加強混凝去除金門太湖原水天然有機物之探討

Abstract

本研究中，以加強混凝去除金門太湖原水之天然有機物，並針對天然有機物 (NOMs) 中的化學性質，將其分成親水性及疏水性有機物，來探討其中去除機制以及對於混凝效果之影響並建立水中溶解性有機碳 (DOC) 的混凝去除預測模式。 研究結果顯示，傳統混凝劑對於太湖原水之濁度去除有良好的效果，但對於天然有機物的去除效果卻無法達到加強混凝之指定標準，主要是由於原水SUVA值過低，不利於混凝程序。此外，DAX-8樹脂分離實驗顯示，疏水性有機物較易被去除，主要的去除機制包含了電性中和以及吸附沉澱，而親水性有機物較不易被混凝單元去除，其去除機制主要是藉由電性中和。 另一方面，考量天然有機物中親疏水的性質差異，修正Kastl (2004) 的溶解性有機碳 (DOC) 混凝去除預測模式，能獲得一個準確度較高的預測模式。建構完成的模式，藉由原水SUVA值、原水的溶解性有機碳、添加混凝劑量以及混凝反應時的pH值，可以預測出準確度高的殘餘的溶解性有機碳。

In this investigation, the enhanced coagulation process was introduced to treat the source water from Tai-Lake in Kinmen. The objectives of this research work were intended to investigate the effects of natural organic matters (NOMs) characters, i.e. hydrophilic NOMs and hydrophobic NOMs, on coagulation performance, and formulate the predictive dissolved organic carbon (DOC) removal model. The results of this investigation reveal that coagulation with traditional coagulant, i.e. alum and ferric chloride, was found to be effective for removing turbidity from source water. However, during the enhanced coagulation process, the DOC removal percentage was hard to meet the requirements of US D/DBP rules due to the lower value of SUVA in source water. Besides, the results of DAX-8 resin separation experiments reveal that hydrophobic NOMs were relatively easily removed. It suggests that “charge neutralization” and “adsorption” mechanisms should be both involved in the process. Hydrophilic NOMs were relatively hard to be removed, and the DOC removal mechanism in hydrophilic is charge neutralization. This “Modified-Kastl’s model” can predict the residual DOC by given parameters, i.e. the initial SUVA and DOC of raw water, adding dosage and operated pH level. By providing the specific characters of hydrophilic and hydrophobic NOMs, the modified-Kastl’s can predict more accurately than the Kastl’s. Keywords: enhanced coagulation, DOC, hydrophilic, hydrophobic, predictive DOC removal model