超濾薄膜積垢模式理論分析與驗證之研究;Theoretical Analysis and Verification of the Fouling Model for Ultrafiltration

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題名:	超濾薄膜積垢模式理論分析與驗證之研究;Theoretical Analysis and Verification of the Fouling Model for Ultrafiltration
作者:	黃韋閔;Huang,Wei-Min
貢獻者:	環境工程研究所
關鍵詞:	積垢機制;薄膜積垢;Hermia修正模式;理論分析;超過濾;fouling mechanism;Hermia modified model;membrane fouling;ultrafiltration;theoretical analysis
日期:	2012-07-29
上傳時間:	2012-09-11 18:19:06 (UTC+8)
出版者:	國立中央大學
摘要:	本研究主要目的包含：(1)藉由理論分析Hermia修正模式，了解參數對超過率通量趨勢之影響；(2)藉由實驗了解不同微粒粒徑(62、99、130和280nm)和飼水濃度(50、100和200mg/L)以及不同操作壓力(2、3和4kg/cm2)和掃流速度(0.01、0.03和0.05m/s)對超濾薄膜效能的影響；(3)藉由模擬並驗證Hermia修正模式以了解超過濾程序之積垢機制。理論分析結果顯示，各積垢模式常數對單位時間通量變化影響顯著，隨常數提高呈線性增加趨勢，可作為判斷各積垢嚴重程度之指標。實驗結果顯示，初始通量衰減速率隨粒徑減少、濃度提高而增加，表示減少粒徑、增加飼水濃度會加快薄膜阻塞趨勢，而過濾後期也有較低通量。另外，初始通量衰減速率也隨操作壓力提高而增加，而在本研究之掃流速度範圍內，則對初始通量衰減速率沒有顯著影響趨勢。此外，提高操作壓力與掃流速度可在過濾後期得到更高之過濾通量。藉由SEM觀察膜面結果顯示，提高掃流速度可減少薄膜表面生成之濾餅厚度。根據實驗結果之通量數據以Hermia修正模式模擬，發現以中等阻塞模式模擬初始通量快速衰減階段，而濾餅過濾模式模擬緩慢變化之穩定階段，可得到非常良好之模擬結果。因此，藉由中等阻塞模式和濾餅過濾模式以兩階段模擬整體通量變化，更適合解釋超過濾之積垢機制(R-square可達0.99)。實驗模擬與理論分析結果顯示，因本研究所使用之微粒粒徑皆大於膜孔，因此標準阻塞機制不會發生。此外，中等阻塞模擬常數(Ki)與初始通量衰減速率(-dJ/dt)的變化趨勢一致，故推測中等阻塞機制適合用於解釋過濾初期之積垢現象。而濾餅過濾常數(Kca)則與初始通量變化(-dJ/dt)沒有顯著的關係，所以濾餅過濾機制不足以解釋UF薄膜過濾初期之積垢機制。The objectives of this study included: (1) Through the theoretical analysis of Hermia modified model to understand the parameters that affect the trend of flux curve for ultrafiltration (UF) membrane process; (2) Carried on the experiments to understand the effects of various particle sizes (62, 99, 130 and 280nm) and concentrations (50, 100 and 200mg/L) in water as well as different operating pressure (2, 3 and 4kg/cm2) and cross-flow velocity (0.01, 0.03 and 0.05m/s) on the performance of UF process; and (3) By means of simulation and verification of Hermia modified model to understand the fouling mechanisms on UF process. The results of theoretical analysis show that the initial decline velocity of flux in per unit time (-dJ/dt) was affected significantly by the constants of the fouling modes. In general, -dJ/dt is increased linearly with the increase of the model constant that could be the indicator of the extent of fouling. The experimental results indicated that -dJ/dt was increased with the decrease of particle size and the increase of particle concentration in water. This means reducing the particles size and increasing the particle concentration of feed water would accelerate the trend of membrane blocking, which resulted in lower flux at the later period of filtration. In addition, the increase of operating pressure also increase -dJ/dt, but the variation of cross-flow velocity in the range of this study had no significant effect on -dJ/dt. However, higher flux was obtained with the increase of operating pressure and cross-flow velocity at the later period of filtration. The SEM observation of membrane surface at the end of filtration revealed that increasing cross-flow velocity could reduce the cake thickness formed on the membrane surface. Simulation of Hermia modified model based on the flux data of experimental results, it found that the flux curve could be fitted very well by intermediate blocking model for the initial fast flux decline stage and by cake filtration model for the slow change of flux at the steady stage of filtration. Consequently, using intermediate blocking model and cake filtration model to simulate the overall variation of flux by two-stage is more suitable (R-square is greater than 0.99) to explain the fouling mechanism of UF membrane filtration. The results of experimental simulation and theoretical analysis revealed that there was no standard blocking mechanism occurred in this study because the particle size used in this experiment were all larger than the membrane pore size. In addition, the change tendency of simulated constants of intermediate blocking model (Ki) was consistent with the variation of the initial flux decline velocities (-dJ/dt). Therefore, it could be predicted that the intermediate blocking mechanism is suitable to explain the fouling phenomenon in the preceding period of filtration. On the other hand, the constants of cake filtration model (Kca) had insignificant relationship with the variation of flux in the preceding period of filtration, thus the cake filtration mechanism is inadequate to explain the fouling mechanism for the beginning of UF filtration.
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