A bioreactor, in short, is a vessel designed to facilitate a biological reaction or transformation.

It encompasses a wide range of biological systems including enzymes, microorganisms, animal cells, plant cells and tissues. The core mission of a bioreactor is to provide an optimized external environment for these biological systems to meet their growth and production needs in order to achieve an efficient output of the biological process. In this process, there are intricate interactions between biological systems and physical and chemical factors.

In order to build bioreactors that are suitable for specific biological processes, we must probe deeply into the properties of biological systems, such as cell growth, metabolism, gene manipulation, and the expression of proteins or other products, to clarify the cellular demands on the physical and chemical environment. As the understanding of biological systems has deepened, a wide variety of bioreactor types and configurations have been developed and refined.

At the same time, control of bioreactor operating parameters, such as dissolved oxygen concentration, pH, temperature, degree of mixing, and nutrient supplementation, is critical for maintaining the function of living cells or enzymes. Given that bioreactors integrate two bodies of knowledge, molecular biology and process engineering, and that they play a central role in biological processes, the term "bioreactor engineering" is used in the systems science context, as opposed to "bioreactor" or the traditional term "fermenter". The term "bioreactor engineering" is more appropriate than "bioreactor" or traditional "fermenter".

Bioreactor design and application

Bioreactors occupy a central position in many biological processes. When designing a bioreactor system, it is first necessary to define the ultimate goal of the bioprocess, which is usually determined by market demand or a beneficial biotransformation process. Thanks to the rapid advances in recombinant DNA technology and genome sequencing, the same product or bioprocess can be realized by different biological systems, such as microorganisms, plant cells, animal cells or enzymes. Therefore, it is crucial to understand the gene expression, metabolic manipulation and biological reaction pathways of these systems. Next, we need to determine the media requirements needed for the efficient operation of the selected biological system, which can be achieved through chemometrics and experimental data. Kinetic studies, on the other hand, help to reveal biological reaction rates, including cell growth, substrate consumption, product synthesis, and by-product formation. The impact of the physical environment on biological performance should also not be overlooked, with factors such as shear stress, mass transfer, mixing, pH and temperature. In addition, downstream process requirements are also factors that must be considered when designing a bioreactor.

A variety of factors need to be weighed in selecting the type of bioreactor that is suitable for a particular biological process, such as oxygen transfer, mixing, shear, operational stability and reliability, scale-up, and cost. Characterization of the selected bioreactor and optimization of the mode of operation are essential to improve biological performance. An efficient bioreactor system is not possible without the cooperation of its control and support systems. The bioreactor system, although important, must be tightly and efficiently integrated with the overall production system. Therefore, other process requirements and constraints need to be considered when designing and operating a bioreactor.

The purpose of this chapter is to introduce a variety of bioreactor systems and to provide an overview of recent advances in their design, control, and application. Despite our attempts to categorize them based on their unique properties, there is still some crossover between different bioreactors. Given the breadth of the bioreactor engineering field, it is difficult to cover everything in this chapter, but we hope to provide the reader with a comprehensive understanding.