Periodic peristalsis enhancing the high solids enzymatic hydrolysis performance of steam exploded corn stover biomass

Enzymatic hydrolysis beyond 15% solid loading offers many advantages such as increased sugar and ethanol concentrations and decreased capital cost. However, difficult mixing and handling limited its industrialized application. A novel intensification method, periodic peristalsis, had been exploited to improve the high solids enzymatic hydrolysis performance of steam exploded corn stover (SECS). The optimal steam explosion conditions were 200 °C and 8 min, under which glucan and xylan recovery was 94.3% and 64.8%, respectively. Glucan and xylan conversions in periodic peristalsis enzymatic hydrolysis (PPEH) were 28.0–38.5% and 25.0–36.0% higher than those in static state enzymatic hydrolysis with solid loading increasing from 1% to 30%, respectively, while they were 1.0–11.2% and 3.0–9.2% higher than those in incubator shaker enzymatic hydrolysis (ISEH). Glucan and xylan conversion in PPEH at 21% solid loading reached 71.2% and 70.3%, respectively. Periodic peristalsis also facilitated fed-batch enzymatic hydrolysis of which SECS was added completely before transition point. Results presented that PPEH shortened the transition point time from solid state to slurry state, decreased the viscosity of hydrolysis mixture, and reduced the denaturation effect of enzymes compared with ISEH, and hence improve the high solids enzymatic hydrolysis efficiency.     

Effect of doping pretreated corn stover conditions on yield of bioethanol in immobilized cell systems

The surface characteristics of immobilized yeast before and after adding CO₂-laser pretreated corn stover (LPCS) substrates were investigated using bioethanol production. Response surface methodology (RSM), based on the Box–Behnken design (BBD) for experiments, was used to optimize the doping condition. An optimum experimental condition was obtained at pH 4.5, 2.08% yeast concentration, and 0.20% LPCS substrates. Under this condition, doping LPCS increased the yield of bioethanol from 53% to 84%, which matched the predicted value. After doping LPCS, the results of inverted microscope (IM) and atomic force microscopy (AFM) illustrated that the immobilized gel beads changed from rod-like in shape with a smooth surface to a larger rod-like ultrastructure with a rougher surface. The yield was relatively stable within 28 d, with a downward trend subsequently appearing.     

Ash reduction strategies in corn stover facilitated by anatomical and size fractionation

There is growing interest internationally to produce fuels from renewable biomass resources. Inorganic components of biomass feedstocks, referred to collectively as ash, damage equipment and decrease yields in thermal conversion processes, and decrease feedstock value for biochemical conversion processes. Decreasing the ash content of feedstocks improves conversion efficiency and lowers process costs. Because physiological ash is unevenly distributed in the plant, mechanical processes can be used to separate fractions of the plant based on ash content. This study focuses on the ash separation that can be achieved by separating corn stover by particle size and anatomical fraction. Baled corn stover was hand-separated into anatomical fractions, ground to <19.1 mm, and size separated using six sieves ranging from 9.5 to 0.150 mm. Size fractions were analyzed for total ash content and ash composition. Particle size distributions observed for the anatomical fractions varied considerably. Cob particles were primarily 2.0 mm or greater, while most of the sheath and husk particles were 2.0 mm and smaller. Particles of leaves greater than 0.6 mm contained the greatest amount of total ash, ranging from approximately 8 to 13% dry weight of the total original material, while the fractions with particles smaller than 0.6 mm contained less than 2% of the total ash of the original material. Based on the overall ash content and the elemental ash, specific anatomical and size fractions can be separated to optimize the feedstocks being delivered to biofuels conversion processes and minimize the need for more expensive ash reduction treatments.     

Anaerobic digestion of corn silage on a commercial scale: Differential utilization of its chemical constituents and characterization of the solid digestate

The utilization of different chemical constituents of corn silage during industrial-scale anaerobic digestion was determined. Corn silage together with the resulting solid digestate generated during biogas production were collected from an industrial plant during a regular operating period. Moisture, water and ethanol extractives, ash, total nitrogen, starch, cellulose, the monomeric composition of hemicellulose, acid soluble and acid insoluble lignin were measured in both corn silage and corn silage solid digestate. The relative consumption of each component of corn silage during its anaerobic digestion was estimated with reference to acid insoluble lignin. It was assumed that lignin was not digested throughout the process. Starch and large fractions of extractives and acid soluble lignin were digested. In contrast, the digestion of cellulose and particularly hemicellulose were limited (40% and 29% respectively). Of the hemicellulose monomers, xylose was the least digested (20%). The present work shows that the digestate produced by commercial corn-silage anaerobic digestion contains a notable quantity of cell wall polymers. These could potentially be used in biorefinery processes, e.g. ethanol and xylo-oligosaccharide production.     

Corn stover ethanol yield as affected by grain yield,Bt trait,and environment

Literature values for glucose release from corn stover are highly variable which would likely result in tremendous variability in bio-refinery ethanol yield from corn stover feedstock. A relatively recent change in United States corn genetics is the inclusion of the Bacillus thuringiensis (Bt) trait, which now accounts for three-fourths of all US planted corn acreage. The objective of this study was to evaluate the effect of corn grain yield, inclusion of the Bt trait, and location environment on corn stover quality for subsequent ethanol conversion. Two hybrid pairs (each having a Bt and non-Bt near-isoline) were analyzed giving a total of 4 hybrids. In 2010 and 2011, field plots were located in Michigan at four latitudinal differing locations in four replicated plots at each location. Stover composition and enzymatic digestibility was analyzed and estimated ethanol yield (g g⁻¹) was calculated based on hydrolyzable glucan and xylan levels. Analysis showed that there were no significant differences in total glucose or xylose levels nor in enzymatically hydrolyzable glucan and xylan concentrations between Bt corn stover and the non-Bt stover isolines. Regression analyses between corn grain yield (Mg ha⁻¹) and corn stover ethanol yield (g g⁻¹) showed an inverse relationship indicative of a photosynthate source-sink relationship. Nevertheless, the quantity of stover produced was found to be more critical than the quality of stover produced in maximizing potential stover ethanol yield on a land area basis.     

Second-generation bioethanol of hydrothermally pretreated stover biomass from maize genotypes

Twelve maize genotypes, were agronomically evaluated and their stover hydrothermally pretreated in a temperature range of 210–225 °C to assess the effects of genotype and pretreatment severity on stover recalcitrance toward bioethanol conversion. Maize genotypes exhibited significant variation for biomass yield and all agronomic evaluated, while among all cell wall constituents measured in the unpretreated stover, only ash content showed differences among genotypes. The pretreatment severities assayed impacted most stover compositional traits, and the glucose recovered after enzymatic hydrolysis displayed a similar profile among genotypes with similar genetic background. Harsher pretreatment conditions maximized the potential cellulosic bioethanol production (208–239 L/t), while the mildest maximized the bioethanol from the hemicellulosic hydrolysates (137–175 L/t). Consequently, when both pentose and hexose sugars were considered, the total potential bioethanol produced at the lowest and highest pretreatment temperatures was similar in all genotypes (292–358 L/t), indicating that the lowest temperature (210 °C) was the optimal among all assayed. Importantly, the ranking of genotypes for bioethanol yield (L/ha) closely resembled the ranking for stover yield (t/ha), indicating that breeding for biomass yield would increase the bioethanol production per hectare regardless of the manufacturing process. Similarly, the genetic regulation of corn stover moisture is possible and relevant for efficient energy production as biomass moisture has a potential impact on stover transportation, storage and processing requirements. Overall, these results indicate that local landrace populations are important genetic resources to improve cultivated crops, and that simultaneous breeding for production of grain and stover bioethanol is possible in corn.     

Sunflower as a biofuels crop: An analysis of lignocellulosic chemical properties

Four accessions of cultivated sunflower (Helianthus annuus) and silverleaf sunflower (Helianthus argophyllus), were each grown in three locations (Georgia, British Columbia, and Iowa) at different planting densities and phenotyped for biomass-related traits and wood biochemistry. In most environments, H. argophyllus produced significantly more biomass than H. annuus. Cell wall chemistry for a subset of plants grown in Georgia and Iowa was assessed using analytical wet chemistry methods to measure lignin and sugar content/composition. The analysis of lignin and the S/G-lignin ratios for a larger number of samples (n > 250) was also assessed by high-throughput pyrolysis Molecular Beam Mass Spectrometry. Average pyMBMS estimated lignin content (i.e., dry weight fraction) for 60 °C dried basal stem samples of H. annuus and H. argophyllus was 29.6% (range, 24.0%–34.6%) and 28.6% (range, 24.6%–33.3%), respectively when averaged across all environments. The average S/G lignin mass ratio was 1.5 (range, 1.0–2.0) for H. annuus and 1.7 (range, 1.0–2.4) in H. argophyllus. Stem samples from these two species only differed statistically for a few cell wall chemistry traits; however, accession level differences within each species were apparent. Cell wall chemistry in both species was significantly affected by both location and planting density, thus demonstrating the need to select for these traits in the environment for which the crop will be produced. Overall, these results show that cultivated sunflower and silverleaf sunflower both possess the necessary phenotypic diversity to facilitate the development of a hybrid sunflower with improved lignocellulosic biofuels traits, namely increased biomass, decreased lignin, and increased glucan.     

The improved CO2 capture system with heat recovery based on absorption heat transformer and flash evaporator

Absorption heat transformer (AHT) and flash evaporator (FE) are used to reduce the heat consumption of CO₂ capture processes and an AHT–FE-aided capture system is proposed. Analyses are carried out to verify the effectiveness in reducing heat consumption. Compared with the base CO₂ capture system of 3000 t/d CO₂ capture capacity from a 660 MW coal-fired power unit, the AHT–FE-aided capture system reduces the heat consumption from 3.873 GJ/tCO₂ to 3.772 GJ/tCO₂, and the corresponding energy saving is 2.62%. The economic analysis shows that the annual profit would be 2.94 million RMB Yuan. The payback period of the AHT–FE-aided capture system is approximately 2.4 years. Therefore, the AHT–FE-aided capture system is both economically and technically feasible for improving the CO₂ capture energy performance.     

Structural and chemical analysis of process residue from biochemical conversion of wheat straw (Triticum aestivum L.) to ethanol

Biochemical conversion of lignocellulose to fermentable carbohydrates for ethanol production is now being implemented in large-scale industrial production. Applying hydrothermal pretreatment and enzymatic hydrolysis for the conversion process, a residue containing substantial amounts of lignin will be generated. So far little is known about the composition of this lignin residue which at present is mainly incinerated for heat and power generation and not yet converted so much into more valuable products.In this study, the structural and chemical composition of the solid and liquid fractions of lignin residue from wheat straw were analysed and processing factors discussed. Roughly 70 and 15% of the solid mass fraction consisted of lignin and ash, respectively. Residual carbohydrates mostly originated from hemicellulose in the liquid fraction and from cellulose in the solid fraction. The solid fraction also contained significant amounts of protein, which is a valuable by-product when used as animal feed or when enzymes and yeast cells are separated for process recycling. Silica was the dominant constituent in the mineral fraction and except for few fragments of lignified middle lamellae most particles in the solid fraction appeared as silica coated by lignin, hampering separation of the two components before incineration or refinement of the residue.     

The 2013 reforms of the Flemish renewable electricity support: Missed opportunities

The Flemish renewable electricity support system has struggled to address a number of problematic issues in the past. These included excessive profit margins and general malfunctioning of the green certificate market, as well as a lack of qualification of various existing renewable energy technologies. The Flemish government responded to these issues by introducing major reforms in 2013, including “banding” to differentiate the support for various technologies. However, reliable methods for differentiating renewable electricity technologies and calculating support levels have not been sufficiently developed. The main objective of the 2013 reforms was to reduce support costs, but application of German feed-in tariffs on 18 reference technologies has shown that most projects in Flanders continue to receive high levels of support. The 2013 reforms did not succeed in addressing malfunctioning of the green certificate market. On the contrary, the confidence of investors in renewable electricity plants has decreased as the terms of support can be altered retroactively by adjusting remuneration levels and through political interventions. Future adaptations are likely to be made which will further decrease the overall stability and effectiveness of the system.     

Experimental study on the role of ethanol on performance emission trade-off and tribological characteristics of a CI engine

An experimental study of engine combustion, performance and emission characteristics using diesel–ethanol blends along with investigation of tribological effects of ethanol on engine oil was done in present work using 1-butanol as emulsifier. Thorough observations of diesel–ethanol miscibility resulted that 25% v/v ethanol is miscible with diesel using only 3% v/v emulsifier. Tribological effects of ethanol on engine oil were investigated by analyzing the engine oil samples through FT-IR (Fourier Transform Infrared Spectroscopy). Overall experimentation re-evaluated the potential of ethanol in reduction of NO_x, Soot and in-cylinder temperature with slight penalty for HC, CO and BSEC prominently at low load. All fuels produced more NO but lesser NO₂ at higher load satisfying Zeldovich mechanism. A comparative trade-off analysis was done in between NHC, Soot and BSEC to reflect the performance and emission characteristics at a time. Trade-off study revealed D78E20B02 (78% diesel 20% ethanol 2% butanol) as optimal blend among all fuels used in present work. FT-IR analysis depicted negligible variation in the compounds in engine oil samples for the specified operational period. Statistical analysis showed larger Coefficient of variation for D78E20B02 blend due to higher absorbance of a particular compound.     

Experimental study of the functionality of a semisubmersible wind turbine combined with flap-type Wave Energy Converters

In the present paper the functionality of the Semisubmersible wind energy and Flap-type wave energy Converter (SFC) is examined experimentally. In order to study the functionality of the SFC, the focus is on operational environmental conditions. SFC is a combined concept that utilizes offshore wind energy and ocean wave energy for power production. Details are presented as far as the physical modelling of the wind turbine with the use of a redesigned small-scale rotor and of the Power Take-Off mechanism of the Wave Energy Converters (WECs) with the use of a configuration that is based on a mechanical rotary damper. Tests with quasi-static excitation, motion decay, regular and irregular waves without and with wind that is uniform are conducted on an 1:50 scale physical model. The experimental data are compared with numerical predictions obtained by a fully coupled numerical model using Simo/Riflex tool. A good agreement is observed between experimental and numerical predictions. The combined operation of WECs doesn't affect the tension of mooring lines nor the acceleration of nacelle and the bending moment in tower's base. The produced power of the WECs of the SFC and consequently the functionality of the SFC is estimated.     

Enhanced substrate degradation and methane yield with maleic acid pre-treatments in biomass crops and residues

Organic acids are envisaged as alternative catalysts to strong mineral acids, in pre-treatment of ligno-cellulosic biomass for anaerobic digestion (AD). To evaluate this hypothesis, an untreated control and four pre-treatments (25 °C for 24 h) involving two levels of maleic acid (34.8 and 69.6 kg m⁻³), alone and combined with sulphuric acid (4 kg m⁻³), were studied in three agricultural substrates: Arundo (aka giant reed), Barley straw and B133 fibre sorghum. Methane production was assessed in a batch AD assay (35 °C for 51 days) with 4 g L⁻¹ of volatile solid (VS) load. Fibre composition and structure were investigated through chemical analysis and Fourier transform infrared (FTIR) spectrometry. Arundo and B133 that were the most and least recalcitrant substrate, respectively, staged the highest and lowest increase in methane with high maleic acid: +62% over 218 cm³ g⁻¹ of VS in untreated Arundo; +36% over 284 cm³ g⁻¹ of VS in untreated B133. Barley straw showed an intermediate behaviour (+41% over 269 cm³ g⁻¹ of VS). H₂SO₄ addition to maleic acid did not improve CH₄ output. The large increase in methane yield determined by pre-treatments was reflected in the concurrent decrease of fibre (between 14 and 39% depending on fibrous component). Based on FTIR spectra, bands assigned to hemicellulose and cellulose displayed lower absorbance after pre-treatment, supporting the hypothesis of solubilisation of structural carbohydrates and change in fibre structure. Hence, maleic acid was shown a suitable catalyst to improve biodegradability of ligno-cellulosic biomass, especially in recalcitrant substrates as Arundo.     

Breakeven price of biomass from switchgrass,big bluestem,and Indiangrass in a dual-purpose production system in Tennessee

The objective was to determine the breakeven price for switchgrass (SG) (Panicum virgatum L.), a mix of big bluestem (Andropogon gerardii Vitman) and Indiangrass (BBIG) (Sorghastrum nutans L. Nash), and a combination of SG and BBIG (SG/BBIG) produced under three harvest treatments. Two-harvest treatments included a forage harvest at early boot (EB) and at early seedhead (ESH) plus a biomass harvest at fall dormancy (FD). The third harvest treatment was a single biomass harvest at FD. Mixed models were used to determine if there were differences in yield, crude protein, and nutrient removal for each of the native warm-season grass (NWSG) treatments at each harvest. The EB plus FD harvest system would be preferred over the ESH plus FD harvest system for all NWSG treatments. BBIG was the only NWSG treatment with a breakeven price for biomass that decreased with an EB harvest. For all three NWSG treatments, a producer would be better off harvesting once a year for biomass than twice for forage and biomass. The cost of harvesting and replacing the nutrients for the forage harvest was greater than the revenue received from selling the forage.     

Biopower from direct firing of crop and forestry residues in China: A review of developments and investment outlook

This paper reviews developments in the direct-fired biomass power sector and provides an up to date investment outlook by calculating the Net Present Value of new investments, and the appropriate level of Feed-in-Tariff needed to stimulate future investment. An overview is provided of support policies, historical growth in installations, and main market players. A number of data sources is combined to build a database with detailed information of individual biopower projects. This data is used to describe technological and market trends, which are used in a cash flow model to calculate the NPV of a typical project. The NPV for new projects is estimated to be negative, and investment should be expected to stall without proper policy intervention. Increasing fuel prices, local competition over biomass fuel resources, lower than expected operational performance and a downturn in carbon markets have deteriorated the investment outlook. In order to ensure reasonable profitability, the Feed-In-Tariff should be increased, from the current level of 90.9 € MWh⁻¹, to between 97 and 105 € MWh⁻¹. Where possible, government organizations should help organize demand for the supply of heat. Local rural energy bureaus may help organize supply networks for biomass fuels throughout the country, in order to reduce seasonal and local fuel scarcity and price fluctuations.     

Ethanologens vs. acetogens: Environmental impacts of two ethanol fermentation pathways

Bioconversion production of ethanol from cellulosic feedstock is generally proposed to use direct fermentation of sugars to ethanol. Another potential route for ethanol production is fermentation of sugars to acetic acid followed by hydrogenation to convert the acetic acid into ethanol. The advantage of the acetogen pathway is an increased ethanol yield; however, using an acetogen requires the additional hydrogenation, which could substantially affect the life cycle global warming potential of the process. Assuming a poplar feedstock, a cradle to grave Life cycle assessment (LCA) is used to evaluate the environmental impacts of an acetogen based fermentation pathway. An LCA of a fermentation pathway that uses ethanologen fermentation is developed for comparison. It is found that the ethanologen and acetogen pathways have Global Warming Potentials (GWP) that are 92% and 46% lower than the GWP of gasoline, respectively. When the absolute GWP reduction compared to gasoline is calculated using a unit of land basis, the benefit of the higher ethanol yield using the acetogen is observed as the two pathways achieve similar GWP savings. The higher ethanol yield in the acetogen process plays a crucial role in choosing a lignocellulosic ethanol production method if land is a limited resource.     

Biosynthesis of β-caryophyllene,a novel terpene-based high-density biofuel precursor,using engineered Escherichia coli

β-caryophyllene is a common sesquiterpene compound currently being studied as a promising precursor for the production of high-density fuels. Acute demand for high-density fuels has provided the impetus to pursue biosynthetic methods to produce β-caryophyllene from reproducible sources. In this study, we produced β-caryophyllene by assembling a biosynthetic pathway in an engineered Escherichia coli strain of which phosphoglucose isomerase gene has been deleted. The 1- deoxy-d-xylulose 5-phosphate (DXP) or heterologous mevalonate (MVA) pathways were employed. Meanwhile, geranyl diphosphate synthase, glucose-6-phosphate dehydrogenase and β-caryophyllene synthase genes were co-overexpressed in the above strain. The final genetically modified strain, YJM59, produced 220 ± 6 mg/L of β-caryophyllene in flask culture. We also evaluated the use of fed-batch fermentation for the production of β-caryophyllene. After induction for 60 h, the YJM59 strain produced β-caryophyllene at a concentration of 1520 mg/L. The volumetric production fermented in the aerobic fed-batch was 0.34 mg/(L·h·OD₆₀₀) and the conversion efficiency of glucose to β-caryophyllene (gram to gram) was 1.69%. Our results are the first successful attempt to produce β-caryophyllene using E. coli BL21(DE3), and provide a new strategy that is green and sustainable for the production of β-caryophyllene.     

Anaerobic digestion of maize and cellulose under thermophilic and mesophilic conditions – A comparative study

The aim of this study was to advance in understanding of digestion process of energy crops. Cellulose and maize silage were fermented in batch mode at mesophilic (38 °C) and thermophilic (55 °C) conditions and corresponding organic loads of 5.5 ± 0.2 kgVS/m³, 11.2 ± 0.3 kgVS/m³ and 16.7 ± 0.4 kgVS/m³.For both substrates more stable and faster digestion took place at 38 °C. Due to complex structure maize degradation was characterized by varying digestion rate and longer total digestion time resulting form breakdown of hard-degradable fractions. The digestion retard at increased OLRs of cellulose and lower degradation level obtained for all cellulose series confirm a higher overloading potential for systems dealing with single-component-substrates but also the enhanced sensitivity of such systems to any inconvenient digestion conditions.Based on observed patterns of volatile fatty acids and oxidation-reduction potential, different fermentation mechanisms can be concluded for cellulose and maize, but also for different temperature modes. Conversion of maize at highly reductive conditions with increased concentrations of butyric acid was accompanied by much higher activity of hydrogenotrophic methanogens than for cellulose digestion.Two factors showed a strong potential to influence test results: an insufficient VS content of inoculum, which caused reduced biogas yields, and a high natural biodiversity of maize silage, resulting in higher biogas yields than calculated based on the maize composition.     

Climate change impacts of power generation from residual biomass

The European Union relies largely on bioenergy to achieve its climate and energy targets for 2020 and beyond.We assess, using Attributional Life Cycle Assessment (A-LCA), the climate change mitigation potential of three bioenergy power plants fuelled by residual biomass compared to a fossil system based on the European power generation mix. We study forest residues, cereal straws and cattle slurry.Our A-LCA methodology includes: i) supply chains and biogenic-CO₂ flows; ii) explicit treatment of time of emissions; iii) instantaneous and time-integrated climate metrics.Power generation from cereal straws and cattle slurry can provide significant global warming mitigation by 2100 compared to current European electricity mix in all of the conditions considered.The mitigation potential of forest residues depends on the decay rate considered. Power generation from forest logging residues is an effective mitigation solution compared to the current EU mix only in conditions of decay rates above 5.2% a⁻¹. Even with faster-decomposing feedstocks, bioenergy temporarily causes a STR(i) and STR(c) higher than the fossil system.The mitigation potential of bioenergy technologies is overestimated when biogenic-CO₂ flows are excluded. Results based solely on supply-chain emissions can only be interpreted as an estimation of the long-term (>100 years) mitigation potential of bioenergy systems interrupted at the end of the lifetime of the plant and whose carbon stock is allowed to accumulate back.Strategies for bioenergy deployment should take into account possible increases in global warming rate and possible temporary increases in temperature anomaly as well as of cumulative radiative forcing.