Hydrolysis Of Rice Straw Research Articles

Development of cell recycle technology incorporating nutrient supplementation for lignocellulosic ethanol fermentation using industrial yeast Saccharomyces cerevisiae

For the efficient production of lignocellulosic ethanol, a technology of recycling yeast cells at a high-solid load was developed. The yeast Saccharomyces cerevisiae TJ14 grew up to 5.0 × 107 cells/mL at 39 °C during the simultaneous saccharification and fermentation of hydrothermally pretreated rice straw. By exploiting the viability of the cells, a portion of the fermentation residue was recycled, yielding 52.3 g/L ethanol (90.3% yield) at 1.12 g/(L·h) in six batches. This result is attributable to the maintenance of a viable cell count (cells/mL) on the order of 107. In accordance with this principle, the effects of low-cost nutrients on yeast recycling were elucidated, where 0.125% corn steep liquor was deemed sufficient for fermenting rice straw and empty fruit bunch hydrolysates. The supplementation of sugarcane molasses into bagasse was found to be a practical approach, resulting in 63.5–67.7 g/L ethanol and 5.3 × 106–4.4 × 107 cells/mL in six batches. Here, we describe that the high cell-growth potential in industrially relevant media minimizes the retention of lignocellulosic residues in subsequent batches, thus eliminating the problematic operations in yeast recycling.

Improved synthesis of 2,5-bis(hydroxymethyl)furan from 5-hydroxymethylfurfural using acclimatized whole cells entrapped in calcium alginate

Upgrading of biomass-derived 5-hydroxymethylfurfural (HMF) has attracted considerable interest recently. In this work, efficient synthesis of 2,5-bis(hydroxymethyl)furan (BHMF) from HMF was reported with the acclimatized Meyerozyma guilliermondii SC1103 cells entrapped in calcium alginate beads. Catalytic activities of the cells as well as their HMF-tolerant level increased significantly upon acclimatization and immobilization. BHMF was obtained within 7–24 h with good yields (82–85%) and excellent selectivities (99%) when the substrate concentrations were 200–300 mM. In scale-up synthesis, BHMF of up to 181 mM was produced within 7 h, and its productivity was approximately 3.3 g/L h. In addition, the immobilized biocatalyst showed satisfactory operational stability; the cell viability of 70% was retained after reuse 4 times. With rice straw hydrolysate as co-substrate, both the reaction rate and selectivity decreased, likely due to the deleterious influence of xylose in the hydrolysate.

Bioethanol production from rice straw by simultaneous saccharification and fermentation with statistical optimized cellulase cocktail and fermenting fungus

BackgroundRice straw is one of the abundant lignocellulosic biomass with potential as a feedstock for bioethanol production. To produce ethanol from the biomass biologically, enzymatic hydrolysis is necessary that can effectively degrade rice straw into fermentable sugars such as glucose and xylose. Many researches utilized many kinds of commercial cellulase reagents on the hydrolysis of cellulose. Since these have different enzyme activities, enzyme reagents suitable for each biomass must be selected. In this study, three appropriate cellulase reagents were selected by multivariate analysis technique and then optimized by design of experiments method for efficient hydrolysis of alkali-pretreated rice straw. Moreover, an ethanol production from the treated straw was performed by simultaneous saccharification and fermentation (SSF) with the optimized enzyme cocktail and xylose-fermenting fungus of Mucor circinelloides.ResultsPretreatment by alkali solution of rice straw resulted in the increase of fermentable sugar content from 56.3 to 80.0%. The desirable commercial enzyme reagents for saccharification of the straw were determined as a combination of “Cellulase Onozuka 3S”, “Cellulase T Amano 4”, and “Pectinase G Amano” by a multivariate analysis based on various cellulolytic activities of each reagent. The optimum mixing ratio was calculated by response surface method based on design of experiment method. The optimized cocktail successfully achieved 75.3 g/L in production of the total fermentable sugar by hydrolysis of alkali-treated rice straw that agreed with the hydrolysis efficiency of 94.1%. SSF of 100 g/L treated rice straw with the optimal cocktail and M. circinelloides under aerobic condition resulted in 30.5 g/L ethanol concentration for 36 h.ConclusionThe construction of cellulase cocktail by the proposed statistical method enabled efficient hydrolysis of alkali-treated rice straw. SSF process combining the optimized cocktail and a xylose-fermenting fungus could be expected as a promising system for ethanol production from various lignocellulosic biomasses.

Controllable synthesis of monoacrylate‐modified adsorption resins and enhancing adsorption toward fermentation inhibitors from rice straw hydrolysate

AbstractBACKGROUNDA series of monoacrylate modified adsorption resins from reactive mixtures with different amounts and types of monoacrylate have been synthesized by an oil/water (O/W) suspension polymerization technique and utilized to remove fermentation inhibitors and pigments from rice straw hydrolysate for the first time. The modified resin was characterized by Fourier transform infrared spectroscopy (FT‐IR), scanning electron microscopy (SEM) and N2 adsorption–desorption isotherms. Batch experiments were carried out to determine the adsorption performance of the modified resin for fermentation inhibitors. Regeneration and reusability experiments were performed to evaluate the economic value.RESULTSThe modified resin with 80% glycidyl methacrylate (GMA) feed and epoxy group showed optimal selectivity of fermentation inhibitors from rice straw hydrolysate. The adsorption capacities of acid soluble lignin (ASL), formic acid, acetic acid, levulinic acid, 5‐hydroxymethylfurfural (5‐HMF) and furfural onto 80% GMA modified resin were enhanced by 45%, 156%, 86%, 79%, 131%, 52%, respectively. Furthermore, the decolorization rate was improved by 12% over unmodified styrene‐divinylbenzene (St‐DVB) adsorption resin with approximately 5% sugar loss.CONCLUSIONThis work not only provides a potential adsorbent for the removal of fermentation inhibitors from rice straw hydrolysate, but also provides guidance for choosing and modifying the adsorbent to detoxify lignocellulose hydrolysate. © 2018 Society of Chemical Industry

Ethanol production from acid-pretreated and detoxified rice straw as sole renewable resource

Renewable resources are the most abundant available and inexpensive materials on the earth. This study was undertaken not only to optimize acid pretreatment conditions of rice straw but also to produce ethanol from the detoxified rice straw hydrolysate (RSH) by the yeasts Saccharomyces cerevisiae and Scheffersomyces stipitis. Box-Behnken response surface design was used to determine optimum temperature (105–135 °C), dilute sulfuric acid ratio (1–5%, w/v), and solid-to-liquid ratio (1:19–1:15, w/v). Results indicated that the optimum hydrolysis conditions of rice straw were 126.5 °C, 1:15 solid-to-liquid ratio (w/v) and 5% acid ratio (w/v). Reducing sugar concentration (RSC) was 21.50 g/L (0.323 g sugar/g biomass) under optimal conditions. After detoxification process with activated charcoal, the percentage removal of acetic acid, hydroxymethyl furfural, 2-furaldehyde, and phenolics was 2.01, 78.58, 100, and 94.67%, respectively. The catalytic efficiency of sulfuric acid was achieved to be 3.40 and 5.33 g/g in non-detoxified and detoxified RSHs, respectively. The ethanol yields and maximum production rates for S. cerevisiae and S. stipitis (ATCC 58784 and ATCC 58785) were calculated as 47.20% of theoretical ethanol yield and 0.37 g/L/h, 42.95% of theoretical ethanol yield and 0.09 g/L/h, and 48.81% of theoretical ethanol yield and 0.07 g/L/h, respectively. Consequently, rice straw can be a good substrate source for production of value-added products such as ethanol by fermentation. Besides, in the case of further improvement of fermentation media in terms of inhibitors, especially of acetic acid, better fermentation results would be obtained.

Optimization of sodium hydroxide pretreatment and enzyme loading for efficient hydrolysis of rice straw to improve succinate production by metabolically engineered Escherichia coli KJ122 under simultaneous saccharification and fermentation

Rice straw was pretreated with sodium hydroxide (NaOH) before subsequent use for succinate production by Escherichia coli KJ122 under simultaneous saccharification and fermentation (SSF). The NaOH pretreated rice straw was significantly enhanced lignin removal up to 95%. With the optimized enzyme loading of 4% cellulase complex + 0.5% xylanase (endo-glucanase 67 CMC-U/g, β-glucosidase 26 pNG-U/g and xylanase 18 CMC-U/g dry biomass), total sugar conversion reached 91.7 ± 0.8% (w/w). The physicochemical analysis of NaOH pretreated rice straw indicated dramatical changes in its structure, thereby favoring enzymatic saccharification. In batch SSF, succinate production of 69.8 ± 0.3 g/L with yield and productivity of 0.84 g/g pretreated rice straw and 0.76 ± 0.02 g/L/h, respectively, was obtained. Fed-batch SSF significantly improved succinate concentration and productivity to 103.1 ± 0.4 g/L and 1.37 ± 0.07 g/L/h with a comparable yield. The results demonstrated a feasibility of sequential saccharification and fermentation of rice straw as a promising process for succinate production in industrial scale.

Controllable Synthesis of Styrene-divinylbenzene Adsorption Resins and the Effect of Textural Properties on Removal Performance of Fermentation Inhibitors from Rice Straw Hydrolysate

The purification of lignocellulosic hydrolysate has great practical significance in the field of bioenergy and biorefinery. In this study, the effects of textural properties of styrene-divinylbenze...

Studies on Alkaline Pretreatment of Sugarcane Bagasse and Rice Straw Hydrolysis for the Recovery of Reducing Sugar

Studies on Alkaline Pretreatment of Sugarcane Bagasse and Rice Straw Hydrolysis for the Recovery of Reducing Sugar

Toxicity evaluation of lignocellulose-derived phenolic inhibitors on Saccharomyces cerevisiae growth by using the QSTR method

Quantitative Structure-toxicity Relationship (QSTR) models were built to evaluate the toxicity of lignocellulose-derived phenolic inhibitors on the growth of Saccharomyces cerevisiae in a bioethanol production process. The established models were proved to be reliable after rigorous validation and showed values of R2 > 0.6 and Q2LOO > 0.5. They could provide accurate guidance for alleviating the most toxic inhibitors in pretreated lignocellulosic hydrolysates, thus facilitating bioethanol production. The results showed that the inhibitors that possessed unsaturated bonds, formyl groups and carbonyl group substituents showed obvious toxicity effects. The toxicity of the inhibitors with ortho-electron-withdrawing substituents was stronger than that of metra- or para-electron-donating substituents. Ferulic acid was chosen to analyze its toxicity in practical alkali-pretreated rice straw hydrolysates because of its strong toxicity and high concentration. The results showed that its toxicity was up to 82%, which was suggested to be dominantly detoxified in the bioethanol production process.

Notable mixed substrate fermentation by native Kodamaea ohmeri strains isolated from Lagenaria siceraria flowers and ethanol production on paddy straw hydrolysates

BackgroundBioethanol obtained by fermenting cellulosic fraction of biomass holds promise for blending in petroleum. Cellulose hydrolysis yields glucose while hemicellulose hydrolysis predominantly yields xylose. Economic feasibility of bioethanol depends on complete utilization of biomass carbohydrates and an efficient co-fermenting organism is a prerequisite. While hexose fermentation capability of Saccharomyces cerevisiae is a boon, however, its inability to ferment pentose is a setback.ResultsTwo xylose fermenting Kodamaea ohmeri strains were isolated from Lagenaria siceraria flowers through enrichment on xylose. They showed 61% glucose fermentation efficiency in fortified medium. Medium engineering with 0.1% yeast extract and peptone, stimulated co-fermentation potential of both strains yielding maximum ethanol 0.25 g g−1 on mixed sugars with ~ 50% fermentation efficiency. Strains were tolerant to inhibitors like 5-hydroxymethyl furfural, furfural and acetic acid. Both K. ohmeri strains grew well on biologically pretreated rice straw hydrolysates and produced ethanol.ConclusionsThis is the first report of native Kodamaea sp. exhibiting notable mixed substrate utilization and ethanol fermentation. K. ohmeri strains showed relevant traits like utilizing and co-fermenting mixed sugars, exhibiting excellent growth, inhibitor tolerance, and ethanol production on rice straw hydrolysates.

Platform Study on the Development of a Nondetoxified Rice Straw Hydrolysate to Its Application in Lipid Production from Mortierella alpina

In the present work, a mild acid saccharification approach for rice (Oryza Sativa) straw was developed by Response Surface Optimization. A 23 central composite experimental design with variable factors as duration (minutes), mild acid concentration % (v/v) and minimum solid loading % (w/v) was chosen to optimize the hydrolysis process, fixing the operating temperature to a moderate minimum of 121°C. The study determined 5% solid loading, 0.75% acid concentration and 150 (min)-residence duration as optimum, for enhanced reducing sugar release. To compensate the reduced saccharification efficiency under mild operating conditions, a novel approach of multi-tier saccharification was implemented at optimal conditions of saccharification. HPLC analysis revealed the final reducing sugar yield of 0.76 g reducing sugar/gram straw (47.9g/l and 35g/l concentration in two consecutive saccharification cycles) and glucose, galactose, and xylose as major reducing sugars in hydrolysate. On assessing the hydrolysate as a ...

Enhanced coproduction of hydrogen and butanol from rice straw by a novel two-stage fermentation process

Lignocellulosic biomass has been increasingly used for biofuel production, such as biohydrogen and biobutanol. However, the enzymes used in hydrolysis result in a large increase in production cost. To reduce the enzyme involvement in lignocellulosic butanol, a novel two-stage fermentation process was constructed by combining a Carboxylate Platform and acetone-butanol-ethanol (ABE) fermentation. First, without enzyme involvement, lignocellulose was converted to volatile fatty acids (VFAs) using the Carboxylate Platform. Subsequently, the VFAs were used as feedstock to generate butanol by ABE fermentation of Clostridium beijerinckii NCIMB 8052. Fed with 20 g/L pretreated rice straw, the acidogenic fermentation produced 660 mL/L hydrogen and 6.87 g/L butyric acid, with a total VFAs of 9.52 g/L in the supernatant of fermentation culture (SFC). With 40% rice straw hydrolysate and 60% SFC as co-substrate, hydrogen and butanol productions of 5897 mL/L and 13.8 g/L, respectively, were obtained in the ABE fermentation. Mass balance and energy generation analysis showed that the specific butanol and energy yields from rice straw reached 230 g/kg and 9633.7 kJ/kg, respectively. Additionally, the carbon-flow distribution analysis indicated that the SFC supplement decreased the metabolic flux of acetone producing pathway and increased the metabolic flux of butanol producing pathway. The novel two-stage fermentation process was a more effective approach for energy generation from lignocellulose that avoided external addition of commercial butyric acid and reduced enzyme involvement for fermentation product.

Butyric acid production from lignocellulosic biomass hydrolysates by engineered Clostridium tyrobutyricum overexpressing Class I heat shock protein GroESL

Lignocellulosic biomass is the most abundant and renewable substrate for biological fermentation, but the inhibitors present in the lignocellulosic hydrolysates could severely inhibit the cell growth and productivity of industrial strains. This study confirmed that overexpressing of native groESL in Clostridium tyrobutyricum could significantly improve its tolerance to lignocellulosic hydrolysate-derived inhibitors, especially for phenolic compounds. Consequently, ATCC 25755/groESL showed a better performance in butyric acid fermentation with hydrolysates of corn cob, corn straw, rice straw, wheat straw, soybean hull and soybean straw, respectively. When corn straw and rice straw hydrolysates, which showed strong toxicity to C. tyrobutyricum, were used as the substrates, 29.6 g/L and 30.1 g/L butyric acid were obtained in batch fermentation, increased by 26.5% and 19.4% as compared with the wild-type strain, respectively. And more importantly, the butyric acid productivity reached 0.31 g/L·h (vs. 0.20–0.21 g/L·h for the wild-type strain) due to the shortened lag phase.

Synergy of lignocelluloses pretreatment by sodium carbonate and bacterium to enhance enzymatic hydrolysis of rice straw

We studied a new strategy for pretreatment of rice straw (RS) to enhance enzymatic hydrolysis under mild condition. This approach uses the synergy of sodium carbonate (Na2CO3) and the bacterial strain Cupriavidus basilensis B-8 (hereafter B-8). After synergistic Na2CO3 and B-8 pretreatment (SNBP), the reducing sugar yield varied from 335.3mg/g to 799.6mg/g under different conditions. This increased by 13–31% over Na2CO3 pretreatment (284.2–719.2mg/g) and 3.42–8.15times over the untreated RS (98mg/g). Moreover, the composition of RS was changed significantly through decreases in lignin and hemicellulose. We confirmed this change by compositional analysis and physicochemical characterization of the structure of RS before and after pretreatment. We also elaborated a mechanism for SNBP to better explain RS changes and bacterial effects on enzymatic hydrolysis.

Novel dihydrogen-bonding deep eutectic solvents: Pretreatment of rice straw for butanol fermentation featuring enzyme recycling and high solvent yield

Rice straw (RS) is one of the most abundant lignocellulosic biomasses in China, which contains mainly of cellulose, hemicellulose and lignin. In this study, a novel deep eutectic solvent (DES), foraceline, was prepared with choline chloride and double hydrogen bond donors (formic acid and acetic acid). By combining foraceline and sodium carbonate (1%), a two-stage pretreatment method was developed and applied in RS pretreatment to improve the biodegradability of lignocellulose. The highest glucose and total sugar of 37.3 g·L−1 and 42.8 g·L−1 were obtained after hydrolysis of 24 h using 50 FPU·gtotal solid-1 of cellulase. The cellulase attached to RS was reutilized for five continuous cycles in which enzyme loading was reduced from 50 FPU·gtotal solid-1 (Cycle I) to 30 FPU·gtotal solid-1 (Cycle V), resulting in total sugar of 41.3–42.6 g·L−1 for each cycle. RS hydrolysates (Cycle I and V) was utilized in butanol fermentation by Clostridium saccharobutylicum DSM 13864, achieving butanol titer and yield of 9.5 g·L−1 and 0.25 g·gtotal sugar-1, similar to those of glucose medium. This study demonstrated the feasibility of this newly developed biomass pretreatment by dihydrogen bonding DES featuring cellulase recycling and high butanol yield.

Improved physicochemical pretreatment and enzymatic hydrolysis of rice straw for bioethanol production by yeast fermentation

Lignocellulosic biomass such as agricultural and forest residues are considered as an alternative, inexpensive, renewable, and abundant source for fuel ethanol production. In the present study, three different pretreatment methods for rice straw were carried out to investigate the maximum lignin removal for subsequent bioethanol fermentation. The chemical pretreatments of rice straw were optimized under different pretreatment severity conditions in the range of 1.79-2.26. Steam explosion of rice straw at 170°C for 10min, sequentially treated with 2% (w/v) KOH (SEKOH) in autoclave at 121°C for 30min, resulted in 85±2% delignification with minimum sugar loss. Combined pretreatment of steam explosion and KOH at severity factor (SF 3.10) showed improved cellulose fraction of biomass. Furthermore, enzymatic hydrolysis at 30 FPU/g enzyme loading resulted in 664.0±5.39mg/g sugar yield with 82.60±1.7% saccharification efficiency. Consequently, the hydrolysate of SEKOH with 58.70±1.52g/L sugars when fermented with Saccharomyces cerevisiae OBC14 showed 26.12±1.24g/L ethanol, 0.44g/g ethanol yield with 87.03±1.6% fermentation efficiency.

Minimizing mixing intensity to improve the performance of rice straw anaerobic digestion via enhanced development of microbe-substrate aggregates

The aim of this work was to study the effect of the differential development of microbe-substrate aggregates at different mixing intensities on the performance of anaerobic digestion of rice straw. Batch and semi-continuous reactors were operated for up to 50 and 300days, respectively, under different mixing intensities. In both batch and semi-continuous reactors, minimal mixing conditions exhibited maximum methane production and lignocellulose biodegradability, which both had strong correlations with the development of microbe-substrate aggregates. The results implied that the aggregated microorganisms on the particulate substrate played a key role in rice straw hydrolysis, determining the performance of anaerobic digestion. Increasing the mixing speed from 50 to 150rpm significantly reduced the methane production rate by disintegrating the microbe-substrate aggregates in the semi-continuous reactor. A temporary stress of high-speed mixing fundamentally affected the microbial communities, increasing the possibility of chronic reactor failure.

Comparison between free cells and immobilized cells of Candida shehatae in ethanol production from rice straw hydrolysate using repeated batch cultivation

Ethanol production by xylose-fermenting Candida shehatae ATCC 22984 was studied in repeated batch fermentations of rice straw hydrolysate using both free cells and immobilized cells. Terracotta beads, coconut bract and corncob were investigated as supporting materials for cell immobilization. Ethanol production was stable at least 5 cycles when using cells immobilized on coconut bract. Average ethanol concentrations obtained from each batch were 16.7 g/L in free-cell system and 17.2 g/L in immobilized-cell system. Repeated batch using free cell system resulted in a slightly higher volumetric productivity than the use of immobilized cells. Ethanol that could be produced per ton of dried rice straw was 120 L using free cell system and 117 L using immobilized cell on coconut bract in glass column system.

Inhibition efficiency evaluation of lignocellulose-derived compounds for bioethanol production

The toxicity and inhibition efficiency of lignocellulose-derived compounds on two kinds of bacteria were evaluated based on Quantitative Structure-Activity Relationship method, which could guide us to eliminate fermentation inhibitors existed in hydrolysates specifically. The results revealed that phenols exhibited the most significant toxicity on microbes, in which the functional group attached to benzene ring could dramatically influence toxicity degree. Furans showed moderate toxicity on microbes, however, short chain fatty acids exhibited feeble toxicity. GC-MS analysis identified inhibitors in rice straw hydrolysates after alkali-pretreatment as main constituent of phenols and acids, the concentration of which were 1.965 mM and 2.965 mM, respectively. Moreover, inhibition efficiency of these inhibitors was evaluated based on their toxicity and concentration. The results showed that inhibition efficiency of long chain fatty acids and phenol acids were significantly more enormous than that of other compounds, in which octadecanoic acid and ferulic acid had maximum inhibition efficiency value.

A vertical ball mill as a new reactor design for biomass hydrolysis and fermentation process

A vertical ball mill (VBM) reactor was evaluated for use in biomass conversion processes. The effects of agitation speed (100–200 rpm), number of glass spheres (0–30 units) and temperature (40–46 °C) on enzymatic hydrolysis of rice straw and on glucose fermentation by a thermotolerant Kluyveromyces marxianus strain were separately studied. The results revealed an important role of the spheres during biomass' fiber liquefaction and yeast's fermentative performance. For hydrolysis, the spheres were the only variable with significant positive impact on cellulose conversion, while for fermentation all the variables have influenced the ethanol volumetric productivity (QP). For QP, the spheres showed an interactive effect with temperature, being obtained a maximum of 2.16 g/L.h when both variables were used in the lowest level. By applying the needed adjustments on the levels of the variables for each process (hydrolysis and fermentation), the VBM reactor could be efficiently used for biomass conversion into ethanol.