Investigation of Oxygen Transfer in a Two-phase Partition Stirred Tank Bioreactor in the Presence of Silicone Oil

A. Karimi, F. Golbabaei, M. Neghab, M. R. Mehrnia, K. Mohammad, M. R. Pourmand and A. Nikpey

Abstract
A lab scale bioreactor was designed for treatment of waste gas containing benzene, toluene and xylene (BTX). Initial characterization of the bioreactor involved quantification of the oxygen transfer coefficient (kLa) as a function of some main operational variables. To evaluate and obtain optimal conditions in the 2.36 L bioreactor, the effect on oxygen transfer rate in several operational conditions including different proportions of organic phase (0, 5, 10, 20 and 30 %) in eleven agitation speeds (0 to 1000) and five aeration levels (1 to 5 L min–1) were tested. The results showed that the presence of silicone oil caused a reduction in the kLa of the aqueous phase for all the concentrations studied. Reduction of kLa due to the presence of silicone oil increased with augmentation of silicone oil fractions. The positive impact of agitation speed and gas flow on oxygen transfer was also observed in the presence of silicone oil, although their impact was somewhat reduced at higher silicone oil content. In addition, it was found that total power consumption declined with addition of different fractions of silicone oil to bioreactor aqueous phase. It was deduced that the most optimal silicone oil fraction and stirring rate are 10 % and 800 rpm respectively, from the viewpoint of oxygen transfer and total power consumption rate. Empirical correlations for the oxygen transfer rate in the bioreactor with the presence of different fractions of silicone oil revealed that the experimental kLa lay within the values predicted. Variations pattern in exponents of correlations showed that addition of silicone oil up to 10 % improves the superficial gas velocity that leads to enhanced kLa of oxygen and higher proportion of silicone oil, which may have negative effect.

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Keywords
Oxygen transfer rate, two-phase partition, stirred bioreactor, silicone oil