ABSTRACT
It should be evident from the discussion and various illustrations in Chapter 2 that even in its simplest form, the representation of dynamic and steady-state behavior of a bioprocess is multivariate in nature. Even a simple unstructured kinetic representation for biomass formation would require knowledge / monitoring / prediction of a minimum of two variables, namely concentrations / amounts of biomass and at least one specie (substrate) which leads to production of cell mass. Recognizing that biomass formation is the sum total of a large number of intracellular chemical reactions, each of which is catalyzed by an enzyme, and that activity of each enzyme is very sensitive to intracellular pH and temperature, one can appreciate that this simplest black box representation would be applicable only if the intracellular pH and temperature, and therefore indirectly the culture (composite of abiotic and biotic phases) pH and temperature were kept invariant. Considering that the pH and temperature in the biotic portion of the culture and culture as a whole, if left uncontrolled, would vary with time because of the large number of intracellular chemical reactions, it is obvious that maintaining the culture pH and temperature at desired values would require addition of an acid or a base and addition/removal of thermal energy (heating/cooling) as appropriate. Thus, even in the simplest scenario where the focus in the forefront is on formation of biomass and consumption of a single substrate, one must consider in the background manipulation of rates of acid/base addition and heating/cooling to keep culture pH and temperature at the desired values.
