Continuous processes permit the decrease of product
inhibition effect. Through cascade of continuous reactors,
ethanol obtained in first reactors is easily transported to
the following reducing its inhibitory effect. Other configurations
employing one fermentor can also reduce the product
inhibition as in the case of the Biostill technology
(Kosaric and Velikonja, 1995). Other variants of continuous
fermentation have been proposed, but many of them
still have not reached the commercial level. Some of them
require the use of highly flocculating yeast strains like in
tower and fluidized-bed reactors. These types of reactors
allow much higher cell concentrations (70–100 g/L) and
ethanol productivities, and have a long-term stability due
to the self replenishing of fresh yeasts. Moreover, these
reactors do not require stirring devices or centrifugation
(Gong et al., 1999). One approach to increase process productivity
is the continuous ethanol removal from culture
broth during fermentation by means of vacuum (see Table
3) or membranes, but the capital costs are increased. These
configurations involving the application of reaction-separation
integration were analyzed in a previous review (Cardona
and Sa´nchez, 2007).
Continuous processes permit the decrease of productinhibition effect. Through cascade of continuous reactors,ethanol obtained in first reactors is easily transported tothe following reducing its inhibitory effect. Other configurationsemploying one fermentor can also reduce the productinhibition as in the case of the Biostill technology(Kosaric and Velikonja, 1995). Other variants of continuousfermentation have been proposed, but many of themstill have not reached the commercial level. Some of themrequire the use of highly flocculating yeast strains like intower and fluidized-bed reactors. These types of reactorsallow much higher cell concentrations (70–100 g/L) andethanol productivities, and have a long-term stability dueto the self replenishing of fresh yeasts. Moreover, thesereactors do not require stirring devices or centrifugation(Gong et al., 1999). One approach to increase process productivityis the continuous ethanol removal from culturebroth during fermentation by means of vacuum (see Table3) or membranes, but the capital costs are increased. Theseconfigurations involving the application of reaction-separationintegration were analyzed in a previous review (Cardonaand Sa´nchez, 2007).
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