Bioconversion of barley straw and corn stover to butanol (a biofuel) in integrated fermentation and simultaneous product recovery bioreactors

In these studies concentrated sugar solutions of barley straw and corn stover hydrolysates were fermented using Clostridium beijerinckii P260 with simultaneous product recovery and compared with the performance of a control glucose batch fermentation process. The control glucose batch fermentation resulted in the production of 23.25 g L⁻¹ ABE from 55.7 g L⁻¹ glucose solution resulting in an ABE productivity and yield of 0.33 g L⁻¹ h⁻¹ and 0.42, respectively. The control reactor (I) was started with 62.5 g L⁻¹ initial glucose and the culture left 6.8 g L⁻¹ unused sugar due to butanol toxicity resulting in incomplete sugar utilization. Barley straw (BS) hydrolysate sugars (90.3 g L⁻¹) resulted in the production of 47.20 g L⁻¹ ABE with a productivity of 0.60 g L⁻¹ h⁻¹ and a yield of 0.42. Fermentation of corn stover (CS) hydrolysate sugars (93.1 g L⁻¹) produced 50.14 g L⁻¹ ABE with a yield of 0.43 and a productivity of 0.70 g L⁻¹ h⁻¹. These productivities are 182–212% higher than the control run. The culture was able to use 99.4–100% sugars (CS & BS respectively) present in these hydrolysates and improve productivities which were possible due to simultaneous product removal. Use of >100 g L⁻¹ hydrolysate sugars was not considered as it would have been toxic to the culture in the integrated (simultaneous fermentation and recovery) process.