Batch culture is a closed culture system which contains an initial, limited amount of nutrient. The inoculated cuture will pass through a number of phases, as illustrated in Fig. 2.1. After inoculation there is a period during which it appears that no growth takes place; this period is referred to as the lag phase and may be considered as a time of adaptation. In a commercial process the length of the lag phase should be reduced as much as possible and this may be achieved by using a suitable inoculum, as described in Chapter 6. Following a period during which the growth rate of the cells gradually increases, the cells grow at a constant, maximum, rate and this period is known as the log, or exponential, phase. The exponential phase may be described by the equation:
where x is the concentration of microbial biomass, t is time, in hours and fx is the specific growth rate, in hours-1. On integration equation (2.1) gives:
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