- 學位論文
以臭氧/針鐵礦三相流體化床處理水中氨氮
Aqueous Ammonia Removal by Catalytic Ozonation in a Three-phase Fluidized Bed Reactor
摘要
在石化產業、半導體產業中會產生大量的氨氮廢水，且含有高濃度氨氮之廢水排入水體會造成水中優養化及危害水中生物。傳統之生物處理法佔地面積大、反應速率慢，而傳統化學氧化的主要產物為硝酸氮，仍屬放流水列管物質。本研究將探討使用臭氧與針鐵礦觸媒於三相流體化床反應器中處理含氨氮廢水，期望能將產物由硝酸氮轉化成氮氣，探討pH、觸媒重量、溴離子對處理效果及氮氣生成率的影響，同時也利用批次實驗探討氮氣生成的可能機制。 以氣相臭氧搭配針鐵礦作為觸媒使用三相流體化床反應器處理含氨氮之廢水，實驗結果顯示pH對於去除氨氮之反應速率有明顯之影響。在pH 9.0時，氨氮二階反應速率為20.6 M-1s-1 ，在pH 6.0時二階反應速率常數為0.13 M-1s-1，pH越高反應速率越快。在pH 9搭配觸媒0.75與2.3公斤時，分別有14%與55%的氨氮轉化成氮氣，顯示觸媒重量增加氮氣產率隨著增加。分解氨氮所需的臭氧劑量方面，在pH6與9時，有觸媒存的臭氧消耗劑量分別比無觸媒時低10%與11%，顯示有針鐵礦觸媒存在時，氨氮與臭氧有不同之反應途徑。在有觸媒的反應下，氨氮總量降解速率較無觸媒存在時慢，可能與氨氮與FeOOH吸附-脫附速率有關，須等吸附在觸媒上的氨氮脫附於水中後再進行反應。比較填充床與流體化床對於氨氮轉化的影響，使用流體化床可將氮氣選擇率從50.36提高至90%。添加溴離子於反應系統中使氨氮反應速率快於無溴離子存在時。將半導體廠之實際廢水添加溴離子，氨氮去除率為80%。 有關氨氮轉化為氮氣的機制，推論可能是水中氫氧自由基與氯離子反應生成氯原子自由基，在進一步生成次氯酸，再以折點加氯方式將氨氮轉化成氮氣。批次實驗中發現氮氣的生成量的確與與氯離子濃度呈正比，間接證實以上推論。 關鍵字：臭氧/觸媒反應、三相流體化床、氨氮
並列摘要
Semiconductor and some petrochemical industries generate high ammonia-containing wastewater, and their discharge into water body can cause eutrophication and threats to aquatic lives. Conventional biological treatment is limited to low concentration wastewater with slow reaction rate as compared to chemical oxidation. However, the end product of oxidized ammonia is nitrate, which also causes eutrophication. In this study, a three-phase fluidized bed reactor was used to treat ammonia-containing wastewater with ozone and goethite as the catalyst. The effects of pH, weights of catalyst, and addition of Br- were examined. Results indicate part of the ammonia was converted toN2. Effect of pH influences the reaction rate dramatically. The second order reaction rate constant at pH 9 and 6 were 20.6 and 0.13 M-1s-1, respectively. This result is consistent with the molar fraction of molecular ammonia, the only reactive species with ozone or hydroxyl radical instead of ammonium, at corresponding pHs. The conversion to nitrogen gas was higher with the increasing amount of catalyst applied. The conversion to nitrogen gas with 0.75 and 2.3 kg catalyst at pH 9 were 14 and 55%, respectively. Ozone demands with catalyst were about 10% lower than without using catalyst at pH 6 and 9. Though the use of catalyst can convert ammonia to N2, the ammonia reaction rates were not was not enhanced. The addition of Br- enhanced the conversion to N2. The mechanism for converting ammonia to N2 is proposed. The generated HO‧ reacts with Cl- or Br- to form Cl‧ or Br -, which in turn converted to form HOCl or HOBr, and proceeds the so-called “break-point dechlorination” to form N2. A batch experiment was conducted by controlling different amount of Cl-, and results confirmed the N2 formation is propotional to the amount of Cl- applied in the system. Keyword：catalytic ozonation ; three-phase fluidized bed; ammonia
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