| Summary: | 碩士 === 國立中興大學 === 化學工程學系所 === 105 === Petroleum-derived plastics improved people’s lives a lot, but the disposal of petroleum-derived plastics was a difficult issue that was needed to be solved. Biodegradable plastics are excellent material to replace petroleum-derived plastics because they are not only biodegradable but also renewable. In previous study, performance of Caldimonas manganoxidans was proof to be potential for industrial application, including high PHB content and high glycerol tolerance. Therefore, the effect of operation parameters after scaling up was investigated in this study, including dissolved oxygen and pH value. Glycerol was used as carbon source because it was cheap and abundant as a by-product of bio-diesel industry. High PHB content could be obtained under constant 200 rpm agitation speed, but low cell density brought out low PHB concentration which was 1.9 g/L. high biomass could be obtained with 10% dissolved oxygen, but the rapid decrease of pH seriously restricted the accumulation of PHB which was 0.43 g/L only. With the control of pH, the PHB concertation could increase from 0.48 g/L under no pH control to 4.3 g/L under pH 7. Lower PHB concentration under pH 8 was caused by the increased activity of PhaZ. Further improvement in PHB concentration was obtain with pH-stat fed-batch fermentation. The PHB concentration increased by 140% with the productivity of 0.388 g/L/h. Stopping of PHB accumulation may be inhibited by the increased glycerol concentration in medium and this could be improved by the adjustment of feeding strategy. Compared to the previous shake flask experiment, the yield of PHB remained unchanged after scaling up, which was an advantage for industrial application. The MW of PHB obtained by fed-batch fermentation was only 160±23, which was possibly caused by the long exposure to glycerol. The PHB production from bio-diesel derived glycerol (raw glycerol) was examined. 12 hours delayed growth was observed and possibly caused by the impurity of raw glycerol. The ability of producing PHB from raw glycerol is another huge advantage for industrial application.
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