Enhanced bioreactors requirement

Pressure Most bioreactors are operated at normal atmospheric pressure however, in some cases with high oxygen requirements, such as high-density cultivation, a bioreactor must be pressurized in order to enhance the oxygen transfer rate. In such cases, the control of vessel pressure is essential. 

The possibility of having membrane systems also as tools for a better design of chemical transformation is today becoming attractive and realistic. Catalytic membranes and membrane reactors are the subject of significant research efforts at both academic and industrial levels. For biological applications, synthetic membranes provide an ideal support to catalyst immobilization due to their biomimic capacity enzymes are retained in the reaction side, do not pollute the products and can be continuously reused. The catalytic action of enzymes is extremely efficient, selective and highly stereospecific if compared with chemical catalysts moreover, immobilization procedures have been proven to enhance the enzyme stability. In addition, membrane bioreactors are particularly attractive in terms of eco-compatibility, because they do not require additives, are able to operate at moderate temperature and pressure, and reduce the formation of by-products. 

Membrane technology may become essential if zero-discharge mills become a requirement or legislation on water use becomes very restrictive. The type of membrane fractionation required varies according to the use that is to be made of the treated water. This issue is addressed in Chapter 35, which describes the apphcation of membrane processes in the pulp and paper industry for treatment of the effluent generated. Chapter 36 focuses on the apphcation of membrane bioreactors in wastewater treatment. Chapter 37 describes the apphcations of hollow fiber contactors in membrane-assisted solvent extraction for the recovery of metallic pollutants. The apphcations of membrane contactors in the treatment of gaseous waste streams are presented in Chapter 38. Chapter 39 deals with an important development in the strip dispersion technique for actinide recovery/metal separation. Chapter 40 focuses on electrically enhanced membrane separation and catalysis. Chapter 41 contains important case studies on the treatment of effluent in the leather industry. The case studies cover the work carried out at pilot plant level with membrane bioreactors and reverse osmosis. Development in nanofiltration and a case study on the recovery of impurity-free sodium thiocyanate in the acrylic industry are described in Chapter 42. 

Mechanically stirred hybrid airlift reactors (see Fig. 6) are well suited for use with shear sensitive fermentations that require better oxygen transfer and mixing than is provided by a conventional airlift reactor. Use of a low-power axial flow impeller in the downcomer of an airlift bioreactor can substantially enhance liquid circulation rates, mixing, and gas-liquid mass transfer relative to operation without the agitator. This enhancement increases power consumption disproportionately and also adds other disadvantages of a mechanical agitation system. 

For effective co-disposal, the draft document for consultation (DoE, 1994a) states that "flushing bioreactor conditions are needed. This leads to a separate requirement for containment and possibly recirculation" (see Chapter 7). Under enlumced conditions of gas generation (and hence microbial activity) the potential for effective co-disposal will be enhanced accordingly. Although at the moment very few landfill sites undertake leachate recirculation, it is a concept that is receiving a great deal of attention and one that appears to facilitate both codisposal practice and more sustainable landfill development. 

The industrial production of SAM has been achieved in bioreactors with working volumes usually greater than 100 L. In order to enhance SAM synthesis while depress its conversion, strain modification is not sufficient and optimization of the process is also required. 

Bioreactors are designed to enhance cell growth and maximize the conversion of substrate to desired product by providing a controlled environment for biological processes. The selection of a specific bioreactor design requires understanding of basic microbiology and... 

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