Influence of bark on fuel ethanol production from steam-pretreated spruce

Abstract

BackgroundBark and bark-containing forest residues have the potential for utilization as raw material for lignocellulosic ethanol production due to their abundance and low cost. However, the different physical properties and chemical composition of bark compared to the conventionally used wood chips may influence the spruce-to-ethanol bioconversion process. This study assesses the impact of bark on the overall bioconversion in two process configurations, separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF), utilizing steam-pretreated spruce bark and wood mixtures.ResultsMixtures of different proportions of spruce bark and wood chips were subjected to SO2-catalyzed steam pretreatment at 210°C for five minutes, which has been shown to be effective for the pretreatment of spruce wood chips. The final ethanol concentration was the highest without bark and decreased significantly with increasing proportions of bark in both process configurations. However, this decrease cannot be attributed solely to the lower availability of the carbohydrates in mixtures containing bark, as the ethanol yield also decreased, from 85 to 59% in SSF and from 84 to 51% in SHF, as the mass fraction of bark was increased from 0 to 100%.ConclusionsThe results show that it was significantly more difficult to hydrolyse spruce bark to monomeric sugars than wood chips. Bark had an adverse effect on the whole bioconversion process due to its lower enzymatic hydrolyzability. On the other hand, bark inclusion had no detrimental effect on the fermentability of steam-pretreated spruce wood and bark mixtures. It was also observed that lower amounts of inhibitory degradation products were formed during the steam pretreatment of spruce bark than during the steam pretreatment of wood chips.

Valorization of Eucalyptus nitens bark by organosolv pretreatment for the production of advanced biofuels

“…Moreover, recent works showed the optimization of bioethanol production from delignified Eucalyptus globulus wood pretreated by organosolv using ethanol and glycerol as solvents (Muñoz et al, 2011;Romaní et al, 2016). The results obtained in this work can be positively compared with the ones reported in literature using SO 2 -catalyzed steam pretreated spruce bark, in which 87% of ethanol yield was obtained by separate hydrolysis and fermentation (SHF) (Frankó et al, 2015). The whole Eucalyptus grandis tree (including barks, branches and leaves) was pretreated by steam explosion and used as substrate for ethanol production, achieving an ethanol yield of 90% using 20% of solids and 60 FPU/g (McIntosh et al, 2017).…”

Removal of Water-Soluble Extractives Improves the Enzymatic Digestibility of Steam-Pretreated Softwood Barks

“…The digestibility of pretreated softwood barks has been reported to be rather low [ 10 , 51 ]. One factor that has been suggested to contribute to this is the condensation of water-soluble phenolic compounds during acid-catalyzed steam pretreatment.…”

“…Extractives contents between studies should be compared with caution, even for the same species, because they also depend on age, felling season, storage conditions [ 4 , 15 ], and extraction method [ 7 ]. A wide range of extractives content has consequently been reported for spruce and pine barks, ranging from 4.5 to 28.2% for spruce bark [ 10 , 14 , 24 ] versus 3.5 to 19.3% for pine bark [ 24 , 27 , 45 ]. The results of this study are consistent with the extractives content for spruce and pine barks using similar extraction schemes.…”

“…Unfortunately, the structural complexity and heterogeneity of bark render it more difficult to utilize than wood fractions. Softwoods are generally considered the most recalcitrant type of lignocellulosic feedstock for the production of monomeric sugars by pretreatment and enzymatic hydrolysis [ 11 , 19 ], but the breakdown of softwood barks to generate monomeric sugars from the carbohydrate part has proved to be even more challenging [ 10 , 52 ].…”

Bioethanol and lipid production from the enzymatic hydrolysate of wheat straw after furfural extraction

“…Hydrolysis was performed in a bioreactor as described earlier (Frankó et al 2015) with some modifications: Treatment was performed with 15 filter paper units Cellic CTec3 enzyme cocktail (Novozyme A/S, Bagsværd, Denmark) per g dry weight at pH 4.8.…”