Chapter 3 D(h") D(hr" re 3.2 Theoretical relationships for(a)qs against dilution rate and for(b)Yp inst dilution rate. The micro-organism is grown aerobically in a nitrogen limited chemostat These observations can be explained by considering the substrate uptake rates growth rates there is relatively little difference between the organisms po substrate uptake rate and the substrate requirement for growth. However, at low growth rates relatively little substrate is required for growth but the potential substrate uptake rate is unaltered-this means that the organism can channel more of its substrate to product Can you think of a disadvantage of operating a process at low dilution rate? High productivities at low dilution rate would require expression of substrate uptake rates near their potential maximum tight control of respiratory activity to ensure that substrate is converted to product and not to co 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.46 Chapter 3 Figure 3.2 Theoretical relationships for (a) qs against dilution rate and for (b) Yps and YvS against dilution rate. The micro-organism is grown aerobically in a nitrogen limited chemostat culture. These observations can be explained by considering the substrate uptake rates. At high growth rates there is relatively little difference between the organisms potential substrate uptake rate and the substrate requirement for growth. However, at low growth rates relatively little substrate is required for growth but the potential substrate uptake rate is unaltered - this means that the organism can channel more of its substrate carbon into product. n Can you think of a disadvantage of operating a process at low dilution rate? The main disadvantage is that, although high yields of product might be achieved, it is difficult to achieve high productivities (kg product m-3 h-'1. High productivities at low dilution rate would require: expression of substrate uptake rates near their potential maximum; tight control of respiratory activity to ensure that substrate is converted to product and not to COZ. 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