Oxygen uptake rate in microbial processes: An overview

In aerobic process oxygen must be continuously supplied in order to achieve acceptable productivities, Since the role of oxygen in microorganism growth and its metabolism is of vital importance, both the oxygen consumption by the cell and the oxygen transfer rate (OTR) into the system have to be understood. The main function of a properly designed bioreactor is to provide a controlled environment and a concentration of nutrients (dissolved oxygen, mainly) sufficient to achieve optimal growth and/or optimal product formation in a particular bioprocess. Dissolved oxygen in the broths is the result of a balance of its consumption rate in the cells, and the rate of oxygen transfer from the gas to the liquid phase. Monitoring dissolved oxygen in the broth is mandatory because often oxygen becomes the factor governing the metabolic pathways in microbial cells. In this work the oxygen uptake rate (OUR) in different fermentation broths is examined. Experimental techniques have been compiled from the literature and their applicability to microbial processes reviewed. The reciprocal influence of OUR and OTR is presented and an analysis of rate-limiting variables is carried out. Mathematical models are a fundamental tool in bioprocess design, optimisation, scale-up, operation and control at large-scale fermentation. Kinetic models describing aerobic bioprocesses have to include an oxygen balance taking into account OTR and OUR. Many different specific rate expressions for cell growth, substrate consumption, product formation and oxygen uptake have been developed and incorporated in the models, and simulations of different bioprocess have been carried out. Some of them are presented here.