Production Of Bacterial Cellulose From Different Potential Cost Effective Feedstocks In A Submerged Mechanical Agitating Fermentor

Bacterial cellulose (BC) is a class of extracellular polysaccharide secreted by some microbes. As with many excellent physical and chemical properties, it has a great potential in applications in many fields, such as food, paper, pharmaceutical and audio devices. Presently, the industrial production of bacterial cellulose remains elusive, which greatly limits the wide application of BC. The biggest bottleneck in industrial production is the high production cost, especially carbon source. Therefore in order to achieve industrial production of bacterial cellulose, to find one or several inexpensive carbon sources is becoming an urgent thing. In this topic, cassava, sugar cane molasses, and crude glycerin were selected as carbon sources to study the difference in bacterial cellulose production. In addition, reduction of stirring shear force by adding agar in the fermentation was explored to expect to lay foundation for bacterial cellulose industrialization road accordingly.Firstly we used cassava, molasses and glycerol as carbon sources, respectively, and evaluated the influence situation through the carbon consumption rate, cell growth, dissolved oxygen rate and BC yield. In molasses fermentation and glycerol fermentation, BC yield reached4.5g/L and4.1g/L, respectively. The maximum cell concentration reached0.95×106cells/mL1.12×106cells/mL, when enzymatic hydrolyzate of cassava was used as carbon source, BC production reached6.3g/L, compared with the previous two feedstocks, increased by39.3%and52.2%, the maximum bacteria concentration reached1.94×106cells/mL, increased by104.2%and73.2%, respectively. The result indicated that cassava hydrolysate as the carbon source (40g/L) was better than the other two feedstocks, and thereafter it can be used as an ideal material in bacterial cellulose industrial production. Since bacterial cellulose has darker color which is from the sugar cane molasses and it is difficult to remove it, considering cellulose postprocess cost, treatment of molasses with active carbon was studied. The pretreatment of molasses and effect of pH on decoloration was evaluated. The result showed that decolorization rate of non-pretreated molasses was highest at pH5, but the decoloration efficiency (decolorization rate/molasses adsorption rate) was highest (3.96) at pH6.The decolorization rate of heat-acid treatment molasses was highest at pH5as well, but decolorization efficiency was4.5at pH6, which is significantly higher than the first group.Secondly, when molasses and cassava was used as carbon source, respectively, agar of different concentrations (0-0.8%) was added into the fermentation medium to study whether reduction of shear force caused by fermentation broth viscosity could affect bacteria cellulose production. This study showed that when0.2%agar was added, BC production by using cassava hydrolyzate reached a maximum of7.3g/L, obviously higher than that without any agar (6.3g/L), increased by16.4%. While molasses was used as a feedstock, the largest output was6.5g/L when0.6%agar was added, increased by up to44.9%. The results indicated that the addition of agar could increase the viscosity of the fermentation broth, thereby reduce shear forces suffered by cells, and increase bacterial cellulose production at last.Finally, pure glycerin, two crude glycerol byproducts produced in the industrial production of biodiesel, called "bio-glycerin" and "plant glycerin" were used as fermentation carbon sources, respectively, and mechanical agitation dynamic fermentation and static culture were used as well to explore the influence of types of crude glycerol and culture methods on bacterial cellulose production. The results showed that when the glycerol concentration was25g/L in static fermentation, pure glycerol, bio-glycerol and plant glycerol were used as carbon sources, BC yields were7.3g/L,6.9g/L, and3.3g/L, respectively. Taking into account the actual cost, bio-glycerol can be used as potential carbon source. While in dynamic fermentation, the BC yields were6.6g/L,5.7g/L, and3.0g/L respectively.