Effect of aeration and agitation rates and scale-up on oxygen transfer coefficient, kLa in exopolysaccharide production from Enterobacter cloacae WD7

Abstract

In the exopolysaccharide production from Enterobacter cloacae WD7 under aerobic fermentation, biopolymer yield increased with aeration and agitation rates increasing at pilot plant scale, but decreased when agitation increased at bench scale because of shear thinning character (from 3.07 to 2.28 g/g over the range 200–800 rpm). However, it increased with increase of aeration rate (from 2.79 to 3.07 g/g over the range 0.5–1.25 vvm, respectively). By a dynamic gassing-out technique, the effects of aeration rate, agitation rate, character and size of fermentor and its accessories on the volumetric oxygen transfer coefficient k La were studied. Values of k La in the exponential and stationary phases increased with aeration and agitation rates to 9.97 and 9.72 h −1 in exponential and stationary phases at aeration rate 1.25 vvm of bench scale fermentation and 9.68 and 9.50 h −1 in exponential and stationary phases at aeration rate 1.75 vvm of pilot plant scale fermentation, respectively. Scale-up in the pilot plant performed by ‘ k La fixing’, controlling the oxygen change in the fermentor broth by holding the k La value to equal to the value obtained from small fermentor, resulted in a biopolymer yield of 3.20 g/g c.f. 3.07 g/g at bench scale.