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[Display omitted] • The basic principles and developments of hydrothermal pretreatment are reviewed. • The ultrastructural alterations during hydrothermal pretreatment are discussed. • The effects of hydrothermal pretreatment on bioethanol production are addressed. • The prospects for future developments are proposed and discussed. In recent years, visualization and characterization of lignocellulose at different scales elucidate the modifications of its ultrastructural and chemical features during hydrothermal pretreatment which include degradation and dissolving of hemicelluloses, swelling and partial hydrolysis of cellulose, melting and redepositing a part of lignin in the surface. As a result, cell walls are swollen, deformed and de-laminated from the adjacent layer, lead to a range of revealed droplets that appear on and within cell walls. Moreover, the certain extent morphological changes significantly promote the downstream processing steps, especially for enzymatic hydrolysis and anaerobic fermentation to bioethanol by increasing the contact area with enzymes. However, the formation of pseudo-lignin hinders the accessibility of cellulase to cellulose, which decreases the efficiency of enzymatic hydrolysis. This review is intended to bridge the gap between the microstructure studies and value-added applications of lignocellulose while inspiring more research prospects to enhance the hydrothermal pretreatment process. [ABSTRACT FROM AUTHOR]

[Display omitted] • PC/PB composites were synthesized with the help of the self-activation. • Many micro/meso/macropores were developed in the PC/PB composites. • PC/PB composites showed an excellent SMX sorption capacity, reaching 844 mg g−1. • Pore filling dominated the sorption capacity of SMX onto the PC/PB composites. Excellent biochar properties are crucial for sorption performance, and a developed pore structure is especially important. Herein, novel porous carbon/porous biochar (PC/PB) composites, in which the porous biochar and porous carbon were prepared at the same time, were synthesized via a green method from algal biomass with the help of the self-activation of citrate for the first time, and the composites were evaluated for the sorption of sulfamethoxazole (SMX). Many micro/meso/macropores were introduced into the PC/PB composites, which showed high specific surface areas (up to 1415 m2/g) and pore volumes (up to 1.08 cm3 g−1). The PC/PB composites displayed excellent SMX sorption capacities, which reached 844 mg g−1. Pore filling played a crucial role in determining the sorption capacity, and hydrogen bonding, electrostatic interactions and π-π stacking controlled the sorption rate. This study provides an improved method for preparation of porous biochar. [ABSTRACT FROM AUTHOR]

[Display omitted] • A coassisted method with HCOOK/(HCOO) 2 Ca was proposed to prepare porous carbons. • Porous carbons displayed excellent pore structures and abundant oxygen contents. • Porous carbons showed a high sorption quantity for diethyl phthalate: 761 mg g−1. • Pore filling, hydrogen bonding and π-π stacking dominated the sorption process. Porous carbons are excellent sorbents for removing organic pollutants. Green conversion of biowaste into advanced porous carbons is crucial for industrialized production and practical applications, which, however, have rarely been investigated. This study develops a coassisted carbonization method for the preparation of porous carbons with the environmentally friendly agents HCOOK and (HCOO) 2 Ca for the first time. The bamboo waste-derived hydrochar was transformed into oxygen-doped porous carbons, which displayed a large surface area and pore volume, abundant oxygen content, graphene structure and many surface functional groups. These properties contributed to the extremely high sorption of large quantities of diethyl phthalate, which reached 761 mg g−1. Surface adsorption, including pore filling, hydrogen bonding, and π-π stacking, rather than partitioning, was the main sorption process. Therefore, this study provides a sustainable and promising route for the preparation of porous carbons that can be applied in the efficient removal of organic pollutants. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ultrafast alkaline DES pretreatment was developed for fractionation of xylose residue. • The precipitation of lignin and recovery of DES was achieved by injecting CO 2. • Recovered alkaline DES still had distinguished pretreatment performance. • The obtained DES lignin nanoparticles (LNPs) had excellent antioxidant activity. • The highest glucose yield (90.12%) had been achieved under the mild condition. An aspirational pretreatment method for efficient fractionation and tailored valorization of large industrial biomass can ensure the realizability of sustainable biorefinery strategies. In this study, an ultrafast alkaline deep eutectic solvents (DES) pretreatment strategy was developed to efficiently extract the lignin nanoparticles and retain cellulose residues that could be readily enzymatic saccharified to obtain fermentative glucose for the bioenergy production from industrial xylose residue. Results showed that the DES pretreatment had excellent delignification performance and the regenerated DES lignin nanoparticles exhibited well-preserved structures and excellent antioxidant activity, as well as low molecular weights and relatively uniform size distribution, which could facilitate downstream catalytic degradation for production of chemicals and preparation of lignin-based materials. Under the optimal condition (DES pretreatment: 80 °C, 10 min; saccharification: 10 FPU/g, 5 wt%, 100 mg/g Tween 80), the glucose yield of 90.12% could be achieved, which was dramatically increased compared to raw materials. [ABSTRACT FROM AUTHOR]

[Display omitted] • Freezing-low temperature treatment promoted SCFAs production from WAS. • The potentially recovered carbon source increased to 321 mg COD/g VSS. • Both solubilization and hydrolysis steps of WAS were accelerated. • Macellibacteroides, Paraclostridium and Romboutsia were mainly enriched. • A shortened sludge retention time inhibited methanogenesis but a longer promoted. This study proposed a novel and high-efficiency strategy, i.e., freezing followed by low-temperature thermal treatment, to significantly promote short-chain fatty acids (SCFAs) production from waste activated sludge compared to traditional freezing/thawing treatment. The maximal production of SCFAs was 212 mg COD/g VSS with a shortened retention time of five days, and the potentially recovered carbon source, including SCFAs, soluble polysaccharides and proteins, reached 321 mg COD/g VSS, increased by 92.1 and 28.3% compared to sole freezing and thermal treatment. Both the solubilization and hydrolysis steps of WAS were accelerated, and the acid-producing microorganisms, such as Macellibacteroides , Romboutsia and Paraclostridium , were greatly enriched, with a total abundance of 13.9%, which was only 0.54% in control. Interestingly, the methane production was inhibited at a shortened retention time, resulting in SCFAs accumulation, whereas it was increased by 32.0% at a longer sludge retention time, providing a potential solution for energy recovery from WAS. [ABSTRACT FROM AUTHOR]