Chemical pretreatment for algae and organic matter removal by flotation in Tai-hu Water Treatment Plant
|摘要:||金門太湖淨水場含藻及有機物之原水容易造成淨水場操作效能低落及供水水質不佳之問題，淨水場一般採用前加氯降低原水中藻類之活性，以提昇混凝去穩定藻類之成效，但氯會與原水有機物反應而生成三鹵甲烷，影響供水水質。本研究採取太湖淨水場不同含藻及有機物原水進行氧化程序搭配混凝浮除之瓶杯試驗，探討二氧化氯搭配次氯酸鈉氧化對藻類及有機物氧化之反應，並評估前加氯模式對硫酸鋁及聚矽酸鐵混凝浮除藻類及有機物之效能，建立提昇太湖淨水場混凝及浮除效能之最適前加氯模式。研究結果顯示，水場抽取太湖水庫水及田埔水庫水之混合水作為原水時，水中藻類數量高於80,000 cells/mL，其優勢藻種為柱孢藻，且總有機碳濃度超過20 mg/L以上，此時使用二氧化氯搭配次氯酸鈉氧化，雖然藻類會因氧化劑攻擊而破裂，導致水中小分子親水性有機物質(< 1 kDa)濃度增加，但卻仍有效提昇硫酸鋁及聚矽酸鐵混凝浮除柱孢藻及疏水性有機物之效能，同時總三鹵甲烷生成潛能也可大幅降低。當水場抽取太湖水庫水及金湖水庫水之混合水作為原水時，水中藻類數量減少至10,000 cells/mL以下，其優勢藻為微囊藻，水中總有機碳濃度約等於10 mg/L，此時單獨使用次氯酸鈉或二氧化氯搭配次氯酸鈉氧化均會造成藻類破裂，並有效提昇硫酸鋁及聚矽酸鐵混凝浮除藻類效能，但卻會導致水中大分子疏水性有機物(> 10 kDa)濃度顯著增加而增加水中溶解性有機物含量，使混凝浮除有機物之效能不彰，致三鹵甲烷生成潛能無法有效降低。|
The source water with abundant algae and organic matter would lower the operational performance and worsen the quality of water supply for Tai-hu Water Treatment Plant (WTP) in Kinmen. Chlorination precede coagulation has been commonly used to reduce the activity of algae for WTP, which substantially facilitates the destabilization of algae. However, various trihalomethanes can be formed with chlorination to significantly affect the quality of water supply. Oxidation and coagulation-flotation process has been conducted with different raw water to investigate the interaction of chlorination with NaOCl and ClO2 between algae and organic matter. The effect of chlorination strategy before Alum and polysilicate iron (PSI) coagulation on the removal in algae and organic matter by flotation was also investigated to establish the optimal pre-chlorination strategy for improving the performance of coagulation and flotation for Tai-hu WTP. The results have shown that the majority of algae is Cylindrospermopsis (> 80,000 cells/mL) and organic matter (> 20 mg/L) exist in the mixed raw water from Tai-hu and Tain-Pu reservoirs. Algae cells suffer damage and break up when the chlorination with NaOCl and ClO2 was carried out, which result in the increase in the concentration of hydrophilic organic matter with less than 1 kDa in molecular weight. However, the removal in hydrophobic organic matter and Cylindrospermopsis can be effectively improved by flotation coupled with Alum or PSI coagulation and the total trihalomethane production potential (TTHMFP) can be substantially reduced. The algae counts are lower than 10,000 cells/mL and the concentration of organic matter is around 10 mg/L in the mixed raw water from Tai-hu and King-hu reservoirs, where the majority of algae is Microcystis exist. The majority of algae break up for NaOCl chlorination with and without ClO2, which effectively improves the removal in algae. However, the increase in the concentration of organic matter along with hydrophobic organic matter with larger than 10 kDa in molecular weight was occurred. Then, the removal in organic matter is poor by flotation coupled with Alum and PSI coagulation, and then the TTHMFP cannot be effectively reduced.