CH4 Synthesis Research Articles

Fungal Methane Production Under High Hydrostatic Pressure in Deep Subseafloor Sediments

Fungi inhabiting deep subseafloor sediments have been shown to possess anaerobic methane (CH4) production capabilities under atmospheric conditions. However, their ability to produce CH4 under in situ conditions with high hydrostatic pressure (HHP) remains unclear. Here, Schizophyllum commune 20R-7-F01, isolated from ~2 km below the seafloor, was cultured in Seawater Medium (SM) in culture bottles fitted with sterile syringes for pressure equilibration. Subsequently, these culture bottles were transferred into 1 L stainless steel pressure vessels at 30 °C for 5 days to simulate in situ HHP and anaerobic environments. Our comprehensive analysis of bioactivity, biomass, and transcriptomics revealed that the S. commune not only survived but significantly enhanced CH4 production, reaching approximately 2.5 times higher levels under 35 MPa HHP compared to 0.1 MPa standard atmospheric pressure. Pathways associated with carbohydrate metabolism, methylation, hydrolase activity, cysteine and methionine metabolism, and oxidoreductase activity were notably activated under HHP. Specifically, key genes involved in fungal anaerobic CH4 synthesis, including methyltransferase mct1 and dehalogenase dh3, were upregulated 7.9- and 12.5-fold, respectively, under HHP. Enhanced CH4 production under HHP was primarily attributed to oxidative stress induced by pressure, supported by intracellular reactive oxygen species (ROS) levels and comparative treatments with cadmium chloride and hydrogen peroxide. These results may provide a strong theoretical basis and practical guidance for future studies on the contribution of fungi to global CH4 flux.

In situ synthetic H2 on composite cathode surface for CH4 production from CO2 in microbial electrosyntshesis

Microbial electrosynthesis (MES) is an innovative technology that employs microbes to synthesize chemicals by reducing CO2.This study explores the CH4 production performance at different cathodic reduction potentials in MES. In this study, in situ H2 production on the surface of composite electrode was realized by regulating cathode potential. Pathway for H2-mediated CH4 synthesis was the main synthesis pathway, but it was susceptible to interfere from the external environment (such as cathode potential, pH). The optimal CH4 production potential was −1.0 V vs Ag/AgCl, meanwhile the CH4 synthesis rate was 58 ± 0.4 mLm−2d−1 and the CE was 67 ± 0.5%. Excessively high reduction potentials (−1.4 V vs Ag/AgCl) reduce the activity of microbial populations at the cathode. Synergistic interactions between H2-producing bacteria (Hydrogenophaga, Clostridium, Enterobacter, and Escherichia coli) and Hydrogenotrophic methanogens (Methanobacterium and Methanomassiliicocus) promoted efficient synthesis of CH4. These insights provide new perspectives on reactor operation, thus contributing to the efficiency of MES.

Ru/CeO2 catalyst derived from Ce-based MOF for highly efficient catalytic CO2 methanation integrated with renewable hydrogen

A series of highly ordered microporous Ce-based metal-organic frameworks (MOFs) were synthesized as the precursors for catalyst construction. The corresponding Ru catalysts were prepared by Ru impregnation on the derived CeO2 by pyrolysis of Ce-MOF, and investigated for the CH4 synthesis via CO2 hydrogenation. Among the catalysts, Ru catalyst supported on the CeO2-B derived from Ce-BDC exhibited a highly competitive efficiency for CO2 methanation, giving a CH4 selectivity of 100% with a CO2 conversion of 62% at 275 °C and 0.1 MPa, and the CH4 productivity reached 0.49 mol/(molRu·h). Characterization results revealed that more oxygen vacancies and corresponding surface oxygen species formed on the surface of CeO2-B derived from Ce-BDC caused to the stronger interaction between Ru and CeO2-B, which promoted the CO2 adsorption and hydrogenation capacity of the catalyst, resulting in its better catalytic property. In situ diffuse reflectance infrared Fourier transform (DRIFT) studies further revealed that the route of HCOO* into CH4 is a more competitive way of CO2 hydrogenation to CH4.

Effects of Caragana korshinskii tannin on fermentation, methane emission, community of methanogens, and metabolome of rumen in sheep.

The purpose of this research was to investigate the impact of dietary supplementation of Caragana korshinskii tannin (CKT) on rumen fermentation, methane emission, methanogen community and metabolome in rumen of sheep. A total of 15 crossbred sheep of the Dumont breed with similar body conditions, were divided into three groups (n = 5), which were fed with CKT addition at 0, 2 and 4%/kg DM. The study spanned a total of 74 days, with a 14-day period dedicated to adaptation and a subsequent 60-day period for conducting treatments. The results indicated that the levels of ammonia nitrogen (NH3-N) and acetate were reduced (p < 0.05) in rumen sheep fed with 2 and 4% CKT; The crude protein (CP) digestibility of sheep in 2 and 4% CKT groups was decreased(p < 0.05); while the neutral detergent fiber (NDF) digestibility was increased (p < 0.05) in 4% CKT group. Furthermore, the supplementation of CKT resulted in a decrease (p < 0.05) in daily CH4 emissions from sheep by reducing the richness and diversity of ruminal methanogens community, meanwhile decreasing (p < 0.05) concentrations of tyramine that contribute to methane synthesis and increasing (p < 0.05) concentrations of N-methy-L-glutamic acid that do not contribute to CH4 synthesis. However, CH4 production of DMI, OMI, NDFI and metabolic weight did not differ significantly across the various treatments. To sum up, the addition of 4% CKT appeared to be a viable approach for reducing CH4 emissions from sheep without no negative effects. These findings suggest that CKT hold promise in mitigating methane emissions of ruminant. Further investigation is required to evaluate it effectiveness in practical feeding strategies for livestock.

Difference in reaction mechanism between ZnZrOx and InZrOx for CO2 hydrogenation.

Oxide solid-solution catalysts, such as Zn-doped ZrO2 (ZnZrOx) and In-doped ZrO2 (InZrOx), exhibit distinctive catalytic capabilities for CH3OH synthesis via CO2 hydrogenation. We investigated the active site structures of these catalysts and their associated reaction mechanisms using both experimental and computational approaches. Electron microscopy and X-ray absorption spectroscopy reveal that the primary active sites are isolated cations, such as Zn2+ and In3+, dissolved in tetragonal ZrO2. Notably, for Zn2+, decomposition of the methoxy group, which is an essential intermediate in CH4 synthesis, is partially suppressed because of the relatively high stability of the methoxy group. Conversely, the methyl group strongly adsorbs on In3+, facilitating the conversion of the methoxy species into methyl groups. The decomposition of CH3OH is also suggested to contribute to CH4 synthesis. These results highlight the generation of CH4 as a byproduct of the InZrOx catalyst. Understanding the active site structure and elucidating the reaction mechanism at the atomic level are anticipated to contribute significantly to the future development of oxide solid-solution catalysts.

In-Situ-Formed Potassium-Modified Nickel-Zinc Carbide Boosts Production of Higher Alcohols beyond CH4 in CO2 Hydrogenation.

Ni-based catalysts have been widely studied in the hydrogenation of CO2 to CH4 , but selective and efficient synthesis of higher alcohols (C2+ OH) from CO2 hydrogenation over Ni-based catalyst is still challenging due to successive hydrogenation of C1 intermediates leading to methanation. Herein, we report an unprecedented synthesis of C2+ OH from CO2 hydrogenation over K-modified Ni-Zn bimetal catalyst with promising activity and selectivity. Systematic experiments (including XRD, in situ spectroscopic characterization) and computational studies reveal the in situ generation of an active K-modified Ni-Zn carbide (K-Ni3 Zn1 C0.7 ) by carburization of Zn-incorporated Ni0 , which can significantly enhance CO2 adsorption and the surface coverage of alkyl intermediates, and boost the C-C coupling to C2+ OH rather than conventional CH4 . This work opens a new catalytic avenue toward CO2 hydrogenation to C2+ OH, and also provides an insightful example for the rational design of selective and efficient Ni-based catalysts for CO2 hydrogenation to multiple carbon products.

In‐Situ‐Formed Potassium‐Modified Nickel‐Zinc Carbide Boosts Production of Higher Alcohols beyond CH4 in CO2 Hydrogenation

AbstractNi‐based catalysts have been widely studied in the hydrogenation of CO2 to CH4, but selective and efficient synthesis of higher alcohols (C2+OH) from CO2 hydrogenation over Ni‐based catalyst is still challenging due to successive hydrogenation of C1 intermediates leading to methanation. Herein, we report an unprecedented synthesis of C2+OH from CO2 hydrogenation over K‐modified Ni−Zn bimetal catalyst with promising activity and selectivity. Systematic experiments (including XRD, in situ spectroscopic characterization) and computational studies reveal the in situ generation of an active K‐modified Ni−Zn carbide (K‐Ni3Zn1C0.7) by carburization of Zn‐incorporated Ni0, which can significantly enhance CO2 adsorption and the surface coverage of alkyl intermediates, and boost the C−C coupling to C2+OH rather than conventional CH4. This work opens a new catalytic avenue toward CO2 hydrogenation to C2+OH, and also provides an insightful example for the rational design of selective and efficient Ni‐based catalysts for CO2 hydrogenation to multiple carbon products.

Effects of melatonin on rumen microorganisms and methane production in dairy cow: results from in vitro and in vivo studies

BackgroundMethane (CH4) is a major greenhouse gas, and ruminants are one of the sources of CH4 which is produced by the rumen microbiota. Modification of the rumen microbiota compositions will impact the CH4 production. In this study, the effects of melatonin on methane production in cows were investigated both in the in vitro and in vivo studies.ResultsMelatonin treatment significantly reduced methane production in both studies. The cows treated with melatonin reduced methane emission from their respiration by approximately 50%. The potential mechanisms are multiple. First, melatonin lowers the volatile fatty acids (VFAs) production in rumen and reduces the raw material for CH4 synthesis. Second, melatonin not only reduces the abundance of Methanobacterium which are responsible for generating methane but also inhibits the populations of protozoa to break the symbiotic relationship between Methanobacterium and protozoa in rumen to further lowers the CH4 production. The reduced VFA production is not associated with food intake, and it seems also not to jeopardize the nutritional status of the cows. This was reflected by the increased milk lipid and protein contents in melatonin treated compared to the control cows. It is likely that the energy used to synthesize methane is saved to compensate the reduced VFA production.ConclusionThis study enlightens the potential mechanisms by which melatonin reduces rumen methane production in dairy cows. Considering the greenhouse effects of methane on global warming, these findings provide valuable information using different approaches to achieve low carbon dairy farming to reduce the methane emission.6uXNnBCVHjJWi7WJQ32EAMVideo

CH4 Synthesis from CO2 and H2O of an Electron Source over Rh-Ru Cocatalysts Loaded on NaTaO3:Sr Photocatalysts.

CO2 reduction as an artificial photosynthetic system is a promising technology to produce green energies and chemicals because it uses light energy to convert H2O and CO2 into valuable products such as CO, HCOOH, CH3OH, CH4, and preferably higher hydrocarbons. In photocatalytic reduction, water should be used as hydrogen and electron sources for CO2 reduction. Moreover, CH4 formation is an attractive and challenging topic because of the eight-electron-reducing product of CO2. Herein, we report the development of a new Rh-Ru cocatalyst decorated on an alkaline earth-doped NaTaO3 surface for the photocatalytic CO2 reduction to form CH4 using water as an electron donor. CH4 was obtained by a photocatalytic "uphill" reaction of CO2 reduction using Rh-Ru cocatalyst-loaded NaTaO3:Sr, water, and CO2 in an aqueous suspension system. About 10% of a selectivity (electronic efficiency) was obtained for CH4 formation under ambient conditions accompanied with O2 evolution of the oxidation product of H2O.

Carbon Dioxide Valorization into Methane Using Samarium Oxide-Supported Monometallic and Bimetallic Catalysts

Samarium oxide (Sm2O3) is a versatile surface for CO2 and H2 interaction and conversion. Samarium oxide-supported Ni, samarium oxide-supported Co-Ni, and samarium oxide-supported Ru-Ni catalysts were tested for CO2 methanation and were characterized by X-ray diffraction, nitrogen physisorption, infrared spectroscopy, H2-temperature programmed reduction, and X-ray photoelectron spectroscopy. Limited H2 dissociation and widely available surface carbonate and formate species over 20 wt.% Ni, dispersed over Sm2O3, resulted in ~98% CH4 selectivity. The low selectivity for CO could be due to the reforming reaction between CH4 (methanation product) and CO2. Co-impregnation of cobalt with nickel over Sm2O3 had high surface adsorbed oxygen and higher CO selectivity. On the other hand, co-impregnation of ruthenium and nickel over Sm2O3 led to more than one catalytic active site, carbonate species, lack of formate species, and 94% CH4 selectivity. It indicated the following route of CH4 synthesis over Ru-Ni/Sm2O3; carbonate → unstable formate → CO → CH4.

A comprehensive DFT study of CO2 methanation on the Ru-doped Ni(111) surface

Ru−Ni bimetallic catalysts show excellent performance for CO2 methanation, but the underlying mechanism remains unclear. In this study, the mechanism of CH4 synthesis on Ru-doped Ni(111) is investigated with the density functional theory methods. Through the discussion of the adsorption of all possible species, the relatively weak O* adsorption indicates that the introduction of Ru into the Ni catalyst can effectively protect the Ni active sites from being oxidized. Meanwhile, the partial density of states analyses reveals that CO2* is well activated on the catalyst. In addition, the optimal route for CO2 hydrogenation into CH4 is obtained, with an activation barrier of 1.13 eV for the rate-determining step. It shows that Ru-doped Ni(111) possesses superior catalytic activity for CO2 hydrogenation to CH4. Additionally, the activation barriers of all the surface C* formation reactions significantly increase, manifesting that the resistance to carbon deposition of Ru-doped Ni(111) is improved.

The origin of methane in serpentinite-hosted hyperalkaline hot spring at Hakuba Happo, Japan: Radiocarbon, methane isotopologue and noble gas isotope approaches

Methane (CH4) associated with marine and terrestrial sites of serpentinization has been proposed to be abiotic in origin. However, the source of carbon and the depth and temperature of CH4 synthesis often remain inconclusive. We measured the radiocarbon (14C), bulk stable isotope ratios (δ13C and δD) and isotopologue abundance (Δ13CH3D) of CH4, and noble gas isotope composition of gas samples from two hyperalkaline geothermal wells (Happo #1 and Happo #3) at Hakuba Happo, Japan, to constrain the source of carbon and the CH4 generation processes. The CH4 samples from both sites were nearly 14C-free, whereas the carbonate precipitates inside the Happo #1 well contained 14C corresponding to 51 to 62 percent modern carbon, indicating that the majority of CH4 was not generated from the reduction of dissolved carbonate in the hot spring water. CH4 samples from Happo #1 and Happo #3 yielded Δ13CH3D-based apparent temperatures of 206−40+52°C and 323−85+143°C, respectively, which are much higher than the measured well water temperatures (∼50°C). Therefore, 14C and clumped isotopologue temperatures suggest that Hakuba Happo CH4 was generated below the depth where the shallow meteoric water circulated. The 3He/4He ratios were 4.10 and 4.47 Ratm for Happo #1 and Happo #3, respectively. The 3He/4He and 4He/20Ne ratios revealed that approximately 50% of He was of mantle origin, suggesting that the Hakuba Happo hot spring received volatiles, including CO2, from the mantle. However, the observed δ13CCH4 values (approximately −35‰) were significantly lower than those of typical mantle-derived carbon (–5‰), implying that mantle-derived CO2 is not the major carbon source for CH4 formation. High CH4 concentrations in the Hakuba Happo fluids, compared to those in hot springs in the area not associated with serpentinization, suggest that CH4 was generated from 13C-depleted fossil carbon sources and serpentinization-derived H2 at high temperatures (>200°C), and subsequently entrained into the cooler circulating meteoric water system.

Enhanced biological phosphorus removal from wastewater by current stimulation coupled with anaerobic digestion

The integrated wastewater discharge standard for phosphorus has become increasingly strict. In this study, a synergetic current stimulation system coupled with anaerobic digestion was used to enhance phosphorus removal from wastewater. The effects of current intensity, pH, and methane (CH4) synthesis on phosphorus removal were investigated. As direct current was supplied to an anaerobic bioreactor, the removal of sewage total phosphorus was significantly enhanced. The conditions of weak acid and low negative oxidation-reduction potential facilitated the phosphorus removal from wastewater. The optimal parameters for the dephosphorisation process were a current intensity of 100 mA and a pH of 6.0. When the anaerobic digestion process was inhibited by the reagent 2-bromoethanesulphonic acid sodium (BES), abundant metabolic intermediates accumulated and methanogenesis clearly decreased. Affected by the current stimulation and the inhibition of CH4 synthesis, the formation of gaseous phosphine (PH3) was greatly improved, and then PH3 escaped from the digestion mixture after it was absorbed by microbial cells. The maximum PH3 content of the digestion gas was 41.8 mg m−3 in the reactor supplied with a current of 100 mA and BES addition of 10 mmol L−1, and the phosphorus removal in this digestion system reached 55.2% at 6 d; however, the removal in the conventional anaerobic digestion system was only 17.7% after the same amount of time. Finally, a pathway of enhanced anaerobic biological phosphorus removal was proposed to better understand the inherent synergistic mechanism.

Numerical investigation on the heterogeneous pulsed dielectric barrier discharge plasma catalysis for CO2 hydrogenation at atmospheric pressure: Effects of Ni and Cu catalysts on the selectivity conversions to CH4 and CH3OH

AbstractThe simulation model of the pulsed dielectric barrier discharge plasma catalytic CO2 hydrogenation is established to numerically investigate the effects of Ni and Cu catalysts on the selectivity conversions to CH4 and CH3OH. Under plasma without catalyst, the electron impact CO2 and CO produce CO and C, and then stepwise hydrogenations of CO and C generate CH3OH and CH4. Under plasma with Ni catalyst, Langmuir–Hinshelwood (LH) reactions mainly form the CHx(s) and Eley–Rideal (ER) reaction CH3(s) + H → CH4 are the key paths of CH4 synthesis. Under plasma with Cu catalyst, the intermediate CH3O(s) is principally produced by the LH reaction between CH2O(s) and H(s), followed by the ER reaction CH2O(s) + H → CH3O(s). While CH3OH(s) is mainly produced by the ER reaction CH3O(s) + H → CH3OH(s), CH3O(s) + H(s) → CH3OH(s) + S is a rate‐limiting step owing to the higher reaction energy barrier.

Co-metabolic Effect of Glucose on Methane Production and Phenanthrene Removal in an Enriched Phenanthrene-Degrading Consortium Under Methanogenesis.

Anaerobic digestion is used to treat diverse waste classes, and polycyclic aromatic hydrocarbons (PAHs) are a class of refractory compounds that common in wastes treated using anaerobic digestion. In this study, a microbial consortium with the ability to degrade phenanthrene under methanogenesis was enriched from paddy soil to investigate the cometabolic effect of glucose on methane (CH4) production and phenanthrene (a representative PAH) degradation under methanogenic conditions. The addition of glucose enhanced the CH4 production rate (from 0.37 to 2.25mg⋅L−1⋅d−1) but had no influence on the degradation rate of phenanthrene. Moreover, glucose addition significantly decreased the microbial α-diversity (from 2.59 to 1.30) of the enriched consortium but showed no significant effect on the microbial community (R2=0.39, p=0.10), archaeal community (R2=0.48, p=0.10), or functional profile (R2=0.48, p=0.10). The relative abundance of genes involved in the degradation of aromatic compounds showed a decreasing tendency with the addition of glucose, whereas that of genes related to CH4 synthesis was not affected. Additionally, the abundance of genes related to the acetate pathway was the highest among the four types of CH4 synthesis pathways detected in the enriched consortium, which averagely accounted for 48.24% of the total CH4 synthesis pathway, indicating that the acetate pathway is dominant in this phenanthrene-degrading system during methanogenesis. Our results reveal that achieving an ideal effect is diffcult via co-metabolism in a single-stage digestion system of PAH under methanogenesis; thus, other anaerobic systems with higher PAH removal efficiency should be combined with methanogenic digestion, assembling a multistage pattern to enhance the PAH removal rate and CH4 production in anaerobic digestion.

Aerobic bacterial methane synthesis

Reports of biogenic methane (CH4) synthesis associated with a range of organisms have steadily accumulated in the literature. This has not happened without controversy and in most cases the process is poorly understood at the gene and enzyme levels. In marine and freshwater environments, CH4 supersaturation of oxic surface waters has been termed the "methane paradox" because biological CH4 synthesis is viewed to be a strictly anaerobic process carried out by O2-sensitive methanogens. Interest in this phenomenon has surged within the past decade because of the importance of understanding sources and sinks of this potent greenhouse gas. In our work on Yellowstone Lake in Yellowstone National Park, we demonstrate microbiological conversion of methylamine to CH4 and isolate and characterize an Acidovorax sp. capable of this activity. Furthermore, we identify and clone a gene critical to this process (encodes pyridoxylamine phosphate-dependent aspartate aminotransferase) and demonstrate that this property can be transferred to Escherichia coli with this gene and will occur as a purified enzyme. This previously unrecognized process sheds light on environmental cycling of CH4, suggesting that O2-insensitive, ecologically relevant aerobic CH4 synthesis is likely of widespread distribution in the environment and should be considered in CH4 modeling efforts.

Diverse serpentinization and associated abiotic methanogenesis within multiple types of olivine-hosted fluid inclusions in orogenic peridotite from northern Tibet

Hydrothermal fluids percolating through peridotite are highly enriched in abiotic CH4, which can fuel chemosynthetic microbial activity and potentially early life. In contrast to the paradigm favoring coupled abiotic methanogenesis and fluid circulation, recent studies have suggested that leaching of CH4 included in peridotite can account for elevated levels of CH4 in serpentinization fluids. As such, CH4 venting at continental gas seepage hosted in orogenic peridotite should be derived mostly from CH4 that originated within the host peridotite. However, the origin of CH4 included in orogenic peridotite remains elusive, as the included CH4 is reported to form either in situ during serpentinization within fluid inclusions, or to originate from reduced external fluids. Moreover, varying associations of step-daughter minerals documented in CH4-bearing fluid inclusions in orogenic peridotite demonstrate the diversity of fluid–mineral interactions within fluid inclusions. Here we present a detailed petrological investigation into olivine-hosted CH4-bearing fluid inclusions in ophiolitic harzburgite from the North Qilian orogen in northern Tibet, which reveals the occurrence of abiotic CH4 synthesis during diverse serpentinization within multiple types of olivine-hosted fluid inclusions. Three types of CH4-bearing fluid inclusions are newly identified in the harzburgite. Type I fluid inclusions contain CH4(g) + antigorite + brucite + magnetite + magnesite, which imply abiotic CH4 synthesis during hydration of olivine directly into antigorite. This contradicts the previous proposal that suggests the inhibition of H2 and CH4 production during high-temperature serpentinization in the stability field of antigorite. Type II fluid inclusions consist of CH4(g) + N2(g) + lizardite + brucite ± magnetite or CH4(g) + N2(g) + lizardite + magnetite, with brucite-bearing inclusions yielding less CH4 compared with brucite-free inclusions. The crystallization of brucite in type II fluid inclusions was probably controlled by the concentration of dissolved Si in the trapped fluids. Type III fluid inclusions are composed of CH4(g) + antigorite + magnesite + graphite ± magnetite ± dolomite. High concentrations of oxidized inorganic carbon in type III fluid inclusions likely promoted the precipitation of carbonate and crystallization of antigorite. Moreover, the presence of relict lizardite in minor type III fluid inclusions suggests that antigorite growth accompanying carbonate saturation is probably a two-step process, with initial hydration of olivine into lizardite being followed by transformation of lizardite into antigorite. Above all, this study demonstrates that CH4-bearing fluid inclusions in orogenic peridotite can be very abundant, and may be a significant reservoir of abiotic CH4 in serpentinite-hosted hydrothermal systems. Moreover, the multiple types of CH4-bearing fluid inclusions in orogenic peridotite presented in this study indicate that olivine-hosted CH4-bearing fluid inclusions can potentially be a novel window for studying abiotic CH4 synthesis during serpentinization under different conditions.

Optimization of a newly developed electromethanogenesis for the highest record of methane production

The development of an effective biocathode with high catalytic ability and dense biomass is a major challenge for the industrial applications of electromethanogenesis (EM) process. In our previous study, intact anaerobic granular sludge (AnGS) biocathode and EM hybrid system (AnGS-EM) showed superior ability and stability when treating raw biogas, but its maximum CO2-to-CH4 conversion potential and the response to different operating conditions are still unknown. Herein, we optimized the performance of the AnGS-EM system and explored its maximum CH4 production capacity. The AnGS-EM system achieved a maximum methane production rate of 202.15 L CH4/m2catproj/d, which is over 3 times higher than the maximum value reported so far. Within a certain range, the methane production rate increased with the buffer concentration, applied voltage, and bicarbonate concentration. Excessive applied voltage and carbonate concentration not only led to resource waste but also inhibited methanogen performance. The AnGS biocathode could withstand oxygen exposure for 24 h, the acidic (pH of 5.5), and alkaline conditions (pH over 9). Illumina sequencing results showed that hydrogenotrophic methanogen (especially Methanobacterium) were dominant. This work using AnGS as biocathode for CH4 synthesis offers insight into the development of scalable, efficient, and cost-effective biocathode for biofuels and value-added chemicals production.

CH4 Synthesis from CO2 with Microwave Plasma Technique

CH4 Synthesis from CO2 with Microwave Plasma Technique

Combining Crude Glycerin with Chitosan Can Manipulate In Vitro Ruminal Efficiency and Inhibit Methane Synthesis.

Simple SummaryMethane (CH4) inhibition approaches in ruminants are considered to provide economic benefits and reduce global greenhouse gases. The inclusion of crude glycerin at 21% in to total mixed ration (TMR) diets with chitosan supplementation at 2% enhanced ruminal propionate concentration and reduced methane production without causing any detrimental effect on the gas kinetics or nutrient digestibility.It was hypothesized that the combination of glycerin and chitosan improves ruminal fermentation efficiency via an enhanced propionate (C3) and reduces in vitro CH4 production. This was explored through in vitro gas production with substrates containing crude glycerin, which replaced cassava chips in the studied ration. The experimental design was organized following a 3 × 3 factorial in completely randomized design and the arrangement of treatments were different levels of crude glycerin supplementations 0, 10.5, and 21% of total mixed ration (TMR) and chitosan levels were added at 0, 1, and 2% dry matter (DM) of substrate. Then, 0.5 g of TMR substrates were added into 40 mL bottles, together with respective doses of chitosan and then incubated at 39 °C. The dietary treatments were performed in three replicates within the incubation, and incubations were repeated on three separate days (runs). No interactions were found between crude glycerin and chitosan doses in terms of theoretical maximum of asymptotic gas production (b), rate of gas production (c), the discrete lag time prior to gas production (L), or the cumulative gas production at 96 h of incubation (p > 0.05). Cumulative gas production at 96 h of incubation was similar among the doses of crude glycerin and levels of chitosan, which ranged from 64.27 to 69.66 mL/g DM basis of substrate (p > 0.05). The concentration of ruminal NH3-N after 2 and 4 h of incubation ranged from 14.61 to 17.10 mg/dL and did not change with the addition of crude glycerin with chitosan (p > 0.05). The concentration of CH4 after 2 h of incubation did not change among treatments (p > 0.05), whereas after 4 h of incubation, CH4 synthesis was significantly reduced by enhancing doses of crude glycerin and chitosan (p < 0.05). The combination of 21% of crude glycerin in TMR with 2% chitosan depressed CH4 production as much as 53.67% when compared to the non-supplemented group. No significant crude glycerin and chitosan interaction effect was detected for in vitro digestibility of nutrients after incubation for 12 and 24 h using the in vitro gas production technique (p > 0.05). In addition, no significant changes (p > 0.05) were observed in total volatile fatty acids, acetate (C2) or butyrate content among treatments and between the main effects of crude glycerin with chitosan. At 4 h of incubation, ruminal C3 content and the C2 to C3 ratio changed significantly when crude glycerin and chitosan was added (p < 0.05). The 21% crude glycerin incorporate into TMR, in combination with 2% additional chitosan, increased C3 content by 26.41%, whereas the ratio of C2 to C3 was reduced by 31% when compared to the control group. Propionate concentration increased by 11.75% when increasing levels of chitosan at 2% of substrate, whereas the C2 to C3 ratio decreased by 13.99% compared to the 0% chitosan group. The inclusion of crude glycerin at 21% in TMR diets with chitosan supplementation at 2% enhanced ruminal propionate concentration and reduced methane production without causing any detrimental effect on the gas kinetics or nutrient digestibility.