| Summary: | 碩士 === 逢甲大學 === 化學工程學系 === 88 === A genetically modified Escherichia coli NO3 strain was used to study the kinetics of azo-dye decolorization. The genetic manipulation and screening of the decolorizing strain was demonstrated. The effects of medium composition, biocatalyst types (suspended or immobilized), and metabolites on decolorization kinetics were investigated. The efficiency of repeated uses of the biocatalyst was also evaluated to assess its feasibility in practical application for color-removal of dye-containing wastewater.
The results show that the recombinant plasmid harbored by E. coli NO3 may not contain genes encoding for the decolorization ability, which could originate from genes located on the chromosome. The medium composition is critical to the decolorization efficiency. It was found that decolorization with LB broth was the most effective. The optimal decolorization rates for suspended and immobilized cells were 92.6 and 28.4 mg/g cell/h, respectively, both occurred at a dye concentration of 2000 mg/L. This indicates that the strain can be operated at high dye concentrations for color removal. Decolorization was inhibited as the temperature was higher than 47oC. The suspended cells of E. coli NO3 exhibited better decolorization ability at a pH range of 7-9, while decolorization with the immobilized cells were insensitive to pH. Decolorization could not take place when the dissolved oxygen level exceeded 0.5 mg/L. In general, the decolorization rate of suspended cells was superior to that of immobilized ones. After repeated batch operations, the specific decolorization rate was enhanced to nearly 100 mg/g cell/h, probably due to the presence of decolorization metabolites. Long-term repeated batch tests conducted in a 500-mL bioreactor showed that E. coli NO3 exhibited excellent stability as it maintained high decolorization rates after consecutive operation for 48 days.
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