Maintenance energy requirement

Ideally, we would wish for high substrate uptake in the absence of growth and in the absence of maintenance energy requirements. Since aerobic micro-organisms control their rates of substrate uptake when growth is slow or absent, manipulation of substrate uptake may be necessary. 

We have seen that both the maintenance energy requirement and the P/O quotient of the process micro-organism influences the rate of product formation. In the following sections we will consider how these two factors can be determined, together with the maximum biomass yield. 

Determination of maintenance energy requirement and maximum biomass yield... 

Maintenance energy requirements can be defined in terms of rate of substrate consumption per unit of biomass for maintenance this is known as the maintenance coefficient (m). 

This discrepancy is due to die fact that other products such as formate, are formed in very small amounts as byproducts of the metabolic routes leading to L-phenylalanine and polymer synthesis. Of course, part of die glucose is also used for die metabolic activities in the micro-organism necessary to maintain the cells in a viable state, this is termed the maintenance energy requirement... 

Few models include the effects of in situ gas formation on the fluidization properties of the reactors this improvement, along with improvements in other areas, such as inclusion of improved structured models of microbial kinetics or inclusion of maintenance energy requirements or the effects of suspended cells on the reaction rate, might produce more accurate models, though it is unclear at this point whether the increased complexity would be justified. 

The maintenance energy requirement rate, /mam[, of the suspended biomass is as follows ... 

If Ss is not sufficiently available to support the biomass maintenance energy requirement. 

Maintenance energy requirement Hydrolysis, fraction 1 (fast) -1 1 -1 -1 1 Equation b Equation c,n= 1... 

Before adding the readily biodegradable substrate, the maintenance energy requirement of the active biomass should ideally correspond to the amount of readily biodegradable substrate produced by hydrolysis of the slowly biodegradable COD fraction, i.e., an equilibrium corresponding to an almost constant OUR must be seen. 

This means that, under conditions of catabolite limitation, Eqn. 70 will give the most easily interpretable relation. Conversely, under anabolite limitation, Eqn. 71 will be the most practical. Both equations predict a linear relation between rate of substrate utilization and biomass formation. Furthermore, the relation between catabolism and anabolism has a positive intersection point with the ordinate. This positive catabolism at (extrapolated) zero growth rate has been interpreted as maintenance energy requirement [52]. It follows naturally from the simple description of bacterial metabolism as we have used it here. 

The maintenance energy model (Pirt, 1975) states that energy consumption can be divided into that needed for growth and that needed for maintenance. Through the use of yield ratios, an empirical expression can be written for a specific substrate consumption rate as a function of the maintenance energy requirement and the specific production rates of all products that require the consumption of that substrate. This type of model is useful in microbial systems, for which there... 

Suggested calorie intakes for maintenance and normal growth of healthy infants and children are shown in Table 135-10. For children, these maintenance energy requirements are approximately 150% of basal metabolic rate (BMR) with the additional calories... 

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