Continuous Fermentation of Wheat Straw Hydrolysate by Clostridium tyrobutyricum with In-Situ Acids Removal

The present study focused on fermentative butyric acid production by Clostridium tyrobutyricum from pre-treated and hydrolysed wheat straw (PHWS) based on continuous operation mode and in situ acids extraction by reverse electro enhanced dialysis (REED). Different dilutions of PHWS in a synthetic medium (60-100 % v/v) were tested. It was found that continuous fermentation of PHWS greatly enhanced the sugar consumption rates and butyric acid productivity compared to batch tests, while application of REED enhanced them even further. Specifically, applying combined continuous operation mode and REED system for the fermentation of 70 % PHWS resulted in 19- and 53-fold higher glucose (1.37 g L^-1 h^-1) and xylose (0.80 g L^-1 h^-1) consumption rates, respectively, compared to those obtained by batch processing. Fermentation of 100 % PHWS continued unhindered with just urea and K₂HPO₄ added with butyric acid production rate, yield and selectivity being 1.30 g L^-1 h^-1, 0.45 g g^-1 sugars and 0.88 g g^-1 acids, respectively. These results were also confirmed in a 20 L pilot plant bioreactor system.