Dynamic behavior of an internal-loop airlift bioreactor for degradation of waste gas containing toluene

Abstract

Experiments were performed to study the transient behavior of an internal-loop airlift bioreactor for degradation of toluene in a waste gas stream. The gas pollutant flowed into the reactor from the bottom, and it was then degraded by the microorganisms suspended in the liquid phase. Whenever the operating condition was changed, the gas phase toluene concentration initially increased sharply and the time required to reach a new steady-state concentration was short except when the dissolved oxygen decreased to below about 2 K O , where K O was Monod constant for oxygen in the microbial kinetics. However, even though the gas phase toluene concentration had already reached a new steady state, the whole system still did not yet reach a new steady state. It took 960–1850 s for the whole system to reach a new steady-state except when the dissolved oxygen decreased to below about 2 K O in this airlift bioreactor. For latter cases, it took 4990–7065 s. Moreover, the time required to reach a new steady state for the whole system increased with increasing input gas phase toluene concentration. A mathematical model was developed to describe the dynamic behavior of toluene degradation in the internal-loop airlift bioreactor. The mathematical model took into account the gas and liquid flow patterns in various sections (e.g. riser, gas–liquid separator, downcomer and bottom), the gas–liquid mass transfer of the reactants and the microbial kinetics. The dynamic behavior of the internal-loop airlift bioreactor simulated by the proposed model showed good agreement with the experimental results.