Nannochloropsis oculata
CCMP 525,
Dunaliella salina
FACHB 435, and
Chlorella sorokiniana
CCTCC M209220 were compared in mixotrophic and photoautotrophic cultures in terms of growth rate, protein, and ...lipid content. Growth improved in glucose, and the biomass productivities of
N. oculata
,
D. salina
, and
C. sorokiniana
were found to be 1.4-, 2.2- and 4.2-fold that observed photoautotrophically. However, biomass and lipid production decreased at the highest glucose concentrations. Meanwhile, the content of protein and lipid were significantly augmented for mixotrophic conditions at least for some species.
C. sorokiniana
was found to be well suited for lipid production based on its high biomass production rate and lipid content reaching 51% during mixotrophy. Expression levels of
acc
D (heteromeric acetyl-CoA carboxylase beta subunit),
acc
1 (homomeric acetyl-CoA carboxylase),
rbc
L (ribulose 1, 5-bisphosphate carboxylase/oxygenase large subunit) genes in
C. sorokiniana
were studied by real-time PCR. Increased expression levels of
acc
D reflect the increased lipid content in stationary phase of mixotrophic growth, but expression of the
acc
1 gene remains low, suggesting that this gene may not be critical to lipid accumulation. Additionally, reduction of expression of the
rbc
L gene during mixotrophy indicated that utilization of glucose was found to reduce the role of this gene and photosynthesis.
Roadmaps towards sustainable bioeconomy, including the production of biofuels, in many EU countries mostly rely on biomass use. However, although biomass is renewable, the efficiency of biomass ...production is too low to be able to fully replace the fossil fuels. The use of land for fuel production also introduces ethical problems in increasing the food price. Harvesting solar energy by the photosynthetic machinery of plants and autotrophic microorganisms is the basis for all biomass production. This paper describes current challenges and possibilities to sustainably increase the biomass production and highlights future technologies to further enhance biofuel production directly from sunlight. The biggest scientific breakthroughs are expected to rely on a new technology called “synthetic biology”, which makes engineering of biological systems possible. It will enable direct conversion of solar energy to a fuel from inexhaustible raw materials: sun light, water and CO₂. In the future, such solar biofuels are expected to be produced in engineered photosynthetic microorganisms or in completely synthetic living factories.
The use of different input data, functional units, allocation methods, reference systems and other assumptions complicates comparisons of LCA bioenergy studies. In addition, uncertainties and use of ...specific local factors for indirect effects (like land-use change and N-based soil emissions) may give rise to wide ranges of final results. In order to investigate how these key issues have been addressed so far, this work performs a review of the recent bioenergy LCA literature. The abundance of studies dealing with the different biomass resources, conversion technologies, products and environmental impact categories is summarized and discussed. Afterwards, a qualitative interpretation of the LCA results is depicted, focusing on energy balance, GHG balance and other impact categories. With the exception of a few studies, most LCAs found a significant net reduction in GHG emissions and fossil energy consumption when bioenergy replaces fossil energy.
The development of an economic and sustainable catalytic system was crucial for lignin-based biorefinery. Herein, we reported a low-cost Cu/CuMgAlO x catalyst with promising activity toward lignin ...hydrodeoxygenation (HDO) through a H2-free method. Supercritical methanol was used as the hydrogen donor, solvent, and reactant simultaneously. Guaiacol was employed as a representative lignin model compound to reveal the HDO mechanism of lignin derivatives. HDOs of guaiacol performed at 250, 275, 300, and 350 °C with durations ranging from 15 to 120 min indicated a high HDO efficiency of the catalytic system. The obtained liquid products were categorized to oxygen-containing unsaturated products (OUPs), oxygen-containing saturated products (OSPs), and cycloalkanes. A kinetic model based on a simplified reaction process containing the three following conversion steps was established: guaiacol transformed to OUPs through the initial HDO, then hydrogenated to OSPs (medium HDO), and eventually turned to cycloalkanes by the deep HDO. The deep HDO was the rate-determining step, and the apparent activation energies of the three steps were all lower than those in the literature. Phenol, 1,2-cyclohexanediol, anisole, and veratrole were the major intermediates, the HDOs of which were programed for pathway verification. Remarkably, catechol (the culprit of condensation) was not produced in this system. Overall, a detailed reaction network of guaiacol HDO was established, and the veil of Cu/CuMgAlO x -catalyzed lignin-derivatives HDO in supercritical methanol was revealed. This work paved the way for the application of Cu/CuMgAlO x catalyst in lignin-derivatives upgrading.
Conductive materials play a vital role in electron transfer during the hydrogen (H2) fermentation process. In this work, a novel nitrogen-doped biochar (NDBC) was produced from corncob to improve ...biohydrogen production at 37 °C. Material analysis revealed that the nitrogen-rich biochar (BC) had a specific surface area of 831.13 m2/g, which was slightly lower than that of the corncob-derived BC (944.09 m2/g), while the electrical conductivity of the former was 13.91 times higher than that of the latter. The highest H2 yield of 230 mL/g glucose was obtained at 600 mg/L NDBC, which was higher than the corncob-derived BC (159 mL/g glucose) and control (without any BC) (140 mL/g glucose) group yields. The microbial community structure illustrated that NDBC greatly reduced the abundance of Dysgonomonas (9.2%) and increased the abundance of Clostridium butyricum (10.9%). The NDBC and corncob-derived BC materials played obviously different roles: the former enriched the dominant bacteria and acted as an electron conduit promoting electron transfer, while the latter mainly provided favorable sites for microbial colonization. The results also indicated that cleaner energy production with a high H2 yield was attained with the nitrogen-doped BC material.
This article presents results of a European Commission Joint Research Centre study to analyse the Greenhouse Gas (GHG) emissions and energy efficiency of various options for alternative aviation ...fuels. Interest in alternative aviation fuels is growing, as the sector seeks viable options to reduce increasing GHG emissions. For biofuels non-biogenic emissions arise from cultivation, harvesting and transport of the feedstock, as well as from their conversion into biofuel. It is important to consider whether any emissions reductions benefits are justified by the energy efficiency of each alternative. This article is focussed on American Society for Testing and Materials (ASTM) certifiable alternative drop-in biojet fuels 1, i.e. non-fossil hydrocarbon fuels which have (i) the same chemical structure and (ii) can be blended with conventional jet fuels, (iii) can use the same jet fuel supply infrastructure, and (iv) do not require modification of the aircraft. The results indicate that the biofuels studied tended to exhibit lower GHG than conventional jet fuels although indirect effects or existing uses of materials were not included in this study. Some biofuels performed better at reducing GHG than others (for example biofuels from wastes and residues). A large and important effect on emissions is seen due to land type used for cultivation and whether methane capture is used for certain pathways. GHG savings results vary due to the Life Cycle Analysis (LCA) methodology chosen for dealing with emissions and co-products. Certain pathways are notably more energy intensive than others and strong GHG reduction does not always coincide with high energy efficiency. An overview of industry initiatives and critical EU legislation relating to aviation biofuels is given. The insights from this work are expected to be of use for decision-makers considering investment options in this sector.
•Aviation biofuels production method can have a considerable effect on GHG.•Biofuels may produce higher GHG than standard aviation fuel.•Advanced biofuels may need more energy input than first generation biofuels.•Methodology and how emissions are allocated effect GHG results.•Further work on feedstock displacement effects is needed.
Bioalcohols produced by microorganisms from renewable materials are promising substitutes for traditional fuels derived from fossil sources. For several years already ethanol is produced in large ...amounts from feedstocks such as cereals or sugar cane and used as a blend for gasoline or even as a pure biofuel. However, alcohols with longer carbon chains like butanol have even more suitable properties and would better fit with the current fuel distribution infrastructure. Moreover, ethical concerns contradict the use of food and feed products as a biofuel source. Lignocellulosic biomass, especially when considered as a waste material offers an attractive alternative. However, the recalcitrance of these materials and the inability of microorganisms to efficiently ferment lignocellulosic hydrolysates still prevent the production of bioalcohols from these plentiful sources. Obviously, no known organism exist which combines all the properties necessary to be a sustainable bioalcohol producer. Therefore, breeding technologies, genetic engineering and the search for undiscovered species are promising means to provide a microorganism exhibiting high alcohol productivities and yields, converting all lignocellulosic sugars or are even able to use carbon dioxide or monoxide, and thereby being highly resistant to inhibitors and fermentation products, and easy to cultivate in huge bioreactors. In this review, we compare the properties of various microorganisms, bacteria and yeasts, as well as current research efforts to develop a reliable lignocellulosic bioalcohol producing organism.
Dye‐decolorizing peroxidases (DyP) were originally discovered in fungi for their ability to decolorize several different industrial dyes. DyPs catalyze the oxidation of a variety of substrates such ...as phenolic and nonphenolic aromatic compounds. Catalysis occurs in the active site or on the surface of the enzyme depending on the size of the substrate and on the existence of radical transfer pathways available in the enzyme. DyPs show the typical features of heme‐containing enzymes with a Soret peak at 404–408 nm. They bind hydrogen peroxide that leads to the formation of the so‐called Compound I, the key intermediate for catalysis. This then decays into Compound II yielding back Fe(III) at its resting state. Each catalytic cycle uses two electrons from suitable electron donors and generates two product molecules.
DyPs are classified as a separate class of peroxidases. As all peroxidases they encompass a conserved histidine that acts as the fifth heme ligand, however all primary DyP sequences contain a conserved GxxDG motif and a distal arginine that is their characteristic. Given their ability to attack monomeric and dimeric lignin model compounds as well as polymeric lignocellulose, DyPs are a promising class of biocatalysts for lignin degradation that not only represents a source of valuable fine chemicals, but it also constitutes a fundamental step in biofuels production. Research efforts are envisioned for the improvement of the activity of DyPs against lignin, through directed evolution, ration protein design, or one‐pot combination with other enzymes to reach satisfactory conversion levels for industrial applications.
Dye‐decolorizing peroxidases can be exploited to degrade lignin and produce biofuel.
The current review explores the potential application of algal biomass for the production of biofuels and bio-based products. The variety of processes and pathways through which bio-valorization of ...algal biomass can be performed are described in this review. Various lipid extraction techniques from algal biomass along with transesterification reactions for biodiesel production are briefly discussed. Processes such as the pretreatment and saccharification of algal biomass, fermentation, gasification, pyrolysis, hydrothermal liquefaction, and anaerobic digestion for the production of biohydrogen, bio-oils, biomethane, biochar (BC), and various bio-based products are reviewed in detail. The biorefinery model and its collaborative approach with various processes are highlighted for the production of eco-friendly, sustainable, and cost-effective biofuels and value-added products. The authors also discuss opportunities and challenges related to bio-valorization of algal biomass and use their own perspective regarding the processes involved in production and the feasibility to make algal research a reality for the production of biofuels and bio-based products in a sustainable manner.
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•Critical analysis of pathways involves in bio-valorization of algal biomass.•Mass of 1 kg oils extracted from algal biomass can produce 1 kg biodiesel.•The yields of biochar per unit dry weight of algal biomass are in the range of 8.1–62.4%.•The foremost challenges in production of 3rd generation biofuel are its non-cost effectiveness.
Lignocellulosic biomass (LCB) is globally available and sustainable feedstock containing sugar-rich platform that can be converted to biofuels and specialty products through appropriate processing. ...This review focuses on the efforts required for the development of sustainable and economically viable lignocellulosic biorefinery to produce carbon neutral biofuels along with the specialty chemicals. Sustainable biomass processing is a global challenge that requires the fulfillment of fundamental demands concerning economic efficiency, environmental compatibility, and social responsibility. The key technical challenges in continuous biomass supply and the biological routes for its saccharification with high yields of sugar sources have not been addressed in research programs dealing with biomass processing. Though many R&D endeavors have directed towards biomass valorization over several decades, the integrated production of biofuels and chemicals still needs optimization from both technical and economical perspectives. None of the current pretreatment methods has advantages over others since their outcomes depend on the type of feedstock, downstream process configuration, and many other factors. Consolidated bio-processing (CBP) involves the use of single or consortium of microbes to deconstruct biomass without pretreatment. The use of new genetic engineering tools for natively cellulolytic microbes would make the CBP process low cost and ecologically friendly. Issues arising with chemical characteristics and rigidity of the biomass structure can be a setback for its viability for biofuel conversion. Integration of functional genomics and system biology with synthetic biology and metabolic engineering undoubtedly led to generation of efficient microbial systems, albeit with limited commercial potential. These efficient microbial systems with new metabolic routes can be exploited for production of commodity chemicals from all the three components of biomass. This paper provides an overview of the challenges that are faced by the processes converting LCB to commodity chemicals with special reference to biofuels.
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