Evaluation of Alkali-Pretreated Soybean Straw for Lignocellulosic Bioethanol Production

Abstract

Soybean straw is a renewable resource in agricultural residues that can be used for lignocellulosic bioethanol production. To enhance enzymatic digestibility and fermentability, the biomass was prepared with an alkali-thermal pretreatment (sodium hydroxide, 121°C, 60 min). The delignification yield was 34.1~53%, in proportion to the amount of sodium hydroxide, from 0.5 to 3.0 M. The lignin and hemicellulose contents of the pretreated biomass were reduced by the pretreatment process, whereas the proportion of cellulose was increased. Under optimal condition, the pretreated biomass consisted of 74.0±0.1% cellulose, 10.3±0.1% hemicellulose, and 10.1±0.6% lignin. During enzymatic saccharification using Cellic® CTec2 cellulase, 10% (w/v) of pretreated soybean straw was hydrolyzed completely and converted to 67.3±2.1 g/L glucose and 9.4±0.5 g/L xylose with a 90.9% yield efficiency. Simultaneous saccharification and fermentation of the pretreated biomass by Saccharomyces cerevisiae W303-1A produced 30.5±1.2 g/L ethanol in 0.5 L fermented medium containing 10% (w/v) pretreated biomass after 72 h. The ethanol productivity was 0.305 g ethanol/g dry biomass and 0.45 g ethanol/g glucose after fermentation, with a low concentration of organic acid metabolites. Also, 82% of fermentable sugar was used by the yeast for ethanol fermentation. These results show that the combination of alkaline pretreatment and biomass hydrolysate is useful for enhancing bioethanol productivity using delignified soybean straw.

Xylitol Production From Byproducts Generated During Sequential Acid-/Alkali-Pretreatment of Empty Palm Fruit Bunch Fiber by an Adapted Candida tropicalis

“…Lignocellulosic biomass including agricultural plant byproducts, forestry wood residues, and other cellulosic materials are all potential resources of low-cost fermentable sugars, which could be used as biofuels and biorefinery chemicals Kim, 2012, 2014;Brethauer and Studer, 2015;Caicedo et al, 2016;Kim, 2018a). These materials are composed of three major components: cellulose, hemicellulose and lignin.…”

Enhancing Bioethanol Productivity Using Alkali-Pretreated Empty Palm Fruit Bunch Fiber Hydrolysate

“…Sodium hydroxide treatment was effective for delignification of the biomass. The main advantage is that the alkali process condition is relatively mild [ 12 , 14 , 18 ]. These mild conditions prevent condensation of lignin, resulting in a high lignin solubility.…”

“…An abundant byproduct in the palm oil industry is empty palm fruit bunch fiber (EPFBF), which consists of 27.6-32.5% lignin, 41.3-46.5% cellulose, and 25.3-33.8% hemicellulose [ 9 , 10 ]. EPFBF contains a relatively higher lignin content rather than other agriculture residual biomasses and feedstocks as a comparison of per gram of biomass (% lignin: % cellulose: % hemicellulose); soybean straw (19.2:44.2:5.9); wheat straw (23.4:38.2:21.2); corn stover (17.6:37.5:22.4); and switch grass (17.6:31.0:20.4) [ 11 – 14 ]. Lignocellulosic EPFBF is potentially a low-cost material and an alternative renewable bioresource, instead of food sources, such as corn, sugar cane, and other food stocks, for the production of bioethanol [ 7 , 8 , 11 ].…”

Isolation and Characterization of the Stress-Tolerant Candida tropicalis YHJ1 and Evaluation of Its Xylose Reductase for Xylitol Production From Acid Pre-treatment Wastewater

“…Levels of xylose, other sugars, and organic acids were determined using an HPLC system equipped with a refractive index detector, an auto-sampler, and an Aminex HPX-87P column (Bio-Rad, Hercules, CA, USA) for monosaccharide analysis, or a Rezex ROA-Organic Acid H+ column (Phenomenex Inc., Torrance, CA, USA) for organic acid analysis, as described previously (Kim, 2018b,c, 2019). All samples were clarified through filtration with a 0.20-μm filter and then injected into the analytical HPLC column.…”