The Measurement of the Aeration of Culture Media

Abstract

SUMMARY:The aeration of culture media can be measured in terms of q5L (defined below) which is dependent on rate of air flow, agitation, etc. Two methods of measuring q5L are given, based on the polarographic estimation of dissolved oxygen. For penicillin and streptomycin fermentations there is a correlation between the amount of antibiotic produced and q5 L .Recent advances in industrial stirred and aerated fermentations have emphasized the need for a suitable technique to measure aeration in terms of the oxygen available to the organism rather than in terms of the volume of air which is passed through the medium. In the case of submerged cultures, the organism is dependent upon the oxygen dissolved in solution. In order to assess the efficiency of the aeration it is therefore necessary to compare the rate of solution of oxygen into the culture medium with the rate of consumption of oxygen by the organism. Determination of the oxygen demandThe Warburg apparatus is usually used for measuring oxygen demands, but in the present work it was found convenient to use a polarographic method first used by Petering & Daniels (1938). The culture is saturated with air and then the air supply is cut off. The concentration of dissolved oxygen in the culture medium decreases steadily from the saturation concentration to zero as the organism consumes the oxygen. A typical determination is shownin Fig. 1, from which it will be seen that the graph of the concentration of dissolved oxygen against time is linear, i.e. the oxygen demand is of zero order with respect to time and oxygen concentration over the period of measurement. This behaviour was always found with the organisms studied, and in the following theory it is assumed that the oxygen demand at a particular moment is of zero order. The polarographic measurements required only a few minutes so that no significant growth occurred during the measurement. The oxygen demand of the culture varies comparatively slowly with time as growth proceeds, and by measuring the oxygen demand of samples taken a t various times throughout the culture period it is possible to draw the curve connecting oxygen demand with the time after the inoculation of the medium.It has many times been noted (for a review see Tang, 1933) that the oxygen demand of many organisms is of zero order although only above a critical oxygen tension. Below the critical oxygen tension, the oxygen demand becomes first order. The critical oxygen tensions found are very low. For instance, in the present work the critical oxygen tensions were too low to be apparent from curves such as those shown in Fig. 1, so that the assumption that the oxygen demand is of zero order is justified.

Combined effects of agitation and aeration on the chitinolytic enzymes production by the Antarctic fungus Lecanicillium muscarium CCFEE 5003

“…The volumetric mass-transfer coefficient (K L a) of the bioreactors was determined by the static method of gassing out of Wise [33] using BM at different combinations of aeration rates (0.5, 1.0 and 1.5 vvm) and stirrer speeds (200, 300, 400 and 500 rpm) as suggested by the model. Tests were carried out at 25°C.…”

Effects of rheological change by addition of carboxymethylcellulose in culture media of an air-lift fermentor on poly-D-3-hydroxybutyric acid productivity in autotrophic culture of hydrogen-oxidizing bacterium, Alcaligenes eutrophus

“…The viscosity of the culture medium was measured using an Ostwald-type viscometer. The volumetric mass transfer coefficient (K L a) of the fermentor was determined by the static method (Wise, 1951).…”

Microbubble fermentation of recombinant Pichia pastoris for human serum albumin production

“…: is equal to the slope of the tangent at point Y. (Wise, 1951) and depicted in Figure 2.4. Integration of equation (2-2) yields:…”

“…In this technique, first described by Wise (1951), the oxygen concentration of the solution is lowered by gassing the liquid out with nitrogen gas, so that the solution is 'scrubbed' free of oxygen. The deoxygenated liquid is then aerated and agitated and the increase in dissolved oxygen monitored using some form of dissolved oxygen probe.…”