Energy consumption and interfacial mass transfer area in an air-lift fermentor

Abstract

This work concerns energy consumption and aeration efficiency in a 15 dm 3 concentric cylinder gas-lift fermentor with the ejector nozzle located at the base of the central tube. Pressures are measured at ejector input and output and in the fermentor, and are compared with those predicted using Bernoulli's theorem and momentum balance at different points in the apparatus. Energy consumption per unit volume is the sum of isothermal expansion and gas-jet kinetic energy terms, the second of which becomes dominant at volumetric aeration rates above 2 vvm (volume of gas per liquid volume per min). Energy consumed is always lower than that for a classical agitated aerated fermentor. Oxygen transfer rate is determined by the sodium sulphite technique (with cobalt catalyst). Transfer can be strongly enhanced by the chemical reaction. The specific interfacial area for mass transfer, a′, depends on the power dissipated according to a′ = 3.66 (E/V ℓ) 0.73 (S.I. units) This correlation accounts for results obtained by other authors for larger fermentors (0.06 – 2 m 3).