Acetone-butanol-ethanol (ABE) production by Clostridium beijerinckii from wheat straw hydrolysates: efficient use of penta and hexa carbohydrates

Carbon catabolite repression during the simultaneous utilization of lignocellulose-derived sugars in lactic acid production: Influencing factors and mitigation strategies

Lignocellulose is the most abundant, sustainable, and comparatively economical renewable biomass containing ample fermentable sugars for bio-based chemical production, such as lactic acid (LA). LA is a versatile chemical with substantial global demand. However, the concurrent utilization of mixed sugars derived from lignocellulose, including glucose, xylose, and arabinose, remains a formidable challenge because of the metabolic regulation of carbon catabolite repression (CCR), in which glucose is preferentially utilized over non-glucose sugars, resulting in the loss of carbon resources and a decrease in biorefinery efficacy. Most current studies on CCR have concentrated on elucidating the principles and their impact on specific bacterial species using mixed carbon sources. However, there remains a notable dearth of comprehensive reviews summarizing the underlying principles and corresponding mitigation strategies across other bacterial strains encountering similar challenges. In light of this, this article delineates the possible factors that lead to CCR, including signal transduction and metabolic pathways. Additionally, the fermentation conditions and nutrients are described. Finally, this study proposes appropriate mitigation strategies to overcome the aforementioned obstacles and presents new insights into the rapid and simultaneous consumption of mixed sugars to bolster the production yields of biofuels and chemicals in the future.

The Potential of Brewer’s Spent Grain in the Circular Bioeconomy: State of the Art and Future Perspectives

Brewer’s spent grain (BSG) accounts for approximately 85% of the total mass of solid by-products in the brewing industry and represents an important secondary raw material of future biorefineries. Currently, the main application of BSG is limited to the feed and food industry. There is a strong need to develop sustainable pretreatment and fractionation processes to obtain BSG hydrolysates that enable efficient biotransformation into biofuels, biomaterials, or biochemicals. This paper aims to provide a comprehensive insight into the availability of BSG, chemical properties, and current and potential applications juxtaposed with the existing and emerging markets of the pyramid of bio-based products in the context of sustainable and circular bioeconomy. An economic evaluation of BSG for the production of highly valuable products is presented in the context of sustainable and circular bioeconomy targeting the market of Central and Eastern European countries (BIOEAST region).

A Review of the Sustainable Utilization of Rice Residues for Bioenergy Conversion Using Different Valorization Techniques, Their Challenges, and Techno-Economic Assessment

The impetus to predicting future biomass consumption focuses on sustainable energy, which concerns the non-renewable nature of fossil fuels and the environmental challenges associated with fossil fuel burning. However, the production of rice residue in the form of rice husk (RH) and rice straw (RS) has brought an array of benefits, including its utilization as biofuel to augment or replace fossil fuel. Rice residue characterization, valorization, and techno-economic analysis require a comprehensive review to maximize its inherent energy conversion potential. Therefore, the focus of this review is on the assessment of rice residue characterization, valorization approaches, pre-treatment limitations, and techno-economic analyses that yield a better biofuel to adapt to current and future energy demand. The pre-treatment methods are also discussed through torrefaction, briquetting, pelletization and hydrothermal carbonization. The review also covers the limitations of rice residue utilization, as well as the phase structure of thermochemical and biochemical processes. The paper concludes that rice residue is a preferable sustainable biomass option for both economic and environmental growth.

Recent advances in lignocellulosic biomass for biofuels and value-added bioproducts - A critical review

Lignocellulosic biomass is a highly renewable, economical, and carbon-neutral feedstock containing sugar-rich moieties that can be processed to produce second-generation biofuels and bio-sourced compounds. However, due to their heterogeneous multi-scale structure, the lignocellulosic materials have major limitations to valorization and exhibit recalcitrance to saccharification or hydrolysis by enzymes. In this context, this review focuses on the latest methods available and state-of-the-art technologies in the pretreatment of lignocellulosic biomass, which aids the disintegration of the complex materials into monomeric units. In addition, this review deals with the genetic engineering techniques to develop advanced strategies for fermentation processes or microbial cell factories to generate desired products in native or modified hosts. Further, it also intends to bridge the gap in developing various economically feasible lignocellulosic products and chemicals using biorefining technologies.

Comparative genome analysis of Clostridium beijerinckii strains isolated from pit mud of Chinese strong flavor baijiu ecosystem

Clostridium beijerinckii is a well-known anaerobic solventogenic bacterium which inhabits a wide range of different niches. Previously, we isolated five butyrate-producing C. beijerinckii strains from pit mud (PM) of strong-flavor baijiu (SFB) ecosystems. Genome annotation of the five strains showed that they could assimilate various carbon sources as well as ammonium to produce acetate, butyrate, lactate, hydrogen, and esters but did not produce the undesirable flavors isopropanol and acetone, making them useful for further exploration in SFB production. Our analysis of the genomes of an additional 233 C. beijerinckii strains revealed an open pangenome based on current sampling and will likely change with additional genomes. The core genome, accessory genome, and strain-specific genes comprised 1567, 8851, and 2154 genes, respectively. A total of 298 genes were found only in the five C. beijerinckii strains from PM, among which only 77 genes were assigned to Clusters of Orthologous Genes categories. In addition, 15 transposase and 12 phage integrase families were found in all five C. beijerinckii strains from PM. Between 18 and 21 genome islands were predicted for the five C. beijerinckii genomes. The existence of a large number of mobile genetic elements indicated that the genomes of the five C. beijerinckii strains evolved with the loss or insertion of DNA fragments in the PM of SFB ecosystems. This study presents a genomic framework of C. beijerinckii strains from PM that could be used for genetic diversification studies and further exploration of these strains.

Orange Bagasse Pellets as a Carbon Source for Biobutanol Production

Due to the environmental concerns, the conversion of lignocellulosic waste can be the key to produce bioproducts and biofuels such as butanol. This study aimed to present and evaluate orange bagasse pellets (OBP) as a carbon source to produce butan-1-ol production via ABE fermentation using Clostridium beijerinckii. These bagasse pellets were characterized, holocellulose (18.99%), alfacellulose (5.37%), hemicellulose (13.62%), lignin (6.16%), pectin (7.21%), protein (3.14%), and was tested under three different pretreatments, which were the following: (a) ultrasound, (b) autohydrolysis, and (c) acid-diluted hydrolysis followed by enzymatic hydrolysis to verify an amount of fermentable total reducing sugars. ANOVA was used and pretreatments followed by enzymatic hydrolysis do not enhance a significant amount of available sugars compared to raw bagasse. The ABE fermentation was carried out in batch reactors at 37 °C under agitation of 160 rpm and anaerobic conditions, using OBP without treatment followed by enzymatic hydrolysis. Using a non-mutant microorganism, the fermentation achieved butyric acid yields of 3762.68 mg L^-1 for control and 2488.82 mg L^-1 for OBP and the butanol production was 63.86 mg L^-1 and 196.80 mg L^-1 for OBP and the control (glucose) assay, respectively. The results of this solvent's production have shown that OBP has the potential for ABE fermentation and a promising feedstock.

Enhanced butanol-hydrogen coproduction by Clostridium beijerinckii with biochar as cell's carrier

In this study, the effects of biochar on the fermentation performance of butanol-hydrogen coproduction by Clostridium beijerinckii F-6 were investigated. Results showed that the biochar with rich porous and graphitized structure can significantly promote the coproduction of butanol and hydrogen. The productivity of butanol and hydrogen reached 0.148 g/L/h and 0.299 mmol/L/h with biochar addition which were 20.23% and 48.76% higher than that in control without biochar addition, respectively. Moreover, the whole energy conversion efficiency calculated based on the heat value showed increment from 43.69% to 51.75% with biochar addition. Combined analysis of organic acids accumulation and oxidation-reduction potential fluctuation proved that biochar can regulate reducing power during fermentation and accelerate the conversion of acid phase to solvent phase. Scanning electron microscope images showed that biochar acted as carriers for cells absorption. Confirmation experiment further proved that biochar enhanced the butanol tolerant ability of Clostridium beijerinckii F-6.

Clostridium sp. as Bio-Catalyst for Fuels and Chemicals Production in a Biorefinery Context

Clostridium sp. is a genus of anaerobic bacteria capable of metabolizing several substrates (monoglycerides, diglycerides, glycerol, carbon monoxide, cellulose, and more), into valuable products. Biofuels, such as ethanol and butanol, and several chemicals, such as acetone, 1,3-propanediol, and butyric acid, can be produced by these organisms through fermentation processes. Among the most well-known species, Clostridium carboxidivorans, C. ragsdalei, and C. ljungdahlii can be highlighted for their ability to use gaseous feedstocks (as syngas), obtained from the gasification or pyrolysis of waste material, to produce ethanol and butanol. C. beijerinckii is an important species for the production of isopropanol and butanol, with the advantage of using hydrolysate lignocellulosic material, which is produced in large amounts by first-generation ethanol industries. High yields of 1,3 propanediol by C. butyricum are reported with the use of another by-product from fuel industries, glycerol. In this context, several Clostridium wild species are good candidates to be used as biocatalysts in biochemical or hybrid processes. In this review, literature data showing the technical viability of these processes are presented, evidencing the opportunity to investigate them in a biorefinery context.

Butanol production from lignocellulosic biomass: revisiting fermentation performance indicators with exploratory data analysis

After just more than 100 years of history of industrial acetone-butanol-ethanol (ABE) fermentation, patented by Weizmann in the UK in 1915, butanol is again today considered a promising biofuel alternative based on several advantages compared to the more established biofuels ethanol and methanol. Large-scale fermentative production of butanol, however, still suffers from high substrate cost and low product titers and selectivity. There have been great advances the last decades to tackle these problems. However, understanding the fermentation process variables and their interconnectedness with a holistic view of the current scientific state-of-the-art is lacking to a great extent. To illustrate the benefits of such a comprehensive approach, we have developed a dataset by collecting data from 175 fermentations of lignocellulosic biomass and mixed sugars to produce butanol that reported during the past three decades of scientific literature and performed an exploratory data analysis to map current trends and bottlenecks. This review presents the results of this exploratory data analysis as well as main features of fermentative butanol production from lignocellulosic biomass with a focus on performance indicators as a useful tool to guide further research and development in the field towards more profitable butanol manufacturing for biofuel applications in the future.

Butanol and butyric acid production from Saccharina japonica by Clostridium acetobutylicum and Clostridium tyrobutyricum with adaptive evolution

Optimal conditions of hyper thermal (HT) acid hydrolysis of the Saccharina japonica was determined to a seaweed slurry content of 12% (w/v) and 144 mM H2SO4 at 160 °C for 10 min. Enzymatic saccharification was carried out at 50 °C and 150 rpm for 48 h using the three enzymes at concentrations of 16 U/mL. Celluclast 1.5 L showed the lowest half-velocity constant (Km) of 0.168 g/L, indicating a higher affinity for S. japonica hydrolysate. Pretreatment yielded a maximum monosaccharide concentration of 36.2 g/L and 45.7% conversion from total fermentable monosaccharides of 79.2 g/L with 120 g dry weight/L S. japonica slurry. High cell densities of Clostridium acetobutylicum and Clostridium tyrobutyricum were obtained using the retarding agents KH2PO4 (50 mM) and NaHCO3 (200 mM). Adaptive evolution facilitated the efficient use of mixed monosaccharides. Therefore, adaptive evolution and retarding agents can enhance the overall butanol and butyric acid yields from S. japonica.

The significance of proline on lignocellulose-derived inhibitors tolerance in Clostridium acetobutylicum ATCC 824

When lignocellulosic biomass was used for acetone-butanol-ethanol (ABE) fermentation, several lignocellulose-derived inhibitors, which are toxic to Clostridium acetobutylicum, were generated during acid hydrolysis process and seriously hindered the industrialization of lignocellulosic butanol. In this study, an engineered strain 824(proABC) with significantly improved tolerance to multiple lignocellulose-derived inhibitors (formic acid and phenolic compounds) was constructed by strengthening the proline biosynthesis. The engineered strain exhibited more effective synthesis ability of proline and scavenging ability of reactive oxygen species (ROS). Consequently, the butanol produced by 824(proABC) was 1-, 2.4- or 3.4-fold higher than that of the wild type strain when using the undetoxified hydrolysate of soybean straw, rice straw or corn straw as the substrate, respectively. Therefore, enhancing the proline biosynthesis can be used as an effective strategy to improve the tolerance of C. acetobutylicum to multiple lignocellulose-derived inhibitors, and 824(proABC) has great potential to produce butanol from undetoxified lignocellulosic hydrolysates.

Dielectric barrier discharge plasma microbubble reactor for pretreatment of lignocellulosic biomass

A novel lignocellulosic biomass pretreatment reactor has been designed and tested to investigate pretreatment efficacy of miscanthus grass. The reactor was designed to optimize the transfer of highly oxidative species produced by dielectric barrier discharge plasma to the liquid phase immediately after generation, by arranging close proximity of the plasma to the gas-liquid interface of microbubbles. The reactor produced a range of reactive oxygen species and reactive nitrogen species, and the rate of production depended on the power source duty cycle and the temperature of the plasma. Ozone and other oxidative species were dispersed efficiently using energy efficient microbubbles produced by fluidic oscillations. A 5% (w/w) miscanthus suspension pretreated for 3 h at 10% duty cycle yielded 0.5% acid soluble lignin release and 26% sugar release post hydrolysis with accelerated pretreatment toward the latter stages of the treatment demonstrating the potential of this approach as an alternative pretreatment method. © 2018 The Authors. AIChE Journal published by Wiley Periodicals, Inc. on behalf of American Institute of Chemical Engineers. © 2018 The Authors. AIChE Journal published by Wiley Periodicals, Inc. on behalf of American Institute of Chemical Engineers. AIChE J, 64: 3803-3816, 2018.

Influence of size reduction treatments on sugar recovery from Norway spruce for butanol production

This study investigated whether the effectiveness of pretreatment is limited by a size reduction of Norway spruce wood in biobutanol production. The spruce was milled, chipped, and mashed for hydrogen peroxide-acetic acid (HPAC) and dilute acid (DA) pretreatment. Sugar recoveries from chipped and mashed spruce after enzymatic hydrolysis were higher than from milled spruce, and the recoveries were not correlated with the spruce fiber length. HPAC pretreatment resulted in almost 100% glucose and 88% total reducing sugars recoveries from chipped spruce, which were apparently higher than DA pretreatment, demonstrating greater effectiveness of HPAC pretreatment on sugar production. The butanol and ABE yield from chipped spruce were 126.5 and 201.2 g/kg pretreated spruce, respectively. The yields decreased with decreasing particle size due to biomass loss in the pretreatment. The results suggested that Norway spruce chipped to a 20 mm length is applicable to the production of platform sugars for butanol fermentation.

State of the art review of biofuels production from lignocellulose by thermophilic bacteria

Biofuels, including ethanol and butanol, are mainly produced by mesophilic solventogenic yeasts and Clostridium species. However, these microorganisms cannot directly utilize lignocellulosic materials, which are abundant, renewable and non-compete with human demand. More recently, thermophilic bacteria show great potential for biofuels production, which could efficiently degrade lignocellulose through the cost effective consolidated bioprocessing. Especially, it could avoid contamination in the whole process owing to its relatively high fermentation temperature. However, wild types thermophiles generally produce low levels of biofuels, hindering their large scale production. This review comprehensively summarizes the state of the art development of biofuels production by reported thermophilic microorganisms, and also concludes strategies to improve biofuels production including the metabolic pathways construction, co-culturing systems and biofuels tolerance. In addition, strategies to further improve butanol production are proposed.

Biobutanol production from brewer's spent grain hydrolysates by Clostridium beijerinckii

Brewer's spent grain (BSG) is a promising feedstock for ABE fermentation. Sulfuric acid pretreatment of BSG at pH 1, 121°C and different solid loadings (5-15% w/w) was investigated. Enzymatic hydrolysis and ABE fermentation by Clostridium beijerinckii DSM 6422 of non-washed and washed pretreated BSG were performed to compare monosaccharide release and butanol production. Pretreatment at 15% w/w BSG resulted in higher availability of sugars in both the enzymatic hydrolysates and pretreatment liquid, and overall yields of 75gbutanol/kg BSG and 95gABE/kg BSG were obtained. When the enzymatic hydrolysate from the washed pretreated BSG was fermented, butanol (6.0±0.5g/L) and ABE (7.4±1.0g/L) concentrations were lower compared with 7.5±0.6g/L butanol and 10.0±0.8g/L ABE from a control. The fermentation of the liquid released in the pretreatment at 15% w/w resulted in a butanol production of 6.6±0.8g/L with a total ABE of 8.6±1.3g/L after overliming.

Modulation of the Acetone/Butanol Ratio during Fermentation of Corn Stover-Derived Hydrolysate by Clostridium beijerinckii Strain NCIMB 8052

Producing biobutanol from lignocellulosic biomass has shown promise to ultimately reduce greenhouse gases and alleviate the global energy crisis. However, because of the recalcitrance of a lignocellulosic biomass, a pretreatment of the substrate is needed which in many cases releases soluble lignin compounds (SLCs), which inhibit growth of butanol-producing clostridia. In this study, we found that SLCs changed the acetone/butanol ratio (A/B ratio) during butanol fermentation. The typical A/B molar ratio during Clostridium beijerinckii NCIMB 8052 batch fermentation with glucose as the carbon source is about 0.5. In the present study, the A/B molar ratio during batch fermentation with a lignocellulosic hydrolysate as the carbon source was 0.95 at the end of fermentation. Structural and redox potential changes of the SLCs were characterized before and after fermentation by using gas chromatography/mass spectrometry and electrochemical analyses, which indicated that some exogenous SLCs were involved in distributing electron flow to C. beijerinckii, leading to modulation of the redox balance. This was further demonstrated by the NADH/NAD⁺ ratio and trxB gene expression profile assays at the onset of solventogenic growth. As a result, the A/B ratio of end products changed significantly during C. beijerinckii fermentation using corn stover-derived hydrolysate as the carbon source compared to glucose as the carbon source. These results revealed that SLCs not only inhibited cell growth but also modulated the A/B ratio during C. beijerinckii butanol fermentation.IMPORTANCE Bioconversion of lignocellulosic feedstocks to butanol involves pretreatment, during which hundreds of soluble lignin compounds (SLCs) form. Most of these SLCs inhibit growth of solvent-producing clostridia. However, the mechanism by which these compounds modulate electron flow in clostridia remains elusive. In this study, the results revealed that SLCs changed redox balance by producing oxidative stress and modulating electron flow as electron donors. Production of H₂ and acetone was stimulated, while butanol production remained unchanged, which led to a high A/B ratio during C. beijerinckii fermentation using corn stover-derived hydrolysate as the carbon source. These observations provide insight into utilizing C. beijerinckii to produce butanol from a lignocellulosic biomass.

Effect of ozonolysis parameters on the inhibitory compound generation and on the production of ethanol by Pichia stipitis and acetone-butanol-ethanol by Clostridium from ozonated and water washed sugarcane bagasse

Sugarcane bagasse (SCB) was ozone pretreated and detoxified by water washing, applying a L9(3)(4) orthogonal array (OA) design of experiments to study the effect of pretreatment parameters (moisture content, ozone concentration, ozone/oxygen flow and particle size) on the generation of inhibitory compounds and on the composition of hydrolysates of ozonated-washed samples. Ozone concentration resulted the highest influence process parameter on delignification and sugar release after washing; while, for inhibitory compound formation, moisture content also had an important role. Ozone expended in pretreatment related directly with sugar release and inhibitory compound formation. Washing detoxification was effective, providing non-inhibitory hydrolysates. Maximum glucose and xylose release yields obtained were 84% and 67%, respectively, for ozonated-washed SCB. Sugar concentration resulted in the decisive factor for biofuels yields. Ethanol production achieved an 88% yield by Pichia stipitis, whereas Clostridium acetobutylicum produced 0.072gBUTANOL/gSUGAR and 0.188gABE/gSUGAR, and, Clostridium beijerinckii 0.165gBUTANOL/gSUGAR and 0.257gABE/gSUGAR.

Enhanced isopropanol and n-butanol production by supplying exogenous acetic acid via co-culturing two clostridium strains from cassava bagasse hydrolysate

The focus of this study was to produce isopropanol and butanol (IB) from dilute sulfuric acid treated cassava bagasse hydrolysate (SACBH), and improve IB production by co-culturing Clostridium beijerinckii (C. beijerinckii) with Clostridium tyrobutyricum (C. tyrobutyricum) in an immobilized-cell fermentation system. Concentrated SACBH could be converted to solvents efficiently by immobilized pure culture of C. beijerinckii. Considerable solvent concentrations of 6.19 g/L isopropanol and 12.32 g/L butanol were obtained from batch fermentation, and the total solvent yield and volumetric productivity were 0.42 g/g and 0.30 g/L/h, respectively. Furthermore, the concentrations of isopropanol and butanol increased to 7.63 and 13.26 g/L, respectively, under the immobilized co-culture conditions when concentrated SACBH was used as the carbon source. The concentrations of isopropanol and butanol from the immobilized co-culture fermentation were, respectively, 42.62 and 25.45 % higher than the production resulting from pure culture fermentation. The total solvent yield and volumetric productivity increased to 0.51 g/g and 0.44 g/L/h when co-culture conditions were utilized. Our results indicated that SACBH could be used as an economically favorable carbon source or substrate for IB production using immobilized fermentation. Additionally, IB production could be significantly improved by co-culture immobilization, which provides extracellular acetic acid to C. beijerinckii from C. tyrobutyricum. This study provided a technically feasible and cost-efficient way for IB production using cassava bagasse, which may be suitable for industrial solvent production.

Butanol production employing fed-batch fermentation by Clostridium acetobutylicum GX01 using alkali-pretreated sugarcane bagasse hydrolysed by enzymes from Thermoascus aurantiacus QS 7-2-4

Sugarcane bagasse (SB) is a potential feedstock for butanol production. However, biological production of butanol from SB is less economically viable. In this study, evaluation of eight pretreatments on SB showed that alkali pretreatment efficiently removed lignin from SB while retaining the intact native structure of the released microfibrils. In total, 99% of cellulose and 100% of hemicellulose in alkali-pretreated SB were hydrolysed by enzymes from Thermoascus aurantiacus. The hydrolysate was used to produce butanol in a fed-batch fermentation by Clostridium acetobutylicum. At 60h, 14.17 and 21.11gL(-1) of butanol and acetone-butanol-ethanol (ABE) were produced from 68.89gL(-1) of total sugars, respectively, yielding 0.22 and 0.33gg(-1) of sugars. The maximum yield of butanol and ABE reached 15.4g and 22.9g per 100g raw SB, respectively. This established process may have potential application for butanol production from SB.

Enhancing bio-butanol production from biomass of Chlorella vulgaris JSC-6 with sequential alkali pretreatment and acid hydrolysis

This study presents a successful butanol production method using alkali and acid pretreated biomass of Chlorella vulgaris JSC-6. The butanol concentration, yield, and productivity were 13.1g/L, 0.58mol/mol sugar, 0.66g/L/h, respectively. Nearly 2.93L/L of biohydrogen was produced during the acidogenesis phase in ABE fermentation. The hydrogen yield and productivity were 0.39mol/mol sugar and 104.2g/L/h respectively. In addition, the high glucose consumption efficiency (97.5%) suggests that the hydrolysate pretreated with NaOH (1%) followed by H2SO4 (3%) did not contain inhibitors to the fermentation. It was also discovered that an excess amount of nitrogen sources arising from hydrolysis of highly concentrated microalgal biomass negatively affected the butanol production. This work demonstrates the technical feasibility of producing butanol from sustainable third-generation feedstock (i.e., microalgal biomass).

Exploring the inhibitory characteristics of acid hydrolysates upon butanol fermentation: A toxicological assessment

This study aimed to quantitatively evaluate the inhibitor tolerance of butanol-producing bacterium Clostridium acetobutylicum. The inhibitory effect of the inhibitors generated by acid pretreatment of biomass feedstock on butanol fermentation decreased in the order of formic acid>oxalic acid>furfural>5-HMF>Na2SO4. C. acetobutylicum has a small tolerance range for furfural (1.06-2.6g/L) and 5-HMF (1.99-2.3g/L). However, the inhibitory effect of Na2SO4 appears to have a wide range, with a chronic toxicity for C. acetobutylicum. All the results could explain, in quantitative manner, the instability of butanol fermentation with C. acetobutylicum from various acid-pretreated feedstocks caused by the fermentation inhibitors.

Adsorption of butanol vapor on active carbons with nitric acid hydrothermal modification

Butanol can be produced from biomass via fermentation and used in vehicles. Unfortunately, butanol is toxic to the microbes, and this can slow fermentation rates and reduce butanol yields. Butanol can be efficiently removed from fermentation broth by gas stripping, thereby preventing its inhibitory effects. Original active carbon (AC) and AC samples modified by nitric acid hydrothermal modification were assessed for their ability to adsorb butanol vapor. The specific surface area and oxygen-containing functional groups of AC were tested before and after modification. The adsorption capacity of unmodified AC samples was the highest. Hydrothermal oxidation of AC with HNO3 increased the surface oxygen content, Brunauer-Emmett-Teller (BET) surface area, micropore, mesopore and total pore volume of AC. Although the pore structure and specific surface area were greatly improved after hydrothermal oxidization with 4M HNO3, the increased oxygen on the surface of AC decreased the dynamic adsorption capacity.

Acetone-butanol-ethanol production in a novel continuous flow system

This study investigates the potential of using a novel integrated biohydrogen reactor clarifier system (IBRCS) for acetone-butanol-ethanol (ABE) production using a mixed culture at different organic loading rates (OLRs). The results of this study showed that using a setting tank after the fermenter and recycle the settled biomass to the fermenter is a practical option to achieve high biomass concentration in the fermenter and thus sustainable ABE fermentation in continuous mode. The average ABE concentrations of 2.3, 7.0, and 14.6gABE/L which were corresponding to ABE production rates of 0.4, 1.4, and 2.8gABE/Lreactorh were achieved at OLRs of 21, 64, and 128gCOD/Lreactord, respectively. The main volatile fatty acids components in the effluent were acetic, propionic, and butyric acids. Acetic acid was the predominant component in the OLR-1, while butyric acid was the predominant acid in OLRs 2 and 3.

Efficient acetone-butanol-ethanol production by Clostridium beijerinckii from sugar beet pulp

Sugar beet pulp (SBP) has been investigated as a promising feedstock for ABE fermentation by Clostridium beijerinckii. Although lignin content in SBP is low, a pretreatment is needed to enhance enzymatic hydrolysis and fermentation yields. Autohydrolysis at pH 4 has been selected as the best pretreatment for SBP in terms of sugars release and acetone and butanol production. The best overall sugars release yields from raw SBP ranged from 66.2% to 70.6% for this pretreatment. The highest ABE yield achieved was 0.4g/g (5.1g/L of acetone and 6.6g/L butanol) and 143.2g ABE/kg SBP (62.3g acetone and 80.9g butanol) were obtained when pretreated SBP was enzymatically hydrolyzed at 7.5% (w/w) solid loading. Higher solid loadings (10%) offered higher acetone and butanol titers (5.8g/L of acetone and 7.8g/L butanol). All the experiments were carried out under not-controlling pH conditions reaching about 5.3 in the final samples.

Lignin degradation in corn stalk by combined method of H2O2 hydrolysis and Aspergillus oryzae CGMCC5992 liquid-state fermentation

BACKGROUND

Lignin peroxidase (LiP) is the primary enzyme responsible for lignin degradation. In our previous work, in order to shorten the pretreatment time and increase the lignin degradation, we have pretreated the corn stalk (CS) using a combination of Aspergillus oryzae CGMCC 5992 solid-state fermentation and H2O2 treatment.

RESULTS

In the present study, one-factor-at-a-time design and response surface design were applied to optimize the nutritional constituents for LiP production in liquid-state fermentation by A. oryzae CGMCC 5992 and the conditions for CS degradation by A. oryzae CGMCC 5992. The optimal medium included CS of 30 g/L, glucose of 4.6 g/L, sodium nitrate of 1.2 g/L, corn steep liquor of 1 g/L, yeast extract of 1.2 g/L, and vitamin B1 of 0.15 g/L. Under these optimal conditions, the LiP production reached its maximum of 652.34 U/L. The optimal condition for CS degradation included CS of 20 g, A. oryzae CGMCC 5992 broth of 50 mL, 1.5 % H2O2 solution of 80 mL, H2O2 flow rate of 0.4 mL/min, water volume of 240 mL (water/material ratio of 12:1), hydrolysis temperature of 39 °C, and hydrolysis time of 8 h. Before hydrolysis, CS and water were pretreated at 113 °C for 11 min. Under these optimal conditions, the sugar yield reached its maximum of 46.28 %.

CONCLUSIONS

Our newly developed method had great advantages in pretreatment of CS due to its quickness, convenience, safety, no special equipment and high sugar yield.Graphical abstractThe schematic diagram of corn straw hydrolysis.

Biobutanol production by Clostridium acetobutylicum using xylose recovered from birch Kraft black liquor

Acetone-butanol-ethanol (ABE) fermentation was studied using acid-hydrolyzed xylan recovered from hardwood Kraft black liquor by CO2 acidification as the only carbon source. Detoxification of hydrolyzate using activated carbon was conducted to evaluate the impact of inhibitor removal and fermentation. Xylose hydrolysis yields as high as 18.4% were demonstrated at the highest severity hydrolysis condition. Detoxification using active carbon was effective for removal of both phenolics (76-81%) and HMF (38-52%). Batch fermentation of the hydrolyzate and semi-defined P2 media resulted in a total solvent yield of 0.12-0.13g/g and 0.34g/g, corresponding to a butanol concentration of 1.8-2.1g/L and 7.3g/L respectively. This work is the first study of a process for the production of a biologically-derived biofuel from hemicelluloses solubilized during Kraft pulping and demonstrates the feasibility of utilizing xylan recovered directly from industrial Kraft pulping liquors as a feedstock for biological production of biofuels such as butanol.