Abstract
Green technology is becoming more of a driving force in most industrial sectors because of the current demand to decrease the pollution caused by chemical processing, and the future needs to replace the environmental unsustainable hydrocarbon economy with a renewable environmentally sound carbohydrate economy. As a building block compound which is currently produced by petroleum-based process, bio-based succinic acid and its derived compounds have attracted increasing interest due to its industrial potential in cleaner production and extensive applications, especially in food and pharmaceutical industries.In the format of Project I "Enhancing platform chemical production through a novel bioreactor design", a novel in-situ fibrous bed bioreactor (isFBB) for enhanced succinic acid (SA) production by aerobic Yarrowia lipolytica PGC01003 was developed for the first time in Chapter 2. After optimization of isFBB fermentation parameters, SA productivity up to 1.46 g/L/h was achieved. The isFBB was demonstrated to have great operation stability in the long-term repeated batch fermentation. In order to decrease fermentation cost, the feasibility of using agricultural wastes and crude glycerol from biodiesel industry for SA production via isFBB fermentation was illustrated in Chapter 3. By fed-batch fermentation, the highest SA production that ever reported worldwide (209.7 g/L) was achieved. Then, the inhibition of substrate and end-products on cell growth and SA production was studied in Chapter 4. The strong tolerance of PGC01003 strain to high concentration of substrate and end-products was demonstrated, which indicates the great potential of Y. lipolyitca for up-scale production of SA. Afterwards, to further decrease SA production cost from glycerol, statistical optimization of fermentation parameters for SA production from glycerol was carried out for the first time in Chapter 5, in which a new and cost-effective fermentation process was developed in shake flasks. An increase of 84% in SA yield and 56% decrease in SA fermentation cost were resulted as compared to that obtained under the initial conditions.
The second project proposed to recycle agro-waste for SA production using engineered Y. lipolytica. Within the project, the feasibility of using glucose-based hydrolysate from fruit and vegetable waste (FVW) for SA production via engineered Y. lipolytica PSA02004 was demonstrated for the first time in Chapter 6. Hydrolysate with glucose concentration of 44.3 g/L was obtained from FVW by enzymatic hydrolysis, and SA was produced from the hydrolysate with a titer of 43.1 g/L and yield of 0.46 g/g using PSA02004. In order to reduce the downstream SA recovery cost, Y. lipolytica PSA3.0 that can produce SA from glucose at low pH was obtained by metabolic evolution of PSA02004 for the first time in Chapter 7. The evolved strain PSA3.0 was demonstrated can produce SA from YPD with a productivity of 0.52 g/L/h and yield of 0.29 g/g at pH 3.0. In addition, it could utilize glucose-rich hydrolysate from waste streams for SA production at pH 3.0.
After the accomplishment of the projects, bio-refinery for efficient and green SA production by engineered Y. lipolytica has been successfully developed. The studies presented in this thesis would promote the commercializaion process of bio-based SA and contribute to the sustainable development of green and circular economy.
| Date of Award | 3 Aug 2018 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Sze Ki Carol LIN (Supervisor) |