Study Of Morphology, Rheology And Fluid Dynamics In Avermectin Fermentation Process

In this paper, mycelial morphology and broth rheology during the avermectin fermentation process were investigated on laboratory-scale (15 L) and production-scale (150 m3) fermentor, respectively. Computational fluid dynamics (CFD) was further used to study the fluid dynamics characteristics in the fermentor. The information obtained from CFD simulation was used to analyze the relationship between fluid dynamics in fermentor and control operation during fermentation. These studies were useful for scale-up of avermectin fermentation process.Study on 15L-fermentor experiment revealed that the broth showed classic shear-thinning property, and its rheology changed during the fermentation process. Its change process can be divided into three phases:1) pre-phase (0-50 h). In this phase apparent viscosity and consistency coefficient rapidly increased and reached their max at 50h; 2) mid-phase (50-120 h). In this phase apparent viscosity and consistency began to decrease slowly and the rheology property in the fermentor was improved; 3) post-phase (120 h-fermentation over). Apparent viscosity and consistency coefficients maintained with a const value and flow field in the fermentor was stable.The micro-environment in flow field of the fermentor was simulated using CFD tools, and the results showed that there was great difference between flow field of shear-thinning fluid and Newtonian fluid. It was interesting that shear intensity in the flow field was not only dependent on impeller agitation speed but also influenced by gas flow rate and rheological properties of fermentation broth.Studies on production-scale fermentation process showed that broth rheology in this scale underwent similar three phases as in lab-scale fermentation, but mid-phase in this scale showed longer period. Morphological characters investigation showed decreasing trend for pellet diameter, roughness and perimeter of pellet. Avermectin production increased about 12.2% by changing the medium granularity (soybean pulp), which caused the improving of flow field in the fermentation.