以電解混凝法處理苦鹹水中之矽酸通入逆滲透薄膜解決積垢現象之可行性評估

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Title:	以電解混凝法處理苦鹹水中之矽酸通入逆滲透薄膜解決積垢現象之可行性評估
Other Titles:	The feasibility study of electrocoagulation for the removal of silicic acid in brackish water-attenuation of reverse osmosis fouling
Authors:	王家駿 Wang, Chia-Chun
Contributors:	鄧宗禹 Den, Walter 東海大學環境科學與工程學系
Keywords:	電解混凝法;矽酸;積垢現象;苦鹹水 Electrocoagulation;Silicic acid;membrane fouling
Date:	2006
Issue Date:	2011-05-24T08:45:20Z (UTC)
Abstract:	摘要逆滲透（Reverse Osmosis，RO）系統應用於苦鹹水淡化廠上，最常發生之問題為濾心阻塞。其原因為二氧化矽於薄膜表面形成難去除之矽垢。為達到淡化廠之出水量要求，且考慮薄膜因阻塞而降低使用壽命之癥結，需添加大量之抑垢劑以防止矽鹽之形成，往往造成更大之成本負擔。以電解混凝法去除水中之陰離子與帶電顆粒已被證實具有良好之去除效果。因此本研究欲以連續流之電解混凝程序，評估其去除苦鹹水中矽酸的效率，再經薄膜過濾觀察其通量變化，來判定達到去除矽酸的作用時，是否有效降低薄膜阻塞的現象。本研究之電解混凝操作參數包括極板材質、極板排列方式、操作電流、水力停留時間。陽極以鋁作為極板，陰極則以不?鋼作為極板。在批次實驗中，偶極極板排列方式矽酸去除率較單極極板排列方式高，且有效降低電解混凝處理時間、增加陽極面積及提高金屬離子釋出量，故極板排列方式採偶極極板方式。實驗結果顯示，提高操作電流或增長水力停留時間，均能使矽酸之去除率增加。且於最佳之操控條件下(0.5 A、30分鐘水力停留時間)，人工水樣與實廠水樣之矽酸去除率皆可達70%。此外，將電解混凝程序處理過之水樣，通入薄膜系統觀察。結果發現，電混後之水樣，除了矽酸濃度降低外，對於薄膜比通量也較未電混水樣為佳，以電子顯微鏡進行薄膜之表面觀察，發現薄膜表面積垢物較未電混水樣少。研究結果顯示，以電解混凝法去除水中矽酸濃度，可有效降低薄膜阻塞的現象。 AbstractThe major problem associated with desalination of Penghu’s brackish water by reverse osmosis systems is membrane fouling, primarily due to silica scaling on membrane surfaces. In order to accommodate the desalination plant’s supply volume and to compensate for the reduced service life of the membranes, the plant operators have followed the conventional way of adding large amount of anti-scalant to prevent the formation of silica scale, thereby significantly increased the cost of plant operation. Alternative, electrocoagulation (EC) has been demonstrated as an effective process for the removal of anions and charged particles from water and wastewater. This study, therefore, intended to evaluate the feasibility of the continuous-flow EC process as a pretreatment to reverse osmosis by removing silicic acid from the brackish water. Furthermore, to verify whether the process could attenuate membrane fouling by silica scaling, a series of membrane filtration experiments were performed to monitor the permeate flux variation with EC as a pretreatment step.The effects of several important operating parameters, include electrode arrangement, current density, and hydraulic retention time (HRT), were studied based on the removal efficiency of silicic acid. Aluminum and stainless steel plates were employed as the anodes and cathodes, respectively. The results from the batch experiments suggested that bipolar arrangement attained higher silicic aid removal efficiency than monopolar arrangement, and thus bipolar arrangement was used throughout the ensuing continuous-flow studies. In general, increase in the current density and/or HRT improved the removal efficiency of silicic acid. Under the optimum operating condition (applied current of 0.5 A with HRT of 30 min), removal efficiency up to 70% for both artificial and actual brackish water could be attained. Nanofiltration studies showed that the normalized permeate flux for the brackish water pretreated with EC was markedly higher than those without EC pretreatment, regardless of the starting silicic acid concentration in the raw water. Therefore, reduction of silicic acid concentration by EC is a highly feasible method to prevent membrane fouling.
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