本研究著重淨水廠低濁原水處理，傳統上因鋁鹽混凝劑所形成之膠羽質量較輕，低濁原水須依賴高加藥量鋁鹽，但此時混凝形成膠羽較鬆散，且會產生大量污泥；若採用鐵鹽混凝劑(如氯化鐵)，雖然膠羽生成密實，但高加藥量鐵鹽形成殘餘鐵，則可能會增加水中色度殘留。
本研究針對潭頂及南化淨水場低濁度之原水(濁度皆低於30 NTU)，以實驗室自製之聚矽酸鐵(PSI)，對淨水廠低濁原水之混凝效果進行試驗。針對淨水廠原水，藉由瓶杯試驗從中找出最適加藥量，再進一步比較聚矽酸鐵與氯化鐵濁度之沉降去除效果。
依照淨水廠原水帶負電的特性，對PSI之矽鐵比做出整體評估，經試驗後選擇矽鐵比為0.5和1，以二者處理低濁原水，經沉降後濁度皆能在2NTU以下。另亦探討不同鐵型態（Fa、Fb、Fc）之大小差異性對於淨水廠原水濁度沉降效果之影響，再進一步與氯化鐵及市售聚合鐵相互比較。對於低濁原水，使用Si/Fe = 1之PSI，則最佳加藥量為2 ppm；由於Si/Fe = 1 PSI之Fb、Fc鐵型態占比高，處理低濁原水成效亦較佳。綜上述，PSI可有效處理淨水廠低濁之原水，並可藉由不同的矽鐵比來調整處理效能，而自製PSI則以Si/Fe=1為最佳矽鐵比。 This study focused on the low turbidity raw water treatment in the water purification plant.Traditionally, the low turbidity raw water depends on the high dosage of aluminum salt. However, the formed aggregates by the aluminum salt coagulant are light and loose. A large amount of sludge will be formed when using aluminum salt. When iron salt coagulant (such as ferric chloride) was used for low turbidity water, denser aggregates could be formed. However, the high residual iron may increase the residual color in water.
In this study, the raw water below 30 NTU from the Tanding and Nanhua water purification plants was tested by the self-made Poly Silicate Iron (PSI). The Jar-test was carried out to evaluate the optimal dosage and turbidity removal effect.The coagulation effect of the poly silicate iron and the ferric chloride was further compared.
The experimental results show that the PSI's silicon/iron ratio selected is based on the negative characteristics of the raw water in the water purification plant. The silicon/iron ratios are 0.5 and 1 after the tests, and both can reduce the turbidity to be lower than 2 NTU after sedimentation. The difference in the size of the various PSI type (Fa、Fb、Fc) will affect their turbidity removal efficiency. The results of this work show that at Si/Fe = 1, since the fraction of Fb and Fc is higher, it has the best performance. Moreovr, by varying the PSI loading, it is found 2 ppm is the optimal dosage. In conclusion, this study exhibits self-made PSI can effectively treat low turbidity raw water, and the performance of PSI will vary with the Si/Fe ratio.
