| Summary: | 碩士 === 逢甲大學 === 化學工程學所 === 90 === Abstract
Azo dyes (C.I. Reactive Red 22; RR22, C.I. Reactive Black B; RBB and C.I. Reactive Acid Yellow 72; RAY72) were decolorized by a locally-isolated bacterium (Pseudomonas luteola), an Escherichia coli mutant (E. coli NO3) and a recombinant strain (E. coli CY1) harboring decolorizing genes from Rhodoccocus sp. Decolorization kinetics and operation stability of the strains were characterized quantitatively by repeated batch processes and an modified continuous-flow stirred-tank reactor (CSTR) to assess its feasibility in practical application for color-removal of dye-containing wastewater.
The three bacterial strains were unable to decolorize RAY72 effectively due to its high bio-toxicity, while biosorption of RAY72 by the bacterial mass occurred. Decolorization of RBB by P. luteola was inefficient with only 65% conversion, while the color-removal efficiency exceeded 90% for the two E. coli strains. The NO3 and CY1 strains have similar maximum specific decolorized rate (85 mg dye g cell-1 h-1) when RBB concentration reached 1500 mg l-1 for NO3 and 1800 mg l-1 for CY1. This indicated that NO3 and CY1 could be operated in high RBB concentration. In addition, the specific decolorized rate of NO3 was more sensitive to variations in pH than CY1. Neutral and slightly basic pH values were favorable for RBB decolorization by the NO3 and CY1 strains. The specific decolorization rate increased as the temperature rose, until a sharp decrease occurred when the temperature exceeded 37 and 45oC for CY1 and NO3, respectively. A dissolved oxygen (DO) level of 0.35 mg l-1 or above appeared to significantly inhibit the activity of azoreductase for both NO3 and CY1 strains. E. coli NO3 was more stable than CY1 during repeated operations.
For the mixed-dye (RR22 and RBB) system, the color-removal efficiency exceeded 90% for P. luteola and E. coli NO3 strains. The decolorization activity of P. luteola was better than that of NO3 and could operate at higher dye concentrations. The maximum specific decolorized rate was 38000 ADMI g cell-1 h-1 and 8900 ADMI g cell-1 h-1 for P. luteola and E. coli NO3, respectively. The specific decolorized rate of NO3 was also more sensitive to pH changes than P. luteola. Slightly basic pH values were favorable for mixed dye decolorization by P. luteola and NO3 strains. In addition, when the temperature exceeded 43oC, the decolorization efficiency of P. luteola and NO3 began to descend. The dissolved oxygen (DO) level of 0.35 mg l-1 or above also led to inhibit decolorization of the mixed dye by P. luteola and NO3 strains. The results indicate that the P. luteola and E. coli NO3 strains hold excellent reusability and persistence in repetitive decolorization operations.
An anaerobic-aerobic intermittent CSTR process was used to decolorize mixed dye with E. coli NO3 strain at a hydraulic retention time (HRT) of 32, 18, and 10 h. The color-removal efficiency was around 70 ~ 80%. Under steady operation for over 117 h, the total decolorization was 10900, 18200, and 7590 (ADMI × L) for HRT=32, 18, and 10 h, respectively. After repeated operation cycles, the decolorization rate of E. coli NO3 was always higher than the original cycle. This may be attributed to the acclimation effect since the E. coli NO3 cells were repeatedly exposed to the azo dye.
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