Bioreactor batch mode

The operation of the bioreactor was in the batch mode up to time t=2 2 h. The dialysis flow rate was kept at 2 Ud up to time t=91.5 h when a sharp drop in the viability was observed. In order to increase further the viable cell density, the dialysis flow rate was increased to 4 L/d and at 180 h it was further increased to 5 L/d and kept at this value for the rest of the experiment. 

The bioreactor operation mode is normally defined at the outset of process configuration. Insect cells have been cultured in almost all known cultivation modes batch [10], repeated-batch [70], perfusion [71-74], fed-batch [75, 76], semi-continuous [77,78] and continuous [79]. In spite of this multitude of different strategies, the batch or, eventually, fed-batch mode is normally preferred due to the lytic infection cycle of the baculovirus. 

Cabral and coworkers [253] have investigated the batch mode synthesis of a dipeptide acetyl phenylalanine leucinamide (AcPhe-Leu-NH2) catalyzed by a-chymotrypsin in a ceramic ultrafiltration membrane reactor using a TTAB/oc-tanol/heptane reverse micellar system. Separation of the dipeptide was achieved by selective precipitation. Later on the same group successfully synthesized the same dipeptide in the same reactor system in a continuous mode [254] with high yields (70-80%) and recovery (75-90%). The volumetric production was as high as 4.3 mmol peptide/l/day with a purity of 92%. The reactor was operated for seven days continuously without any loss of enzyme activity. Hakoda et al. [255] proposed an electro-ultrafiltration bioreactor for separation of RMs containing enzyme from the product stream. A ceramic membrane module was used to separate AOT-RMs containing lipase from isooctane. Application of an electric field enhanced the ultrafiltration efficiency (flux) and it further improved when the anode and cathode were placed in the permeate and the reten-tate side respectively. 

Compeau et al. (1990) reported a full-scale slurry-phase PCP remediation. The system consisted of soil washing and screening and resulted in clean soil and wash solution. The wash solution was a slurry containing PCP and < 60-mesh-size soil particles at approximately 20% solids concentration. Slurry was treated subsequently in on-site slurry-phase bioreactors. A 50 m3 slurry reactor was operated in batch mode and inoculated by an uncharacterized PCP-mineralizing culture (107 cells/ml of slurry). After 14 days, 370mg PCP/kg slurry had been degraded to below 0.5 mg/kg. For effective biogradation to occur, inoculation was required. 

Fed-batch production of pyruvic acid [CH3COCOOH] from an engineered strain (Escherichia coli YYC202) was optimized by resorting to ED to prevent potential product inhibition in the bioreactor (Zelic et al., 2004). In this way, by continuous separation of pyruvate from the fermentation medium, high values of the pyruvate-to-glucose molar yield (1.78 mol/mol), volumetric productivity (145 kg m 3day ), and pyruvate concentration (79 kg/m3) were achieved by the repeated fed-batch mode. 

The design of bioreactors for perfusion operation is more sophisticated, which makes the equipment more expensive. However, the productivity increases obtained by perfusion operation allow the use of much more compact systems than those operated under batch or fed-batch mode. In this way, perfusion bioreactors can be up to 10-fold smaller for a given production scale (Bibila and Robinson, 1995), decreasing the costs not only of the bioreactors themselves, but also of storage tanks and downstream processing equipment. 

Parameter Stirred-tank bioreactors operated in batch and fed-batch mode Stirred-tank bioreactors operated in perfusion mode Heterogeneous bioreactors (packed-bed or hollow-fiber) operated in perfusion mode... 

Recombinate is produced in CHO cells cultivated in 2500 L bioreactors, operated in fed-batch mode. The purification process starts by removing cells by a filtration step, followed by three chromatographic steps immunoaffinity, anion exchange, and cation exchange (Bhattacharyya et al., 2003). 

Semibatch Reactors Some of the reactants are loaded into the reactor, and the rest of the reactants are fed gradually. Alternatively, one reactant is loaded into the reactor, and the other reactant is fed continuously. Once the reactor is full, it may be operated in a batch mode to complete the reaction. Semibatch reactors are especially favored when there are large heat effects and heat-transfer capability is limited. Exothermic reactions may be slowed down and endothermic reactions controlled by limiting reactant concentration. In bioreactors, the reactant concentration may be limited to minimize toxicity. Other situations that may call for semibatch reactors include control of undesirable by-products or when one of the reactants is a gas of limited solubility that is fed continuously at the dissolution rate. 

Cells are inoculated and grown to a certain density, as in the batch mode. Subsequently the medium is continually pumped into the bioreactor at a constant rate and the cell suspension containing antibodies is withdrawn at the same rate. 

A graphic presentation of a murine hybridoma grown in a fixed-bed bioreactor under batch mode is given in Figures 5.9.4 and 5.9.5. The medium used in these examples was Dulbecco s modified Eagle s medium (DMEM) with 4.5 g glucose, 4mM glutamine and 5% foetal calf serum (FCS). 

Sequencing batch bioreactors (SBRs), as indicated by its name, operate in a batch mode with two or more bioreactors in a typical system. Treatment in a SBR is accomplished by operating the reactor in a sequence of events within a cycle (see Figure 10). For a treatment plant with two SBRs, wastewater is... 

A third type of bioremediation involves the use of a bioreactor in a dedicated treatment area. The contaminated soil is excavated, slurried with water, and treated in the reactor. The horizontal drum and airlift-type reactors are usually operated in the batch mode but may also be operated in a continuous mode. Because there is considerable control over the operating conditions, treatment often is quick and effective. Contaminated groundwater and effluent also may be treated in either fixed-film or stirred-tank bioreactors. However, bioreactors are still in the developmental stages and further research is required to optimize their efficiency and cost effectiveness (Wilson and Jones 1993). 

CoUins and Dauguhs [46] used industrial grade oleyl alcohol as the diluent in a two-phase partitioning bioreactor. This was inoculated with Pseudomonas sp. ATCC 55595, and the authors studied the biodegradation ofbenzene, toluene, and p-xylene, individuaUy and in different mixtures. The authors compared the efficiency of the aromatic hydrocarbon removal in the batch mode and the fed-batch mode. In a mixture of benzene and... 

In conventional shake-flask cultivation, D. discoideum cells can reach maximum cell densities of 1-2x10 cells mL in HL-5 and up to 3 X10 cells mL in FM medium. A small-scale industrial facility can easily increase this number to 5 x 10 cells (5 kg) per week. Improvement of the original FM medium to compensate Hmitations with respect to amino acids (SIH medium) increased the densities of D. discoideum cultures to 5-6x10 cells mL [105]. Growth of D. discoideum cells in bioreactors in batch and fed-batch mode in a stirred tank-type bioreactor is a convenient fermentation method [107]. Under these conditions, it is possible to accumulate 36 g cell material (dry weight) from 7 L of cell culture in about 4 days (E. Flaschel, personal communication). 

Fig. 14.1 Wave bioreactor system equipped with inoculation bottle as well as medium supply for fed-batch mode.

Batch bio reactors—This is the simplest bioreactor process. In this mode, all nutrients needed for cell growth are formulated into the basal medium and added to the production reactor with the cell inoculum at the initiation of the run. The cells grow for a finite period and are harvested after the nutrients become limited and the cell viability decreases to a predetermined level. Although simple to operate, batch mode is least likely to be used as other modes of operation yield higher product titers. 

Fed-batch bioreactors—This method begins as a batch mode of operation as cells undergo their initial growth phase. However, run time, cell mass, and product titer are increased with the addition of supplemental nutrients, or feeds, to the bioreactor. These reactors are cost effective to run because higher product titers can be achieved from a single extended reactor run, increasing volumetric productivity. However, volumetric output is fundamentally restricted by the size of the vessel, and formation of toxic cellular metabolites can limit the duration of each reactor run. 

If a bioieactor malfunclions and produces off-specificadon efQuent with a high organic chemical content, the affected bioreactor module (consisting of four ICB units) is isolated from the rest of the system and operated in batch mode until the problem is resolved. 

Municipal wastewater can be treated biologically in a bioreactor, consisting of a basin containing wastewater and activated sludge (solids with active microbes). In a batch mode, (1) the reactor is filled with wastewater, (2) the mixture of wastewater and sludge is aerated, (3) the contents are allowed to settle, (4) effluent is decanted and some sludge is removed, and (5) the system idles until the next cycle. Sometimes there are problems with anoxic conditions odor, low capacity, and poor effluent quality. What are possible causes and solutions for these problems ... 

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