Hydrolysis Of Rice Straw Research Articles

Optimization of enzymatic hydrolysis and ethanol fermentation from AFEX-treated rice straw

An abundant agricultural residue, rice straw (RS) was pretreated using ammonia fiber expansion (AFEX) process with less than 3% sugar loss. Along with commercial cellulase (Spezyme CP) at 15 filter paper unit/g of glucan, the addition of Multifect Xylanase at 2.67 mg protein/g glucan and Multifect Pectinase at 3.65 mg protein/g glucan was optimized to greatly increase sugar conversion of AFEX-treated RS. During enzymatic hydrolysis even at 6% glucan loading (equivalent to 17.8% solid loading), about 80.6% of glucan and 89.6% of xylan conversions (including monomeric and oligomeric sugars) were achieved. However, oligomeric glucose and xylose accounted for 12.3% of the total glucose and 37.0% of the total xylose, respectively. Comparison among the three ethanologenic strains revealed Saccharomyces cerevisiae 424A(LNH-ST) to be a promising candidate for RS hydrolysate with maximum ethanol metabolic yield of 95.3% and ethanol volumetric productivity of 0.26 g/L/h. The final concentration of ethanol at 37.0 g/L was obtained by S. cerevisiae 424A(LNH-ST) even with low cell density inoculum. A biorefinery combining AFEX pretreatment with S. cerevisiae 424A(LNH-ST) in separate hydrolysis and fermentation could achieve 175.6 g EtOH/kg untreated rice straw at low initial cell density (0.28 g dw/L) without washing pretreated biomass, detoxification, or nutrient supplementation.

Enhanced enzymatic hydrolysis of rice straw pretreated by alkali assisted with photocatalysis technology

AbstractBACKGROUND: The fermentable sugars in lignocellulose are derived from cellulose and hemicellulose, which are not readily accessible to enzymatic hydrolysis because of their biological resistance, so that pretreatment of lignocellulose is needed for this process. In this work, a novel lignocellulose pretreatment method using alkali solution assisted by photocatalysis was investigated.RESULTS: The reaction conditions of nano‐TiO2 dosage and photocatalysis time were optimized at 2 g L−1 and 1 h, respectively. After pretreatment under these conditions, cellulose in rice straw was increased from 37.5% to 71.5%, and lignin decreased from 18.5% to 9.0%. The results of X‐ray diffraction (XRD), Fourier transform infrared (FT‐IR) and scanning electron microscopy (SEM) analysis showed that the physical properties and microstructure of the straw were changed by this pretreatment, which favored the following enzymatic hydrolysis. The enzymatic hydrolysis rate of the straw pretreated using this technology was verified to be 73.96%, which was 2.56 times higher than that obtained with the alkali procedure.CONCLUSION: The proposed photocatalysis pretreatment technology was more efficient at degrading the lignin and hemicellulose in rice straw than alkali pretreatment, making it more readily available for the following enzymatic hydrolysis process. Copyright © 2009 Society of Chemical Industry

Enhanced ethanol production by fermentation of rice straw hydrolysate without detoxification using a newly adapted strain of Pichia stipitis

An enhanced inhibitor-tolerant strain of Pichia stipitis was successfully developed through adaptation to acid-treated rice straw hydrolysate. The ethanol production obtained by fermentation of NaOH-neutralized hydrolysate without detoxification using the adapted P. stipitis was comparable to fermentation of overliming-detoxified hydrolysate. The ethanol yield using the adapted P. stipitis with both types of hydrolysate at pH 5.0 achieved 0.45 g p g s −1, which is equivalent to 87% of the maximum possible ethanol conversion. Furthermore, the newly adapted P. stipitis demonstrated significantly enhanced tolerance to sulfate and furfural despite the fact that both inhibitors had not been removed from the hydrolysate by NaOH neutralization. Finally, the ethanol conversion could be maintained at 60% and above when the neutralized hydrolysate contained 3.0% sulfate and 1.3 g L −1 furfural.

Wet disk milling pretreatment without sulfuric acid for enzymatic hydrolysis of rice straw

Rice straw has recently attracted interest in Japan as a potential source of raw material for ethanol production. Wet disk milling, a continuous pretreatment to enhance the enzymatic digestibility of rice straw, was compared with conventional ball milling and hot-compressed water treatment. Pretreated rice straw was evaluated by enzymatic hydrolysis using Acremonium cellulase and characterized by X-ray diffraction and scanning electron microscopy. Glucose and xylose yields by wet disk milling, ball milling, and hot-compressed water treatment were 78.5% and 41.5%, 89.4% and 54.3%, and 70.3% and 88.6%, respectively. Wet disk milling and hot-compressed water treatment increased sugar yields without decreasing their crystallinity. The feature size of the wet disk milled rice straw was similar to that of hot-compressed water-treated rice straw. The energy consumption of wet disk milling was lower than that of other pretreatments. Thus, wet disk milling is an economical, practical pretreatment for the enzymatic hydrolysis of lignocellulosic biomass, especially herbaceous biomass such as rice straw.

Pretreatment of Rice Straw by a Hot-Compressed Water Process for Enzymatic Hydrolysis

Hot-compressed water (HCW) is among several cost-effective pretreatment processes of lignocellulosic biomass for enzymatic hydrolysis. The present work investigated the characteristics of HCW pretreatment of rice straw including sugar production and inhibitor formation in the liquid fraction and enzymatic hydrolysis of pretreated material. Pretreatment was carried out at a temperature ranging from 140 to 240 degrees C for 10 or 30 min. Soluble oligosaccharides were found to constitute almost all the components of total sugars in the liquid fraction. The maximal production of total glucose at 180 degrees C and below accounted for 4.4-4.9% of glucan in raw material. Total xylose production peaked at 180 degrees C, accounting for 43.3% of xylan in raw material for 10-min pretreatment and 29.8% for 30-min pretreatment. The production of acetic acid increased at higher temperatures and longer treatment time, indicating more significant disruption of lignocellulosic structure, and furfural production achieved the maximum (2.8 mg/ml) at 200 degrees C for both 10-min and 30-min processes. The glucose yield by enzymatic hydrolysis of pretreated rice straw was no less than 85% at 180 degrees C and above for 30-min pretreatment and at 200 degrees C and above for 10-min pretreatment. Considering sugar recovery, inhibitor formation, and process severity, it is recommended that a temperature of 180 degrees C for a time of 30 min can be the most efficient process for HCW pretreatment of rice straw.

Influence of metal addition on ethanol production with Pichia stipitis ATCC 58784

Trace metals always act as cofactors or coenzymes in many cellular processes. Deficiency or excess of some metals will affect the fermentation of lignocellulosic hydrolysate. In order to make sure the deficient or excessive states of metals in culture medium, metal contents analysis was conducted in Pichia stipitis ATCC 58784 cells, synthetic medium, and diluted acid hydrolysate of rice straw. The results showed that Cu, Ni, and Co were deficient, and Al was a little excessive. So the influences of Cu(2+), Al(3+), Ni(2+), and Co(2+) additions on the growth and ethanol production of ATCC 58784 were further researched. Low concentration additions of Cu(2+) and Al(3+) (<0.24 mM and <0.23 mM, respectively) improved biomass growth of ATCC 58784 by 34 and 13%, respectively; however, higher concentrations decreased biomass growth. On the other hand, addition of Cu(2+) (0.39 mM) did not affect volumetric ethanol production significantly (P = 0.05) and addition of Al(3+) (0.38 mM) showed no influence on volumetric ethanol production (P = 0.68). Addition of 0.074 mM Co(2+) inhibited biomass growth of ATCC 58784 by 13% and volumetric ethanol production by 10%. The biomass growth and volumetric ethanol production of ATCC 58784 was arrested by the addition of 0.33 mM of Ni(2+) by 53 and 65%, respectively.

Cellulase production using biomass feed stock and its application in lignocellulose saccharification for bio-ethanol production

A major constraint in the enzymatic saccharification of biomass for ethanol production is the cost of cellulase enzymes. Production cost of cellulases may be brought down by multifaceted approaches which include the use of cheap lignocellulosic substrates for fermentation production of the enzyme, and the use of cost efficient fermentation strategies like solid state fermentation (SSF). In the present study, cellulolytic enzymes for biomass hydrolysis were produced using solid state fermentation on wheat bran as substrate. Crude cellulase and a relatively glucose tolerant BGL were produced using fungi Trichoderma reesei RUT C30 and Aspergillus niger MTCC 7956, respectively. Saccharification of three different feed stock, i.e. sugar cane bagasse, rice straw and water hyacinth biomass was studied using the enzymes. Saccharification was performed with 50 FPU of cellulase and 10 U of β-glucosidase per gram of pretreated biomass. Highest yield of reducing sugars (26.3 g/L) was obtained from rice straw followed by sugar cane bagasse (17.79 g/L). The enzymatic hydrolysate of rice straw was used as substrate for ethanol production by Saccharomyces cerevisiae. The yield of ethanol was 0.093 g per gram of pretreated rice straw.

A thermotolerant β-glucosidase isolated from an endophytic fungi, Periconia sp., with a possible use for biomass conversion to sugars

A fungal strain, BCC2871 ( Periconia sp.), was found to produce a thermotolerant β-glucosidase, BGL I, with high potential for application in biomass conversion. The full-length gene encoding the target enzyme was identified and cloned into Pichia pastoris KM71. Similar to the native enzyme produced by BCC2871, the recombinant β-glucosidase showed optimal temperature at 70 °C and optimal pH of 5 and 6. The enzyme continued to exhibit high activity even after long incubation at high temperature, retaining almost 60% of maximal activity after 1.5 h at 70 °C. It was also stable under basic conditions, retaining almost 100% of maximal activity after incubation for 2 h at pH ⩾ 8. The enzyme has high activity towards cellobiose and other synthetic substrates containing glycosyl groups as well as cellulosic activity toward carboxymethylcellulose. Thermostability of the enzyme was improved remarkably in the presence of cellobiose, glucose, or sucrose. This β-glucosidase was able to hydrolyze rice straw into simple sugars. The addition of this β-glucosidase to the rice straw hydrolysis reaction containing a commercial cellulase, Celluclast ® 1.5L (Novozyme, Denmark) resulted in increase of reducing sugars being released compared to the hydrolysis without the β-glucosidase. This enzyme is a candidate for applications that convert lignocellulosic biomass to biofuels and chemicals.

Enzymatic hydrolysis of alkali-pretreated rice straw by Trichoderma reesei ZM4-F3

To minimize the cost of cellulase production, both pretreatment of the rice straw and on-site enzyme production were realized. Rice straw was first pretreated by 2% NaOH, which could increase cellulose by 54.83%, and decreased hemicellulose by 61.07% and lignin by 36.24%, respectively. Detected by SEM, significant morphological changes were observed in the tissue. Through orthogonal experiments, temperature 35 °C, initial pH value 4.5 and the rotation speed of shaking bed 180 rpm were determined to be the optimal conditions for hydrolysis of rice straw by Trichoderma reesei ZM4-F3. After hydrolysis for 96 h, the production of FPA and reducing sugars could achieve 2.231 g l−1 and 12.92 U ml−1, respectively. Moreover, T. reesei ZM4-F3 can decompose 68.21% of pretreated rice straw after 120 h of hydrolysis. By GC analysis, it showed that glucose is the main component of the enzymatic hydrolysates, which made GC seem to be more effective than the DNS method for analysis of the enzymatic hydrolysates as it can detect the concentration of each kind of monosaccharide more accurately.

Xylitol Production from Rice Straw Hemicellulose Hydrolyzate by Polyacrylic Hydrogel Thin Films with Immobilized Candida subtropicalis WF79

Xylose from rice straw hemicellulose hydrolysate was fermented for xylitol production using Candida subtropicalis WF79 cells immobilized in polyacrylic hydrogel thin films of 200 mum thickness. Cell immobilization was conducted by first suspending the yeast cells in a mixture of 2-hydroxyethyl methacrylate (HEMA, hydrophilic monomer), polyethylene glycol diacrylate (PEG-DA, crosslinking agent), and benzoin isopropyl ether (photoinitiator). The mixture was then allowed to form polyacrylic hydrogel thin films, between two pieces of glass sheets, by UV-initiated photopolymerization. The hemicellulose of rice straw was hydrolyzed using dilute sulfuric acid at 126 degrees C. The hydrolysate was neutralized with calcium hydroxide. After separating the solid residues and calcium sulfate precipitates by filtration, the hydrolysate was treated with charcoal to partially remove potential inhibitory substances, followed by vacuum concentration to obtain solutions of desired xylose concentrations for yeast fermentation. The thin films with immobilized yeast cells were submerged in the xylose solution from rice straw hydrolysate for fermentation in an Erlenmeyer flask. The maximum yield was 0.73 g of xylitol per gram of xylose consumed. In the 52.5-day long durability test, after 40 d of repeated batchwise operation, the fermentation activities of the cell immobilized in thin films began to decline to a yield of 0.57 g/g at the end.

Acid in ionic liquid: An efficient system for hydrolysis of lignocellulose

Acid in ionic liquid was demonstrated as an efficient system for hydrolysis of lignocellulosic materials with improved total reducing sugars (TRS) yield under mild conditions. TRS yields were up to 66%, 74%, 81% and 68% for hydrolysis of corn stalk, rice straw, pine wood and bagasse, respectively, in C4mimCl in the presence of 7 wt% hydrogen chloride at 100 °C under atmospheric pressure within 60 min. Different combinations between ionic liquids, such as C6mimCl, C4mimBr, AmimCl, C4mimHSO4, and SbmimHSO4, and acids, including sulfuric acid, nitric acid, phosphoric acid, as well as maleic acid, afforded similar results albeit longer reaction time was generally required comparing with the combination of C4mimCl and hydrochloric acid. FT-IR spectra and elemental analysis of the recovered residues indicated that modification of lignin occurred during sulfuric acid catalyzed hydrolysis. In addition, kinetic modeling based on experimental data suggested that the hydrolysis likely followed a consecutive first-order reaction sequence, where k1 and k2, the rate constants for TRS formation and TRS degradation, were determined as 0.068 min−1 and 0.007 min−1, respectively. This novel system may be valuable to facilitate cost-efficient conversion of biomass into biofuels and biobased products.

Aqueous two‐phase extraction using thermoseparating copolymer: a new system for phenolic compounds removal from hemicelullosic hydrolysate

AbstractBACKGROUND: The hydrolysis of hemicellulosic material can provide liquor with high xylose concentration (which can be used as a fermentation medium) and phenolic compounds (Phs), potentially immunostimulating compounds. However, these hydrolysates must be detoxified in order to remove the Phs that can act as inhibitors in bioconversions.RESULTS: Aqueous two‐phase systems composed of thermoseparating copolymers were used for rice straw hydrolysate detoxification. The hydrolysis process was able to promote chemical breakdown of 85% of the total hemicellulose content, 14% of the cellulose, and 2% of the lignin. The hydrolysate obtained contained 19.7 g L−1 of xylose and several phenolic compounds, such as vanillin, vanillic acid, ferullic acid, etc. The phenolics extraction was studied as a function of copolymer molar mass (1100 g mol−1, 2000 g mol−1 and 2800 g mol−1), their percentages (from 5% to 50%) and Phs initial concentration. Phenolic compounds extraction of around 80% was obtained under the following conditions: 20% (w/w) and 35% (w/w) copolymer 1100 g mol−1, 35% (w/w) copolymer 2000 g mol−1 and 35% (w/w) copolymer 2800 g mol−1 at 25 °C.CONCLUSIONS: The results demonstrated the viability of this method for the removal of Phs from rice straw hydrolysate, which has potential uses in bioconversion processes. Copyright © 2007 Society of Chemical Industry

L-lactic acid production from Lactobacillus casei by solid state fermentation using rice straw

In order to make full use of rice straw (RS) produced at large quantity in China and to reduce the production cost of L-lactic acid, attempts were made to utilize the hydrolysate of RS as sole carbon source and the lignocellulose as inert support for producing L-lactic acid using solid state fermentation (SSF). The pretreated rice straw was enzymatically hydro- lyzed by cellulase, and the hydrolyzate, containing reducing sugars supplemented with a minimum of (NH4)2SO4, MnSO4, and yeast extract, was used as moistening agent to impregnate 5g of RS, which was used as the inert support for SSF. Maximum L-lactic acid production of 3.467g per 5g of support was obtained at 37 oC, using Lactobacillus casei as inoculum, after 5 days of fermentation with optimized process parameters such as 72% moisture content, 4g per 5g support of reducing sugars, 2.5ml per 5g support of inoculum size, 3g per 5g support of CaCO3, and pH 6.5.

Use of surfactants in enzymatic hydrolysis of rice straw and lactic acid production from rice straw by simultaneous saccharification and fermentation

Rice straw (RS) is one of the most abundant lignocellulosic waste by-products worldwide and provides an alternative substrate to produce useful chemicals such as bioethanol and lactic acid. However, higher enzyme loadings are needed to obtain a higher product yield, which makes the large-scale utilization economically difficult. The presence of non-ionic surfactants and poly(ethylene glycol) (PEG) during the enzymatic hydrolysis of lignocellulosics has been found to increase the conversion of cellulose into fermentable sugars. We have found that adding 0.2g g-1 substrate of polyoxyethylene(20) sorbitan monooleate (PSM) or high-mass PEG increased the sugar yield by 22% and 12%, respectively, when enzyme loading was at 10FPU g-1 for 24h. PSM behaved better than PEG when different substrate concentrations, temperatures, and enzyme loadings were investigated. PSM provides an opportunity to reduce enzyme dosage while still keeping the same extent of hydrolysis. We also investigated the effect of PSM on the simultaneous saccharification and fermentation of pretreated RS to lactic acid. Results showed that addition of 0.7g L-1 PSM improved the lactic acid production by 24% compared to the reference without PSM addition at 72h.

Use of surfactants in enzymatic hydrolysis of rice straw and lactic acid production from rice straw by simultaneous saccharification and fermentation

Rice straw (RS) is one of the most abundant lignocellulosic waste by-products worldwide and provides an alternative substrate to produce useful chemicals such as bioethanol and lactic acid. However, higher enzyme loadings are needed to obtain a higher product yield, which makes the large-scale utilization economically difficult. The presence of non-ionic surfactants and poly(ethylene glycol) (PEG) during the enzymatic hydrolysis of lignocellulosics has been found to increase the conversion of cellulose into fermentable sugars. We have found that adding 0.2g g-1 substrate of polyoxyethylene(20) sorbitan monooleate (PSM) or high-mass PEG increased the sugar yield by 22% and 12%, respectively, when enzyme loading was at 10FPU g-1 for 24h. PSM behaved better than PEG when different substrate concentrations, temperatures, and enzyme loadings were investigated. PSM provides an opportunity to reduce enzyme dosage while still keeping the same extent of hydrolysis. We also investigated the effect of PSM on the simultaneous saccharification and fermentation of pretreated RS to lactic acid. Results showed that addition of 0.7g L-1 PSM improved the lactic acid production by 24% compared to the reference without PSM addition at 72h.

THE ENHANCEMENT OF AMMONIA PRETREATMENT ON THE FERMENTATION OF RICE STRAW HYDROLYSATE TO XYLITOL

In xylitol fermentation from rice straw hydrolysate by Candida tropicalis As2.1776, ammonia steeping was employed to pretreat the rice straw. Experimental results showed that the content of toxic compounds created in the hydrolysis process, such as acetic acid and phenolic compounds, was greatly reduced and the fermentation of the hydrolysate was enhanced. Xylitol fermentation was investigated in flasks and a 2-L bioreactor, respectively. The xylitol yield factor and volumetric productivity were 0.746 g/g and 0.686 g/(L·h) in the lab-flask fermentation, respectively. The corresponding results conducted in bioreactor fermentation were 0.689 g/g and 0.697 g/(L·h), respectively.

Comparison of Three Microwave/Chemical Pretreatment Processes for Enzymatic Hydrolysis of Rice Straw

The microwave/chemical Pretreatment is a more effective rice-straw Pretreatment technique than the conventional heating chemical Pretreatment by accelerating reactions during the Pretreatment process. In this paper, three microwave/chemical Pretreatment processes of rice straw, viz microwave/alkali, microwave/acid/alkali and microwave/acid/alkali/H2O2 were investigated for its enzymatic hydrolysis and the xylose recovery from the Pretreatment liquor. Firstly, the effect of three microwave/chemical Pretreatment processes of rice straw on its weight loss and chemical composition was examined. The results show that the rice straw pre-treated by microwave/acid/alkali/H2O2 had the highest weight loss and cellulose content. Then, the xylose recovery from Pretreatment liquor was studied. The xylose could not be recovered during the microwave/alkali Pretreatment process, but it could be recovered as crystalline xylose during the microwave/acid/alkali and microwave/acid/alkali/H2O2 Pretreatment processes. Finally, the enzymatic hydrolysis of pre-treated rice straw (substrate concentration 50 g l−1, pH 4·8 and enzyme loading 20 mg g−1 substrate) was also investigated and the results indicate that the rice straw pre-treated by microwave/acid/alkali/H2O2 had the highest hydrolysis rate and glucose content in the hydrolysate.

Structural properties and enzymatic hydrolysis of rice straw

Rice straw was divided into fractions by morphological character, and the enzymatic hydrolysis of these fractions was investigated. Chemical composition and the proportions of cells of different compositions were very variable in different fractions. This has a fundamental effect on the enzyme adsorption capability and hydrolysis performance. Cellulose and hemicellulose contents affected hydrolysis performance positively, silica and lignin in the rice straw had a negative effect. Morphological separation appears to be necessary if rice straw fractions are to be useful as carbohydrate sources.

Conversion of rice straw to sugars by dilute-acid hydrolysis

Abstract Hydrolysis of rice straw by dilute sulfuric acid at high temperature and pressure was investigated in one and two stages. The hydrolyses were carried out in a 10-l reactor, where the hydrolysis retention time (3–10 min), pressure (10–35 bar) and acid concentration (0–1%) were examined. Optimization of first stage hydrolysis is desirable to achieve the highest yield of the sugars from hemicellulose and also as a pretreatment for enzymatic hydrolysis. The results show the ability of first stage hydrolysis to depolymerize xylan to xylose with a maximum yield of 80.8% at hydrolysis pressure of 15 bar, 10 min retention time and 0.5% acid concentration. However, the yield of glucose from glucan was relatively low in first stage hydrolysis at a maximum of 25.8%. The solid residuals were subjected to further dilute-acid hydrolysis in this study. This second-stage hydrolysis without addition of the acid could not increase the yield of glucose from glucan beyond 26.6%. On the other hand, the best results of the hydrolysis were achieved, when 0.5% sulfuric acid was added prior to each stage in two-stage hydrolysis. The best results of the second stage of the hydrolysis were achieved at the hydrolysis pressure and the retention time of 30 bar and 3 min in the second stage hydrolysis, where a total of 78.9% of xylan and 46.6% of glucan were converted to xylose and glucose, respectively in the two stages. Formation of furfural and HMF were functions of the hydrolysis pressure, acid concentration, and retention time, whereas the concentration of acetic acid was almost constant at pressure of higher than 10 bar and a total retention time of 10 min.

Optimization of glucose-6-phosphate dehydrogenase releasing from Candida guilliermondii by disruption with glass beads

The release of glucose-6-phosphate dehydrogenase (G6PD) from Candida guilliermondii, grown on rice straw hydrolysate, by vortex agitation with glass beads was studied. The effects of cell suspension concentration and disruption time on volumetric activity, total protein and specific activity were evaluated from a 2 2 full-factorial central composite design. By using the response surface methodology, a second-order model was proposed to represent enzyme specific activity as a function of disruption time ( X 1) and cell suspension concentration ( X 2). Under optimum conditions ( X 1 = 5 min and X 2 = 11.5 g l −1 the model predicted a G6PD specific activity of 0.88 U mg −1.