An overview of key pretreatment processes for biological conversion of lignocellulosic biomass to bioethanol

Abstract

Second-generation bioethanol can be produced from various lignocellulosic biomasses such as wood, agricultural or forest residues. Lignocellulosic biomass is inexpensive, renewable and abundant source for bioethanol production. The conversion of lignocellulosic biomass to bioethanol could be a promising technology though the process has several challenges and limitations such as biomass transport and handling, and efficient pretreatment methods for total delignification of lignocellulosics. Proper pretreatment methods can increase concentrations of fermentable sugars after enzymatic saccharification, thereby improving the efficiency of the whole process. Conversion of glucose as well as xylose to bioethanol needs some new fermentation technologies to make the whole process inexpensive. The main goal of pretreatment is to increase the digestibility of maximum available sugars. Each pretreatment process has a specific effect on the cellulose, hemicellulose and lignin fraction; thus, different pretreatment methods and conditions should be chosen according to the process configuration selected for the subsequent hydrolysis and fermentation steps. The cost of ethanol production from lignocellulosic biomass in current technologies is relatively high. Additionally, low yield still remains as one of the main challenges. This paper reviews the various technologies for maximum conversion of cellulose and hemicelluloses fraction to ethanol, and it point outs several key properties that should be targeted for low cost and maximum yield.

Metabolomics, biomass and lignocellulosic total sugars analysis in foxtail millet (Setaria italica) inoculated with different combinations of plant growth promoting bacteria and mycorrhiza

“…In the current study, foxtail millet subjected to different microbial inoculations showed significant increase in total sugars as part of metabolites compared to control in most of the treatments, which may be due to metabolic shift towards biomass enhancement. Although the lignocellulosic saccharification methods cannot convert 100% biomass into fermentable sugars (Maurya et al 2015) alkali pretreatment for switchgrass and big bluestem obtained 88% and 90% total sugars, respectively Muthukumarappan 2009, 2011). The lignocellulosic saccharification of biomass for bioethanol production has more environmental and economic benefits in comparison to ethanol production from sugar or starch (Zheng and Rehmann 2014).…”

Pretreatment Conditions for Hydrolysates from Unbleached Pulp Waste for Ethanol Fermentation with Xylose-fermenting Yeast, <i>Candida intermedia</i> 4-6-4T2

“…Sugars, acetic acid, formic acid, 4-oxopentanoic acid , Hiroshi NAGASAKI 1) , Tomoaki IKEDA 1) , Kiyotaka SAGA 2) , Koji YOSHIDA 2) , and Shigeyuki WATANABE Steam explosion conditions were evaluated as pretreatment for unbleached pulp waste to prepare fermentable sugars with xylose fermenting yeast, Candida intermedia 4-6-4T2. The hydrolysates pretreated under low or moderate severity conditions (severity factor (Ro) 3.53 or 4.12) did not contain known inhibitors to fermentation such as organic acids, furans and lignin-derived aromatic compounds in the LC-Mass (LC-MS) and HPLC analyses.…”

Emerging Technologies for the Production of Renewable Liquid Transport Fuels from Biomass Sources Enriched in Plant Cell Walls

“…Studies show alkaline methods are unfavorable as the reagent may be converted to salt during the reaction, which is costly or impossible to remove (Mosier et al, 2005). Ammonia (ammonia fiber expansion, AFEX) has also been considered as a chemical biomass pre-treatment (Harmsen et al, 2010; Maurya et al, 2015). More recently, non-volatile solvents classified as ionic liquids (IL) have been used for the dissolution of the plant cell wall and regeneration of polysaccharides such as cellulose (Mäki-Arvela et al, 2010).…”