Alternative Fermenters

Many alternative fermenters have been proposed and tested. These fermenters were designed to improve either the disadvantages of the stirred tank fermenter-high power consumption and shear damage, or to meet a specific requirement of a certain fermentation process, such as better aeration, effective heat removal, cell separation or retention, immobilization of cells, the reduction of equipment and operating costs for inexpensive bulk products, and unusually large designs. 

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G. R. Cysewski, C.R. Wilke, Process design and economic studies of alternative fermentation methods for the production of ethanol, Biotechnology Bioengineering, 20(9), 1421-1444, 1978... 

It is among the most capable of invertebrate anaerobes, the helminths and the marine bivalves, that we find the best examples of alternative fermentation pathways. Many of these have been reviewed several times elsewhere, so only a brief summary will be considered here. Current concepts view the organization of anaerobic metabolism as a series of linear, and loosely linked, pathways. The most important of these, aside from classical glucose — lactate fermentation (yielding 2 moles ATP per mole glucose) are summarized by Hochachka and Somero (1984) as follows (see chapter 2) ... 

Current chemical methods involve the use of toxic or corrosive reagents as well as high-pressure equipment. An alternative fermentation process, available for lactic acid production, is affected by low productivity and severe purification problems. 

Many alternative fermenters have been proposed in order to provide better aeration, heat transfer, and cell retention. They are usually classified based on their vessel type such as tank, column, or loop fermenters [17]. Another way to classify fermenters is based on how the fermenter contents are mixed by compressed air, by mechanical agitators, or by external liquid pumping. Representative fermenters in each category are listed in Table 19.7, and the advantages and disadvantages of three basic fermenter types are listed in Table 19.8. 

FIGURE 19.5 Alternative fermenters (a) bubble column (b) packed colurtm (c) air lift. 

Isoprene is a commodity chemical used in the production of synthetic rubber, adhesives, and specialty elastomers. Manufacturing of isoprene is currently based on petrochemical sources, but significant progress has been made to develop an alternative fermentation-based isoprene source (Whited et al., 2010). 

Ergot alkaloids can be manufactured also by alternative fermentation processes, e.g. by those using nontraditional substrates or immobilized cells of Claviceps spp. or their subunits. Semicontinuous or continuous cultivations represent other alternatives of the saprophytic cultivation. 

Assnming that the global market of antibiotic growth stimulators was worth 237 million US dollars in its peak in 1996 (Greathead 2003), it is not difQcult to predict the implications related to the increasing interest in alternative fermentation modulators, including the whole plants, plant oils, plant extracts, essential oils or, finally, the very biologically active factors. 

This is why a significant amount of research on biobutanol production has been made on the use of alternative fermentation and product recovery methods (Lee et al. 2008 Ezeji et al. 2007b). Some of these methods include, besides distillation. 

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