Hydrolysis Of Rice Straw Research Articles

Evaluation of biobutanol production from non-pretreated rice straw hydrolysate under non-sterile environmental conditions

The study aims to investigate a cost-effective approach to convert non-pretreated rice straw hydrolysate into biobutanol. The influences of the initial cell concentration and incubation temperature on biobutanol production were evaluated under both sterile and non-sterile conditions. Results indicate that 100% glucose utilization could be achieved for initial cell concentrations greater than 2100mg/L under both sterile and non-sterile conditions. Regression analyses resolve that under the sterile condition, the maximum butanol productivity of 1.45g/L/d was projected at 1.96g/L of cells and 32.3°C, while the maximum butanol yield of 0.22g/g was predicted at 2.01g/L of cells and 26.3°C. These two maximum values could not be projected by the regression analyses for the non-sterile condition. However, this study confirms that a high initial cell concentration of Clostridium saccharoperbutylacetonicum N1-4 can minimize interference from other microbes so that non-sterile biobutanol production is comparable to sterile biobutanol production.

Production and characterization of multiple cellulolytic enzymes by isolated Streptomyces sp. MDS

Among four isolated cellulolytic microorganisms, Streptomyces sp. MDS can utilize a broad range of cellulosic substrates including: carboxymethyl cellulose, avicel, xylan, cellobiose, filter paper, wood straw and rice straw by producing a large amount of endoglucanase, exoglucanase, cellobiase, xylanase and glucoamylase. Effects of different physicochemical parameters to achieve maximum production of cellulolytic enzymes were systematically investigated. It was found that the cellulolytic enzyme activities were mainly located at extracellular location. It was observed that supplementation of CaCl2 (5 mM) as a metal additive significantly induced the whole enzyme system. These cellulases also have high thermal stability as evidenced by retaining 60–70% activity at 90 °C and pH 5 and alkalotolerance as more than 55–60% of the activity at pH 10 and 40 °C and 60 °C (for endoglucanase) after 1 h of incubation. The enzymes also retained up to 50–70% of its initial activity upon incubation in the presence of commercials detergents for 1 h. Finally, the efficiency of fermentative conversion of the CMC and rice straw hydrolyzate by Saccharomyces cerevisiae (KCTC 7296) resulted in 55.8 and 57.2% of maximum theoretical ethanol yield based on sugar (glucose and xylose) fermentation, respectively.

Sensing of plant hydrolysate-related phenolics with an aaeXAB::luxCDABE bioreporter strain of Escherichia coli

A bioluminescent Escherichia coli bioreporter strain to detect hydrolysate related phenolics was developed by cloning the aaeXAB promoter from E. coli upstream of the luxCDABE genes. E. coli str. DH5α carrying this plasmid (pDMA3) was responsive to sub-inhibitory concentrations of plant hydrolysate-related phenolics, such as ferulic and vanillic acids, responding to these compounds at concentrations as low as 9.8 and 4.9mg/L, respectively. Experiments with a mixture of the compounds showed similar responses as with single compound tests, with a minimum detectable concentration of 19.5mg/L. Finally, tests using rice straw hydrolysates were conducted, with E. coli str. DH5α/pDMA3 showing a maximum induction of 33-fold and a minimum detectable phenolic concentration of 9.3mg/L, based upon Folin–Ciocalteu’s reagent. These results demonstrate that this bioreporter maintains its sensitivity even with hydrolysate samples and that it can be potentially applied within biofuel industries to detect phenolics present within plant hydrolysates.

Sodium carbonate–sodium sulfite pretreatment for improving the enzymatic hydrolysis of rice straw

The performance of sodium carbonate–sodium sulfite (Na2CO3–Na2SO3) pretreatment on improving the enzymatic hydrolysis of rice straw was investigated. The results indicated that both Na2CO3 and Na2SO3 pretreatments are effective in improving the enzymatic digestibility of rice straw. A higher ratio of Na2SO3 in pretreatment liquor performed better at softening the rice straw through degradation of hemicellulose, delignification, and lignin sulfonation, while it was conserving more polysaccharides during the pretreatment than Na2CO3. The highest sugar recovery of pretreated rice straw, 74.5%, 82.7%, and 59.5% for total sugar, glucan, and xylan, respectively, was obtained at cellulase loading of 20FPU/g-cellulose after the pretreatment at 140°C, chemical charge of 12%, Na2CO3–Na2SO3 ratio of 0:1 (i.e., only Na2SO3 pretreatment). The corresponding delignification ratio of pretreated solid was 53.4%, and 91.4% of the polysaccharides were conserved. The sugar recovery of only Na2CO3 pretreatment at the ratio of 1:0 was 67.1%, 74.4%, and 53.7% for total sugar, glucan, and xylan, respectively, at 140°C, chemical charge of 12%, and enzyme loading of 20FPU/g-cellulose. Its corresponding delignification ratio was 40.3%, and polysaccharides conservation ratio was 88.9%.

Producing 2,3-butanediol from agricultural waste using an indigenous Klebsiella sp. Zmd30 strain

This study aimed to develop a low cost and high efficiency process for 2,3-butanediol (2,3-BDO) production by using Klebsiella sp. Zmd30 isolated from a hydrogen-producing anaerobic sludge. First, the effects of glucose concentration and nitrogen source on 2,3-BDO production with the Zmd30 strain were examined. The results show that the productivity and concentration of 2,3-BDO reached the highest values of 0.92g/l/h and 58g/l, respectively, when the glucose concentration was in the range of 160–180g/l. Urea was a better nitrogen source when considering both the 2,3-BDO production performance and the cost. Next, medium composition for the growth of the Zmd30 strain was optimized using the response surface methodology (RSM) to enhance 2,3-BDO production. Based on the RSM analysis, the optimal composition of glucose, urea and MnCl2·4H2O, H3BO3 and CoCl2·6H2O was 160, 2.28, 7.01×10−4, 1.49×10−4 and 5.70×10−3g/l, respectively. With this optimal medium, the 2,3-BDO productivity was improved to 1.15g/l/h. To reduce the production cost, bagasse and rice straw were used as feedstock for 2,3-BDO production. It was found that using hydrolyzed rice straw resulted in better productivity than using hydrolyzed bagasse, as the highest productivity (2.08g/l/h) and yield (62%) were obtained at an initial rice straw concentration of 150g/l.

Improve the Recovery of Fermentable Sugar from Rice Straw by Sonication and Its Mathematical Modeling

Rice straw is waste renewable agricultural biomass, which contains sufficient amount of fermentable sugars like glucose, galactose fructose, xylose etc. These sugars can be treated with fermentation pathway to produce ethanol. Hydrolysis of pretreated rice straw in dilute sulfuric acid was investigated at different acid concentrations (0.25–0.75 % w/v), and sonication was carried out to improve the extent of sugar extraction. The current work examines the effect of sonication on extraction of total reducing sugar (TRS) and an empirical mathematical model has been established to predict it. Effects of various operating variables of sonication, including amplitude (60–100 %), cycle (0.6–1.0), treatment time (0–15 min) have been analyzed for each acid concentration. Observation shows that on optimization of the sonication conditions (100 % amplitude, 0.8 cycle and 10 min) around 90 % improvement of TRS extraction occurs at 0.5 % (w/v) acid concentration.

Enhanced enzymatic hydrolysis of rice straw by removal of phenolic compounds using a novel laccase from yeast Yarrowia lipolytica

An extracellular laccase-producing yeast was isolated from soil and identified as Yarrowia lipolytica by its morphology and by comparison of its internal transcribed spacer rDNA gene sequence. Extracellular laccase (YlLac) from Y. lipolytica was purified to homogeneity by anion-exchange and gel filtration chromatography. YlLac is a monomeric glycoprotein with 14% carbohydrate content and a molecular mass of 67kDa. It showed a higher catalytic efficiency towards 2,2′-Azino-bis (3-ethylbenzthiazoline-6-sulfonic acid) (kcat/Km=19.3s−1μM−1) and 2,6-dimethoxyphenol (kcat/Km=13s−1μM−1) than any other reported laccase. This enzyme was able to oxidize phenolic compounds present in pretreated rice straw. Several parameters (temperature, enzyme concentration, and mediator compounds) to enhance removal of phenolic compounds from pretreated rice straw were optimized using response surface methodology. The use of YlLac for the removal of cellulase inhibitory compounds from biomass slurries was found to be a promising approach for improving the efficiency of biorefineries.

Production of cellulases by solid state fermentation with Aspergillus terreus and enzymatic hydrolysis of mild alkali-treated rice straw

Rice straw was used as substrate for cellulase production by solid state fermentation with Aspergillus terreus. Substrate concentration, moisture ratio, inoculum size and initial pH were optimized using response surface methodology involving Box-Behnken design. The predicted filter paper activity under optimized parameters was 9.73U/g and the validated filter paper activity was 10.96U/g. Hydrolysis of the biomass pretreated with 0.125% to 1% NaOH for 24h at room temperature was performed using crude cellulase preparation. Treatment with 0.5% NaOH at room temperature for 24h was the most efficient treatment method for saccharification. Under the optimized conditions, rice straw yielded 676mg reducing sugars per gram of substrate at a cellulase loading of 9FPUg−1 substrate. The present study establishes the possibility of using mild alkali pretreated rice straw for the production of fermentable sugars with 74.19% efficiency which can be further utilized for the production of ethanol.

The Study of the Dilute Acid Pretreatment Technology of Corn Stover and Rice Straw

Ethanol production from lignocellulosic materials provides an alternative energy production system. Dilute sulfuric acid pretreatment of corn straw and rice straw and enzymatic hydrolysis of cellulose were investigated in this study. The straw was pretreated at 121°C with different sulfuric acid concentrations (1, 2, 3, 4and 5%, v/v) and residence times (30, 60, and 90 min). The concentration and conversion of total reducing sugars were analyzed. Pretreatment residence time play a key role in increase glucose concentration comparing to sulfuric acid concentration. Cellulose remaining in the pretreated feedstock was highly digestible by cellulases from Trichoderma viride. The result that the saccharification yield of 72.38% and 82.84% from corn straw and rice straw by using 2% (v/v) acid pretreatment at 121°C for 60 min and saccharifying with cellulase preparations.

Biodiesel synthesis by a one-step method in a genetically engineered Escherichia coli using rice straw hydrolysate and restaurant oil wastes as raw materials

To reduce the cost of biodiesel, the utilization of rice straw hydrolysate and restaurant oil wastes as the substrates for biodiesel production in a recombinant strain by a one-step method was investigated. A recombinant Escherichia coli pET28a (+)-PAW, which encodes enzymes for the ethanol pathway and acyltransferase, was constructed. Fermentation results in Luria-Bertani medium revealed that xylose was favourable for fatty acid ethyl esters (FAEEs) production (2.79 g l(-1) ) by E. coli pET28a (+)-PAW. When rice straw hydrolysate and restaurant oil wastes were utilized as the monosaccharide substituent and the fatty acids substituent, 0.27 g l(-1) FAEEs and 0.249 g l(-1) FAEEs were obtained, respectively. 1.27 g l(-1) FAEEs was obtained in the restaurant oil wastes medium supplemented by 2% sodium oleate. The fermentation results indicated that the strain was effective in biodiesel production. The rice straw hydrolysate and restaurant oil wastes could be utilized by E. coli as the substrates for FAEE production. This novel exploration might pave the way for biodiesel production from waste materials by genetically engineered microorganism.

Process optimization for sugars production from rice straw via pretreatment with sulfur trioxide micro-thermal explosion

The effects of sulfur trioxide micro-thermal explosion (STEX) and enzyme loading on reducing sugars conversion of STEX-treated rice straw and enzymatic hydrolysates were researched. Important process parameters in the pretreatment of biomass were identified by a Plackett-Burman design, and parameters with significant effects were optimized using a Box-Behnken design (BBD) and response surface methodology (RSM). The optimal conditions were a temperature of 80 °C and a treatment time of 30 min when only single factors were considered. Meanwhile, glucose and xylose were primary components in the enzymatic hydrolysates. Subsequently, STEX time, liquid-solid ratio, and soaking temperature were the main factors governing the enzymatic saccharification of rice straw. The optimum pretreatment conditions were STEX time 23.3 min, liquid-solid ratio 13.3 (V/m), and soaking temperature 62.2 °C. The chemical composition analysis of straw further demonstrated that STEX collaborative dilute lye pretreatment could remove lignin and hemicellulose.

Optimisation of synergistic biomass-degrading enzyme systems for efficient rice straw hydrolysis using an experimental mixture design

Synergistic enzyme system for the hydrolysis of alkali-pretreated rice straw was optimised based on the synergy of crude fungal enzyme extracts with a commercial cellulase (Celluclast™). Among 13 enzyme extracts, the enzyme preparation from Aspergillus aculeatus BCC 199 exhibited the highest level of synergy with Celluclast™. This synergy was based on the complementary cellulolytic and hemicellulolytic activities of the BCC 199 enzyme extract. A mixture design was used to optimise the ternary enzyme complex based on the synergistic enzyme mixture with Bacillus subtilis expansin. Using the full cubic model, the optimal formulation of the enzyme mixture was predicted to the percentage of Celluclast™: BCC 199: expansin=41.4:37.0:21.6, which produced 769mg reducing sugar/gbiomass using 2.82FPU/g enzymes. This work demonstrated the use of a systematic approach for the design and optimisation of a synergistic enzyme mixture of fungal enzymes and expansin for lignocellulosic degradation.

Kinetic Studies on the Product Inhibition of Enzymatic Lignocellulose Hydrolysis

In order to understand the product inhibition of enzymatic lignocellulose hydrolysis, the enzymatic hydrolysis of pretreated rice straw was carried out over an enzyme loading range of 2 to 30 FPU/g substrate, and the inhibition of enzymatic hydrolysis was analyzed kinetically based on the reducing sugars produced. It was shown that glucose, xylose, and arabinose were the main reducing sugar components contained in the hydrolysate. The mass ratio of glucose, xylose, and arabinose to the total reducing sugars was almost constant at 52.0%, 29.7% and 18.8%, respectively, in the enzyme loading range. The reducing sugars exerted competitive inhibitory interferences to the enzymatic hydrolysis. Glucose, xylose, and arabinose had a dissociation constant of 1.24, 0.54 and 0.33 g/l, respectively. The inhibitory interferences by reducing sugars were superimposed on the enzymatic hydrolysis. The enzymatic hydrolysis could be improved by the removal of the produced reducing sugars from hydrolysate.

Direct ethanol production from rice straw by coculture with two high-performing fungi

To develop efficient and economical direct ethanol production from fine rice straw crashed mechanically, two high-performing fungi, which can secret hyperactive cellulases and/or ferment effectively various sugars, were selected from some strains belong to Mucor circinelloides preserved in our laboratory. The simultaneous saccharification and fermentation (SSF) by coculture with these fungi was investigated. The screening of highperforming fungi resulted in the selection of NBRC 4572 as an ethanol-producing fungus and NBRC 5398 as a cellulase-secreting fungus. The strain 4572 produced ethanol aerobically from glucose and xylose in high yields of 0.420 g/g at 36 h and 0.478 g/g at 60 h, respectively, but secreted fairly low cellulases. On the other hand, the strain 5398 also produced ethanol from glucose in yield of 0.340 g/g though it had a little growth in xylose culture. However, it secreted hyperactive cellulases that are essential for hydrolysis of rice straw in culture and the maximum activities of endo-β-glucanase and β-glucosidase were 2.11 U/L and 1.47 U/L, respectively. In SSF of rice straw by coculture with two fungi selected, the ethanol production reached 1.28 g/L after 96 h when the inoculation ratio of the strain 5398 to the strain 4572 was 9.

Novel renewable ionic liquids as highly effective solvents for pretreatment of rice straw biomass by selective removal of lignin

Cholinium amino acids ionic liquids ([Ch][AA] ILs), a novel type of bio-ILs that can easily be prepared from renewable biomaterials, were investigated for pretreatment of rice straw by selective extraction of lignin from this abundant lignocellulosic biomass material. Of the eight ILs examined, most were demonstrated to be excellent pretreatment solvents. Upon pretreatment using these ILs, the initial saccharification rates of rice straw residues were substantially improved as well as the extent to which polysaccharides could be digested (>90% for cellulose and >60% for xylan). Enzymatic hydrolysis of pretreated rice straw by Trichoderma reesei cellulase/xylanase furnished glucose and xylose with the yields in excess of 80% and 30%, respectively. Detailed spectroscopic characterization showed that the enhancement of polysaccharides degestibility derived mainly from delignification rather than changes in cellulose crystallinity. The yields of fermentable reducing sugars were significantly improved after individual optimization of pretreatment temperature and duration. With [Ch][Lys] as the solvent, the sugar yields of 84.0% for glucose and 42.1% for xylose were achieved after pretreatment at 90°C for 5 h. The IL [Ch][Lys] showed excellent reusability across five successive batches in pretreatment of rice straw. These bio-ILs performed as well as or better than previously investigated non-renewable ILs, and thus present a new and environmentally friendly way to pretreat lignocellulose for production of fermentable sugars and total utilization of the biomass.

Pilot-scale ethanol production from rice straw hydrolysates using xylose-fermenting Pichia stipitis

Ethanol was produced at pilot scale from rice straw hydrolysates using a Pichia stipitis strain previously adapted to NaOH-neutralized hydrolysates. The highest ethanol yield was 0.44±0.02gp/gs at an aeration rate of 0.05vvm using overliming-detoxified hydrolysates. The yield with hydrolysates conditioned by ammonia and NaOH was 0.39±0.01 and 0.34±0.01gp/gs, respectively, were achieved at the same aeration rate. The actual ethanol yield from hydrolysate fermentation with ammonia neutralization was similar to that with overliming hydrolysate after taking into account the xylose loss resulting from these conditioning processes. Moreover, the ethanol yield from ammonia-neutralized hydrolysates could be further enhanced by increasing the initial cell density by two-fold or reducing the combined concentration of furfural and 5-hydroxymethyl furfural to 0.6g/L by reducing the severity of operational conditions in pretreatment. This study demonstrated the potential for commercial ethanol production from rice straw via xylose fermentation.

Modeling of the separation of inhibitory components from pretreated rice straw hydrolysate by nanofiltration membranes

The main objective of this work was to remove inhibitors and concentrate sugars in hydrolysates obtained from dilute acid-treated rice straw. The Donnan steric pore flow model (DSPM) was applied for membrane characterization and it captured the membrane transport adequately. The polyamide and polyethylene sulfate nanofiltration membranes of 150Da molecular weight cut-off showed a separation factor of 3 for acetic acid over glucose and xylose and 7 over cellobiose for a simulated mixture at the optimum pH of 3. A separation factor of 3 was also found for the inhibitors hydroxymethyl furfural, ferulic and vanilic acids over sugars. The concentration of rice straw acid hydrolysate by a volume concentration ratio of 4 increased the concentrations of xylose, glucose, arabinose, cellobiose and inhibitor by 100%, 104%, 93%, 151% and 3%, respectively which indicates the membrane can be used for separating the inhibitors from acid-pretreated rice straw hydrolysate while simultaneously concentrating sugars.

Effects of operation conditions on enzymatic hydrolysis of high-solid rice straw

In the present work, the performances of high-solids enzymatic hydrolysis of rice straw were experimentally studied. Moreover, the heat flow and weight loss of the pre- and post-hydrolysis of rice straw were measured by the simultaneous thermogravimetric analyzer. It is found that the output and yield of reducing sugar initially increased and then reduced with an increase of supplied water, hydrolysis temperature and substrate mesh, while the cellulose content in residual substrate had an opposite trends. Furthermore, a high enzyme loading resulted in a constant saccharification efficiency of cellulose. The output and yield of the sugar, 77.7mg/(g substrate) and 0.44g/g, were respectively achieved under the optimal conditions of the supplied water of 1.0ml/(g substrate), enzymolysis temperature of 50°C, rice straw of 60 mesh and the cellulase dosage of 2.0mg/(g substrate). Simultaneous thermogravimetric analysis on the rice straw indicates that the chemical compositions of rice straw changed after enzymolysis.

Study of the Enzymatic Hydrolysis of Alkaline-Pretreated Rice Straw Using Cellulase of Various Sources and Compositions

The study of the enzymatic hydrolysis of alkaline-pretreated rice straw was conducted using mixture of cellulases produced from Trichoderma reesei and from Aspergillus niger. 2 % NaOH was found effective in reducing the lignin content in rice straw as evidenced from quantitative data and confirmed by the SEM image. The enzymatic hydrolysis was performed at pH 5.5 and 40 oC, a condition which was determined upon compromising between the optimum values of pH and temperature and the enzyme stability. The mixture of crude cellulases was able to give higher conversion than cellulase from one source of fungi and also higher than the conversion using pure commercial cellulase from A. niger. Addition of 1 U activity of crude cellulase from A. niger to every 2 U activity of crude cellulase from T. reesei at 0.47 U/mL enzyme activity increased the concentration of reducing sugar by about 16%

Deletion of the PHO13 gene in Saccharomyces cerevisiae improves ethanol production from lignocellulosic hydrolysate in the presence of acetic and formic acids, and furfural

For efficient bioethanol production from lignocellulosic biomass by Saccharomyces cerevisiae, it is necessary to improve cellular tolerance to toxic compounds released during the pretreatment of biomass. The gene encoding p-nitrophenylphosphatase, PHO13, was disrupted in a recombinant xylose-fermenting S. cerevisiae strain, which improved ethanol production from xylose in the presence of three major inhibitors, acetic and formic acids, and furfural. In medium supplemented with 30mM acetic acid, the ethanol yield obtained by the ΔPHO13 mutant was 0.45 g-ethanol/g-xylose. Notably, the specific ethanol productivity of the mutant in the presence of 90mM furfural was fourfold higher than that of the control strain. The PHO13-disrupted strain produced ethanol from rice straw hydrolysate obtained by liquid hot-water pretreatment with a greater than fourfold higher xylose consumption rate than the control. Together, our findings demonstrate that PHO13 deletion is a simple, but effective, approach for improving cellulosic bioethanol production by S. cerevisiae.