The growing advocacy for greener climates, coupled with increasing global energy demand driven by urbanization and population growth, highlights the need for sustainable solutions. Repurposing food wastes as substrates offers a promising approach to enhancing cleaner energy generation and promoting a circular economy. This study investigated the potential of spent coffee grounds (SC) and biosolids cake (BS) from tea wastes as substrates for producing valuable fuels and chemicals through acetone–ethanol–butanol (ABE) fermentation. Clostridium beijerinckii NCIMB 8052 was used to ferment 100% and 50% hydrolysates derived from Parr-treated enzyme-hydrolyzed (PEH, PEH50), Parr-treated non-hydrolyzed (PNEH, PNEH50), and non-Parr-treated hydrolyzed (NPEH) SC wastes, as well as enzyme-hydrolyzed (BSH, BSH50) and non-hydrolyzed BS wastes (NBH, NBH50). Fermentation of unmodified hydrolysates by C. beijerinckii was poor. Following CaCO3 modification of SC and BS hydrolysates, ABE titer, yield, and productivity increased, with the highest values obtained with PEH50 and NBH. Specifically, CaCO3 modification of SC hydrolysates led to increased butanol titer, yield, and productivity in PEH50, while the NBH exhibited higher butanol yield and productivity than the non-CaCO3-modified hydrolysates. Additionally, H2 gas production with PEH50 and NBH was 1.41- and 1.13-fold higher, respectively, than in other hydrolysates. These findings suggest that SC and BS hydrolysates can be valorized to butanol and hydrogen gas and, thereby, can contribute to global food wastes management, energy sustainability, and cost-effective biofuel production.

Biomanufacturing platform chemicals from food waste through electro-fermentation presents significant commercial potential. This study is the first to investigate the impact of mono- and co-culture fermentation on platform chemical production in both conventional and electro-fermentation systems, highlighting a novel synergistic interaction between bacterial species. Co-culture fermentation demonstrated higher product yields, with butyric acid and butanol emerging as the primary products in conventional fermentation, following the order: butanol > ethanol > acetone. In electro-fermentation, co-culture systems predominantly produced C-2 compounds such as acetone and acetic acid, showcasing their potential for targeted chemical production. A constant cathode potential was maintained during electro-fermentation using an external voltage. Notably, at -0.1 V, butanol production was 12 times higher than at -0.2 V. Mono-culture electro-fermentation primarily produced C-2-C-4 compounds such as acetone, butanol, and butyric acid, while co-cultures achieved higher yields of select acids and alcohols. Additionally, waste samples were valorized with up to 60 % of the efficiency observed in the control experiments, yielding butanol concentrations of 12 g/L after 72 h of fermentation. Moreover, lowering the applied voltage may allow for the replacement of the potentiostat with a simpler fixed DC power supply, improving the overall practicality, cost-efficiency, and scalability of the electro-fermentation system.

Developing efficient strategies to capture carbon dioxide (CO2) is essential to addressing the escalating challenges of global warming. Despite being a major greenhouse gas, CO2 holds significant potential as a sustainable feedstock for chemical production. It can serve as a solvent, a preservative, a raw material for producing fuels, carbonates, polymers, and chemicals, and as a recovery agent for processes such as enhanced coal bed methane and oil recovery. This review highlights significant progress made in CO2 capture and its integration into various industrial applications. While technologies such as adsorption, absorption, membrane separation, and cryogenics have shown promise, challenges related to cost, scalability, and the efficiency of capture and utilization continue to pose significant barriers to widespread adoption. Innovative strategies, including integrated carbon capture and conversion (ICCC) and integrated carbon capture and utilization (ICCU), present promising pathways to reduce costs by combining capture and utilization processes within a single facility. Additionally, catalytic processes and biological systems, such as microalgae and microbial strains (e.g., acetogens), are paving the way for sustainable CO2 conversion into high-value products. Successful large-scale deployment of these technologies will require sustained interdisciplinary collaboration, robust policy frameworks, and increased investment in research and development. Prioritizing sustainable energy development and management offers the potential to significantly reduce anthropogenic CO2 emissions while creating useful products. Advancing these technologies will not only help in mitigating climate change but also promote the transition to a circular carbon economy, which aligns with global sustainability goals.

Biodiesel, derived from non-edible and spent oils, presents a cleaner and more sustainable alternative fuel source for diesel-powered engines. This study investigates the potential of converting non-edible Cupressus sempervirens seed oil into eco-friendly biodiesel using tellurium oxide nanoparticles synthesized with aqueous leaf extract of Calendula arvensis. Advanced techniques were utilized to characterize the catalyst, revealing its crystalline structure, with particles averaging 45nm. Remarkably, the catalyst demonstrated efficient reusability over four cycles, achieving a peak yield of 93% under specific reaction conditions: a methanol to oil molar ratio of 8:1, a catalyst loading of 0.62wt.%, a reaction time of 120min, and a temperature of 92.5oC. Results from nuclear magnetic resonance spectrometry (1H and 13C-NMR) confirmed the successful conversion of the non-edible seed oil into methyl ester. Gas chromatography mass spectrometry (GC-MS) analysis identified 9-octadecenoic acid methyl ester as the predominant fatty acid methyl ester. The fuel properties of the synthesized biodiesel met international standards, with a high flash point (98°C), and ultra-low sulfur content of 0.0002%, highlighting its clean and cost-effective nature. This study contributes significantly to advancing bioproducts for a sustainable bioeconomy, presenting an integrated approach to bioenergy production that simultaneously addresses environmental and socio-economic concerns.

The escalating environmental concerns and burgeoning energy crises, coupled with the desire to achieve net-zero carbon emissions by 2050 to avert potential climate change disaster, highlight the urgent need for sustainable production methods, and innovative technological advancements. Microbial fermentation plays a pivotal role in the pursuit of sustainable production of biofuels and chemicals with properties similar to those of fossil-derived fuels and chemicals. Biofuels, such as biohydrogen and biobutanol derived from renewable sources, offer a promising, cost-effective, and eco-friendly solution for mitigating long-term carbon footprint. Currently, there is a surge of interest in biohydrogen (bioH2) and biobutanol production through dark fermentation using diverse biomass feedstocks, due to its capacity to simultaneously generate gas and liquid fuels from renewable nonfood resources. Furthermore, the incorporation of nanoparticles in fermentation process has demonstrated considerable potential in enhancing bioH2 yields. Similarly, biobutanol emerges as an eco-friendly, less polluting, and potentially commercially viable substitute for conventional gasoline. This review emphasizes the diverse spectrum of nanoparticle applications in biomanufacturing, with a particular focus on their role in enhancing microbial activities to boost bioH2 and biobutanol yields. Additionally, the review highlights potential underlying mechanisms of nano-catalyzed fermentation pathways, future trends, and the prospects of nano-catalysts in advancing biofuel technology.

The use of high-value biomass resources for the green and renewable synthesis of biodiesel is an effective strategy for reducing greenhouse gas emissions and providing a sustainable alternative to depleting fossil fuels. In the present study, Nannorrhops ritchieana, a highly promising seed oil feedstock with 25 % oil content, was evaluated for biodiesel production using zinc oxide nanoparticles (ZnONPs) synthesized with aqueous leaf extract of Alternanthera pungens. The highest biodiesel yield of 95 % was achieved under optimum reaction conditions: a methanol to oil molar ratio of 7: 1, catalyst loading of 0.18 wt%, a reaction temperature of 80 °C, and a reaction time of 180 min. Analysis of the synthesized ZnONPs revealed its pure, thermally stable and nanoscale nature, with an average particle size of 22 nm. Gas chromatography mass spectroscopy (GC-MS) analysis identified distinct peaks of methyl esters, with 9-Octadecenoic acid, (Z)-methyl ester having the highest concentration. The fuel properties of the biodiesel— density (0.912 kg/m3), viscosity (6.45 mm2/s), flash point (93 °C), cloud (-7 °C), and pour point (-10 °C)— aligned with international fuel standards.

Executive summary Microbes are all pervasive in their distribution and influence on the functioning and well‐being of humans, life in general and the planet. Microbially‐based technologies contribute hugely to the supply of important goods and services we depend upon, such as the provision of food, medicines and clean water. They also offer mechanisms and strategies to mitigate and solve a wide range of problems and crises facing humanity at all levels, including those encapsulated in the sustainable development goals (SDGs) formulated by the United Nations. For example, microbial technologies can contribute in multiple ways to decarbonisation and hence confronting global warming, provide sanitation and clean water to the billions of people lacking them, improve soil fertility and hence food production and develop vaccines and other medicines to reduce and in some cases eliminate deadly infections. They are the foundation of biotechnology, an increasingly important and growing business sector and source of employment, and the centre of the bioeconomy, Green Deal, etc. But, because microbes are largely invisible, they are not familiar to most people, so opportunities they offer to effectively prevent and solve problems are often missed by decision‐makers, with the negative consequences this entrains. To correct this lack of vital knowledge, the International Microbiology Literacy Initiative–the IMiLI–is recruiting from the global microbiology community and making freely available, teaching resources for a curriculum in societally relevant microbiology that can be used at all levels of learning. Its goal is the development of a society that is literate in relevant microbiology and, as a consequence, able to take full advantage of the potential of microbes and minimise the consequences of their negative activities. In addition to teaching about microbes, almost every lesson discusses the influence they have on sustainability and the SDGs and their ability to solve pressing problems of societal inequalities. The curriculum thus teaches about sustainability, societal needs and global citizenship. The lessons also reveal the impacts microbes and their activities have on our daily lives at the personal, family, community, national and global levels and their relevance for decisions at all levels. And, because effective, evidence‐based decisions require not only relevant information but also critical and systems thinking, the resources also teach about these key generic aspects of deliberation. The IMiLI teaching resources are learner‐centric, not academic microbiology‐centric and deal with the microbiology of everyday issues. These span topics as diverse as owning and caring for a companion animal, the vast range of everyday foods that are produced via microbial processes, impressive geological formations created by microbes, childhood illnesses and how they are managed and how to reduce waste and pollution. They also leverage the exceptional excitement of exploration and discovery that typifies much progress in microbiology to capture the interest, inspire and motivate educators and learners alike. The IMiLI is establishing Regional Centres to translate the teaching resources into regional languages and adapt them to regional cultures, and to promote their use and assist educators employing them. Two of these are now operational. The Regional Centres constitute the interface between resource creators and educators–learners. As such, they will collect and analyse feedback from the end‐users and transmit this to the resource creators so that teaching materials can be improved and refined, and new resources added in response to demand: educators and learners will thereby be directly involved in evolution of the teaching resources. The interactions between educators–learners and resource creators mediated by the Regional Centres will establish dynamic and synergistic relationships–a global societally relevant microbiology education ecosystem–in which creators also become learners, teaching resources are optimised and all players/stakeholders are empowered and their motivation increased. The IMiLI concept thus embraces the principle of teaching societally relevant microbiology embedded in the wider context of societal, biosphere and planetary needs, inequalities, the range of crises that confront us and the need for improved decisioning, which should ultimately lead to better citizenship and a humanity that is more sustainable and resilient. Abstract The biosphere of planet Earth is a microbial world: a vast reactor of countless microbially driven chemical transformations and energy transfers that push and pull many planetary geochemical processes, including the cycling of the elements of life, mitigate or amplify climate change (e.g., Nature Reviews Microbiology, 2019, 17, 569) and impact the well‐being and activities of all organisms, including humans. Microbes are both our ancestors and creators of the planetary chemistry that allowed us to evolve (e.g., Life's engines: How microbes made earth habitable, 2023). To understand how the biosphere functions, how humans can influence its development and live more sustainably with the other organisms sharing it, we need to understand the microbes. In a recent editorial (Environmental Microbiology, 2019, 21, 1513), we advocated for improved microbiology literacy in society. Our concept of microbiology literacy is not based on knowledge of the academic subject of microbiology, with its multitude of component topics, plus the growing number of additional topics from other disciplines that become vitally important elements of current microbiology. Rather it is focused on microbial activities that impact us–individuals/communities/nations/the human world–and the biosphere and that are key to reaching informed decisions on a multitude of issues that regularly confront us, ranging from personal issues to crises of global importance. In other words, it is knowledge and understanding essential for adulthood and the transition to it, knowledge and understanding that must be acquired early in life in school. The 2019 Editorial marked the launch of the International Microbiology Literacy Initiative, the IMiLI. Here, we present our concept of how microbiology literacy may be achieved and the rationale underpinning it; the type of teaching resources being created to realise the concept and the framing of microbial activities treated in these resources in the context of sustainability, societal needs and responsibilities and decision‐making; and the key role of Regional Centres that will translate the teaching resources into local languages, adapt them according to local cultural needs, interface with regional educators and develop and serve as hubs of microbiology literacy education networks. The topics featuring in teaching resources are learner‐centric and have been selected for their inherent relevance, interest and ability to excite and engage. Importantly, the resources coherently integrate and emphasise the overarching issues of sustainability, stewardship and critical thinking and the pervasive interdependencies of processes. More broadly, the concept emphasises how the multifarious applications of microbial activities can be leveraged to promote human/animal, plant, environmental and planetary health, improve social equity, alleviate humanitarian deficits and causes of conflicts among peoples and increase understanding between peoples (Microbial Biotechnology, 2023, 16(6), 1091–1111). Importantly, although the primary target of the freely available (CC BY‐NC 4.0) IMiLI teaching resources is schoolchildren and their educators, they and the teaching philosophy are intended for all ages, abilities and cultural spectra of learners worldwide: in university education, lifelong learning, curiosity‐driven, web‐based knowledge acquisition and public outreach. The IMiLI teaching resources aim to promote development of a global microbiology education ecosystem that democratises microbiology knowledge.

Solventogenic Clostridium species are important for establishing the sustainable industrial bioproduction of fuels and important chemicals such as acetone and butanol. The inherent versatility of these species in substrate utilization and the range of solvents produced during acetone butanol–ethanol (ABE) fermentation make solventogenic Clostridium an attractive choice for biotechnological applications such as the production of fuels and chemicals. The functional qualities of these microbes have thus been identified to be related to complex regulatory networks that play essential roles in modulating the metabolism of this group of bacteria. Yet, solventogenic Clostridium species still struggle to consistently achieve butanol concentrations exceeding 20 g/L in batch fermentation, primarily due to the toxic effects of butanol on the culture. Genomes of solventogenic Clostridium species have a relatively greater prevalence of genes that are intricately controlled by various regulatory molecules than most other species. Consequently, the use of genetic or metabolic engineering strategies that do not consider the underlying regulatory mechanisms will not be effective. Several regulatory factors involved in substrate uptake/utilization, sporulation, solvent production, and stress responses (Carbon Catabolite Protein A, Spo0A, AbrB, Rex, CsrA) have been identified and characterized. In this review, the focus is on newly identified regulatory factors in solventogenic Clostridium species, the interaction of these factors with previously identified molecules, and potential implications for substrate utilization, solvent production, and resistance/tolerance to lignocellulose-derived microbial inhibitory compounds. Taken together, this review is anticipated to highlight the challenges impeding the re-industrialization of ABE fermentation, and inspire researchers to generate innovative strategies for overcoming these obstacles.

Presently, the world faces pressing global challenges encompassing social, economic, and sustainable development, all of which demand a growing scale of energy production and associated services. With abundant waste biomass at our disposal, there exists immense potential for harnessing it to produce biofuels. In this study, we synthesized biodiesel using waste seed oil from Cestrum nocturnum, employing a green nano catalyst composed of antimony oxide (Sb2O3NPs). Active ingredients were extracted from the leaf of Chenopodium album and used as a reducing agent. Using Fourier-Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy-Disperse X-ray Spectroscopy (EDX), Transmission Electron Microscopy (TEM) and Thermogravimetric Analysis (TGA), the synthesized Sb2O3 nanoparticles was characterized for chemical composition, functional groups, crystalline structure, and thermal stability. Additionally, the produced biodiesel was quantitatively evaluated using Nuclear Magnetic Resonance Spectrometry (1H and 13C NMR) and Gas Chromatography Mass Spectrometry (GC-MS). The highest yield (94 %) of methyl ester was obtained at optimum reaction conditions of 0.56 wt% of the catalyst, methanol to oil molar ratio of 8:1, at 95 degrees C for 180 min. Fatty acid profiles of synthesized biodiesel revealed elevated levels of 9-octadecenoic acid content. The cold properties (pour point, -11 degrees C and cloud point, -8 degrees C) and flash point (99 degrees C) of the biodiesel were within international requirements. The reusability of Sb2O3NPs revealed a maximum catalytic performance up to 5 cycles. The conversion of waste seed oil from Cestrum nocturnum to clean bioenergy has shown to be a successful waste management strategy for mitigating environmental pollution.

Microbial CO2 utilization reduces the carbon footprint, providing economic potential. Biochar, rich in minerals and trace metals, can enhance microbial activity. This study investigates poultry litter and switchgrass biochars produced at 350 and 700 degrees C (PLB350, PLB700, SGB350 and SGB700, respectively) affect CO2 conversion to C2-C6 alcohols and acids by Clostridium muellerianum P21, C. ragsdalei P11 and C. carboxidivorans P7. Fermentations were in 250-mL bottles containing H-2:CO2:N-2 (60:20:20) shaken at 125 rpm and 37 degrees C. SGB350 increased alcohol titers by 1.1-2.1 fold, and PLB350 enhanced acid concentrations by 1.2-1.7 fold compared to the control without biochar. About 2.0-3.3 fold more ethanol was formed by strain P11 compared to strains P7 and P21 with SGB350. However, strain P21 produced 2.4-fold more butanol than strain P7 with SGB350, including unique hexanol production. These results highlight the potential of biochar in enhancing C2-C6 alcohol production from CO2, thereby boosting process feasibility.

Amidst the dual challenges of burgeoning global population and escalating climate change, the desire to develop and implement sustainable conversion of lignocellulosic biomass (LB) to value-added products becomes more pronounced. Green products, particularly bio-derived fuels and chemicals, emerge as powerful solutions for mitigating greenhouse gas (GHG) emissions, combating global warming, and satisfying the energy needs of humanity. Today, concerted efforts are underway to produce petroleum-derived liquid fuels like butanol and diesel from renewable sources (e.g., LB). Despite LB currently serving as a significant energy source for many nations, the widespread adoption of technologies that can advance LB beyond burning for energy generation remains limited. Moreover, utilization of LB-derived sugars for fermentative production of fuels and chemicals is plagued with poor performance, largely due to the generation of lignocellulose-derived microbial inhibitory compounds (LDMICs) during pretreatment and hydrolysis of LB into sugars. This review provides an overview of global LB production and utilization, providing insights into both its current status and potential future directions. Specifically, the review paper focuses on various pretreatment options for the conversion of LB into sugars, delving into the mechanistic effects and strategies to abate the generation of LDMICs during pretreatment. Additionally, it explores innovative renewable strategies aimed at optimizing the utilization of second-generation feedstocks in biodiesel synthesis, thereby highlighting promising mitigating strategies toward achieving zero emissions.

Methods such as gas stripping and vacuum-assisted gas stripping (VAGS) result in significant removal of water from the bioreactor, thus requiring continuous water replenishment in the bioreactor. In this study, we developed a hydrophobic stainless steel meshes capable of selectively recovering concentrated ABE stream from the bioreactor during VAGS. Three stainless steel meshes with pore sizes of 180 µm, 300 µm, and 425 µm were made hydrophobic and oleophilic with zinc oxide (ZnO) and polydimethylsiloxane (PDMS). Butanol concentrations in the model solutions range from 3 to 10 g/L which mimic concentrations typically produced during batch ABE fermentation. The meshes were integrated in a 5-L bioreactor containing 2.5 L of operational ABE model solution followed by the evaluation of selective extraction of ABE from both cell-free and Clostridium beijerinckii-rich ABE model solutions. The results show that the 180-µm ZnO/PDMS-coated mesh retained 54–64

Butanol is a colorless flammable four-carbon alcohol with a characteristic banana-like odor that is currently used as an industrial solvent in the manufacturing of plasticizers, butylamines, butyl acetate, butyl acrylate and methacrylate, glycol ethers and amino resins. In addition, butanol has some properties that make it a viable transportation fuel. These properties include a low flash point, hydrophilicity, vapor pressure and volatility, large energy content per unit mass, and miscibility with hydrocarbon-based fuels. Some of these properties make butanol less corrosive and compatible with the existing oil infrastructure. As interest in environmentally compatible fuels intensifies, butanol is one of the chemicals that have gained attention of scientists and engineers as a potential replacement for gasoline. Meanwhile, butanol fermentation, popularly known as acetone-butanol-ethanol (ABE) fermentation, has a rich history that dates to Louis Pasteur, who in 1861 observed that bacteria can produce butanol. The ABE fermentation is plagued with less-than-optimal butanol titers in the bioreactor due to the inhibitory effect of butanol on fermenting microorganisms. The cost of butanol recovery from the fermentation broth, however, is the second largest contributor to the production cost, the first being the substrate cost. Development of knowledge-based strategies to resolve complex issues related to substrate compatibility and butanol toxicity to butanol-producing microorganisms is evolving. Consequently, in this chapter, there is elaboration on the scope of butanol-producing microorganisms, butanol production from food- and nonfood-based feedstock, technology innovations to advance butanol fermentation, and significance and applications of butanol and butanol derivatives.

Valorization and utilization of industrial food processing waste as value added products, platform chemicals and biofuels, are needed to improve sustainability and reduce waste management costs. Various industrial food waste stream samples were characterized with respect to their physico-chemical characteristics and elemental composition. A subset of starchy food wastes and milk dust powder were evaluated in batch fermentation to acetone, a useful platform chemical. Production levels were similar to acetone produced from glucose but were achieved more quickly. Lactose concentration negatively affected fermentation and led to 50 % lower acetone concentration from milk dust powder than from starchy wastes. Uncooked starch waste can produce 20 % more acetone than cooked and modified starch waste. Fatty waste and mineral waste can be digested anaerobically generating biogas. Calorific value of soybean waste was 40 MJ/kg sufficiently high for biodiesel production. Low C/N ratios of wastewater and solids from food processing waste makes them unsuitable for anaerobic digestion but these waste types can be converted thermochemically to hydrochar and used as soil amendments. Low calorific content (10-15 MJ/kg) vegetable wastes also are not ideal for energy production, but are rich in flavonoids, antioxidants and pigments which can be extracted as valuable products. A model mapping food waste characteristics to best valorization pathway was developed to guide waste management and future cost and environmental impact analyses. These findings will help advance food industry knowledge and improve sustainable food production through valorized processing waste management.

EDITORIAL article Front. Bioeng. Biotechnol., 03 March 2023Sec. Bioprocess Engineering Volume 11 - 2023 | https://doi.org/10.3389/fbioe.2023.1163513

A Michaelis-Menten-like kinetic model is proposed to simulate the effects of redox balance on Clostridium beijerinckii NCIMB 8052 metabolism during fermentation of biomass-derived xylose to acetone-butanol-ethanol (ABE). The model builds on previous metabolic kinetic models by introducing six mass balance differential equations for the redox pairs NADH/NAD+, NADPH/NADP+, and oxidized/reduced ferredoxin. Batch cultures were conducted using laboratory-grade or eucalyptus-derived xylose, and kinetic parameters were estimated by minimizing the difference between experimental (substrate, metabolites, and cell) and model results using a genetic optimization algorithm. The simulations agreed well with experimental data, and a sensitivity analysis showed that the rate of reoxidation of reduced ferredoxin used for NADPH regeneration is the most relevant reaction for the synthesis of acids and ABE. Furthermore, an increase in NADPH consumption due to the reduction of eucalyptus-derived furfural to furfuryl alcohol was only significant for the production of butanol. Differences in the values of the Michaelis-Menten constants, Km's, depending on the xylose source, suggest that a decrease in the conversion rates of lactate to pyruvate and acetate to acetyl-CoA considerably affected the biosynthesis of butanol from eucalyptus-derived xylose. The proposed model was effective in assessing the effects of redox balance on ABE fermentation, suggesting its use for the design of metabolic engineering strategies to improve butanol synthesis from furfural-containing biomass hydrolysates.

The goal of this study was to improve resource use efficiency in agricultural systems and agro-based industries, reduce wastes that go to landfills and incinerators, and consequently, improve the economics of 2,3-butanediol (2,3-BD) production. This study evaluated the feasibility of 2,3-BD production by replacing the mineral nutrients, and buffers with anaerobic digestate (ADE), poultry-litter (PLBC)- and forage-sorghum (FSBC)-derived biochars. Fermentation media formulations with ADE and 5–20 g/L PLBC or FSBC were evaluated for 2,3-BD production using Paenibacillus polymyxa as a biocatalyst. An optimized medium containing nutrients and buffers served as control. While 2,3-BD production in the ADE cultures was 0.5-fold of the maximum generated in the control cultures, 2,3-BD produced in the PLBC and FSBC cultures were ~1.3-fold more than the control (33.6 g/L). Cost analysis showed that ADE and biochar can replace mineral nutrients and buffers in the medium with the potential to make bio-based 2,3-BD production profitably feasible.

The presence of lignocellulose-derived microbial inhibitory compounds (LDMICs) in lignocellulosic biomass (LB) hydrolysates is a barrier to efficient conversion of LB hydrolysates to fuels and chemicals by fermenting microorganisms. Results from this study provide convincing evidence regarding the effectiveness of metabolically engineered C. beijerinckii NCIMB 8052 for the fermentation of LB-derived hydrolysates to acetone–butanol–ethanol (ABE). The engineered microbial strain (C. beijerinckii_SDR) was produced by the integration of an additional copy of a short-chain dehydrogenase/reductase (SDR) gene (Cbei_3904) into the chromosome of C. beijerinckii NCIMB 8052 wildtype, where it is controlled by the constitutive thiolase promoter. The C. beijerinckii_SDR and C. beijerinckii NCIMB 8052 wildtype were used for comparative fermentation of non-detoxified and detoxified hydrothermolysis-pretreated switchgrass hydrolysates (SHs) with and without (NH4)2CO3 supplementation. In the absence of (NH4)2CO3, fermentation of non-detoxified SH with C. beijerinckii_SDR resulted in the production of 3.13- and 2.25-fold greater quantities of butanol (11.21 g/L) and total ABE (20.24 g/L), respectively, than the 3.58 g/L butanol and 8.98 g/L ABE produced by C. beijerinckii_wildtype. When the non-detoxified SH was supplemented with (NH4)2CO3, concentrations were similar for butanol (9.5 compared with 9.2 g/L) and ABE (14.2 compared with 13.5 g/L) produced by C. beijerinckii_SDR and C. beijerinckii_wildtype, respectively. Furthermore, when C. beijerinckii_SDR and C. beijerinckii_wildtype were cultured in detoxified SH medium, C. beijerinckii_SDR produced 1.11- and 1.18-fold greater quantities of butanol and ABE, respectively, than when there was culturing with C. beijerinckii_wildtype. When the combined results of the present study are considered, conclusions are that the microbial strain and medium modifications of the fermentation milieu resulted in greater production of fuels and chemicals from non-detoxified LB hydrolysates.