Developing the control criterion for a continuous culture of microorganisms

A short survey and a critical analysis of previously proposed criteria for growth control of populations of microorganisms in the chemostat are presented. Based on the analysis of a mathematical model of the steady state of a microbial population in the chemostat, an adequate control criterion is suggested, along with a method to identify the corresponding control factors. The new control criterion is expressed as a product of the factor transformation coefficient and the sensitivity coefficient (SC) of the biomass with respect to the change in the factor at the chemostat inlet (hereinafter, the biomass SC). The control criterion determines the strength of the control exerted by a factor. The method of determining control factors consists in experimental determination of the real SCs for factors and the biomass and calculation on this basis of the corresponding ideal SCs, assuming constant factor transformation coefficients. The ideal SCs are shown to add up to integer values, a constraint that we call quantization relationships. Such relationships are used to test the completeness of the list of control factors. The proposed method was applied to both our own and literature data.