Bioreactor concept

The ex vivo expansion of hematopoietic cells is a rapidly growing area of tissue engineering with many potential applications in medicine. During the last few years a variety of bioreactor concepts and cultivation strategies have been developed, but no final decision has been made about the optimal system for hematopoietic culture. 

The bioreactor has been introduced in general terms in the previous section. In this section the basic bioreactor concepts, i.e., the batch, the fed-batch, the continuous-flow stirred-tank reactor (CSTR), the cascade of CSTRs and the plug-flow reactor, will be described. 

An alternative bioreactor concept - the fermentationAeaching wet cell (F/L wet-cell) has been developed by Lee and Jones-Lee (1993). This concept also aims to effectively stabilise the waste and leach the soluble potentially polluting components. The design requires that the waste is shredded prior to emplacement to try to ensure contact of the liquid with all waste components. According to Lee and Jones-Lee (1993) who cite Ham (1975), this will also eliminate the need for daily cover, and has the potential to increase the capacity of landfill by about 20%. The other key feature of F/L wet-cell is the use of a clean water system beneath the clay of the composite liner to maintain movement of water up through the clay, thus preventing any leachate leakages to escape from the containment system. 

Thus it seems that while the theory is fine, and indeed may work in laboratory scale studies, it will be very difficult to achieve in practice. Even in studies such as the Brogborough test-cell investigations (ETSU, 1993), where some successful manipulation of waste reactions has been achieved, it may be many years before a stable waste is produced, if indeed this ever occurs. However, while there are many uncertainties, there are sufficient encouraging results to warrant further investigation, if not at this stage, whole-hearted support of the bioreactor concept. 

Matos, C.T., Velizarov, S., Reis, M.A. Crespo, J.G. (2008) Removal of bromate from drinking water using the ion exchange membrane bioreactor concept. Environmental Science Technology, 42, 7702-7708. 

Shorrock, V.J., Chartrain, M., and Woodley, J.M. (2004) An alternative bioreactor concept for application of an isolated oxidoreductase for asymmetric ketone reduction. Tetrahedron, 60, 781-788. 

The constant shear concept has been applied for bioreactor scale-up that utilises mycelia, where the fermentation process is shear sensitive and the broth is affected by shear rate of impeller tip velocity. For instance, in the production of novobicin, the yield of antibiotic production is dependent on impeller size and impeller tip velocity. 

The two patents described above were particularly important in the initiation of the developments of biodesulfurization catalysts. The bioreactor arrays required for operation and growth method constituted key elements in the following developments of the area, which would condition viability and successful path to industrialization. A sulfur bioavailability assay was incorporated into the screen for monitoring the sulfur uptake by the microorganisms, and the concept formed a claim in the patents [67,91], The objective... 

In the development of cell or enzyme-based processes, many process configurations exist, including batch, fed batch and continuous operation. In general, the conversion and the separation processes (downstream processing) are regarded as separate units, and most industrial processes are based on this approach. In the last decades, however, more attention is paid to the integration of conversion and separation, leading to the development of membrane bioreactors [49, 50], and some of these concepts have reached an industrial scale. The membranes used for this type of reactors are almost exclusively polymeric, as temperatures seldomly exceed 100 °C for obvious reasons. 

Cruz et al. [69] have optimised bioreactor operational conditions for HIV-VLPs production using the concept of minimising local shear stress, i.e., they assumed that all the energy liberated by the stirring turbine was dissipated... 

This chapter describes the different types of batch and continuous bioreactors. The basic reactor concepts are described as well as the respective basic bioreactors design equations. The comparison of enzyme reactors is performed taking into account the enzyme kinetics. The modelhng and design of real reactors is discussed based on the several factors which influence their performance the immobilized biocatalyst kinetics, the external and internal mass transfer effects, the axial dispersion effects, and the operational stabihty of the immobilized biocatalyst. 

In this chapter we provide the fundamental concepts of chemical and biochemical kinetics that are important for understanding the mechanisms of bioreactions and also for the design and operation of bioreactors. First, we shall discuss general chemical kinetics in a homogeneous phase and then apply its principles to enzymatic reactions in homogeneous and heterogeneous systems. 

In the design and operation of various bioreactors, a practical knowledge of physical transfer processes - that is, mass and heat transfer, as described in the relevant previous chapters - are often also required in addition to knowledge of the kinetics of biochemical reactions and of cell kinetics. Some basic concepts on the effects of diffusion inside the particles of catalysts, or of immobilized enzymes or cells, is provided in the following section. 

Flow dynamics predict that flow through a pipe is nonuniform with regard to velocity across the diameter of a pipe, for instance. The flow at pipe walls is assumed to be zero. In our idealized biochemical reactor, this concept is represented by a boundary layer in contact with the biofilm. It does not have, of course, a discrete dimension. Rather, it is represented as an area in the structure that has reduced flow and therefore different kinetics than what we would assume exist in a bulk liquid. The boundary layer is affected by turbulence and temperature and this is unavoidable to a degree. Diffusion within the boundary layers is controlled by the chemical potential difference based on concennation. Thus the rate of transfer of pollutant to the organisms is controlled by at least two physical chemical principles, and these principles differentiate an attached growth bioreactor from a suspended growth bioreactor. 

---