CH4 Yield Research Articles

Light-Induced Dynamic Activation of Copper/Silicon Interface for Highly Selective Carbon Dioxide Reduction.

Numerous studies have shown a fact that phase transformation and/or reconstruction are likely to occur and play crucial roles in electrochemical scenarios. Nevertheless, a decisive factor behind the diverse photoelectrochemical activity and selectivity of various copper/silicon photoelectrodes is still largely debated and missing in the community, especially the possibly dynamic behaviors of metal catalyst/semiconductor interface. Herein, through in situ X-ray absorption spectroscopy and transmission electron microscope, a model system of Cu nanocrystals with well-defined facets on black p-type silicon (BSi) is unprecedentedly demonstrated to reveal the dynamic phase transformation of forming irreversible silicide at Cu nanocrystal-BSi interface during photoelectrocatalysis, which is validated to originate from the atomic interdiffusion between Cu and Si driven by light-induced dynamic activation process. Significantly, the adaptive junction at Cu-Si interface is activated by an expansion of interatomic Cu-Cu distance for CO2 electroreduction, which efficiently restricts the C-C coupling pathway but strengthens the bonding with key intermediate of *CHO for CH4 yield, resulting in a remarkable 16-fold improvement in the product ratio of CH4/C2 products and an intriguing selectivity switch. This work offers new insights into dynamic structural transformations of metal/semiconductor junction and design of highly efficient catalysts toward photosynthesis.

Study on the preparation of CdS/TiO2 corn straw biochar composite materials for photocatalytic reduction of CO2 and collaborative H2 production.

A thermal synthesis method was employed in this work to prepare CdS/TiO2 corn straw biochar photocatalytic composite materials suitable for synergistic hydrogen production with the photocatalytic reduction of CO2. The structure and synergistic reaction of these composite materials were characterized by its photogenerated electron transfer process. Compared with pure TiO2, the energy band gap of the optimal CdS/TiO2 corn straw biochar composite material was reduced to 2.89eV. The heterostructure coupling between TiO2 and CdS in the biochar accelerated the transfer of photogenerated electrons and reduced the recombination rate of photogenerated electrons and holes. Under visible light irradiation, the photocatalytic H2 yield of this CdS/TiO2 corn straw-derived biochar composite material was 1200µmol·h-1·g-1, the CO yield was 150µmol·h-1·g-1, and the CH4 yield was 55µmol·h-1·g-1. The key to this synergistic reaction is the formation of heterojunctions between CdS and TiO2 as well as the rapid oxidation of holes in the composite material caused by the doping of biochar.

Advancing CO2 to CH4 conversion: The pivotal role of RuCu alloy in crystalline red phosphorus photocatalysis

Crystalline red phosphorus (CRP), a newly emerging photocatalyst, shows promise for selective CH4 production from CO2 and H2O. Yet, its potential remains largely untapped, particularly in enhancing photocatalytic performance. We address this gap by incorporating RuCu alloy nanoparticles into CRP, significantly boosting its efficiency in converting CO2 to CH4. Advanced analyses demonstrate that the synergistic mechanism between the RuCu alloy and CRP facilitates improved charge separation and expands the availability of active sites, leading to an impressive CH4 yield of 19.7 μmol g−1 h−1. Importantly, the inclusion of Cu in the alloy modifies the catalytic reaction pathways facilitated by Ru, achieving an exceptional CO2 to CH4 selectivity of 96 %. This performance surpasses that of many existing elemental-based and Ru-containing photocatalysts. Our research highlights the potential of functionalized elemental photocatalysts and the importance of alloy composition in photocatalyst design for sustainable CO2 conversion.

Volatile fatty acid and methane production from vinasse and microalgae using two-stage anaerobic co-digestion.

The effects of adding vinasse (VIN) as a co-substrate on the stability and production of volatile fatty acids (VFA) and methane (CH4) during the anaerobic digestion (AD) of microalgal biomass (MB) were evaluated. The AD system consisted of an acidogenic reactor (AR) followed by a methanogenic reactor (MR). The experiment was divided into phase I-start-up and AD of VIN; phase II-MB+VIN co-digestion (50:50 based on chemical oxygen demand (COD)); and phase III-co-digestion of pretreated MB and VIN (PTMB+VIN, 50:50). In phase I, the total amount of VFA in the AR increased from 240 to 2126 mg/L. In the MR, the conversion of VFA into CH4 yielded an average of 71 ± 37 NmL CH4/g CODin. In phase II, the initial CH4 production was 246 ± 31 mL CH4/g CODin but it decreased to 63 mL CH4/g CODin due to the accumulation of longer chain acids. More stable conditions were achieved after two hydraulic retention cycles and the average CH4 yield in this phase was 183 mL CH4/g CODin. In phase III, when using PTMB, 197 ± 72 NmL CH4/g CODin were obtained, i.e., a 2.7- and 1.1-fold increases compared to phases I and II, respectively. The predominance of acetate producers and syntrophic organisms suggests acetoclastic methanogenesis, confirmed by the occurrence of Methanosaeta (10.5%).

Heterogeneous g-C3N4/polyaniline composites enhanced the conversion of organics into methane during anaerobic wastewater treatment

In this study, g-C3N4/PANI was prepared by in situ oxidative polymerization. Graphite-phase carbon nitride (g-C3N4) with surface defects was deposited onto the surface of conductive polyaniline (PANI) to form a p-n heterojunction. This construction aimed to create an efficient heterogeneous catalyst, increasing the surface defect level and active sites of the composite, and augmenting its capability to capture and transfer extracellular electrons under anaerobic conditions. This addresses the challenge of low efficiency in direct interspecies electron transfer between bacteria and archaea during anaerobic digestion for methane production. The results showed that the prepared g-C3N4/PANI increased the CH4 yield and CH4 production rate by 82% and 96%, respectively. Notably, the conductivity and XPS test results showed that the ratio of g-C3N4 to PANI was 0.15, and the composite exhibited favorable conductivity, with a uniform distribution of pyrrolic nitrogen, pyridinic nitrogen, and graphitic nitrogen, each accounting for approximately 30%. Furthermore, g-C3N4/PANI effectively enhanced the metabolic efficiency of intermediate products such as acetate and butyrate. Analysis of the microbial community structure revealed that g-C3N4/PANI led to a significant increase in the abundance of hydrogenotrophic methanogen Methanolinea (from 48% to 64%) and enriched Clostridium (a rise of 1%) with direct interspecies electron transfer capability. Microbial community function analysis demonstrated that the addition of g-C3N4/PANI boosted the activities of key enzymes involved in anaerobic digestion, including phosphate transacetylase (PTA), phospho-butyryl transferase (PTB), and NAD-independent lactate dehydrogenase (NNLD), by 47%, 135%, and 153%, respectively. This acceleration in enzymatic activity promoted the metabolism of acetyl-CoA, butyryl-CoA, and pyruvate. Additionally, the function of ABC transporters was enhanced, thereby improving the efficiency of material and energy exchange among microorganisms.

Identifying reliable microbial indicators in anaerobic digestion of organic solid waste: Insights from a meta-analysis

The identification of microbial indicators holds significant promise for detecting key challenges of anaerobic digestion, driving microbial management. In order to be considered reliable, microbial indicators must possess certain features, such as universality, significant abundance changes under stressful conditions, and the ability to predict CH4 yield. To investigate the performance of microbial indicators, a meta-analysis was conducted on 178 publicly available 16 S rRNA gene sequences from 12 studies that examined the anaerobic digestion process of organic solid wastes. The analysis identified key taxa that achieved microbial indicator features through two different approaches: whole community and core microbiome analysis. The alpha diversity analysis indicated that a specialized genus-level microbial community with a high number of sOTUs was crucial for achieving high CH4 yield. Aminobacterium, Clostridium, HA73, T78, Corynebacterium, Lactobacillus, and Prevotella exhibited a higher number of microbial indicators attributes, including a significant response in their abundance and predictive capability for CH4 yield, along with relevant metabolic roles associated with inhibitory compounds. Among them, Corynebacterium, Lactobacillus, and Prevotella demonstrated robust fold-change features to increase the likelihood of successful categorization and, Aminobacterium, Clostridium, HA73, and T78 showed universality, suggesting easy detection across various anaerobic digestion processes. Understanding the advantages and drawbacks of reliable microbial indicators and considering their features will aid in the selection of appropriate detection techniques, offering valuable insights for future validation and implementation for AD processes improvement or control.

Comparison of methane yield of a novel strain of Methanothermobacter marburgensis in pure and mixed adapted culture derived from a methanation bubble column bioreactor

The ongoing discussion regarding the use of mixed or pure cultures of hydrogenotrophic methanogenic archaea in Power-to-Methane (P2M) bioprocess applications persists, with each option presenting its own advantages and disadvantages. To address this issue, a comparison of methane (CH4) yield between a novel methanogenic archaeon belonging to the species Methanothermobacter marburgensis (strain Clermont) isolated from a biological methanation column, and the community from which it originated, was conducted. This comparison included the type strain M. marburgensis str. Marburg. The evaluation also examined how exposure to oxygen (O2) for up to 240 min impacted the CH4 yield across these cultures. While both Methanothermobacter strains exhibit comparable CH4 yield, slightly higher than that of the mixed adapted culture under non-O2-exposed conditions, strain Clermont does not display the lag time observed for strain Marburg.

Photocatalytic CO2 reduction to CH4 in continuous flow reactor using Fe2TiO5 enhanced by magnetron sputtering-deposited CuO nanoparticles cocatalyst

Fe2TiO5 is a promising and underexplored material as a semiconductor photocatalyst for CO2 reduction reaction (PCO2RR), aimed at mitigating greenhouse gas emissions. In this study, pure Fe2TiO5 was synthesized via solvothermal method and subsequently calcined across temperatures ranging from 600 to 900 °C. The performance was evaluated within a PCO2RR under simulated sunlight, generating CH4 as a single detectable product. Further enhancement was achieved by depositing CuO nanoparticles below 5 nm onto the Fe2TiO5 surface using magnetron sputtering deposition. The yield of CH4 increased from 0.032 to 0.042 µmol. As far as we know, this marks the inaugural application of Fe2TiO5 as a photocatalyst for CO2 reduction.

Rational design of spatial charge separation and targeted active site Cu for highly selective photocatalytic CO2 reduction to CH4

Photocatalytic CO2 reduction reaction (CO2RR) is usually constrained by sluggish kinetics and low product selectivity. Herein, a Cu-doping multi-tier hierarchical S-scheme heterostructure Cu-ZnIn2S4/ZIF-67 was fabricated, achieving highly efficient photocatalytic CO2RR under visible light without additional thermal input. At low pressure (absolute pressure 40 kPa), the optimized catalyst 2Cu-ZISF demonstrated a CH4 yield of 22.27 μmol g−1h−1 with a selectivity of 94.7 %. In situ XPS and EPR confirmed that the photogenerated charge transfer obeys an S-scheme mechanism, with Cu sites serving as electron-rich centers, facilitating spatial charge separation. In situ DRIFT detected reaction intermediates of photocatalytic CO2RR mechanism, and Gibbs free energy calculations via Density Functional Theory revealed that Cu incorporation significantly stabilizes surface CO* species, thus reducing CO(g) production and facilitating hydrogenation, thereby acting as targeted active sites for CH4 production. This work overcomes the limitations of slow reaction kinetics and offers an in-depth understanding of how to design effective S-scheme heterojunction photocatalysts and their charge transfer mechanisms.

Novel spherical InVO4/floral Bi2MoO6 Z-scheme heterojunction for efficient photocatalytic carbon dioxide reduction

The development of efficient CO2 reduction photocatalysts is of great significance to improving the global greenhouse effect and alleviating the energy crisis. In this paper, spherical InVO4/floral Bi2MoO6 (IVO/BMO) Z-scheme heterojunction was prepared by a hydrothermal method, and the surface structure, chemical composition, and photovoltaic properties of the samples were characterized and tested for their CO2 reduction performance. The experimental results show that 1.5 %-IVO/BMO exhibits excellent photocatalytic activity for CO2 reduction under the irradiation of 300 W Xenon lamp, with a CO yield of 34.08 µmol/g/h and a CH4 yield of 4.49 µmol/g/h, which are 2.55 and 1.05 times higher than that of the pure Bi2MoO6, respectively. The enhanced photocatalytic activity can be attributed to the formation of an IVO/BMO Z-scheme heterojunction, which promotes electron separation and reduces charge recombination at the interface, facilitating the reaction process. This study provides a novel Z-scheme photocatalyst for efficient carbon dioxide reduction.

Dimensionally Intact Construction of Ultrathin S-Scheme CuFe2O4/ZnIn2S4 Heterojunctional Photocatalysts for CO2 Photoreduction.

The conversion of CO2 into carbon-neutral fuels such as methane (CH4) through selective photoreduction is highly sought after yet remains challenging due to the slow multistep proton-electron transfer processes and the formation of various C1 intermediates. This research highlights the cooperative interaction between Fe3+ and Cu2+ ions transitioning to Fe2+ and Cu+ ions, enhancing the photocatalytic conversion of CO2 to methane. We introduce an S-scheme heterojunction photocatalyst, CuFe2O4/ZnIn2S4, which demonstrates significant efficiency in CO2 methanation under light irradiation. The CuFe2O4/ZnIn2S4 heterojunction forms an internal electric field that aids in the mobility and separation of exciton carriers under a wide solar spectrum for exceptional photocatalytic performance. Remarkably, the optimal CuFe2O4/ZnIn2S4 heterojunction system achieved an approximately 68-time increase in CO2 conversion compared with ZnIn2S4 and CuFe2O4 nanoparticles using only pure water, with nearly complete CO selectivity and yields of CH4 and CO reaching 172.5 and 202.4 μmol g-1 h-1, respectively, via a 2-electron oxygen reduction reaction (ORR) process. The optimally designed CuFe2O4/ZnIn2S4 heterojunctional system achieved approximately 96% conversion of BA and 98.5% selectivity toward benzaldehyde (BAD). Additionally, this photocatalytic system demonstrated excellent cyclic stability and practical applicability. The photogenerated electrons in the CuFe2O4 conduction band enhance the reduction of Fe3+/Cu2+ to Fe2+/Cu+, creating a microenvironment conducive to CO2 reduction to CO and CH4. Simultaneously, the appearance of holes in the ZnIn2S4 valence band facilitates water oxidation to O2. The synergistic function within the CuFe2O4/ZnIn2S4 heterojunction plays a pivotal role in facilitating charge transfer, accelerating water oxidation, and thereby enhancing CO2 reduction kinetics. This study offers valuable insights and a strategic framework for designing efficient S-scheme heterojunctions aimed at achieving carbon neutrality through solar fuel production.

High-Rate and Selective C2H6-to-C2H4 Photodehydrogenation Enabled by Partially Oxidized Pdδ+ Species Anchored on ZnO Nanosheets under Mild Conditions.

Photocatalytic C2H6-to-C2H4 conversion is very promising, yet it remains a long-lasting challenge due to the high C-H bond dissociation energy of 420 kJ mol-1. Herein, partially oxidized Pdδ+ species anchored on ZnO nanosheets are designed to weaken the C-H bond by the electron interaction between Pdδ+ species and H atoms, with efforts to achieve high-rate and selective C2H6-to-C2H4 conversion. X-ray photoelectron spectra, Bader charge calculations, and electronic localization function demonstrate the presence of partially oxidized Pdδ+ sites, while quasi-in situ X-ray photoelectron spectra disclose the Pdδ+ sites initially adopt and then donate the photoexcited electrons for C2H6 dehydrogenation. In situ electron paramagnetic resonance spectra, in situ Fourier transform infrared spectra, and trapping agent experiments verify C2H6 initially converts to CH3CH2OH via ·OH radicals, then dehydroxylates to CH3CH2· and finally to C2H4, accompanied by H2 production. Density-functional theory calculations elucidate that loading Pd site can lengthen the C-H bond of C2H6 from 1.10 to 1.12 Å, which favors the C-H bond breakage, affirmed by a lowered energy barrier of 0.04 eV. As a result, the optimized 5.87% Pd-ZnO nanosheets achieve a high C2H4 yield of 16.32 mmol g-1 with a 94.83% selectivity as well as a H2 yield of 14.49 mmol g-1 from C2H6 dehydrogenation in 4 h, outperforming all the previously reported photocatalysts under similar conditions.

Systematic review for optimizing sample size in dairy cow methane emission studies in temperate regions: a comprehensive methodological approach.

This research introduces a systematic framework for calculating sample size in studies focusing on enteric methane (CH4, g/kg of DMI) yield reduction in dairy cows. Adhering to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, we conducted a comprehensive search across the Web of Science, Scopus, and PubMed Central databases for studies published from 2012 to 2023. The inclusion criteria were: studies reporting CH4 yield and its variability in dairy cows, employing specific experimental designs (Latin Square Design (LSD), Crossover Design, Randomized Complete Block Design (RCBD), and Repeated Measures Design) and measurement methods (Open-circuit respirometry chambers (RC), the GreenFeed system, and the sulfur hexafluoride tracer technique), conducted in Canada, the United States and Europe. A total of 150 studies, which included 177 reports, met our criteria and were included in the database. Our methodology for using the database for sample size calculations began by defining 6 CH4 yield reduction levels (5, 10, 15, 20, 30, and 50%). Utilizing an adjusted Cohen's f formula and a power analysis we calculated the sample sizes required for these reductions in balanced LSD and RCBD reports from studies involving 3 or 4 treatments. The results indicate that within-subject studies (i.e., LSD) require smaller sample sizes to detect CH4 yield reductions compared with between-subject studies (i.e., RCBD). Although experiments using RC typically require fewer individuals due to their higher accuracy, our results demonstrate that this expected advantage is not evident in reports from RCBD studies with 4 treatments. A key innovation of this research is the development of a web-based tool that simplifies the process of sample size calculation (samplesizecalculator.ucdavis.edu). Developed using Python, this tool leverages the extensive database to provide tailored sample size recommendations for specific experimental scenarios. It ensures that experiments are adequately powered to detect meaningful differences in CH4 emissions, thereby contributing to the scientific rigor of studies in this critical area of environmental and agricultural research. With its user-friendly interface and robust backend calculations, this tool represents a significant advancement in the methodology for planning and executing CH4 emission studies in dairy cows, aligning with global efforts toward sustainable agricultural practices and environmental conservation.

Concentrated solar CO2 reduction in H2O vapour with >1% energy conversion efficiency

H2O dissociation plays a crucial role in solar-driven catalytic CO2 methanation, demanding high temperature even for solar-to-chemical conversion efficiencies <1% with modest product selectivity. Herein, we report an oxygen-vacancy (Vo) rich CeO2 catalyst with single-atom Ni anchored around its surface Vo sites by replacing Ce atoms to promote H2O dissociation and achieve effective photothermal CO2 reduction under concentrated light irradiation. The high photon flux reduces the apparent activation energy for CH4 production and prevents Vo from depletion. The defects coordinated with single-atom Ni, significantly promote the capture of charges and local phonons at the Ni d-impurity orbitals, thereby inducing more effective H2O activation. The catalyst presents a CH4 yield of 192.75 µmol/cm2/h, with a solar-to-chemical efficiency of 1.14% and a selectivity ~100%. The mechanistic insights uncovered in this study should help further the development of H2O-activating catalysts for CO2 reduction and thereby expedite the practical utilization of solar-to-chemical technologies.

Effect of carbohydrate type in silages and concentrates on feed intake, enteric methane, and milk yield from dairy cows

Dietary carbohydrate manipulation can be used to reduce enteric CH4 emission, but there is a lack of studies on the interaction of different types of carbohydrates that can affect feed intake and ruminal fermentation. Understanding this interaction is necessary to make the most out of CH4 mitigation feeding strategies using different dietary carbohydrates. The aim of this study was to test the effect on enteric CH4 emission, feed intake and milk production response when cows were fed either grass-clover (GCS) or corn silage (CS) as the sole forage source (55% of dry matter, DM), in combination with either barley (BAR) or dried beet pulp (DBP) as a concentrate (21.5% of DM). Twenty-four (half first and half second parity) cows were used in a crossover design with 2 periods of 21 d each, receiving 2 of 4 diets obtained from a 2 × 2 factorial arrangement of the experimental diet. Feed intake, CH4 emission metrics and milk production were recorded at the end of the experimental periods. The diets had NDF concentrations between 258 and 340 g/kg of DM, and starch concentrations between 340 and 7.45 g/kg of DM (CS-BAR and GCS-DBP, respectively). The effects of silage and concentrate on dry matter intake (DMI) were additive, with the highest feed intake in cows fed COR-BAR, followed by cows fed COR-DBP, GCS-BAR, and GCS-DBP (21.2, 19.9, 19.1, and 18.3 kg/d). Energy corrected milk (ECM) yield was not affected by silage source in first parity cows, but it was higher for cows fed CS than cows fed GCS in second parity. The effects of silage and concentrate on CH4 production (g/d), yield (g/kg of DMI) and intensity (g/kg of ECM) were not additive as cows fed GCS had similar responses regardless of the concentrate used, but cows fed CS had lower CH4 production, yield and intensity, when fed BAR instead of DBP. The lower CH4 production, yield and intensity in cows fed CS-BAR compared with other diets could be partially explained by the nonlinear relationship between ruminal VFA and carbohydrates (NDF and starch) concentration reported in literature, however, we observed a linear relationship between acetate:propionate ratio and CH4 yield, suggesting possible other effects. The effects of silage and concentrate on the ruminal VFA were additive in first parity cows, but not in second parity cows. The interaction between dietary CHO type and parity might indicate an effect of feed intake or the energy balance of the cow. Feeding cows silage and concentrate both rich in starch can result in the lowest enteric CH4 emission.

Direct conversion of CO2 to CH4 on Pd/graphdiyne single-crystalline.

A major impediment to the development of the efficient use of artificial photosynthesis is the lack of highly selective and efficient photocatalysts toward the conversion of CO2 by sunlight energy at room temperature and ambient pressure. After many years of hard work, we finally completed the synthesis of graphdiyne-based palladium quantum dot catalysts containing high-density metal atom steps for selective artificial photosynthesis. The well-designed interface structure of the catalyst is composed of electron-donor and acceptor groups, resulting in the obvious incomplete charge-transfer phenomenon between graphdiyne and plasmonic metal nanostructures on the interface. These intrinsic characteristics are the origin of the high performance of the catalyst. Studies on its mechanism reveal that the synergism between 'hot electron' from local surface plasmon resonance and rapid photogenerated carrier separation at the ohmic contact interface accelerates the multi-electron reaction kinetics. The catalyst can selectively synthesize CH4 directly from CO2 and H2O with selectivity of near 100% at room temperature and pressure, and exhibits transformative performance, with an average CH4 yield of 26.2 μmol g-1 h-1 and remarkable long-term stability.

Internal electric field-modulated dual S-scheme ZnO@Co3O4/CsPbBr3 nanocages for highly active and selective photocatalytic CO2 reduction

The rational design of a step-scheme (S-scheme) heterojunction with strong internal electric field (IEF) and high redox capacity is a promising strategy for photocatalytic CO2 reduction reaction (CO2RR). However, the precise process of charge transport on the multi-interfaces remains a great challenge. Herein, a dual S-scheme heterojunction constructed in the ZnO@Co3O4/CsPbBr3 hierarchical nanocage was prepared for enhancing CO2RR activity. Without sacrificial agent and photosensitizer, the optimal photocatalyst exhibits a competitive CH4 yield rate of 238.8 μmol g−1h−1 with high selectivity (90.9%), affording an apparent quantum efficiency of 4.6 % at 400 nm, outperforming most previously comparable photocatalysts. In situ X-ray photoelectron spectroscopy (in situ XPS), photoelectrochemical measurement and theoretical calculation verifies the dual S-schematic charge-transport pathway. The remarkably improved performance in CO2RR is due to the rapid charge separation through O-Co-Br bridge driven by the strong internal electric field. This research furnishes a new insight to reveal dynamic charge transfer mechanism for CO2 conversion applications.

Nitrate-promoted gas–solid reactions of H2 and CaCO3 for mid-temperature integrated CO2 capture and methanation

Integrated CO2 capture and methanation (ICCM) technology has attracted increasing attention for Carbon Neutrality. However, in the mid-temperature ICCM studies dominated by MgO, which involves the gas–gas catalytic pathway, the problems of high CO2 escape and low CH4 yield are common. Replacing MgO with CaO reduced CO2 escape because the reaction proceeded via the gas–solid pathway. However, the lower CaCO3 conversion rate limits its further applications. Here, we present an ICCM process with efficient CaCO3 conversion using alkali metal nitrates (KNO3, LiNO3, and (Li-K)NO3) to promote Ru/CeO2-CaO. The results showed that the doping of nitrates led to a decrease in the specific surface area of CaO, thus losing part of the CO2 capture performance. On the other hand, forming the molten liquid layer facilitated the gas–solid reaction between CaCO3 and H2, which improved the CaCO3 conversion. Compared with the Ru/CeO2-Neat CaO without nitrate promotion, the CaCO3 conversion of Ru/CeO2-KNO3/CaO was increased by 42% and CH4 yield by 52% after five ICCM cycles. Furthermore, kinetic analysis and in situ DRIFTS experiments demonstrated that molten KNO3 facilitated mass transfer in the diffusion-controlled stage of direct CaCO3 hydrogenation.

Effect of combining the methanogenesis inhibitor 3-nitrooxypropanol and cottonseeds on methane emissions, feed intake, and milk production of grazing dairy cows

No single enteric CH4 mitigating strategy has been consistently effective or is readily applicable to ruminants in grassland systems. When CH4 mitigating strategies are effective under grazing conditions, mitigation is mild to moderate at best. A study was conducted to evaluate the potential of combining two CH4 mitigation strategies deemed feasible to apply in grazing dairy cows, the methanogenesis inhibitor 3-nitrooxypropanol additive (3-NOP) and cottonseed supplementation (CTS), seeking to enhance their individual CH4 mitigating potential. Forty-eight dairy cows were evaluated in a continuous grazing study and supplemented with either a starch-based concentrate (STA) or one that contained cottonseeds (1.75 kg DM/d; CTS), and with either 19 g/d of 10% 3-NOP (Bovaer®) or the additive’s carrier (placebo), in a 2 × 2 factorial arrangement of treatments. Treatments were supplied mixed with a concentrate supplement (5 kg/d as fed) and offered in two equal rations at milking. Methane emissions were measured on weeks 4 and 8 using the sulphur hexafluoride tracer gas technique over a 5-d period. The 3-NOP and CTS treatments tended to interact on absolute CH4 such that 3-NOP decreased CH4 by 13.4% with STA, but there was no mitigation with 3-NOP and CTS. Treatment interactions were also obtained for CH4 yield, where 3-NOP tended to decrease CH4 when supplied with STA, and tended to increase it with CTS. The increase in CH4 yield with the CTS diet was driven by a numerical decrease in DM intake. Methane intensity was not affected by the 3-NOP or CTS treatments. Total volatile fatty acids in ruminal fluid were not affected by 3-NOP supplementation, but a reduction in acetate and an increase in propionate proportion occurred, resulting in decreased acetate: propionate. The 3-NOP additive decreased grass intake; however, energy−corrected milk yield and milk composition were largely unaffected. Milk urea increased with 3-NOP supplementation. Combining twice daily supplementation of 3-NOP and CTS did not enhance their CH4 mitigation potential when fed to grazing dairy cows. The relatively low inhibition of CH4 production by 3-NOP compared to studies with total mixed rations may result from the mode of delivery (pulse dosed twice daily) and time gap caused by experimental handling and moving of animals to pasture after 3-NOP supplementation in the milking parlour, which could have impaired the synchrony between the additive presence in the rumen and grass intake in paddocks.

Comparing the effects of magnetite-mediated direct interspecies electron transfer with biogas mixing-driven interspecies hydrogen transfer on anaerobic digestion

Although the promotive effect of direct interspecies electron transfer (DIET) on methane production has been well-documented, the practical applicability of DIET in different scenarios have not yet been systematically studied. This study compared the effects of magnetite-mediated DIET with conventional biogas mixing-driven interspecies hydrogen transfer (IHT) on anaerobic digestion (AD) of swine manure (SM). Compared with control, magnetite supplementation, biogas circulation, and their integration enhanced the CH4 yield by 19.3%, 25.9%, and 26.2%, respectively. Magnetite mainly enriched DIET-related syntrophic bacteria (Anaerolineae and Synergistia) and methanogens (Methanosarcina) to accelerate acidification and establish DIET, while biogas circulation mainly enriched hydrolytic bacteria (Clostridia) and hydrogenotrophic methanogens (Methanolinea and Methanobacterium) to promote hydrolysis and accelerate IHT. Coupling magnetite addition with biogas circulation led to the enrichment of the above six microorganisms to different extents. The effectiveness of the strategies for lowering the H2 pressure followed: magnetite + biogas circulation ≈ biogas circulation > magnetite. Under stress-free environment, the enhancement effect of magnetite-induced DIET was not even as pronounced as biogas circulation—a simple and common mixing strategy in commercial AD plants, and the promotion effect of magnetite was insignificant in the well-mixed digesters. In short, the magnetite-mediated DIET is not always effective in improving AD of SM.