Axial inhomogeneities in steady-state dissolved oxygen in airlift bioreactors: predictive models

Abstract

Models were developed for prediction and interpretation of the observed steady-state axial dissolved oxygen concentration profiles in tall airlift bioreactors. The observed concentration profiles were non-linear because of a combination of hydrodynamic and mass transport factors. The profiles were influenced mainly by the liquid-phase axial dispersion coefficient, the volumetric overall gas-liquid mass transfer coefficient, the gas velocity, the induced liquid circulation velocity. The model-predicted concentration profiles agreed within ±2% with the measured data in a tall (working aspect ratio ∼ 15) airlift vessel operated under aeration regimens that are typically used during wastewater treatment. Axial inhomogeneities in dissolved oxygen increased with increasing aeration rate. This phenomenon may influence activated sludge processes in airlift and deep-shaft reactors. The maximum attainable concentration of dissolved oxygen at the bottom of a typically aerated airlift reactor, ≥ 3.5 m deep, always remained at <80% of air saturation value even when oxygen was not being consumed. Also, at steady state and without a net transfer of oxygen, the gas-phase mole fraction of oxygen varied by > 10% axially up the reactor.

Enhanced Oxygen Mass Transfer in an External Loop Airlift Bioreactor Using a Packed Bed

“…The obtained oxygen mass transfer coefficient for this ELAB without packing is in acceptable agreement with the reported empirical relation of Rubio et al and others, ,, who assumed the ELAB behaved like a well-mixed vessel. If the ELAB can be considered as a completely stirred reactor, the slope of Ln( c *-c)/( c *- c 0 ) vs time can be used to evaluate K L a .…”

Research on Mass Transfer Coefficient Measurement Model of External-Loop Airlift Reactor

“…This axial concentration profile is similar to Fig. 3 in the literature [11], which was obtained experimentally. The steady concentration in liquid phase is not the concentration corresponding to the static pressure.…”

Analysis of gas phase characteristics and mixing performance in an activated sludge bioreactor using electrical resistance tomography

“…Many experimental and modeling studies have been conducted in this regard [8][9][10][11][12]. However, a wide range of activated sludge concentrations has not been employed in these research works.…”