Factors affecting oxygen-transfer rates in headspace-gas respirometers.

Satisfactory measures of the biological-oxygen-uptake rate in headspace-gas respirometers can only be achieved if the rate of oxygen transfer from the headspace gas to liquid is greater than the rate of oxygen uptake by microorganisms. In the authors' study, factors potentially affecting oxygen-transfer limitations in headspace-gas respirometers were evaluated quantitatively. Tests were conducted to measure maximum-oxygen-uptake rates by operating a respirometer under various test conditions. Analysis of respirometric data indicated that limiting oxygen-transfer rates were related to mixing intensity, length of magnetic stirring bar, volume of sample, and oxygen content in the headspace gas. A multivariable model was developed to describe the overall contribution of these factors to the limiting oxygen-transfer rate. This model should be useful for estimating maximum-oxygen-transfer rates for essentially all headspace-gas respirometers.