Fermentors enzyme reactions

Bioreactors that use enzymes but not microbial cells could be regarded as fer-mentors in the broadest sense. Although their modes of operation are similar to those of microbial fermentors, fed-batch operation is not practiced for enzyme reactors, because problems such as excessive cell growth rates and resultant high oxygen transfer rates do not exist with enzyme reactors. The basic equations for batch and continuous reactors for enzyme reactions can be derived by combining material balance relationships and the Michaelis-Menten equation for enzyme reactions. 

Reactions of cell growth or those using immobilized enzymes are instances of gas-liquid-solid reactions. In principle, accordingly, any of the types of reactors described in Section 8.3 could be employed as fermentors. Mostly, however, mechanically agitated tanks are the type adopted. Aeration supplies additional agitation as well as metabolic need, and moreover sweeps away C02 and noxious byproducts. 

Bioreactors are the apparatus in which practical biochemical reactions are performed, often with the use of enzymes and/or living cells. Bioreactors that use living cells are usually called fermentors, and specific aspects of these are discussed in Chapter 12. Ihe apparatus applied to waste water treatment using biochemical reactions is another example of a bioreactor. Even blood oxygenators, that is, artificial lungs as discussed in Chapter 15, can also be regarded as bioreactors. 

As most biochemical reactions occur in the liquid phase, bioreactors usually handle liquids. Processes in bioreactors often also involve a gas phase, as in cases of aerobic fermentors. Some bioreactors must handle particles, such as immobilized enzymes or cells, either suspended or fixed in a liquid phase. With regard to mass transfer, microbial or biological cells may be regarded as minute particles. 

A number of selective-screening methodologies have been devised that have allowed isolation of a series of hyperproducing and catabolite repression-resistant mutants of T. reesei. Yields of cellulase of 15 units/ mL under controlled fermentor conditions have been achieved with both Rut-NG14 and Rut-C30. Quantitative reaction of Rut-NG14 enzyme preparation with purified antibodies to cellobiohydrolase shows that in this mutant, the cellobiohydrolase is specifically hyperproduced relative to the rest of the enzymes in the cellulase complex. Rut-C30, which was derived from Rut-NG14, shows resistance to catabolite repression for... 

Where S, G, X, E and Enz are respectively the starch, glucose, cells, ethanol and enzyme concentrations inside the reactor, Si is the starch concentration on the feed, F is the feed flow rate, V is the volume of hquid in the fermentor and (pi, (p2, (ps represent the reaction rates for starch degradation, cells growth and ethanol production, respectively. The unstructured model presented in (Ochoa et al., 2007) is used here as the real plant. The ki (for i=l to 4) kinetic parameters of the model for control were identified by an optimization procedure given in Mazouni et al. (2004), using as error index the mean square error between the state variables of the unstructured model and the model for control. 

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