Increased H2 Production Research Articles

Sugarcane bagasse and iron ore tailings thermochemical conversion towards sustainable iron recovery with biogenic carbon and hydrogen production

The recovery of valuable chemical elements from industrial waste is essential for production processes' economic and environmental sustainability. The interaction between the iron ore tailings and sugarcane bagasse, both wastes, has the potential to provide a secondary iron source for future iron and steelmaking processes. This study evaluated the use of volatiles from sugarcane bagasse (SCB) and iron ore tailings (IOT) to the synergistic promotion of carbon deposition, H2 production and conversion of weak magnetic iron oxides in strong magnetic iron phases. The experiments were carried out at 400, 600, 800, and 1000 ºC with different SCB/IOT ratios under an N2 atmosphere. In all tests, SCB and IOT were heated simultaneously in separate beds to prevent direct contact between the materials. The combination of 600 ºC and higher SCB/IOT ratio resulted in a product with 96.7% magnetite, 98% magnetic fraction recovery, and 3.5% deposited carbon. The use of lower SCB/IOT ratio provided an increase in H2 production. Regardless of the mass ratio, heating the IOT and SCB simultaneously up to 1000 ºC led to significant mineralogical transformations, reaching reduced phases such as wüstite, fayalite and metallic iron, which impaired magnetic separation efficiency. The results indicate an alternative for recovering iron from IOT using biomass waste as a renewable reducing agent for the steel industry.

Hydrogen Yield Enhancement in Biogas Dry Reforming with a Ni/Cr Catalyst: A Numerical Study

This numerical study investigates the impact of the reaction temperature, molar ratio of CH4:CO2, and catalyst porosity (εp) on the H2 yield and H2 selectivity during biogas dry reforming over a Ni/Cr catalyst. Using COMSOL Multiphysics, we conducted detailed simulations to elucidate the underlying reaction characteristics. Our findings reveal that increasing εp from 0.1 to 0.95 significantly provides a 5 times increase in H2 production and a 2.3% increase in H2 selectivity while simultaneously reducing CO selectivity by 2.3%. This effect is attributed to the improved mass transfer within the catalyst bed, leading to more efficient reactant conversion and product formation. Additionally, we observed a strong correlation between higher reaction temperatures and increased H2 yield and H2 selectivity. By optimizing these operational parameters, our results suggest that Ni/Cr catalysts can be effectively employed for the sustainable production of H2 from biogas.

Er3+:Y3Al5O12/Pt/ZnO material for photocatalytic hydrogen production under UV–Vis light

Hydrogen is a promising energy source, requiring increasingly efficient photocatalysts for production under UV–Vis light. For the first time, this study evaluated the photocatalytic generation of H2 using the Er3+:Y3Al5O12/Pt/ZnO material. The effect of the Er3+:Y3Al5O12 garnet on the photocatalytic activity of Pt/ZnO under UV–Vis light was evaluated. Firstly, both the ZnO and the Er3+:Y3Al5O12 garnet were synthesized by a sol-gel method, and the Pt-coating of the ZnO was performed using a sonochemical method. The samples were characterized through XRD, SEM-EDX, Raman, UV–Vis-DRS, N2 adsorption-desorption, XPS, and fluorescence spectroscopy. The H2 production under UV–Vis light was measured using mass spectrometry, and the effect of methanol as a sacrificial agent was evaluated. The synthesis method allowed obtaining ZnO with a defined spherical morphology and high crystallinity, with the H2 generation of 676 μmolh−1g−1. In the meantime, the Pt-coating reduced oxygen vacancies and the recombination rate of e−/h+ pairs, and the garnet addition in a mass ratio of Pt/ZnO:garnet at 1.0:0.3 led to the highest H2 production (1304 μmolh−1g−1), with only a 20 % decrease after 5 production cycles. Finally, adding 10 % v/v methanol significantly enhanced the H2 generation (3026 μmolh−1g−1). Altogether, the Er3+:Y3Al5O12/Pt/ZnO material with the sacrificial agent (10 % v/v methanol) improved H2 production from ZnO by a factor of 4.5. Thus, this study demonstrates that the Er3+:Y3Al5O12 garnet is an efficient alternative for significantly increasing H2 production from Pt/ZnO.

Limosilactobacillus Regulating Microbial Communities to Overcome the Hydrolysis Bottleneck with Efficient One-Step Co-Production of H2 and CH4.

The efficient co-production of H2 and CH4 via anaerobic digestion (AD) requires separate stages, as it cannot yet be achieved in one step. Lactic acid bacteria (LAB) (Limosilactobacillus) release H2 and acetate by enhancing hydrolysis, potentially increasing CH4 production with simultaneous H2 accumulation. This study investigated the enhanced effect of one-step co-production of H2 and CH4 in AD by LAB and elucidated its enhancement mechanisms. The results showed that 236.3 times increase in H2 production and 7.1 times increase in CH4 production are achieved, resulting in profits of 469.39 USD. Model substrates lignocellulosic straw, sodium acetate, and H2 confirmes LAB work on the hydrolysis stage and subsequent sustainable volatile fatty acid production during the first 6 days of AD. In this stage, the enrichment of Limosilactobacillus carrying bglB and xynB, the glycolysis pathway, and the high activity of protease, acetate kinase, and [FeFe] hydrogenase, jointly achieved rapid acetate and H2 accumulation, driving hydrogenotrophic methanogenesis dominated. From day 7 to 24, with enriched Methanosarcina, and increased methenyltetrahydromethanopterin hydrogenase activity, continuously produced acetate led to the mainly acetoclastic methanogenesis shift from hydrogenotrophic methanogenesis. The power generation capacity of LAB-enhanced AD is 333.33 times that of China's 24,000m3 biogas plant.

Biomass-to-Green Hydrogen: A Review of Techno-Economic-Enviro Assessment of Various Production Methods

H2 is considered a practical substitute for fossil fuels, especially for transportation by road and air, created either from fossil fuels or through the process of electrolysis of water. Research questions were included based on numerous research and the analysis of articles. The cost analysis of H2 processes, techno-economic hurdles in commercialization, and the economic comparison of various H2-production methods were the basis for the study of papers. The current research examines the different methods of thermochemical, biological, and electrochemical processes utilized in converting biomass into hydrogen. The benefits, constraints, and significant enhancements of every procedure are outlined. The examination assesses the cost of production, the level of technology readiness, and the potential for scalability. Thermochemical techniques, such as gasification and steam reforming, are effective at producing hydrogen. Steam gasification is perfect for moist and dry biomass in the absence of an oxidizing agent. Dark fermentation is more efficient for biological conversion because it requires less energy. Moreover, the electrochemical procedure is viable for biomass. Thermochemical treatment is significantly more advanced than biological or electrochemical treatment when it comes to scaling opportunities based on comparisons of current processes. The results of this research show that biomass–hydrogen processes have the potential for increasing H2 production, but further enhancements are needed to produce larger quantities for competitiveness.

Tailored Cu-Fe-based oxygen carrier for moderate-temperature chemical looping hydrogen generation from blast furnace gas

Chemical looping hydrogen generation (CLHG) offers a promising solution for producing H2 from industrial off-gas, such as blast furnace gas. However, increasing H2 production capacity of the oxygen carrier (OC) at moderate temperature remains a significant challenge. In this study, a novel Cu-Fe-based OC is tailored for moderate-temperature CLHG from blast furnace gas. The results demonstrates that the tailored OC exhibits a superior H2 production capacity of 12.99 mmol·g−1 at 550 °C, which is 6.5 times higher than that of Fe2O3 at the same temperature. The addition of Cu leads to the formation of oxygen defects, which facilitate the migration of lattice oxygen, thereby the activity of the OC is enhanced. Furthermore, cyclical experiments demonstrates that O2-assisted regeneration strategy can effectively suppress the segregation of Cu during the cycling process, and the tailored OC shows good stability during 10 redox cycles. No additional separation process was required and the purity of the hydrogen was higher than 99%. The findings here open a new avenue for efficient CLHG from industrial off-gas at moderate operation temperature.

Electrolytic production of NaOH and H2 from alkaline solution containing CO2 using cation exchange membranes

Amid climate change concerns, a revolutionary reinvention of industrial processes is urgently needed to mitigate CO2 emissions. Carbon capture, storage, and utilisation (CCSU) technologies have been proposed to reduce the release of CO2 into the atmosphere. In this study, six cation exchange membranes (CEMs) in a membrane electrolysis (ME) setup are evaluated in the regeneration of NaOH and production of H2 from a CO2-captured alkaline solution. The temperature, current intensity, and catholyte type were varied in the experiments. This study focuses on the commercially available membrane CMF based on its superior performance, but similar trends were observed for all six CEMs. The results indicate that the current intensity strongly influences the membrane electrolysis performance, with a higher current density increasing H2 production and catholyte pH. Furthermore, the investigation of the influence of temperature on performance demonstrates that higher temperatures lead to reduced overpotentials and have no significant effect on H2 production or NaOH regeneration. Thus, efficient NaOH regeneration occurs at reduced currents, especially at 298–303 K. Deionised water is recommended as the ideal catholyte for enhanced performance.

Liquid-Liquid Phase Separation-Mediated Photocatalytic Subcellular Hybrid System for Highly Efficient Hydrogen Production.

Plant chloroplasts have a highly compartmentalized interior, essential for executing photocatalytic functions. However, the construction of a photocatalytic reaction compartment similar to chloroplasts in inorganic-biological hybrid systems (IBS) has not been reported. Drawing inspiration from the compartmentalized chloroplast and the phenomenon of liquid-liquid phase separation, herein, a new strategy is first developed for constructing a photocatalytic subcellular hybrid system through liquid-liquid phase separation technology in living cells. Photosensitizers and in vivo expressed hydrogenases are designed to coassemble within the cell to create subcellular compartments for synergetic photocatalysis. This compartmentalization facilitates efficient electron transfer and light energy utilization, resulting in highly effective H2 production. The subcellular compartments hybrid system (HM/IBSCS) exhibits a nearly 87-fold increase in H2 production compared to the bare bacteria/hybrid system. Furthermore, the intracellular compartments of the photocatalytic reactor enhance the system's stability obviously, with the bacteria maintaining approximately 81% of their H2 production activity even after undergoing five cycles of photocatalytic hydrogen production. The research brings forward visionary prospects for the field of semi-artificial photosynthesis, offering new possibilities for advancements in areas such as renewable energy, biomanufacturing, and genetic engineering.

Accelerated Dynamic Reconstruction in Metal-Organic Frameworks with Ligand Defects for Selective Electrooxidation of Amines to Azos Coupling with Hydrogen Production.

Electrosynthesis coupled hydrogen production (ESHP) mostly involves catalyst reconstruction in aqueous phase, but accurately identifying and controlling the process is still a challenge. Herein, we modulated the electronic structure and exposed unsaturated sites of metal-organic frameworks (MOFs) via ligand defect to promote the reconstruction of catalyst for azo electrosynthesis (ESA) coupled with hydrogen production overall reaction. The monolayer Ni-MOFs achieved 89.8 % Faraday efficiency and 90.8 % selectivity for the electrooxidation of 1-methyl-1H-pyrazol-3-amine (Pyr-NH2) to azo, and an 18.5-fold increase in H2 production compared to overall water splitting. Operando X-ray absorption fine spectroscopy (XAFS) and various in situ spectroscopy confirm that the ligand defect promotes the potential dependent dynamic reconstruction of Ni(OH)2 and NiOOH, and the reabsorption of ligand significantly lowers the energy barrier of rate-determining step (*Pyr-NH to *Pyr-N). This work provides theoretical guidance for modulation of electrocatalyst reconstruction to achieve highly selective ESHP.

Accelerated Dynamic Reconstruction in Metal–Organic Frameworks with Ligand Defects for Selective Electrooxidation of Amines to Azos Coupling with Hydrogen Production

AbstractElectrosynthesis coupled hydrogen production (ESHP) mostly involves catalyst reconstruction in aqueous phase, but accurately identifying and controlling the process is still a challenge. Herein, we modulated the electronic structure and exposed unsaturated sites of metal–organic frameworks (MOFs) via ligand defect to promote the reconstruction of catalyst for azo electrosynthesis (ESA) coupled with hydrogen production overall reaction. The monolayer Ni‐MOFs achieved 89.8 % Faraday efficiency and 90.8 % selectivity for the electrooxidation of 1‐methyl‐1H‐pyrazol‐3‐amine (Pyr−NH2) to azo, and an 18.5‐fold increase in H2 production compared to overall water splitting. Operando X‐ray absorption fine spectroscopy (XAFS) and various in situ spectroscopy confirm that the ligand defect promotes the potential dependent dynamic reconstruction of Ni(OH)2 and NiOOH, and the reabsorption of ligand significantly lowers the energy barrier of rate‐determining step (*Pyr−NH to *Pyr−N). This work provides theoretical guidance for modulation of electrocatalyst reconstruction to achieve highly selective ESHP.

Hydrogen production in the Chlorella sp. DT mutants carrying heterologous electron donor ferredoxin 1 of Chlamydomonas reinhardtii

BackgroundFerredoxin 1 (Fd1) is the main electron donor to hydrogenase (HydA) for generating molecular hydrogen (H2) in green microalgae. In order to obtain an increased H2 production, the Fd1 of Chlamydomonas reinhardtii (CrFd1, encoded by crfd1) was therefore overexpressed in Chlorella sp. DT (DT) in this study. ResultsThe coding region of crfd1 was constructed into the p121-crfd1 plasmid, which was also constructed with a resistance gene to the antibiotic geneticin (G418) as a selection marker. The p121-crfd1 plasmid was transformed into DT cells by electroporation. Observation of the crfd1 gene fragment in the genomic DNA of DT-crfd1 mutants by PCR indicated that the transgene was successfully transformed. Using western blotting, the overexpressed CrFd1 protein, with a molecular weight of about 14 kDa, was found in DT-crfd1 mutants of DT-crfd1-4, DT-crfd1-22, and DT-crfd1-23. Using an in vitro assay, the H2 production of DT-crfd1-4, DT-crfd1-22, and DT-crfd1-23 mutants was about 4.4-, 5.0-, and 3.8-fold higher, respectively, than the DT wild type (DT-WT). Using an in vivo assay, the H2 production of DT-crfd1-4, DT-crfd1-22, and DT-crfd1-23 mutants was about 1.3-, 1.4-, and 1.2-fold higher, respectively, than the DT-WT. ConclusionsThe results suggested that heterologous overexpression of CrFd1 could enhance H2 production in DT-crfd1 mutants even though in vitro H2 production of DT-crfd1-22 mutant was up to 5-fold higher than the DT-WT.How to cite: Lin YJ, Chien LF. Hydrogen production in the Chlorella sp. DT mutants carrying heterologous electron donor ferredoxin 1 of Chlamydomonas reinhardtii. Electron J Biotechnol 2024;69. https://doi.org/10.1016/j.ejbt.2024.03.001.

Reaction mechanism and light gas conversion in pyrolysis and oxidation of dimethyl ether (DME): A ReaxFF molecular dynamics study

To uncover the microscopic reaction mechanisms of dimethyl ether (DME) pyrolysis and oxidation, reactive molecular dynamics simulations were employed to investigate the reaction processes under various O2/DME ratios and impurity environments at 2200 K–3200 K. The results show that DME pyrolysis begins with a decomposition reaction of CH3OCH3 → CH3O + CH3, ultimately leading to the formation of CO, H2 and PAHs. The reaction pathways of DME oxidation contain light gas conversion and combustion. In fuel rich conditions, the oxidation produces mainly H2 and CO, while in fuel lean conditions, the oxidation products tend to be H2O and CO2. The carbon components of DME are completely converted into CO2 and CO regardless of O2 content. In the presence of impurities H2O or CO2, the oxidation reaction pathway is altered, causing consumption and transformation of these impurities into active radicals such as OH, further promoting the progress of the reaction. The top three light gases produced are hydrogen, methanol and methane, and increasing H2 production in the DME oxidation process can be achieved through both oxygen subtraction and water addition. The rate of formaldehyde generation during pyrolysis is higher than that during oxidation. However, a higher oxygen content leads to increased formaldehyde production.

Synergistic solar energy integration for enhanced biomass chemical looping hydrogen production: Thermodynamics and techno-economic analyses

The concept of solar-assisted biomass chemical looping hydrogen (H2) production (BCLHP), wherein solar energy is directly integrated into the thermochemical H2 production process, was proposed. The mechanism behind the increased H2 production due to solar assistance was elucidated. Subsequently, a system design was proposed based on this principle, accompanied by strategies for managing solar energy fluctuations during system operation. Thermodynamics and techno-economic analyses were then conducted. The results indicate that the key principle behind the increased H2 production in solar-assisted BCLHP lies in substituting solar energy for the direct oxidation of the oxygen carrier, enabling full utilization of the oxygen carrier for H2 production without the need to maintain thermal balance. The integrated system based on this principle achieves a high solar-to-H2 exergy efficiency, with a theoretical maximum exceeding 30%, outperforming the exergy efficiencies of photovoltaic (PV) and solar thermal H2 production methods, while increasing the molar ratio of H2 to CO2 from 1.31 to 1.74. The economic viability of solar-assisted BCLHP systems and systems combining PV-based H2 production with BCLHP depends on a comprehensive assessment of local PV panel costs, heliostat costs, H2 selling prices, and solar conditions. This research presents a novel approach to enhance solar-to-H2 efficiency.

Application study of pyrolysis and steam gasification of modified fly ash mixed with coal

Coal fly ash (CF) is used in coal pyrolysis or gasification as a result of the high content of oxide metals. However, CaSO4 and SiO2 in CF inhibited catalytic activity. Herein, the application of acid-base modified CF to steam gasification of coal (CA). It was found that the order of acid-alkali modification had different effects on the H2 production. NaOH–HF (A-E) modified CF, there was no CaSO4 present on the surface of CF, and the surface SiO2 shell structure was destroyed, releasing more α-Fe and α-Fe2O3. A new Fe active phase (FexFy) had been formed. Meanwhile, the functional groups on the surface of modified CF changed, resulting in more C–H bonds, which provided more H sources for gasification. The α-Fe and α-Fe2O3 in NaOH–HF modified CF were in full contact with coal and steam, breaking the O–H bonds in the H2O, the aliphatic side-chain hydrocarbons and C–H bonds in the coal to produce more H2. α-Fe2O3 and α-Fe undergoes mutual transformation at the action of H2, providing more Fe to increasing H2 production. When the gasification temperature was 900 °C, the steam flow rate was 1 mL/min and the heating rate was 10 °C/min, the H2 yield increased from 915.97 mL/g-(E-A) to 1539.72 mL/g-(A-E), the carbon conversion of coal gasification was 99.68%.

Nanostructuration Effect of Carbon‐Based Phenylene Vinylene Conjugated Porous Polymers on TiO2 Hybrid Materials for Artificial Photosynthesis

This work examines the role of polymer nanostructuration of phenylene vinylene (PV) conjugated porous polymers (PV‐CPPs) as highly active photocatalysts for both hydrogen production and CO2 photoreduction reactions. It is found that nanostructured PV‐CPP hybrids with TiO2 show a high increase in H2 production being the most active example, the n‐IEP‐20@T‐10 sample with an evolution rate of 3.24 mmol g−1 h−1 (ξ = 1.20%), that is, 8 times higher than that of its non‐nanostructured and 65‐fold higher than TiO2. In contrast, CO2 photoreduction in both nanostructured polymers shows a significant improvement in CH4 production compared with bare TiO2, and a clear change of selectivity toward C2+ products. In particular, C2+/C1 ratios are obtained with n‐IEP‐20‐based hybrids increased by one order of magnitude that obtained for TiO2. The beneficial effect of this synthetic strategy is associated with an increase of the dispersion on nanostructured CPPs over TiO2 leading to an improvement on the surface interaction between them that favors longer‐lived photogenerated carriers in spatially separated redox active sites, which favor the production and selectivity to highly electron demanding products. The use of these nanostructuration strategies opens new opportunities for the production of more processable polymers for different energy technologies.

Investigation on bio-oil pyrolysis with Ni/Al2O3 blending: Influence of the blended catalyst on coke formation

Bio-oil can be converted into syngas, chemicals, and carbon materials via thermochemical and/or catalytic conversion routes. However, coking remains a significant challenge during the heating of bio-oil. In this study, we investigated the influence of pre-blending Ni/Al2O3 and bio-oil in an in-situ catalytic pyrolysis process on the coking behaviours of bio-oil. Our results indicate that the presence of Ni/Al2O3 significantly reduces coke yield and increases gas yield (for example, by a 14.2 % reduction in coke and a 44.1 % increase in gas at 700 °C). This is attributed to the suppression of the cross-linking reactions responsible for coke formation through the pre-elimination of O-containing groups into CO and CO2. Additionally, pre-blending of Ni/Al2O3 is highly desirable for transforming or stabilising the highly reactive substances in the early pyrolysis stage of bio-oil, minimising their tendency to polymerise. Furthermore, the presence of Ni/Al2O3 facilitates the cracking of C–H bonds and self-reforming of bio-oil, increasing H2 production (which is increased by 42.3 % at 700 °C), thereby promoting the breakage of side chains of lignin-derived aromatics and the hydrogenation of unsaturated structures, suppressing the formation of small aromatic systems in coke (<6 rings). Nevertheless, enhanced formation of alkyl-aryl C–C bonds during aromatisation leads to more condensed coke structures.

EXPLORANDO ADITIVOS PARA MEJORAR LA PRODUCCIÓN FERMENTATIVA DE BIOHIDRÓGENO

Dark fermentation appears as a promising strategy in the new energy landscape, as it enables the production of biohydrogen using a wide range of biomass substrates, thus also contributing to waste management. However, this process exhibits lower yields compared to conventional thermochemical processes for H2 production, such as reforming. To overcome this limitation, the use of additives has been explored to enhance microbial activity and increase dark fermentation yields. However, the application of additives remains limited in practice. This study aims to address this gap by examining the effects of three types of additives (zero-valent iron, activated carbon, and hydrochar) on dark fermentation and hydrogen generation. The results reveal that hydrochar shows the most promising outcomes, increasing H2 production by 20.3%, with the highest biohydrogen yield at 92 mLH2/g-glucose. Volatile fatty acid analysis reveals that butyric and acetic pathways are utilized for H2 production in this case. It is also important to consider the alkalinity of the feedstock, as high levels can increase the pH in the medium and promote methane (CH4) production as the main fermentation product instead of H2. When this occurs, Fe(0) NPs appear to be the additive that most favors methane generation, resulting in a 6.1% higher production compared to the control experiment. This confirms the interest in the use of certain additives in fermentative processes. Keywords: Activated carbon, Addition, Dark fermentation, Fe(0) nanoparticles, Green hydrogen, Hydrochar, VFA.

Black Phosphorus as Promoter for Noble Metal‐Free Photocatalytic Hydrogen Production

AbstractPhotocatalysts which are stable to photocorrosion and noble metal‐free, are highly desirable to achieve a light‐driven hydrogen production which satisfies the criteria of low production cost and environmental sustainability. Herein, a new heterostructure TiO2/BP/CoP has been developed, in which the BP nanosheets interact strongly with TiO2 and CoP, speeding up the transfer of photogenerated electrons and thus increasing H2 production. Once BP is added to TiO2 (P25) as only 1 % wt., the H2 evolution rate increases up to 4 times reaching a value of 830 μmol/g ⋅ h under UV‐Vis light irradiation. By integrating CoP nanoparticles as a cocatalyst up to 2 % wt., H2 production is further promoted to 7400 μmol/g ⋅ h, 37 times higher than pristine TiO2. Photoluminescence and electrochemical impedance measurements show that this heterostructure achieves a much more efficient charge separation and reduction of the internal resistance in comparison to pristine TiO2. Combining these data with UV‐Vis diffuse reflectance and Mott‐Schottky, a plausible mechanism was proposed.

Digestate recirculation rate optimization for the enhancement of hydrogen production: The case of disposable nappies and fruit/vegetable waste valorization in a mesophilic two-stage anaerobic digestion system

After the anaerobic digestion involvement in waste management, several attempts have been made for the biogas yields enhancement. The implementation of methanogenic effluent (digestate) recirculation has been proposed as an alternative for the pH adjustment in two-stage reactors, leading to decreased alkali solution requirements, which could subsequently reduce operational costs. In the current study, a mixture of 40–60% (w/w) fruits/vegetable waste-disposable nappies hydrolysate was valorized through the anaerobic digestion process. The digestate recirculation rate (RR) optimization took place in a continuous acidogenic reactor, followed by the two-stage system operation under various experimental conditions. Particularly, the RRs of 0-0.25-0.5-0.75-1 were tested, indicating up to 208% H2 production increase (RR0.25). The single- and two-stage configurations comparison followed, under the hydraulic retention time (HRT) of 25 d, while the two-stage operation was evaluated for pH adjustment (5.5) not only with alkali solution but also with the applied RR0.5 (reduced alkali solution requirements compared to RR0.25). During the two-stage system operation under RR, additional scenarios were investigated regarding the HRTmethanogenic reduction and the pH adjustment, while using exclusively digestate. Although the RR implementation seems promising, the digestate alkalinity content can significantly determine the system's efficiency.

Effect of nitrate supplementation, dietary protein supply, and genetic yield index on performance, methane emission, and nitrogen efficiency in dairy cows

The objective was to investigate the effect of nonprotein nitrogen source, dietary protein supply, and genetic yield index on methane emission, N metabolism, and ruminal fermentation in dairy cows. Forty-eight Danish Holstein dairy cows (24 primiparous cows and 24 multiparous cows) were used in a 6 × 4 incomplete Latin square design with 4 periods of 21-d duration. Cows were fed ad libitum with the following 6 experimental diets: diets with low, medium, or high rumen degradable protein (RDP):rumen undegradable protein (RUP) ratio (manipulated by changing the proportion of corn meal, corn gluten meal, and corn gluten feed) combined with either urea or nitrate (10 g NO3-/kg of dry matter) as nonprotein nitrogen source. Samples of ruminal fluid and feces were collected from multiparous cows, and total-tract nutrient digestibility was estimated using TiO2 as flow marker. Milk samples were collected from all 48 cows. Gas emission (CH4, CO2, and H2) was measured by 4 GreenFeed units. We observed no significant interaction between dietary RDP:RUP ratio and nitrate supplementation, and between nitrate supplementation and genetic yield index on CH4 emission (production, yield, intensity). As dietary RDP:RUP ratio increased, intake of crude protein, RDP, and neutral detergent fiber and total-tract digestibility of crude protein linearly increased, and RUP intake linearly decreased. Yield of milk, energy-corrected milk, and milk protein and lactose linearly decreased, whereas milk fat and milk urea nitrogen concentrations linearly increased as dietary RDP:RUP ratio increased. The increase in dietary RDP:RUP ratio resulted in a linear increase in the excretion of total purine derivatives and N in urine, but a linear decrease in N efficiency (milk N in % of N intake). Nitrate supplementation reduced dry matter intake (DMI) and increased total-tract organic matter digestibility compared with urea supplementation. Nitrate supplementation resulted in a greater reduction in DMI and daily CH4 production and a greater increase in daily H2 production in multiparous cows compared with primiparous cows. Nitrate supplementation also showed a greater reduction in milk protein and lactose yield in multiparous cows than in primiparous cows. Milk protein and lactose concentrations were lower for cows receiving nitrate diets compared with cows receiving urea diets. Nitrate supplementation reduced urinary purine derivatives excretion from the rumen, whereas N efficiency tended to increase. Nitrate supplementation reduced proportion of acetate and propionate in ruminal volatile fatty acids. In conclusion, no interaction was observed between dietary RDP:RUP ratio and nitrate supplementation, and no interaction between nitrate supplementation and genetic yield index on CH4 emission (production, yield, intensity) was noted. Nitrate supplementation resulted in a greater reduction in DMI and CH4 production, and a greater increase in H2 production in multiparous cows than in primiparous cows. As the dietary RDP:RUP ratio increased, CH4 emission was unaffected and RDP intake increased, but RUP intake and milk yield decreased. Genetic yield index did not affect CH4 production, yield, or intensity.