Two-liquid-phase bioreactor

The present review deals with the same topic as the articles cited above, but modified with different parameters influencing biocatalysis and reactant partition in water-organic two-liquid phase bioreactors. Interactions between these phenomena are also discussed. 

Secondary metabolites Scaling-up and safety (explosion danger) in two-liquid phase bioreactors... 

Majcherczyk A, Johannes C, Huttermeinn A (1998) Oxidation of polycyclic eiromatic hydrocarbons (PAH) by laccase oiTrametes versicolor. Enzyme Microb Technol 22(5) 335-341 Marcoux J, Deziel E, VHlemur R et td. (2(XX)) Optimization of high-molecultir-weight polycyclic aromatic hydrocarbons degradation in a two-liquid-phase bioreactor. J Appl Microbiol... 

In 1982, Lilly [21] reviewed the first two-liquid phase biocatalysis. In 1987 and 1992, Lilly s group [39,40] published reviews dealing with process engineering of biphasic bioreactors. In 1993, Van Sonsbeek et al. [41] gave an overview on biocatalysis in different biphasic... 

To get some idea of the prices to be expected for compounds produced with these approaches, we have estimated the total cost of producing 10,000 tons per annum of 1-octanol from w-octane, based on data collected for this conversion by P. oleovorans, during growth in a two-liquid-phase system containing 15% (v/v) hexadecane as a carrier phase. n-Octane is dissolved in the carrier phase to a concentration of 5-10% (v/v), converted by the P. oleovorans cells in the aqueous phase, and the product 1 -octanol dissolves in the hexadecane phase once more. Downstream processing consists of a phase separation, followed by two distillation steps. In the first step, the C8 alkane/alkanol are separated from the hexadecane, which is recycled into the bioreactor. In the second step, the w-octane is distilled off the n-octanol the octane is recycled to the bioreactor, and the octanol is collected as the desired product. This approach leads to a very clean product stream of >98% pure 1-octanol. ... 

Conversions in two-liquid-phase systems are promising. Although these reactions can be performed in a stirred emulsion system, the use of membrane bioreactors can be advantageous. In addition to retaining the biocatalyst in the reactor, the membrane also serves as a separator between aqueous and organic phase, thus avoiding energydemanding phase separations (Prazeres and Cabral, 1994). 

A novel bioreactor, especially designed to work with two liquid phases, is the liquid-impelled loop reactor (Figme 11.10), in which the advantages of air lifts and... 

G. J. Eye, J. M. Woodley, (Advances in the selection and design of two liquid phase biocatalytic reactors), in Multiphase Bioreactor Design, J. M. S. Cabral, M. Mota, J. Tramper (eds.), Taylor Francis, Fondon, pp. 115-134, 2001. 

An example of integration of part of the downstream processing in the actual bioreactor is two-liquid-phase biocatalysis (see above), in which the organic-solvent phase is used as extractant for the product. The liquid-impelled loop reactor (Fig. 7.3) is specifically designed for this purpose. It is based on the well-known air-lift principle, but instead of air, a water-immiscible, heavier or lighter organic solvent is injected. 

The effect of the wetting characteristics of membrane bioreactors on the operation of organic-aqueous two-liquid phase systems was discussed by Vaidya and co-workers [127, 157, 184]. A similar discussion, but considering the use of membranes for separation of liquid/liquid mixtures downstream of a bioreactor, was carried out by Schroen and Woodley [126]. Some trends for the use of membranes in organic-aqueous two-liquid phase systems can be summarized from these works. The use of UF hydrophilic or amphiphilic membranes was usually advised for two-phase bioreactors [127], although fluo-ropolymer-based membranes could present an exception [126]. PTFE membranes, on the other hand, led to low breakthrough pressures, and therefore their use was limited. 

The organic phase may also be used as a substrate reservoir, besides their use for product stripping from the aqueous phase. The effectiveness of membrane-assisted organic-aqueous two-phase bioconversions relative to direct-contact two-phase emulsion reactors was demonstrated by Westgate et al. [150]. These authors observed a fivefold increase in the maximum specific activity of hydrolysis of menthyl acetate catalyzed by B. subtilis cells when a 0.2 pm nylon flat membrane reactor was used, as compared to an emulsion reactor. This result was attributed to a continuous interfacial contact, which could only be achieved in an emulsion bioreactor at the cost of high power inputs. Doig and co-workers operated a dense membrane bioreactor for the production of citronellol from geraniol with a product accumulation rate similar to the one obtained in an emulsion reactor [124]. Some examples of membrane-assisted two-liquid phase bio-conversions/fermentations are presented in Table 9. 

The typical bioreactor is a two-phase stirred tank. It is a three-phase stirred tank if the cells are counted as a separate phase, but they are usually lumped with the aqueous phase that contains the microbes, dissolved nutrients, and soluble products. The gas phase supplies oxygen and removes by-product CO2. The most common operating mode is batch with respect to biomass, batch or fed-batch with respect to nutrients, and fed-batch with respect to oxygen. Reactor aeration is discussed in Chapter 11. This present section concentrates on reaction models for the liquid phase. 

Porous membrane modules were therefore effectively used in bioreactors as an alternative to direct two-liquid contact systems, as long as phase breakthrough was avoided. This required a careful control of the transmembrane pressure, particularly if surface-active material was produced during bioconversions [126,184, 187]. Fouling problems also developed in membrane-assisted multi-phase separation systems. This was observed by Conrad and Lee in the recovery of an aqueous bioconversion product from a broth containing 20% soybean oil by using ceramic membranes fouling was caused mainly by soluble proteins and surfactants [188]. 

Reis, C.N., Goncalves, M., Aguedo, N., Gomes, J.A., Teixeira, and Vicente, A.A. (2006). Application of a novel oscillatory flow micro-bioreactor to the production of gamma-decalactone in a two immiscible liquid phase medium. Biotech. Letters, Vol. 28, pp. 485 90. 

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