Examples of Batch Fermentation
Batch fermentation is mostly a laboratory-scale technique for research and development work. Some representative examples in using batch fermentation on different biomass forms are shown in Table 9.1.
In fed-batch fermentation, nutritional environment is maintained approximately constant during the course of the fermentation process. In order to keep up the concentrations, sugar solution or biomass hydrolyzate is continuously added to the reactor with microorganisms during the fed-batch fermentation. Hence, microorganism works at low substrate concentration with an increasing ethanol concentration during the course of the fermentation process. Fed-batch cultures often provide better yields and productivities than batch cultures for the production of microbial metabolites. For practical reasons, therefore, some batch and continuous operations have been replaced by fed-batch processes.
Fed-batch fermentation can be considered as a technique in between batch fermentation and continuous fermentation. An elaborate series of equipment is required to maintain appropriate feed
|
Biomass |
Pretreatment and Saccharification |
Fermentation type/Microorganism |
Reference |
|
Corn stover |
Ammonia fiber expansion |
Simultaneous saccharification and fermentation, Saccharomyces cerevisiae 424A (LNH-ST) |
[1] |
|
Sugarcane bagasse |
Concentrated phosphoric acid (83.0— 85.9%), 50°C for 30-60 min |
Zymomonas mobilis cells immobilized in calcium alginate (CA) and polyvinyl alcohol (PVA) using simultaneous saccharification and fermentation and separate hydrolysis and fermentation |
[2] |
|
Rice straw |
Alkali-treated enzyme saccharification |
Immobilized Saccharomyces cerevisiae cells |
[3] |
|
Pulp and paper sludge |
Enzyme saccharification |
Saccharomyces cerevisiae CICC 1001 |
[4] |
|
Sorghum bicolor |
1% sulfuric acid, 121°C, 60 min enzyme saccharification — cellulase (celluclast 1.5L) and //-glucosidase (Novozyme 188) |
Saccharomyces cerevisiae |
[5] |
|
Corncobs |
1% (v/v) sulfuric acid for 30 min at a solid-to-liquid ratio of 1:10 |
Saccharomyces cerevisiae BCRC 21812 |
[6] |
|
Fermentation II — Fermenter Configuration and Design 341 |
rates with the right component constitution in the fed-batch reactors. However, the fed-batch fermentation technique offers many advantages over batch and continuous cultures. The production of byproducts that are generally related to the presence of high concentrations of substrate can also be controlled or avoided in the fed-batch fermentation. When high concentrations of substrate are present, the cells get overloaded, and this is when the oxidative capacity of the cells is exceeded, and due to the Crabtree effect, products other than the one of interest are produced, reducing the efficacy of the carbon flux. Besides, these byproducts even prove to contaminate the product of interest.
Sometimes, controlling the substrate is also important in fed — batch fermentation due to catabolic repression. Catabolite repression allows bacteria to adapt quickly to a preferred, rapidly metabolizable carbon and energy source first. Since the fed-batch fermentation usually permits the extension of the operating time, high cell concentrations can be achieved, thereby improving the productivity.