釋出鋁物種之程度及差異。透過膠羽影像分析儀(FlocCAM)監測混凝膠羽聚集、破碎及再生長過程之膠羽粒徑，以計算膠羽強度特性差異，同時比較不同膠羽鋁物種釋出之程度，並且於上述過程中取懸浮液進行鋁物種及DOC濃度分析，以進一步探討混凝膠羽的鋁物種釋出現象。研究結果顯示，無機及有機顆粒水樣之混凝膠羽破碎及再生長均會導致鋁釋出，而其中由於PACl-H之聚合鋁(Alb)>50%，強電性中和作用下能夠降低水中的溶解鋁(Als)濃度，因此破碎導致釋出的溶解鋁較少，相比之下單體鋁(Ala)>50%之PACl (PACl-W)及膠體鋁(Alc)>50%之PACl (PACl-C)透過沉澱絆除聚集形成的膠羽雖然尺寸較大，但無法幫助降低水中溶解鋁濃度，於膠羽破碎後皆會明顯釋出溶解鋁。此外，PACl鋁形態對混凝膠羽破碎及再生長釋出或吸附可溶性鋁(Allp)及非可溶性鋁(Ali)之程度差異大，顆粒水樣中存在有機物會明顯降低破碎膠羽的鋁釋出程度。因此，水場的混凝去穩定顆粒或有機物之程序中，應避免膠羽破碎及再生長，以減少溶解鋁釋出，避免增加清水鋁殘留量，淨水場可採用高聚合鋁(Alb>50%)之PACl以減少溶解鋁殘留。
並列摘要
Drinking water treatment plants (DWTPs) usually use polyaluminum chloride (PACl) to purify drinking water. However, water treatment plant tend to overdosed coagulant in order to reduce excessive residual turbidity. Although removal of particulate matter can be achieved, coagulant may remain in the water. Hence, it is a key issue to effectively reduce the residual aluminum in water. Aluminum species distribution of PACl coagulant is known to affect the aggregation, breakage and regrowth of flocs. The changes of aluminum hydrolysis species in these processes are also associated to the concentration of residual aluminum in the treated water. Therefore, the purpose of this study is to investigate the released extent and difference of aluminum forms from different PACl flocs during floc aggregation, breakage and regrowth processes. In this study, three Al-based chemicals, namely laboratory-made PACl (PACl-H), water treatment plant PACl (PACl-W) and Chung Hua Chemistry PACl (PACl-C) were used to evaluate the floc aggregation, breakage and regrowth process for inorganic and organic water samples (i.e., 30 NTU kaolin particles with and without 2 mg/L dissolved organic carbon (DOC)) in Jar test. Flocs size monitored during different processes by using floc image analyzer to calculate floc characteristics, and then the Al and DOC release after floc formation, breakage and regrowth were determined. The results showed that whether raw water alone or with organic matter presence, aluminum released from flocs when floc breakage or regrowth. Besides, PACl of high polymeric aluminum (Alb>50%) shows lower soluble aluminum (Als) released, while coagulant with high monomer aluminum (Ala>50%) and high colloidal aluminum (Alc>50%) resulted in the increase in Als. Besides, different PACl species distribution lead to significant difference in adsorption or release of leachable particulate aluminum (Allp) and inert aluminum (Ali) after floc breakage or regrowth for both water samples. The aluminum released from flocs is significantly reduced in the presence of organic matter during floc breakage and regrowth. Therefore, it is necessary to avoid floc breakage and regrowth in PACl coagulation to reduce the release of aluminum and its residue in finished water. It is suggested that the use of high polymer aluminum(Alb>50%) PACl is effective to reduce soluble aluminum residue for DWTPs.