Solvent production from rice straw by a co-culture of Clostridium acetobutylicum and Saccharomyces cerevisiae: effect of pH control
Miguel Capilla, Alejo Valles, Pau San‐Valero, Francisco Javier Álvarez‐Hornos, Carmen Gabaldón
Abstract
Abstract One of the challenges in biofuel production from lignocellulosic wastes is to improve its conversion to solvents; therefore, new strategies to enhance xylose uptake are required due to be the secondary abundant sugar. In this context, a novel fermentation strategy integrating a co-culture of Clostridium acetobutylicum and Saccharomyces cerevisiae with pH control was developed. Initially, two different buffers, ammonium acetate and calcium carbonate, were tested under pH min > 4.8 by fermenting 60 g L −1 of glucose with the C. acetobutylicum monoculture. Ammonium acetate was selected for fermenting media as butanol production was increased from 9.8 to 10.9 g L −1 over the calcium carbonate test. Comparing with the spontaneous acetone-butanol-ethanol (ABE) fermentation with C. acetobutylicum when no xylose consumption was observed, xylose consumption was efficiently increased by controlling pH min > 4.8. The xylose consumption was > 47% either by using a 45:15 g L −1 glucose:xylose mixture or with rice straw (RS) hydrolysate. Clostridium monoculture using RS hydrolysate and pH min > 4.8 produced a butanol (ABE) concentration of 6.5 (9.5) g L −1 . While it increased to 7.0 (13.1) g L −1 when the co-culture with S. cerevisiae was used using same pH regulation strategy mainly due to ethanol increase up to 2.7 g L −1 . Moreover, the xylose uptake doubled to 94% due to amino-acid secretion by yeast. Overall, this combined strategy was a very effective method for promoting sugar consumption and ABE solvent production from lignocellulosic waste.