A Sequential Steam Explosion and Reactive Extrusion Pretreatment for Lignocellulosic Biomass Conversion within a Fermentation-Based Biorefinery Perspective

Abstract

The present work evaluates a two-step pretreatment process based on steam explosion and extrusion technologies for the optimal fractionation of lignocellulosic biomass. Two-step pretreatment of barley straw resulted in overall glucan, hemicellulose and lignin recovery yields of 84%, 91% and 87%, respectively. Precipitation of the collected lignin-rich liquid fraction yielded a solid residue with high lignin content, offering possibilities for subsequent applications. Moreover, hydrolysability tests showed almost complete saccharification of the pretreated solid residue, which when combined with the low concentration of the generated inhibitory compounds, is representative of a good pretreatment approach. Scheffersomyces stipitis was capable of fermenting all of the glucose and xylose from the non-diluted hemicellulose fraction, resulting in an ethanol concentration of 17.5 g/L with 0.34 g/g yields. Similarly, Saccharomyces cerevisiae produced about 4% (v/v) ethanol concentration with 0.40 g/g yields, during simultaneous saccharification and fermentation (SSF) of the two-step pretreated solid residue at 10% (w/w) consistency. These results increased the overall conversion yields from a one-step steam explosion pretreatment by 1.4-fold, showing the effectiveness of including an extrusion step to enhance overall biomass fractionation and carbohydrates conversion via microbial fermentation processes.

Biorefinery of the Olive Tree—Production of Sugars from Enzymatic Hydrolysis of Olive Stone Pretreated by Alkaline Extrusion

“…In the present case, the xylose production could be boosted by a sequential treatment to reach the values obtained in the papers previously cited [38][39][40]. For instance, alkaline extrusion could work as a second step following a preliminary step of steam explosion, a combination that has already been proven successful with other biomasses such as barley straw [21].…”

“…Extrusion has been described as a versatile pretreatment due to its capacity to adapt to different process configurations and feedstocks [18][19][20]. Extrusion alone is a mechanical process that provides high shear, fast heat transfer and thorough mixing [20] and the possibility to combine it with other pretreatments adds interest to the process application [21,22]. Chemical reagents and biocatalysts can also be added during extrusion [17,[23][24][25], resulting in a mixture of physical, thermal, chemical and/or biological effects that enhance the disruption of the lignocellulosic matrix.…”

Recent Trends in the Pretreatment of Lignocellulosic Biomass for Value-Added Products

“…The effects of this excessive dependence are already evident in the escalation of fuel prices, over the past decade and the severe environmental impacts like climate change. With a mere 23.7% utilization of renewable energy sources for energy needs, it is vital that world switches over to renewable and sustainable energy alternatives, on an urgent basis (Hussain et al, 2017;Oliva et al, 2017). Amidst the existing alternative sources for energy, bioenergy derived from the renewable and sustainable resources, LCB for the production of biofuels like biodiesel/ biogasoline, high value chemicals such as ethanol fuels, acids, saccharides, phenols, aldehydes, xylitol, and cellulose acetate with low carbon emissions are the most promising (Behera et al, 2014;Chen et al, 2017).…”

Bioraffinerien auf Basis schwach verholzter Biomasse

“…Nebenprodukten, für die es bislang keine oder nur unzureichende Anwendungsmöglichkeiten gibt, wie z. B. Zuckerrohr-Bagasse, organischer städtischer Abfall oder (Gersten-)Stroh [3,4,6]. Biomasse eignet sich für den Einsatz in Bioraffinerien insbesondere, wenn es sich um schwach verholzte Biomasse mit geringem Ligninanteil handelt.…”