BIOENERGY AND BIOFUELS Comparison of separate hydrolysis and fermentation and simultaneous saccharification and fermentation processes for ethanol production from wheat straw by recombinant Escherichia coli strain FBR5

Ethanol production by recombinant Escherichia coli strain FBR5 from dilute acid pretreated wheat straw (WS) by separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF) was studied. The yield of total sugars from dilute acid (0.5% H2SO4) pretreated (160 °C, 10 min) and enzymatically saccharified (pH 5.0, 45 °C, 72 h) WS (86 g/l) was 50.0± 1.4 g/l. The hydrolyzate contained 1,184±19 mg furfural and 161±1 mg hydroxymethyl furfural per liter. The recombinant E. coli FBR5 could not grow at all at pH controlled at 4.5 to 6.5 in the non-abated wheat straw hydrolyzate (WSH) at 35 °C. However, it produced 21.9± 0.3 g ethanol from non-abated WSH (total sugars, 44.1± 0.4 g/l) in 90 h including the lag time of 24 h at controlled pH 7.0 and 35 °C. The bioabatement of WS was performed by growing Coniochaeta ligniaria NRRL 30616 in the liquid portion of the pretreated WS aerobically at pH 6.5 and 30 °C for 15 h. The bacterium produced 21.6±0.5 g ethanol per liter in 40 h from the bioabated enzymatically saccharified WSH (total sugars, 44.1±0.4 g) at pH 6.0. It produced 24.9±0.3 g ethanol in 96 h and 26.7±0.0 g ethanol in 72 h per liter from bioabated WSH by batch SSF and fed-batch SSF, respectively. SSF offered a distinct advantage over SHF with respect to reducing total time required to produce ethanol from the bioabated WS. Also, fed-batch SSF performed better than the batch SSF with respect to shortening the time requirement and increase in ethanol yield.