Comparison of mild alkaline and oxidative pretreatment methods for biobutanol production from brewer’s spent grains

Abstract

In this study, a comparative analysis of different pretreatment strategies on hydrolysis and fermentation of brewers’ spent grain for biobutanol production by C. beijerinckii is presented. Ozone (2.7% w/w, 30 min, 40–60% w/w humidity), sodium hydroxide (1–5 % w/w NaOH, 30 min, 120 ºC, 5–15 % w/w BSG) and hydrogen peroxide (5% w/w H2O2, pH 11.5, 60–180 min, 50 °C, 5–15 % w/w BSG) were the pretreatments analyzed.Ozonolysis was not very effective for either the degradation of lignin or the recovery of fermentable sugars in the enzymatic process under the tested operation conditions. Maximum butanol and ABE concentrations, 5.3± 0.2 g butanol/L and 6.8 ± 0.2 g ABE/L, were observed when low moisture content was used (40% w/w).The peroxide alkaline pretreatment was found to be the most effective for BSG, when it was conducted at 5% BSG for 60 min. Under these conditions, sugar enzymatic yields of 62.8% for glucose and 28.1% for xylose and arabinose, referred to untreated BSG, and product concentrations of 11.0± 0.2 g butanol/L and 13.7 ± 0.2 g ABE/L, were achieved. The alkaline pretreatment at 15% BSG with 1% w/w NaOH also provided high butanol and ABE concentrations (7.3 ± 0.1 g butanol/L and 8.9 ± 0.1 g ABE/L).Both the sodium hydroxide alkaline and peroxide alkaline methods were highly successful as pretreatments of BSG for ABE production, with overall yields of 44.4 g butanol/kg BSG and 54.0 g ABE/kg BSG for NaOH pretreatment (15% BSG, 1% w/w NaOH) and 45.1 g butanol/kg BSG and 56.1 g ABE/kg BSG for H2O2 pretreatment (5% BSG, 60 min).