Biochemical engineering deals with the processing of biological or chemical materials using enzymes or living cells as biological catalysts.
At a central position in a biotechnological process is the bioreactor. Its role is frequently dominant on the overall technical and economical performance of the process. The characteristics of the biological reaction can also affect the requirements on the other steps of the process, such as the preparation of the media and the downstream operations for product recovery and purification.
For the optimal design and control of biological reactors, the biochemical engineer can make use of the technologies and concepts developed in the field of chemical reactor engineering. Specially with respect to the more physical aspects of mixing, mass and heat transport, and to the general methodologies of reactor modelling and computer control. But when dealing with bioreactors, theories and practice have to be adapted to the peculiarities of the biotogical catalysts. Simplest are the enzymes, the protein catalysts, which, despite generally more complex kinetics, have many common features with chemical catalysts. Much more complex are the living cells. These growing and adaptive catalysts present many new challenges in reactor design and control.
During the last twenty years the area of bioreactor engineering has considerably evolved, in some cases with very significant increase in reactor activities and selectivities (1.2). Nevertheless, if compared to chemical reactors, biological reactors still suffer serious weaknesses.
First, relatively low concentrations. reaction rates and productivities, as a result of the relatively dilute culture media. Second, problems of stability with continuous processes. The scale-up and the automation of bioreactors is still in its infancy, due to insufficient understanding of the rate limiting steps and a severe lack of on-line sensors. Sterility is an additional constraint on the design of bioreactors. Safety and toxicity problems, and the associate legal complexities and constraints can also be important in some cases.