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This eBook is a collection of articles from a Frontiers Research Topic. Frontiers Research Topics are very popular trademarks of the Frontiers Journals Series: they are collections of at least ten articles, all centered on a particular subject. With their unique mix of varied contributions from Original Research to Review Articles, Frontiers Research Topics unify the most influential researchers, the latest key findings and historical advances in a hot research area! Find out more on how to host your own Frontiers Research Topic or contribute to one as an author by contacting the Frontiers Editorial Office: frontiersin.org/about/contact

biodegradable polymers --- biodegradable composites --- biodegradability --- material characterization --- environmental sustainability --- recyclability

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The bioeconomy initially focused on resource substitution, including the production of biomass from various resources; its conversion, fractionation, and processing by means of biotechnology; and chemistry and process engineering towards the production and marketing of food, feed, fuel, and fibre. Nevertheless, although resource substitution is still considered important, the emphasis has been recently shifted to the biotechnological innovation perspective of the bioeconomy, in terms that ensure environmental sustainability. It is estimated that around one-third of the food produced for human consumption is wasted throughout the world, posing not only a sustainability problem related to food security but also a significant environmental problem. Food waste streams, mainly derived from fruits and vegetables, cereals, oilseeds, meat, dairy, and fish processing, have unavoidably attracted the interest of the scientific community as an abundant reservoir of complex carbohydrates, proteins, lipids, and functional compounds, which can be utilized as raw materials for added-value product formulations. This Special Issue focuses on innovative and emerging food and by-products processing methods for the sustainable transition to a bioeconomy era.

ash content --- sorghum milling waste --- lipids --- compost --- oleic acid --- microbial oil --- bioprocess development --- glucoamylase --- fatty acid methyl esters --- oleaginous yeast --- integrated biorefineries --- biorefineries --- hydrophobic substrates --- food processing --- hydrophilicity --- biodiesel --- films --- biodegradability --- clarified butter sediment waste --- submerged fungal fermentation --- blood plasma protein powder --- Morchella --- hydrogels --- heat-induced gelation --- sustainability --- bacterial cellulose --- bioprocesses --- circular economy --- olive waste --- prebiotics --- Rhodosporidium toruloides --- carotenoids --- waste valorization --- glucosamine --- food-processing --- size exclusion chromatography (SEC) --- bioeconomy --- food waste valorization --- whey proteins --- arabinoxylan --- Ostwald ripening --- emulsion --- emulsifier --- food biotechnology --- drying method --- polysaccharides --- food packaging --- texture --- lactose esters --- morel mushrooms --- circular-economy --- solid state fermentation --- bioactive compounds --- edible films --- hydrolysis --- Aspergillus awamori

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Bioenergy is renewable energy obtained from biomass—any organic material that has stored sunlight in the form of chemical energy. Biogas is among the biofuels that can be obtained from biomass resources, including biodegradable wastes like manure, sewage sludge, the organic fraction of municipal solid wastes, slaughterhouse waste, crop residues, and more recently lignocellulosic biomass and algae. Within the framework of the circular economy, biogas production from biodegradable waste is particularly interesting, as it helps to save resources while reducing environmental pollution. Besides, lignocellulosic biomass and algae do not compete for arable land with food crops (in contrast with energy crops). Hence, they constitute a novel source of biomass for bioenergy.Biogas plants may involve both high-tech and low-tech digesters, ranging from industrial-scale plants to small-scale farms and even households. They pose an alternative for decentralized bioenergy production in rural areas. Indeed, the biogas produced can be used in heaters, engines, combined heat and power units, and even cookstoves at the household level. Notwithstanding, digesters are considered to be a sustainable technology that can improve the living conditions of farmers by covering energy needs and boosting nutrient recycling. Thanks to their technical, socio-economic, and environmental benefits, rural biogas plants have been spreading around the world since the 1970s, with a large focus on farm-based systems and households. However, several challenges still need to be overcome in order to improve the technology and financial viability.

Mixing --- optimised --- household digester --- Chinese dome digester (CDD) --- self-agitation --- blank --- mixing --- Chinese dome digester --- impeller mixed digester --- unstirred digester --- hydraulically mixed --- total solids (TS) concentration --- plug-flow reactor --- anaerobic digestion --- animal manures --- biogas --- unconfined gas injection mixing --- mixing recirculation --- biomethane potential tests --- Italy --- manure --- energy crops --- agriculture residues --- digestate --- biochemical methane potential --- micro-aeration --- iron --- bioenergy --- H2S scrubber --- methane --- fermentation --- dairy --- poultry --- absorbent --- ammonia --- inhibition --- acclimatization --- trace elements --- anaerobic treatment --- energy assessment --- rural sanitation --- sludge --- wastewater --- agricultural runoff --- biomethane --- biorefinery --- microalgae --- photobioreactor --- pretreatment --- low cost digester --- psychrophilic anaerobic digestion --- thermal behavior --- anaerobic co-digestion --- slaughterhouse wastewater --- synergistic effects --- kinetic modeling --- biodegradability

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Since the turn of the last century when the field of catalysis was born, iron and cobalt have been key players in numerous catalysis processes. These metals, due to their ability to activate CO and CH, haev a major economic impact worldwide. Several industrial processes and synthetic routes use these metals: biomass-to-liquids (BTL), coal-to-liquids (CTL), natural gas-to-liquids (GTL), water-gas-shift, alcohol synthesis, alcohol steam reforming, polymerization processes, cross-coupling reactions, and photocatalyst activated reactions. A vast number of materials are produced from these processes, including oil, lubricants, waxes, diesel and jet fuels, hydrogen (e.g., fuel cell applications), gasoline, rubbers, plastics, alcohols, pharmaceuticals, agrochemicals, feed-stock chemicals, and other alternative materials. However, given the true complexities of the variables involved in these processes, many key mechanistic issues are still not fully defined or understood. This Special Issue of Catalysis will be a collaborative effort to combine current catalysis research on these metals from experimental and theoretical perspectives on both heterogeneous and homogeneous catalysts. We welcome contributions from the catalysis community on catalyst characterization, kinetics, reaction mechanism, reactor development, theoretical modeling, and surface science.

polynuclear cobalt complexes --- water oxidation --- artificial photosynthesis --- Fe/Cu catalytic-ceramic-filler --- nitrobenzene compounds wastewater --- pilot-scale test --- biodegradability-improvement --- Fischer–Tropsch synthesis (FTS) --- oxygenates --- iron --- cobalt --- ruthenium --- Anderson-Schulz-Flory (ASF) distribution --- Fischer–Tropsch --- catalyst deactivation --- potassium --- liquid-phase catalytic oxidation --- limonene --- carvone --- zeolitic imidazolate frameworks --- Fischer-Tropsch synthesis --- chain growth --- CO insertion --- kinetic isotope effect --- DFT --- hydrogenation of CO --- iron catalysts --- syngas --- monometallic iron catalysts --- Fischer–Tropsch product distribution --- reaction mechanism --- catalysis --- process synthesis and design --- energy conversion --- iron–cobalt bimetal catalysts --- electrochemical application --- hydrogen evolution --- oxygen evolution --- oxygen reduction --- RWGS --- iron oxides --- CO2 conversion --- gas-switching --- Synthetic natural gas (SNG) --- Cobalt --- Iron --- C2–C4 hydrocarbons --- paraffin ratio --- asymmetric hydrogenation --- homogeneous catalysis --- structural design --- conformational analysis --- NMR spectroscopy --- alumina --- strong metal support interactions --- CO2 hydrogenation --- pressure --- temperature --- cobalt carboxylate --- coating --- autoxidation --- alkyd --- siccative --- polymerization --- manganese --- Fischer–Tropsch synthesis --- modeling --- kinetics --- Co --- Al2O3 --- Pt --- Cd --- In --- Sn --- hydrocarbon selectivity --- synergic effect --- GTL --- additives --- reducibility --- XANES --- mesoporous silica based catalysts --- kinetic studies --- 3-D printed microchannel microreactor --- cobalt–nickel nanoparticles --- cobalt–nickel alloys --- nickel --- HAADF-STEM --- TPR-EXAFS/XANES --- CO hydrogenation --- CSTR --- n/a --- Fischer-Tropsch synthesis (FTS) --- Fischer-Tropsch --- Fischer-Tropsch product distribution --- iron-cobalt bimetal catalysts --- C2-C4 hydrocarbons --- cobalt-nickel nanoparticles --- cobalt-nickel alloys

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The aim of this reprint is to highlight the progress and fundamental aspects for the synthesis, characterization, properties, and application of novel polymeric materials, as well as their copolymers, composites, and nanocomposites.

Plastics & polymers technology --- poly(lactic acid) --- epoxidized natural rubber --- polymer blend --- natural additives --- antioxidant --- polymer blending --- radiation crosslinking --- polyethylene --- polyurethane --- heat resistance --- mechanical property --- aramid fiber --- ballistic test --- failure mechanism --- cyclotriphosphazane --- flame retardancy --- dielectric properties --- azo compound --- liquid crystal --- structure–property relationship --- axial behavior --- geopolymer concrete (GC) --- ferrocement --- finite element analysis (FEA) --- polyacrylonitrile --- lignin --- electrospinning --- selective chemical dissolution --- porous nanofibers --- nanofibers --- soft template --- peat soil --- cement --- stabilization --- fly ash --- polypropylene fiber --- unconfined compressive strength (UCS) --- California bearing ratio (CBR) --- scanning electron microscopy (SEM) --- bio-based polyurethanes --- jatropha oil --- algae oil --- recovered palm oil --- epoxy composite --- green composite --- corn cob --- polycarbonates --- transesterification --- polycondensation --- polymer --- hydrogen --- hydrophobic --- sensing --- nanostructures --- palladium --- polymer composite --- fibre-prestressing --- residual stresses --- PCL–SBA-15 nanocomposites --- real-time variable-temperature synchrotron measurements --- confinement --- mechanical behavior --- nanoclay --- nanocomposites --- mechanical properties --- impact properties --- hardness --- polymer composites --- graphene quantum dots --- bioactive --- biomedical --- synthesis --- PVK --- hexylthiophene --- PANI --- nanocomposite --- photovoltaic cells --- DFT --- polyhydroxyalkanoates --- fibers --- biodegradability --- packaging --- patents --- poly(aminopropyl/phenyl)silsesquioxane --- thiol-ene --- kinetics --- activation energy --- polymer characterization --- viscoelasticity --- DMA --- solution blow spinning --- polyethylene oxide --- morphology --- materials characterization --- polymer dissolution --- kaolin flocculation --- aggregate resistance --- salinity --- flocculation kinetic --- shear rate --- thermoplastic starch --- silane --- foam --- carbon dioxide --- microcapsules --- dip coating --- encapsulation --- spectroscopy --- microscopy --- antibacterial silver --- polyaniline --- dodecylbenzene sulfonic acid --- γ-Al2O3 --- in situ polymerization --- core–shell nanocomposite --- polyphosphazene --- micro-nanospheres --- species-absorbing mechanisms --- hydrophobicity --- thermochemical --- PVDF --- alkali-grafting --- α-methyl styrene --- acrylonitrile --- proton exchange membrane --- block copolymers --- random copolymers --- catalytic membranes --- esterification --- isopropyl acetate --- bioinspired bottlebrush polymers --- aqueous boundary lubrication --- friction --- wear resistance --- supramolecular hydrogel --- acrylic acid --- maleic anhydride --- terpyridine --- coordination interaction --- thermoplastic polyurethanes --- surface free energy --- dithiol --- differential scanning calorimetry --- optical properties --- arsine --- ligands --- polypropylene --- catalyst --- degradation --- sol-gel process --- 3D network hybrid materials --- nanoparticles --- nanodispersity --- ionic liquids --- n/a --- structure-property relationship --- PCL-SBA-15 nanocomposites --- core-shell nanocomposite