Continuous membrane fermentor

Figure 2.63 Flow schematic of continuous membrane fermentor.

Mobile Cells. Figure 3.10275 shows one of the earliest concepts of a continuous membrane fermentor. The membrane retains the biomass while products of the fermentation are continuously withdrawn through the membrane. In addition, metabolic waste products, which inhibit cell growth, are removed continuously through the membrane, thereby improving cell growth and fermentor productivity. 

Other continuous membrane fermentors show similar results. In the continuous production of ethanol from Zymomonas mobilis, the production rate was 120 g/hr/E compared to less than 8 g/hr/E for the batch system.77... 

What has been previously said about the advantages of continuous membrane fermentors also applies to such complex systems. UF membranes can in fact be used to recycle both enzymes and microbial cells thus increasing overall system productivity.98... 

As the ethanol produced in fermentation acts as an inhibitor for the process, continuous ethanol removal is generally used to improve the productivity/ yield of the fermentation process. Garhyan and Elnashaie (8) modeled a continuous-membrane fermentor with in situ removal of ethanol produced using a sweep liquid as shown in Figure P6.21. The rate of ethanol removal is considered to be proportional to the ethanol concentration gradient across the membrane and area of permeation. 

Extend the four-dimensional model of Problem 6.20 to model this continuous-membrane fermentor. List all of the assumptions you make and justify them. 

Figure 13.18 Continuous recycle fermentor membrane reactor. An ultrafiltration module removes the liquid products of fermentation as a clean product. This system is being developed for production of ethanol, acetone and butanol by fermentation of food processing waste streams...

In the stationary phase of the batch fermentation, enzyme activity begins to decrease due to an increasingly unfavorable environment. In the membrane fermentor, protease (the enzyme) continued to be excreted by the growing biomass for 50 hours. The ratio of enzyme excreted per unit mass of cell produced in the membrane system (70 units/mg) was almost twice that from the batch system (45 units/mg). This would indicate that under the more favorable environment in the membrane fermentor, the organism is more efficient. 

It may also be economical to remove the inhibitory product directly from the ongoing fermentation by extraction, membranes, or sorption. The use of sorption with simultaneous fermentation and separation for succinic acid has not been investigated. Separation has been used to enhance other organic acid fermentations through in situ separation or separation from a recycled side stream. Solid sorbents have been added directly to batch fermentations (18,19). Seevarantnam et al. (20) tested a sorbent in the solvent phase to enhance recovery of lactic acid from free cell batch culture. A sorption column was also used to remove lactate from a recycled side stream in a free-cell continuously stirred tank reactor (21). Continuous sorption for in situ separation in a biparticle fermentor was successful in enhancing the production of lactic acid (16,22). Recovery in this system was tested with hot water (16). 

Chen and Lee [24] studied lactic acid production from dilute acid pretreated a-cellulose and switchgrass by L. delbruckii NRRL-B445 in the presence of a fungal cellulase in a fermentor extractor employing a microporous hollow fiber membrane (MHF). This reactor system was operated in a fed-batch mode with continuous removal of lactic acid by in situ extraction. A tertiary amine (alamine... 

Increasing interest is developing in continuous fermentation processes where microporous membranes are used to separate the fermentation broth from the product stream, thus retaining viable cells in the fermentor. 

Continuous fermentation processes can also be carried out in a hollow fiber fermentor (HFF).85 Cells are packed into the shell side of a hollow fiber module, while substrate solution is fed to the core of the fibers (Figure 7.41). Since the cell slurry is separated from the substrate solution by the membrane, HFFscan be used for fermentation of liquid streams containing low molecular weight fermentable substances. A careful choice of membrane molecular weight cut-off can also assure that the cell environment is fully sterilized. Figure 7.45 shows typical performance of an HFF for whey permeate fermentation to ethanol by... 

O Brien and Craig (1996) used commercially available polydimethyl-siloxane membrane for EtOH production in a continuous fermentation/membrane PV system. The PV module contained 0.1 m of a commercially available polydimethylsilox-ane membrane and consistently produced permeate of 20%-23% (w/w) EtOH while maintaining a level of 4%-6% EtOH in a stirred-tank fermentor. PV flux and EtOH selectivities were 0.31-0.79 1/m h and 1.8-6.5 respectively. 

The use of advanced fermentor configuration (immobilized packed bed) with ethanol-selective membranes for the continuous removal of ethanol from the fermentation mixture. 

This part includes modeling (46,53) for the continuous-stirred tank fermen-tor with/without ethanol-selective membranes. It includes modeling for each of the different feedstocks and each of the different strains of micro-organisms suggested. The biokinetic models and parameters obtained from the literature should be used in the modeling of the continuous-stirred tank fermentor proposed in this part. The membrane flux equations and parameters obtained from the literature should also be used for the membrane continuous-stirred tank fermentor. 

For example, different fermentation schemes have been developed for the production of ethanol. Conventional batch, continuous, cell recycle and immobilized cell processes, as well as membrane, extraction and vacuum processes, which selectively remove ethanol from the fermentation medium as it is formed, were compared on identical bases using a consistent model for yeast metabolism (Maiorella et al., 1984). The continuous flow stirred tank reactor (CSTR) with cell recycle, tower and plug flow reactors all showed similar cost savings of about 10% compared to batch fermentation. Cell recycle increases cell density inside the fermentor, which is important in reducing fermentation cost. 

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