Cell immobilization stirred-tank reactor

Ogbonna, J. C., Matsumura, M., and Kataoka, H. (1991) Production of glutamine by micro-gel bead-immobilized Corynebacterium glutamicum 9703-T cells in stirred tank reactor. Bioprocess Eng. 7, 11-18. 

The immobilization of the white rot fungus F. trogii in Na-ALG beads allowed the decolorization of the dye Acid Black 52 in a stirred tank reactor operated in batch [55]. Three enzymes, laccase, MnP, LiP, secreted by fungus were reported during decolorization process. Results showed that laccase enzyme activity increased with increasing alginate concentration from 0 to 4%. Cell growth at immobilized cultivation was maintained more stably than suspended cultivation. Total amount of removed dye was reported to be 469 mg/L for immobilized cultures and 440 mg/L for suspended cultures. 

Isolated rat hepatocytes were immobilized in cellulose multiporous microcarriers by Kino et al. [24]. The microcarriers had a pore size of 100 pm and protected the cells from external shear stress. A newly developed stirred tank reactor contained the microcarrier-immobilized hepatocytes. The 02-supply was improved by using an oxygenator. The performance of microcarrier-im-mobihzed hepatocytes in the reactor was as good as that in floating culture and they demonstrated good ammonia metaboUsm. 

FBBR, fluidized-bed biofilm reactor CFSTR, completely mixed stirred tank reactor PUR, polyurethane immobilized cells UASB, upflow anaerobic sludge blanket reactor NS, not specified. 

Removal of acid dyes in a stirred tank reactor by free bacterial (P. putida) cells and bacteria immobilized on GAC F400 at 298 K, adapted from [112]... 

Added productivity of lactic acid fermentations can be achieved by combining continuous systems with mechanisms that allow higher bacterial cell concentrationsResearch is concentrated on two mechanisms (1) membrane recycle bioreactors (MRBs) and (2) immobilized cell systems (ICSs). The MRB consists of a continuous stirred-tank reactor in a semiclosed loop with a hollow fiber, tubular, flat, or cross flow membrane unit that allows cell and lactic acid separation and recycle of cells back to the bioreactor. The results of a number of laboratory studies with various MRB systems demonstrate the effect of high cell concentrations on raising lactic acid productivity (Litchfield 1996). O Table 1.12 lists examples of published results employing various MRB systems. 

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. 

Enzyme techniques are primarily developed for commercial reasons, and so information about immobilization and process conditions is usually limited. A commercially available immobilized penicillin V acylase is made by glutaraldehyde cross-linking of a cell homogenate. It can be used in batch stirred tank or recycled packed-bed reactors with typical operating parameters as indicated in Table 2 (38). Further development may lead to the creation of acylases and processes that can also be used for attaching side chains by enzymatic synthesis. 

The term fermentation is used to describe the biological transformation of chemicals. In its most generic application, a fermentor may be batch, continuous-stirred tank (chemostat), or continuous plug flow (immobilized cell). Most industrial fermentors are batch. Several configurations exist for these batch reactors to facilitate aeration. These include sparged tanks, horizontal fermentors, and biological towers. 

Another favorable aspect of stirred batch reactors is the fact that they are compatible with most forms of a biocatalyst. The biocatalyst may be soluble, immobilized, or a whole-cell preparation in the latter case a bioconversion might be performed in the same vessel used to culture the organism. Recovery of the biocatalyst is sometimes possible, typically when the enzyme is immobilized or confined within a semi-permeable membrane. The latter configuration is often referred to as a membrane reactor. An example is the hollow fiber reactor where enzymes or whole cells are partitioned within permeable fibers that allow the passage of substrates and products but retain the catalyst. A hollow-fiber reactor can be operated in conjunction with the stirred tank and operated in batch or... 

Unfortunately, most enzymes do not obey simple Michaelis-Menten kinetics. Substrate and product inhibition, presence of more than one substrate and product, or coupled enzyme reactions in multi-enzyme systems require much more complicated rate equations. Gaseous or solid substrates or enzymes bound in immobilized cells need additional transport barriers to be taken into consideration. Instead of porous spherical particles, other geometries of catalyst particles can be apphed in stirred tanks, plug-flow reactors and others which need some modified treatment of diffusional restrictions and reaction technology. 

A series of papers concerning the use of immobilized enzymes in industrial reactors has been published.The operational effectiveness factors of immobilized enzyme systems have been described.Analytical expressions have been developed that allow the generation of effectiveness graphs for immobilized whole-cell hollow-fibre reactors. A theoretical method of determining the kinetic constants of immobilized enzymes in continuous stirred tank and plug-flow reactors by transformation of rate-equation variables has been presented. 

Perhaps the first decision to be made in process development is the difficult decision of whether the enzymes to be used should be used in an integrated format. Such a question does not arise with conventional single biocatalytic steps but is highly important in multienzyme processes. One of the key criteria here is whether the enzymes can be operated together without compromise to any of the individual enzyme s activity or stability. An interaction matrix (see Section 10.6) can be used to assist such decision making. In cases where the cost of one or more of the enzyme(s) is not critical, it will be possible to combine in a one-pot operation. In other cases, where the cost of an individual enzyme becomes critical, then it may be necessary to separate the catalysts, such that each can operate under optimal conditions. Likewise, selection of the biocatalyst format (immobilized enzyme, whole cell, cell-free extract, soluble enzyme, or combinations thereof) in combination with the basic reactor type (packed bed, stirred tank, or combinations thereof) and biocatalyst recovery (mesh, microfiltration, ultrafiltration, or combinations thereof) will determine the structure of the process flowsheet and therefore is an early consideration in the development of any bioprocess. The criterion for selection of the final type of biocatalyst and reactor combination is primarily economic and may best be evaluated by the four metrics in common use to assess the economic feasibility of biocatalytic processes [29] ... 

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