Interaction of mechanical stresses and productivity of biological agglomerates in stirred fermenters

本项目旨在研究搅拌发酵罐中丝状微生物所受的机械应力。在第一个资助期，建立了表征机械应力的必要方法。根据所获得的结果和开发的方法，第二次浮选的目标主要集中在三个方面：1.在第一次浮选中，以黑曲霉的发酵液为基础，开发了模型系统，并用于定量搅拌槽中的颗粒应力。模型系统将得到进一步的应用。在第二个FP中，为了更好地接近真正的培养液，同时又保证良好的重现性，将在稀释液的基础上进行碎裂实验。这一实验程序可以确保生产出更多具有相似特性的发酵液。此外，由于可以将肉汤的流变性设置在所需的水平，同时可以更容易地在稀释的肉汤中表征生物聚集物的形态，因此它允许对系统的性质进行受控设计。在几个工作包的框架内，将在该部门进行培养，并与SPP的其他小组合作，以利用对其他微生物的调查结果扩大数据库，从而使结论得以概括。在第一个FP中，在对传统搅拌器和新型搅拌器类型的基础调查中，进一步确定了对实验室和大型发酵罐具有特殊重要性的影响因素。搅拌系统结构的微小变化(例如，挡板位置)会影响槽内的流体动力学。这些影响将用第一个FP中确定的方法进行调查。传统的搅拌器类型将得到优化，新型搅拌器几何结构的开发将扩展到新的径向流搅拌器类型。多个搅拌器配置也将是研究的一部分。搅拌槽中单个生物凝聚体的应力历史分析除了对系统整体性质的宏观研究外，第一个FP中的数值工作表明，局部现象以及对反应器内单个粒子轨迹的研究为解释粒子应力的影响提供了深刻的见解和巨大的潜力。粒子沿其轨迹所经历的应力和其在特定剪切速率区域中的停留时间的特征将在第二个FP中进一步发展。在与其他小组的联合工作中，结果将与不同的生物系统和设备进行比较，并进一步深入分子水平的研究。作为调查的结果，将建立一个选择搅拌槽结构和搅拌器类型的基础，以便与当前的生物技术过程相比，能够更好地定义和控制生物技术过程的操作。

This project aims at investigating the mechanical stress acting on filamentous microorganisms in stirred fermenters. In the first funding period, the necessary methods to characterise mechanical stress were established. Based on the obtained results and developed methods, the goals set for the 2nd FP focus on three main topics:1. From cultivation broth to model solution and backIn the 1st FP, based on cultivation broths of Aspergillus niger, model systems were developed and used to quantify the particle stress in stirred tanks. The model systems will be further used. In the 2nd FP, to approach better to real cultivation broth while still ensuring good reproducibility, fragmentation experiments will be performed based on diluted broths. This experimental procedure can ensure that a larger number of broths with similar characteristics is produced. Moreover, it allows a controlled design of the properties of the system since the rheology of the broth can be set at a desired level, while the morphology of the bio-agglomerates can be easier characterised in the diluted broth. In the frame of several working packages, cultivations will be performed at the department and in cooperation with other groups of the SPP to broad the data base with results from investigations with other microorganisms, allowing a generalization of the conclusions.2. Fluid dynamic characterization of stirred tanks in diverse configurationsIn the 1st FP, during fundamental investigations of conventional and new stirrer types further influencing factors of specific importance for lab and larger scale fermenters were identified. Small changes in the configuration of the stirred system (e.g., baffle position) can influence the fluid dynamics in the tank. Such effects will be investigated with the methods established in the 1st FP. Conventional stirrer types will be optimized and the development of the novel stirrer geometries will be expanded to new radial flow stirrer types. Multiple stirrer configurations will also be part of the study.3. Analysis of the stress history of single bio-agglomerates in the stirred tankBesides the macroscopic investigation of global properties in the system, the numerical work in the 1st FP showed that local phenomena, as well as the investigation of single particle tracks within the reactor gives a deep insight and significant potential to interpret the impact of particle stress. The characterization of the stress experienced by a particle along its track and its residence time in a region of specific shear rates will be further developed in the 2nd FP. In a joined work with other groups, the results will be compared to different biological systems and apparatuses and further investigated down to molecular level.As outcome of the investigations a base for the choice of stirred tank configurations and stirrer types will be built, to allow a better defined and controlled operation of biotechnological processes in comparison to the current ones.