高濃度酚在微孔性中空纖維模組中生物降解之程序與動力學

Biodegradation Process and Kinetics of High-Strength Phenol in Microporous Hollow Fiber Modules

鍾翠萍(Tsuey-Ping Chung)

指導教授 ： 莊 瑞 鑫

元智大學/工程學院/化學工程與材料科學學系/博士(2004年)

摘要

實驗細菌Pseudomonas putida CCRC 14365經培養後，自五個不同的生長時期（遲滯期、對數期、後指數期、靜止期及死亡期）收集作實驗，量測各生長期細菌之比生長速率及酚之比降解速率。結果發現細胞經由100 mg/L的酚活化誘導後，能在15至26小時內完全降解100 mg/L的酚，若未經酚化合物的誘導，則需23至33小時才能完全降解。再者，從後指數期收集的細胞，不論是否經過誘導適應過程，均能最有效率的完全降解酚化合物。與未受誘導的細胞相較之下，經過誘導的細胞雖然比生長速率較大，其比降解速率卻較小。也就是說，實驗前經過受質誘導的細菌能長出更高密度的細菌生物量，從而加強分解效率，儘管比降解速率並不高。
有關P. putida CCRC 14365在懸浮態系統中降解酚化合物及細胞生長動力學的情況，由於存在基質本身的毒性抑制效應，懸浮態細胞完全降解酚濃度大約到400 mg/L，最高能忍受約600 mg/L，但無法完全降解。在動力學方面，懸浮態細胞降解酚有基質抑制的現象，在酚濃度25-600 mg/L下，求得Haldane model之動力參數值。由於使用傳統的Haldane model預測批次反應中的細胞生長量及酚降解程序，其準確度不理想。於是進一步推演出Two-phase model，它植基於Haldane model，以細胞生長期中的兩個時期，包含遲滯期及對數期的代謝生長模式。它的有效性經由實驗數據驗證，結果顯示本研究所開發的Two-phase model可以更準確的預測批次反應中的細胞生長量及酚降解動態，特別是亦涵蓋了遲滯期轉變到對數期之間的過渡狀態，解決了使用傳統Haldane model的最大困擾。
比較P. putida CCRC 14365在懸浮態系統及藻酸鈉固定化系統中降解酚化合物的情況，發現兩個系統在酸鹼值(pH)及溫度效應的趨勢相似。由於基質的毒性抑制效應，藻酸鈉固定化系統雖然降解速率較低，但可忍受酚的濃度高達1000 mg/L。固定化細胞在85-400 mg/L酚濃度範圍，能看到降解過程之中間產物（鄰苯二酚），但是在懸浮態及較低與較高濃度之固定化實驗下均不明顯。推論酚傳輸進入藻酸鈣固定化材質時，受到擴散延遲的影響，這可能有助於中間產物的探求。
建立微孔性中空纖維膜生物反應器模組 (HFMBR) 以探討P. putida對酚之生物降解，模組中的聚丙烯纖維先經過乙醇潤濕為親水性膜。主要探討流速、不同酚濃度及分散劑（四鈉焦磷酸鹽）等對降解速率及細胞生長之影響。結果顯示，當細胞被中空纖維膜固定化及與廢水端分開時，實驗一開始約10%的酚就被中空纖維吸附，P. putida細胞能在92小時內完全降解3000 mg/L的酚。四鈉焦磷酸鹽分散劑經酚降解及電子顯微鏡檢實驗證實，其對生物反應器中殼側細菌端控制薄膜上生物積垢有明顯的效果，減少生物膜上的積垢可以加速酚的降解效率。在中空纖維生物反應器中降解的過程發展，將依不同濃度範圍分階段充分討論。在高初始酚濃度的降解反應中,酚通過薄膜的質傳並非限制步驟,伴隨細胞生長的降解反應才是其限制步驟。為瞭解中空纖維膜生物反應器模組中酚的傳送，算出從管側穿過薄膜至殼側酚的總質傳係數的理論值及實驗值。建立中空纖維生物反應器的生物膜質傳模式，以零次方平板模式(zero-order flat sheet model) 預測反應器的去除率其修正係數 R2 可達0.94。對這個零次方平板模式各個重要參數作敏感度測試，發現去除率與生物膜的相關參數有很強的函數關係，尤其是當生物膜的生物量密度及擴散係數下降時，去除率會呈現線性下降的趨勢。
當以懸浮態、藻珠固定化及中空纖維固定化三個反應系統作比較時，在較低的酚濃度(< 400 mg/L)，基質抑制不嚴重的情況下，以懸浮態系統處理含酚廢液較有利。然而，只有固定化系統能忍受高於600 mg/L的酚濃度，特別是在高於1000 mg/L 酚濃度時，這套中空纖維生物反應器中的固定化細胞，能先將酚降解至可忍受的基質濃度，接著伴隨著反應器中快速生長的懸浮態細胞，可以更快速地將酚完全降解。中空纖維生物反應器系統同時具有基質分配控制能力及含有提高耐受力的生物膜，這兩種功能使HFMBR有效率的降解高濃度的酚有機污染物。

關鍵字

酚化合物 ； 生物降解 ； 比生長速率 ； 降解速率 ； 懸浮態系統 ； 基質抑制 ； 酚降解程序 ； 動力學 ； 藻酸鈣固定化 ； 微孔性中空纖維膜 ； 生物反應器模組 ； 生物積垢 ； 生物膜 ； 質傳模式 ； 零次方平板模式 ； 基質分配控制

並列摘要

The specific growth rates of Pseudomonas putida CCRC 14365 abstracted from five different phases (the lag, log, late-exponential, stationary, and death), along with its specific rates for phenol degradation, were determined. The cells harvested from the late-exponential phase were the most effective for complete consumption of phenol.
Phenol degradation by P. putida CCRC 14365 and cell growth kinetics were detected in the free suspension systems. Due to the substrate inhibitory effect, the free cells could completely degrade phenol only up to about 400 mg/L within 43 h. However, free cells have poor degradation efficiency when initial concentration up to 600 mg/L. The growth kinetics of free cells for degradation of phenol in the concentration range 25~600 mg/L was described by the Haldane model.
A simple two-phase model, originated from the Haldane model, was presented to predict the behavior of batch culture operations. The model was based on the two regions of metabolic activity: the lag phase and the log phase. In contrast to the one-phase Haldane model, it was demonstrated that the proposed two-phase Haldane model much better predicted the dynamics of biomass growth including the transient region from the lag to the log phases.
Phenol degradation by P. putida CCRC 14365 were compared between the free and Ca-alginate gel-immobilized systems. It was shown that the trends of the effects of pH and temperature on phenol degradation were similar for both free and immobilized cells. Due to the substrate inhibition effect, the free cells could degrade phenol only up to about 600 mg/L. The immobilized cells could tolerate a higher level up to 1000 mg/L, though the degradation rate was slower. Unlike the case of free cells, an intermediate catechol was detected using the immobilized cells at a phenol level of 85~400 mg/L. This implied that the occurrence of medium diffusion resistance in the immobilized systems, which retarded the degradation reaction, might be useful for detection of the intermediates.
The degradation of phenol (100-3000 mg/L) by the cells of P. putida CCRC 14365 in a microporous hollow fiber membrane bioreactor (HFMBR) was studied, in which the polypropylene fibers were pre-wetted with ethanol. The effects of flow velocity, pH, the concentrations of phenol and the added dispersive agent tetrasodium pyrophosphate on phenol degradation and cell growth were focused. It was shown that about 10% of phenol was sorbed on the fibers at the beginning of the degradation process. The cells of P. putida fully degraded 3000 mg/L of phenol within 92 h when the cells were immobilized and separated by the fibers. SEM studies showed that the biofilm become thinner on addition of TSP. The effect of thinner biofilm company with more free cells resulting from TSP addition is more advantageous for biodegradation. The process development in HFMBR system was discussed. Judging from the high residual phenol concentration in shell side of HFMBR, it obvious that the mass transfer of phenol across the membrane was sufficient to supply the carbon source to the microorganism and that the bacterial growth was the limiting-step for phenol biodegradation. The mass transfer of phenol across the membranes was estimated by theoretical and experimental study. Biofilm model of the HFMBR were created. The zero-order flat sheet model fit the data well, correlation coefficient R2 = 0.94. Sensitivity analysis of the zero-order model indicated that removal was a strong function of the biofilm phase. It is especially for biomass density and also of the biofilm diffusion coefficient, with both values downward resulting in linear decreased removal rates.
When comparing with free and Ca-alginate gel-immobilized systems, it was more advantageous to treat the solution in a suspended system at relatively low phenol levels (< 400 mg/L), where substrate inhibition was not severe. However, only immobilized cells can tolerate higher phenol levels (> 600 mg/L). Especially higher than 1000 mg/L phenol levels, HFMBR system, which combined the functions of substrate partition control and the tolerance enhancement by biofilm, could be applied to degrade phenol down to a tolerable concentration with weak substrate-inhibition, and the followed degradation alternately accompanied by a suspended culture would result in larger degradation rate.

並列關鍵字

specific growth rates ； Pseudomonas putida CCRC 14365 ； phenol degradation ； kinetics ； suspension systems ； substrate inhibitory effect ； Haldane model ； Ca-alginate gel-immobilized systems ； microporous hollow fiber ； membrane bioreactor ； degradation process ； biofilm ； mass transfer ； zero-order flat sheet model ； substrate partition control