Pretreatment, Enzymatic Hydrolysis, and Fermentation Applied to Ethanol from Lignocellulosic Biomasses

A special issue of Biomass (ISSN 2673-8783).

Deadline for manuscript submissions: closed (31 July 2023) | Viewed by 9814

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Chemical Engineering Department, Federal University of Rio Grande do Norte, Natal, Brazil
Interests: biomass; chemical engineering; fermentation; second-generation ethanol
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Dear Colleagues,

The growing world demand for increased food production, combined with pressure from society and environmental agencies to reduce the need for fuels obtained from non-renewable energy sources, makes the production of ethanol obtained from lignocellulosic residues, also known as second-generation ethanol, of particular importance in the current scenario. In 2021, the production of ethanol in the world’s largest producing countries of this commodity, the United States of America and Brazil, was 15 and 7.5 billion liters of liters, respectively, which are considerable values if we take into account the effect of COVID-19 on the world by 2020. However, unlike molasses and starchy materials or other saccharine sources, the recovery of sugars from lignocellulosic materials and the reduction in enzyme costs are some of the challenges to be overcome for the effective use of ethanol production at an industrial level. In this context, the pre-treatment and hydrolysis steps are essential for a successful process, with two more steps, fermentation and distillation. The latter is not the focus of this edition. Pre-treatment removes hemicellulose and lignin, the latter associated with low enzymatic digestibility. In turn, hydrolysis and fermentation steps have been carried out by means of different strategies, e.g., separate hydrolysis and fermentation (SHF), simultaneous saccharification and fermentation (SSF), and saccharification and semi-simultaneous fermentation (SSSF). They aim to reach a higher yield of fermentable sugars and a higher conversion of sugars into ethanol. In this context, the present edition highlights these three main steps and the use of different strategies applied to lignocellulosic biomass for second-generation ethanol. Additionally, it aims to contribute to the state of the art and to highlight the importance of ethanol from lignocellulosic biomass.

Prof. Dr. Everaldo Silvino dos Santos
Guest Editor

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Keywords

  • biomass pretreatment
  • cellulase enzymatic loading
  • lignocellulosic enzymes
  • saccharification and semi-simultaneous fermentation (SSSF)
  • second-generation ethanol production
  • separate hydrolysis and fermentation (SHF)
  • simultaneous saccharification and fermentation (SSF)

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Published Papers (2 papers)

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Research

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15 pages, 2806 KiB  
Article
Extraction of Cellulases Produced through Solid-State Fermentation by Trichoderma reesei CCT-2768 Using Green Coconut Fibers Pretreated by Steam Explosion Combined with Alkali
by Alan O. Campos, Estéfani A. Asevedo, Pedro F. Souza Filho and Everaldo S. dos Santos
Biomass 2024, 4(1), 92-106; https://doi.org/10.3390/biomass4010005 - 2 Feb 2024
Cited by 4 | Viewed by 1872
Abstract
The industrial processing of coconut to produce valuable foods, such as water and milk, generates large volumes of waste, especially the fruit shell. Despite this, material can be used in bioprocess applications, e.g., the production of enzymes, its recalcitrance hinders the cultivation of [...] Read more.
The industrial processing of coconut to produce valuable foods, such as water and milk, generates large volumes of waste, especially the fruit shell. Despite this, material can be used in bioprocess applications, e.g., the production of enzymes, its recalcitrance hinders the cultivation of microorganisms, and low productivity is usually achieved. In this study, the production of cellulolytic enzymes through solid-state fermentation (SSF) and their extraction was investigated using the green coconut fiber pretreated by steam explosion, followed by alkali. The fungus Trichoderma reesei CCT-2768 was cultivated, using an experimental design, to study the effect of the water activity and the amount of biomass in the reactor. The combination of the pretreatment strategies yielded more porous biomass, with less hemicellulose (5.38%, compared to 10.15% of the raw biomass) and more cellulose (47.77% and 33.96% in the pretreated and raw biomasses, respectively). The water activity significantly affected the production of cellulases, with maximum activity yielded at the highest investigated value (0.995). Lastly, the extraction of the enzymes from the cultivation medium was studied, and a 9 g/L NaCl solution recovered the highest CMCase and FPase activities (5.19 and 1.19 U/g, respectively). This study provides an important contribution to the valorization of the coconut residue through (i) the application of the steam explosion technology to optimize the production of cellulases using the SSF technology and (ii) their extraction using different solvents. Full article
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Review

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12 pages, 1768 KiB  
Review
The Role of Lignin Structure on Cellulase Adsorption and Enzymatic Hydrolysis
by Wenjuan Wu, Penghui Li, Lijing Huang, Yumeng Wei, Jiaquan Li, Lu Zhang and Yongcan Jin
Biomass 2023, 3(1), 96-107; https://doi.org/10.3390/biomass3010007 - 1 Mar 2023
Cited by 25 | Viewed by 7050
Abstract
Lignin is one of the important components of lignocellulosic cell walls, which endows plant cell walls with rigidity and strength and protects them from microbial invasion. The presence of lignin is thought to hinder the conversion of biomass to bioenergy, so understanding enzyme-lignin [...] Read more.
Lignin is one of the important components of lignocellulosic cell walls, which endows plant cell walls with rigidity and strength and protects them from microbial invasion. The presence of lignin is thought to hinder the conversion of biomass to bioenergy, so understanding enzyme-lignin interactions is very important in order to reduce the inhibition of lignin and improve the hydrolysis yields. Conversion of lignocellulosic raw materials into bioethanol is divided into pretreatment, enzymatic hydrolysis, and fermentation. In this paper, both pretreatment and enzymatic hydrolysis of lignocellulose are described in detail. Finally, the reasons why lignin hinders enzymatic hydrolysis efficiency, mainly from forming spatial barriers and interacting with cellulase, are discussed, and the influencing factors and mechanisms of action of cellulase hydrolysis are explored with a view to targeted regulation of lignin structure to improve lignocellulosic saccharification. Full article
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