Anaerobic digestion of corn stovers for methane production in a novel bionic reactor

To improve the biogas production from corn stovers, a new bionic reactor was designed and constructed. The bionic reactor simulated the rumen digestion of ruminants. The liquid was separated from corn stovers and refluxed into corn stovers again, which simulated the undigested particles separated from completely digested materials and fed back again for further degradation in ruminant stomach. Results showed that the bionic reactor was effective for anaerobic digestion of corn stovers. The liquid amount and its reflux showed an obvious positive correlation with biogas production. The highest biogas production rate was 21.6 ml/gVS-addedd, and the total cumulative biogas production was 256.5 ml/gVS-added. The methane content in biogas ranged from 52.2% to 63.3%. The degradation of corn stovers were greatly enhanced through simulating the animal digestion mechanisms in this bionic reactor.

From biowaste to bioresource: Effect of a lignocellulosic filler on the properties of poly(3-hydroxybutyrate)

A lignin-rich residue (LRR) obtained as a by-product from the fermentative bioethanol production process, and commercial alkali lignin (AL), were used as fillers for the preparation of bio-based blends and composites with poly(3-hydrobutyrate) (PHB). Chemical characterization of LRR demonstrated that the filler contained sugar residues. Rheological and thermal characterization of the blends demonstrated that LRR did not affect thermal stability of PHB, while AL had a strong pro-degrading effect. Addition of suitable amounts of LRR dramatically affected the rheological behavior of the polymer melt, suggesting that the additive can modify polymer processability. LRR was also a heterogeneous nucleating agent, potentially able to control the physical aging of PHB. Lower resilience and elongation at break values were found for the biocomposites, due to the poor interfacial adhesion between filler and matrix. Biodegradation behavior of the composites was qualitatively assessed by analyzing the surface of soil buried films. Significant surface degradation was observed for PHB, while the process was retarded at high filler concentration, as LRR inhibited hydrolytic and biotic polymer degradation. The reported results demonstrated the feasibility of the conversion of an agro-industrial by-product into a bio-resource in an environmentally friendly and cost-effective way.

Oleaginous fungal lipid fermentation on combined acid- and alkali-pretreated corn stover hydrolysate for advanced biofuel production

A combined hydrolysis process, which first mixed dilute acid- and alkali-pretreated corn stover at a 1:1 (w/w) ratio, directly followed by enzymatic saccharification without pH adjustment, has been developed in this study in order to minimize the need of neutralization, detoxification, and washing during the process of lignocellulosic biofuel production. The oleaginous fungus Mortierella isabellina was selected and applied to the combined hydrolysate as well as a synthetic medium to compare fungal lipid accumulation and biodiesel production in both shake flask and 7.5L fermentor. Fungal cultivation on combined hydrolysate exhibited comparable cell mass and lipid yield with those from synthetic medium, indicating that the integration of combined hydrolysis with oleaginous fungal lipid fermentation has great potential to improve performance of advanced lignocellulosic biofuel production.

Enzymatic hydrolysis of steam exploded corncob residues after pretreatment in a twin-screw extruder

A modified twin-screw extruder incorporated with a filtration device was used as a liquid/solid separator for xylose removal from steam exploded corncobs. A face centered central composite design was used to study the combined effects of various enzymatic hydrolysis process variables (enzyme loading, surfactant addition, and hydrolysis time) with two differently extruded corncobs (7% xylose removal, 80% xylose removal) on glucose conversion. The results showed that the extrusion process led to an increase in cellulose crystallinity, while structural changes could also be observed via SEM. A quadratic polynomial model was developed for predicting the glucose conversion and the fitted model provided an adequate approximation of the true response as verified by the analysis of variance (ANOVA).

Cultivation of lipid-producing bacteria with lignocellulosic biomass: effects of inhibitory compounds of lignocellulosic hydrolysates

Lignocellulosic biomass has been recognized as a promising feedstock for the fermentative production of biofuel. However, the pretreatment of lignocellulose generates a number of by-products, such as furfural, 5-hydroxylmethyl furfural (5-HMF), vanillin, vanillic acids and trans-p-coumaric acid (TPCA), which are known to inhibit microbial growth. This research explores the ability of Rhodococcus opacus PD630 to use lignocellulosic biomass for production of triacylglycerols (TAGs), a common lipid raw material for biodiesel production. This study reports that R. opacus PD630 can grow well in R2A broth in the presence of these model inhibitory compounds while accumulating TAGs. Furthermore, strain PD630 can use TPCA, vanillic acid, and vanillin as carbon sources, but can only use TPCA and vanillic acid for TAG accumulation. Strain PD630 can also grow rapidly on the hydrolysates of corn stover, sorghum, and grass to accumulate TAGs, suggesting that strain PD630 is well-suited for bacterial lipid production from lignocellulosic biomass.

Two-step sequential liquefaction of lignocellulosic biomass by crude glycerol for the production of polyols and polyurethane foams

A two-step sequential biomass liquefaction process was developed to produce bio-based polyols and polyurethane (PU) foams using crude glycerol as a liquefaction solvent. The first step, acid-catalyzed liquefaction, was highly effective in liquefying biomass, while the second step, base-catalyzed liquefaction, featured extensive condensation reactions. By using the developed two-step liquefaction process, the polyols produced from lignocellulosic biomass and crude glycerol containing 26-40% organic impurities showed hydroxyl numbers ranging from 536 to 936mgKOH/g, viscosities from 20.6 to 28.0Pas, and molecular weights (Mw) from 444 to 769g/mol. The PU foams produced had densities ranging from 0.04 to 0.05g/cm(3), compressive strengths from 223 to 420kPa, and thermal conductivities from 32.2 to 38.9mW/mK. Polyols and PU foams produced from the two-step liquefaction process had improved properties over their analogs derived from a one-step biomass liquefaction by crude glycerol process catalyzed by acid or base.

Pretreatment of lignocellulosic biomass using Fenton chemistry

In an attempt to mimic white-rot fungi lignin degradation via in vivo Fenton chemistry, solution phase Fenton chemistry (10 g biomass, 176 mmol hydrogen peroxide and 1.25 mmol Fe(2+) in 200 mL of water) was applied to four different biomass feedstocks. An enzymatic saccharification of Fenton pretreated biomass showed an average 212% increase relative to untreated control across all four feedstocks (P<0.05, statistically significant). A microbial fermentation of the same Fenton pretreated biomass showed a threefold increase in gas production upon a sequential co-culture with Clostridium thermocellum and Clostridium beijerinckii. These results demonstrate the use of solution phase Fenton chemistry as a viable pretreatment method to make cellulose more bioavailable for microbial biofuel conversion.

Importance of glucose-6-phosphate dehydrogenase (G6PDH) for vanillin tolerance in Saccharomyces cerevisiae

Vanillin is derived from lignocellulosic biomass and, as one of the major biomass conversion inhibitors, inhibits yeast growth and fermentation. Vanillin was recently shown to induce the mitochondrial fragmentation and formation of mRNP granules such as processing bodies and stress granules in Saccharomyces cerevisiae. Furfural, another major biomass conversion inhibitor, also induces oxidative stress and is reduced in an NAD(P)H-dependent manner to its less toxic alcohol derivative. Therefore, the pentose phosphate pathway (PPP), through which most NADPH is generated, plays a role in tolerance to furfural. Although vanillin also induces oxidative stress and is reduced to vanillyl alcohol in a NADPH-dependent manner, the relationship between vanillin and PPP has not yet been investigated. In the present study, we examined the importance of glucose-6-phosphate dehydrogenase (G6PDH), which catalyzes the rate-limiting NADPH-producing step in PPP, for yeast tolerance to vanillin. The growth of the null mutant of G6PDH gene (zwf1Δ) was delayed in the presence of vanillin, and vanillin was efficiently reduced in the culture of wild-type cells but not in the culture of zwf1Δ cells. Furthermore, zwf1Δ cells easily induced the activation of Yap1, an oxidative stress responsive transcription factor, mitochondrial fragmentation, and P-body formation with the vanillin treatment, which indicated that zwf1Δ cells were more susceptible to vanillin than wild type cells. These findings suggest the importance of G6PDH and PPP in the response of yeast to vanillin.

Biorefining of wheat straw using an acetic and formic acid based organosolv fractionation process

To assess the potential of acetic and formic acid organosolv fractionation of wheat straw as basis of an integral biorefinery concept, detailed knowledge on yield, composition and purity of the obtained streams is needed. Therefore, the process was performed, all fractions extensively characterized and the mass balance studied. Cellulose pulp yield was 48% of straw dry matter, while it was 21% and 27% for the lignin and hemicellulose-rich fractions. Composition analysis showed that 67% of wheat straw xylan and 96% of lignin were solubilized during the process, resulting in cellulose pulp of 63% purity, containing 93% of wheat straw cellulose. The isolated lignin fraction contained 84% of initial lignin and had a purity of 78%. A good part of wheat straw xylan (58%) ended up in the hemicellulose-rich fraction, half of it as monomeric xylose, together with proteins (44%), minerals (69%) and noticeable amounts of acids used during processing.

Effects of compositional changes of AFEX-treated and H-AFEX-treated corn stover on enzymatic digestibility

Corn stover is one of the main agricultural residues being considered as a cellulosic ethanol feedstock. This work evaluated the effectiveness of AFEX™(1) pretreatment for converting corn stover to fermentable sugars, both with and without pre-soaking in hydrogen peroxide. The compositional changes and enzymatic digestibility of AFEX-treated and H-AFEX-treated biomass were investigated. Results showed that most of the polysaccharides remained intact following each of these two methods. Compared with AFEX pretreatment, the H-AFEX process enhanced delignification and enzymatic hydrolysis yields of both glucose and xylose. The maximum glucan and xylan digestibility of H-AFEX process were 87.78% and 90.64%, respectively, and were obtained using 0.7 (w/w) water loading, 1.0 (w/w) ammonia loading, 0.5 (w/w) 30wt.% hydrogen peroxide loading, and 130°C for 10min. The results of the present work show that H-AFEX is a feasible pretreatment to improve the enzymatic saccharification of corn stover for bioethanol production.

Enzymatic and metabolic activities of four anaerobic sludges and their impact on methane production from ensiled sorghum forage

Biochemical methane potential (BMP) tests were run on ensiled sorghum forage using four inocula (urban, agricultural, mixture of agricultural and urban, granular) and differences on their metabolic and enzymatic activities were also discussed. Results indicate that no significant differences were observed in terms of BMP values (258±14NmLCH4g(-1)VS) with a slightly higher value when agricultural sludge was used as inoculum. Significant differences can be observed among different inocula, in terms of methane production rate. In particular the fastest biomethanization occurred when using the urban sludge (hydrolytic kinetic constant kh=0.146d(-1)) while the slowest one was obtained from the agricultural sludge (kh=0.049d(-1)). Interestingly, positive correlations between the overall enzymatic activities and methane production rates were observed for all sludges, showing that a high enzymatic activity may favour the hydrolysis of complex substrate and accelerate the methanization process of sorghum.

Comparison of biogas production from wild and cultivated varieties of reed canary grass

The chemical composition and efficiency of biogas production in the methane fermentation process of silages of wild and cultivated varieties of reed canary grass were compared. An attempt was made to answer the question on how the habitat and the way of utilization of plants affect chemical composition and biogas yield. Physicochemical properties such as dry matter, organic dry matter, protein, fat, crude fiber fraction, macro- and microelements content were considered. The anaerobic digestion process and FTIR analysis were also carried out. The results showed that the two varieties differ essentially in their physical and chemical properties. The cultivated variety was characterized by higher biogas yield (406Ndm(3)kg(-1) VS) than the wild one (120Ndm(3)kg(-1) VS). This was probably related to the chemical composition of plants, especially the high content of indigestible crude fiber fractions and ash. These components could reduce biogas quantity and quality.

Direct hydro-liquefaction of sawdust in petroleum ether and comprehensive bio-oil products analysis

The effect of temperature, time, hydrogen pressure and amount of catalyst on production distribution and the bio-oil yield obtained from the direct liquefaction of sawdust in the petroleum ether (60-90°C) are investigated. The highest sawdust conversion obtained was 72.32% with a bio-oil yield of 47.69% were obtained at 370°C, 40min and 5wt.% catalyst content with the initial H2 pressure of 3.0MPa. Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) approach was utilized to analyze the non-volatile fraction. In this study, the composition of bio-oil could be analyzed in an unprecedented detail through a combination of GC-MS and FT-ICR MS techniques.

Addition of alkali to the hydrothermal-mechanochemical treatment of Eucalyptus enhances its enzymatic saccharification

The effects of alkali on hydrothermal-mechanochemical treatment (hydrothermal treatment combined with wet-milling) were examined with the aim of improving pretreatment of lignocellulosic biomass before enzymatic saccharification. After enzymatic saccharification, the highest glucose yield was obtained by autoclaving at 170°C in the presence of 20% NaOH per substrate weight. The wood fiber was unraveled into finer nanofibers by hydrothermal-mechanochemical treatment, thus increasing the specific surface area of the substrate from 11 to 132m(2)/g. Adding 20% NaOH to the treatment further increased the specific surface area of the already fibrillated substrate by 76% (232m(2)/g) due to lignin removal and ester bond cleavage between lignin and hemicellulose. This increase in specific surface area was closely related to the increase in enzymatic digestibility; therefore, NaOH addition may have enhanced the effect of hydrothermal-mechanochemical treatment.

A novel kinetic model for polysaccharide dissolution during atmospheric acetic acid pretreatment of sugarcane bagasse

Acetic acid (AcH) pretreatment of sugarcane bagasse with the catalysis of sulfuric acid (SA) could greatly enhance the enzymatic digestibility of cellulose. However, polysaccharide dissolution happened inevitably during the pretreatment. It was found that the simplest model, which assumes that the total polysaccharides were reactive to be dissolved, could not well describe the kinetic behavior of polysaccharide dissolution. A novel pseudo-homogenous kinetic model was thus developed by introducing a parameter termed as "potential dissolution degree" (δ(d)) based on the multilayered structure of cell wall. It was found that solid xylan and glucan dissolutions were a first-order reaction with respect to the dissolvable fraction. Due to the delignification action of AcH, polysaccharide dissolutions were enhanced in AcH media compared with those in aqueous system. Acetylizations of cellulose and sugars were also observed, and AcH concentration showed a significant influence on the degree of acetylization.

Extrusion of xylans extracted from corn cobs into biodegradable polymeric materials

Solvent casting technique, which comprises multiple energy demanding steps including the dissolution of a polymer in a solvent followed by the evaporation of the solvent from the polymer solution, is currently the main technique for the production of xylan based polymeric materials. The present study shows that sufficient water content renders arabinoglucuronoxylan (AGX) polymers extrudable, enabling the production of AGX based polymeric materials in a single step via extrusion, which is economically advantageous to solvent casting process for mass production. AGX polymers with water content of 27% were found to yield extrudates at an extrusion temperature of 90°C. The extruded strips showed very good mechanical properties with an ultimate tensile strength of 76 ± 6 MPa and elongation at break value of 35 ± 8%, which were superior to the mechanical properties of the strips obtained from polylactic acid.

Ionic liquid pretreatment to enhance the anaerobic digestion of lignocellulosic biomass

Four lignocellulosic biomasses, water hyacinth, rice straw, mango leaves and spruce were pretreated by ionic liquid (IL) to enhance anaerobic digestion. The effect of pretreatment conditions, such as alkyl chain length of IL, temperature, time and operation cycle on lignocellulosic composition, structure and biogas production was evaluated. The enhancement of biogas production by [C4mim]Cl pretreatment at 120°C for 2 h decreases in the order of water hyacinth>spruce>rice straw>mango leaves. Higher methane production of regenerated rice straw and mango leaves could reach 233 and 125 mL/g carbohydrates under 140°C or 2 h and 140°C for 8, respectively. Furthermore, the technology of aqueous biphasic systems was developed to recovery IL, and the recovery rate of ILs was in the range of 54.3-94.6%.

Bioflocculants from hydrolysates of corn stover using isolated strain Ochrobactium ciceri W2

This study isolated a total of seven pure cultures from activated sludge that could produce bioflocculants from 1.7% v/v H2SO4 treated hydrolysates of corn stover. The most effective strain amongst the seven isolates was identified as Ochrobactrum ciceri W2. The W2 cells produced biopolymers in logarithm growth phase, peaking at 3.8 g l(-1)in productivity on 16 h. The yielded bioflocculant was primarily consisting of polysaccharides and proteins, and maintained its flocculating activity to 0.5% w/w kaolin suspensions over pH 1-10 (at 30°C) and 30-100°C (at pH 7). This study also revealed that the strain W2 could utilize biopolymers from hydrolysate of corn stover without addition of excess phosphate salts, which could largely reduce production costs of bioflocculants.

Influence of different demineralization treatments on physicochemical structure and thermal degradation of biomass

To study the catalytic role of alkali and alkaline earth metallic species and eliminate their negative impact during biomass thermal utilization, different leaching methods have been applied in numerous experiments. Thus it is necessary to investigate the potential influence on biomass physicochemical structure using different agents. Rice straw was selected to study the demineralization impact on physicochemical structure and pyrolysis characteristics. It is shown that strong acid leaching exhibited higher removal efficiency of minerals, but it introduced more notable impact on physicochemical structure of biomass comparing to water and weak acid leaching. Different leaching methods give chance to study catalysis characteristics of intrinsic metals on biomass thermal reaction. Contrast to alkaline earth metals especially Ca hindering thermal decomposition, alkali metals promoted this reaction obviously. In addition, comparing to physicochemical structure changes created by leaching process, the influence of removal of minerals played the dominant role in biomass thermal behavior.

Effects of Kraft lignin on hydrolysis/dehydration of sugars, cellulosic and lignocellulosic biomass under hot compressed water

The effect of Kraft lignin presenting on the hydrolysis and dehydration of C5 and C6 sugars, cellulose, hemicelluloses and biomass under hot compressed water (HCW) in the presence of H3PO4 catalyst was intensively studied. The lignin strongly inhibited the acid hydrolysis of cellulose and hemicellulose to glucose and xylose, respectively. Interestingly, the admixed lignin markedly promoted the isomerization of glucose to fructose, and dehydration of fructose (except at the low catalyst loading), resulting in high 5-hydroxymethylfurfural yields. Nonetheless, lignin inhibited the hydrolysis of xylan to xylose and dehydration of xylose to furfural. Moreover, the acidity of the system significantly affects the hydrolysis/dehydration of biomass. It was revealed that the presence of lignin strongly interfered the yields of sugars and furans produced from raw corncob, while the delignified corncob provided significant improvement of product yields, confirming the observed role of lignin in the biomass conversion system via sugar platforms.

Evaluation of hot compressed water pretreatment and enzymatic saccharification of tulip tree sawdust using severity factors

Tulip tree sawdust was pretreated using hot compressed water with different pretreatment severities (LogR0, 3.05-5.01) by varying reaction temperatures (180-220°C) and residence time (1-30 min). It is found that the chemical composition and physicochemical properties of the pretreated products can be characterized and correlated with severity. Removal of most of the xylan and other hemicellulosic sugars from the raw material was observed at a severity of 4.5. Thus, the residual solids were recovered with increased cellulose and lignin contents. Nearly complete glucan conversion was achieved after 48 h of hydrolysis with 10 FPU/g of wet residual solid obtained above a severity of 4.8. The characteristics of the pretreated solids according to the pretreatment severity were strongly related with the glucose yield. The removal of structural barriers to the enzyme attack was the dominant factor affecting enzyme accessibility to the substrate.

Thermogravimetric-mass spectrometric analysis on combustion of lignocellulosic biomass

Combustion characteristics of biomass main components and three lignocellulosic biomass (fir wood, eucalyptus wood and pine bark) were investigated by thermogravimetric analysis coupled with mass spectrometry. The combustion of biomass was divided into two main steps, devolatilization and char oxidation stage. Heating rate effect was also studied. Generally, the higher the heating rate, the higher the decomposition temperature. Furthermore, the weight loss rate decreased due to particle temperature gradients. Combustion kinetics were studied. Models based on reaction order (Oi), nucleation (Ni) and diffusion (Di) achieved the best fitting to the experimental data. Cellulose oxidation presented the highest activation energies. CO, CO2 and H2O were the main components evolved from combustion. Additionally, light hydrocarbons (CH4 and C2H5) were also present. Finally, nitrogen compounds were in a higher proportion than sulfur compounds being released as primary amines and NOx.

Environmentally friendly pretreatment of plant biomass by planetary and attrition milling

This study evaluated the use of planetary and attrition milling as pretreatment processes for lignocellulosic biomass using rice straw. Planetary milling reduced the rice straw crystallinity from 0.48 to 0.11. Since the samples could be milled and enzymatically treated using the same media, loss of the biomass due to washing was effectively eliminated. In contrast, conventional sodium hydroxide and soaking in aqueous ammonia (SAA) processes showed a loss of 34.2% and 14.8%, respectively. Furthermore, milling produced significantly lower concentrations of soluble phenolics than the alkali treatments. Using a bioluminescent bioreporter strain that is sensitive to these phenolics, neither of the milled samples elicited a response while the sodium hydroxide and SAA samples led to a 25.8 and 4.7 -fold induction, respectively. Although planetary milling produced more reducing sugars than attrition milling before saccharification, both had similar monosaccharide yields, i.e., 0.38 and 0.34 g/g-biomass, respectively, when 40 g/l rice straw was treated.

Benefit of sodium hydroxide pretreatment of ensiled sorghum forage on the anaerobic reactor stability and methane production

The assessment of the pretreatment effect on the anaerobic digestion process is generally based on the results of batch tests, which may fail in truly predicting full-scale anaerobic reactors performance. Therefore, in this study, the effect of alkaline pretreatment on the anaerobic digestion of ensiled sorghum forage was evaluated by comparing the results of two semi-continuous CSTR (Continuously Stirred Tank Reactor) anaerobic reactors. Results showed that an alkaline pretreatment step, prior to the anaerobic digestion of ensiled sorghum forage, can have a beneficial effect both in enhancing methane production (an increase of 25% on methane production was observed, if compared to that of untreated sorghum) and in giving more stability to the anaerobic digestion process.

Capability of Thai Mission grass (Pennisetum polystachyon) as a new weedy lignocellulosic feedstock for production of monomeric sugar

Mission grass (Pennisetum polystachyon) grown in Pakchong District, Nakornratchasima Province, Thailand, with high cellulose and hemicellulose contents were harvested to determine the fermentable monomeric sugars for bioethanol production by two-stage microwave/chemical pretreatment process. Microwave-assisted NaOH pretreatment effectively removed approximately 85% lignin content in Mission grass, using 3% (w/v) NaOH, 15:1 liquid-to-solid ratio (LSR) at 120 °C temperatures for 10 min. As a result, in the second stage, microwave-assisted H2SO4 pretreatment of an alkaline-pretreated Mission grass solid releasedan impressively high fermentable sugar content (34.3±1.3 g per 100 g of dried biomass), consisting mainly of 31.1±0.8 g of glucose per 100 g of dried biomass, using 1% (w/v) H2SO4, 15:1 LSR at 200 °C temperature for a very short pretreatment time (5 min). The total monomeric sugar yield obtained via two-stage microwave/chemical process was 40.9 g per 100 g of dried biomass.