| Biopolymer fermentation is an environmentally friendly process compared to petroleum-based polymer production. The goal of this study was to evaluate the feasibility of producing xanthan gum, an important biopolymer widely used in food and oil-recovery industries, from whey lactose, a low-value byproduct from cheese manufacturing in the dairy industry, in an integrated fermentation-ultrafiltration process. First, the fermentation kinetics of xanthan gum production from glucose, galactose, and their mixture, respectively, were studied with Xanthomonas campestris in stirred tank fermentors. In general, comparable fermentation performance in terms of productivity, product yield, and final product titer and quality (rheological properties) was obtained with these various carbon sources. Further batch fermentations with hydrolyzed whey permeate (lactose) showed the feasibility of xanthan gum production using whey permeate as an alternative low-cost feedstock.;However, the high broth viscosity due to product accumulation can cause serious mixing and mass (especially oxygen) transfer problems in conventional stirred-tank bioreactors, resulting in low product yields and poor product quality. A rotating fibrous bed bioreactor (RFBB) operated under a high gravity field can increase mass transfer in viscous xanthan gum fermentation due to the shear-thinning property of xanthan gum broth, thus increasing reactor productivity and final product titer. Furthermore, cells immobilized in the RFBB would allow continuous production of xanthan gum in a low-cell or cell-free broth that can be readily concentrated by ultrafiltration (UF) before alcohol precipitation, thus reducing the amount of alcohol and energy used in the downstream processing by 10-fold. Ultrafiltration also allows the recycle of the fermentation spent medium in subsequent batch xanthan gum fermentations. The effects of recycling the ultrafiltration permeate on xanthan gum fermentation were thus studied, and the results showed no significant changes in productivity, yield, titer, and product quality when the fermentation medium consisted of 75% of recycled permeate, confirming the feasibility of recycling the fermentation medium through the integrated RFBB-UF process.;To evaluate the scalability of the RFBB, xanthan gum fermentations in 20-liter RFBB operated in a repeated-batch mode were studied, and the results showed comparable performance to those obtained with 5-liter RFBB. A mathematical model for predicting the oxygen transfer rate, which affects the xanthan gum productivity, in the RFBB was also developed for process scale up. Finally, process and economic analyses were performed using SuperPro Designer, and the results confirmed that the integrated RFBB-UF process can reduce the xanthan gum production cost significantly, largely due to the improved reactor productivity and reduced raw materials and energy costs. Overall, the integrated RFBB-UF process is environmentally friendly and cost effective in producing xanthan gum from whey permeate. |
