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1.
In this study, production of hydrogen (H2) from glucose, xylose, galactose, mannose, arabinose and rhamnose by a strain isolated from activated sludge was investigated. The strain, named as Citrobacter sp. CMC-1, was enriched in cellobiose amended minimal media. Based on 16S rRNA sequence, the CMC-1 strain is a close relative of Citrobacter amalonaticus strain SA01 (99%). Optimal cultivation parameters for H2 production and growth such as pH and temperature were investigated. H2 yields from glucose at optimal conditions (pH 6.0 and 34 °C) were 1.82 ± 0.02 mol-H2/mol-glucose. Strain CMC-1 fermented galactose, mannose, xylose, arabinose and rhamnose. After 48 h incubation, the strain CMC-1 completely fermented all sugars tested, except arabinose. Increase in fermentation period lowered residual formate level in the media and improved H2 production for galactose, mannose and xylose (1.68 ± 0.24, 1.93 ± 0.14 and 1.63 ± 0.07 mol-H2/mol-substrate respectively).  相似文献   

2.
Cryptococcus curvatus has great potential in fermenting unconditioned hydrolysates of sweet sorghum bagasse. With hydrolysates obtained by enzymatic hydrolysis of the solid pretreated by microwave with lime, the maximal yeast cell dry weight and lipid content were 10.83 g/l and 73.26%, respectively. For hydrolysates obtained in the same way but without lime, these two parameters were 15.50 g/l and 63.98%, respectively. During yeast fermentation, glucose and xylose were consumed simultaneously while cellobiose was released from the residual bagasse. The presence of lime, on one hand, made cellulose more accessible to enzymes as evidenced by higher total reducing sugar release compared to that without during enzymatic hydrolysis step; on the other hand, it caused the degradation of sugars to non-sugar chemicals during pretreatment step. As a result, higher lipid yield of 0.11 g/g bagasse or 0.65 ton/hectare of land was achieved from the pathway of microwave pretreatment and enzymatic hydrolysis while 0.09 g/g bagasse or 0.51 ton/hectare of land was attained from the process of lime-assisted microwave pretreatment followed by the same enzymatic saccharification.  相似文献   

3.
An environmentally friendly pretreatment process was developed to fractionate cellulose, hemicellulose and lignin from almond (Prunus dulcis) shells, consisting of hot water pretreatment (HWP) coupled with organic solvent (organosolv) pretreatment of water/ethanol (OWEP). This integrated pretreatment process proved more effective on the basis of yield of fermentable sugar and lignin separation compared with HWP alone, dilute acid pretreatment (DAP), ammonia pretreatment (AP), lime pretreatment LP, organosolv water/ethanol pretreatment (OWEP), and organosolv water/acetone pretreatment (OWAP). In the coupled hot water-organosolv process, hemicellulose sugars were recovered in the first residual liquid while varying amounts of cellulose was retained in the residual solid. The lignin fraction was obtained by simply adjusting the pH from the second liquid. The optimal two-stage process consisted of first HWP stage at 195 °C for 30 min, resulting in wglucose = 95.4% glucose recovery yield and wxylose = 92.2% xylose removal. The second organosolv OWEP stage was operated at 195 °C for 20 min, in ethanol in water mixtures of <phi>ethanol = 50% and resulted in nearly wglucose = 100% glucose recovery yield, wxylose = 90% xylose and wlignin = 61% lignin removal. After enzymatic hydrolysis, glucose yield was up to wglucose = 95%, compared to 61% yield from untreated almond. Images obtained via scanning electron microscopy (SEM) highlighted the differences in almond structure from the varying pretreatment methods during biomass fractionation.  相似文献   

4.
Microbial inhibitors arise from lignin, hemicellulose, and degraded sugar during pretreatment of lignocellulosic biomass. The fungus Coniochaeta ligniaria NRRL30616 has native ability to metabolize a number of these compounds, including furan and aromatic aldehydes known to act as inhibitors toward relevant fermenting microbes. In this study, C. ligniaria was used to metabolize and remove inhibitory compounds from pretreated rice hulls, which comprise a readily available agricultural residue rich in glucose (0.32–0.33 g glucan/g hulls) and xylose (0.15–0.19 g xylan/g hulls). Samples were dilute-acid pretreated and subjected to bioabatement of inhibitors by C. ligniaria. The bioabated rice hull hemicellulose hydrolyzates were then utilized for ethanol fermentations. In bioabated liquors, glucose was converted to 0.58% (w/v) ethanol by Saccharomyces cerevisiae D5a at 100% of theoretical yield, while fermentations of unabated hydrolyzates either failed to exit lag phase or had reduced ethanol yield (80% of theoretical). In fermentations using ethanologens engineered for conversion of pentoses, bioabatement of hydrolyzates similarly improved fermentations. Fermentation of xylose and arabinose by ethanologenic Escherichia coli FBR5 yielded 2.25% and 0.05% (w/v) ethanol from bioabated and unabated samples, respectively. Fermentations using S. cerevisiae YRH400 had decreased fermentation lag times in bioabated hydrolyzates. However, xylose metabolism in S. cerevisiae YRH400 was strongly affected by pH and acetate concentration.  相似文献   

5.
In the present work, various carbon sources, xylose, glucose, galactose, sucrose, cellobiose, and starch were tested for thermophilic (60 °C) fermentative hydrogen production (FHP) by using the anaerobic mixed culture. An inoculum was obtained from a continuously-stirred tank reactor (CSTR) operated at pH 5.5 and HRT 12 h, and fed with tofu processing waste. The dominant species in the CSTR were found to be Thermoanaerobacterium thermosaccharolyticum and Clostridium thermosaccharolyticum, which are well known thermophilic H2-producers in anaerobic-state, and have the ability to utilize a wide range of carbohydrates. When initial pH was adjusted to 6.8 ± 0.1 but not controlled during fermentation, vigorous pH drop began within 5 h, and finally reached 4.0–4.5 in all carbon sources. Although over 90% of substrate removal was achieved for all carbon sources except cellobiose (71.7%), the fermentation performances were profoundly different with each other. Glucose, galactose, and sucrose exhibited relatively higher H2 yields whereas lower H2 yields were observed for xylose, cellobiose, and starch. On the other hand, when pH was controlled (pH ≥ 5.5), the fermentation performance was enhanced in all carbon sources but to a different extent. A substantial increase in H2 production was observed for cellobiose, a 1.9-fold increase of H2 yield along with a substrate removal increase to 93.8%, but a negligible increase for xylose. H2 production capabilities of all carbon sources tested were as follows: sucrose > galactose > glucose > cellobiose > starch > xylose. The maximum H2 yield of 3.17 mol H2/mol hexoseadded achieved from sucrose is equivalent to a 26.5% conversion of energy content in sucrose to H2. Acetic and butyric acids were the main liquid-state metabolites of all carbon sources while lactic acid was detected only in cellobiose, starch and xylose exhibiting relatively lower H2 yields.  相似文献   

6.
Hydrogen producing novel bacterial strain was isolated from formation water from oil producing well. It was identified as Thermoanaerobacter mathranii A3N by 16S rRNA gene sequencing. Hydrogen production by novel strain was pH and substrate dependent and favored pH 8.0 for starch, pH 7.5 for xylose and sucrose, pH 8.0–9.0 for glucose fermentation at 70 °C. The highest H2 yield was 2.64 ± 0.40 mol H2 mol glucose at 10 g/L, 5.36 ± 0.41 mol H2 mol – sucrose at 10 g/L, 17.91 ± 0.16 mmol H2 g – starch at 5 g/L and 2.09 ± 0.21 mol H2 mol xylose at 5 g/L. The maximum specific hydrogen production rates 6.29 (starch), 9.34 (sucrose), 5.76 (xylose) and 4.89 (glucose) mmol/g cell/h. Acetate-type fermentation pathway (approximately 97%) was found to be dominant in strain A3N, whereas butyrate formation was found in sucrose and xylose fermentation. Lactate production increased with high xylose concentrations above 10 g/L.  相似文献   

7.
A hydrogen producing facultative anaerobic alkaline tolerant novel bacterial strain was isolated from crude oil contaminated soil and identified as Enterobacter cloacae DT-1 based on 16S rRNA gene sequence analysis. DT-1 strain could utilize various carbon sources; glycerol, CMCellulose, glucose and xylose, which demonstrates that DT-1 has potential for hydrogen generation from renewable wastes. Batch fermentative studies were carried out for optimization of pH and Fe2+ concentration. DT-1 could generate hydrogen at wide range of pH (5–10) at 37 °C. Optimum pH was; 8, at which maximum hydrogen was obtained from glucose (32 mmol/L), when used as substrate in BSH medium containing 5 mg/L Fe2+ ion. Decrease in hydrogen partial pressure by lowering the total pressure in the fermenter head space, enhanced the hydrogen production performance of DT-1 from 32 mmol H2/L to 42 mmol H2/L from glucose and from 19 mmol H2/L to 33 mmol H2/L from xylose. Hydrogen yield efficiency (HY) of DT-1 from glucose and xylose was 1.4 mol H2/mol glucose and 2.2 mol H2/mol xylose, respectively. Scale up of batch fermentative hydrogen production in proto scale (20 L working volume) at regulated pH, enhanced the HY efficiency of DT-1 from 2.2 to 2.8 mol H2/mol xylose (1.27 fold increase in HY from laboratory scale). 84% of maximum theoretical possible HY efficiency from xylose was achieved by DT-1. Acetate and ethanol were the major metabolites generated during hydrogen production.  相似文献   

8.
In this study, hydrogen and ethanol production by a facultative anaerobic bacterium Escherichia coli XL1-Blue immobilized in calcium-alginate beads have been investigated. Batch fermentations were carried out at mesophilic temperature (35 °C) and an initial cultivation pH of 6.5. Firstly, the influence of biomass concentration in terms of dry cell weight (expressed in g DCW/L, range 0.2–1.0) was investigated using fructose (5 g/L) as a carbon source. The peak hydrogen yield (HY) of 1.17 mol-H2/mol-fructoseutilized was obtained at an initial cell concentration of 0.4 g DCW/L. The hydrogen production potential of other simple carbon sources (glucose and xylose) was evaluated at this optimized cell concentration and peak HY values were attained as 0.96 mol-H2/mol-glucoseutilized and 0.69 mol-H2/mol-xyloseutilized, respectively. In addition, utilization of the beverage wastewater (BWW) showed the peak cumulative hydrogen production and ethanol concentration of 120 mL and 5.65 g/L, attained at the substrate concentration of 20 g(glucose equivalent)/L. However, peak HY (1.65 mol-H2/mol-glucose eqivalent utilized) was observed at low substrate concentration of 5 g(glucose equivalent)/L. The percentage of sugar utilization of BWW was ranged between 80 and 96.  相似文献   

9.
Batch tests were conducted to investigate the effect of co-substrates, including glucose, xylose and starch, on thermophilic anaerobic conversion of microcrystalline cellulose using mixed culture enriched from anaerobic digestion sludge (ADS). Up to 30.9% of cellulose was utilized with xylose as co-substrate. When using glucose as co-substrate, cellulose conversion rate reached the maximum of 0.048 g/l/h at cellulose loading of 5.0 g/l. Illumina high-throughput sequencing of the 16S rRNA gene revealed that the thermophilic consortium exclusively consisted of Clostridium (more than 70% of all sequences). Growth of Thermoanaerobacterium over Clostridium would inhibit cellulose conversion capacity of the consortium. But the growth of Thermoanaerobacterium could be repressed by pH higher than pH 6.0. Co-substrates caused noticeable variation of bacterial community structure. Predominance of Thermoanaerobacterium over Clostridium was observed when monosugars (glucose and xylose) were used as co-substrate without pH control. Starch was ineffective as co-substrate because it competed with cellulose for Clostridium.  相似文献   

10.
The hydrogen-producing bacterium SP-H2 was isolated from a thermophilic acidogenic reactor inoculated with municipal sewage sludge and processing a carbohydrate-rich simulated food waste. Based on the 16S rRNA gene sequence, the bacterium was identified as Thermoanaerobacterium thermosaccharolyticum. The maximum growth rate was observed at 55–60 °C and pH 7.5. The H2-producing activity of the bacterium was studied using mono-, di- and tri-saccharides related to both hexoses (maltose, glucose, mannose, fructose, lactose, galactose, sucrose, raffinose, cellobiose) and pentoses (xylose and arabinose), as well as using real wastewaters (cheese whey, confectionery wastewater, sugar-beet processing wastewater). The highest H2 yield was observed during dark fermentation (DF) of maltose (1.91 mol H2/mol hexose or 77.8 mmol H2/L). The maximum H2 production rate was observed during DF of xylose (13.3 ml H2/g COD/h) and cellobiose (2.47 mmol H2/L/h). The main soluble metabolite products were acetate, ethanol and butyrate. The acetate concentration had a statistically significant positive correlation with the H2 content in biogas and the specific H2 yield. Based on the results of the correlation analysis, it was tentatively assumed that in the formic acid (mixed-acid) type fermentation, the rate of H2 production was higher than in the butyric acid type fermentation. With regard to real wastewater, cheese whey and confectionery wastewater were distinguished by a higher H2 yield (152 ml H2/g COD) and H2 production rate (0.57 mmol H2/L/h), respectively. The highest concentrations of confectionery wastewater and cheese whey, at which the DF process took place, were 5915 and 7311 mg COD/L, respectively. At the same time, SP-H2 dominated in the microbial community, despite the presence of indigenous microorganisms in wastewater. Thus, T. thermosaccharolyticum SP-H2 is a promising strain for DF of carbohydrate-rich unsterile wastewater under thermophilic conditions.  相似文献   

11.
Hydrogen (H2) production and end-product synthesis were characterized in a novel, mesophilic, cellulolytic, anaerobic bacterium, Clostridium termitidis strain CT1112, isolated from the gut of the termite, Nasutitermes lujae. Growth curves, pH patterns, protein content, organic acid synthesis, and H2 production were determined. When grown on 2 g l−1 cellobiose and 2 g l−1 α-cellulose, C. termitidis displayed a cell generation time of 6.5 h and 18.9 h, respectively. The major end-products synthesized on cellobiose included acetate, hydrogen, CO2, lactate, formate and ethanol, where as on cellulose, the major end-products included hydrogen, acetate, CO2 and ethanol. The concentrations of acetate were greater than ethanol, formate and lactate on both cellobiose and α-cellulose throughout the entire growth phase. Maximum yields of acetate, ethanol, hydrogen and formate on cellobiose were 5.9, 3.7, 4.6 and 4.2 mmol l−1 culture, respectively, where as on cellulose, the yields were 7.2, 3.1, 7.7 and 2.9 mmol l−1 culture, respectively. Hydrogen and ethanol production rates were slightly higher in C. termitidis cultured on cellobiose when compared to α-cellulose. Although, the generation time on α-cellulose was longer than on cellobiose, H2 production was favored corresponding to acetate synthesis, thereby restricting the carbon flowing to ethanol. During log phase, H2, CO2 and ethanol were produced at specific rates of 4.28, 5.32, and 2.99 mmol h−1 g dry weight−1 of cells on cellobiose and 2.79, 2.59, and 1.1 mmol h−1 g dry weight−1 of cells on α-cellulose, respectively.  相似文献   

12.
A thermophilic hydrogen producer was isolated from hot spring sediment and identified as Thermoanaerobacterium thermosaccharolyticum KKU19 by biochemical tests and 16S rRNA gene sequence analysis. The strain KKU19 showed the ability to utilize various kinds of carbon sources. Xylose was the preferred carbon source while peptone was the preferred organic nitrogen source. The optimum conditions for hydrogen production and cell growth on xylose were an initial pH of 6.50, temperature of 60 °C, a carbon to nitrogen ratio of 20:1, and a xylose concentration of 10.00 g/L. This resulted in a maximum cumulative hydrogen production, hydrogen production rate and hydrogen yield of 3020 ± 210 mL H2/L, 3.95 ± 0.20 mmol H2/L h and 2.09 ± 0.02 mol H2/mol xylose consumed, respectively. Acetic and butyric acids were the main soluble metabolite products suggesting acetate and butyrate type fermentation.  相似文献   

13.
In the present study the effect of temperature, reaction time and dilute oxalic acid (OA) concentration during steam-pretreatment of Miscanthus × gigantueus has been evaluated using the combined severity factor (CS). At the highest CS glucan and lignin content in the water insoluble fraction (WIF) increased, while xylan content decreased. While glucose recovery in the water soluble fraction (WSF) was found at low concentration when mild CS were used (≤5.0 g L−1 at CS ≤ 2.17), xylose and arabinose concentrations were higher at low-mild CS (1.58–2.17) with a concentration peak at CS 2.03 (39.9 and 3.2 g L−1 for xylose and arabinose, respectively). The decrease in pentoses coincided with inhibitory formation in the WSF, namely acetic acid, furfural, HMF and phenolic compounds. Glucan conversion rose from 46.1% at CS 1.54 to 91.2% at CS 2.76. Likewise, maximum ethanol concentration was achieved at CS 2.76, corresponding to 20.2 g L−1 and a volumetric ethanol productivity of 0.28 g L−1 h−1. Negative correlations have been found between xylan vs. glucan conversion and xylan vs. ethanol production, suggesting that decreasing the xylan content in WIF increases both saccharification rate and ethanol concentration (R2 0.91 and R2 0.93, respectively). On the other hand, a positive correlation was found between ethanol production and glucan conversion (R2 0.93). Fermentation of WSF by Scheffersomyces (Pichia) stipitis CBS 6054 at CS 1.54 produced 12.1 g L−1 of ethanol after 96 h incubation with a volumetric ethanol productivity of 0.13 g L−1 h−1.  相似文献   

14.
The present study investigated hydrogen production potential of novel marine Clostridium amygdalinum strain C9 isolated from oil water mixtures. Batch fermentations were carried out to determine the optimal conditions for the maximum hydrogen production on xylan, xylose, arabinose and starch. Maximum hydrogen production was pH and substrate dependant. The strain C9 favored optimum pH 7.5 (40 mmol H2/g xylan) from xylan, pH 7.5–8.5 from xylose (2.2–2.5 mol H2/mol xylose), pH 8.5 from arabinose (1.78 mol H2/mol arabinose) and pH 7.5 from starch (390 ml H2/g starch). But the strain C9 exhibited mixed type fermentation was exhibited during xylose fermentation. NaCl is required for the growth and hydrogen production. Distribution of volatile fatty acids was initial pH dependant and substrate dependant. Optimum NaCl requirement for maximum hydrogen production is substrate dependant (10 g NaCl/L for xylose and arabinose, and 7.5 g NaCl/L for xylan and starch).  相似文献   

15.
Dark fermentative hydrogen production by a hot spring culture was studied from different sugars in batch assays and from xylose in continuous stirred tank reactor (CSTR) with on-line pH control. Batch assays yielded hydrogen in following order: xylose > arabinose > ribose > glucose. The highest hydrogen yield in batch assays was 0.71 mol H2/mol xylose. In CSTR the highest H2 yield and production rate at 45 °C were 1.97 mol H2/mol xylose and 7.3 mmol H2/h/L, respectively, and at 37 °C, 1.18 mol H2/mol xylose and 1.7 mmol H2/h/L, respectively. At 45 °C, microbial community consisted of only two bacterial strains affiliated to Clostridium acetobutulyticum and Citrobacter freundii, whereas at 37 °C six Clostridial species were detected. In summary hydrogen yield by hot spring culture was higher with pentoses than hexoses. The highest H2 production rate and yield and thus, the most efficient hydrogen producing bacteria were obtained at suboptimal temperature of 45 °C for both mesophiles and thermophiles.  相似文献   

16.
Jian Xu  Shijie Liu 《Renewable Energy》2009,34(11):2353-2356
Hot-water extracts from sugar maple chips prior to papermaking was employed in this study to produce ethanol by Pichia stipitis 58784. The effects of several factors, seed culture age, fermentation time, inoculum quantity, agitation rate, percent extract, concentration of inorganic nitrogen source (NH4)2SO4 and pH value, on ethanol production were investigated by orthogonal experiments. Orthogonal analysis shows that the optimal fermentation was obtained in the condition of 48-h seed culture, 120-h fermentation, 16% inoculum, 180 rpm, containing 30% extracts, 8% ammonium sulphate supplement and pH 5. This optimal condition was verified at 800-mL level in a 1.3 L fermentor. The ethanol yield reached 82.27% of the theoretical (20.57 g/L) after 120 h.  相似文献   

17.
《Biomass & bioenergy》1999,16(5):333-339
Microorganisms with the ability to produce xylitol from high concentrations of xylose were screened from soils by enrichment culture using xylose as a sole carbon source. The selected strain was classified and determined as Candida sp. according to a taxonomic identification. In this strain, various conditions for xylitol production were investigated. Organic nutrients such as peptone and yeast extract were essential for xylitol production, and the optimal initial pH and kLa were between 4.0 and 6.0, and 5.2/h, respectively. Under the optimal condition, xylitol production from 200 g/l of xylose was 173 g/l after 5 days incubation, a 99.3% yield of the theoretical value. In order to produce a higher concentration of xylitol, a fed-batch culture of xylose was carried out by feeding 2.0 g of xylose per 10 ml of culture medium. The production from 4.0 g of xylose was 2.9 g of xylitol (concentration of 256 g/l) after 11.5 days which is a yield of 85.0%.  相似文献   

18.
To investigate the bioethanol production from sweet potato, the saccharification and fermentation conditions of co-immobilization of saccharolytic molds (Aspergillus oryzae and Monascus purpureus) with Saccharomyces cerevisiae were analyzed. The immobilized yeast cells showed that at 10% glucose YPD (yeast extract peptone dextrose) the maximum fermentation rate was 80.23%. Viability of yeasts cells were 95.70% at a final ethanol concentration of 6%. Immobilization enhanced the ethanol tolerance of yeast cells. In co-immobilization of S. cerevisiae with A. oryzae or M. purpureus, the optimal hardening time of gel beads was between 15 and 60 min. Bioethanol production was 3.05-3.17% (v v−1) and the YE/s (yield of ethanol production/starch consumption) was 0.31-0.37 at pH 4, 30 °C and 150 rpm during 13 days fermentation period. Co-immobilization of S. cerevisiae with a mixed cultures of A. oryzae and M. purpureus at a ratio of 2:1, the bioethanol production was 3.84% (v v−1), and the YE/s was 0.39 for a 11 days incubation. However a ratio of A. oryzae and M. purpureus at 1:2 resulted a bioethanol production rate of 4.08% (v v−1), and a YE/s of 0.41 after 9 days of fermentation.  相似文献   

19.
Sugars released from lignocellulose biomass are a promising substrate for biohydrogen production. This study evaluates the effect of pH controlled between 4.0 and 7.5 on continuous dark-fermentative H2 production from the mixture of cellobiose, xylose and arabinose. High hydrogen production rate was obtained for pH values between 6.0 and 7.0 with a maximum of 7.41 ± 0.16 L/L-d at pH 7.0. On the other hand, the highest H2 yields of around 1.74 ± 0.02 mol/molconsumed were obtained at pH 4.5, 5.0 and 6.0. Cellobiose was completely utilized in nearly the entire pH range, while the highest consumption of xylose and arabinose was obtained at pH 6.0 and 7.0, respectively. It shows the challenges in selecting optimum pH for fermentation of mixed sugars. Significant impact of pH conditions on the microbial structure was observed. Between pH 4.0 and 7.0 Clostridium genus dominated the consortium, while above pH 7.0 relative abundance of Bacillus genus increased significantly.  相似文献   

20.
Simultaneous utilization of mixed sugars is one of the major challenges for biofuel production utilizing lignocellulosic biomass as feedstock. Our previous work proved that the oleaginous yeast Cryptococcus curvatus could efficiently produce lipids, the precursors of hydrocarbons with high energy density, from lignocellulosic hydrolysates. However, the strain's capability of simultaneously utilizing primary sugars was still unknown. Thus, this work comprehensively explored the co-utilization of glucose, xylose and cellobiose by C. curvatus. The results indicated that the consumption of both xylose and cellobiose was repressed by glucose, while xylose and cellobiose could be simultaneously consumed at similar rates. The total sugar consumption rates remained constant at about 0.6 g L−1 h−1 regardless of the sugar composition in the mixtures, and the cell biomass and lipid production by C. curvatus cultured on the different sugar mixtures were similar. Moreover, compared with glucose and xylose, cellobiose could lead to higher dry cell weights and lipid yields, suggesting an excellent carbon source for lipid production. Based on these findings, this study demonstrated an effective approach for alleviating glucose repression for microbial lipid production by C. curvatus through xylose/cellobiose co-utilization which would greatly contribute to a more efficient and economical cellulosic biofuel production.  相似文献   

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