Review of methane mitigation technologies with application to rapid release of methane from the Arctic

Pyrogenic Black Carbon Suppresses Microbial Methane Production by Serving as a Terminal Electron Acceptor

Methane (CH4) is the second most important greenhouse gas, 27 times as potent as CO2 and responsible for >30% of the current anthropogenic warming. Globally, more than half of CH4 is produced microbially through methanogenesis. Pyrogenic black carbon possesses a considerable electron storage capacity (ESC) and can be an electron donor or acceptor for abiotic and microbial redox transformation. Using wood-derived biochar as a model black carbon, we demonstrated that air-oxidized black carbon served as an electron acceptor to support anaerobic oxidation of organic substrates, thereby suppressing CH4 production. Black carbon-respiring bacteria were immediately active and outcompeted methanogens. Significant CH4 did not form until the bioavailable electron-accepting capacity of the biochar was exhausted. An experiment with labeled acetate (13CH3COO-) yielded 1:1 13CH4 and 12CO2 without biochar and predominantly 13CO2 with biochar, indicating that biochar enabled anaerobic acetate oxidation at the expense of methanogenesis. Methanogens were enriched following acetate fermentation but only in the absence of biochar. The electron balance shows that approximately half (∼2.4 mmol/g) of biochar's ESC was utilized by the culture, corresponding to the portion of the ESC > +0.173 V (vs SHE). These results provide a mechanistic basis for quantifying the climate impact of black carbon and developing ESC-based applications to reduce CH4 emissions from biogenic sources.

Process concepts and analysis for co-removing methane and carbon dioxide from the atmosphere

Methane is the second largest contributor to global warming after CO2, and it is hard to abate due to its low concentration in the emission sources and in the atmosphere. However, removing methane from the atmosphere will accelerate achieving net-zero targets, since its global warming potential is 28 over a 100-year period. This work presents first-of-its-kind process concepts for co-removal of methane and CO2 that combines the catalytic conversion of methane step (thermal/photo-catalytic) with CO2 capture. Proposed processes have been analyzed for streams with lean methane concentrations, which are non-fossil emissions originating in the agricultural sector or natural emissions from wetlands. If the proposed processes can overcome challenges in catalyst/material design to convert methane at low concentrations, they have the potential to remove more than 40% of anthropogenic and natural methane emissions from the atmosphere at a lower energy penalty than the state-of-the-art technologies for direct air capture of CO2.

Proteomic profiling of robust acetoclastic methanogen in chrysene-altered anaerobic digestion: Global dissection of enzymes

Methanogen is a pivotal player in pollution treatment and energy recovery, and emerging pollutants (EPs) frequently occur in methanogen-applied biotechnology such as anaerobic digestion (AD). However, the direct effect and underlying mechanism of EPs on crucial methanogen involved in its application still remain unclear. The positive effect of chrysene (CH) on semi-continuous AD of sludge and the robust methanogen was dissected in this study. The methane yield in the digester with CH (100 mg/kg dry sludge) was 62.1 mL/g VS substrate, much higher than that in the control (46.1 mL/g VS substrate). Both methane production from acetoclastic methanogenesis (AM) and the AM proportion in the methanogenic pathway were improved in CH-shaped AD. Acetoclastic consortia, especially Methanosarcina and functional profiles of AM were enriched by CH in favor of the corresponding methanogenesis. Further, based on pure cultivation exposed to CH, the methanogenic performance, biomass, survivability and activity of typical Methanosarcina (M. barkeri) were boosted. Notably, iTRAQ proteomics revealed that the manufacturing (transcription and translation), expression and biocatalytic activity of acetoclastic metalloenzymes, particularly tetrahydromethanopterin S-methyltransferase and methyl-coenzyme M reductase with cobalt/nickel-cofactor (F₄₃₀ and cobalamin), and acetyl-CoA decarbonylase/synthase with cobalt/nickel-active site, of M. barkeri were upregulated significantly with fold changes in the range of 1.21-3.20 due to the CH presence. This study shed light on EPs-affecting industrially crucial methanogen at the molecular biology level during AD and had implications in the technical relevance of methanogens.

Non-Fossil Methane Emissions Mitigation From Agricultural Sector and Its Impact on Sustainable Development Goals

The agriculture sector contributes to ∼40% of methane emissions globally. Methane is also 28 times (Assessment Report 5) more potent greenhouse gas than CO2. In this study, we assess the impact of measures for mitigating methane emissions from the agricultural sector on the achievement of all the 17 United Nations’ Sustainable Development Goals (SDGs). A keyword literature review was employed that focused on finding the synergies and trade-offs with non-fossil methane emissions from the agricultural sector and respective SDGs’ targets. The results were in broad consensus with the literature aimed at finding the relationship between SDGs and measures targeting climate change. There is a total of 88 synergies against eight trade-offs from the 126 SDGs’ targets that were assessed. It clearly shows that measures to mitigate methane emissions from the agricultural sector will significantly help in achieving the SDGs. Since agriculture is the primary occupation and the source of income in developing countries, it can further be inferred that methane mitigation measures in developing countries will play a larger role in achieving SDGs. Measures to mitigate methane emissions reduce poverty; diversify the source of income; promote health, equality, education, sanitation, and sustainable development while providing energy and resource security to the future generations.

Mitigation of Methane, NMVOCs and Odor Emissions in Active and Passive Biofiltration Systems at Municipal Solid Waste Landfills

Biofiltration systems are emerging technological solutions for the removal of methane and odors from landfill gas when flaring is no longer feasible. This work analyzed and compared two full-scale biofiltration systems: biofilter and biowindows. The emission mitigation of methane, non-methane volatile organic compounds (NMVOCs) and odors during a two-year management and monitoring period was studied. In addition to diluted methane, more than 50 NMVOCs have been detected in the inlet raw landfill gas and the sulfur compounds resulted in the highest odor activity value. Both systems, biofilter and biowindows, were effective for the oxidation of methane (58.1% and 88.05%, respectively), for the mitigation of NMVOCs (higher than 80%) and odor reduction (99.84% and 93.82% respectively). As for the biofilter monitoring, it was possible to define the oxidation efficiency trend and in fact to guarantee that for an oxidation efficiency of 80%, the methane load must be less than 6.5 g CH4/m2h with an oxidation rate of 5.2 g CH4/m2h.

Selective CO2 or CH4 adsorption of two anionic bcu-MOFs with two different counterions: experimental and simulation studies

Two new bcu-MOFs with counterions tuned from Li(H₂O)₄⁺ to DMA⁺ have been successfully synthesized and their selective CO₂ or CH₄ adsorption over N₂ gas has been systematically investigated in-depth by both experimental and simulation studies.

Simultaneous mitigation of methane and odors in a biowindow using a pipe network

In this study, a biowindow with a piped gas collection network is proposed as an area-efficient landfill gas treatment system. A 9-m² biowindow was constructed for treating landfill gas collected from an area of 450 m² in a sanitary landfill, and its performance was evaluated for 224 days. The methane removal efficiency was 59-100% at 146.3-675.1 g-CH₄ m^-2 d^-1. Odorous compounds were also removed by the biowindow, with a complex odor intensity removal rate of 93-100%. In particular, the removal efficiency for hydrogen sulfide and methanethiol, major contributors to the complex odor intensity, was 97% and 91%, respectively. Metagenomic analysis showed that the dominant bacterial genera shifted from Acinetobacter and Pseudomonas to Methylobacter and Methylocaldum due to the high concentration of methane. A high bacterial diversity was maintained, which may have contributed to the robust performance of the biowindow against environmental fluctuations. At 1/50th of the size of conventional biocovers, the proposed biowindow can greatly reduce the required installation area and represents a competitive method for the simultaneous treatment of methane and odor in landfills.

CO2 fluxes from aquaculture ponds of a tropical wetland: Potential of multiple lime treatment in reduction of CO2 emission

Partial pressure of CO₂ in water [pCO₂(water)] and air-water CO₂ flux were estimated in two aquaculture ponds (one received no lime treatment (NTP) and in the other lime treatment was performed (LTP) four times a year) every month throughout an annual cycle, situated in East Kolkata Wetlands, a Ramsar Site in eastern India. It was hypothesized that lime treatment can potentially lower the pCO₂(water) in aquaculture ponds and hence make these aquatic bodies sinks for CO₂. The results portrayed that NTP acted as a source of CO₂ throughout the year (annual mean: 1929 ± 1397 μmol m^-2 h^-1), whereas, LTP acted as CO₂ sinks post lime addition (monthly mean ranged from -366 ± 16 to -449 ± 32 μmol m^-2 h^-1), though the effect of lime addition was found to diminish by the next month and it acted as source for CO₂ in the months when no lime treatment was done (LTP annual mean: 1010 ± 1617 μmol m^-2 h^-1). Lime treatment increased the pH level and reduced the turbidity which facilitated optimum photosynthesis and the productivity increased rapidly. Beyond the critical pH value of 8.9-9.0, the pCO₂(water) values became under-saturated with respect to atmospheric CO₂ concentration. The effect of lime treatment was not found to prevail in the following months as a steady source of sewage from the Kolkata metropolis which feeds these aquaculture constantly bring in a huge carbon source both in inorganic and organic form. As soon as the flocculation effect of the lime dies off, the water column starts becoming turbid again which aids in converting the system into a net heterotrophic one from a net autotrophic. Based on the results we could successfully accept our hypothesis that lime treatment can not only reduce the CO₂ emission but also make the system a CO₂ sink.

Development of a novel methanotrophic process with the helper micro-organism Hyphomicrobium sp. NM3

AIMS

Microbial consortia can be more efficient at biological processes than single isolates. The purposes of this study were to design and evaluate a synthetic microbial consortium containing the methanotroph Methylocystis sp. M6 and the helper Hyphomicrobium sp. NM3, and develop a novel methanotrophic process for this consortium utilizing a dialysis membrane.

METHODS AND RESULTS

Hyphomicrobium increased the methane-oxidation rate (MOR), biomass and stability at a dilution rate of 0·067 day^-1 in fed-batch co-culture. qRT-PCR showed that Methylocystis population increased gradually with time, whereas Hyphomicrobium population remained stable despite cell washing, confirming synergistic population interaction. At 0·1 day^-1 , spiking of Hyphomicrobium effectively increased the methanotrophic activity, after which Hyphomicrobium population decreased with time, indicating that the consortium is optimal at <0·1 day^-1 . When Hyphomicrobium was grown in dialysis membrane within the bioreactor, MOR increased linearly up to 155·1 ± 1·0 mmol l^-1  day^-1 at 0·067, 0·1, 0·2 and 0·4 day^-1 , which is the highest observed value for a methanotrophic reactor.

CONCLUSIONS

Hyphomicrobium sp. NM3 is a promising helper micro-organism for methanotrophs. Hyphomicrobium-methanotroph consortia used concurrently with existing methods can produce an efficient and stable methane oxidation system.

SIGNIFICANCE AND IMPACT OF THE STUDY

This novel methanotrophic process is superior to those previously reported in the literature, and can provide efficient and stable methane oxidation.

Mitigating Methane: Emerging Technologies To Combat Climate Change's Second Leading Contributor

Methane (CH₄) is the second greatest contributor to anthropogenic climate change. Emissions have tripled since preindustrial times and continue to rise rapidly, given the fact that the key sources of food production, energy generation and waste management, are inexorably tied to population growth. Until recently, the pursuit of CH₄ mitigation approaches has tended to align with opportunities for easy energy recovery through gas capture and flaring. Consequently, effective abatement has been largely restricted to confined high-concentration sources such as landfills and anaerobic digesters, which do not represent a major share of CH₄'s emission profile. However, in more recent years we have witnessed a quantum leap in the sophistication, diversity and affordability of CH₄ mitigation technologies on the back of rapid advances in molecular analytical techniques, developments in material sciences and increasingly efficient engineering processes. Here, we present some of the latest concepts, designs and applications in CH₄ mitigation, identifying a number of abatement synergies across multiple industries and sectors. We also propose novel ways to manipulate cutting-edge technology approaches for even more effective mitigation potential. The goal of this review is to stimulate the ongoing quest for and uptake of practicable CH₄ mitigation options; supplementing established and proven approaches with immature yet potentially high-impact technologies. There has arguably never been, and if we do not act soon nor will there be, a better opportunity to combat climate change's second most significant greenhouse gas.

“Explosive” synthesis of metal-formate frameworks for methane capture: an experimental and computational study

We present an ultrafast “explosive” synthesis of nickel-formate frameworks, which show prominent performance for methane capture from nitrogen, proved using experiments and simulations.

Microporous rod metal–organic frameworks with diverse Zn/Cd–triazolate ribbons as secondary building units for CO2 uptake and selective adsorption of hydrocarbons

Three rod MOFs exhibiting remarkable CO₂ uptake and high CO₂ and C₂-hydrocarbons over CH₄ selectivity, as well as high isosteric heat of adsorption for C₂H₂.

Methylotrophs in natural habitats: current insights through metagenomics

The focus of this review is on the recent data from the omics approaches, measuring the presence of methylotrophs in natural environments. Both Bacteria and Archaea are considered. The data are discussed in the context of the current knowledge on the biochemistry of methylotrophy and the physiology of cultivated methylotrophs. One major issue discussed is the recent metagenomic data pointing toward the activity of "aerobic" methanotrophs, such as Methylobacter, in microoxic or hypoxic conditions. A related issue of the metabolic distinction between aerobic and "anaerobic" methylotrophy is addressed in the light of the genomic and metagenomic data for respective organisms. The role of communities, as opposed to single-organism activities in environmental cycling of single-carbon compounds, such as methane, is also discussed. In addition, the emerging issue of the role of non-traditional methylotrophs in global metabolism of single-carbon compounds and the role of methylotrophy pathways in non-methylotrophs is briefly mentioned.

Addressing biogenic greenhouse gas emissions from hydropower in LCA

The ability of hydropower to contribute to climate change mitigation is sometimes questioned, citing emissions of methane and carbon dioxide resulting from the degradation of biogenic carbon in hydropower reservoirs. These emissions are, however, not always addressed in life cycle assessment, leading to a bias in technology comparisons, and often misunderstood. The objective of this paper is to review and analyze the generation of greenhouse gas emissions from reservoirs for the purpose of technology assessment, relating established emission measurements to power generation. A literature review, data collection, and statistical analysis of methane and CO2 emissions are conducted. In a sample of 82 measurements, methane emissions per kWh hydropower generated are log-normally distributed, ranging from micrograms to 10s of kg. A multivariate regression analysis shows that the reservoir area per kWh electricity is the most important explanatory variable. Methane emissions flux per reservoir area are correlated with the natural net primary production of the area, the age of the power plant, and the inclusion of bubbling emissions in the measurement. Even together, these factors fail to explain most of the variation in the methane flux. The global average emissions from hydropower are estimated to be 85 gCO2/kWh and 3 gCH4/kWh, with a multiplicative uncertainty factor of 2. GHG emissions from hydropower can be largely avoided by ceasing to build hydropower plants with high land use per unit of electricity generated.