H2 Sink Research Articles

The Molecular Cloud Life Cycle. II. Formation and Destruction of Molecular Clouds Diagnosed via H2 Fluorescent Emission

Molecular hydrogen (H2) formation and dissociation are key processes that drive the gas life cycle in galaxies. Using the SImulating the LifeCycle of Molecular Clouds zoom-in simulation suite, we explore the utility of future observations of H2 dissociation and formation for tracking the life cycle of molecular clouds. The simulations used in this work include nonequilibrium H2 formation, stellar radiation, sink particles, and turbulence. We find that at early times in the cloud evolution H2 formation rapidly outpaces dissociation and molecular clouds build their mass from the atomic reservoir in their environment. Rapid H2 formation is also associated with a higher early star formation rate. For the clouds studied here, H2 is strongly out of chemical equilibrium during the early stages of cloud formation but settles into a bursty chemical steady state about 2 Myr after the first stars form. At the latest stage of cloud evolution, dissociation outweighs formation and the clouds enter a dispersal phase. We discuss how theories of the molecular cloud life cycle and star formation efficiency may be distinguished with observational measurements of H2 fluorescence with a space-based high-resolution far-UV spectrometer, such as the proposed Hyperion and Eos NASA Explorer missions. Such missions would enable measurements of the H2 dissociation and formation rates, which we demonstrate can be connected to different phases in a molecular cloud’s star-forming life, including cloud building, rapidly star forming, H2 chemical equilibrium, and cloud destruction.

Methane emission, nitrogen excretion, and energy partitioning in Hanwoo steers fed a typical TMR diet supplemented with Pharbitis nil seeds.

Two in vivo experiments were conducted to evaluate the potential of Pharbitis nil seeds (PA) as an anti-methanogenic additive to ruminant feed. In experiment 1, six Hanwoo steers (459.0 ± 25.8 kg) were fed either a total mixed ration (TMR; 32-d period) or TMR supplemented with PA at 5% dry matter (DM) intake (TMR-PA; 45-d period) for two consecutive periods. Fecal and urine outputs were measured in an apparent digestibility trial in both periods. Methane (CH4) yield and heat energy (HE) were measured using respiratory chambers equipped with gas analyzers. In experiment 2, five rumen cannulated Holstein steers (744 ± 35 kg) were fed the same TMR or TMR-PA diets for 40 days; rumen samples were collected at 0, 1.5, and 3 h after feeding on the last day of the feeding period. In experiment 1, although there were no differences (p > 0.05) in nutrients or gross energy intake (GEI) between the groups, an increase (p < 0.05) in the apparent digestibility of DM (9.1%) and neutral detergent fiber (22.9%) was observed in the TMR-PA fed Hanwoo steers. Pronounced decreases (p < 0.05) in CH4 (g/Kg DM; 17.1%) and urinary N excretion (% N intake; 7.6%) were observed in the TMR-PA group, leading to a 14.7% increase in metabolizable energy intake (% GEI). However, only a numerical increase (p > 0.05) in retained energy was observed due to the increase in HE loss. In experiment 2, a drastic decrease (p < 0.05) in rumen ammonia concentration (56.3%) associated with an increased (p = 0.091) rumen short-chain fatty acid concentration 1.5 h after feeding were observed in TMR-PA fed Holstein steers. A 26.6% increase (p < 0.05) in the propionate proportion during the treatment period clearly reflected a shift in the ruminal H2 sink after 3 h of feeding. A 40% reduction (p = 0.067) in the relative abundance of rumen protozoa Entodinium caudatum was also observed. It was concluded that PA could be a natural feed additive for CH4 and N emission abatement.

Order–disorder and ionic conductivity in calcium nitride-hydride

Recently nitrogen-hydrogen compounds have successfully been applied as co-catalysts for mild conditions ammonia synthesis. Ca2NH was shown to act as a H2 sink during reaction, with H atoms from its lattice being incorporated into the NH3(g) product. Thus the ionic transport and diffusion properties of the N–H co-catalyst are fundamentally important to understanding and developing such syntheses. Here we show hydride ion conduction in these materials. Two distinct calcium nitride-hydride Ca2NH phases, prepared via different synthetic paths are found to show dramatically different properties. One phase (β) shows fast hydride ionic conduction properties (0.08 S/cm at 600 °C), on a par with the best binary ionic hydrides and 10 times higher than CaH2, whilst the other (α) is 100 times less conductive. An in situ combined analysis techniques reveals that the effective β-phase conducts ions via a vacancy-mediated phenomenon in which the charge carrier concentration is dependent on the ion concentration in the secondary site and by extension the vacancy concentration in the main site.

Challenges of Industrial-Scale Testing Infrastructure for Green Hydrogen Technologies

Green hydrogen is set to become the energy carrier of the future, provided that production technologies such as electrolysis and solar water splitting can be scaled to global dimensions. Testing these hydrogen technologies on the MW scale requires the development of dedicated new test facilities for which there is no precedent. This perspective highlights the challenges to be met on the path to implementing a test facility for large-scale water electrolysis, photoelectrochemical and photocatalytic water splitting and aims to serve as a much-needed blueprint for future test facilities based on the authors’ own experience in establishing the Hydrogen Lab Leuna. Key aspects to be considered are the electricity and utility requirements of the devices under testing, the analysis of the produced H2 and O2 and the safety regulations for handling large quantities of H2. Choosing the right location is crucial not only for meeting these device requirements, but also for improving financial viability through supplying affordable electricity and providing a remunerated H2 sink to offset the testing costs. Due to their lower TRL and requirement for a light source, large-scale photocatalysis and photoelectrochemistry testing are less developed and the requirements are currently less predictable.

Rumen microbial system, methanogenesis, and methane mitigation strategies in ruminants

Much of the biomass in this world is rich in fibre which is utilised by the ruminants with the help of rumen microbes to produce a good quality protein for human consumption. However, this conversion of fibre to high-quality protein is paralleled by the production of methane which represents the wastage of feed energy and is a powerful greenhouse gas harmful to the global climate. The microbial community in the rumen has co-evolved with their host animal in a symbiotic relationship over millions of years and methanogenesis has emerged as a result of the refinement of the fermentation process in the rumen. The one-to-one relationship between the methanogen population and the methanogenesis has not been established yet, which indicates the role of associated rumen microbiota, substrate availability, and other functional parameters of the rumen. This review has focused on the total rumen microbial structure, methanogen structure, rumen fermentation process, methanogenesis, factors affecting methane production, and methane mitigation strategies. The balance between the H2 producers and H2 consumers in the rumen determines the level of methane production in the rumen. Therefore, decreasing the availability of H2 in the rumen by fostering alternative H2 sinks, such as propionate production, is very instrumental in reducing the rumen methane emissions. Any strategy of methane abatement should concurrently consider the enhancement of propionate production to prevent the inhibition of rumen functions. Although a great deal of information regarding the rumen microbial community structure, rumen physiology, and methane mitigation strategies is currently available, more research is still needed. The majority of the in vivo experiments pertaining to methane abatement strategies discussed in this review are the short term experiments in which long term unwanted effects could not be precisely predicted. Therefore, there is a need for long-term experiments to draw valid and logical conclusions on the methane abatement strategies.

The biological sink of atmospheric H2 is more sensitive to spatial variation of microbial diversity than N2O and CO2 emissions in a winter cover crop field trial

The integration of winter cover crop (WCC) in culture rotations promotes multiple ecosystem services, but concomitant microbial diversity and functioning responses in soil have received less attention. A field trial was established to test the hypothesis that enhanced crop diversity with the integration of WCC in a conventional maize-soy rotation promotes microbial diversity and the biological sink of H2 in soil, while reducing N2O emissions to the atmosphere. Vicia villosa (hairy vetch), Avena sativa (oat), and Raphanus sativus (Daikon radish) were cultivated alone or in combinations and flux measurements were performed throughout two subsequent growing seasons. Soil acted as a net sink for H2 and as a net source for CO2 and N2O. CO2 flux was the most sensitive to WCC whereas a significant spatial variation was observed for H2 flux with soil uptake rates observed in the most productive area two-fold greater than the baseline level. Sequencing and quantification of taxonomic and functional genes were integrated to explain variation in trace gas fluxes with compositional changes in soil microbial communities. Fungal communities were the most sensitive to WCC, but neither community abundance nor beta diversity were found to be indicative of fluxes. The alpha diversity of taxonomic and functional genes, expressed as the number of effective species, was integrated into composite variables extracted from multivariate analyses. Only the composite variable computed with the inverse Simpson's index displayed a reproducible pattern throughout both growing seasons, with functional genes and bacterial 16S rRNA gene defining the two most contrasting gradients. The composite variable was decoupled from WCC treatment and explained 19–20% spatial variation of H2 fluxes. The coupling of composite alpha diversity metrics derived from multiple genes with soil processes warrants further investigations to implement novel indicators of soil health in response to changing management practices at the local scale.

Genome-resolved metagenomics reveals how soil bacterial communities respond to elevated H2 availability

Molecular hydrogen (H2) is a major energy source supporting bacterial growth and persistence in soil ecosystems. While recent studies have uncovered mediators of atmospheric H2 consumption, far less is understood about how soil microbial communities respond to elevated H2 levels produced through natural or anthropogenic processes. Here we performed microcosm experiments to resolve how microbial community composition, capabilities, and activities change in upland and wetland soils following H2 supplementation (at mixing doses from 0.5 to 50,000 ppmv). Genome-resolved metagenomic profiling revealed that these soils harbored diverse bacteria capable of using H2 as an electron donor for aerobic respiration (46 of the 196 MAGs from eight phyla) and carbon fixation (15 MAGs from three phyla). H2 stimulated the growth of several of these hydrogenotrophs in a dose-dependent manner, though the lineages stimulated differed between the soils; whereas actinobacterial lineages encoding group 2a [NiFe]-hydrogenases grew most in the upland soils (i.e. Mycobacteriaceae, Pseudonocardiaceae), proteobacterial lineages harboring group 1d [NiFe]-hydrogenases were most enriched in wetland soils (i.e. Burkholderiaceae). Hydrogen supplementation also influenced the abundance of various other genes associated with biogeochemical cycling and bioremediation pathways to varying extents between soils. Reflecting this, we observed an enrichment of a hydrogenotrophic Noviherbaspirillum MAG capable of biphenyl hydroxylation in the wetland soils and verified that H2 supplementation enhanced polychlorinated biphenyl (PCB) degradation in these soils, but not the upland soils. This study constitutes the first genome-resolved analysis of how soil microbial communities respond to elevated H2 availability. Overall, our findings suggest that soils harbour different hydrogenotrophic bacteria that rapidly grow following elevated H2 exposure. In turn, this adds to growing evidence of a large and robust soil H2 sink capable of counteracting growing anthropogenic emissions.

Termite gas emissions select for hydrogenotrophic microbial communities in termite mounds

Organoheterotrophs are the dominant bacteria in most soils worldwide. While many of these bacteria can subsist on atmospheric hydrogen (H2), levels of this gas are generally insufficient to sustain hydrogenotrophic growth. In contrast, bacteria residing within soil-derived termite mounds are exposed to high fluxes of H2 due to fermentative production within termite guts. Here, we show through community, metagenomic, and biogeochemical profiling that termite emissions select for a community dominated by diverse hydrogenotrophic Actinobacteriota and Dormibacterota. Based on metagenomic short reads and derived genomes, uptake hydrogenase and chemosynthetic RuBisCO genes were significantly enriched in mounds compared to surrounding soils. In situ and ex situ measurements confirmed that high- and low-affinity H2-oxidizing bacteria were highly active in the mounds, such that they efficiently consumed all termite-derived H2 emissions and served as net sinks of atmospheric H2 Concordant findings were observed across the mounds of three different Australian termite species, with termite activity strongly predicting H2 oxidation rates (R2 = 0.82). Cell-specific power calculations confirmed the potential for hydrogenotrophic growth in the mounds with most termite activity. In contrast, while methane is produced at similar rates to H2 by termites, mounds contained few methanotrophs and were net sources of methane. Altogether, these findings provide further evidence of a highly responsive terrestrial sink for H2 but not methane and suggest H2 availability shapes composition and activity of microbial communities. They also reveal a unique arthropod-bacteria interaction dependent on H2 transfer between host-associated and free-living microbial communities.

Feeding Systems and Host Breeds Influence Ruminal Fermentation, Methane Production, Microbial Diversity and Metagenomic Gene Abundance.

Our previous research revealed the advantages of separate feeding (SF) systems compared to total mixed ration (TMR) in terms of ruminal methane (CH4) production. The purpose of this experiment was to confirm the advantage of SF as a nutritional strategy for CH4 mitigation, and to determine the effects of different feeding systems (TMR and SF) on the rumen microbiome and associated metagenome of two different breeds and on CH4 emissions. We randomly allocated four Holstein (305 ± 29 kg) and four Hanwoo steers (292 ± 24 kg) to two groups; the steers were fed a commercial concentrate with tall fescue (75:25) as TMR or SF, in a crossover design (two successive 22-day periods). Neither feeding systems nor cattle breeds had an effect on the total tract digestibility of nutrients. The TMR feeding system and Hanwoo steers generated significantly more CH4 (P < 0.05) and had a higher yield [g/d and g/kg dry matter intake (DMI)] compared to the SF system and Holstein steers. A larger rumen acetate:propionate ratio was observed for the TMR than the SF diet (P < 0.05), and for Hanwoo than Holstein steers (P < 0.001), clearly reflecting a shift in the ruminal H2 sink toward CH4 production. The linear discriminant analysis (LDA) effect size (LEfSe) revealed a greater abundance (α < 0.05 and LDA > 2.0) of operational taxonomic units (OTUs) related to methanogenesis for Hanwoo steers compared to Holstein steers. Kendall’s correlation analysis revealed wide variation of microbial co-occurrence patterns between feeding systems, indicating differential H2 thermodynamics in the rumen. A metagenome analysis of rumen microbes revealed the presence of 430 differentially expressed genes, among which 17 and 27 genes exhibited positive and negative associations with CH4 production, respectively (P < 0.001). A strong interaction between feeding system and breed was observed for microbial and metagenomic abundance. Overall, these results suggest that the TMR feeding system produces more CH4, and that Hanwoo cattle are higher CH4 emitters than SF diet and Holstein cattle, respectively. Interestingly, host-associated microbial interactions differed within each breed depending on the feeding system, which indicated that breed-specific feeding systems should be taken into account for farm management.

Abiotic redox reactions in hydrothermal mixing zones: Decreased energy availability for the subsurface biosphere

Subseafloor mixing of high-temperature hot-spring fluids with cold seawater creates intermediate-temperature diffuse fluids that are replete with potential chemical energy. This energy can be harnessed by a chemosynthetic biosphere that permeates hydrothermal regions on Earth. Shifts in the abundance of redox-reactive species in diffuse fluids are often interpreted to reflect the direct influence of subseafloor microbial activity on fluid geochemical budgets. Here, we examine hydrothermal fluids venting at 44 to 149 °C at the Piccard hydrothermal field that span the canonical 122 °C limit to life, and thus provide a rare opportunity to study the transition between habitable and uninhabitable environments. In contrast with previous studies, we show that hydrocarbons are contributed by biomass pyrolysis, while abiotic sulfate (SO42-) reduction produces large depletions in H2 The latter process consumes energy that could otherwise support key metabolic strategies employed by the subseafloor biosphere. Available Gibbs free energy is reduced by 71 to 86% across the habitable temperature range for both hydrogenotrophic SO42- reduction to hydrogen sulfide (H2S) and carbon dioxide (CO2) reduction to methane (CH4). The abiotic H2 sink we identify has implications for the productivity of subseafloor microbial ecosystems and is an important process to consider within models of H2 production and consumption in young oceanic crust.

Effect of dietary corn gluten inclusion on rumen fermentation, microbiota and methane emissions in goats

The study was to evaluate replacing corn meal (CM) by corn gluten (CG) on intake, digestibility, ruminal fermentation, CH4 emissions and microbial abundance in goats. The experiment was performed using randomized block design with 2 dietary treatments (CM and CG with 400 g/kg DM each). Replacing CM with CG increased NDF and CP intake and decreased starch intake. Goats fed CG diet had lower ruminal dissolved hydrogen (dH2) (-43%, P = 0.009) and dissolved methane (dCH4) (-30%, P = 0.001) concentrations than those fed with CM diet. An interaction between treatment and time (P = 0.03) was observed for dH2S with an increase (P < 0.001) in dH2S concentration (CG versus CM, +63%, P < 0.001) happened at 2.5 h after morning feeding. Goats fed with CG diet had lower (P = 0.004) butyrate molar percentage, and greater (P < 0.01) ammonia concentration and molar percentage of valerate and isobutyrate than those fed with the CM diet. Goats fed with CG diet decreased (P = 0.01) CH4 emission expressed as g/d and g/kg DMI. Goats fed with CG diet decreased 16S rRNA gene copies of R. amylophilus (P = 0.003), and increased 18S rRNA gene copies of fungi (P = 0.05) and 16S rRNA gene copies of F. succinogenes (P = 0.03). In summary, replacing CM with CG decreases starch and increases fiber intake, and growth of fibrolytic fungi and F. succinogenes, and inhibits growth of R. amylophilus. An increase in sulfur content after replacing CM with CG provides additional H2 sink, which causes an increase in ruminal dH2S and reduction in CH4 emissions. Corn gluten could be an alternative feed to decrease the enteric CH4 emission in ruminant production.

Genome analyses of uncultured TG2/ZB3 bacteria in 'Margulisbacteria' specifically attached to ectosymbiotic spirochetes of protists in the termite gut.

We investigated the phylogenetic diversity, localisation and metabolism of an uncultured bacterial clade, Termite Group 2 (TG2), or ZB3, in the termite gut, which belongs to the candidate phylum 'Margulisbacteria'. We performed 16S rRNA amplicon sequencing analysis and detected TG2/ZB3 sequences in 40 out of 72 termite and cockroach species, which exclusively constituted a monophyletic cluster in the TG2/ZB3 clade. Fluorescence in situ hybridisation analysis in lower termites revealed that these bacteria are specifically attached to ectosymbiotic spirochetes of oxymonad gut protists. Draft genomes of four TG2/ZB3 phylotypes from a small number of bacterial cells were reconstructed, and functional genome analysis suggested that these bacteria hydrolyse and ferment cellulose/cellobiose to H2, CO2, acetate and ethanol. We also assembled a draft genome for a partner Treponema spirochete and found that it encoded genes for reductive acetogenesis from H2 and CO2. We hypothesise that the TG2/ZB3 bacteria we report here are commensal or mutualistic symbionts of the spirochetes, exploiting the spirochetes as H2 sinks. For these bacteria, we propose a novel genus, 'Candidatus Termititenax', which represents a hitherto uncharacterised class-level clade in 'Margulisbacteria'. Our findings add another layer, i.e., cellular association between bacteria, to the multi-layered symbiotic system in the termite gut.

Ruminal methane emissions, metabolic, and microbial profile of Holstein steers fed forage and concentrate, separately or as a total mixed ration.

Few studies have examined the effects of feeding total mixed ration (TMR) versus roughage and concentrate separately (SF) on ruminant methane production. Therefore, this study compared differences in methane production, ruminal characteristics, total tract digestibility of nutrients, and rumen microbiome between the two feeding methods in Holstein steers. A total six Holstein steers of initial bodyweights 540 ± 34 kg were divided into two groups and assigned to a same experimental diet with two different feeding systems (TMR or SF) in a crossover design with 21 d periods. The experimental diet contained 73% concentrate and 27% forage and were fed twice a day. The total tract digestibility of crude protein, neutral detergent fibre, and organic matter were not affected by the two different feeding systems. Steers fed TMR emitted more methane (138.5 vs. 118.2 L/d; P < 0.05) and lost more gross energy as methane energy (4.0 vs. 3.5% gross energy intake; P = 0.005) compared to those fed SF. Steers fed TMR had greater (P < 0.05) total volatile fatty acid (VFA), ammonia-N concentrations and propionate proportion of total VFA at 1.5 h, whereas lower after that compared to steers fed SF. The greater (P < 0.05) acetate: propionate ratio at 4.5 h for steers fed TMR reflected the shift of H2 sink from propionate towards acetate synthesis. The lower (P < 0.05) isobutyrate and isovalerate proportions of total VFA observed in steers fed TMR implies decrease in net consumption of H2 for microbial protein synthesis compared to SF. There were no differences in both major bacterial and archaeal diversity between TMR and SF, unlike several minor bacterial abundances. The minor groups such as Coprococcus, Succiniclasticum, Butyrivibrio, and Succinivibrio were associated with the changes in ruminal VFA profiles or methanogenesis indirectly. Overall, these results indicate that SF reduces methane emissions from ruminants and increases propionate proportion of total VFA without affecting total tract digestion compared to TMR. There were no evidences that the response differed due to different major underlying microbial population.

Dose-response relationships between environmentally-relevant H2 concentrations and the biological sinks of H2, CH4 and CO in soil

Local H2 accumulations can be found in soil, especially within legume crop agroecosystems, where H2 is an obligate by-product of nitrogen fixation. Recent investigations show that diffusive fluxes of H2 act as additional energy inputs shaping microbial community structure and function in soil. The goal of this study is thus to define dose-response relationships between H2 exposure and soil microbial community dynamics. Community structure and trace gases (i.e. H2, CH4 and CO) oxidation activities were investigated following soil incubation to environmentally-relevant H2 mixing ratios. Despite no evidence of an alteration of microbial diversity, coordinated dose-response relationships between trace gases oxidation rates and H2 exposure were recorded. Measured H2 oxidation rates were implemented into a theoretical framework modeling H2 decay as a function of distance from H2-emitting point sources. Theoretical H2 concentration profiles and dose-response relationships between H2 concentration and trace gases oxidation rates were integrated to predict the impact of H2 on microbial community functioning. While most H2 is oxidized within 1 cm of H2 point sources, trace gases oxidation is predicted to be altered within a 10 cm radius. High-affinity CH4 and CO oxidation capacities dropped by up to 78% and 84% along H2 concentration gradients, respectively. Theoretical distances from H2-emitting point sources required to reactivate 50% of maximal CH4 oxidation rate were 0.3 cm in farmland soil and 0.2 cm in poplar soil. A longer distance was required to reactivate 50% of CO oxidation rate, i.e. 1.5 and 2.7 cm in farmland and poplar soils, respectively. Loss of CH4 oxidation potential observed under elevated H2 exposure was correlated with a gain of low-affinity H2 oxidation activity, while a substrate inhibition of high affinity H2 oxidation rate was paralleled with a decreasing trend of CO oxidation activity. In addition to shedding light on potential interactions between H2, CH4 and CO biogeochemical processes in soil, these novel findings provide evidence that H2 supports metabolic and energetic flexibility in microorganisms supplying a variety of ecosystem services.

Ecosystem fluxes of hydrogen in a mid-latitude forest driven by soil microorganisms and plants.

Molecular hydrogen (H2 ) is an atmospheric trace gas with a large microbe-mediated soil sink, yet cycling of this compound throughout ecosystems is poorly understood. Measurements of the sources and sinks of H2 in various ecosystems are sparse, resulting in large uncertainties in the global H2 budget. Constraining the H2 cycle is critical to understanding its role in atmospheric chemistry and climate. We measured H2 fluxes at high frequency in a temperate mixed deciduous forest for 15months using a tower-based flux-gradient approach to determine both the soil-atmosphere and the net ecosystem flux of H2 . We found that Harvard Forest is a net H2 sink (-1.4±1.1kg H2 ha-1 ) with soils as the dominant H2 sink (-2.0±1.0kg H2 ha-1 ) and aboveground canopy emissions as the dominant H2 source (+0.6±0.8kg H2 ha-1 ). Aboveground emissions of H2 were an unexpected and substantial component of the ecosystem H2 flux, reducing net ecosystem uptake by 30% of that calculated from soil uptake alone. Soil uptake was highly seasonal (July maximum, February minimum), positively correlated with soil temperature and negatively correlated with environmental variables relevant to diffusion into soils (i.e., soil moisture, snow depth, snow density). Soil microbial H2 uptake was correlated with rhizosphere respiration rates (r=0.8, P<0.001), and H2 metabolism yielded up to 2% of the energy gleaned by microbes from carbon substrate respiration. Here, we elucidate key processes controlling the biosphere-atmosphere exchange of H2 and raise new questions regarding the role of aboveground biomass as a source of atmospheric H2 and mechanisms linking soil H2 and carbon cycling. Results from this study should be incorporated into modeling efforts to predict the response of the H2 soil sink to changes in anthropogenic H2 emissions and shifting soil conditions with climate and land-use change.

Multi-period stochastic mathematical model for the optimal design of integrated utility and hydrogen supply network under uncertainty in raw material prices

Utility supply networks and hydrogen (H2) supply networks have been consistently individually studied in terms of techno-economic feasibility of large scale. A number of studies have proposed and improved mathematical models for design of each optimized supply network. However, although two different networks can coexist in a large-scale industrial complex, few studies have been conducted to develop an integrated utility supply and H2 supply network (IUHSN) design in a techno-economic optimization framework. In this study, we design an IUHSN which includes a number of utilities (steam, water, and electricity), and H2 sources (manufacturers) and sinks (end customers). Steam methane reforming (SMR) process is used as an intermediate linkage between both networks. To obtain an optimal design of the IUHSN reflecting the reality, we develop a mathematical model which is formulated as multi-period stochastic mixed integer linear programming concerning uncertain raw material prices. This model allows identification of a promising design strategy to minimize total supply cost, because sources and sinks can be connected to each other to transfer unused resources and products.

Active H2 Harvesting Prevents Methanogenesis in Microbial Electrolysis Cells

Undesired H2 sinks, including methanogenesis, are a serious issue faced by microbial electrolysis cells (MECs) for high-rate H2 production. Different from current top-down approaches to methanogenesis inhibition that showed limited success, this study found active harvesting can eliminate the source (H2) from all H2 consumption mechanisms via rapid H2 extraction using a gas-permeable hydrophobic membrane and vacuum. Active harvesting completely prevented CH4 production and led to H2 yields (2.62–3.39 mol of H2/mol of acetate) much higher than that of the control using traditional spontaneous release (0.79 mol of H2/mol of acetate). In addition, existing CH4 production in the control MEC was stopped once the switch to active H2 harvesting was made. Active harvesting also increased current density by 36%, which increased operation efficiency and facilitated organic removal. Energy quantification shows the process was energy-positive, as the H2 energy produced via active harvesting was 220 ± 10% of external ...

Detection and isolation of plant-associated bacteria scavenging atmospheric molecular hydrogen.

High-affinity hydrogen (H2 )-oxidizing bacteria possessing group 5 [NiFe]-hydrogenase genes are important contributors to atmospheric H2 uptake in soil environments. Although previous studies reported the occurrence of a significant H2 uptake activity in vegetation, there has been no report on the identification and diversity of the responsible microorganisms. Here, we show the existence of plant-associated bacteria with the ability to consume atmospheric H2 that may be a potential energy source required for their persistence in plants. Detection of the gene hhyL - encoding the large subunit of group 5 [NiFe]-hydrogenase - in plant tissues showed that plant-associated high-affinity H2 -oxidizing bacteria are widely distributed in herbaceous plants. Among a collection of 145 endophytic isolates, seven Streptomyces strains were shown to possess hhyL gene and exhibit high- or intermediate-affinity H2 uptake activity. Inoculation of Arabidopsis thaliana (thale cress) and Oryza sativa (rice) seedlings with selected isolates resulted in an internalization of the bacteria in plant tissues. H2 uptake activity per bacterial cells was comparable between plant and soil, demonstrating that both environments are favourable for the H2 uptake activity of streptomycetes. This study first demonstrated the occurrence of plant-associated high-affinity H2 -oxidizing bacteria and proposed their potential contribution as atmospheric H2 sink.

Phylogenic diversity analysis of rumen acetogens in adult sheep fed on conventional roughage diet

The study was conducted to screen the Indian sheep for the presence as well as diversity of rumen acetogens. Rumen liquor samples from 3 adult female sheep (Mandya x Rambouillet) was collected through stomach tube. Genomic DNA was isolated and amplified using touchdown PCR protocol for partial formyltetrahydrofolate synthetase (fhs) gene sequence. Bioinformatic analysis of obtained sequences was done to construct phylogenic tree for molecular characterization and diversity analysis. PCR based amplification and further agarose gel electrophoresis revealed the presence of fhs functional gene in sheep rumen confirming the occurrence of acetogens in adult sheep fed on conventional roughage diet. However, we could not amplify the gene acs conserved with acetogens described by Australian workers. From the phylogenic tree it is clear that act1 group is distant from all other clones (act2 - act10) obtained in this study and represent a distinct uncultured acetogens genera. The act3 and act5 clones are also present in different clusters and are distant to act2, act10, act4 and act6 are closer to each other in the phylogenic tree but distant from act1. From the phylogeny tree it is clear that majority of the acetogens in these sheep are different from those acetogens reported elsewhere in the world. Thus, there is an urgent need to screen our livestock for the acetogens species/strains and to culture them for exploring the prospects of their use as alternate H2 sink for methane mitigation from ruminants.

Effects of three methane mitigation agents on parameters of kinetics of total and hydrogen gas production, ruminal fermentation and hydrogen balance using in vitro technique.

Methane (CH4 ) can be mitigated through directly inhibiting methanogen activity and starving methanogens by hydrogen (H2 ) sink. Three types of mechanism (i.e. bromoethanesulphonate (BES), nitrate and emodin) and doses of CH4 mitigation agents were employed to investigate their pathways of CH4 inhibition. Results indicated that both BES and emodin inhibited CH4 production and altered H2 balance, which could be accompanied by decreased dry matter disappearance (DMD), fractional rate of gH2 formation, volatile fatty acid (VFA) production, ability to produce and use reducing equivalences and molecular H2 , and increased final asymptotic gH2 production, time to the peak of gH2 , discrete lag time of gH2 production and fermentation efficiency. However, emodin decreased gas volume produced by rapidly fermentable components of substrate and the rate of fermentation at early stage of incubation, while BES supplementation inhibited gas volume produced by both rapidly and slowly fermentable components of substrate and the rate of fermentation at middle or late stage of incubation. The nitrate supplementation inhibited CH4 production without affecting VFA profile, because of its dual role as H2 sink and being toxic to methanogens. Nitrate supplementation had more complicated pattern of fermentation, VFA production and profile and H2 balance in comparison to BES and emodin supplementation.