INCREASED OXYGEN MASS TRANSFER RATES FROM SINGLE BUBBLES IN MICROBIAL SYSTEMS AT LOW REYNOLDS NUMBERS

The presence of microorganisms have been shown to increase by over 40% the mass transfer rates from small oxygen bubbles at low Reynolds number flow. This increase was found to be due only to the microbe cells as inert particles disrupting the quasi‐static liquid surface film surrounding the gas bubble and thus decreasing the gas‐liquid interfacial resistance. The observed increase in oxygen mass transfer rates was not dependent on cell viability, no effect was noted due to cell‐liquid interfacial resistance, nor was the phenomenon due to altering the physical properties of the liquid during cell propagation. These results were obtained in a unique plexiglass apparatus designed for observing under a microscope a small (0.4 mm dia.) stationary oxygen bubble collapsing into a flowing fluid. The oxygen bubble was injected by a small hypodermic needle and the fluid was suspensions of the yeast Candida intermedia, the bacterium Pseudomonas ovalis, 0.3μ alumina, as well as base points of cell free broth and pure water. Several well‐known chemical inhibitors of oxidative phosphorylation were used to limit cell oxygen uptake. Calculations of oxygen mass transfer rates were compared with the semi‐empirical model of Frössling, the circulating sphere model of Levich, and the rigid sphere concentration boundary layer model of Fried‐lander, the latter two showing strong Reynolds number dependence that may be due to radial fluid motion. Copyright © 1969 John Wiley & Sons, Inc.