Combination of high solids loading pretreatment and ethanol fermentation of whole slurry of pretreated rice straw to obtain high ethanol titers and yields

Effective semi-fed-batch saccharification with high lignocellulose loading using co-culture of Clostridium thermocellum and Thermobrachium celere strain A9

Maximizing saccharification efficiency of lignocellulose and minimizing the production costs associated with enzyme requirements are crucial for sustainable biofuel production. This study presents a novel semi-fed-batch saccharification method that uses a co-culture of Clostridium thermocellum and Thermobrachium celere strain A9 to efficiently break down high solid-loading lignocellulosic biomass without the need for any external enzymes. This method optimizes saccharification efficiency and enhances glucose production from alkaline-treated rice straw, a representative lignocellulosic biomass. Initially, a co-culture of C. thermocellum and T. celere strain A9 was established with a treated rice straw loading of 150 g/l, supplemented with Tween 20, which enhanced enzymes stability and prevented unproductive binding to lignin, achieving a remarkable glucose concentration of up to 90.8 g/l. Subsequently, an additional 100 g/l of treated rice straw was introduced, resulting in a total glucose concentration of up to 140 g/l, representing 70.1% of the theoretical glucose yield from the 250 g/l treated rice straw load. In contrast, batch saccharification using an initial substrate concentration of 250 g/l of alkaline-treated rice straw without Tween 20 resulted in a glucose concentration of 55.5 g/l, with a theoretical glucose yield of only 27.7%. These results suggest that the semi-fed-batch saccharification method using co-cultivation of C. thermocellum and T. celere strain A9, supplemented with Tween 20 is an efficient microbial method for saccharifying high-concentration biomass. Moreover, this approach effectively manages high solids loading, optimizes efficiency, and reduces the need for external enzymes, thus lowering production costs and simplifying the process for industrial applications.

Design and construction of artificial metabolic pathways for the bioproduction of useful compounds

To efficiently produce useful compounds using biological cells, it is essential to optimally design all metabolic reactions and pathways, including not only the flow of carbon within the cell but also the production and consumption of energy and the balance of oxidation-reduction. Computational scientific methods are effective for the rational design of metabolic pathways and the optimization of metabolic fluxes. Based on this blueprint, it is crucial to accurately construct the cell, test and analyze whether it conforms to the design, and learn from the results to redesign the system in an effective cycle. This review introduces essential metabolic design techniques in synthetic biology and discusses the potential of using plant cells or plant genes effectively in synthetic biology for the production of useful compounds.

Comparative study of ethanol production from sodium hydroxide pretreated rice straw residue using Saccharomyces cerevisiae and Zymomonas mobilis

Rice straw is a suitable alternative to a cheaper carbohydrate source for the production of ethanol. For pretreatment efficiency, different sodium hydroxide concentrations (0.5-2.5% w/v) were tested. When compared to other concentrations, rice straw processed with 2% NaOH (w/v) yielded more sugar (8.17 ± 0.01 mg/ml). An alkali treatment induces effective delignification and swelling of biomass. The pretreatment of rice straw with 2% sodium hydroxide (w/v) is able to achieve 55.34% delignification with 53.30% cellulose enrichment. The current study shows the effectiveness of crude cellulolytic preparation from Aspergillus niger resulting in 80.51 ± 0.4% cellulose hydrolysis. Rice straw hydrolysate was fermented using ethanologenic Saccharomyces cerevisiae (yeast) and Zymomonas mobilis (bacteria). Overall, superior efficiency of sugar conversion to ethanol 70.34 ± 0.3% was obtained with the yeast compared to bacterial strain 39.18 ± 0.5%. The current study showed that pretreatment with sodium hydroxide is an effective method for producing ethanol from rice straw and yeast strain S. cerevisiae having greater fermentative potential for bioethanol production than bacterial strain Z. mobilis.

High-solids loading processing for an integrated lignocellulosic biorefinery: Effects of transport phenomena and rheology - A review

This review aims to present an analysis and discussion on the processing of lignocellulosic biomass in terms of biorefinery concept and circular bioeconomy operating at high solids lignocellulosic (above 15% [w/w]) at the pretreatment, enzymatic hydrolysis stage, and fermentation strategy for an integrated lignocellulosic bioprocessing. Studies suggest high solids concentration enzymatic hydrolysis for improved sugars yields and methods to overcome mass transport constraints. Rheological and computational fluid dynamics models of high solids operation through evaluation of mass and momentum transfer limitations are presented. Also, the review paper explores operational feeding strategies to obtain high ethanol concentration and conversion yield, from the hydrothermal pretreatment and investigates the impact of mass load over the operational techniques. Finally, this review contains a brief overview of some of the operations that have successfully scaled up and implemented high-solids enzymatic hydrolysis in terms of the biorefinery concept.

Optimization of Xylose Recovery in Oil Palm Empty Fruit Bunches for Xylitol Production

The hardest obstacle to make use of lignocellulosic biomass by using green technology is the existence of lignin. It can hinder enzyme reactions with cellulose or hemicellulose as a substrate. Oil palm empty fruit bunches (OPEFBs) consist of hemicellulose with xylan as the main component. Xylitol production via fermentation could use this xylan since it can be converted into xylose. Several pretreatment processes were explored to increase sugar recovery from lignocellulosic biomass. Considering that hemicellulose is more susceptible to heat than cellulose, the hydrothermal process was applied to OPEFB before it was hydrolyzed enzymatically. The purpose of this study was to investigate the effect of temperature, solid loading, and pretreatment time on the OPEFB hydrothermal process. The xylose concentration in OPEFB hydrolysate was analyzed using high-performance liquid chromatography (HPLC). The results indicated that temperature was more important than pretreatment time and solid loading for OPEFB sugar recovery. The optimum temperature, solid loading, and pretreatment time for maximum xylose recovery from pretreated OPEFB were 165 °C, 7%, and 60 min, respectively, giving a xylose recovery of 0.061 g/g of pretreated OPEFB (35% of OPEFB xylan was recovered).

Improved ethanol production from the slurry of pretreated brewers' spent grain through different co-fermentation strategies

The aim of this work was to bioconvert all sugars in BSG into ethanol using a process scheme that includes the enzymatic hydrolysis of the whole slurry resulting from the pretreatment of BSG with phosphoric and sulfuric acid using previously optimised conditions, followed by the co-fermentation of the mixed sugars. More than 90% of the sugars in raw BSG were recovered in the pretreatment and the subsequent enzymatic hydrolysis of the whole slurry. The co-fermentation of the enzymatic hydrolysates with Escherichia coli was then compared with that the co-culture of Scheffersomyces stipitis and Saccharomyces cerevisiae, which resulted in lower ethanol production. The co-fermentation strategy with a single microorganism (E. coli) when BSG was pretreated with phosphoric acid resulted into the highest ethanol concentration, 39 g/L, which means that 222 L of ethanol can be obtained from a ton of BSG without detoxification requirements.

Pretreatment and enzymatic saccharification of oak at high solids loadings to obtain high titers and high yields of sugars

Production of high-titer sugar from lignocellulose is important in terms of process economics of bio-based product industry. In this study, to obtain high titers and yields of sugars, we combined pretreatment and saccharification steps, both at high solids loadings. First, pretreatment of oak was optimized at a 30% (w/w) solids loading. The whole slurry of the pretreated oak was subjected to a fed-batch saccharification step at the final solids loading of 30%, to minimize loss of fermentable sugars and simplify the processes. As a result, high-titer sugars (157.5 g/L) consisting of 120.2 g/L of glucose and 37.3 g/L of xylose were obtained at 75.9% and 58.6%, respectively, of theoretical maximum yields, based on the initial glucan and xylan contents. Thus, through proper optimization processes of oak, the combination of pretreatment and saccharification at high solids loadings was effective in obtaining both high titers and high yields of sugars from lignocellulose.