山上淨水場清水殘餘鋁改善之研究

Study of Residual Aluminum Reduce on Treated Water in Shan-Shang Water Treatment Plant

近年來飲用水中鋁含量與中樞神經系統病變間的相關性陸續被證實，世界各國也相繼訂定飲用水中鋁含量標準或建議值。雖然臺灣飲用水水質標準目前未訂定鋁含量限值，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一。「山上淨水場」位於台南市山上區山上里，原水取自於曾文溪水，濁度經常偏高。淨水場之主要淨水單元包括水躍快混池、初步膠凝池、一次沉澱池、二次膠凝池、二次沉澱池、快濾池及清水池，處理單元流程。原水進入場內後，於水躍池中加入硫酸鋁及次氯酸鈉，原系統設計為分段加藥，而目前二次膠凝池前僅於特殊原水水質狀況，如原水濁度過高時方進行藥劑之添加。本研究主要目的在於改善山上淨水場清水殘餘鋁，首先針對山上淨水場各單元基本水質進行調查分析，會先以瓶杯試驗建立硫酸鋁混凝劑和氯化鐵混凝劑之加藥曲線，而後評估原水場使用硫酸鋁混凝劑之殘餘鋁狀況，山上淨水場原添加硫酸鋁混凝劑，無法藉由降低加藥量來降低清水殘餘鋁，所以接續以實場混凝劑替換測試，將硫酸鋁混凝劑替換成氯化鐵混凝劑進行測試，評估各單元殘餘鋁改善效果及水中殘餘鐵，最後評估二種混凝劑之所需藥劑成本差異。根據本試驗顯示將硫酸鋁混凝劑替換成氯化鐵混凝劑，無論沉澱水、過濾水、及清水，鋁含量皆有下降之趨勢，鋁含量為0.15~0.10 mg/L、清水濁度降為1 NTU以下，總鐵濃度為0.02 mg/L，都可達飲水水質標準，結果顯示混凝劑替換為氯化鐵是可有效減少水中殘餘鋁。

In recent years, high aluminum content in drinking water has been identified to cause health problems such as damage to the central nervous system. Countries such as Canada have set the drinking water standard for aluminum content. The United States Environmental Protection Agency included aluminum in the list of National Secondary Drinking Water Regulations, of which many states have implemented. Currently, Taiwan still does not include aluminum as a regulated parameter in the drinking water standards. The Shan-Shang water purification plant treats raw water obtained from Zengwun dam, which usually has high turbidity. The treatment plant is composed of the following process treatment units: an initial coagulation unit, primary sedimentation tank, secondary coagulation unit, secondary sedimentation tank, and filtration system. The framework of the water treatment process includes two-stage dosing, where secondary coagulation is applied only when turbidity of treated water after primary coagulation does not meet water quality standards. Due to the two stages of coagulation, the presence of increased residual alum concentration was observed in treated water. In this study, the main objective is to determine the efficiency of ferric chloride in the removal of residual alum from treated waters from Shan-Shang treatment plant. Jar tests were used to establish dosing curves of alum and ferric chloride as individual coagulants. The effect of pH and ferric chloride dosage on the removal of residual alum was investigated. In addition, cost analysis of using alum and ferric chloride was also carried out. Ferric chloride proves to be a better coagulant in comparison to alum. Both alum and ferric chloride can obtain the following water parameters: residual alum content of 0.15 to 0.10 mg /L, turbidity of 1 NTU or less, total iron concentration of 0.02 mg/L, which meets the drinking water quality standards. The results showed that the ferric chloride coagulation can effective reduce the residual alum in water treatment plant.