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|上傳時間: ||2013-03-28 13:45:22 (UTC+8)|
|摘要: ||近年來世界各國相繼訂定飲用水中鋁含量標準或建議值，雖然臺灣目前飲用水水質標準尚未訂定鋁含量限值，但日前行政院環保署已將其列入飲用水水質列管污染物篩選目標之ㄧ。有鑑於目前的淨水場大多是以聚氯化鋁與硫酸鋁為主要混凝劑，而根據台灣自來水公司於98與99年度的調查結果，發現部分淨水場於清水中的總鋁濃度有超過0.2 mg/L的情況，台灣自來水公司面對未來的飲用水中含鋁的水質標準，遂推動本計畫。爰此，本計畫即針對如何減少清水中的殘餘鋁提出有效之策略，首先，針對目標淨水場的各處理單元進行採樣，以研析淨水流程中鋁含量之變化情形，作為未來研訂降低水中鋁含量改善對策之參考依據。接著以實驗室瓶杯試驗測試鋁含量之最適改善方案，並依此建立台水公司淨水場降低水中鋁含量最適改善方案與標準作業程序，以作為各淨水場改善清水鋁含量之指引。本計畫目前主要以第五及第六區處的淨水場為調查對象，首先透過淨水場現場各處理單元的的採樣與分析，從原水、沉澱水、過濾水、清水與反洗廢水中各單元之中研析總鋁、溶解性鋁及顆粒性鋁，結果顯示大部分的淨水場內的清水之中的溶解性鋁落於0.17~0.40 mg/L，且溶解性鋁應為淨水場所加的鋁系混凝劑所貢獻；此外，部分淨水場的清水中因存在顆粒性鋁導致總鋁明顯超出 0.2 mg/L，研判為水中的氫氧化鋁顆粒穿透濾池或因清水pH值的變動，而形成氫氧化鋁顆粒所導致。 II 接下來，再針對各淨水場採取原水於實驗室進行瓶杯試驗，第一階段乃結合殘餘濁度及殘餘鋁的混凝加藥曲線進行評估混凝劑量，結果顯示，目前淨水場的混凝加藥操作機制大多為沉澱掃除，但若考量殘餘鋁的控制，建議應先針對其混凝劑進行減量，可控制在電性中和機制的混凝劑量。此外，瓶杯結果顯示pH值的調整與高聚合度的PACl混凝劑皆有降低處理水中總鋁濃度的效果，但過濾出水的濁度也應控制在0.2 NTU以下，以防止顆粒性鋁穿透濾池。而使用非鋁系的氯化鐵做為混凝劑，於實驗室瓶杯測試中表現出良好的濁度去除效果，其處理水中的總鋁含量亦維持在0.1mg/L以下，顯示使用氯化鐵可有效改善清水中鋁含量超過0.2 mg/L之問題。經由實場調查與瓶杯試驗之評估結果，僅有蘭潭、林內、新港及成功淨水場，可經由降低加藥量而使殘餘溶解鋁降至限值(<0.2 mg/L)。而為降低清水殘餘鋁的產生，並針對各淨水場之殘餘鋁特性與建議未來評估方向如下：(1) 可先行以降低劑量與聚合度高之PACl的測試殘餘鋁控制者：蘭潭、林內、公園、新港、成功、南化；(2) 建議評估鐵鹽之使用者：潭頂、山上、楠玉、水上、林內、公園、新港、成功；(3) 建議評估pH控制者：烏山頭、公園、成功；(4) 建議須檢視沉澱、過濾單元效能者：鏡面、楠玉、南化、公園。而考量現場操作之調整便利與接受度，目前計畫執行團隊已於楠玉、山上、水上與竹崎淨水場進行氯化鐵置換硫酸鋁進行混凝加藥之現場操 III 作，結果皆顯示氯化鐵混凝劑可有效去除濁度與並得到較低清水鋁濃度(<0.1 mg/L)，研判氯化鐵大都以可濾性的顆粒鐵氧化合物或氫氧化鐵存在，並且於濾出水中的總鐵皆可控制在0.05mg/L以下，且色度也可控制在3以下。但仍須注意氯化鐵的最適加藥不同於鋁系混凝劑，因此須重新審視各淨水場的加藥操作經驗曲線，建議未來改用氯化鐵混凝劑的淨水場，需連續監測過濾水的色度與總鐵濃度。|
In recent years, many countries around the world have set up a standard or suggested values for aluminum in drinking water. Although Taiwan did not issued the limiting value of aluminum in drinking water, the Environmental Protection Administration still controls it as one of the contaminant candidate lists in drinking water. Thus, most of drinking water treatment plants (DWTP) in Taiwan use polymeric aluminum chloride (PACl) and aluminum sulfate as the major coagulant. Moreover, according to the Taiwan Water Corporation (TWC) investigation report at year 2009 and 2010, it indicated that the clean water contained more than 0.2 mg/L aluminum concentration in some drinking water treatment plants. Therefore, TWC will face the future control standard of aluminum in water quality and execute the possible solutions to overcome the challenge. This project has focused on the target of decreasing the residual aluminum in clean water and promoted the possible solutions. First of all, this study focused on each process unit in drinking water treatment plant and sampled it, which could analyze its distributions of aluminum. It could also be the reference for establishing the future strategy. Second, the Jar Tests were executed to examine the optimal control conditions of aluminum in water, which could be the guidance for establishing the project in optimal V improvement and setting up the standard operation procedure, thus, this study could also be the guidance for decreasing residual aluminum concentration in each drinking water treatment plant. Currently, this project focused on the 5th and 6th district as the investigation target. First of all, based on the sampling and analysis of total, dissolved and particle aluminum at each process unit in drinking water treatment plant, including original water, sedimentation water, filtration water, clean water and back wash water, it indicated that the dissolved aluminum concentrations in most of drinking water treatment plants were at 0.17~0.40 mg/L, which is mostly contributed by aluminum type coagulants. Moreover, the clean water in some drinking water treatment plants contained total aluminum more than 0.2 mg/L owing to the present of particle aluminum. It is because that the particles of aluminum hydroxides penetrated the filtration tank or the pH values changed in clean water to form aluminum hydroxides particles. The Jar Tests of original water from each drinking water treatment plant were executed in laboratory. The first step is to evaluate the dosage of coagulant by the adding curve of combining the residual turbidity and aluminum. The result indicated that the coagulation mechanism for drinking water treatment plant is sweep coagulation. Based on the consideration of residual aluminum controlling, it suggested that the decreasing amount of VI coagulant is needed at the first stage. it also suggested that the dosage could be controlled at the mechanism of charge neutralization. Moreover, the results of Jar Tests also indicate that the change of pH values and the usage of highly polymerized PACL coagulant could assist the decrease of residual aluminum, where the turbidity should control lower than 0.2 NTU to avoid the penetration of particle aluminum in filtration. Furthermore, using iron type coagulant, such as ferric chloride, has executed better turbidity removal than aluminum type coagulant. Their total aluminum concentration of treated water could maintained lower than 0.1mg/L. It indicated that the ferric chloride could be the solution to avoid the problems of clean water containing residual aluminum over 0.2 mg/L. In conclusion of J-test at different DWTP, this project suggests that the plants could lower the dosages of PACL are Lantan、Linnei、Gongyuan、Singang、Chenggong、Nanhua, could evaluate to use iron type coagulants are Tanding、Shanshang、Nanyu、Shueishang、Linnei、Gongyuan、Singang、Chenggong, could evaluate the pH control are Wushantou、Gongyuan、Chenggong, and should examine the efficiency of sedimentation and filtration units are Jingmian、Nanyu、Nanhua、Gongyuan. Moreover, the pH control has the potential risk of industry safety. The bad control will result in the phase exchange of dissolved aluminum and particle aluminum, which will not easy to VII control the amounts of residual aluminum. It suggests that the pH control will be the last choice to consider. Considering the convenience of on-site operation, this project has executed the coagulants exchange from aluminum sulfide to ferric chloride at Nanyu、Shanshang、Shueishang and Jhuci drinking water treatment plants. It indicated that the ferric chloride could remove the turbidity efficiently and obtain lower residual aluminum in clean water (<0.1 mg/L). It is estimated that the most of ferric chloride in water were exited as ferric-oxygen chemical in particle type or ferric hydroxide that could filter out from water. The total iron of filtrated water could be controlled lower than 0.05mg/L, as well as the color is lower than 3. However, the experience adding and operation curve of each drinking water treatment plant has to be re-examined, as well as the total iron concentration and color have to be monitored at the plant that uses ferric chloride as coagulant.
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