study of lead removal using crab shell media in a fluidized-bed reactor

[[abstract]]利用廢棄物去除污染物，為污染防治方法中最能符合經濟及環保效益的方式。蟹殼為常見的海產廢棄物，含高含量的自然高分子-幾丁質成份，而幾丁質製成幾丁聚醣可去除多種重金屬。本研究嘗試以蟹殼為基本材料，經化學改質後，利用流體化床反應器中的吸附及結晶沉澱作用，達到去除水中鉛離子之目的，並可解決傳統含重金屬廢水所衍生大量污泥問題。 本研究首先以批次方式進行鉛吸附平衡及動力實驗，比較蟹殼及改質蟹殼的吸附能力、反應速率及pH值對反應的影響；其後，再進行流體化床吸附實驗，探討反應速率及流速、床高與貫穿曲線的關係，並建立相關之吸附方程式；此外，在蟹殼結晶運用方面，本研究利用已吸附飽和的蟹殼顆粒作為流體化床的擔體，並添加結晶劑Na2CO3進行結晶實驗，探討pH值、流率、加藥比等因子，對水中鉛去除率的影響，並找出較佳的操作條件。 由吸附實驗結果可發現，蟹殼顆粒吸附能力與pH值高低有明顯關係，其對鉛的吸附能力依序為：改質蟹殼pH= 5 >蟹殼pH= 5 >改質蟹殼pH= 3 5 >蟹殼pH= 3 5 >改質蟹殼pH= 2 >蟹殼pH= 2。經由由吸附動力實驗，可發現改質蟹殼吸附鉛的反應速率近似一階反應(R2為0 96~0 99)。吸附實驗中，改質蟹殼顆粒吸附於pH= 5時，吸附量達714 29 mg(Pb)/g(crab)為最高，其次，由流體化床吸附實驗數據發現，吸附反應近為一階反應(R2為0 99以上)，當pH值升高時，吸附速率亦隨之提高。流速固定時，當擔體填充高度增加，Tb(貫穿時間)及Te(耗竭時間)亦大幅增加；床高固定時，流速增加將造成，Tb及Te大幅縮短。實驗數據線性迴歸後，以BDST方程式適於表現吸附動力模式。 流體化床結晶法實驗中，不論是否控制出流水pH值，CT/Pb加藥比過高或太低時，去除率皆會下降。流速過高時，擔體表面結晶物會磨擦脫落，而流速過低則因反應動力不足，皆會造成出流水鉛濃度偏高。出流水pH控制於5-7範圍，去除效率最高。 本研究以SEM-EDS進行觀察與分析，改質蟹殼表面微孔結構更加明顯；經流體化結晶之擔體，其表面結晶物則比反應前更為緊密，鉛的成份比例也增加，表面層被結晶物所覆蓋，原蟹殼成份中Ca的測值為零。[[abstract]]Abstract Applying recycled industrial solid waste to pollution control has be widely investigated which is considered as a clean technology able to solve both concerned environmental problems including pollutants removal and solid waste disposal It has been reported that the chitosan converted from chitin can be applied as an efficient adsorbent for varieties of heavy metals It also has been found that crab shell one of the most common seafood wastes contains natural chitin abundantly Accordingly this study attempts to apply wasted crab shell as an adsorbent for removing lead ion from artificial lead-containing wastewater in a fluidized bed reactor in which lead precipitates and crystallizes on the crab shell surface Many tasks were conducted in this study for evaluating the lead adsorption capacities by both original crab shell and NaOH treated crab shell which includes conducting both lead adsorption experiments in both batch and fluidized reactors and Several operational parameters such as solution pH level water flow velocity and the presence of carbonate in the adsorption system were tested in the study Some important experimental results were observed in this study The results indicate high adsorption capacity of lead in high pH-level conditions and the NaOH-treated crab shell achieving higher adsorption capacity than the original crab shell The adsorption capacity of lead by NaOH-treated crab shell can be as high as 714 3 mg-Pb/g-crab as solution pH= 5 0 It is also observed that the lead adsorption by the crab shell basically follows a first-order reaction relationship based on adsorption dynamic analyses Higher adsorption rate is observed in higher pH conditions For the adsorption of lead in the fluidized bed reactor the lead removal ratio is affected by solution pH water flow rate and added concentration of Na2CO3 It has better to control solution pH between 5 and 7 and the molar ratio of carbonate to lead equal to 6 0 Observation and analysis by SEM-EDS NaOH modified crab shell surface cellular structure to be more obvious the surface of media after the fluidized crystallization is more tighter than the original shell The component proportion of lead increases the surface layer is covered by the crystal but the component Ca in original crab shell is very trac