Chapter 2 and the products do not have rigid quality specifications; rather they are marketed on the basis of overall product performance criteria 2.5 Modes of operation of bioprocesses batch mode As you might have already gathered, the majority of industrial fermentations are batch processes. In closed batch systems, the growth medium is inoculated with cells and growth and product formation is allowed to proceed until the required amount of conversion has taken place. After harvesting the culture the vessel is cleaned, sterilised the feedstock prior to inoculation, as is done in closed batch fermentations, is undesirable and it is preferable to incrementally add the carbon source as the fermentation proceeds. Such a process is known as fed-batch culture and the approach is often used to extend the life cultures are considered further in Section 2.1 res and thus product yields; fed-batch fetime of batch cul continuous The alternative to batch mode operation is continuous operation. In the continuous mode mode there is a continuous flow of medium into the fermentor and of product stream out of the fermentor. Continuous bioprocesses often use homogenously mixed whole cell suspensions. However, immobilised cell or enzyme processes generally operate in continuous plug flow reactors, without mixing(see Figure 2.1, packed-bed reactors) ∏I Complete the following statements by filling in the missing words Conditions change with in batch fermentations but with distance along the reactor in reactors conditions are maintained in continuous suspended fermentations The missing words aretime,, plug flowand'constant Advantages of the batch mode over the continuous mode of operation include several different products can be made using the same bioreactor, thus providing operational flexibi genetic stability of the process organisms is not as great a problem the risk of contamination is relatively small; it is possible to identify all the material involved in making a particular batch of product, which may be important in quality control Advantages of the continuous mode over the batch mode of operation include: the proportion of the down-time(time spent preparing the bioreactor for a new run) to fermentation time is relatively small they are relatively easy to operate and control when in steady state; e demand on services are relatively constant during operation the product streams have a relatively constant composition (it may be difficult to prevent batch-to-batch variability); waste products of metabolism are unlikely to accumulate to inhibitory levelsChapter 2 batch mode continuous mode advantages of batch mode advantages of continuous mode and the products do not have rigid quality specifications; rather they are marketed on the basis of overall product performance criteria. 2.5 Modes of operation of bioprocesses As you might have already gathered, the majority of industrial fermentations are batch processes. In closed batch systems, the growth medium is inoculated with cells and growth and product formation is allowed to proceed until the required amount of conversion has taken place. After harvesting the culture the vessel is cleaned, sterilised and filled with fresh medium prior to inoculation. For some processes, addition of all the feedstock prior to inoculation, as is done in closed batch fermentations, is undesirable and it is preferable to incrementally add the carbon source as the fermentation proceeds. Such a process is known as fed-batch culture and the approach is often used to extend the lifetime of batch cultures and thus product yields; fed-batch cultures are considered further in Section 2.7.4. The alternative to batch mode operation is continuous operation. In the continuous mode there is a continuous flow of medium into the fermentor and of product stream out of the fermentor. Continuous bioprocesses often use homogenously mixed whole cell suspensions. However, immobilised cell or enzyme processes generally operate in continuous plug flow reactors, without mixing (see Figure 2.1, packed-bed reactors). n Complete the following statements by filling in the missing words. Conditions change with in batch fermentations but with distance along the reactor in reactors. conditions are maintained in continuous suspended fermentations. The missing words are 'time', 'plug flow' and 'constant'. Advantages of the batch mode over the continuous mode of operation include: several different products can be made using the same bioreactor, thus providing operational flexibility; genetic stability of the process organisms is not as great a problem; the risk of contamination is relatively small; it is possible to identify all the material involved in making a particular batch of product, which may be important in quality control. Advantages of the continuous mode over the batch mode of operation include: the proportion of the down-time (time spent preparing the bioreactor for a new run) to fermentation time is relatively small; they are relatively easy to operate and control when in steady state; the demand on services are relatively constant during operation; the product streams have a relatively constant composition (it may be difficult to prevent batch-to-batch variability); waste products of metabolism are unlikely to accumulate to inhibitory levels