Improvement of sugar yields from corn stover using sequential hot water pretreatment and disk milling

Poly(3-hydroxybuyrate) production from industrial hemp waste pretreated with a chemical-free hydrothermal process

In this study, a mild two-stage hydrothermal pretreatment was employed to optimally valorize industrial hemp (Cannabis sativa sp.) fibrous waste into sugars for Poly(3-hydroxybuyrate) (PHB) production using recombinant Escherichia coli LSBJ. Biomass was pretreated using hot water at 160, 180, and 200°C for 5 and 10 minutes (15% solids), followed by disk refining. The sugar yields during enzymatic hydrolysis were found to improve with increasing temperature and the yields for hot water-disk refining pretreatment (HWDM) were higher compared to only hot water pretreatment at all conditions. The maximum glucose (56 g/L) and cellulose conversion (92%) were achieved for HWDM at 200°C for 10 minutes. The hydrolysate obtained was fermented at a sugar concentration of 20 g/L. The PHB inclusion and concentration of 48% and 1.8 g/L, respectively, were similar to those from pure sugars. A pH-controlled fermentation resulted in a near bi-fold increase in PHB yield (3.46 g/L).

Multivariable Analysis Reveals the Key Variables Related to Lignocellulosic Biomass Type and Pretreatment before Enzymolysis

In this study, partial least square (PLS), a multivariable analysis, was used to simultaneously quantitatively evaluate the effects of variables related to three pretreatments (alkaline, hot water and acid) and the biomass properties of poplar, salix and corncob. The results showed that biomass type was the most important variable influencing enzymolysis reducing sugar yield (ERSY). The biomass compositions affected the ERSY more than the pretreatment conditions, among which hemicellulose and lignin played vital roles. The alkaline pretreatment had a more positive effect on the ERSY than the acid and hot water pretreatments, in which alkaline content had more influence than temperature. This work provides a deeper understanding of the material properties and the pretreatment conditions in different complex systems before enzymolysis, which might be a guidance to future study.

The correlation between the physicochemical properties and enzymatic hydrolyzability of hydrothermal pretreated wheat straw: A quantitative analysis

Hydrothermal pretreatment with diluted acid or alkali can disrupt the compact structure of wheat straw at a moderate temperature for efficient enzymatic saccharification. However, the quantitative analysis between the physicochemical properties and enzymatic hydrolyzability of hydrothermal pretreated lignocellulose was rarely investigated, which hindered the development of model-based applications for process design and control. Herein, correlation analysis (CA) and principal component analysis (PCA) were conducted to elucidate the dominant factors affecting the enzymatic hydrolyzability and quantitative relationship between them. CA results suggested the major positive factor affecting carbohydrate conversion was cellulose content (r = 0.86). Through logarithmic processing and linear combination, these intercorrelated factors were successfully converted into two newly uncorrelated variables named the first principal component (PC1) and the second principal component (PC2). The initial hydrolysis rate and carbohydrate conversion can be well predicted by PC1 and PC2 scores through multiple linear regression with a high R-squared (0.91 and 0.80).

Mechanical pretreatment of lignocellulosic biomass toward enzymatic/fermentative valorization

Lignocellulosic biomass (LCB) has the potential to replace fossil fuels, thanks to the concept of biorefinery. This material is formed mainly by cellulose, lignin, and hemicellulose. To maximize the valorization potential of this material, LCB needs to be pretreated. Milling is always performed before any other treatments. It does not produce chemical change and improves the efficiency of the upcoming processes.

Additionally, it makes LCB easier to handle and increases bulk density and transfer phenomena of the next pretreatment step. However, this treatment is energy consuming, so it needs to be optimized. Several mills can be used, and the equipment selection depends on the characteristics of the material, the final size required, and the operational regime: continuous or batch. Among them, ball, knife, and hammer mills are the most used at the laboratory scale, especially before enzymatic or fermentative treatments. The continuous operational regime (knife and hammer mill) allows us to work with high volumes of raw material and can continuously reduce particle size, unlike the batch operating regime (ball mill).

This review recollects the information about the application of these machines, the effect on particle size, and subsequent treatments. On the one hand, ball milling reduced particle size the most; on the other hand, hammer and knife milling consumed less energy. Furthermore, the latter reached a small final particle size (units of millimeters) suitable for valorization.

Coprocessing Corn Germ Meal for Oil Recovery and Ethanol Production: A Process Model for Lipid-Producing Energy Crops

Efforts to engineer high-productivity crops to accumulate oils in their vegetative tissue present the possibility of expanding biodiesel production. However, processing the new crops for lipid recovery and ethanol production from cell wall saccharides is challenging and expensive. In a previous study using corn germ meal as a model substrate, we reported that liquid hot water (LHW) pretreatment enriched the lipid concentration by 2.2 to 4.2 fold. This study investigated combining oil recovery with ethanol production by extracting oil following LHW and simultaneous saccharification and co-fermentation (SSCF) of the biomass. Corn germ meal was again used to model the oil-bearing energy crops. Pretreated germ meal hydrolysate or solids (160 and 180 °C for 10 min) were fermented, and lipids were extracted from both the spent fermentation whole broth and fermentation solids, which were recovered by centrifugation and convective drying. Lipid contents in spent fermentation solids increased 3.7 to 5.7 fold compared to the beginning germ meal. The highest lipid yield achieved after fermentation was 36.0 mg lipid g−1 raw biomass; the maximum relative amount of triacylglycerol (TAG) was 50.9% of extracted oil. Although the fermentation step increased the lipid concentration of the recovered solids, it did not improve the lipid yields of pretreated biomass and detrimentally affected oil compositions by increasing the relative concentrations of free fatty acids.

Balancing sugar recovery and inhibitor generation during energycane processing: Coupling cryogenic grinding with hydrothermal pretreatment at low temperatures

Pretreatment of lignocellulosic biomass at high temperatures or with oxidizing chemicals generate various inhibitors that restrict the efficient bioconversion of sugars in subsequent steps. The present study systematically investigates individual and combinatorial effects of pretreatment parameters on the generation of inhibitors. A plot between pretreatment temperature and inhibitor revealed optimum pretreatment temperature for energycane bagasse i.e., 170 °C beyond which total inhibitor production increased exponentially. No inhibitor production was observed on mechanical processing i.e., disk milling/cryogenic grinding of biomass. Evaluation of response surface regression exhibited that biomass solids loading has a significant effect on inhibitor generation at higher temperatures. The concentrations of certain inhibitors such as acetic acid, furfurals, and HMF increased more than 3-folds on doubling the solids loading. Furthermore, a novel low-severity approach of low-temperature hydrothermal pretreatment coupled with cryogenic grinding for lignocellulosic biomasses has been introduced which improved sugar yields while maintaining a low inhibitor concentration.

Advanced Bioethanol Production: From Novel Raw Materials to Integrated Biorefineries

The production of so-called advanced bioethanol offers several advantages compared to traditional bioethanol production processes in terms of sustainability criteria. This includes, for instance, the use of nonfood crops or residual biomass as raw material and a higher potential for reducing greenhouse gas emissions. The present review focuses on the recent progress related to the production of advanced bioethanol, (i) highlighting current results from using novel biomass sources such as the organic fraction of municipal solid waste and certain industrial residues (e.g., residues from the paper, food, and beverage industries); (ii) describing new developments in pretreatment technologies for the fractionation and conversion of lignocellulosic biomass, such as the bioextrusion process or the use of novel ionic liquids; (iii) listing the use of new enzyme catalysts and microbial strains during saccharification and fermentation processes. Furthermore, the most promising biorefinery approaches that will contribute to the cost-competitiveness of advanced bioethanol production processes are also discussed, focusing on innovative technologies and applications that can contribute to achieve a more sustainable and effective utilization of all biomass fractions. Special attention is given to integrated strategies such as lignocellulose-based biorefineries for the simultaneous production of bioethanol and other high added value bioproducts.

Optimization of two-stage pretreatment for maximizing ethanol production in 1.5G technology

Two-stage pretreatment conditions were optimized to convert corn fiber, separated from whole stillage in a corn dry grind ethanol plant, to fermentable sugars via hydrolysis. Liquid hot water pretreatment (25% solids) at 180 °C for 10 min, followed by three cycles of disk milling, provided maximum glucose, xylose, and arabinose yields of 88.5%, 41.0%, and 30.4% respectively after hydrolysis with Cellulase I. The glucose, xylose, and arabinose yields with Cellulase II at optimum conditions were 94.9%, 74.2%, and 66.3%, respectively. SSF of corn fiber using engineered yeast, with both Cellulase I and II, provided maximum ethanol concentrations of 2.13% and 2.73% (v/v). The protein content in the residual solid after fermentation was 47.95% and 52.05% for Cellulase I and II, respectively. This technology provides additional ethanol in a dry grind plant by converting corn fiber into ethanol and increases the protein content of DDGS, thereby improving the quality.

High solids loading biorefinery for the production of cellulosic sugars from bioenergy sorghum

A novel process applying high solids loading in chemical-free pretreatment and enzymatic hydrolysis was developed to produce sugars from bioenergy sorghum. Hydrothermal pretreatment with 50% solids loading was performed in a pilot scale continuous reactor followed by disc refining. Sugars were extracted from the enzymatic hydrolysis at 10% to 50% solids content using fed-batch operations. Three surfactants (Tween 80, PEG 4000, and PEG 6000) were evaluated to increase sugar yields. Hydrolysis using 2% PEG 4000 had the highest sugar yields. Glucose concentrations of 105, 130, and 147 g/L were obtained from the reaction at 30%, 40%, and 50% solids content, respectively. The maximum sugar concentration of the hydrolysate, including glucose and xylose, obtained was 232 g/L. Additionally, the glucose recovery (73.14%) was increased compared to that of the batch reaction (52.74%) by using two-stage enzymatic hydrolysis combined with fed-batch operation at 50% w/v solids content.

Recoveries of Oil and Hydrolyzed Sugars from Corn Germ Meal by Hydrothermal Pretreatment: A Model Feedstock for Lipid-Producing Energy Crops

Vegetable oil is extracted from oil rich seeds, such as soybeans. Genetic engineering of green plants to accumulate oil in vegetative tissue is a future source of oil that promises increased land productivity and the use of marginal lands. However, the low concentration of lipids in current engineered plant biomass samples makes the oil extraction process challenging and expensive. In this study, liquid hot water (LHW) pretreatment was investigated to enhance oil recovery from the solids and increase enzymatic hydrolysis efficiency of such feedstocks. Corn germ meal was chosen as a model feedstock representing lipid-producing energy crops. Germ meal was pretreated at 160 and 180 °C for 10 and 15 min at 20% w/w solids loading. Enzymatic hydrolysis on the pretreated solid was performed. After pretreatment, the oil concentration increased by 2.2 to 4.2 fold. The most severe pretreatment condition of LHW, at 180 °C for 15 min, gave the maximum oil concentration (9.7%, w/w), the highest triacylglycerol (TAG) content of the extracted oil (71.6%), and the highest conversions of glucose and xylose (99.0% and 32.8%, respectively). This study demonstrates that the optimal pretreatment condition for corn germ meal is 180 °C LHW for 15 min. Pretreatment improves lipids recovery from oil bearing biomass with little or no effect on the lipid profile.

Chemical Free Two-Step Hydrothermal Pretreatment to Improve Sugar Yields from Energy Cane

Energy cane is an attractive lignocellulosic feedstock for processing into biofuels and bioproducts. A low-severity two-step hydrothermal pretreatment was investigated on energy cane for the production of monomeric sugar. Pretreatment temperature and time, in addition to the effect of disk milling, were observed for the glucose and xylose yields during hydrolysis. At residence times above 5 min in case of pretreatment at 200 °C, all of the hemicellulose was observed to be solubilized. The pretreatment condition of 200 °C for 10 min with disk milling was observed to provide the highest glucose concentration of 5.4%, and 200 °C for 5 min with disk milling provided the highest xylose concentration of 2.15%. The effect of disk milling in improving the sugar concentrations during hydrolysis was significant, especially at lower pretreatment temperatures and times. Low xylose yields at higher temperatures were attributed to the formation of degradation products at increased severity.

Lignocellulosic Biomass as a Substrate for Oleaginous Microorganisms: A Review

Microorganisms capable of accumulating lipids in high percentages, known as oleaginous microorganisms, have been widely studied as an alternative for producing oleochemicals and biofuels. Microbial lipid, so-called Single Cell Oil (SCO), production depends on several growth parameters, including the nature of the carbon substrate, which must be efficiently taken up and converted into storage lipid. On the other hand, substrates considered for large scale applications must be abundant and of low acquisition cost. Among others, lignocellulosic biomass is a promising renewable substrate containing high percentages of assimilable sugars (hexoses and pentoses). However, it is also highly recalcitrant, and therefore it requires specific pretreatments in order to release its assimilable components. The main drawback of lignocellulose pretreatment is the generation of several by-products that can inhibit the microbial metabolism. In this review, we discuss the main aspects related to the cultivation of oleaginous microorganisms using lignocellulosic biomass as substrate, hoping to contribute to the development of a sustainable process for SCO production in the near future.

An integrated approach to obtain xylo-oligosaccharides from sugarcane straw: From lab to pilot scale

Sugarcane straw (SS) is a widely available agricultural processing feedstock with the potential to produce 2nd generation bioethanol and bioproducts, in addition to the more conventional use for heat and/or electrical power generation. In this study, we investigated the operational parameters to maximize the production of xylo-oligosaccharides (XOS) using mild deacetylation, followed by hydrothermal pretreatment. From the laboratory to the pilot-scale, the optimized two-stage pretreatment promoted 81.5% and 70.5% hemicellulose solubilization and led to XOS yields up to 9.8% and 9.1% (w/w of initial straw), respectively. Moreover, different fungal xylanases were also tested to hydrolyze XOS into xylobiose (X2) and xylotriose (X3). GH10 from Aspergillus nidulans performed better than GH11 xylanases and the ratio of the desired products (X2 + X3) increased to 72% due to minimal monomeric sugar formation. Furthermore, a cellulose-rich fraction was obtained, which can be used in other high value-added applications, such as for the production of cello-oligomers.

Production of xylose enriched hydrolysate from bioenergy sorghum and its conversion to β-carotene using an engineered Saccharomyces cerevisiae

A new bioprocess has been developed that allows for producing β-carotene from the xylose portion of bioenergy sorghum. Bioenergy sorghum was pretreated in a pilot-scale continuous hydrothermal reactor followed by disc refining. Xylose was extracted using low-severity dilute acid hydrolysis. A xylose yield of 64.9% (17.4 g/L) was obtained by hydrolyzing at 120 °C for 5 min with 2% sulfuric acid. The xylose-enriched syrup was separated and concentrated to either 32 g xylose/L (medium-concentrated hydrolysate, MCB) or 66 g xylose/L (high-concentrated hydrolysate, HCB). The non- (NCB), medium-, and high-concentrated xylose syrup were neutralized and fermented to β-carotene using Saccharomyces cerevisiae strain SR8B, which had been engineered for xylose utilization and β-carotene production. In HCB, MCB, and NCB cultures, the yeast produced β-carotene titers of 114.50 mg/L, 93.56 mg/L, and 82.50 mg/L, which corresponds to specific yeast biomass productions of 7.32 mg/g DCW, 8.10 mg/g DCW, and 8.29 mg/g DCW, respectively.

Sugar production from bioenergy sorghum by using pilot scale continuous hydrothermal pretreatment combined with disk refining

Chemical-free pretreatments are attracting increased interest because they generate less inhibitor in hydrolysates. In this study, pilot-scaled continuous hydrothermal (PCH) pretreatment followed by disk refining was evaluated and compared to laboratory-scale batch hot water (LHW) pretreatment. Bioenergy sorghum bagasse (BSB) was pretreated at 160-190 °C for 10 min with and without subsequent disk milling. Hydrothermal pretreatment and disk milling synergistically improved glucose and xylose release by 10-20% compared to hydrothermal pretreatment alone. Maximum yields of glucose and xylose of 82.55% and 70.78%, respectively were achieved, when BSB was pretreated at 190 °C and 180 °C followed by disk milling. LHW pretreated BSB had 5-15% higher sugar yields compared to PCH for all pretreatment conditions. The surface area improvement was also performed. PCH pretreatment combined with disk milling increased BSB surface area by 31.80-106.93%, which was greater than observed using LHW pretreatment.

Economic Analysis of Cellulosic Ethanol Production from Sugarcane Bagasse Using a Sequential Deacetylation, Hot Water and Disk-Refining Pretreatment

A new process for conversion of sugarcane bagasse to ethanol was analyzed for production costs and energy consumption using experimental results. The process includes a sequential three-stage deacetylation, hot water, and disk-refining pretreatment and a commercial glucose-xylose fermenting S. cerevisiae strain. The simultaneous saccharification and co-fermentation (SScF) step used was investigated at two solids loadings: 10% and 16% w/w. Additionally, a sensitivity analysis was conducted for the major operating parameters. The minimum ethanol selling price (MESP) varied between $4.91and $4.52/gal ethanol. The higher SScF solids loading (16%) reduced the total operating, utilities, and production costs by 9.5%, 15.6%, and 5.6%, respectively. Other important factors in determining selling price were costs for fermentation medium and enzymes (e.g. cellulases). Hence, these findings support operating at high solids and producing enzymes onsite as strategies to minimize MESP.

Improving ethanol yields with deacetylated and two-stage pretreated corn stover and sugarcane bagasse by blending commercial xylose-fermenting and wild type Saccharomyces yeast

Corn stover and sugarcane bagasse are the most widely available agriculture processing biomass and could serve as feedstocks for production of biofuel. In this study, three different technologies are combined to develop a more efficient conversion process for each of these feedstocks. The three technologies are diluted alkaline deacetylation process, combined thermochemical and mechanical shear pretreatment, and fermentation using a combined inoculum of two commercial Saccharomyces yeast strains. The two yeast strains used were a non-GMO and GMO strain engineered for xylose fermentation. The final ethanol concentrations obtained were 35.7 g/L from deacetylated corn stover and 32.9 g/L from sugarcane bagasse. Blending the two yeast reduced residual xylose content from 1.24 g/L to 0.48 g/L and increased ethanol production by 6.5% compared to solely using the C5/C6 yeast. The optimized yeast blend also lowered the amount of C5/C6 yeast required for inoculation by 80%.

Feasibility of Continuous Pretreatment of Corn Stover: A Comparison of Three Commercially Available Continuous Pulverizing Devices

We determined the potential of three mechanical pulverizers—a continuous ball mill (CBM), an air classifier mill (ACM), and a high-speed mill (HSM)—in the continuous pretreatment of corn stover. The mean diameters of the pulverized biomasses were not significantly different in the three cases, and the glucose yields from the CBM-, ACM-, and HSM-pulverized samples were 29%, 49%, and 44%, respectively. The energy requirements and process capacities for the ACM and HSM were similar. We conclude that the ACM and HSM could be used in the continuous pretreatment of corn stover and would be useful in biofuel production.

A microwave-assisted aqueous ionic liquid pretreatment to enhance enzymatic hydrolysis of Eucalyptus and its mechanism

A novel pretreatment strategy based on combination of microwave and ionic liquid [TBA][OH] was developed for enhancing enzymatic hydrolysis of Eucalyptus sawdust. The sugar yield of pretreated sample achieved 410.67 mg/g in 48 h, which suffered from optimized microwave-assisted [TBA][OH] pretreatment. The work mechanism was illuminated by chemical composition, Fourier transform infrared spectroscopy (FTIR), ¹³C cross polarization/magic-angle spinning solid state NMR (¹³C solid NMR), X-ray diffraction (XRD) and scanning electron microscope (SEM) analyses. The combined effect of microwave and [TBA][OH] leads to the violent deconstruction of lignin, removal of hemicelluloses, destruction of crystalline region and an eroded, pored and irregular micro-morphology. As a green, relatively inexpensive and high efficient pretreatment, microwave-assisted [TBA][OH] pretreatment has great potential in the field of bio-refinery.

Hydrolysis of untreated lignocellulosic feedstock is independent of S-lignin composition in newly classified anaerobic fungal isolate, Piromyces sp. UH3-1

BACKGROUND

Plant biomass is an abundant but underused feedstock for bioenergy production due to its complex and variable composition, which resists breakdown into fermentable sugars. These feedstocks, however, are routinely degraded by many uncommercialized microbes such as anaerobic gut fungi. These gut fungi express a broad range of carbohydrate active enzymes and are native to the digestive tracts of ruminants and hindgut fermenters. In this study, we examine gut fungal performance on these substrates as a function of composition, and the ability of this isolate to degrade inhibitory high syringyl lignin-containing forestry residues.

RESULTS

We isolated a novel fungal specimen from a donkey in Independence, Indiana, United States. Phylogenetic analysis of the Internal Transcribed Spacer 1 sequence classified the isolate as a member of the genus Piromyces within the phylum Neocallimastigomycota (Piromyces sp. UH3-1, strain UH3-1). The isolate penetrates the substrate with an extensive rhizomycelial network and secretes many cellulose-binding enzymes, which are active on various components of lignocellulose. These activities enable the fungus to hydrolyze at least 58% of the glucan and 28% of the available xylan in untreated corn stover within 168 h and support growth on crude agricultural residues, food waste, and energy crops. Importantly, UH3-1 hydrolyzes high syringyl lignin-containing poplar that is inhibitory to many fungi with efficiencies equal to that of low syringyl lignin-containing poplar with no reduction in fungal growth. This behavior is correlated with slight remodeling of the fungal secretome whose composition adapts with substrate to express an enzyme cocktail optimized to degrade the available biomass.

CONCLUSIONS

Piromyces sp. UH3-1, a newly isolated anaerobic gut fungus, grows on diverse untreated substrates through production of a broad range of carbohydrate active enzymes that are robust to variations in substrate composition. Additionally, UH3-1 and potentially other anaerobic fungi are resistant to inhibitory lignin composition possibly due to changes in enzyme secretion with substrate. Thus, anaerobic fungi are an attractive platform for the production of enzymes that efficiently use mixed feedstocks of variable composition for second generation biofuels. More importantly, our work suggests that the study of anaerobic fungi may reveal naturally evolved strategies to circumvent common hydrolytic inhibitors that hinder biomass usage.

Ethanol Production from Corn Fiber Separated after Liquefaction in the Dry Grind Process

Conversion of corn fiber to ethanol in the dry grind process can increase ethanol yields, improve coproduct quality and contribute to process sustainability. This work investigates the use of two physio-chemical pretreatments on corn fiber and effect of cellulase enzyme dosage to improve ethanol yields. Fiber separated after liquefaction of corn was pretreated using (I) hot water pretreatment (160 °C for 5, 10 or 20 min) and (II) wet disk milling and converted to ethanol. The conversion efficiencies of hot water pretreated fiber were higher than untreated fiber, with highest increase in conversion (10.4%) achieved for 5 min residence time at 160 °C. Disk milling was not effective in increasing conversion compared to other treatments. Hydrolysis and fermentation of untreated fiber with excess cellulase enzymes resulted in 33.3% higher conversion compared to untreated fiber.

Combined Ball Milling and Ethanol Organosolv Pretreatment to Improve the Enzymatic Digestibility of Three Types of Herbaceous Biomass

A combined ball milling and ethanol organosolv process is proposed for the pretreatment of three types of herbaceous biomass, giant miscanthus, corn stover, and wheat straw. The combined pretreatment was effective at both removing lignin and increasing the glucan content. After 120 min pretreatment, the glucan content increased to 63.09%, and 55.89% of the acid-insoluble lignin was removed from the giant miscanthus sample. The removal of cellulose, hemicellulose, and acetyl groups were correlated with the removal of lignin. The pretreatment of corn stover showed the highest removal of cellulose, but this was dependent on the removal of acid-insoluble lignin. The slope of the regression lines, which shows the correlation between the removal of lignin and cellulose, was lower than other correlations. The changes in biomass size were analyzed using size distribution graphs. With increasing pretreatment time, the particle size reduction improved in the three types of herbaceous biomass. Because of the combined physicochemical pretreatment, the enzymatic digestibility improved, and a maximum of 91% glucan digestibility was obtained from the pretreated corn stover when 30 FPU/g-glucan enzyme was added. Finally, compositional analysis of the recovered lignin from the remaining black liquor was investigated.

Fermentation of undetoxified sugarcane bagasse hydrolyzates using a two stage hydrothermal and mechanical refining pretreatment

In this study, liquid hot water pretreatment was combined with disk milling for pretreatment of sugarcane bagasse. Sugarcane bagasse was pretreated using liquid hot water (LHW) at 140-180 °C for 10 min (20% w/w solids content) and then disk milled. Disk milling improved glucose release 41-177% and ethanol production from glucose/xylose cofermentation by 80% compared to only using LHW pretreatment. The highest ethanol conversion efficiency achieved was 94%, which was observed when bagasse was treated at 180 °C with LHW and disk milled. However, a small amount of residual xylose (3 g/L) was indicative that further improvement could be achieved to increase ethanol production.

Evaluation of Screened Lignin-degrading Fungi for the Biological Pretreatment of Corn Stover

The biological pretreatment of lignocellulosic biomass is a low-cost and eco-friendly method for facilitating enzymatic hydrolysis. In this study, strains with lignin depletion capability were screened using a high-throughput screening method. Sixty-three strains were screened out and Myrothecium verrucaria secreted three lignin-degrading enzymes simultaneously during the bio-pretreatment process. The activity levels of laccase, lignin peroxidase and manganese peroxidase were 6.61, 0.78 and 1.31 U g⁻¹ dry biomass. The content of lignin in corn stover decreased by 42.30% after bio-pretreatment, and the conversion rate increased by 123.84% during the subsequent saccharification process in comparison with the untreated corn stover. Furthermore, the effects of bio-pretreatment on the structure of corn stover were presented using a scanning electron microscope (SEM), Brunauer-Emmet-Teller (BET), X-ray diffractometer (XRD) and Fourier transform infrared spectroscopy (FTIR). The results showed that M.V. is a promising lignin-degrading fungus. This research demonstrated an efficient pretreatment approach for enhancing the enzymatic saccharification of corn stover.

Enzyme hydrolysis kinetics of micro-grinded maize straws

This study applied micro-grinding to disintegrate the maize straws and then use the micro-grinded straws of particle sizes particle size 53-61, 80-96 or 150-180μm, for subsequent enzyme hydrolysis tests. The reducing sugar productivity was increased with reducing particle size. A kinetic model considering product inhibition was developed as follows t=aln[S]₀[S]₀-[P]+b[P], where S, P and t are the substrate, enzyme and hydrolysis time, respectively, and a and b are fitting parameters. The initial substrate concentration is proportional to the total exposed surface area. Additionally, the mechanical grinding can increase the biomass affinity for enzyme attack, suggesting the enhanced local action of shearing on the fiber matrix surfaces. The enhanced hydrolysis efficiency of the micro-grinded straws is welcomed by the subsequent refinery steps.

Microwave-assisted inorganic salt pretreatment of sugarcane leaf waste: Effect on physiochemical structure and enzymatic saccharification

This paper presents a method to pretreat sugarcane leaf waste using microwave-assisted (MA) inorganic salt to enhance enzymatic saccharification. The effects of process parameters of salt concentration, microwave power intensity and pretreatment time on reducing sugar yield from sugarcane leaf waste were investigated. Pretreatment models based on MA-NaCl, MA-ZnCl₂ and MA-FeCl₃ were developed with high coefficients of determination (R² >0.8) and optimized. Maximum reducing sugar yield of 0.406g/g was obtained with 2M FeCl₃ at 700W for 3.5min. Scanning electron microscopy (SEM), Fourier Transform Infrared analysis (FTIR) and X-ray diffraction (XRD) showed major changes in lignocellulosic structure after MA-FeCl₃ pretreatment with 71.5% hemicellulose solubilization. This regime was further assessed on sorghum leaves and Napier grass under optimal MA-FeCl₃ conditions. A 2-fold and 3.1-fold increase in sugar yield respectively were observed compared to previous reports. This pretreatment was highly effective for enhancing enzymatic saccharification of lignocellulosic biomass.

Quantitative characterization of enzyme adsorption and hydrolytic performance for ultrafine grinding pretreated corn stover

Quantitative analysis of enzyme adsorption and hydrolysis were performed for sieve-based grinding corn stover (SGCS) and ultrafine grinding corn stover (UGCS)¹ with different enzyme consumptions. The UGCS presented significantly higher enzyme adsorption quantity (5.15mg/g for UGCS, 1.33mg/g for SGCS), higher glucose yield (49.75% for UGCS, 28.75% for SGCS) under 20FPU/g and higher binding enzyme proportion (41.32% for UGCS, 10.64% for SGCS under 5FPU/g) which can be attributed to the more accessible microstructure properties. The relationship between enzyme adsorption and hydrolytic production was directly proportional for SGCS (GY₁=21.04×AQ₁+1.86 (R²=0.95)) while was exponential for UGCS (GY₂=49.42×(1-e^-0.57×AQ₂) (R²=0.99)),² indicating that overmuch enzyme consumption was not advisable for UGCS at economical aspect.

Impact of disk milling on corn stover pretreated at commercial scale

In cellulosic biofuel production, chemical pretreatment performed at laboratory or pilot scale, followed by mechanical refining, has been demonstrated to be effective to increase feedstock enzyme digestibility. To take the combined pretreatment process one step closer to commercialization, disk milling was performed with commercially pretreated corn stover. Dilute acid pretreated samples with combined severity factors (cSF) of 0.09 (DA09) and 0.43 (DA43) were obtained from a commercial plant. Effects of pretreatment conditions (DA09 and DA43), milling cycles (0, 3, 9, and 15) and enzyme dosages (7.8, 15.6 and 31.2mgcellulase/g dry biomass) were evaluated. Milling improved glucose yields by 0.7 to 1.2-fold. Higher enzyme dosages enhanced sugar yields. Milling was more effective to improve glucose yields, while enzyme dosage was more effective to improve xylose yields. However, dilute acid pretreatment condition was the most important factor to increase final sugar yields compared to milling cycles and enzyme dosages.

Optimization of organosolv pretreatment of rice straw for enhanced biohydrogen production using Enterobacter aerogenes

Ethanol organosolv pretreated rice straw was used to produce biohydrogen using Enterobacter aerogenes. The effect of temperature (120-180°C), residence time (30-90min), and ethanol concentration (45-75%v/v) on the hydrogen yield, residual biomass, and lignin recovery was investigated using RSM. In contrast to the residual solid and lignin recovery, no considerable trend could be observed for the changes in the hydrogen yield at different treatment severities. The maximum hydrogen yield of 19.73mlg^-1 straw was obtained at the ethanol concentration of 45%v/v and 180°C for 30min. Furthermore, the potential amount of biohydrogen was estimated in the top ten rice producing nations using the experimental results. Approximately 355.8kt of hydrogen and 11.3Mt of lignin could globally be produced. Based on a Monte Carlo analysis, the production of biohydrogen from rice straw has the lowest risk in China and the highest in Japan.

A two-stage pretreatment using acidic dioxane followed by dilute hydrochloric acid on sugar production from corn stover

A two-stage pretreatment method was developed to improve sugar recovery in this study.