Combined Sugarcane Pretreatment for the Generation of Ethanol and Value-Added Products

Abstract

In this work, we have tested individual and combination of applications of ozonolysis and liquid hot water (LHW) to pretreat sugarcane bagasse (SCB) for the removal of enzyme and/or microbial inhibitors and generation of potential value-added chemicals. A solid content with 80% cellulose and a liquid phase (liquor) rich in phenolic derived compounds (3 g.L−1) from lignin, sugars (>20 g.L−1), and other compounds, such as furfural and hydroxymethylfurfural (HMF), were generated. Maximal (59%) glucan conversion occurred in the presence of double-pretreated bagasse, which had 32–50% more glucan available than the samples that were individually LHW or ozone-pretreated, resulting in maximal ethanol production (92% after 42 h) from double-pretreated SCB enzyme hydrolyzate. In summary, this work showed that ozone reacts effectively with lignin without the use of any other chemical reagent, and LHW pretreatment, followed by a washing step, was effective in solubilizing and cleaning up the fiber enzyme and microbial inhibitory compounds with ozone being effective against phenolics. Moreover, the generated cellulose-rich substrate is readily fermentable. The acidic liquor fraction removed by sequential washings and containing mainly sugars and phenolic compounds may be evaluated for use in green chemistry bioconversions processes.

Inhibition of cellulase activity by liquid hydrolysates from hydrothermally pretreated soybean straw

“…This is consistent with our previous works that cellulase enzyme components are reversibly and irreversibly inhibited by the sugars and phenolic compounds present in the water-soluble fraction of hydrothermally pretreated lignocellulose (Kim et al, 2011;Kim et al, 2013;Ladeira Ázar et al, 2020). Our results also indicate that effective alleviation/detoxification strategies (e.g., one-pot biomass conversion (Xu et al, 2016) and double pretreatment (Bordignon et al, 2022)) are required to minimize the utilization of water in the water-wash step and lignin-derived potential inhibitors for economical and feasible lignocellulosic biorefinery. The inhibitory effects are even more pronounced as the solids loading in the pretreatment increases, the concentration of chemicals, and the severity factor that are necessary for a cost-effective lignocellulose conversion.…”

“…The cellulose crystallinity index (CrI) of raw and pretreated biomass samples, analyzed by solid-state 13 C cross-polarization magic angle spinning (CP/MAS) NMR based on our previous study (Wang et al, 2020), presented that cellulose CrI of soybean straw (28) was slightly increased to 34 with the cellulose from H 2 O 2 pretreated straw and 35 with the one from NaOHpretreated sample, possibly due to the removal of amorphous components like hemicellulose and lignin (Supplementary data), which is in accord with the chemical composition changes (higher cellulose content in pretreated samples in Table 1). However, these small changes in the cellulose CrI may not have notable effects on enzyme activities, as described in the previous studies (Martelli-Tosi et al, 2017;Bordignon et al, 2022). In addition to the changes in carbohydrate contents, the degradation of lignin and some ester groups affiliated with hemicellulose during NaOH pretreatment gave a higher phenolic concentration (716.2 mg/L) than those from the H 2 O 2 liquid (622.5 mg/L).…”

“…Thus the observed inhibition is likely to be mainly due to the ligninderived phenolic compounds. Previous work has reported that furan derivatives and small organic acids can significantly inhibit microbial cell growth, sugar consumption rate, and microbial metabolisms but not affect enzyme performances (Palmqvist and Hahn-Hagerdal, 2000a;Palmqvist and Hahn-Hagerdal, 2000b;Bordignon et al, 2022). Similar studies (Trejirian and Xu, 2011;Zhai et al, 2016) demonstrated that the oligomeric sugars derived from both softwood and hardwood exhibited little inhibition in cellulose hydrolysis by enzymes, while phenolics more significantly limited cellulase activity through reversible inhibition or irreversible deactivation mechanisms indicated by precipitation of the phenolic-cellulase complexes.…”

“…Soybean straw, the primary residual by-product, is ordinarily released during grain processing and the harvest of soybean; it has been considered a potential resource for renewable energy and sugar platform industries due to the high chemical composition of cellulose and hemicellulose (Karki et al, 2011;Liu et al, 2016, Liu et al, 2015. However, an efficient pretreatment step is required to alleviate biomass recalcitrance because of the complex crystalline structure between cellulosehemicellulose-lignin in the lignocellulosic biomass, including soybean straw (Bordignon et al, 2022;Kim et al, 2022). It is well-established that a pretreatment process can facilitate biomass saccharification by solubilizing hemicellulose and/or lignin and disrupting the crystalline structure of the cellulose to increase conversion yields by allowing more enzyme accessibility to the surface of the cellulose (Cao et al, 2015;Kim et al, 2016).…”

Enhanced enzymolysis and bioethanol yield from tobacco stem waste based on mild synergistic pretreatment

“…The glucose yield increase was consistent with the increase of the cellulose content after pretreatment. For two-step pretreatment (Liquid hot water/Ozonolysis), 43.0 g/L glucose was generated after enzymatic hydrolysis at 10% (w/v) of pretreated sugarcane, corresponding to 59% of conversion Frontiers in Energy Research frontiersin.org from initial glucan vs. 20, 47, 37, and 10% for untreated, ozone, liquid hot water, and two-step pretreated samples, respectively (Bordignon et al, 2022). Compared with present study, the higher glucose concentration obtained from two-step pretreatment (Liquid hot water/Ozonolysis) is possible due to the higher glucan content of pretreated sugarcane.…”