Alkaline-pretreated Corn Stover Research Articles

Kinetic studies of alkaline-pretreated corn stover co-digested with upset dairy manure under solid-state

Prolonged lag phase and reactor instability make methane yield description and prediction challenging in upset solid-state anaerobic digestion (SSAD). Seven kinetic models (first-order (FOM), modified first-order (MFOM), Fitzhugh (FzM), logistic (LM), modified logistic (MLM), Cone (CM), and modified Gompertz (MGM) were employed for treatment evaluation. The treatments were dairy manure blended with calcium pretreated stover (8% Ca CSDM) or sodium pretreated corn stover (4% Na CSDM) or 2% aqueous ammonia pretreated corn stover (2% NH4 CSDM), or 4% aqueous ammonia pretreated corn stover (4% NH4 CSDM). The LM, CM, MLM with MGM, and MGM best described methane yield for 4% Na CSDM, 2% NH4 CSDM, 4% NH4 CSDM, and 8% Ca CSDM, respectively. Optimal hydraulic retention time predicted for the least inhibited treatment, 8% Ca CSDM, was 60 days. Therefore, non-hydrolysis rate limiting models (LM, MLM, FzM, MGM, and CM) could simulate methane yield, design of reactor’s volume, and develop degradation rate models in full-scale SSAD.

Comparison of the Reactor Performance of Alkaline-Pretreated Corn Stover Co-digested with Dairy Manure Under Solid-State

Solid-state anaerobic digestion is a promising path to optimize green energy generation from waste management. This mesophilic study investigated the performance of sodium hydroxide (4%NaOH), ammonium hydroxide (2%NH4OH, and 4%NH4OH), and calcium hydroxide (8%Ca(OH)2) pretreated corn stover (Cs) co-digested with dairy manure (Dm) to achieve 4%NaCsDm, 2%AqCsDm, 4%AqCsDm, and 8%CaCsDm treatments. Results showed that 8%CaCsDm had shortened detention time (79 days) and increased methane yield (178 L/kg VS) in comparison with other treatments. In addition, propionic acid concentration in treatment 4%NaCsDm was elevated beyond a safe threshold (> 0.9 g/L) for methanogens, which is unlike the significant bioconversion that occurred for other treatments. Though, free ammonia concentration for 2%AqCsDm and 4%AqCsDm pre-digestates were within the safe limit (< 53 mg/L) relative to other treatments, 8%CaCsDm sufficiently reduced the initial inhibitory concentration to a safe threshold at the cessation of the experiment. Additionally, 8%CaCsDm treatment had the highest VFA bioconversion rate (80%). Therefore, this study demonstrated that 8%CaCsDm treatment could effectively improve reactor performance in solid-state anaerobic co-digestion.

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.

Sequential Extraction and Characterization of Lignin-Derived Compounds from Thermochemically Processed Biorefinery Lignins

As the most abundant source of renewable aromatic compounds on the planet, lignin is an attractive feedstock for producing a range of chemicals and products that are currently derived from petroleum. Despite its great potential, separation of lignin depolymerization products remains one of the main obstacles toward cost-effective lignin valorization. Two lignin-rich streams, residues from enzymatic hydrolysis of the dilute acid and alkaline-pretreated corn stover, were depolymerized via pyrolysis using induction heating and catalytic transfer hydrogenolysis (CTH), respectively. Differences in phenolic compounds from gas chromatography–mass spectrometry and gel permeation chromatography analyses suggest that both pretreatment conditions and lignin depolymerization methods affected the product distribution. CTH lignin oils contain less polar compounds as compared to pyrolysis lignin oils, probably due to saturation of the derived compounds as a result of the reductive chemistry. The resulting liquid oils we...

Production of cellulosic organic acids via synthetic fungal consortia.

Consolidated bioprocessing (CBP) is a potential breakthrough technology for reducing costs of biochemical production from lignocellulosic biomass. Production of cellulase enzymes, saccharification of lignocellulose, and conversion of the resulting sugars into a chemical of interest occur simultaneously within a single bioreactor. In this study, synthetic fungal consortia composed of the cellulolytic fungus Trichoderma reesei and the production specialist Rhizopus delemar demonstrated conversion of microcrystalline cellulose (MCC) and alkaline pre-treated corn stover (CS) to fumaric acid in a fully consolidated manner without addition of cellulase enzymes or expensive supplements such as yeast extract. A titer of 6.87 g/L of fumaric acid, representing 0.17 w/w yield, were produced from 40 g/L MCC with a productivity of 31.8 mg/L/hr. In addition, lactic acid was produced from MCC using a fungal consortium with Rhizopus oryzae as the production specialist. These results are proof-of-concept demonstration of engineering synthetic microbial consortia for CBP production of naturally occurring biomolecules.

How does cellulosome composition influence deconstruction of lignocellulosic substrates in Clostridium (Ruminiclostridium) thermocellum DSM 1313?

BackgroundBioethanol production processes involve enzymatic hydrolysis of pretreated lignocellulosic biomass into fermentable sugars. Due to the relatively high cost of enzyme production, the development of potent and cost-effective cellulolytic cocktails is critical for increasing the cost-effectiveness of bioethanol production. In this context, the multi-protein cellulolytic complex of Clostridium (Ruminiclostridium) thermocellum, the cellulosome, was studied here. C. thermocellum is known to assemble cellulosomes of various subunit (enzyme) compositions, in response to the available carbon source. In the current study, different carbon sources were used, and their influence on both cellulosomal composition and the resultant activity was investigated.ResultsGlucose, cellobiose, microcrystalline cellulose, alkaline-pretreated switchgrass, alkaline-pretreated corn stover, and dilute acid-pretreated corn stover were used as sole carbon sources in the growth media of C. thermocellum strain DSM 1313. The purified cellulosomes were compared for their activity on selected cellulosic substrates. Interestingly, cellulosomes derived from cells grown on lignocellulosic biomass showed no advantage in hydrolyzing the original carbon source used for their production. Instead, microcrystalline cellulose- and glucose-derived cellulosomes were equal or superior in their capacity to deconstruct lignocellulosic biomass. Mass spectrometry analysis revealed differential composition of catalytic and structural subunits (scaffoldins) in the different cellulosome samples. The most abundant catalytic subunits in all cellulosome types include Cel48S, Cel9K, Cel9Q, Cel9R, and Cel5G. Microcrystalline cellulose- and glucose-derived cellulosome samples showed higher endoglucanase-to-exoglucanase ratios and higher catalytic subunit-per-scaffoldin ratios compared to lignocellulose-derived cellulosome types.ConclusionThe results reported here highlight the finding that cellulosomes derived from cells grown on glucose and microcrystalline cellulose are more efficient in their action on cellulosic substrates than other cellulosome preparations. These results should be considered in the future development of C. thermocellum-based cellulolytic cocktails, designer cellulosomes, or engineering of improved strains for deconstruction of lignocellulosic biomass.

Production and Characteristics of a Novel Xylose- and Alkali-tolerant GH 43 \u03b2-xylosidase from Penicillium oxalicum for Promoting Hemicellulose Degradation

β-xylosidase is a pivotal enzyme for complete degradation of xylan in hemicelluloses of lignocelluloses, and the xylose- and alkali-tolerant β-xylosidase with high catalytic activity is very attractive for promoting enzymatic hydrolysis of alkaline-pretreated lignocellulose. In this study, a novel intracellular glycoside hydrolase family 43 β-xylosidase gene (xyl43) from Penicillium oxalicum 114-2 was successfully high-level overexpressed in Pichia pastoris, and the secreted enzyme was characterized. The β-xylosidase Xyl43 exhibited great pH stability and high catalytic activity in the range of pH 6.0 to 8.0, and high tolerance to xylose with the Ki value of 28.09 mM. The Xyl43 could effectively promote enzymatic degradation of different source of xylan and hemicellulose contained in alkaline-pretreated corn stover, and high conversion of xylan to xylose could be obtained.

Process yield and economic trade-offs for enzymatic hydrolysis of alkaline pretreated corn stover

Response surface methodology was used to investigate the interaction of pH, temperature, and enzyme loadings on corn stover hydrolysis rates following soaking in aqueous ammonia pretreatment. Economic tradeoffs were estimated for cellulase and hemicellulase loadings under different hydrolysis conditions. Enzyme loadings had a more significant effect on rates than did pH or temperature. The effect of hydrolysis pH was independent of temperature and enzyme loadings, and the optimal pH for glucose and xylose yields were 4.5 and 4.3, respectively. Conducting hydrolysis at 50 °C rather than 37 °C enables either a 10% glucose yield increase, or a comparable yield with 40% and 65% reduction in cellulase and hemicellulase loadings, respectively. Although yield models showed that hydrolysis rates increase with higher enzyme loadings, economic models showed that optimal cellulase and hemicellulase loadings were as much as 47% and 23% lower, respectively, than the maximum loadings tested. Optimal enzyme loadings change with fluctuations in enzyme costs and ethanol price, but cellulase loadings were more sensitive to these changes than hemicellulase loadings. Enzyme loadings were also more sensitive to enzyme price at lower processing temperatures. Enzyme loadings can be adjusted to increase return based on enzyme costs, ethanol price, and process temperature.

Cellulase production by recombinant Trichoderma reesei and its application in enzymatic hydrolysis of agricultural residues

Fed-batch fermentation was employed to improve the productivity of Trichoderma reesei cellulase. The optimal conditions were fed-batch initiating time 48h, lactose concentration 15% and ratio of carbon to nitrogen 7. Fed-batch fermentation produced 2.11 times higher cellobiohydrolase activity than batch fermentation. The cellulase from T. reesei transformant C10 with enhanced cellobiohydrolase activity was applied to the enzymatic hydrolysis of the alkaline pretreated corn stover and rice straw. In comparison with the cellulase from T. reesei ZU-02, C10 cellulase showed better yields in the enzymatic hydrolysis of both corn stover and rice straw. A high yield of 93.8% was obtained when 20FPIU/g dry substrate C10 cellulase, 10IU/g dry substrate cellobiase and 300U/g dry substrate xylanase were used in the enzymatic hydrolysis of alkaline pretreated corn stover.

Lipid production from corn stover by the oleaginous yeast Cryptococcus curvatus

BackgroundMicrobial lipids produced from lignocellulosic biomass hold great promise for the biodiesel industry. These lipids usually consist of three major processes: pretreatment, enzymatic hydrolysis and lipid production. However, the conventional strategy of using biomass hydrolysates as the feedstock for lipid production suffers from low lipid coefficient and prohibitively high costs. More cost-effective and integrated processes are required to advance lignocellulosic biomass-based microbial lipid technology.ResultsThree different strategies were tested using the oleaginous yeast Cryptococcus curvatus ATCC 20509 as a lipid producer and alkaline-pretreated corn stover as a model material. It was found that the separate hydrolysis and enhanced lipid production process required more cellulolytic enzymes yet afforded a low lipid coefficient of 115.6 mg/g pretreated corn stover. When biomass hydrolysis and lipid production were integrated, the amounts of cellulase and xylanase were reduced and no β-glucosidase was required. The simultaneous saccharification and lipid production process gave a lipid coefficient of 129.4 mg/g pretreated corn stover. A higher lipid coefficient of 159.4 mg/g pretreated corn stover was obtained using the simultaneous saccharification and enhanced lipid production (SSELP) process. Furthermore, cellulolytic enzymes were found recoverable and reusable upon recycling the spent supernatants of the SSELP process, which could reduce enzyme consumption and wastewater discharge.ConclusionsThe SSELP process was superior to other processes in terms of converting alkaline-pretreated corn stover into lipids by C. curvatus, as it required less cellulolytic enzymes and had a higher lipid coefficient. Moreover, the process facilitated easy enzyme recycling that should lead to further reduction of enzyme consumption. These results provide valuable information for cost-effective lipid production from lignocelluloses, which should be particularly important in achieving a sustainable production of biodiesel.

Identification of oleaginous yeast strains able to accumulate high intracellular lipids when cultivated in alkaline pretreated corn stover.

Microbial oil is a potential alternative to food/plant-derived biodiesel fuel. Our previous screening studies identified a wide range of oleaginous yeast species, using a defined laboratory medium known to stimulate lipid accumulation. In this study, the ability of these yeasts to grow and accumulate lipids was further investigated in synthetic hydrolysate (SynH) and authentic ammonia fiber expansion (AFEX™)-pretreated corn stover hydrolysate (ACSH). Most yeast strains tested were able to accumulate lipids in SynH, but only a few were able to grow and accumulate lipids in ACSH medium. Cryptococcus humicola UCDFST 10-1004 was able to accumulate as high as 15.5 g/L lipids, out of a total of 36 g/L cellular biomass when grown in ACSH, with a cellular lipid content of 40 % of cell dry weight. This lipid production is among the highest reported values for oleaginous yeasts grown in authentic hydrolysate. Preculturing in SynH media with xylose as sole carbon source enabled yeasts to assimilate both glucose and xylose more efficiently in the subsequent hydrolysate medium. This study demonstrates that ACSH is a suitable medium for certain oleaginous yeasts to convert lignocellullosic sugars to triacylglycerols for production of biodiesel and other valuable oleochemicals.

Quantitative characterization of the impact of pulp refining on enzymatic saccharification of the alkaline pretreated corn stover

In this work, corn stover was refined by a pulp refining instrument (PFI refiner) after NaOH pretreatment under varied conditions. The quantitative characterization of the influence of PFI refining on enzymatic hydrolysis was studied, and it was proved that the enhancement of enzymatic saccharification by PFI refining of the pretreated corn stover was largely due to the significant increment of porosity of substrates and the reduction of cellulose crystallinity. Furthermore, a linear relationship between beating degree and final total sugar yields was found, and a simple way to predict the final total sugar yields by easily testing the beating degree of PFI refined corn stover was established. Therefore, this paper provided the possibility and feasibility for easily monitoring the fermentable sugar production by the simple test of beating degree, and this will be of significant importance for the monitoring and controlling of industrial production in the future.

Thermophilic Solid-State Anaerobic Digestion of Alkaline-Pretreated Corn Stover

Solid-state anaerobic digestion (SS-AD) of corn stover (CS) was conducted at mesophilic (37 °C) and thermophilic (50 °C) conditions with/without solid-state NaOH pretreatment. Fourier transform infrared (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM) were employed to help with the understanding of the changes of the physicochemical structure of pretreated CS. Additionally, thermophilic SS-AD of pretreated CS and chicken manure (CM) was investigated. First-order, Cone, and modified Gompertz models were used to evaluate the methane production. Results showed that solid-state NaOH pretreatment could partly dissolve lignin and hemicelluloses and significantly increase the internal surface area of CS, which could make it more readily biodegradable. At a substrate/inoculum (S/I) ratio of 3, mesophilic SS-AD of CS failed because of the accumulation of organic acids. However, under thermophilic SS-AD conditions, biogas and methane yields of pretreated CS were found to be 386.3 and 194.8 mL g–1 of VSadded, respectively, which were 29.4 and 40.1% higher than those of untreated CS. Thermophilic solid-state co-digestion of pretreated CS with CM showed no beneficial effects for enhancing the biogas and methane yields, because of the accumulation of volatile fatty acids and ammonia. Methane production could well be explained by the Cone and modified Gompertz models compared to the first-order model, because higher R2 values were obtained. On the basis of the results of the Cone model, the first-order rate constant (k) of thermophilic SS-AD of CS and CM decreased from 0.132 to 0.039 day–1 with the increasing portion of CM. Through the modified Gompertz model, a higher lag phase time (λ) and lower maximal methane production rate (μm) were found, with the content of CM increasing under thermophilic solid-state co-digestion conditions. These results collectively suggested that thermophilic SS-AD of pretreated CS could be a promising way to produce biogas in the future.

Raman Spectroscopic Characterization of Photonanocatalyst Aided Alkaline Pretreated Corn Stover Biomass

The most expensive and principal step in the process of converting cellulosic biomass into biorenewables and biofuel is the pretreatment during which lignin and cellulose crystalline structure is broken down. In this study, TiO2 nanoparticles were utilized as photocatalyst in addition to alkaline (ammonia and sodium hydrate) treatment of corn stover biomass to improve delignification ability and reduce the energy and chemical loadings to make the process more environmentally friendly. Raman Spectroscopic imaging, as an accurate and rapid chemical characterization method, was utilized to investigate the molecular compositional and structural changes occurring during the pretreatment process in the corn stover biomass qualitatively. Lignin characteristic peaks at 1,600, 1,620 and 1,690 cm-1 as well as cellulose characteristic peaks at 1,059 and 2,888 cm-1 were identified through Raman Spectroscopic measurement as indicators of the effects of the pretreatment. Real-time quantitative analysis of these functional peaks revealed the molecular structural changes during delignification, potentially may lead to optimization of the processing parameters to reduce the processing cost in the future.

Succinic acid production from corn stover by simultaneous saccharification and fermentation using Actinobacillus succinogenes

Simultaneous saccharification and fermentation (SSF) technique was applied for succinic acid production by Actinobacillus succinogenes in a 5-l stirred bioreactor with corn stover as the raw material. The process parameters of SSF, including corn stover pretreatment condition, substrate concentration, enzyme loading and fermentation temperature were investigated. Results indicated that pretreating corn stover with diluted alkaline was beneficial for the succinic acid production, and succinic acid yield could be significantly increased when adding the cellulase supplemented with cellobiase. The maximal succinic acid concentration and yield could reach 47.4 g/l and 0.72 g/g-substrate, respectively. The corresponding operation conditions were summarized as follows: SSF operation at 38 °C for 48 h, diluted alkaline pretreated corn stover as substrate with concentration of 70 g/l, enzyme loading of 20 FPU cellulase and 10 U cellobiase per gram substrate. This result suggested an industrial potential of succinic acid production by using SSF and corn stover.

Effect of anatomical fractionation on the enzymatic hydrolysis of acid and alkaline pretreated corn stover

Due to concerns with biomass collection systems and soil sustainability there are opportunities to investigate the optimal plant fractions to collect for conversion. An ideal feedstock would require a low severity pretreatment to release a maximum amount of sugar during enzymatic hydrolysis. Corn stover fractions were separated manually and analyzed for glucan, xylan, acid soluble lignin, acid insoluble lignin, and ash composition. The stover fractions were also pretreated with either 0%, 0.4%, or 0.8% NaOH for 2 h at room temperature, washed, autoclaved and saccharified. In addition, dilute sulfuric acid pretreated samples underwent simultaneous saccharification and fermentation (SSF) to ethanol. In general, the two pretreatments produced similar trends with cobs, husks, and leaves responding best to the pretreatments, the tops of stalks responding slightly less, and the bottom of the stalks responding the least. For example, corn husks pretreated with 0.8% NaOH released over 90% (standard error of 3.8%) of the available glucan, while only 45% (standard error of 1.1%) of the glucan was produced from identically treated stalk bottoms. Estimates of the theoretical ethanol yield using acid pretreatment followed by SSF were 65% (standard error of 15.9%) for husks and 29% (standard error of 1.8%) for stalk bottoms. This suggests that integration of biomass collection systems to remove sustainable feedstocks could be integrated with the processes within a biorefinery to minimize overall ethanol production costs.

Simultaneous saccharification and fermentation of alkaline-pretreated corn stover to ethanol using a recombinant yeast strain

Bio-ethanol converted from cheap and abundant lignocellulosic materials is a potential renewable resource to replace depleting fossil fuels. Simultaneous saccharification and fermentation (SSF) of alkaline-pretreated corn stover for the production of ethanol was investigated using a recombinant yeast strain Saccharomyces cerevisiae ZU-10. Low cellobiase activity in Trichoderma reesei cellulase resulted in cellobiose accumulation. Supplementing the simultaneous saccharification and fermentation system with cellobiase greatly reduced feedback inhibition caused by cellobiose to the cellulase reaction, thereby increased the ethanol yield. 12 h of enzymatic prehydrolysis at 50 °C prior to simultaneous saccharification and fermentation was found to have a negative effect on the overall ethanol yield. Glucose and xylose produced from alkaline-pretreated corn stover could be co-fermented to ethanol effectively by S. cerevisiae ZU-10. An ethanol concentration of 27.8 g/L and the corresponding ethanol yield on carbohydrate in substrate of 0.350 g/g were achieved within 72 h at 33 °C with 80 g/L of substrate and enzyme loadings of 20 filter paper activity units (FPU)/g substrate and 10 cellobiase units (CBU)/g substrate. The results are meaningful in co-conversion of cellulose and hemicellulose fraction of lignocellulosic materials to fuel ethanol.