A novel anaerobic co-culture system for bio-hydrogen production from sugarcane bagasse

Solubilization of sugarcane bagasse by mono and cocultures of thermophilic anaerobes with and without cotreatment

Cotreatment, mechanical disruption of lignocellulosic biomass during microbial fermentation, is a potential alternative to thermochemical pretreatment as a means of increasing the accessibility of lignocellulose to biological attack. Successful implementation of cotreatment requires microbes that can withstand milling, while solubilizing and utilizing carbohydrates from lignocellulose. In this context, cotreatment with thermophilic, lignocellulose-fermenting bacteria has been successfully evaluated for a number of lignocellulosic feedstocks. Here, cotreatment was applied to sugarcane bagasse using monocultures of the cellulose-fermenting Clostridium thermocellum and cocultures with the hemicellulose-fermenting Thermoanaerobacterium thermosaccharolyticum. This resulted in 76 % carbohydrate solubilization (a 1.8-fold increase over non-cotreated controls) on 10 g/L solids loading, having greater effect on the hemicellulose fraction. With cotreatment, fermentation by wild-type cultures at low substrate concentrations increased cumulative product formation by 45 % for the monoculture and 32 % for the coculture. These findings highlight the potential of cotreatment for enhancing deconstruction of sugarcane bagasse using thermophilic bacteria.

A critical review on valorization of food processing wastes and by-products for pullulan production

Pullulan is a commercially available exopolymer biosynthesized by Aureobasidium pullulans supplemented with nitrogen, carbon and other vital components through submerged and solid-state fermentation. These nutrients are very expensive and it raises the cost for the production of pullulan. Hence, the need of alternative cost-effective raw materials for its production is a prerequisite. Owing to its unique physicochemical features, pullulan has various applications in the food, pharmacological, and biomedical domains. Food industrial wastes generate a considerable number of by-products which accumulates and has a negative influence on the environment. These by-products are made up of proteins, carbohydrates, and other components, can be employed as substrates for the production of pullulan. The present review briefs on the pullulan production using food processing waste and by-products and the elements that impact it. It provides an insight into versatile applications of pullulan in food industries. Various challenges and future prospects in the field of research on pullulan production have been uncovered.

Optimization of dark fermentative biohydrogen production from rice starch by Enterobacter aerogenes MTCC 2822 and Clostridium acetobutylicum MTCC 11274

Dark fermentative biohydrogen production (DFBHP) has potential for utilization of rice starch wastewater (RSWW) as substrate. The hydrogen production of Enterobacter aerogenes MTCC 2822 and Clostridium acetobutylicum MTCC 11274, in pure culture and co-culture modes, was evaluated. The experiments were performed in a 2 L bioreactor, for a batch time of 120 h. The co-culture system resulted in highest cumulative hydrogen (1.13 L H₂/L media) and highest yield (1.67 mol H₂/mol glucose). Two parameters were optimized through response surface methodology (RSM)-substrate concentration (3.0-5.0 g/L) and initial pH (5.5-7.5), in a three-level factorial design. A total of 11 runs were performed in duplicate, which revealed that 4.0 g/L substrate concentration and 6.5 initial pH were optimal in producing hydrogen. The metabolites produced were acetic, butyric, propionic, lactic and isobutyric acids. The volumetric H₂ productions, without and with pH adjustments, were 1.24 L H₂/L media and 1.45 L H₂/L media, respectively.

Novel strategies towards efficient molecular biohydrogen production by dark fermentative mechanism: present progress and future perspective

In the scenario of alarming increase in greenhouse and toxic gas emissions from the burning of conventional fuels, it is high time that the population drifts towards alternative fuel usage to obviate pollution. Hydrogen is an environment-friendly biofuel with high energy content. Several production methods exist to produce hydrogen, but the least energy intensive processes are the fermentative biohydrogen techniques. Dark fermentative biohydrogen production (DFBHP) is a value-added, less energy-consuming process to generate biohydrogen. In this process, biohydrogen can be produced from sugars as well as complex substrates that are generally considered as organic waste. Yet, the process is constrained by many factors such as low hydrogen yield, incomplete conversion of substrates, accumulation of volatile fatty acids which lead to the drop of the system pH resulting in hindered growth and hydrogen production by the bacteria. To circumvent these drawbacks, researchers have come up with several strategies that improve the yield of DFBHP process. These strategies can be classified as preliminary methodologies concerned with the process optimization and the latter that deals with pretreatment of substrate and seed sludge, bioaugmentation, co-culture of bacteria, supplementation of additives, bioreactor design considerations, metabolic engineering, nanotechnology, immobilization of bacteria, etc. This review sums up some of the improvement techniques that profoundly enhance the biohydrogen productivity in a DFBHP process.

Biotransformation of Agricultural By-Products into Biovanillin through Solid-State Fermentation (SSF) and Optimization of Different Parameters Using Response Surface Methodology (RSM)

Vanillin is a flavorful and aromatic secondary metabolite found in vanilla plants. Natural vanillin, produced through processed vanilla beans accounts for scarcely 0.2% of industrial requirements. Vanillin produced via chemical methods and microbial fermentation fills the remaining gap. Among naturally available precursors for biovanillin synthesis, ferulic acid is widely used because of its structural similarity and abundant availability. Herein, various agricultural lignocellulosic by-products (sugarcane bagasse, wheat straw, rice straw, rice bran, and corn cob) were scrutinized for their ferulic acid content, and their biotransformation into biovanillin was examined by solid-state fermentation (SSF). Then, different physicochemical parameters, i.e., moisture content, pH, temperature, inoculum size, and incubation days, were optimized to achieve a high yield of biovanillin using central composite design (CCD) of response surface methodology (RSM). Among agricultural by-products tested, sugarcane bagasse produced 0.029 g/100 g of biovanillin using Enterobacter hormaechei through SSF. After optimization, the highest concentration of biovanillin (0.476 g/100 g) was achieved at a moisture content of 70%, temperature of 37.5 °C, pH 7.5, inoculum size of 4 mL and incubation time of 48 h. The F-value of 6.10 and p-value of 0.002 evidenced the ultimate significance of the model. The significance of the constructed model was supported by the 91.73% coefficient of determination (R2), indicating that the effects of moisture, pH, and temperature were significant. HPLC and FTIR confirmed the sample identification and purity (was reported to be 98.3% pure). In conclusion, sugarcane bagasse appears to be a cost-effective substrate choice for large-scale biovanillin production.

Design and engineering of artificial microbial consortia for biohydrogen production

In natural microbial ecosystems the metabolic diversity of the organisms enables interaction among the community members and allows them to engage in syntrophic interactions. With regard to biotechnology, artificial microbial consortium engineering is used to improve productivities and yields of bioprocesses. However, to achieve supreme productivity or efficiency at industrial scale, defined ecosystems must be physiologically well-selected to meet eco-biotechnological demands. Here, we present an artificial microbial consortia design and engineering pipeline for developing dark fermentative biohydrogen production processes. The proposed pipeline might be considered as a blue-print for enhancing other bioprocesses that fundamentally face metabolic restrictions or kinetic limitations.

Transcriptome Profiling-Based Analysis of Carbohydrate-Active Enzymes in Aspergillus terreus Involved in Plant Biomass Degradation

Given the global abundance of plant biomass residues, potential exists in biorefinery-based applications with lignocellulolytic fungi. Frequently isolated from agricultural cellulosic materials, Aspergillus terreus is a fungus efficient in secretion of commercial enzymes such as cellulases, xylanases and phytases. In the context of biomass saccharification, lignocellulolytic enzyme secretion was analyzed in a strain of A. terreus following liquid culture with sugarcane bagasse (SB) (1% w/v) and soybean hulls (SH) (1% w/v) as sole carbon source, in comparison to glucose (G) (1% w/v). Analysis of the fungal secretome revealed a maximum of 1.017 UI.mL^–1 xylanases after growth in minimal medium with SB, and 1.019 UI.mL^–1 after incubation with SH as carbon source. The fungal transcriptome was characterized on SB and SH, with gene expression examined in comparison to equivalent growth on G as carbon source. Over 8000 genes were identified, including numerous encoding enzymes and transcription factors involved in the degradation of the plant cell wall, with significant expression modulation according to carbon source. Eighty-nine carbohydrate-active enzyme (CAZyme)-encoding genes were identified following growth on SB, of which 77 were differentially expressed. These comprised 78% glycoside hydrolases, 8% carbohydrate esterases, 2.5% polysaccharide lyases, and 11.5% auxiliary activities. Analysis of the glycoside hydrolase family revealed significant up-regulation for genes encoding 25 different GH family proteins, with predominance for families GH3, 5, 7, 10, and 43. For SH, from a total of 91 CAZyme-encoding genes, 83 were also significantly up-regulated in comparison to G. These comprised 80% glycoside hydrolases, 7% carbohydrate esterases, 5% polysaccharide lyases, 7% auxiliary activities (AA), and 1% glycosyltransferases. Similarly, within the glycoside hydrolases, significant up-regulation was observed for genes encoding 26 different GH family proteins, with predominance again for families GH3, 5, 10, 31, and 43. A. terreus is a promising species for production of enzymes involved in the degradation of plant biomass. Given that this fungus is also able to produce thermophilic enzymes, this first global analysis of the transcriptome following cultivation on lignocellulosic carbon sources offers considerable potential for the application of candidate genes in biorefinery applications.

Enhancing hemoglobin peptide production from chicken blood fermentation by food-grade nonionic surfactant

This study is focused on employing a potential process technology for enhancing hemoglobin peptides production from chicken blood. Effects of surfactants on chicken blood biodegradation and hemoglobin polypeptide accumulation were evaluated and the bioconversion conditions were optimized. Results suggested that surfactants exhibited the positive effect on hemoglobin peptides production during chicken blood bioconversion by Aspergillus niger. Dodecyl glucopyranoside was selected as the optimal surfactant and added at the 48th hour of the fermentation process (64 H) at the concentration of 6.0 g/L. Under the optimized conditions, 104.5 mg·N/mL amino nitrogen, 638.3 mg·N/mL nonprotein nitrogen, and 766.3 mg·N/mL soluble nitrogen were detected, which increased by approximately 0.7-, 3.7-, and 3.8-fold, respectively, compared with the control. Furthermore, the acid protease stability was remarkably intensified and the accumulated peptides were mainly distributed at 500-2,000 Da. Results from this work corroborate the potential of applying dodecyl glucopyranoside in hemoglobin polypeptide production from chicken blood.

Advances in the development and application of microbial consortia for metabolic engineering

Recent advances in metabolic engineering enable the production of high-value chemicals via expressing complex biosynthetic pathways in a single microbial host. However, many engineered strains suffer from poor product yields due to redox imbalance and excess metabolic burden, and require compartmentalization of the pathway for optimal function. To address this problem, significant developments have been made towards co-cultivation of more than one engineered microbial strains to distribute metabolic burden between the co-cultivation partners and improve the product yield. In this emerging approach, metabolic pathway modules can be optimized separately in suitable hosts that will then be combined to enable optimal functionality of the complete pathway. This modular approach broadens the possibilities to fine tune sophisticated production platforms and thus achieve the biosynthesis of very complex compounds.

Here, we review the different applications and the overall potential of natural and artificial co-cultivation systems in metabolic engineering in order to improve bioproduction/bioconversion. In addition to the several advantages over monocultures, major challenges and opportunities associated with co-cultivation are also discussed in this review.

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Benefits of using co-cultivation system in metabolic engineering.

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Existence of natural consortia and their application.

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Recent advancement in co-cultivation methodology for bioproductions.

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Challenges in implementing microbial consortia for microbial biosynthesis.

A novel strategy to enhance biohydrogen production using graphene oxide treated thermostable crude cellulase and sugarcane bagasse hydrolyzate under co-culture system

Graphene oxide (GO) treated thermostable crude cellulase has been obtained via fungal co-cultivation of strain Cladosporium cladosporioides NS2 and Emericella variecolor NS3 using mix substrate of orange peel and rice straw under solid state fermentation (SSF). Enzyme activity of 60 IU/gds FP, 300 IU/gds EG and 400 IU/gds BGL are recorded in the presence of 1.0% GO in 96 h. This crude enzyme showed 50 °C as optimum incubation temperature, thermally stable at 55 °C for 600 min and stability in the pH range 4.5-8.0. Further, 70.04 g/L of sugar hydrolyzate is obtained from enzymatic conversion of 3.0% alkali pre-treated baggase using GO treated crude cellulase. Finally, 2870 ml/L cumulative biohydrogen production having bacterial biomass ∼2.2 g/L and the complimentary initial pH 7.0 is recorded from sugar hydrolyzate via dark fermentation using co-culture of Clostridium pasteurianum (MTCC116) and a newly isolated Bacillus subtilis PF_1.

Optimization of hydrogen and organic acids productions with autochthonous and allochthonous bacteria from sugarcane bagasse in batch reactors

The individual and mutual effects of substrate concentration (from 0.8 to 9.2 g/L) and pH (from 4.6 to 7.4) on hydrogen and volatile fatty acids production from sugarcane bagasse (SCB) were investigated in batch reactors, using a response surface methodology (RSM) and central composite design (CCD). The maximum of 23.10 mmoL H₂/L was obtained under optimized conditions of 7.0 g SCB/L and pH 7.2, at 37 °C through the acetic acid pathway (1.57 g/L). Butyric and succinic acids were the major volatile fatty acids (VFA) produced in the fermentation process (from 0.66 to 1.88 g/L and from 1.06 to 1.65 g/L, respectively). According to the results, the RSM and CCD were useful tools to achieve high hydrogen production rates using Clostridium, Bacillus and Enterobacter, identified by Illumina sequencing (16S RNAr) in the fermentative consortium, and Clostridium and Paenibacillus, autochthonous bacteria from SCB. Significant changes were observed in the microbial community according to the changes in the independent variables, since the genera in the central point condition (5.0 g SCB/L and pH 6.0) were Lactobacillus, Escherichia and Clostridium, and Bacteroides and Enterobacter, which were identified in the optimized condition (7.0 g SCB/L and pH 7.2).

Investigation on hydrogen production from paper sludge without inoculation and its enhancement by Clostridium thermocellum

The feasibility and performance of hydrogen production from paper sludge without inoculation was investigated under thermophilic conditions. The maximum hydrogen production reached 64.32 mM with 7.4% PS. The dynamic changes in bacterial community structures during hydrogen production were investigated by analyzing 16S rDNA gene sequences using high throughput sequencing technology. The results showed that microbial community was dominated by order Clostridiales and Thermoanaerobacterales. Genus Thermoanaerobacterium and Ruminiclostridium played a leading role in the fermentation process, which was responsible for the hydrolysis of PS and hydrogen production. Effect of inoculation with Clostridium thermocellum on hydrogen production from PS was also studied. The results showed that C. thermocellum supplement significantly increased hydrogen yield and holocellulose degradation rate by 96.80% and 32.95%, respectively. In addition, inoculation of C. thermocellum enhanced VFA generation and shortened the lag phase of hydrogen production. The present study lays the foundation on the valorization of waste lignocellulose.

Bioconversion of Lignocellulosic Biomass to Fermentable Sugars by Immobilized Magnetic Cellulolytic Enzyme Cocktails

Enzyme cocktails of reusable, highly stable cellulolytic enzymes play an inevitable role in bioconversion of biomass to biofuels economically. Cellulase, xylanase and β-1,3-glucanase bound silica-amine functionalized iron oxide magnetic nanoparticles (ISN-CLEAs) were prepared and used as the biocatalyst for the depolymerization of cellulosic biomass into monomeric sugar in the present study. The Fe₃O₄-NPs and Fe₃O₄@SiO₂-NH₂-NPs and ISN-CLEAs had an average hydrodynamic size of 82.2, 86.4, and 976.9 nm, respectively, which was confirmed by dynamic light scattering (DLS). About 97% of protein binding was achieved with 135 mM glutaraldehyde at 10 h of cross-linking time and successful binding was confirmed by Fourier transform infrared spectroscopy (FTIR). The ISN-CLEAs exhibited the highest thermal stability of 95% at 50 °C for 2 h and retained extended storage stability of 97% compared to 60% of its free counterpart. Besides, cross-linking allowed ISN-CLEAs reuse for at least eight consecutive cycles retaining over 70% of its initial activity. ISN-CLEAs exhibited approximately 15% increase in carbohydrate digestibility on sugar cane bagasse and eucalyptus pulp than the free enzyme.

Cellulosic ethanol production via consolidated bioprocessing by a novel thermophilic anaerobic bacterium isolated from a Himalayan hot spring

BACKGROUND

Cellulose-degrading thermophilic anaerobic bacterium as a suitable host for consolidated bioprocessing (CBP) has been proposed as an economically suited platform for the production of second-generation biofuels. To recognize the overall objective of CBP, fermentation using co-culture of different cellulolytic and sugar-fermenting thermophilic anaerobic bacteria has been widely studied as an approach to achieving improved ethanol production. We assessed monoculture and co-culture fermentation of novel thermophilic anaerobic bacterium for ethanol production from real substrates under controlled conditions.

RESULTS

In this study, Clostridium sp. DBT-IOC-C19, a cellulose-degrading thermophilic anaerobic bacterium, was isolated from the cellulolytic enrichment cultures obtained from a Himalayan hot spring. Strain DBT-IOC-C19 exhibited a broad substrate spectrum and presented single-step conversion of various cellulosic and hemicellulosic substrates to ethanol, acetate, and lactate with ethanol being the major fermentation product. Additionally, the effect of varying cellulose concentrations on the fermentation performance of the strain was studied, indicating a maximum cellulose utilization ability of 10 g L^-1 cellulose. Avicel degradation kinetics of the strain DBT-IOC-C19 displayed 94.6% degradation at 5 g L^-1 and 82.74% degradation at 10 g L^-1 avicel concentration within 96 h of fermentation. In a comparative study with Clostridium thermocellum DSM 1313, the ethanol and total product concentrations were higher by the newly isolated strain on pretreated rice straw at an equivalent substrate loading. Three different co-culture combinations were used on various substrates that presented two-fold yield improvement than the monoculture during batch fermentation.

CONCLUSIONS

This study demonstrated the direct fermentation ability of the novel thermophilic anaerobic bacteria on various cellulosic and hemicellulosic substrates into ethanol without the aid of any exogenous enzymes, representing CBP-based fermentation approach. Here, the broad substrate utilization spectrum of isolated cellulolytic thermophilic anaerobic bacterium was shown to be of potential utility. We demonstrated that the co-culture strategy involving novel strains is efficient in improving ethanol production from real substrate.

Enhanced saccharification of cellulose and sugarcane bagasse by Clostridium thermocellum cultures with Triton X-100 and β-glucosidase/Cellic®CTec2 supplementation

Increased saccharification and utilization of biomass directly byC. thermocellumcultures with Triton X-100 and β-glucosidase supplementation.

Enhanced biohydrogen and subsequent biomethane production from sugarcane bagasse using nano-titanium dioxide pretreatment

Nano-titanium dioxide (nanoTiO2) under ultraviolet irradiation (UV) followed by dilute sulfuric acid hydrolysis of sugarcane bagasse was used to enhance the production of biohydrogen and biomethane in a consecutive dark fermentation and anaerobic digestion. Different concentrations of 0.001, 0.01, 0.1 and 1g nanoTiO2/L under different UV times of 30, 60, 90 and 120min were used. Sulfuric acid (2%v/v) at 121°C was used for 15, 30 and 60min to hydrolyze the pretreated bagasse. For acidic hydrolysis times of 15, 30 and 60min, the highest total free sugar values were enhanced by 260%, 107%, and 189%, respectively, compared to samples without nanoTiO2 pretreatment. The highest hydrogen production samples for the same acidic hydrolysis times showed 88%, 127%, and 25% enhancement. The maximum hydrogen production of 101.5ml/g VS (volatile solids) was obtained at 1g nanoTiO2/L and 120min UV irradiation followed by 30min acid hydrolysis.

Enhanced isopropanol and n-butanol production by supplying exogenous acetic acid via co-culturing two clostridium strains from cassava bagasse hydrolysate

The focus of this study was to produce isopropanol and butanol (IB) from dilute sulfuric acid treated cassava bagasse hydrolysate (SACBH), and improve IB production by co-culturing Clostridium beijerinckii (C. beijerinckii) with Clostridium tyrobutyricum (C. tyrobutyricum) in an immobilized-cell fermentation system. Concentrated SACBH could be converted to solvents efficiently by immobilized pure culture of C. beijerinckii. Considerable solvent concentrations of 6.19 g/L isopropanol and 12.32 g/L butanol were obtained from batch fermentation, and the total solvent yield and volumetric productivity were 0.42 g/g and 0.30 g/L/h, respectively. Furthermore, the concentrations of isopropanol and butanol increased to 7.63 and 13.26 g/L, respectively, under the immobilized co-culture conditions when concentrated SACBH was used as the carbon source. The concentrations of isopropanol and butanol from the immobilized co-culture fermentation were, respectively, 42.62 and 25.45 % higher than the production resulting from pure culture fermentation. The total solvent yield and volumetric productivity increased to 0.51 g/g and 0.44 g/L/h when co-culture conditions were utilized. Our results indicated that SACBH could be used as an economically favorable carbon source or substrate for IB production using immobilized fermentation. Additionally, IB production could be significantly improved by co-culture immobilization, which provides extracellular acetic acid to C. beijerinckii from C. tyrobutyricum. This study provided a technically feasible and cost-efficient way for IB production using cassava bagasse, which may be suitable for industrial solvent production.

Biohydrogen Production from Hydrolysates of Selected Tropical Biomass Wastes with Clostridium Butyricum

Biohydrogen production has received widespread attention from researchers in industry and academic fields. Response surface methodology (RSM) was applied to evaluate the effects of several key variables in anaerobic fermentation of glucose with Clostridium butyrium, and achieved the highest production rate and yield of hydrogen. Highest H₂ yield of 2.02 mol H₂/mol-glucose was achieved from 24 h bottle fermentation of glucose at 35 °C, while the composition of medium was (g/L): 15.66 glucose, 6.04 yeast extract, 4 tryptone, 3 K₂HPO₄, 3 KH₂PO₄, 0.05 L-cysteine, 0.05 MgSO₄·7H₂O, 0.1 MnSO₄·H₂O and 0.3 FeSO₄·7H₂O, which was very different from that for cell growth. Sugarcane bagasse and Jatropha hulls were selected as typical tropical biomass wastes to produce sugars via a two-step acid hydrolysis for hydrogen production. Under the optimized fermentation conditions, H₂ yield (mol H₂/mol-total reducing sugar) was 2.15 for glucose, 2.06 for bagasse hydrolysate and 1.95 for Jatropha hull hydrolysate in a 3L fermenter for 24 h at 35 °C, with H₂ purity of 49.7–64.34%. The results provide useful information and basic data for practical use of tropical plant wastes to produce hydrogen.

Enhanced biohydrogen production from sugarcane bagasse by Clostridium thermocellum supplemented with CaCO3

Clostridium thermocellum ATCC 27405 was used to degrade sugarcane bagasse (SCB) directly for hydrogen production, which was significantly enhanced by supplementing medium with CaCO3. The effect of CaCO3 concentration on the hydrogen production was investigated. The hydrogen production was significantly enhanced with the CaCO3 concentration increased from 10mM to 20mM. However, with the CaCO3 concentration further increased from 20mM to 100mM, the hydrogen production didn't increase further. Under the optimal CaCO3 concentration of 20mM, the hydrogen production reached 97.83±5.19mmol/L from 2% sodium hydroxide-pretreated SCB, a 116.72% increase over the control (45.14±1.03mmol/L), and the yield of hydrogen production reached 4.89mmol H2/g SCBadded. Additionally, CaCO3 promoted the biodegradation of SCB and the growth of C. thermocellum. The stimulatory effects of CaCO3 on biohydrogen production are mainly attributed to the buffering capacity of carbonate. The study provides a novel strategy to enhance biohydrogen production from lignocellulose.

Comparative evaluation of the hydrogen production by mixed consortium, synthetic co-culture and pure culture using distillery effluent

Wastewater comprises of various carbon sources. So, the use of microbial consortium may improve the hydrogen production and organic reduction. The present study deals with biohydrogen production by acidogenic mixed consortia (AMC), synthetic co-culture (Klebsiella pneumoniae IIT-BT 08 and Citrobacter freundii IIT-BT L139) and pure culture using distillery effluent (DE). Higher hydrogen yield was observed in case of AMC (9.17 mol/kg CODreduced) as compared to the synthetic co-culture and pure culture. PCR-DGGE analysis indicated that the consortium was predominated by species closely affiliated to Clostridium sp. The average hydrogen production rate was 267 mL/Lh. The maximum hydrogen production rate (Rm), hydrogen production potential (P) and lag time (λ) by AMC using DE were 507.2 mL/Lh, 3729 m/L and 2.04 h, respectively. Maximum gaseous energy recovery by AMC was found to be higher by 21.9% and 45.4% than that of using co-culture and pure culture respectively.

Optimization of key factors affecting hydrogen production from sugarcane bagasse by a thermophilic anaerobic pure culture

BACKGROUND

Hydrogen is regarded as an attractive future energy carrier for its high energy content and zero CO2 emission. Currently, the majority of hydrogen is generated from fossil fuels. However, from an environmental perspective, sustainable hydrogen production from low-cost lignocellulosic biomass should be considered. Thermophilic hydrogen production is attractive, since it can potentially convert a variety of biomass-based substrates into hydrogen at high yields.

RESULTS

Sugarcane bagasse (SCB) was used as the substrate for hydrogen production by Thermoanaerobacterium aotearoense SCUT27/Δldh. The key parameters of acid hydrolysis were studied through the response surface methodology. The hydrogen production was maximized under the conditions of 2.3% of H2SO4 for 114.2 min at 115°C. Using these conditions, a best hydrogen yield of 1.86 mol H2/mol total sugar and a hydrogen production rate (HPR) of 0.52 L/L · h were obtained from 2 L SCB hydrolysates in a 5-L fermentor, showing a superior performance to the results reported in the literature. Additionally, no obvious carbon catabolite repression (CCR) was observed during the fermentation using the multi-sugars as substrates.

CONCLUSIONS

Considering these advantages and theimpressive HPR, the potential of hydrogen production using T. aotearoense SCUT27/Δldh is intriguing. Thermophilic, anaerobic fermentation using SCB hydrolysates as the medium by this strain would be a practical and eco-friendly process.

Synergism of cellulase, xylanase, and pectinase on hydrolyzing sugarcane bagasse resulting from different pretreatment technologies

Sugarcane bagasse (SCB) resulting from different pretreatments was hydrolyzed by enzyme cocktails based on replacement of cellulase (Celluclast 1.5 L:Novozym 188=1FPU:4pNPGU) by xylanase or pectinase at different proportions. Lignin content of NaOH pretreated SCB and hemicellulose content of H2SO4 pretreated SCB were the lowest. NaOH pretreatment showed the best for monosaccharide production among the four pretreatments. Synergism was apparently observed between cellulase and xylanase for monosaccharide production from steam exploded SCB (SESB), NaOH, and H2O2 pretreated SCB. No synergism was observed between cellulase and pectinase for producing glucose. Additionally, no synergism was present when H2SO4 pretreated SCB was used. Replacement of 20% of the cellulase by xylanase enhanced the glucose yield by 6.6%, 8.8%, and 9.5% from SESB, NaOH, and H2O2 pretreated SCB, respectively. Degree of synergism between cellulase and xylanase had positive relationship with xylan content and was affected by hydrolysis time.