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年度	107	專案性質	實驗性質
專案類別	研究專案	研究主題	整治
申請機構	國立臺灣大學	申請系所	環境工程學研究所
專案主持人	席行正	職等/職稱	正教授
專案中文名稱	以活性覆蓋法降低污染底泥之汞物種釋出:模擬自然系統與封存機制研究
中文關鍵字	活性覆蓋法、活性碳、汞、甲基汞、底泥
專案英文名稱	Reduction of mercury release from contaminated sediment using active capping method: microcosm and sequestration mechanism studies
英文關鍵字	active capping, activated carbon, mercury, methylmercury, sediment
執行金額	1,019,150元
執行期間	2018/1/10 至 2018/11/30
計畫中文摘要	重金屬汞因為具有高移動性、揮發性、生物有效性及神經毒性，被認為是最具有毒性危害之污染物之一。且人類在近數十年之工業活動所產生之工業廢水，已然使汞污染底泥在全球形成嚴重的污染議題。活性覆蓋法(active capping)為一具有經濟可行性之現地整治工法，以活性材料鋪設於底泥表面製造出薄層覆蓋層，降低污染物釋出至水體中，進而降低人體健康與生態風險。本研究探討以活性碳材做為活性覆蓋材料整治汞汙染底泥之可能性，並針對兩大重要議題進行探討: (1)藉由水相吸附實驗及底泥競爭吸附實驗剖析活性碳封存汞之機制；(2)以模擬環境系統試驗探討在自然水體存在橫向水流與底泥擾動下，以活性碳及黏土組合之活性覆蓋層能否長期且穩定的抑制汞溶出於表水。 水相吸附實驗方面，本研究發現環境鹽度低於一定基準之下時(10‰)，汞易與氯離子形成HgCl3-優勢汞物種提升活性碳對其之吸附量，而鹽度升高可能使汞物種轉換為HgCl42-降低活性碳對汞吸附量。另外，二價硫(S2-)與溶解性有機物(DOM)因為對汞具有較高之鍵結力，與汞結合將優先形成顆粒狀汞，而活性碳所吸附之汞皆來自Hg-S-DOM反應後之剩餘。此外，在S2-與DOM皆存在之環境中，可能促進Hg-S-DOM穩定水相中汞使活性碳吸附量下滑。底泥競爭吸附實驗則發現活性碳對於表水總汞有溶出抑制之效果，但在底泥孔隙水中及底泥上之總汞並沒有隨活性碳之添加而有顯著影響，顯示活性碳對於底泥表層之汞封存作用較有直接關係。 本次擬環境試驗使用橫向流之微型系統並開發可定能量之震動系統以模擬底泥擾動，並針對三種活性覆蓋層探討汞底泥於75天內之溶出抑制效率。結果發現AC(3%)+bentonite(3%)以及AC(3%)+kaolin(3%)在模擬橫向流及表層底泥擾動之條件下，對於實場底泥中THg及MeHg皆能達到約75－95%之溶出抑制效果達75天之久(實驗全時程)。而AC(3%)+montmorillonite(3%)的活性覆蓋層由於montmorillonite在水中沉降性及穩定性較差，使THg及MeHg溶出抑制效率不佳。本研究也發現活性覆蓋層之穩定性相當重要，因為所有覆蓋層經覆蓋後之底泥由於阻隔效應造成ORP下降，可能間接增加底泥中汞甲基化潛勢。若在底泥表層擾動或較深層底泥擾動條件下，穩定性較差之活性覆蓋層可能造成MeHg大量溶出。
計畫英文摘要	With high mobility, toxicity, volatility, and bioaccumulation ability, mercury (Hg) is considered one of the most toxic heavy metals in the environment. Over decades of human industrial activities, wastewater has been discharged to river streams causing severe pollution problems across the globe. Active capping is an economically-feasible in-situ method for sediment remediation; using activated materials to form a thin-layer caps could reduce contaminant release from sediment to overlying water, subsequently reduce human health risks and ecological risks. This research evaluated the feasibility of applying activated carbon-based active capping to Hg-contaminated sediment by focusing on two main issues: (1) clarifying the mechanism of Hg sequestration by activated carbon (AC) in aqueous and sediment phase, by carrying out aqueous adsorption tests and sediment competition tests；(2) evaluating the Hg leaching inhibition performance of different active caps under horizontal flows and sediment turbation with microcosms and artificial vibration system. For aqueous adsorption tests, chloride ion was discovered to have the largest adsorption to AC with 10‰ chloride concentration due to forming HgCl3- dominant species. As chloride increased to greater than 10‰, the dominant mercury species transformed to HgCl42-, therefore inhibited Hg sorption to AC. Sulfide (S2-) and dissolved organic carbon (DOM) were considered with superior complexation ability to Hg; this study further discovered that Hg tended to bind to S2- or DOM rather than AC, forming particulate Hg. The Hg fraction adsorbed on AC was parts of residue fraction in the aqueous phase after particulate Hg formed. In addition, with the presence of both S2- and DOM , Hg-S-DOM complexation was further enhanced thus stabilized Hg in the aqueous phase and reduced sorption to AC. Sediment competition tests revealed that AC was effective in reducing Hg in overlying water but had little effect on porewater Hg reduction and sediment Hg reduction, indicating the AC has a more direct impact on Hg speciation on surface sediment. Microcosms designed in this study were with horizontal overlying water flow and artificial vibration systems to mimic sediment turbation, and thus put three combinations of active caps into performance tests. The results showed that active caps with AC(3%)+bentonite(3%) and AC(3%)+kaolin(3%) were efficient in reducing both total mercury (THg) and methylmercury (MeHg) in overlying water by 75-95% under 75 days operation. On the other hand, AC(3%)+montmorillonite(3%) performed poorly in reducing THg and MeHg in overlying water, probably due to the unstable property of montmorillonite.The result of this study also verified the importance of capping stability. All capping groups showed decrease in ORP, indicating more anaerobic environment was established under caps, therefore, may indirectly increase MeHg synthesis potential. With unstable caps, a high concentration of MeHg breakthrough was observed in the occurrence of turbation in depth.