Enhancement of Oxygen Mass Transfer and Gas Holdup Using Palm Oil in Stirred Tank Bioreactors with Xanthan Solutions as Simulated Viscous Fermentation Broths

Suhaila Mohd Sauid,Jagannathan Krishnan,Murthy V P S Veluri,Tan Huey Ling

doi:10.1155/2013/409675

Suhaila Mohd Sauid, Jagannathan Krishnan + Show 2 more

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https://doi.org/10.1155/2013/409675

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Abstract

Volumetric mass transfer coefficient (k L a) is an important parameter in bioreactors handling viscous fermentations such as xanthan gum production, as it affects the reactor performance and productivity. Published literatures showed that adding an organic phase such as hydrocarbons or vegetable oil could increase the k L a. The present study opted for palm oil as the organic phase as it is plentiful in Malaysia. Experiments were carried out to study the effect of viscosity, gas holdup, and k L a on the xanthan solution with different palm oil fractions by varying the agitation rate and aeration rate in a 5 L bench-top bioreactor fitted with twin Rushton turbines. Results showed that 10% (v/v) of palm oil raised the k L a of xanthan solution by 1.5 to 3 folds with the highest k L a value of 84.44 h−1. It was also found that palm oil increased the gas holdup and viscosity of the xanthan solution. The k L a values obtained as a function of power input, superficial gas velocity, and palm oil fraction were validated by two different empirical equations. Similarly, the gas holdup obtained as a function of power input and superficial gas velocity was validated by another empirical equation. All correlations were found to fit well with higher determination coefficients.

Highlights

In aerobic fermentations, the bioreactor performance greatly depends on its oxygen transfer capacities
They postulated that this method has the ability to solve the viscosity problem and indirectly enhance the oxygen transfer. This was proven by Lo et al [8] who found that in 3.5% of xanthan solution, the kLa values in the xanthan solution-hexadecane emulsion (0.50 v/v) system were higher than the kLa values obtained in a centrifugal packed bed reactor and stirred tank reactor. While those researchers opted for higher organic phase concentration, this study has focused on the effect of palm oil on the viscosity and the oxygen transfer characteristics in xanthan solution at lower oil concentrations
The presence of palm oil in xanthan solution resulted in significant changes in the viscosity and rheological behavior, volumetric mass transfer coefficient, and gas holdup with respect to the different values of palm oil volume fraction, agitation rate, and aeration rate

Summary

Introduction

The bioreactor performance greatly depends on its oxygen transfer capacities. If the oxygen transfer rate to the aqueous phase exceeds the rate of oxygen consumed by the cells, cell growth continues at an exponential rate when other nutrients are not limited. Xanthan gum is a natural polysaccharide produced by Xanthomonas campestris and is an important industrial biopolymer. It is widely used in industries such as foods and cosmetics, pharmaceutical and petroleum industry as emulsion stabilizer, thickener, dispersing agent and drilling fluid, and for many more applications [3]. The fermentations of xanthan gum production are often associated with a significant decrease in oxygen transfer rate because of the increase in viscosity from accumulation of xanthan. Oxygen limitation turns into the controlling step in the whole process of xanthan production [5]

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