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.