Bioreactors continuous operation

Eor an ideal continuous stirred-tank bioreactor (CSTB), the concentrations of the various components of the outlet stream are assumed to be the same as the concentrations in the bioreactor. Continuous operation of a bioreactor can increase the productivity of the reactor significantly by eliminating the downtime and the ease of automation. 

During the continuous operation of the bioreactor the specific MAb production rate at time t is determined by the derivative method as... 

Despite the differences between the estimated derivatives values, the computed profiles of the specific MAb production rate are quite similar. Upon inspection of the data, it is seen that during the batch period (up to t=2I2 h), qM is decreasing almost monotonically. It has a mean value of about 0.5 /ug/(l(f cells-h). Throughout the dialyzed continuous operation of the bioreactor, the average qM is about 0.6 fxg/(l(f cells-h) and it stays constant during the steady state around time... 

Continuous bioreactor treatment was developed for the removal of clofibric acid by T. versicolor (data not yet published). That bioreactor was operated in... 

These findings suggest that a prerequisite for the successful continuous operation of bioreactors for azo-dye conversion is the thorough control of carbon loading the azo-dye conversion degree drops to vanishing levels if carbon depletion occurs. 

Some studies have demonstrated the ability of mixed bacterial cultures to promote azo-dye conversion. The main advantage of mixed cultures is the ability to cope with conversion of both the dye and the main products of dye degradation. Characterization of individual strains in consortia has seldom been accomplished during continuous tests. Only a few attempts have been made to characterize the morphology of bacteria during continuous operation of bioreactors and to relate process efficiency to the bacterial population [32, 33]. 

Biomass containment in continuously operated bioreactors is an essential prerequisite for the feasibility of practical industrial-scale dye biodegradation. Biofilm airlift reactors have demonstrated excellent performance for their ability to control mixing, interphase mass transfer and biofilm detachment rate. Further studies are required to further exploit the potential of this type of reactors with either aggregated cells or biofilm supported on granular carriers. 

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. 

Furthermore, for such application, they would require no maintenance, which would avoid additional risks of contamination and allow a continuous operation of the perfusion bioreactor for several months. 

Figure 11.9 Different arrangements and modes of operation for membrane bioreactors Continuous Stirred Tank Reactor (CSTR) with recirculation arrangement (a), dead-end cell (b), tubular with entrapped enzyme (c).

Potato pulp and potato pulp residue (after acidic treatment) and nutrient salt solution and potato protein liquor, respectively, were used for the production of cellulases and hemicellulases by Trichoderma reesei Rut C30 in a continuously operated bioreactor, (Klingspohn and Schiigerl... 

Bioreactors are operated in discontinuous mode, with a sequential or continuous feed of the substrate (fed-batch operation) or in continuous mode. The choice of the operating mode depends mainly on the reaction characteristics ... 

Immobilization, dehned as the physical confinement or localization of an enzyme into a specihc micro-environment, has been a very common approach to prepare enzymes for aqueous as well as nonaqueous applications. For nonaqueous enzymol-ogy, immobilization improves storage and thermal stability, facilitates enzyme recovery, and enhances enzyme dispersion. In addition, immobilized enzymes are readily incorporated in packed bed bioreactors, allowing for continuous operation of reactions. Moreover, lyophilized enzyme powders often aggregate and attach to reactor walls, particularly when the water activity is moderately high. The major disadvantage of immobilization is low activity, induced by pore diffusion mass transfer limitations and by alteration of protein stmcture. For enzymes in nonaqueous media, the following broad categories of immobilization exist ... 

Degradation of organopollutants by fungal cultures has been carried out successfully at bench and pilot scale, preferentially in batch or semi-continuous operations (Alleman et al. 1995 Fujita et al. 2002 Mielgo et al. 2002). Continuous treatment systems are desirable alternatives to increase process efficiency. A modified conventional configuration (fixed-bed bioreactor) coupled with a pulsation system has... 

Batch, fed-batch, repeated fed-batch, and continuous modes of bioreactor operation have been used in SSF processes, although batch processes are by far the most common. Fed-batch or continuous operations that involve the addition of fresh, uninoculated substrate particles require interparticle colonization to occur, which is a relatively slow process, and will lead to bioreactor dynamics very different from those obtained during similar processes in SLF. Despite this, laboratory studies have demonstrated potential advantages of such operation. Abdullah et al. [68] compared batch, fed-batch, and repeated fed-batch culture of Chaetomium cellulolyticum on wheat straw. Under optimal conditions in batch culture, protein production ceased after three days, with a maximum protein level of 12 g per gram of solids. In fed-batch culture fresh straw was added at three-day intervals. Protein productivity was maintained for 12 days at a slowly declining rate. In the repeated fed-batch culture half of the fermenting straw was removed and replaced with fresh straw at three-day intervals. Protein productivity was maintained for 12 days at a steady rate and the protein level reached a maximum level of 14 g per gram of solids. 

Continuous SSF processes are usually operated in plug flow mode. Such processes will require pasteurization or sterilization of the substrate as it enters the bioreactor, mixing with an inoculum, and at the outlet end of the bioreactor, continuous removal of spent substrate. Such a process was operated on a pilot scale for the production of ethanol from fodder beets by Saccharomyces cerevisiae [81,82]. The bioreactor had a screw within a 4.7 m long and 15.25 cm diameter tube. The screw was rotated intermittently to mix the substrate and move it along the tube. At the front end was a hammer-mill and a pasteurization chamber for substrate preparation and a port for inoculation. New substrate was added, inoculated, and the screw rotated at 12-h intervals, resulting in a residence time of 72 h. 

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