| Summary: | 碩士 === 國立成功大學 === 化學工程學系碩博士班 === 94 === The subject of the study is to increase degradation capability of organic contaminants using an indigenous rhizobium Ralstonia taiwanensis (a genetically relared strain to R. eutropha). Previous studies indicated that Ralstonia taiwanensis was well adapted to remediate several toxic organic and inorganic contaminants. We selected phenol herein as the target pollutant to reveal the performance of biodegradation for R. taiwanensis. Phenol is chemically stable and recalcitrant to several microorganisms, except R. taiwanensis. Due to the toxicity potency of phenol, substrate inhibition effect took place when phenol was used as a growth nutrient for R. taiwanensis. At higher concentrations of phenol, phenol degradation was lagged and degradation rate was lower. To achieve optimal phenol degradation, substrate inhibition of phenol must be avoided inevitably as the basic operation strategy.
For global optimization to industrial applications experimental design also suggested that the optimal temperature of 37℃, agitation at 200 rpm, neutral pH 7, dissolved oxygen less than 55% for operation. In addition, the most feasible medium for high density culture and phenol degradation of R. taiwanensis should include trace metal elements at FeSO4．7H2O 7 mg L-1、MgSO4．7H2O 580 mg L-1、CaCl2 49.15 mg L-1、MnSO4．H2O 0.385 mg L-1、CoCl2．6H2O 0.2 mg L-1、CuSO4．2H2O 0.093 mg L-1.
To prevent substrate inhibition of phenol in order to reach the goal of the most economically-viable biodegradation fed-batch cultures with a pre-determined exponential feeding strategy were carried out as phenol degradation was strongly growth-dependent. This study also used one-step and two-step exponential feeding strategy to enhance phenol degradation and have zero accumulation of phenol.
After deciding the optimal culture conditions, using the principle of fed-batch culture to make feeding rate equipping degradation rate. So the concentration of phenol in the medium will close to zero. By this way it can avoid substrate inhibition. The best strategy for avoiding substrate inhibition is exponential feeding strategy. We use mass-balance to calculate the feeding curve. The curve is F = F0emt，m = α mmax and when α= 0.55(m = 0.286 h-1) can get the shortest degradation time. And then we can construct the optimal feeding model for Ralstonia taiwanensis degrading phenol.
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