Evaluation of hydrogen production from corn cob with the mesophilic bacterium Clostridium hydrogeniproducens HR-1

Corn cob is a promising hydrogen fermentation substrate, not only because of its abundant and low cost, but also because of its high cellulose and hemicellulose content. However, little information is available on the use of corn cob as a feedstock for hydrogen production. In this study, corn cob was hydrolyzed by cellulase after acid steam-explosion, alkali soaking, or steam-explosion pretreatment. The liquid products of pretreatment and the enzymatic hydrolysates were then used as carbon sources for hydrogen production by Clostridium hydrogeniproducens HR-1. Pretreatment followed by enzymatic hydrolysis yielded 720, 670, and 530 mg reducing sugars/g corn cob, and the hydrogen yield from corn cob reached 119, 100, and 83 ml H₂/g corn cob, which is 55.9%, 46.7%, and 38.8% of the theoretical hydrogen yield from corn cob using C. hydrogeniproducens HR-1, respectively.     

Enhance photocatalytic hydrogen evolution by using alkaline pretreated corn stover as a sacrificial agent

In this study, alkali pretreated corn stover was added as a sacrificial agent to the suspension of Pt/TiO₂ to significantly enhanced photocatalytic hydrogen evolution. The changes in structural characteristics of corn stover before and after alkali treatment and photocatalytic reactions were studied. According to the results, the removal of lignin and hemicellulose, as well as the changes in surface morphology, structural components, and functional groups of alkali pretreated corn stover may affect the photocatalytic hydrogen production process. Next, the effects of NaOH concentration, pretreatment time and temperature on hydrogen production were also investigated. Among them, within the scope of the experimental conditions, the optimal hydrogen production is 25.84 μmol h⁻¹. Moreover, the enhancement of photocatalytic hydrogen production is also achieved by using the waste liquid of alkali pretreated. The output of this study may provide a reference for the reuse of alkali-treated biomass residues and waste liquor in some industries, and make more comprehensive, efficient and green use of native lignocellulosic biomass.     

Effects of algal hydrolyzate as reaction medium on enzymatic hydrolysis of lignocelluloses

Effects of an algal hydrolyzate on the enzymatic hydrolysis of lignocelluloses were examined using four bioenergy feedstocks (poplar, corn stover, switchgrass, and anaerobically digested manure fiber). Feedstocks were pretreated using dilute acid or alkali prior to hydrolysis. Hydrolysis reactions were conducted using the neutralized algal hydrolyzate, citrate buffer, or deioinized water as reaction media. Results demonstrated that algal hydrolyzate significantly improved the efficiency of enzymatic hydrolysis of lignin-rich or structurally recalcitrant biomass such as poplar and anaerobically digested manure fiber. This study showed that algal biomass can be used as not only a biofuel feedstock for direct diesel and ethanol production, but also a supplemental feedstock to enhance the performance of lignocellulosic biorefining.     

Acid hydrolysis of corn stover for biohydrogen production using Thermoanaerobacterium thermosaccharolyticum W16

Lignocellulosic biomass, if properly hydrolyzed, can be an ideal feedstock for fermentative hydrogen production. This work considered the pretreatment of corn stover (CS) using a dilute acid hydrolysis process and studied its fermentability for hydrogen production by the strain Thermoanaerobacterium thermosaccharolyticum W16. The effects of sulfuric acid concentration and reaction time in the hydrolysis stage of the process were determined based on a 2² central composite experimental design with respect to maximum hydrogen productivity. The optimal hydrolysis conditions to yield the maximum quantity of hydrogen by W16 were 1.69% sulfuric acid and 117 min reaction time. At these conditions, the hydrogen yield was shown to be 3305 ml H₂ L⁻¹ medium, which corresponds to 2.24 mol H₂ mol⁻¹ sugar. The present results indicate the potential of using T. thermosaccharolyticum W16 for high-yield conversion of CS hemicellulose into bio-H₂ integrated with acid hydrolysis.     

Feasible pretreatment of textile wastewater for dark fermentative hydrogen production

In this study, the yield of hydrogen production was investigated under different feedstock pretreatment conditions. The feedstock for dark fermentative hydrogen production was textile wastewater which was obtained from the de-sizing process in a textile factory, located in northern Taiwan. The wastewater was pretreated with activated carbon, cation exchange resin or was not pretreated before being fed into the batch bottles. Biohydrogen production was carried out in a batch reactor with the sludge of mixed-culture using the feedstock from the pretreated wastewater. The sludge was obtained from the Taichung municipal wastewater treatment plant. The yield of hydrogen production using the two pretreatment methods or non – treatment were compared.     

Hydrothermal pretreatment of switchgrass and corn stover for production of ethanol and carbon microspheres

Pretreatment of biomass is viewed as a critical step to make the cellulose accessible to enzymes and for an adequate yield of fermentable sugars in ethanol production. Recently, hydrothermal pretreatment methods have attracted a great deal of attention because it uses water which is a inherently present in green biomass, non-toxic, environmentally benign, and inexpensive medium. Hydrothermal pretreatment of switchgrass and corn stover was conducted in a flow through reactor to enhance and optimize the enzymatic digestibility. More than 80% of glucan digestibility was achieved by pretreatment at 190 °C. Addition of a small amount of K₂CO₃ (0.45-0.9 wt.%) can enhance the pretreatment and allow use of lower temperatures. Switchgrass pretreated at 190 °C only with water had higher internal surface area than that pretreated in the presence of K₂CO₃, but both the substrates showed similar glucan digestibility. In comparison to switchgrass, corn stover required milder pretreatment conditions. The liquid hydrolyzate generated during pretreatment was converted into carbon microspheres by hydrothermal carbonization, providing a value-added byproduct. The carbonization process was further examined by GC-MS analysis to understand the mechanism of microsphere formation.     

Utilization of excess corn kernels for hydrogen gas biofuel production

Corn kernels are good candidates for production of various value-added products such as gas biofuel, hydrogen due to the carbohydrate-rich composition. In this study, widely grown corn, field corn kernels were dissolved in subcritical water at different temperatures to determine optimal thermal hydrolysis condition. Organic-rich hydrolysate obtained from hydrolysis process was gasified by aqueous-phase reforming (APR) for hydrogen gas production.Since hydrolysis at 200 °C resulted in significantly more total organic carbon release than other temperatures and the lowest amount of insolubilized solid residue. Different concentrations of this hydrolysate (diluted with water at different ratios) were evaluated for high yielding hydrogen gas production. Gasification performance of corn kernels was also compared with lignocellulosic biomass using corn stover as a representative biomass material.The hydrolysate with 2486 mg/L TOC concentration showed the best performance for hydrogen gas production (130 mL H₂/g corn) and left less amount of ungasified solid residue. Corn kernels produced 2.3 times more hydrogen gas compared to corn stover biomass. Thus, corn kernels are promising feed materials for APR process, and excess production of corn can be utilized for hydrogen gas production in higher yield and richer composition.     

Improved hydrogen production via thermophilic fermentation of corn stover by microwave-assisted acid pretreatment

A microwave-assisted acid pretreatment (MAP) strategy has been developed to enhance hydrogen production via thermophilic fermentation of corn stover. Pretreatment of corn stover by combining microwave irradiation and acidification resulted in the increased release of soluble substances and made the corn stover more accessible to microorganisms when compared to thermal acid pretreatment (TAP). MAP showed obvious advantages in short duration and high efficiency of lignocellulosic hydrolysis. Analysis of the particle size and specific surface area of corn stover as well as observation of its cellular microstructure were used to elucidate the enhancement mechanism of the hydrolysis process by microwave assistance. The cumulative hydrogen volume reached 182.2 ml when corn stover was pretreated by MAP with 0.3 N H₂SO₄ for 45 min, and the corresponding hydrogen yield reached 1.53 mol H₂/mol-glucose equivalents converted to organic end products. The present work demonstrates that MAP has potential to enhance the bioconversion efficiency of lignocellulosic waste to renewable biofuel.     

Optimization of alkaline pretreatment on corn stover for enhanced production of 1.3-propanediol and 2,3-butanediol by Klebsiella pneumoniae AJ4

Corn stover is one of the most promising lignocellulosic biomass that can be utilized for producing 1,3-propanediol and 2,3-butanediol. The pretreatment and enzymatic hydrolysis steps are essential for the bioconversion of lignocellulosic biomass to diols. For optimizing the pretreatment step, temperature, time, and NaOH concentration were evaluated based on total sugar recovery. Enzymatic hydrolysis for cellulose and hemicellulose were investigated at different solid-to-liquid ratios. The optimum conditions were found to be alkaline pretreatment with 0.25 mol dm⁻³ NaOH for 1 h at 60 °C followed by enzymatic hydrolysis at 50 °C for 48 h, with a solid slurry concentration of 100 g dm⁻³. Under these conditions, conversion rates of 92.55% and 78.82% were obtained from glucan and xylan, respectively. Diol production from fermentable sugars was 14.8 g dm⁻³, with a conversion yield and productivity of 0.46 g g⁻¹, and 0.98 g dm⁻³ h⁻¹, respectively. Our results are similar for diol production obtained using pure sugars under the same conditions. Therefore, mild alkaline pretreatment of corn stover facilitates delignification, significantly improving the rate of enzymatic saccharification and sugar recovery.     

Biological hydrogen production from corn stover by moderately thermophile Thermoanaerobacterium thermosaccharolyticum W16

This study addressed the utilization of an agro-waste, corn stover, as a renewable lignocellulosic feedstock for the fermentative H₂ production by the moderate thermophile Thermoanaerobacterium thermosaccharolyticum W16. The corn stover was first hydrolyzed by cellulase with supplementation of xylanase after delignification with 2% NaOH. It produced reducing sugar at a yield of 11.2 g L⁻¹ glucose, 3.4 g L⁻¹ xylose and 0.5 g L⁻¹ arabinose under the optimum condition of cellulase dosage 25 U g⁻¹ substrate with supplement xylanase 30 U g⁻¹ substrate. The hydrolyzed corn stover was sequentially introduced to fermentation by strain W16, where, the cell density and the maximum H₂ production rate was comparable to that on simulated medium, which has the same concentration of reducing sugars with hydrolysate. The present results suggest a promising combined hydrogen production process from corn stover with enzymatic hydrolysis stage and fermentation stage using W16.     

Oleaginous yeast Cryptococcus curvatus culture with dark fermentation hydrogen production effluent as feedstock for microbial lipid production

Volatile fatty acids (VFA) from dark fermentation hydrogen production were tested as carbon sources for the culture of oleaginous yeast Cryptococcus curvatus, which is a promising feedstock for biofuel production. The optimal acetate concentration and pH were investigated when potassium acetate was used as the sole carbon source. Comparisons were then made when hydrogen production effluent (HPE) from synthetic wastewater was tested as feedstock. A pH-stat culture fed with acetic acid ultimately produced 168 g/L biomass, with a lipid content of 75.0%. No inhibitor to yeast growth was produced in the hydrogen production process. However, inhibition occurred in culture with HPE from food waste (FW), indicating that inhibitors may be present in the original raw food waste. This inhibition could be avoided by a process that uses glucose as the initial carbon source and then is continuously fed with FW-HPE. The biomass productivity in this continuous culture process reached 0.34 g/L/h, but the lipid content was only 13.5%. These results suggest that FW-HPE alone is not an optimal feedstock, but HPE derived from nitrogen-deficient waste streams could be good feedstocks. This study provides preliminary evidence for the feasibility of using organic waste for the co-production of hydrogen and lipid.     

Key techniques and parameters for briquetting corn stover sprayed with biogas slurry in a cold region in China

Densification of biomass is often necessary to combat the negative storage and handling characteristics of these low-bulk-density materials. Corn stover is an important feedstock being considered for production of renewable fuels and energy in China. Densification of corn stover would help reduce the problems and costs of bulk transportation, handling, and storage of biomass feedstock. In cold regions, some thermosetting binder will be added when briquette fuel is made with corn stover because of its high water and lignin content. It is important to understand the synthesis mechanism of thermosetting binder under certain temperature and pressure combined with strong alkaline slurry to explore develop ment of a new process of briquetting corn stover based on only alkaline slurry as an environment-friendly binder. In this study, flat-die briquetting machine has been used with a cone-shaped press roller, and a matching die hole on the press plate. At the same time, orthogonal experiments were designed from the results of single-factor experiments to obtain optimal briquetting conditions. The effects of spray quantity of biogas-slurry, size of die hole, and water content of corn stover on the durability and bulk density of corn stover briquettes were investigated. Moreover, the model for whole factors and the model for interaction between factors for indexes have been built, emulated the optimum processing parameters. The results show briquettes of corn stover with durability of 83.33% were produced when the spray liquid flow quantity of biogas-slurry, size of die hole, and water content of corn stover were 0.45 L/kg, 28 mm, and 20%, respectively. Bulk density of 616 kg/m³ was produced when the spray liquid flow quantity of biogas-slurry, size of die hole, and water content of corn stover were 0.3 L/kg, 24 mm, and 25%, respectively. These results have been checked by verification testing. The successful implementation of this project provides theoretical support and test instruction for the development of green biomass energy for sustainable development.     

Effect of biomass species and plant size on cellulosic ethanol: A comparative process and economic analysis

The effects of five different biomass species and their chemical composition on the overall process efficiency and economic performance considering feedstock availability and feedstock costs to manufacture ethanol from lignocellulose were studied. First is a comparison of ethanol production and excess electricity generated between different biomass species. Results show that, at the same feedstock rate of 2000 Mg day^?1, aspen wood has larger ethanol production than switchgrass, hybrid poplar and corn stover, while the excess electricity generated is as follows in increasing order: aspen < corn stover < hybrid poplar/switchgrass. Second, our results show that the ethanol production is largely linear with holocellulose (cellulose plus hemicellulose) composition of the various biomass species. However, the relationship between excess electricity generated and non-holocellulose combustible component is nonlinear. Last, on environmental performance, it is found that the water losses per unit ethanol production are in the following order: aspen wood < corn stover < hybrid poplar < switchgrass. While corn stover is a potential feedstock to produce cellulosic ethanol with the lowest ethanol production cost at the present time, hybrid poplar and switchgrass are the two promising future energy crops.The effects of plant size analysis showed that the estimated feedstock delivered costs, ethanol production, excess electricity generated and solid and gaseous waste emissions all increase with plant size for the various biomass species. The ethanol production costs decrease with the increase in plant size with optimal plant sizes for corn stover in the range from 2000 dry Mg day^?1 to 4000 dry Mg day^?1.     

Integrating livestock manure with a corn–soybean bioenergy cropping system improves short-term carbon sequestration rates and net global warming potential

Carbon cycling and the global warming potential (GWP) of bioenergy cropping systems with complete biomass removal are of agronomic and environmental concern. Corn growers who plan to remove corn stover as a feedstock for the emerging cellulosic ethanol industry will benefit from carbon amendments such as manure and compost, to replace carbon removed with the corn stover. The objective of this research was to determine the effect of beef cattle feedlot manure and composted dairy manure on short-term carbon sequestration rates and net global warming potential (GWP) in a corn–soybean rotation with complete corn-stover removal. Field experiments consisting of a corn–soybean rotation with whole-plant corn harvest, were conducted near East Lansing, MI over a three-year period beginning in 2002. Compost and manure amendments raised soil carbon (C) at a level sufficient to overcome the C debt associated with manure production, manure collection and storage, land application, and post-application field emissions. The net GWP in carbon dioxide equivalents for the manure and compost amended cropping systems was ?934 and ?784 g m^?2 y^?1, respectively, compared to 52 g m^?2 y^?1 for the non-manure amended synthetic fertilizer check. This work further substantiates the environmental benefits associated with renewable fuels and demonstrates that with proper management, the integration of livestock manures in biofuel cropping systems can enhance greenhouse gas (GHG) remediation.     

Variation in corn stover composition and energy content with crop maturity

How to harvest and process corn stover to maximize its quality as a fuel or industrial feedstock and minimize material losses are compelling issues in the industrial utilization of corn stover. The objectives of this investigation were to evaluate the variation in the chemical composition and energy content of aboveground components of the corn plant over time and to evaluate how composition changes after grain physiological maturity is reached and the plants are weathered while undergoing further field drying. Above ground biomass distribution and composition of two almost identical corn cultivars (Pioneer 32K61 and 32K64 Bt) were studied from an estimated 2 weeks before corn kernel physiological maturity until 4 weeks after the grain had already reached a moisture content suitable for combine harvesting. Compositional analysis of corn stover fractions gathered over the course of maturation, senescence, and weathering using NIR spectroscopy showed (1) a rapid drop in soluble glucan, (2) increase in lignin, and (3) increase in xylan. By day 151 after planting, about when grain from surrounding non-test plots was harvested at about 15.5% moisture, composition of the different fractions remained fairly constant. Since product yield in fermentation-based biomass conversion processes is proportional to the structural carbohydrate content of the feedstock, timing of stover collection and the proportion of anatomical fractions collected affect the quality of corn stover as fermentation feedstock. Since the energy content of corn stover anatomical fractions is shown to remain fairly constant over time and from one plant to another (16.7–20.9 kJ g⁻¹), insofar as combustion processes are concerned, it apparently makes little difference which part of the plant is used, or at what time the material is harvested.     

Rheological properties of corn stover hydrolysate and photo-fermentation bio-hydrogen producing capacity under intermittent stirring

Rheological properties of substrates significantly affect energy consumption and hydrogen production potential in the process of hydrogen production with stirring. Hence, the rheological properties of corn stover hydrolysate with diverse concentrations and its hydrogen producing capacities under intermittent stirring conditions were investigated in this paper. The results showed that corn stover hydrolysate exhibited pseudo-plastic flow behavior at total solid (TS) of 2.76%–7.65%, and was well fitted by the Power law model. Among four intermittent stirring modes, intermittent stirring C2 (static time: stirring time is 2:1) obtained the highest hydrogen yield of 57.63 ± 1.75 mL g⁻¹ VS, which was 18.97% higher compared with static-culture. Moreover, the maximum hydrogen production rate of intermittent stirring C2 increased by 65.05% compared to continuous stirring. It's a feasible way to improve hydrogen production performance with proper intermittent stirring.     

Enhanced microbial oil production by activated sludge microorganisms from sugarcane bagasse hydrolyzate

The use of sugarcane bagasse hydrolyzate as a carbon source for enhanced oil production by activated sludge microbial cultures was investigated. Cultivation of raw activated sludge inoculum using pure xylose as carbon source was necessary prior to bagasse hydrolyzate feeding for microbial acclimation to this pentose sugar, the major component of the hydrolyzate. Lipid contents from 40 to 47% (dry cell weight) were achieved under high C:N ratio following bagasse hydrolyzate feeding; however nutrient supplementation was found to be necessary in order to maintain viable cell biomass levels (>10 g/L) to achieve a high lipid titer (7.62 g/L). Hence, a process involving sequential batch feeding of hydrolyzate with and without nutrients was proposed and simulated using the Logistic and Luedeking–Piret models. Analysis of the product lipids showed up to 50% saponifiable fractions and dominance of C₁₆ and C₁₈ fatty acids, demonstrating their suitability as biofuel feedstock.     

High dry matter whole-plant corn as a biomass feedstock

This research investigated the harvest, ambient pre-treatment, and storage of whole-plant corn as an alternative to conventional systems where corn grain and stover are fractionated at harvest. Harvesting the whole-plant, both grain and most of the above ground stover, after physiological maturity can reduce the intense logistics challenges typically associated with corn harvest and expand the harvest window. To determine the feasibility of the proposed system, corn was harvested at 350–840 g kg⁻¹ whole-plant dry matter (DM) using a forage harvester and then ensiled in pilot-scale silos. Ambient pretreatment during storage was investigated using both dilute acid and lime. Both pretreated and control whole-plant silages were very well conserved during anaerobic storage with DM losses generally less than 40 g kg⁻¹. Hydrodynamic separation of the grain and stover fractions after storage was found to be more effective at fractionating starch and fiber than conventional dry grain harvest, and both fractions had desirable composition. The effects of pretreatment on the silage were very pronounced at 30 and 100 g (kg DM)⁻¹ sulfuric acid loading with less than 100 g (kg DM)⁻¹ of the hemicellulose still bound in the cell wall at DM contents greater than 500 g kg⁻¹. The whole-plant harvest and storage system was shown to be a viable alternative to conventional corn grain and stover systems for producing feedstocks for biochemical conversion.     

Enhancement of energy efficiency and economics of process designs for catalytic co‐production of bioenergy and bio‐based products from lignocellulosic biomass

This study presents an integrated strategy for the co‐production of bioenergy (biofuels: butene oligomers) and bio‐based products (biomaterials: cyclopentanone (CPON) and alkylphenols) from hemicellulose (C₅), cellulose (C₆), and lignin fractions of lignocellulosic biomass based on experimental catalysis studies. To evaluate techno‐economic feasibility of the strategy, we performed a system‐level design study with three steps: process synthesis, energy analysis, and economic analysis. The results of process synthesis show that all biomass fractions are effectively converted with high numerical carbon yields (C₆‐to‐butene oligomers: 52.5%, C₅‐to‐CPON: 68.2%, and lignin‐to‐alkylphenols: 13.3%) but an efficient separation system for high recovery of bioenergy and bio‐based products is crucial. Moreover, an efficient design of a heat exchanger network leads that the total energy requirements of the process are satisfied by the combustion of biomass degradation products (humins). Finally, an economic analysis is performed to estimate the minimum selling price of CPON as the highest energy material (201 Mt/day of CPON production using 2000 Mt/day of corn stover feedstock processing). This result shows that the process ($1.79/kg CPON) can be cost competitive with current petro‐based production approaches. Copyright © 2017 John Wiley & Sons, Ltd.     

Applying life-cycle assessment to low carbon fuel standards—How allocation choices influence carbon intensity for renewable transportation fuels

The Energy Independence and Security Act (EISA) of 2007 requires life-cycle assessment (LCA) for quantifying greenhouse gas emissions (GHGs) from expanded U.S. biofuel production. To qualify under the Renewable Fuel Standard, cellulosic ethanol and new corn ethanol must demonstrate 60% and 20% lower emissions than petroleum fuels, respectively. A combined corn-grain and corn-stover ethanol system could potentially satisfy a major portion of renewable fuel production goals. This work examines multiple LCA allocation procedures for a hypothetical system producing ethanol from both corn grain and corn stover. Allocation choice is known to strongly influence GHG emission results for corn-ethanol. Stover-derived ethanol production further complicates allocation practices because additional products result from the same corn production system. This study measures the carbon intensity of ethanol fuels against EISA limits using multiple allocation approaches. Allocation decisions are shown to be paramount. Under varying approaches, carbon intensity for corn ethanol was 36–79% that of gasoline, while carbon intensity for stover-derived ethanol was −10% to 44% that of gasoline. Producing corn-stover ethanol dramatically reduced carbon intensity for corn-grain ethanol, because substantially more ethanol is produced with only minor increases in emissions. Regulatory considerations for applying LCA are discussed.