| Summary: | 博士 === 元智大學 === 化學工程學系 === 93 === 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.
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