About this Research Topic
Lignocellulosic biomass is composed of three major units i.e., cellulose, hemicellulose and lignin, and is a renewable bioresource for the generation of fermentable sugar . Cellulose and hemicellulose can be hydrolyzed or enzymatically degraded to glucose and to a variety of pentose and hexose sugars. To obtain fermentable sugars from lignocellulose within chemically complex and resistant structures, a pretreatment process is the most important step for achieving enzymatic digestibility and thus producing useful amounts of fermentable sugars. Although physical, chemical, and biological pretreatment methods are under development, chemical pretreatments, e.g., acid, alkali, cosolvent, ionic liquid pretreatments in combination with high temperature, high pressure, or mechanical disruption have been applied in conventional biomass pretreatment processes.
Despite its efficiency and simplicity compared to other pretreatment processes, chemical pretreatment usually generates large amounts of wastewater during the pretreatment steps used to eliminate the fractions of both hemicellulose and lignin in biomasses. Wastewater contains solubilized lignocellulosic substances and residual chemicals, which result in highly concentrated organic carbon species and extremely high or low pH. Process design and cost estimation in a case study for ethanol production using lignocellulosic biomass indicated that approximately 20% of total direct costs could be consumed by managing wastewater and byproducts in biorefinery process. Therefore, a reduction of the costs associated with byproducts treatment would decrease the overall costs of biomass-based biorefinery processes. Moreover, wastewater from chemical pretreatments still includes the alkali or acid catalysts. Chemical catalysts can potentially be recycled for further biomass pretreatment processes. In addition, the lignocellulosic substances containing a lot of aromatic compounds as well as xylose solubilized in wastewater could be separated for utilization as a renewable resource . The residual byproducts also still contain non-utilized monosaccharides and other organic acids. These aromatic compounds and xylose would be potential compounds as value-added lignin or hemicelluloses to reduce the production cost in the process as well as to recycle or reuse byproducts for zero emission technologies . Unfortunately, wastewater recycling, chemical catalyst recovery, and residual byproducts in biorefinery process have not been evaluated.
This Research Topic provides an overview of the recycling and reusability of lignocellulosic byproducts in biorefinery processes. It describes the current processes for the reutilization of residual lignocellulosic biomass fractions after the process, evaluation of the feasibility of byproducts such as wastewater, lignin and hemicellulose fraction, to reduce the production cost for biorefinery products, and potential value-added applications of these products. The topics covered in this Research Topic include but are not restricted to:
1) Recycling and reuse of chemical catalyst after biomass pretreatment process
2) Novel approaches for fractionation of lignin in byproducts of biorefinery processes
3) Novel biocatalysts for utilization of byproducts generated in biofuel production
4) Microbial strain development for byproduct utilization
5) Application of lignin and hemicelluloses generated from lignocellulosic biomass
6) Upgrade waste streams of pulp and papermaking
7) Novel processes and applications for using recycled fibers from used paper and textiles
8) Biobased chemical production from lignocellulosic biomass byproducts
Keywords: Lignocellulose, Hemicellulose, Byproducts, Biofuels, Lignin
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