INFLUENCE OF POWER INPUT AND AERATION METHOD ON MASS-TRANSFER IN A LABORATORY-ANIMAL CELL-CULTURE VESSEL

Large-scale animal cell operation is costly both in terms of facilitie s and consumables. Hence developmental studies with animal cells norma lly start at laboratory scale, often using small stirred tanks. In ord er to better optimise cell performance, it is necessary to know the ph ysical conditions under which the cells are grown. In this study a lab oratory-scale vessel (2 dm(3) working volume) with two large-bladed pa ddle impellers was characterised hydrodynamically. Three different aer ation methods (surface, sparging and membrane aeration) were investiga ted and compared. Power input and oxygen transfer rates to culture med ium were determined as a function of agitation and gas flow rates. Non dimensional correlations were established for each case, which can be useful for scale-up purposes. The results obtained indicate that power input is quite dependent on the vessel accessories: for the same agit ation rate, the maximum power is required for the membrane structure a nd the minimum for surface aeration, with the addition of the sparger leading to an intermediate situation. Predictions found in the literat ure can be used for simple vessels, but may not be applicable when acc essories are added to the vessel structure; in such cases, the use of experimental relationships are required. Oxygen transfer rate was depe ndent on the aeration method and working conditions (agitation and gas flow rates), particularly for sparger aeration. Membrane aeration gav e larger oxygen transfer but higher gas pressure and flow rates were r equired. Surface aeration was the least effective method, nevertheless requiring gas flow rates similar to those used for membrane aeration. The aeration method of choice depends upon the culture and work speci ficities: surface aeration is limited to small cell concentrations and low oxygen consumption rates. For higher cell concentrations and oxyg en consumption rates, both membrane and sparger aeration methods can b e applied: the use of the sparger is limited to cells that are not aff ected by the presence of bubbles or the addition of surfactants, where as the membrane aeration basket should not be used when a hydrodynamic ally controlled stirred tank is required.