Improved bio-energy yields via sequential ethanol fermentation and biogas digestion of steam exploded oat straw

Using standard laboratory equipment, thermochemically pretreated oat straw was enzymatically saccharified and fermented to ethanol, and after removal of ethanol the remaining material was subjected to biogas digestion. A detailed mass balance calculation shows that, for steam explosion pretreatment, this combined ethanol fermentation and biogas digestion converts 85-87% of the higher heating value (HHV) of holocellulose (cellulose and hemicellulose) in the oat straw into biofuel energy. The energy (HHV) yield of the produced ethanol and methane was 9.5-9.8 MJ/(kg dry oat straw), which is 28-34% higher than direct biogas digestion that yielded 7.3-7.4 MJ/(kg dry oat straw). The rate of biogas formation from the fermentation residues was also higher than from the corresponding pretreated but unfermented oat straw, indicating that the biogas digestion could be terminated after only 24 days. This suggests that the ethanol process acts as an additional pretreatment for the biogas process.     

Comparative study of the effect of ultrasonication on the anaerobic biodegradability of food waste in single and two-stage systems

Five different mesophilic systems were evaluated in this study for the anaerobic treatment of food waste. Systems A and B were one stage methane with unsonicated and sonicated feeds, respectively, while, systems C and D were two-stage hydrogen and methane with unsonicated and sonicated feeds, respectively. System E comprised a novel sonicated biological hydrogen reactor (SBHR) followed by methane reactor. The results showed that sonication inside the reactor in the first stage (system E) showed superior results compared to all other systems. Overall VSS removal efficiencies of 67%, 59%, 51%, 44%, and 36% were achieved in systems E, D, C, B, and A, respectively. Volumetric hydrogen production rates of 4.8, 3.3, and 2.6 L H₂/L_reactor d were achieved in the SBHR, CSTR with and without sonicated feed, respectively, while, methane production rates of 1.6, 2.1, 2.3, 2.6, and 3.2 L CH₄/L_reactor d were achieved in systems A-E, respectively.     

Optimization of microwave-assisted FeCl3 pretreatment conditions of rice straw and utilization of Trichoderma viride and Bacillus pumilus for production of reducing sugars

In this study, Box-Behnken design (BBD) and response surface methodology (RSM) were used to optimize microwave-assisted FeCl₃ pretreatment conditions of rice straw with respect to FeCl₃ concentration, microwave intensity, irradiation time and substrate concentration. When rice straw was pretreated at the optimal conditions of FeCl₃ concentration, 0.14 mol/L; microwave intensity, 160 °C; irradiation time, 19 min; substrate concentration, 109 g/L; and inoculated with Trichoderma viride and Bacillus pumilus, the production of reducing sugars was 6.62 g/L. This yield was 2.9 times higher than that obtained with untreated rice straw. The microorganisms degraded 37.8% of pretreated rice straw after 72 h. The structural characteristic analyses suggest that microwave-assisted FeCl₃ pretreatment damaged the silicified waxy surface of rice straw, disrupted almost all the ether linkages between lignin and carbohydrates, and removed lignin.     

Optimization of thermal-dilute sulfuric acid pretreatment for enhancement of methane production from cassava residues

In this study, the pretreatment of cassava residues by thermal-dilute sulfuric acid (TDSA) hydrolysis was investigated by means of a statistically designed set of experiments. A three-factor central composite design (CCD) was employed to identify the optimum pretreatment condition of cassava residues for methane production. The individual and interactive effects of temperature, H₂SO₄ concentration and reaction time on increase of methane yield (IMY) were evaluated by applying response surface methodology (RSM). After optimization, the resulting optimum pretreatment condition was 157.84 °C, utilizing 2.99% (w/w TS) H₂SO₄ for 20.15 min, where the maximum methane yield (248 mL/g VS) was 56.96% higher than the control (158 mL/g VS), which was very close to the predict value 56.53%. These results indicate the model obtained through RSM analysis is suit to predict the optimum pretreatment condition and there is great potential of using TDSA pretreatment of cassava residues to enhance methane yield.     

Selective production of hemicellulose-derived carbohydrates from wheat straw using dilute HCl or FeCl3 solutions under mild conditions. X-ray and thermo-gravimetric analysis of the solid residues

The present work explores the combined production of hemicellulose-derived carbohydrates and an upgraded solid residue from wheat straw using a dilute-acid pretreatment at mild temperature. Dilute aqueous HCl solutions were studied at temperatures of 100 and 120 °C, and they were compared to dilute FeCl₃ under the same conditions. Comparable yields of soluble sugars and acetic acid were obtained, affording an almost complete removal of pentoses when using 200 mM aqueous solutions at 120 °C. The solid residues of pretreatment were characterized showing a preserved crystallinity of the cellulose, and a almost complete removal of ash forming matter other than Si. Results showed upgraded characteristic of the residues for thermal conversion applications compared to the untreated wheat straw.     

Liquid hot water and alkaline pretreatment of soybean straw for improving cellulose digestibility

Soybean straw was pretreated with either liquid hot water (LHW) (170-210 °C for 3-10 min) or alkaline soaking (4-40 g NaOH/100 g dry straw) at room temperature to evaluate the effects on cellulose digestibility. Nearly 100% cellulose was recovered in pretreated solids for both pretreatment methods. For LHW pretreatment, xylan dissolution from the raw material increased with pretreatment temperature and time. Cellulose digestibility was correlated with xylan dissolution. A maximal glucose yield of 70.76%, corresponding to 80% xylan removal, was obtained with soybean straw pretreated at 210 °C for 10 min. NaOH soaking at ambient conditions removed xylan up to 46.37% and the subsequent glucose yield of pretreated solids reached up to 64.55%. Our results indicated LHW pretreatment was more effective than NaOH soaking for improving cellulose digestibility of soybean straw.     

Microwave, ultrasonic and chemo-mechanical pretreatments for enhancing methane potential of pulp mill wastewater treatment sludge

Microwave (2450 MHz, 1250 W), ultrasonic (20 kHz, 400 W) and chemo-mechanical (MicroSludge® with 900 mg/L NaOH followed by 83,000 kPa) pretreatments were applied to pulp mill waste sludge to enhance methane production and reduce digester sludge retention time. The effects of four variables (microwave temperature in a range of 50-175 °C) and sonication time (15-90 min), sludge type (primary or secondary) and digester temperature (mesophilic and thermophilic) were investigated. Microwave pretreatment proved to be the most effective, increasing specific methane yields of WAS samples by 90% compared to controls after 21 days of mesophilic digestion. Sonication solubilized the sludge samples better, but resulted in soluble non-biodegradable compounds. Based on the laboratory scale data, MicroSludge® was found the least energy intensive pretreatment followed by sonication for 15 min alternative with net energy profits of 1366 and 386 kWh/tonne of total solids (TS), respectively. Pretreatment benefits were smaller for thermophilic digesters.     

Effects of NaOH treatment on condensed tannin contents and gas production kinetics of tree leaves

Effects of NaOH treatment on the crude protein (CP), condensed tannin (CT) and in vitro gas production kinetics of leaves of Arbutus andrachne, Glycyrrhiza glabra L. and wheat straw were determined. Wheat straw, which is tannin-free, was used as the standard. The NaOH treatment was completed by pulverization of samples with 0, 20, 40, 60 and 80 g/L of NaOH solution in the proportion of 1 L of solution to 1 kg of sample. Gas production was determined at 3, 6, 12, 24, 48, 72 and 96 h of incubation. NaOH treatment linearly decreased (P<0.001) the CT contents of leaves of Arbutus andrachne and Glycyrrhiza glabra L. whereas NaOH treatment had no effect on the CP contents of Arbutus andrachne, Glycyrrhiza glabra L. and wheat straw. The 80 g/L NaOH treatment reduced the CT content of leaves of Arbutus andrachne and Glycyrrhiza glabra L. by 59.6% and 86.7%, respectively. NaOH treatment linearly decreased (P<0.01) gas production rate of Arbutus andrachne although it linearly increased (P<0.01) gas production rate of wheat straw. In contrast, NaOH treatment had no effect on gas production rate of leaves of Glycyrrhiza glabra L. NaOH treatment linearly decreased (P<0.001) potential gas production of leaves of Arbutus andrachne and Glycyrrhiza glabra L. whereas NaOH treatment linearly increased (P<0.001) potential gas production of wheat straw. Treatment with NaOH can be used to improve the nutritive value of tannin-free forages such as straw, but not for tannin-containing leaves.     

Supercritical carbon dioxide pretreatment of corn stover and switchgrass for lignocellulosic ethanol production

Supercritical CO₂ (SC-CO₂), a green solvent suitable for a mobile lignocellulosic biomass processor, was used to pretreat corn stover and switchgrass at various temperatures and pressures. The CO₂ pressure was released as quickly as possible by opening a quick release valve during the pretreatment. The biomass was hydrolyzed after pretreatment using cellulase combined with β-glucosidase. The hydrolysate was analyzed for the amount of glucose released. Glucose yields from corn stover samples pretreated with SC-CO₂ were higher than the untreated sample’s 12% glucose yield (12 g/100 g dry biomass) and the highest glucose yield of 30% was achieved with SC-CO₂ pretreatment at 3500 psi and 150 °C for 60 min. The pretreatment method showed very limited improvement (14% vs. 12%) in glucose yield for switchgrass. X-ray diffraction results indicated no change in crystallinity of the SC-CO₂ treated corn stover when compared to the untreated, while SEM images showed an increase in surface area.     

Treatment of rice straw with selected Cyathus stercoreus strains to improve enzymatic saccharification

Seventeen Cyathus stercoreus isolates were tested for their ability to treat rice straw for improved enzymatic saccharification. These isolates showed a negative correlation between cellulase and xylanase activity and enzymatic saccharification yields. Incubation of rice straw pretreated at 60 °C for 15 min with strain C. stercoreus TY-2 for 25 days resulted in an enzymatic saccharification yield of 57% as compared to a yield of 11% for the same straw in the absence of the fungus. These findings highlight the potential of this isolate for biological pretreatment of rice straw under conditions of low energy input.     

Optimization of H2SO4-catalyzed hydrothermal pretreatment of rapeseed straw for bioconversion to ethanol: Focusing on pretreatment at high solids content

A central composite design of response surface method was used to optimize H₂SO₄-catalyzed hydrothermal pretreatment of rapeseed straw, in respect to acid concentration (0.5–2%), treatment time (5–20 min) and solid content (10–20%) at 180 °C. Enzymatic hydrolysis and fermentation were also measured to evaluate the optimal pretreatment conditions for maximizing ethanol production. The results showed that acid concentration and treatment time were more significant than solid content for optimization of xylose release and cellulose recovery. Pretreatment with 1% sulfuric acid and 20% solid content for 10 min at 180 °C was found to be the most optimal condition for pretreatment of rapeseed straw for ethanol production. After pretreatment at the optimal condition and enzymatic hydrolysis, 75.12% total xylan and 63.17% total glucan were converted to xylose and glucose, respectively. Finally, 66.79% of theoretical ethanol yielded after fermentation.     

Efficiency of pretreatments for optimal enzymatic saccharification of soybean fiber

The effectiveness of several pretreatments [high-power ultrasound, sulfuric acid (H₂SO₄), sodium hydroxide (NaOH), and ammonium hydroxide (NH₃OH)] to enhance glucose production from insoluble fractions recovered from enzyme-assisted aqueous extraction processing of extruded full-fat soybean flakes (FFSF) was investigated. Sonication of the insoluble fraction at 144 μm_{pp (peak-to-peak)} for 30 and 60 s did not improve the saccharification yield. The solid fractions recovered after pretreatment with H₂SO₄ [1% (w/w), 90 °C, 1.5 h], NaOH [15% (w/w), 65 °C, 17 h], and NH₃OH [15% (w/w), 65 °C, 17 h] showed significant lignin degradation, i.e., 81.9%, 71.2%, and 75.4%, respectively, when compared to the control (7.4%). NH₃OH pretreatment resulted in the highest saccharification yield (63%) after 48 h of enzymatic saccharification. A treatment combining the extraction and saccharification steps and applied directly to the extruded FFSF, where oil extraction yield and saccharification yield reached 98% and 43%, respectively, was identified.     

Microwave-assisted pretreatment of woody biomass with ammonium molybdate activated by H2O2

Pretreatments for enzymatic saccharification are crucial for the establishment of lignocellulosic biorefineries. In this study, we focused on ammonium ions and peroxometal complexes as potential delignifying agents. We first examined the pretreatment of beech wood with nine different ammonium salts in the presence of H₂O₂. Significant pretreatment effects were found only for ammonium molybdate, which is transformed to a peroxometal complex on reacting with H₂O₂. Since microwave sensitizer effects are expected for (peroxo)molybdate, beech wood was pretreated using external heating and microwave irradiation. As a result, a maximum sugar yield of 59.5% was obtained by microwave irradiation at 140 °C for 30 min, while external heating in an autoclave gave a sugar yield of 41.8%. We also found that an ammonium ion is the key counterion accelerating the pretreatment with molybdate. These results highlight the powerful selective delignifying capability of the H₂O₂-activated ammonium molybdate system energised by microwave radiation.     

Production of furans from rice straw by single-phase and biphasic systems

5-Hydroxymethylfurfural (HMF) and furfural, both of which can be derived from renewable sources, are key components for the production of different chemicals and fuels. In this study, rice straw, a cheap, abundant, and mainly unused agricultural waste, is converted to furans by a dilute acid hydrolysis process. The highest yield of HMF in a single-phase hydrolysis was 15.3 g/kg straw, attained at 180 °C during 3 h with 0.5% sulfuric acid, while the maximum yield of furfural, 59 g/kg straw, was obtained at 150 °C during 5 h. Different extracting solvents, including 2-PrOH, 1-BuOH, methyl isobutyl ketone (MIBK), and acetone at 180 °C for 3 h as well as tetrahydrofuran (THF) at 150 °C for 5 h were examined in biphasic systems. Use of the solvents generally improved the production of HMF compared to the single aqueous phase process. The best results of HMF production, more than 59 g/kg straw, were obtained in the systems containing either 2-PrOH or 1-BuOH. Using THF as an extracting solvent, a relatively high furfural yield, 118.2 g/kg straw, was obtained, and 96% of furfural produced in this system was extracted into THF during the process.     

Microwave pretreatment of rape straw for bioethanol production: focus on energy efficiency

The energy efficiency of microwave-assisted dilute sulfuric acid pretreatment of rape straw for the production of ethanol was investigated. Different microwave energy inputs and solid loadings were tested to find economic pretreatment conditions. The lowest energy consumption was observed when solid loading and energy input were fixed at 50% (w/w) and 54 kJ (900 W for 1 min), respectively, and amounted to 5.5 and 10.9 kJ to produce 1 g of glucose after enzymatic hydrolysis and 1 g ethanol after fermentation, respectively. In general, 1 g ethanol can produce about 30 kJ of energy, and therefore, the energy input for the pretreatment was only 35% of the energy output. The approach developed in this study resulted in 92.9% higher energy savings for producing 1 g ethanol when compared with the results of microwave pretreatments previously reported.     

In vitro ruminal methanogenesis of a hay-rich substrate in response to different combination supplements of nitrocompounds; pyromellitic diimide and 2-bromoethanesulphonate

Sixteen combinations of 5 treatments at 4 levels were designed in a L₁₆(4⁵) orthogonal experimental design to evaluate associative effects of five methanogenesis inhibitors at four dose levels: nitroethane (NE, 0 mM, 5 mM, 10 mM and 15 mM), 2-nitroethanol (NEOH, 0 mM, 5 mM, 10 mM and 15 mM), 2-nitro-1-propanol (NPOH, 0 mM, 5 mM, 10 mM and 15 mM), pyromellitic diimide (PMDI, 0 mM, 0.02 mM, 0.05 mM and 0.07 mM) and 2-bromoethanesulphonate (BES, 0 mM, 0.01 mM, 0.03 mM and 0.05 mM) on in vitro ruminal methane production of the mixed substrate (Chinese wildrye hay:maize meal = 4:1) using a cumulative gas production technique. After 48 h incubation, in vitro dry matter disappearance (IVDMD), total gas production (GP₄₈, ml/g DM) and total volatile fatty acids (VFA) production in various combinations of these inhibitors were decreased by 10.6-56.0, 26.5-44.5 and 20.3-47.6%, respectively (P<0.05). The molar proportion of acetate in the inhibitor combination groups was decreased by 6.6-12.5% while those of propionate and butyrate were increased by 7.0-19.2 and 21.9-56.5% (P<0.01), respectively. Methane proportion (MP) in total gas production was reduced by 79.4-98.5% (P<0.01), and the highest inhibition occurred in the combination of 10 mM NE, 10 mM NPOH, 0.07 mM PMDI and 0.01 mM BES in cultures. The partial correlation coefficients between NE, NEOH, NPOH, PMDI or BES and CH₄ proportion were −0.465 (P<0.01), −0.417 (P<0.01), −0.355 (P<0.05), −0.408 (P<0.01) and −0.345 (P<0.05), respectively, indicating that NE was the most potent inhibitor, followed by NEOH and PMDI, and finally NPOH and BES. In general, VFA production in the inhibitor combinations was substantially shifted to produce much more butyrate and propionate and less acetate. The combination of 15 mM NE, 10 mM NEOH, 5 mM NPOH, 0.07 mM PMDI and 0.01 mM BES in cultures, leading to >95% methane inhibition, may be the optimal application of these inhibitors with less depression of total VFA production. Further feeding trials to validate these combinations is still required on rumen function, methane production, growth performance and milk production.     

Effect of temperature on gas composition and char structural features of pyrolyzed agricultural residues

The gases and chars produced during fast pyrolysis of maize stalk, rice straw, cotton straw and rice husk at temperatures ranging from 600 to 1000 °C were studied by Fourier transform infrared spectroscopy, non-dispersive infrared technique, thermal conductivity detection method, ultimate analysis, X-ray diffraction, helium density measurement and N₂ adsorption method. The gas yield increased by more than 80% from 600 to 1000 °C, while the char and liquid yield decreased. The content of CO₂, CO and CH₄ accounted for more than 86%. The CO and CH₄ content increased with temperature, while the CO₂ content decreased. The hydroxyl, aliphatic CH, carbonyl, olefinic CC and ether groups were lost above 800 °C. Carbon skeleton shrinkage increased by more than 23% when the temperature increased from 600 to 1000 °C. Maximum porosity appeared at 900 °C. This study revealed the relationships between gas composition/char properties and pyrolysis temperature under high heating rate conditions.     

Effect of physical pretreatment on dilute acid hydrolysis of water hyacinth (Eichhornia crassipes)

Effects of different physical pretreatments on water hyacinth for dilute acid hydrolysis process (121 ± 3 °C, 5% H₂SO₄, 60 min) were comparatively investigated. Untreated sample had produced 24.69 mg sugar/g dry matter. Steaming (121 ± 3 °C) and boiling (100 ± 3 °C) for 30 min had provided 35.9% and 52.4% higher sugar yield than untreated sample, respectively. The highest sugar yield (132.96 mg sugar/g dry matter) in ultrasonication was obtained at 20 min irradiation using 100% power. The highest sugar production (155.13 mg sugar/g dry matter) was obtained from pulverized samples. Hydrolysis time was reduced when using samples pretreated by drying, mechanical comminution and ultrasonication. In most methods, prolonging the pretreatment period was ineffective and led to sugar degradations. Morphology inspection and thermal analysis had provided evidences of structure disruption that led to higher sugar recovery in hydrolysis process.     

Enhanced enzymatic saccharification of kenaf powder after ultrasonic pretreatment in ionic liquids at room temperature

This study demonstrates for the first time that the enzymatic hydrolysis of cellulose is drastically enhanced following ultrasonic pretreatment of lignocellulosic material in ionic liquids (ILs) when compared to conventional thermal pretreatment. Five types of ILs, 1-buthyl-3-methylimidazolium chloride (BmimCl), 1-allyl-3-methylimidazolium chloride (AmimCl), 1-ethyl-3-methylimidazolium chloride (EmimCl), 1-ethyl-3-methylimidazolium diethyl phosphate (EmimDep), and 1-ethyl-3-methylimidazolium acetate (EmimOAc) were tested. Cellulose saccharification ratio was about 20% for kenaf powders pretreated in BmimCl, AmimCl, EmimCl, and EmimDep by conventional heating at 110 °C for 120 min. Conversely, 60-95% of cellulose was hydrolyzed to glucose, subsequent to ultrasonic pretreatment in the same ILs for 120 min at 25 °C. The cellulose saccharification ratio of kenaf powder in EmimOAc was 86% after only 15 min of the ultrasonic pretreatment at 25 °C, compared to only 47% in that case of thermal pretreatment in the IL.     

Determination of the water permeability (Lp) of mouse oocytes at −25 °C and its activation energy at subzero temperatures

Typically, subzero permeability measurements are experimentally difficult and infrequently reported. Here we report an approach we have applied to mouse oocytes. Interrupted cooling involves rapidly cooling oocytes (50 °C/min) to an intermediate temperature above the intracellular nucleation zone, holding them for up to 40 min while they dehydrate, and then rapidly cooling them to −70 °C or below. If the intermediate holding temperature and holding time are well chosen, high post thaw survival of the oocytes is possible because the freezable water is removed during the hold. The length of time required for the exit of the freezable water allows the water permeability at that temperature to be determined. These experiments used 1.5 M ethylene glycol in PBS and included a transient hold of 2 min for equilibration at −10 °C, just below the extracellar ice formation temperature. We obtain an Lp = 1.8 × 10⁻³ μm min⁻¹ atm⁻¹ at −25 °C based on a hold time of 30 min yielding 80% survival and the premise that most of the freezable water is removed during the 30 min hold. If we assume that the water permeability is a continuous function of temperature and that its Ea changes at 0 °C, we obtain a subzero Ea of 21 kcal/mol; higher than the suprazero value of 14 kcal/mol. A number of assumptions are required for these water loss calculations and the resulting value of Lp can vary by up to a factor of 2, depending on the choices make.