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To elucidate the effects of lignin repolymerization on the combined pretreatment, the sequential acid and deep eutectic solvent (DES) pretreatment was implemented on Populus (poplar) in this study. Effects of acid pretreatment with or without phenolic additives (2-naphthol (2 N) and resorcinol (RS)) on the DES post-treatment efficiency were examined. The results showed that 2 N inhibited the lignin repolymerization in the first-step pretreatment, and slightly enhanced the lignin removal during DES post-treatment. However, RS intensified the lignin repolymerization, significantly decreasing the delignification of DES post-treatment from 73.6%∼79.4% to 39.0∼43.0%. Moreover, the poorer enzymatic hydrolysis was observed in the combined pretreated substrates as compared to the single DES pretreated ones, due to the higher surface lignin coverage. The addition of 2 N counteracted the adverse effects of acid pretreatment on the hydrolysis yields of combined pretreated substrates, and facilitated the yields from 25.8%∼36.0% to 26.2∼67.3%, while the RS addition further decreased the hydrolysis yields to 8.6∼9.6%. The mechanism for the changes on enzymatic digestibilities of the combined pretreated substrates was elucidated. [Display omitted] • 2-Naphthol inhibited lignin polymerization, while resorcinol intensified it. • Lignin repolymerization hindered the delignification of the DES post-treatment. • 2-Naphthol promoted the hydrolysis of pretreated poplar, but resorcinol impeded it. • 2-Naphthol addition benefited the lignin fractionation and valorization. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel combined H 2 SO 4 -ChCl/Gly pretreatment of reed stalks was developed. • Synergistic effect of H 2 SO 4 and ChCl/Gly eliminated xylan and lignin effectively. • H 2 SO 4 -ChCl/Gly-treated reed stalk was converted to glucose in a high yield of 91.1%. • High saccharification was due to enhanced accessibility and reduced lignin surface. In this study, an efficient combination of pretreatment solvents involving Choline chloride/Glycerol (ChCl/Gly) and H 2 SO 4 was firstly developed to assess the pretreatment performance and determine optimal pretreatment conditions. The results illustrated that the H 2 SO 4 -[ChCl/Gly] combination efficiently removed lignin (52.6%) and xylan (80.5%) from the pretreated reed stalk, and subsequent enzymatic hydrolysis yielded 91.1% of glucose. Furthermore, several characterizations were conducted to examine the structural and morphological changes of the reed stalk, revealing apparently enhanced accessibility (128.4 to 522.6 mg/g), reduced lignin surface area (357.9 to 229.5 m2/g), and substantial changes on biomass surface. Based on the aforementioned study, possible mechanisms for the H 2 SO 4 -[ChCl/Gly] pretreatment of reed stalks were proposed. The comprehensive understanding of combined H 2 SO 4 -[ChCl/Gly] pretreatment system for enhancing the saccharification of the reed stalk was interpreted in this work. Overall, this novel approach could be efficiently applied to pretreat and saccharify reed stalks, empowering the biomass refining industry. [ABSTRACT FROM AUTHOR]

Highlights • Alkali and acid pretreated biomass slurries were mixed for ethanol production. • This approach saved 40–50% alkali/acid use. • This approach improved fermentability. Abstract Alkali and acid pretreatment based processes for lignocellulosic biofuel production typically consume substantial amount of alkali and acid. In addition, alkali pretreatment generates compounds with high toxicity rendering washing/detoxification inevitable. In this work, alkali (AL) and dilute acid (DA) pretreatment based processes were compared side by side for ethanol production from corn stover (CS) using commercial enzymes and Zymomonas mobilis 8b strain. Next, AL and DA pretreated CS slurries (without removing liquid stream) were mixed to neutralize for enzymatic hydrolysis and ethanol fermentation. The digestibility and fermentability of the mixed pretreated biomass were systematically studied and compared to unmixed pretreated biomass. Results showed that mixed biomass process saved 40–50% alkali/acid use and enhanced fermentability compared to AL-CS. This work suggests that it could be beneficial to have both alkali and acid pretreatments operating in a biorefinery, which could accommodate various feedstocks. [ABSTRACT FROM AUTHOR]

A thorough assessment of the microstructural changes and synergistic effects of hydrothermal and/or ultrafine grinding pretreatment on the subsequent enzymatic hydrolysis of corn stover was performed in this study. The mechanism of pretreatment was elucidated by characterizing the particle size, specific surface area (SSA), pore volume (PV), average pore size, cellulose crystallinity (CrI) and surface morphology of the pretreated samples. In addition, the underlying relationships between the structural parameters and final glucose yields were elucidated, and the relative significance of the factors influencing enzymatic hydrolyzability were assessed by principal component analysis (PCA). Hydrothermal pretreatment at a lower temperature (170 °C) combined with ultrafine grinding achieved a high glucose yield (80.36%) at a low enzyme loading (5 filter paper unit (FPU)/g substrate) which is favorable. The relative significance of structural parameters in enzymatic hydrolyzability was SSA > PV > average pore size > CrI/cellulose > particle size. PV and SSA exhibited logarithmic correlations with the final enzymatic hydrolysis yield. [ABSTRACT FROM AUTHOR]

To enhance the cellulose digestibility of energy grass hybrid Pennisetum ( P. americanum × P. purpureum , HP) with low energy-consumption and high efficiency, a novel combinatorial pretreatment of oxygen-aqueous alkaline ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate ([Emim]Ac) media (OEA) was developed in this work. The combinatorial pretreatment was performed under the relatively low temperature (120 °C), short retention time (30 min), and 12 bar oxygen pressure. The combinatorial pretreatment of OEA was demonstrated effectively for pretreatment of hybrid Pennisetum , which evidenced by the removal of lignin, degradation of carbohydrate, and porosity property of the regenerated biomass. Subsequently, a higher glucose recovery (96.9%) at a low enzyme loading (20 FPU/g substrate) was obtained by the OEA pretreatment, and it was 9.1 times as much as the untreated samples. Overall, the novel OEA combinatorial pretreatment has the advantages of low thermal energy input and enzyme usage, and short retention time. [ABSTRACT FROM AUTHOR]

Pretreatment was the essential step for industrial application of lignocellulosic biomass. Combination of steam explosion and fungal treatment was conducted, and synergistic mechanism of the combined pretreatment was evaluated in terms of pore size distribution, crystallinity index, chemical compositions and enzymatic hydrolysis. The results showed that steam explosion destroyed the rigid structure of corn stalk, increased pore size and porosity, and exposed crystalline component of cellulose. Steam explosion broke the lignin-carbohydrate-complex structure of lignocellulosic biomass and facilitated the fungal treatment.Phellinus baumii could selectively degrade 34.7% and 36.58% of lignin for 1.4 MPa and 1.7 MPa steam-exploded corn stalk, respectively. As a result, the highest glucose yield of corn stalk pretreated by the condition of 1.7 MPa steam explosion associated with 21 d P. baumii reached 313.31 g kg-1, which was 2.88 and 1.32 times higher than that of the untreated corn stalk and the 1.7 MPa steam-exploded corn stalk, respectively. The combined pretreatment enhanced the enzymatic hydrolysis, which was a promising technology that might be explored as alternative to the existing pretreatment. [ABSTRACT FROM AUTHOR]

Abstract: Two novel two-step pretreatments for enzymatic hydrolysis of rice hull (RH) were proposed to lower the severity requirement of fungal pretreatment time. They consisted of a mild physical or chemical step (ultrasonic and H2O2) and a subsequent biological treatment (Pleurotus ostreatus). The combined pretreatments led to significant increases of the lignin degradation than those of one step pretreatments. After enzymatic hydrolysis of the pretreated RH, the net yields of total soluble sugar (TS) and glucose (G) increased greatly. The combined pretreatment of H2O2 (2%, 48h) and P. ostreatus (18d) was more effective than sole pretreatment of P. ostreatus for 60d. It could remarkably shorten the residence time and reduce the losses of carbohydrates. Ligninase analyses and SEM observations indicated that the enhancing of the efficiency could possibly attribute to the structure disruption of the RH during the first pretreatment step. So, the combined pretreatment could be recommended to different lignocellulosic materials for enzyme based conversions. [Copyright &y& Elsevier]

• In-situ lignin modification improved enzymatic hydrolysis of acid-pretreated larch. • Lignin modification with 2-naphthol suppressed lignin repolymerization. • Lignin modification with PEGDE lowered the enzyme non-productive binding on lignins. • 2-Naphthol and PEGDE modification synergistically facilitated enzymatic hydrolysis. To overcome the recalcitrance of residual lignins in acid-pretreated larch (AL), a combined acid and alkali pretreatment with in-situ lignin modification was developed in this study. The results showed that introducing in-situ lignin modification with 2-naphthol to acid pretreatment (160 and 180 oC) improved the enzymatic digestibility of AL by 12.7-14.4%, through suppressing lignin repolymerization. The obviously higher improvement (57.8-88.3%) was achieved by applying alkali post-treatment (90 oC) with poly (ethylene glycol) diglycidyl ether (PEGDE) on AL, mainly due to the function of in-situ lignin modification with PEGDE for reducing enzyme non-productive binding on lignins. More importantly, the synergism of 2-naphthol and PEGDE modification facilitated the enzymatic hydrolysis of AL more significantly. Its beneficial mechanism was explored by investigating the effects of in-situ lignin modification on lignin properties, including extraction yields, functional groups, and enzyme affinity of lignins. Results will give insights into establishing an efficient pretreatment of softwood biomass. [ABSTRACT FROM AUTHOR]

• A combined pretreatment was established based on acetic acid and alkali treatment. • The combined pretreatment coproduced XOS and fermentable sugars from poplar sawdust. • Cellulose accessibility was significantly increased during the combined pretreatment. • In-situ lignin modification with PEGDE reduced the enzyme non-productive binding. A novel combined pretreatment process of poplar sawdust was established in this study based on the sequential acetic acid and alkali treatment with poly (ethylene glycol) diglycidyl ether (PEGDE). Effects of each treatment step on chemical composition, cellulose accessibility, and enzymatic digestibility of poplar sawdust was investigated. Acetic acid pretreatment remarkably increased cellulose accessibility while also producing a relatively high quantity of xylooligosaccharides (XOS) (37.6% of raw xylan). However, enzymatic digestibility remained low (28.3%) despite hemicellulose disruption. Post alkali treatment was next applied, leading to improvement on cellulose accessibility and enzymatic hydrolysis. Enzymatic hydrolysis was improved more significantly by successive alkali treatment with PEGDE. Its potential mechanisms attributable to enzymatic hydrolysis improvement were explored by revealing the changes to lignin properties. This work successfully demonstrated that recalcitrant waste woody biomass can be biorefined into both high-value XOS as well as relatively high yield of fermentable sugars. [ABSTRACT FROM AUTHOR]