| Bacterial cellulose (BC) is a natural nano-biopolymer synthesized by some strains of bacteria. Due to its unique physical and chemical properties, BC has a widely industrial applications. The biggest restriction in commercial applications of bacterial cellulose is low productivity. Considering the most popular fermenter in industry is aerated and agitated fermentation tank, the influence of impeller types under aerated and agitated culture was researched in this paper. Ten different types of agitators and combinations were compared in order to select an optimal one for industrial scale production of BC. Then the stirring speed of the impellers was investigated in order to improve the production of BC. Last Com steep liquor (CSL) and cassava hydrolysates were used as feedstock for BC production to find out weather it was an effective way for industrial production of BC.In the research of seven simple impellers, two small impellers-Arrow vanes disc turbine and Slanting blade (big)-and two big ones-Frame blender and Helical ribbon-were suit for BC production. The BC yield were respectively2.7g/L,3.6g/L,3.7g/L and4.5g/L. Then the influence of pH was researched, with Arrow vanes disc turbine and Slanting blade (big) for example, the BC yields were increased by80%and60%when then pH was maintained at5during the fermentation process, up to5.1g/L and5.9g/L. Then Arrow vanes disc turbine and Slanting blade (big) were combined to construct double-layer configurations to be continue searched, and Twin slanting blades (big) is the most effective impeller for BC fermentation, the BC yields were increased to10.3g/L, which is73%more than the single Slanting blade (big). Additional during the dissolved oxygen tests the double-layer impellers and big impellers showed advantages in mixing level, especially in high apparent viscosity conditions at low shear rates.Then stirring speed was researched. It was found that BC yield increased when stirring speed increased from low to high during the fermentation process. For small impellers Arrow vanes disc turbine and Slanting blade (big) the BC yields increased by21.7%and10.1%, the stirring speed regulation method was:200rpm in0～24h,300rpm in24～96h,400rpm after96h. For other big impellers and double-layer impellers-Frame blender, Helical ribbon, Twin arrow vanes disc turbines, Twin slanting blades (big) and Slanting blade (big)+arrow vanes disc turbine-the BC yields increased by58.8%,4.7%,6.1%,5.5%and5.7%, the stirring speed regulation method was:100rpm in0～24h,150rpm in24～96h,200rpm after96h. Among them Twin slanting blades (big) have the highest BC yields,10.8g/L. Frame blender is the second with a BC yield of9.7g/L. The biomass and BC production rate during the whole fermentation process showed that BC synthesis and cell growth was synchronous coupling, and the cell growth process was slightly earlier than cellulose synthesis. It also showed when stirring speed was regulated the delay time of cells growth was shortened, and the growth speed was faster in the logarithmic phase, and the highest biomass was increased. In addition, the biomass did not show obvious decline phase under this condition.Finally, com steep liquor (CSL) and cassava hydrolysates was used to produce BC with stirring speed regulation strategy in a fermeter equipped with Twin slanting blades (big) impeller. When CSL was used as nitrogen source the yield of BC reached9.2g/L. Although the yield was less than that of peptone and yeast extract as nitrogen source (10.8g/L), from an economic point of view, the cost of CSL was only15%. When cassava hydrolysates was used as carbon source the yield of BC reached11.7g/L, which is8%higher than that produced with glucose as carbon source. All of these showed that both CSL and cassava were potential cost-effective feedstocks. When CSL and cassava hydrolysates were used together to produce BC, the yield reached10.1g/L, due to its high performance but low cost, they should be capable of being widely used in production of BC in future. |
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