Hot water extraction and steam explosion as pretreatments for ethanol production from spruce bark

Spruce bark is a source of interesting polyphenolic compounds and also a potential but little studied feedstock for sugar route biorefinery processes. Enzymatic hydrolysis and fermentation of spruce bark sugars to ethanol were studied after three different pretreatments: steam explosion (SE), hot water extraction (HWE) at 80 °C, and sequential hot water extraction and steam explosion (HWE + SE), and the recovery of different components was determined during the pretreatments. The best steam explosion conditions were 5 min at 190 °C without acid catalyst based on the efficiency of enzymatic hydrolysis of the material. However, when pectinase was included in the enzyme mixture, the hydrolysis rate and yield of HWE bark was as good as that of SE and HWE + SE barks. Ethanol was produced efficiently with the yeast Saccharomyces cerevisiae from the pretreated and hydrolysed materials suggesting the suitability of spruce bark to various lignocellulosic ethanol process concepts.

► Hot water extraction (80 °C) and steam explosion were studied as pretreatments.
► Steam explosion of spruce bark should be carried out without acid catalyst.
► Hot water extraction is a suitable pretreatment for spruce bark with right enzymes.
► Ethanol production from pretreated enzymatically hydrolysed barks was efficient.
► Spruce bark is a potential feedstock for the production of lignocellulosic ethanol.