台灣地區自來水主要來自水庫之蓄水，而近年來許多水庫曾發生優養化之現象。在夏季天氣炎熱，較深層之優養化之湖庫，因水溫造成水體分層之狀態。底層水無藻類之光合作用，再加上底泥因微生物分解作用，使其呈現厭氧狀態。在厭氧下微生物會以Mn(Ⅳ)為電子接受者，而將其還原成Mn(Ⅱ)，造成原水中錳含量大幅增加，而使淨水場遭遇水質上的問題。
因此本研究以曾經發生過錳問題之淨水場為對象，添加氯化錳以模擬高錳時期之原水。首先在實驗室比較次氯酸鈉及高錳酸鉀對溶解性錳之氧化效果，以0.45 μm濾紙與UF (MWCO 30,000)過濾來區別水中錳之型態為溶解性、膠體性及顆粒性者。同時進一步以瓶杯試驗來探討混凝對經前氧化後錳之固、液分離效果及其較佳操作條件。接著以模廠試驗加以驗證，並進一步比較石英砂濾床及粒狀活性碳濾床對錳去除之差異。
結果顯示:以次氯酸鈉做為前氧化劑，於中性pH值下，對於錳的氧化效果不佳，而在同樣條件下，高錳酸鉀可以有效氧化溶解性錳，反應非常迅速，但是形成的顆粒性錳造成濁度增加，需要依靠混凝沉澱去除，且加藥量之控制必須非常謹慎，否則過量之高錳酸鉀，又會使清水產生色度問題。模廠試驗中發現，以所使用之濾料規格，石英砂濾料較活性碳濾料去除濁度效果較好，但是活性碳濾料可再去除殘餘之溶解性錳。
由本研究之結果可知錳之去除，首先要經過氧化作用將溶解性之錳顆粒性者，然後經由良好的混沉、過濾之固液分離程序，將其自水中分離。故建議淨水場在碰到清水高錳濃度之問題時，首先要檢查沉澱池出水中所含的錳之型態，如以溶解態者居多，應加強前氧化之單元，如果是以顆粒性錳居多者，則應加強固液分離之程序。

The source water of Taiwan’s public water supply mainly comes from reservoirs. However, many reservoirs face eutrophication problem recently. In summer, thermal stratification may occur for deep reservoirs. The water in the bottom layer of eutrophic reservoirs may become anaerobic, due to lack of oxygen transfer from the atmosphere and algae photosynthesis, and also due to the release of organic impurities from bottom mud. As a result, manganese (usually as insoluble oxides) can be re-dissolve from the sediments into the overlying water, and cause problem for the water treatment plants.
In this study, the water treatment plant with occasional manganese problem was targeted. The source water of that plant was spiked with appropriate amount of manganese chloride to simulate the high Mn concentration scenario. First, the efficacy of sodium hypochloride and potassium permanganate on the oxidation of soluble manganese was compared. Both 0.45 μm filter paper and UF (MWCO 30,000) membrane was used to differenciate various type of Mn, namely soluble, colloidal, and particulate. Next, jar tests were conducted to study the efficiency of coagulation on the removal of preoxidized Mn under various operational conditions. Finally, pilot plant testing was conducted to confirm the results from lab-scale study. In pilot testing, filters with silica sand and granular activated carbon were also compared for Mn removal.
The results show that, under neutral pH, sodium hypochloride was not very efficient for the oxidation of soluble manganese; while potassium permanganate reacted quickly, and transferred the soluble manganese into particulate form. Those particulate manganese can cause the increase in turbidity, which must be removed by good coagulation, sedimentation, and filtration. Further, dosage of permanganate should be controlled carefully; otherwise, excessive dosage may induce color problem for the treated water. The results from pilot testing confirmed the preoxidation role of hypochloride and permanganate toward soluble manganese removal. Pilot testing also found that, based on the specifications of the filter media used, the silica sand had higher turbidity removal than that of granular activated carbon. However, the latter could remove soluble manganese, and therefore had product water with more stable quality.
Based on this study, it can be noticed that, for achieving good manganese removal, the soluble manganese must firstly be transferred into particulate form by oxidation, then the particulates be removed by good solid-liquid separation process. Therefore, it is suggested that when water treatment plant faces high manganese problem in its treated water, the first step is to look into the form of manganese in the effluent of its sedimentation basin. If soluble form dominated, then pre-oxidation should be strengthened. If particulate form dominated, then the solid-liquid separation process, such as coagulation, sedimentation, and filtration, should be reviewed.

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