Bioreactors suspensions

Example 5.12 The activated sludge bioreactor facility of a certain plant is to be expanded. The results of a settling cylinder test of the existing bioreactor suspension are shown below. Q + Qg is 10,000 m /d and the influent MLSS is 3,500 mg/L. Determine the size of the clarifier that will thicken the sludge to 10,000 mg/L of underflow concentration. 

Alternatively, some subunit viral vaccines can be generated by rDNA techniques and expressed in a continuous ceU line or insect ceUs. Recent advances in bioreactor design and operation have improved the successful production of IPV in large-scale bioreactors. However, roUer bottles or flasks are stiU used for most current vaccine production. Development of insect ceU culture will allow for very large-scale Hquid suspension culture (143). Several vaccine candidates such as gpl60 for HIV and gD protein for herpes have been demonstrated in the insect ceU culture system. However, no vaccine has been approved for human use. 

The inoculate was prepared in 250 ml flasks containing 100 ml of growth medium, which is inoculated with 10 ml of spore suspension. The mixture was shaken at 250 rpm and the temperature was controlled at 26 °C for 48 h. Then, 110 ml of resulting mycelia suspension is used to inoculate a 1000 ml broth in the airlift fermenter. The sterilised media are slowly pumped into the bioreactor at a flow rate of about lOOmlh-1 until 2 1 working volume is fully utilised. Aeration rates of 0.5, 1 and 2vvm (1,2 and 4 1 air/min) are used.6,7 Samples were taken at 24 hour intervals and evaluated for biomass, sugars and antibiotic concentrations. 

Figures 12 and 13 show the effects of agitation and time of exposure on suspensions of biological materials in bioreactors [61]. In turbulent flow the energy dissipation rate per unit mass, e, of a stirred bioreactor is normally expressed by the following equation ...

The influence of mechanical forces on cell viability is of great importance when growing the cells in agitated systems. By far the greatest amount of work reported in the literature has been done on suspension cells but adherent cells also experience shear forces not only in bioreactors also in vivo. Therefore, most research has be done on endothelial cells but studies exists done on non-endothelial cells. The influence of shear forces on cell growth, morphology and productivity will be discussed as well as possibilities of making the cells more resistant. 

Soule et al. [141] constructed a sparged, concentric cylinder bioreactor for the cultivation of suspensions of Pirus malus. Growth was reduced under all rotational conditions. Sun and Linden [106] employed a rotating wall vessel (Rotary Cell Culture System, Synthecon, Houston, TX, USA) to cultivate suspensions of Taxus cuspidata under laminar flow conditions. Shear rates were... 

Navia-Osorio, A., Garden, H., Cusido, R.M. et al. (2002) Production of paclitaxel and baccatin III in a 20-L airlift bioreactor by a cell suspension of Taxus wallichiana. Planta Medica, 68, 336-340. 

Mammalian cell suspension cultures are the preferred choice for large-scale recombinant protein production in stirred-tank bioreactors. The most widely used systems are Chinese hamster ovary (CHO) cells and the murine myeloma fines NSO and SP2/0. In half of the biological license approvals from 1996-2000, CHO cells were used for the production of monoclonal antibodies and other recombinant glycosylated proteins, including tPA (tissue plasminogen activator) and an IgGl fusion with the tumor necrosis factor (TNF) receptor, the latter marketed as Enbrel [7]. 

Fischer, R., Emans, N., Schuster, F., Hellwig, S., and Drossard, J. 1999. Towards molecular farming in the future using plant cell suspension cultures as bioreactors. Biotechnology and Applied Biochemistry 30, 109-112. 

Wang ZY, Zhong JJ. (2002) Repeated elicitation enhances taxane production in suspension cultures of Taxus chinensis in bioreactors. Biotechnol Lett 24 445 48. 

Naruse et al. proposed another bioreactor design [22,23], in which porcine hepatocyte spheroids are immobilized on non-woven polyester fabric. This device allows more direct contact between hepatocytes and perfused medium and improves, therefore, the mass transfer capacity. The non-woven fabric module expressed better metabohc and synthetic functions at 24 hours than a hollow fiber module containing spheroids in suspension culture. Longer term results are not yet available and the immunoexclusion properties of this fabric have not been addressed. 

Commercial scale cultivation of mammalian cells is accompHshed using different technologies roller bottles, microcarriers, suspension (batch, fed-batch or perfusion mode) and hollow fiber bioreactors (Table 2). However, especially for products needed in large amounts, suspension cultivation seems to be the most effective system [4, 5]. Suspension-based systems are characterized by a homogeneous concentration of cells, nutrients, metabolites and product, thereby facilitating scale-up [6] and enabling an accurate monitoring and control of the culture [7]. 

Suspension systems can be operated in different modes batch, fed-batch, chemostat, and perfusion (Fig. 1). These operation modes differ basically in the way nutrient supply and metabolite removal are accomplished, which in turn determines cell concentration, product titer and volumetric productivity that can be achieved [8]. The intrinsic limitation of batch processes, where cells are exposed to a constantly changing environment, limits full expression of growth and metabolic potentials. This aspect is partially overcome in fed-batch cultures, where a special feeding strategy prolonges the culture and allows an increase in cell concentration to be achieved. In perfusion and chemostat processes nutrients are continuously fed to the bioreactor, while the same amount of spent medium is withdrawn. However, in perfusion cultures the cells are retained within the bioreactor, as opposed to continuous-flow culture (chemostat), which washes cells out with the withdrawn medium [9]. 

Himmelfarb et al. [80] introduced spin-filters as a cell retention device for high cell density perfusion cultivations of mammalian cells in suspension. Spin-filters are cylinders with a porous wall, which are placed inside stirred tank bioreactors, either mounted on the impeller shaft or driven by an independent motor (Fig. 5). Perfusate is pumped out from inside the spin-filter at the same... 

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