Improved ethanol production from the slurry of pretreated brewers' spent grain through different co-fermentation strategies

The aim of this work was to bioconvert all sugars in BSG into ethanol using a process scheme that includes the enzymatic hydrolysis of the whole slurry resulting from the pretreatment of BSG with phosphoric and sulfuric acid using previously optimised conditions, followed by the co-fermentation of the mixed sugars. More than 90% of the sugars in raw BSG were recovered in the pretreatment and the subsequent enzymatic hydrolysis of the whole slurry. The co-fermentation of the enzymatic hydrolysates with Escherichia coli was then compared with that the co-culture of Scheffersomyces stipitis and Saccharomyces cerevisiae, which resulted in lower ethanol production. The co-fermentation strategy with a single microorganism (E. coli) when BSG was pretreated with phosphoric acid resulted into the highest ethanol concentration, 39 g/L, which means that 222 L of ethanol can be obtained from a ton of BSG without detoxification requirements.