Current advances on fermentative biobutanol production using third generation feedstock

Shape-Selective Molecular Separations Enabled by Rigid and Interconnected Confinements Engineered in Conjugated Microporous Polymer Membranes

Separating molecules with similar sizes but different shapes is essential yet challenging. Here, conjugated microporous polymer (CMP) membranes with narrowly distributed network pores are prepared by diffusion-modulated electropolymerization. This approach precisely controls the monomer diffusion and coupling processes, regulating the crosslinking degree to prevent broad aggregate pores and microporous defects. By altering carbazole-based backbones, pore size and pore connectivity are adjusted. The rigid and interconnected confinements restrict molecular rotation and vibration, enforcing consistent shapes and orientations. This enables the separation of solute molecules (≈1000 g mol-1) with linear and bulky shapes, achieving separation factors of up to 134. When pore size is reduced to angstrom scale (≈5 Å), molecular shape significantly influences organic liquid transport. The CMP membranes demonstrate all-liquid phase separation of linear/branched alkane isomers (<100 g mol-1), enriching hexane to 63.35 mole% from equimolar isomer mixture and achieving permeance orders of magnitude higher than those of state-of-the-art membranes.

Biobutanol production from underutilized substrates using Clostridium: Unlocking untapped potential for sustainable energy development

The increasing demand for sustainable energy has brought biobutanol as a potential substitute for fossil fuels. The Clostridium genus is deemed essential for biobutanol synthesis due to its capability to utilize various substrates. However, challenges in maintaining fermentation continuity and achieving commercialization persist due to existing barriers, including butanol toxicity to Clostridium, low substrate utilization rates, and high production costs. Proper substrate selection significantly impacts fermentation efficiency, final product quality, and economic feasibility in Clostridium biobutanol production. This review examines underutilized substrates for biobutanol production by Clostridium, which offer opportunities for environmental sustainability and a green economy. Extensive research on Clostridium, focusing on strain development and genetic engineering, is essential to enhance biobutanol production. Additionally, critical suggestions for optimizing substrate selection to enhance Clostridium biobutanol production efficiency are also provided in this review. In the future, cost reduction and advancements in biotechnology may make biobutanol a viable alternative to fossil fuels.

Third generation biobutanol production by Clostridium beijerinckii in a medium containing mixotrophically cultivated Dunaliella salina biomass

This study aims the third generation biobutanol production in P2 medium supplemented D. salina biomass mixotrophically cultivated with marble waste (MW). The wastes derived from the marble industry contain approximately 90% of carbon-rich compounds. Microalgal growth in mixotrophic conditions was optimized in the 0.4-2 g/L of MW concentration range. The highest microalgal concentration was obtained as 0.481 g/L in the presence of 1 g/L MW. Furthermore, some important parameters for the production of biobutanol, such as microalgal cultivation conditions, initial mixotrophic microalgal biomass loading (50-300 g/L), and fermentation time (24-96 h) were optimized. The highest biobutanol, total ABE, biobutanol yield and productivity were determined as 11.88 g/L, 13.89 g/L, 0.331 g/g and 0.165 g/L/h at the end of 72 h in P2 medium including 60 g/L glucose and 200 g/L microalgal biomass cultivated in 1 g/L MW, respectively. The results show that D. salina is a suitable raw material for supporting Clostridium beijerinckii DSMZ 6422 cells on biobutanol production. To the best of our knowledge, this is the first study on the use of MW which is a promising feedstock on the mixotrophic cultivation of D. salina for biobutanol production.

Sustainable production of biofuels from the algae-derived biomass

The worldwide fossil fuel reserves are rapidly and continually being depleted as a result of the rapid increase in global population and rising energy sector needs. Fossil fuels should not be used carelessly since they produce greenhouse gases, air pollution, and global warming, which leads to ecological imbalance and health risks. The study aims to discuss the alternative renewable energy source that is necessary to meet the needs of the global energy industry in the future. Both microalgae and macroalgae have great potential for several industrial applications. Algae-based biofuels can surmount the inadequacies presented by conventional fuels, thereby reducing the 'food versus fuel' debate. Cultivation of algae can be performed in all three systems; closed, open, and hybrid frameworks from which algal biomass is harvested, treated and converted into the desired biofuels. Among these, closed photobioreactors are considered the most efficient system for the cultivation of algae. Different types of closed systems can be employed for the cultivation of algae such as stirred tank photobioreactor, flat panel photobioreactor, vertical column photobioreactor, bubble column photobioreactor, and horizontal tubular photobioreactor. The type of cultivation system along with various factors, such as light, temperature, nutrients, carbon dioxide, and pH affect the yield of algal biomass and hence the biofuel production. Algae-based biofuels present numerous benefits in terms of economic growth. Developing a biofuel industry based on algal cultivation can provide us with a lot of socio-economic advantages contributing to a publicly maintainable result. This article outlines the third-generation biofuels, how they are cultivated in different systems, different influencing factors, and the technologies for the conversion of biomass. The benefits provided by these new generation biofuels are also discussed. The development of algae-based biofuel would not only change environmental pollution control but also benefit producers' economic and social advancement.

Glucose Conversion for Biobutanol Production from Fresh Chlorella sorokiniana via Direct Enzymatic Hydrolysis

Microalgae, which accumulate considerable carbohydrates, are a potential source of glucose for biofuel fermentation. In this study, we investigated the enzymatic hydrolysis efficiency of wet microalgal biomass compared with freeze-dried and oven-dried biomasses, both with and without an acidic pretreatment. With the dilute sulfuric acid pretreatment followed by amy (α-amylase and amyloglucosidase) and cellulase hydrolysis, approximately 95.4% of the glucose was recovered; however, 88.5% was released by the pretreatment with 2% (w/v) sulfuric acid, which indicates the potential of the acids for direct saccharification process. There were no considerable differences in the glucose yields among the three kinds of materials. In the direct amy hydrolysis without any pretreatment, a 78.7% glucose yield was obtained, and the addition of cellulase had no significant effect on the hydrolysis to glucose. Compared with the oven-dried biomass, the wet biomass produced a substantially higher glucose yield, which is possibly because the cross-linked cells of the oven-dried biomass prevented the accessibility of the enzymes. According to the results, the fresh microalgal biomass without cell disruption can be directly used for enzymatic hydrolysis to produce glucose. The enzymatic hydrolysate of the wet microalgal biomass was successfully used for acetone–butanol–ethanol (ABE) fermentation, which produced 7.2 g/L of ABE, indicating the application potential of wet microalgae in the bioalcohol fuel fermentation process.

Towards enhancement of fungal hydrolytic enzyme cocktail using waste algal biomass of Oscillatoria obscura and enzyme stability investigation under the influence of iron oxide nanoparticles

Development of low-cost and economic cellulase production is among the key challenges due to its broad industrial applications. One of the main topics of research pertaining to sustainable biomass waste based biorefinaries is the development of economic cellulase production strategies. The main cause of the increase in cellulase production costs is the use of commercial substrates; as a result, the cost of any cellulase-based bioprocess can be decreased by employing a productive, low-cost substrate. The goal of the current study is to develop low-cost cellulase using the carbohydrate-rich, renewable, and widely accessible cyanobacteria algae Oscillatoria obscura as the production substrate. Maximum cellulase was produced utilising the fungus Rhizopus oryzae at substrate concentration of 7.0 g among various tested concentrations of algal biomass. Maximum production rates of 22 IU/gds FP, 105 IU/gds BGL, and 116 IU/gds EG in 72 h were possible under optimal conditions and substrate concentration. Further investigations on the crude enzyme's stability in the presence of iron oxide nanoparticles (IONPs) revealed that it was thermally stable at 60 °C for up to 8 h. Additionally, the crude enzyme demonstrated pH stability by maintaining its complete activity at pH 6.0 for 8 h in the presence of the optimal dose of 15 mg IONPs. The outcomes of this research may be used to investigate the possibility of producing such enzymes in large quantities at low cost for industrial use.

Biobutanol production from sustainable biomass process of anaerobic ABE fermentation for industrial applications

The growing population increases the need to develop advanced biological methods for utilizing renewable and sustainable resources to produce environmentally friendly biofuels. Currently, energy resources are limited for global demand and are constantly depleting and creating environmental problems. Some higher chain alcohols, like butanol and ethanol, processing similar properties to gasoline, can be alternate sources of biofuel. However, the industrial production of these alcohols remains challenging because they cannot be efficiently produced by microbes naturally. Therefore, butanol is the most interesting biofuel candidate with a higher octane number produced naturally by microbes through Acetone-Butanol-Ethanol fermentation. Feedstock selection as the substrate is the most crucial step in biobutanol production. Lignocellulosic biomass has been widely used to produce cellulosic biobutanol using agricultural wastes and residue. Specific necessary pretreatments, fermentation strategies, bioreactor designing and kinetics, and modeling can also enhance the efficient production of biobutanol. The recent genetic engineering approaches of gene knock in, knock out, and overexpression to manipulate pathways can increase the production of biobutanol in a user friendly host organism. So far various genetic manipulation techniques like antisense RNA, TargeTron Technology and CRISPR have been used to target Clostridium acetobutylicum for biobutanol production. This review summarizes the recent research and development for the efficient production of biobutanol in various aspects.

An Alternative Approach to Improve the Butanol Production Efficiency from Sweet Sorghum Stem Juice Using Immobilized Cells Combined with an In Situ Gas Stripping System

The effects of the nitrogen source and buffers used in butanol production with Clostridium beijerinckii TISTR 1461 from sweet sorghum stem juice (SSJ) containing 60 g/L of total sugar were first studied in this paper. Among the various nitrogen sources (dried spent yeast, urea, ammonium acetate, ammonium sulfate), urea was found to be the most suitable for butanol production. SSJ supplemented with urea (0.64 g/L) and cocktail buffers (KH2PO4, 0.5 g/L; K2HPO4, 0.5 g/L; ammonium acetate, 2.2 g/L) gave the highest butanol concentration (PB, 10.13 g/L). Then, the capability of immobilized C. beijerinckii TISTR 1461 cells for butanol fermentation was investigated. Two residual waste materials were examined as immobilized cell carriers. Bamboo chopstick pieces were more appropriate as carriers for cell immobilization than cigarette filter tips. The PB value of the immobilized cells on the bamboo chopstick pieces was ~13% higher than that on the cigarette filter tips. Using the response surface methodology (RSM), 1.9 cm bamboo chopstick pieces with a carrier loading of 1:32 (w/v) were the optimum conditions for cell immobilization for butanol production. Under these conditions, the PB value was 11.62 g/L. To improve the butanol production efficiency, a gas stripping system (GS) was connected to the fermenter. It was found that the PB (14.02 g/L) and butanol productivity (QB, 0.29 g/L·h) values improved by ~21% compared to butanol fermentation using no gas stripping.

A consolidated review of commercial-scale high-value products from lignocellulosic biomass

For decades, lignocellulosic biomass has been introduced to the public as the most important raw material for the environmentally and economically sustainable production of high-valued bioproducts by microorganisms. However, due to the strong recalcitrant structure, the lignocellulosic materials have major limitations to obtain fermentable sugars for transformation into value-added products, e.g., bioethanol, biobutanol, biohydrogen, etc. In this review, we analyzed the recent trends in bioenergy production from pretreated lignocellulose, with special attention to the new strategies for overcoming pretreatment barriers. In addition, persistent challenges in developing for low-cost advanced processing technologies are also pointed out, illustrating new approaches to addressing the global energy crisis and climate change caused by the use of fossil fuels. The insights given in this study will enable a better understanding of current processes and facilitate further development on lignocellulosic bioenergy production.

Field test of water-net based wastewater treatment for nutrient removal and bioethanol production

In this study, an open pond constructed in Myanmar, a region with tropical climate and favorable environmental conditions for algae growth, was considered to conduct field experiments on sewage inflow river water. The nutrient removal efficiency and productivity of Hydrodictyon reticulatum (H. reticulatum) were analyzed, and the maximum fermentation limit concentration for bioethanol production was determined. Three ponds were operated in batch mode to investigate the effect of light intensity. Photoinhibition was caused due to excessive light intensity in summer season in the region with tropical climate resulting in reduced facility efficiency in the absence of shade. For light blocking, a transparent film was found to be more effective than a translucent film. In the transparent film shading facility, the nitrogen and phosphorus removal efficiencies were maintained above 76% and 81%, respectively, and the productivity of H. reticulatum was 2.27 g m^-2 d^-1. For a raceway open pond facility shaded with transparent film, the performance was evaluated based on hydraulic retention time (HRT), and the productivity of algae was found to increase with increasing supply of nitrogen and phosphorous. Maximum biomass production of 3.21 g m^-2 d^-1 was observed with an HRT of 3 d, suggesting the possibility of long-term operation. As a result of evaluating the ethanol production based on the initial concentration of H. reticulatum, the yield of bioethanol at the initial reducing sugar content of 120 g L^-1 was 89.4%, but bioethanol production was only 8.9 g L^-1.

Production of butanol from lignocellulosic biomass: recent advances, challenges, and prospects

Due to energy and environmental concerns, biobutanol is gaining increasing attention as an alternative renewable fuel owing to its desirable fuel properties. Biobutanol production from lignocellulosic biomass through acetone-butanol-ethanol (ABE) fermentation has gained much interest globally due to its sustainable supply and non-competitiveness with food, but large-scale fermentative production suffers from low product titres and poor selectivity. This review presents recent developments in lignocellulosic butanol production, including pretreatment and hydrolysis of hemicellulose and cellulose during ABE fermentation. Challenges are discussed, including low concentrations of fermentation sugars, inhibitors, detoxification, and carbon catabolite repression. Some key process improvements are also summarised to guide further research and development towards more profitable and commercially viable butanol fermentation.

Utilization of agricultural lignocellulosic wastes for biofuels and green diesel production

The ever-growing human population has resulted in the expansion of agricultural activity; evident by the deforestation of rainfoamrests as a means of acquiring fertile land for crops. The crops and fruits produced by such means should be utilized completely; however, there are still losses and under-exploitation of these produces which has resulted in wastes being mounted in landfills. These underutilized agricultural wastes including vegetables and fruits can serve as a potential source for biofuels and green diesel. This paper discusses the main routes (e.g., biological and thermochemical) for producing biofuels such as bioethanol, biodiesel, biogas, bio-oil and green diesel from underutilized crops by emphasizing recent technological innovations for improving biofuels and green diesel yields. The future prospects of a successful production of biofuels and green diesel by this source are also explained. Underutilized lignocelluloses including fruits and vegetables serve as a prospective biofuel and green diesel generation source for the future prosperity of the biofuel industry.

Biohydrogen production from microalgae for environmental sustainability

Hydrogen as a clean energy that is conducive to energy and environmental sustainability, playing a significant role in the alleviation of global climate change and energy crisis. Biohydrogen generation from microalgae has been reported as a highly attractive approach that can produce a benign clean energy carrier to achieve carbon neutrality and bioenergy sustainability. Thus, this review explored the mechanism of biohydrogen production from microalgae containing direct biophotolysis, indirect biophotolysis, photo fermentation, and dark fermentation. In general, dark fermentation of microalgae for biohydrogen production is relatively better than photo fermentation, biophotolysis, and microbial electrolysis, because it is able to consecutively generate hydrogen and is not reliant on energy supplied by natural sunlight. Besides, this review summarized potential algal strains for hydrogen production focusing on green microalgae and cyanobacteria. Moreover, a thorough review process was conducted to present hydrogen-producing enzymes targeting biosynthesis and localization of enzymes in microalgae. Notably, the most powerful hydrogen-producing enzymes are [Fe-Fe]-hydrogenases, which have an activity nearly 10-100 times better than [Ni-Fe]-hydrogenases and 1000 times better than nitrogenases. In addition, this work highlighted the major factors affecting low energy conversion efficiency and oxygen sensitivity of hydrogen-producing enzymes. Noting that the most practical pathway of biohydrogen generation was sulfur-deprivation compared with phosphorus, nitrogen, and magnesium deficiency. Further discussions in this work summarized the recent advancement in biohydrogen production from microalgae such as genetic engineering, microalgae-bacteria consortium, electro-bio-hydrogenation, and nanomaterials for developing enzyme stability and hydrolytic efficiency. More importantly, this review provided a summary of current limitations and future perspectives on the sustainable production of biohydrogen from microalgae.

Algal biomass valorisation to high-value chemicals and bioproducts: Recent advances, opportunities and challenges

Algae are considered promising biomass resources for biofuel production. However, some arguments doubt the economical and energetical feasibility of algal cultivation, harvesting, and conversion processes. Beyond biofuel, value-added bioproducts can be generated via algae conversion, which would enhance the economic feasibility of algal biorefineries. This review primarily focuses on valuable chemical and bioproduct production from algae. The methods for effective recovery of valuable algae components, and their applications are summarized. The potential routes for the conversion of lipids, carbohydrates, and proteins to valuable chemicals and bioproducts are assessed from recent studies. In addition, this review proposes the following challenges for future algal biorefineries: (1) utilization of naturally grown algae instead of cultivated algae; (2) fractionation of algae to individual components towards high-selectivity products; (3) avoidance of humin formation from algal carbohydrate conversion; (4) development of strategies for algal protein utilisation; and (5) development of efficient processes for commercialization and industrialization.

State of art of valorising of diverse potential feedstocks for the production of alcohols and ethers: Current changes and perspectives

Alcohols could be the biggest factor for the improvement of world biofuel economy in the present century due to their excellent properties compared to petroleum products. The primary concerns of sustainable alcohol production for meeting the growing energy demand owing to the selection of viable feedstock and this might enhance the opportunities for developing numerous advanced techniques. In this review, the valorization of alcohol production from several production routes has been exposed by covering the traditional routes to the present state of the art technologies. Even though the fossil fuel conversion could be dominant method for methanol production, many recent innovations like photo electrochemical synthesis and electrolysis methods might play vital role in production of renewable methanol in future. There have been several production routes for production of ethanol and among which the fermentation of lignocellulose biomass would be the ultimate choice for large scale shoot up. The greenhouse gas recovery in the form of alcohols through electrochemistry technique and hydrogenation method are the important methods for commercialization of alcohols in future. It is also observed that algae based renewable bio-alcohols is highly influenced by carbohydrate content and sustainable approaches in algae conversion to bio-alcohols would bring greater demand in future market. There is a lack of innovation in higher alcohols production in single process and this could be bounded by combining dehydrogenation and decarboxylation techniques. Finally, this review enlists the opportunities and challenges of existing alcohols production and recommended the possible routes for making significant enhancement in production.

Cellulase production and efficient saccharification of biomass by a new mutant Trichoderma afroharzianum MEA-12

BACKGROUND

Cellulase plays a key role in converting cellulosic biomass into fermentable sugar to produce chemicals and fuels, which is generally produced by filamentous fungi. However, most of the filamentous fungi obtained by natural breeding have low secretory capacity in cellulase production, which are far from meeting the requirements of industrial production. Random mutagenesis combined with adaptive laboratory evolution (ALE) strategy is an effective method to increase the production of fungal enzymes.

RESULTS

This study obtained a mutant of Trichoderma afroharzianum by exposures to N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), Ethyl Methanesulfonate (EMS), Atmospheric and Room Temperature Plasma (ARTP) and ALE with high sugar stress. The T. afroharzianum mutant MEA-12 produced 0.60, 5.47, 0.31 and 2.17 IU/mL FPase, CMCase, pNPCase and pNPGase, respectively. These levels were 4.33, 6.37, 4.92 and 4.15 times higher than those of the parental strain, respectively. Also, it was found that T. afroharzianum had the same carbon catabolite repression (CCR) effect as other Trichoderma in liquid submerged fermentation. In contrast, the mutant MEA-12 can tolerate the inhibition of glucose (up to 20 mM) without affecting enzyme production under inducing conditions. Interestingly, crude enzyme from MEA-12 showed high enzymatic hydrolysis efficiency against three different biomasses (cornstalk, bamboo and reed), when combined with cellulase from T. reesei Rut-C30. In addition, the factors that improved cellulase production by MEA-12 were clarified.

CONCLUSIONS

Overall, compound mutagenesis combined with ALE effectively increased the production of fungal cellulase. A super-producing mutant MEA-12 was obtained, and its cellulase could hydrolyze common biomasses efficiently, in combination with enzymes derived from model strain T. reesei, which provides a new choice for processing of bioresources in the future.

Biofuels and biorefineries: Development, application and future perspectives emphasizing the environmental and economic aspects

The fossil fuel utilization adversely affected the environmental health due to the rising emission levels of greenhouse gases. Consequently, the challenges of climate change loaded great stress on renewable energy sources. It is noted that extreme consumption of fossil fuels increased the earth temperature by 1.9 °C that adversely influenced the life and biodiversity. Biorefinery is the sustainable process for the production of biofuels and other bio-products from biomass feedstock using different conversion technologies. Biofuel is an important component of renewable energy sources contributing to overall carbon-neutral energy system. Studies reported that on global scale, over 90% of petroleum goods could be produced from renewable resources by 2023, whereas, 33% chemicals, and 50% of the pharmaceutical market share is also expected to be bio-based. This study details the brief review of operation, development, application, limitations, future perspectives, circular bioeconomy, and life cycle assessment of biorefinery. The economic and environmental aspects of biofuels and biorefineries are briefly discussed. Lastly, considering the present challenges, the future perspectives of biofuels and biorefineries are highlighted.

Dehydration of n-butanol on phosphate-modified carbon nanotubes: active site and intrinsic catalytic activity

Dehydration of n-butanol (nB) to corresponding olefins (butene) is an important reaction route to realize efficient utilization of bulk bio-alcohols.

Electrochemical tuning of alcohol oxidase and dehydrogenase catalysis via biosensing towards butanol-1 detection in fermentation media

A novel approach for electrochemical tuning of alcohol oxidase (AOx) and alcohol dehydrogenase (ADH) biocatalysis towards butanol-1 oxidation by incorporating enzymes in various designs of amperometric biosensors is presented. The biosensors were developed by using commercial graphene oxide-based screen-printed electrodes and varying enzyme producing strains, encapsulation approaches (layer-by-layer (LbL) or one-step electrodeposition (EcD)), layers composition and structure, operating conditions (applied potential values) and introducing mediators (Meldola Blue and Prussian Blue) or Pd-nanoparticles (Pd-NPs). Simultaneous analysis/screening of multiple crucial system parameters during the enzyme engineering process allowed to identify within a period of one month that four out of twelve proposed designs demonstrated a good signal reproducibility and linear response (up to 14.6 mM of butanol) under very low applied potentials (from -0.02 to -0.32 V). Their mechanical stability was thoroughly investigated by multi-analytical techniques prior to butanol determination in cell-free samples from an anaerobic butanol fermentation. The EcD-based biosensor that incorporates ADH, NAD⁺, Pd-NPs and Nafion showed no loss of enzyme activity after preparation and demonstrated capabilities towards low potential (-0.12 V) detection of butanol-1 in fermentation medium (4 mM) containing multiple electroactive species with almost 15 times enhanced sensitivity (0.2282 μA/mM ± 0.05) when compared to the LbL design. Furthermore, the ADH-Nafion bonding for the S. cerevisiae strain was confirmed to be 3 times higher than for E. coli.

Genomics and lipidomics analysis of the biotechnologically important oleaginous red yeast Rhodotorula glutinis ZHK provides new insights into its lipid and carotenoid metabolism

Background

Rhodotorula glutinis is recognized as a biotechnologically important oleaginous red yeast, which synthesizes numerous meritorious compounds with wide industrial usages. One of the most notable properties of R. glutinis is the formation of intracellular lipid droplets full of carotenoids. However, the basic genomic features that underlie the biosynthesis of these valuable compounds in R. glutinis have not been fully documented. To reveal the biotechnological potential of R. glutinis, the genomics and lipidomics analysis was performed through the Next-Generation Sequencing and HPLC-MS-based metabolomics technologies.

Results

Here, we firstly assemble the genome of R. glutinis ZHK into 21.8 Mb, containing 30 scaffolds and 6774 predicted genes with a N50 length of 14, 66,672 bp and GC content of 67.8%. Genome completeness assessment (BUSCO alignment: 95.3%) indicated the genome assembly with a high-quality features. According to the functional annotation of the genome, we predicted several key genes involved in lipids and carotenoids metabolism as well as certain industrial enzymes biosynthesis. Comparative genomics results suggested that most of orthologous genes have underwent the strong purifying selection within the five Rhodotorula species, especially genes responsible for carotenoids biosynthesis. Furthermore, a total of 982 lipids were identified using the lipidomics approaches, mainly including triacylglycerols, diacylglyceryltrimethylhomo-ser and phosphatidylethanolamine.

Conclusion

Using whole genome shotgun sequencing, we comprehensively analyzed the genome of R. glutinis and predicted several key genes involved in lipids and carotenoids metabolism. By performing comparative genomic analysis, we show that most of the ortholog genes have undergone strong purifying selection within the five Rhodotorula species. Furthermore, we identified 982 lipid species using lipidomic approaches. These results provided valuable resources to further advance biotechnological applications of R .glutinis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-020-07244-z.

CO2-cofed catalytic pyrolysis of tea waste over Ni/SiO2 for the enhanced formation of syngas

To valorize tea waste (TW), catalytic pyrolysis was done as a practical measure for recovering energy as a form of syngas. Considering CO₂ as a reactive gas medium in place of conventional pyrolysis gas, a sustainable pyrolysis platform was established. In addition, mechanistic effectiveness of CO₂ on TW pyrolysis was examined. In the presence of CO₂, homogeneous reaction with volatile organic compounds (VOCs) derived from TW pyrolysis contributed to CO formation. To enhance the formation of syngas at low pyrolysis temperature, catalytic pyrolysis over a Ni/SiO₂ was investigated. The synergistic effects of Ni/SiO₂ catalyst and CO₂ promoted thermal cracking of VOCs and further homogeneous reaction with CO₂, thereby resulting in the substantial enhancement (28 times more) of H₂ and CO production than non-catalytic pyrolysis. It was also confirmed that CO₂ could be considered a reactive gas medium to produce biochar (34-35 wt.% yield), having competitive porosity and surface area, in comparison to that from pyrolysis in N₂. Therefore, CO₂ can be employed to build a sustainable waste conversion platform for energy and biochar production through pyrolysis instead of using N₂.

Role of efflux in enhancing butanol tolerance of bacteria

N-butanol, a valued solvent and potential fuel extender, could possibly be produced by fermentation using either native producers, i.e. solventogenic Clostridia, or engineered platform organisms such as Escherichia coli or Pseudomonas species, if the main process obstacle, a low final butanol concentration, could be overcome. A low final concentration of butanol is the result of its high toxicity to production cells. Nevertheless, bacteria have developed several mechanisms to cope with this toxicity and one of them is active butanol efflux. This review presents information about a few well characterized butanol efflux pumps from Gram-negative bacteria (P. putida and E. coli) and summarizes knowledge about putative butanol efflux systems in Gram-positive bacteria.

Recent Development of Extremophilic Bacteria and Their Application in Biorefinery

The biorefining technology for biofuels and chemicals from lignocellulosic biomass has made great progress in the world. However, mobilization of laboratory research toward industrial setup needs to meet a series of criteria, including the selection of appropriate pretreatment technology, breakthrough in enzyme screening, pathway optimization, and production technology, etc. Extremophiles play an important role in biorefinery by providing novel metabolic pathways and catalytically stable/robust enzymes that are able to act as biocatalysts under harsh industrial conditions on their own. This review summarizes the potential application of thermophilic, psychrophilic alkaliphilic, acidophilic, and halophilic bacteria and extremozymes in the pretreatment, saccharification, fermentation, and lignin valorization process. Besides, the latest studies on the engineering bacteria of extremophiles using metabolic engineering and synthetic biology technologies for high-efficiency biofuel production are also introduced. Furthermore, this review explores the comprehensive application potential of extremophiles and extremozymes in biorefinery, which is partly due to their specificity and efficiency, and points out the necessity of accelerating the commercialization of extremozymes.

Pathway dissection, regulation, engineering and application: lessons learned from biobutanol production by solventogenic clostridia

The global energy crisis and limited supply of petroleum fuels have rekindled the interest in utilizing a sustainable biomass to produce biofuel. Butanol, an advanced biofuel, is a superior renewable resource as it has a high energy content and is less hygroscopic than other candidates. At present, the biobutanol route, employing acetone-butanol-ethanol (ABE) fermentation in Clostridium species, is not economically competitive due to the high cost of feedstocks, low butanol titer, and product inhibition. Based on an analysis of the physiological characteristics of solventogenic clostridia, current advances that enhance ABE fermentation from strain improvement to product separation were systematically reviewed, focusing on: (1) elucidating the metabolic pathway and regulation mechanism of butanol synthesis; (2) enhancing cellular performance and robustness through metabolic engineering, and (3) optimizing the process of ABE fermentation. Finally, perspectives on engineering and exploiting clostridia as cell factories to efficiently produce various chemicals and materials are also discussed.

Smart fermentation engineering for butanol production: designed biomass and consolidated bioprocessing systems

There is a renewed interest in acetone-butanol-ethanol (ABE) fermentation from renewable substrates for the sustainable and environment-friendly production of biofuel and platform chemicals. However, the ABE fermentation is associated with several challenges due to the presence of heterogeneous components in the renewable substrates and the intrinsic characteristics of ABE fermentation process. Hence, there is a need to select optimal substrates and modify their characteristics suitable for the ABE fermentation process or microbial strain. This "designed biomass" can be used to establish the consolidated bioprocessing systems. As there are very few reports on designed biomass, the main objectives of this review are to summarize the main challenges associated with ABE fermentation from renewable substrates and to introduce feasible strategies for designing the substrates through pretreatment and hydrolysis technologies as well as through the establishment of consolidated bioprocessing systems. This review offers new insights on improving the efficiency of ABE fermentation from designed renewable substrates.

Microalgal bioenergy production under zero-waste biorefinery approach: Recent advances and future perspectives

In view of the globalization and energy consumption, an economic and sustainable biorefinery model is essential to address the energy security and climate change. From this perspective, renewable biofuel production from microalgae along with a wide range of value-added co-products define its potential as a biorefinery feedstock. However, economic viability of microalgal biorefinery at its current state is not considered sustainable. Reduce, recycle, and reuse of waste derived from algal bioenergy conversion process will lead to an energy efficient and sustainable zero-waste microalgal biorefinery. This review focuses on three major aspects of zero-waste microalgal biorefinery approach; (1) recent advances on microalgal bioenergy conversion processes (chemical, biochemical and thermochemical); (2) mitigation and transformation of liquid and solid waste and (3) techno-economic analysis (TEA) and lifecycle assessment (LCA). In addition, the study also focuses on the challenges and future perspectives for an advanced microalgal biorefinery model.

Biofuel Application as a Factor of Sustainable Development Ensuring: The Case of Russia

Diffusion of the biofuels (BF) using is justified by opening up the opportunities for obtaining fuel and energy from previously inaccessible sources and by the existence of energy-deficient regions, in particular in Russia. Works of different scientists on the problems of creating and using BF were the methodological basis of this study. Information on the state and prospects of the development of renewable energy sources in Russian regions was collected from regulatory documents and was obtained by employing a questionnaire survey. For the study of the collected materials, the different methods of comparative analysis, and the methods of expert assessments were used. The results of the Status-Quo analysis of BF production in Russia have shown that the creation of BF performed relatively successfully. However, there are many more perspectives, connected with expanding the utilization of the different raw materials. Also, the analysis of organizational and economic mechanisms applied for production of BF and the obtained data on several organizations-producers allowed for proposing six indexes for the assessment of the BF production effectiveness. It is suggested that BF production in Russia will contribute to the sustainable development of a number of the country’s regions in the near future.

Life cycle assessment of upgraded microalgae-to-biofuel chains

Two individual chains of microalgae-to-diesel and microalgae-to-butanol were upgraded through process integration and design. According to life cycle assessment (LCA) standards, the two proposed chains were compared in terms of 17 categories of LCA impacts and the sensitivity analysis of LCA impacts on two chains with different lipid or carbohydrate content of microalgae cells was performed. Based on the prescribed specifications and conditions for microalgae cultivation, pretreatment and purity level of the products, LCA analysis revealed that the annual ReCiPe end point score of producing 1 kg biobutanol is lower than that of 1 kg biodiesel by 54.4%. The upgraded microalgae-to-butanol chain could reduce the annual ReCiPe end point score of producing 100 MJ diesel/gasoline from crude oil by 5-10%. The microalgae-to-butanol chain is more ecofriendly than the microalgae-to-diesel chain due to lower LCA impacts such as Climate change human health, Climate change ecosystems, and Fossil depletion.

Production of butanol from biomass: recent advances and future prospects

At present, diminishing oil resources and increasing environmental concerns have led to a shift toward the production of alternative biofuels. In the last few decades, butanol, as liquid biofuel, has received considerable research attention due to its advantages over ethanol. Several studies have focused on the production of butanol through the fermentation from raw renewable biomass, such as lignocellulosic materials. However, the low concentration and productivity of butanol production and the price of raw materials are limitations for butanol fermentation. Moreover, these limitations are the main causes of industrial decline in butanol production. This study reviews butanol fermentation, including the metabolism and characteristics of acetone-butanol-ethanol (ABE) producing clostridia. Furthermore, types of butanol production from biomass feedstock are detailed in this study. Specifically, this study introduces the recent progress on the efficient butanol production of "designed" and modified biomass. Additionally, the recent advances in the butanol fermentation process, such as multistage continuous fermentation, metabolic flow change of the electron carrier supplement, continuous fermentation with immobilization and recycling of cell, and the recent technical separation of the products from the fermentation broth, are described in this study.

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.

Direct transformation of butenes or ethylene into propylene by cascade catalytic reactions

Catalysts and processes involved in the direct conversion of ethylene or n-butenes into propylene are reviewed.

Simultaneous organosolv pretreatment and detoxification of municipal solid waste for efficient biobutanol production

Municipal solid waste (MSW) was used as a source for biobutanol production via acetone, butanol, and ethanol (ABE) fermentation. Organosolv pretreatment was used for simultaneous extraction of inhibitors, particularly tannins, and pretreatment of lignocellulosic fraction prior to hydrolysis. The hydrolysates of the pretreated MSW contained appreciable amounts of sugars and soluble starch together with a tolerable amount of inhibitors for Clostridium acetobutylicum. The hydrolysate obtained from MSW pretreated with 85% ethanol at 120 °C for 30 min fermented to the highest ABE concentration of 13.06 g/L with the yield of 0.33 g/g carbon source. Through this process, 102.4 mg butanol, 40.16 mg acetone, and 13.14 mg ethanol were produced from each g of organic fraction of MSW (OFMSW). The pretreatment at mild conditions with higher ethanol concentration accompanied with the lowest glucose yield (0.145 g/g) and the highest starch recovery resulted in the uppermost ABE yield of 0.16 g/g OFMSW.

Semi-hydrolysis with low enzyme loading leads to highly effective butanol fermentation

To improve butanol fermentation efficiencies, semi-hydrolysate with low enzyme loading using H₂SO₄ pretreated rice straw was designed, which preferably produced cellobiose with xylose (instead of glucose). Fermentation of semi-hydrolysates avoided carbon catabolite repression (CCR) and produced higher butanol yield to enzyme loading (0.0290 g U^-1), a newly proposed parameter, than the conventional glucose-oriented hydrolysate (0.00197 g U^-1). Further, overall butanol productivity was improved from 0.0628 g L^-1 h^-1 to 0.265 g L^-1 h^-1 during fermentation of undetoxified semi-hydrolysate by using high cell density. A novel simultaneously repeated hydrolysis and fermentation (SRHF) was constructed by recycling of enzymes and cells, which further improved butanol yield to enzyme loading by 183% and overall butanol productivity by 6.04%. Thus, semi-hydrolysate with SRHF is a smartly designed biomass for efficient butanol fermentation of lignocellulosic materials.

From vapour to gas: optimising cellulose degradation with gaseous HCl

A cellulose degradation technique utilizing a pressurized HCl gas (up to 100 kPa) device is introduced.