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An Anaerobic Fixed Bed (AnFB) reactor was run as an upflow anaerobic reactor with an arrangement of supporting material for growth of a biofilm. The supporting material was made from Liapor-clay-polyethylene sinter lamellas (Herding Co., Amberg).The AnFB reactor was used for treating high concentrations of whey-containing wastewater. Optimal operating conditions for whey treatment at a concentration of COD in the influent of around 50 g whey·l-1 were found for a hydraulic retention time (HRT) in the range of 4-8 days or an organic loading rate (OLR) less than 10 kg COD·m-3·d-1. This is a higher load than normally applied in praxis reactors.Accumulation of volatile fatty acids (VFAs) happened when the AnFB was supplied with surplus whey solution at a high OLR or when it was oxygenated. VFAs were accumulated faster when the HRT was changed from 12 days to 6 days compared to a change of HRT from 6 days to 4 days. However, at a HRT of 6 days, the accumulated VFAs were completely degraded after an adaptation period of about 5 days, whereas the accumulated VFAs at a HRT of 4 days remained constant upon time and could not be degraded during further incubation.The conversion process (acetogenesis and methanogenesis) of VFAs was influenced by the pH in the reactor. Acetate and n-Butyrate were converted faster at neutral or slightly alkaline pH, while propionate was degraded faster at slightly acidic pH-value. The population in the AnFB contained hydrogen-utilizing methanogenic bacteria, formate-utilizing methanogenic bacteria, methanol-utilizing methanogenic bacteria, acetoclastic methanogenic bacteria and sulfate-reducing bacteria as the final-stage organism of whey degradation. Acetogenic and methanogenic bacteria grew slower and were present at much lower numbers than acidogenic bacteria. This made the acid degradation rate less than the acid production rate. The minimal HRT in the whey reactor was thus dependent on acid degradation rates. Acetate-utilizing methanogens seemed to be unable to grow as single cells. They preferred to grow in a particulate or attached manner on a support material. The biofilm on the support materials provided a lower redox potential and an anaerobic environment that was obligately needed by these bacteria. The addition of a reducing agent was necessary to keep the few culturing acetoclastic methanogens in suspended cultures active.H2/CO2 was the best methanogenic substrate for the bacteria in the effluent suspension of whey reactor, followed by formate and methanol. The least degradable substrate in suspension cultures was acetate. The optimal H2 gas concentration for methanogens was provided at 2.25 bar.Ferric ions addition or the addition of a mix of minerals improved acetate degradation and methane production rates more than two-folds. The redox potential + reducing agent was low enough for methanogenesis. An AnFB-reactor would be a suitable means for stabilizing wastewater from dairy processing. Liapor-clay-polyethylene sinter lamellas in a regularly arrangement could be the substratum for biofilm formation. A minimum HRT of 4-6 days should be planned or a maximum OLR rate 10 kg COD·m-3·d-1 not exceeded.

acetogenesis --- whey --- anaerobic fixed bed reactor --- degradation --- methanogenesis --- AnFB reactor

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An Anaerobic Fixed Bed (AnFB) reactor was run as an upflow anaerobic reactor with an arrangement of supporting material for growth of a biofilm. The supporting material was made from Liapor-clay-polyethylene sinter lamellas (Herding Co., Amberg).The AnFB reactor was used for treating high concentrations of whey-containing wastewater. Optimal operating conditions for whey treatment at a concentration of COD in the influent of around 50 g whey·l-1 were found for a hydraulic retention time (HRT) in the range of 4-8 days or an organic loading rate (OLR) less than 10 kg COD·m-3·d-1. This is a higher load than normally applied in praxis reactors.Accumulation of volatile fatty acids (VFAs) happened when the AnFB was supplied with surplus whey solution at a high OLR or when it was oxygenated. VFAs were accumulated faster when the HRT was changed from 12 days to 6 days compared to a change of HRT from 6 days to 4 days. However, at a HRT of 6 days, the accumulated VFAs were completely degraded after an adaptation period of about 5 days, whereas the accumulated VFAs at a HRT of 4 days remained constant upon time and could not be degraded during further incubation.The conversion process (acetogenesis and methanogenesis) of VFAs was influenced by the pH in the reactor. Acetate and n-Butyrate were converted faster at neutral or slightly alkaline pH, while propionate was degraded faster at slightly acidic pH-value. The population in the AnFB contained hydrogen-utilizing methanogenic bacteria, formate-utilizing methanogenic bacteria, methanol-utilizing methanogenic bacteria, acetoclastic methanogenic bacteria and sulfate-reducing bacteria as the final-stage organism of whey degradation. Acetogenic and methanogenic bacteria grew slower and were present at much lower numbers than acidogenic bacteria. This made the acid degradation rate less than the acid production rate. The minimal HRT in the whey reactor was thus dependent on acid degradation rates. Acetate-utilizing methanogens seemed to be unable to grow as single cells. They preferred to grow in a particulate or attached manner on a support material. The biofilm on the support materials provided a lower redox potential and an anaerobic environment that was obligately needed by these bacteria. The addition of a reducing agent was necessary to keep the few culturing acetoclastic methanogens in suspended cultures active.H2/CO2 was the best methanogenic substrate for the bacteria in the effluent suspension of whey reactor, followed by formate and methanol. The least degradable substrate in suspension cultures was acetate. The optimal H2 gas concentration for methanogens was provided at 2.25 bar.Ferric ions addition or the addition of a mix of minerals improved acetate degradation and methane production rates more than two-folds. The redox potential + reducing agent was low enough for methanogenesis. An AnFB-reactor would be a suitable means for stabilizing wastewater from dairy processing. Liapor-clay-polyethylene sinter lamellas in a regularly arrangement could be the substratum for biofilm formation. A minimum HRT of 4-6 days should be planned or a maximum OLR rate 10 kg COD·m-3·d-1 not exceeded.

acetogenesis --- whey --- anaerobic fixed bed reactor --- degradation --- methanogenesis --- AnFB reactor

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This Special Issue on “New Trends in Catalysis for Sustainable CO2 Conversion”, released in the Catalysts open access journal, shows new research about the development of catalysts and catalytic routes for CO2 valorization, in addition to the optimization of the reaction conditions for the process. This issue includes ten articles and three reviews about different innovative processes for CO2 conversion.Carbon capture and storage (CCS) is a physical process consisting of the separation the CO2 (emitted by industry and the combustion processes for energy generation) and its transportation to geological storage isolates it from the atmosphere in the long term. However, the most promising routes for CO2 mitigation are those pursuing its catalytic valorization. By applying specific catalysts and suitable operating conditions, CO2 molecules react with other components to form longer chains (i.e., hydrocarbons). Accordingly, effort should be made to catalytically valorize CO2 (alone or co-fed with syngas) as an alternative way of reducing greenhouse gas emissions and obtaining high-value fuels and chemicals. Carbon capture and utilization (CCU) is a developing field with significant demand for research in the following aspects:The development of new catalysts, catalytic routes, and technologies for CO2 conversion;The study of new processes for obtaining fuels and chemicals from CO2;Optimization of the catalysts and the reaction conditions for these processes;Further steps in advanced processes using CO2-rich feeds (H2+CO2 or CO2 mixed with syngas), increasing product yields.

Technology: general issues --- History of engineering & technology --- Environmental science, engineering & technology --- carbon dioxide --- hydrogenation --- catalyst --- gas hourly space velocity (GHSV) --- fixed-bed reactor --- CO2–H2O photo-co-processing --- VIS-light driven reactions --- CO2 reduction --- photocatalysts properties --- soft oxidant --- oxidation --- dehydrogenation --- nano-catalyst --- electrochemical reduction of CO2 --- ionic liquids --- propylene carbonate --- imidazolium cation --- greenhouse gas --- climate change --- CO2 decomposition --- CO2 utilization --- SrFeO3−x --- CO2 methanation --- Ni-xSi/ZrO2 --- Si promotion --- oxygen vacancies --- CO2 hydrogenation --- light olefins --- catalyst deactivation --- CO2-Fischer-Tropsch (CO2-FT) --- iron-based catalysts --- methanol to olefins --- bifunctional composite catalysts --- SAPO-34 --- photocatalysis --- carbon-TiO2 --- nanocarbon --- carbon allotropes --- carbon nanotubes --- carbon nanofibers --- carbon nano-onions --- carbon dioxide electrolysis --- molten carbonate --- greenhouse gas mitigation --- cycloaddition --- ionic liquid --- deep eutectic solvents --- onium salt --- homogeneous catalysts --- heterogeneous catalysis --- CO2 conversion --- methane --- hydrocarbons --- iron oxide --- copper nanoparticles --- biomass --- Fischer–Tropsch synthesis --- carbon-supported iron catalyst --- gasoline --- diesel --- n/a --- CO2-H2O photo-co-processing --- Fischer-Tropsch synthesis

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Catalysts are widely used in a great variety of technologies, providing remarkable efficiency in order to address sustainable energy production, climate change challenges, and to reduce industrial emissions. In the framework of the Environmental Catalysis section promoted by the Catalysts Editorial Office, this Special Issue, entitled “Environmental Friendly Catalysts for Energy and Pollution Control Applications”, comprises novel studies representing the state-of-the-art research for efficient energy generation and industrial emission control based on new environmentally friendly catalyst materials (EFCs). In particular, in this Special Issue (SI), different kinds of catalysts are presented for catalytic solutions, including the reduction of NOx emissions (new zeolite catalyst modified with Pt), the elimination of volatile organic compounds (Co3O4@SiO2 and acidic surface transformed natural zeolite) and the removal of SO2 emissions (through adsorption processes with sodium citrate). Moreover, novel biocatalysts for bioanodes and new functional nanostructured catalysts based on metal–organic framework (MOFs) for different applications are also included. Additionally, articles compiled in this SI are also focused on the improvement of catalytic processes. Thus, selected processes based on activated carbons (modified with titanium dioxide) and optimized Fenton processes for the removal of aqueous organic pollutants or for the inactivation of bacteria are also presented.

Technology: general issues --- Environmental science, engineering & technology --- photocatalysis --- organic wastewater --- preparation method --- degradation --- characterizations --- hybridization --- exoelectrogen --- biocatalyst --- microenvironment --- porous electrode --- anaerobic --- recalcitrant compounds --- E. coli K12 --- methylene blue --- optimization --- Pareto chart --- perturbation graph --- Pt-based promoter --- CO oxidation --- environmental catalysis --- refinery compliance --- fluid catalytic cracking --- FCC --- sodium citrate --- sodium humate --- SO2 --- absorption --- BaQD --- carbamazepine --- ferric coordination complex --- photo-Fenton --- turbidity --- cyanide --- activated carbon --- titanium dioxide --- composites --- continuous flow --- adsorption --- catalytic ozonation --- Lewis and Brønsted acid sites --- natural zeolite --- reaction mechanism --- toluene --- three-phase modelling --- fixed-bed reactor --- wastewater treatment --- phenol --- granular activated carbon --- Ad/Ox --- volatile organic compounds --- core–shell structures --- spherical polymer templates --- Co3O4 --- Pd-based promoter --- NOx emission --- metal–organic frameworks --- heterogeneous catalysis --- carbon dioxide --- biomass --- hydrogenation --- oxidation --- Fisher-Tropsch

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Catalysts are widely used in a great variety of technologies, providing remarkable efficiency in order to address sustainable energy production, climate change challenges, and to reduce industrial emissions. In the framework of the Environmental Catalysis section promoted by the Catalysts Editorial Office, this Special Issue, entitled “Environmental Friendly Catalysts for Energy and Pollution Control Applications”, comprises novel studies representing the state-of-the-art research for efficient energy generation and industrial emission control based on new environmentally friendly catalyst materials (EFCs). In particular, in this Special Issue (SI), different kinds of catalysts are presented for catalytic solutions, including the reduction of NOx emissions (new zeolite catalyst modified with Pt), the elimination of volatile organic compounds (Co3O4@SiO2 and acidic surface transformed natural zeolite) and the removal of SO2 emissions (through adsorption processes with sodium citrate). Moreover, novel biocatalysts for bioanodes and new functional nanostructured catalysts based on metal–organic framework (MOFs) for different applications are also included. Additionally, articles compiled in this SI are also focused on the improvement of catalytic processes. Thus, selected processes based on activated carbons (modified with titanium dioxide) and optimized Fenton processes for the removal of aqueous organic pollutants or for the inactivation of bacteria are also presented.

photocatalysis --- organic wastewater --- preparation method --- degradation --- characterizations --- hybridization --- exoelectrogen --- biocatalyst --- microenvironment --- porous electrode --- anaerobic --- recalcitrant compounds --- E. coli K12 --- methylene blue --- optimization --- Pareto chart --- perturbation graph --- Pt-based promoter --- CO oxidation --- environmental catalysis --- refinery compliance --- fluid catalytic cracking --- FCC --- sodium citrate --- sodium humate --- SO2 --- absorption --- BaQD --- carbamazepine --- ferric coordination complex --- photo-Fenton --- turbidity --- cyanide --- activated carbon --- titanium dioxide --- composites --- continuous flow --- adsorption --- catalytic ozonation --- Lewis and Brønsted acid sites --- natural zeolite --- reaction mechanism --- toluene --- three-phase modelling --- fixed-bed reactor --- wastewater treatment --- phenol --- granular activated carbon --- Ad/Ox --- volatile organic compounds --- core–shell structures --- spherical polymer templates --- Co3O4 --- Pd-based promoter --- NOx emission --- metal–organic frameworks --- heterogeneous catalysis --- carbon dioxide --- biomass --- hydrogenation --- oxidation --- Fisher-Tropsch