Methane Oxidation Capacity Research Articles

Theoretical analysis and application of immobilized methanotrophs as typical adsorbent materials for adsorption/degradation of trichloroethylene

ABSTRACT Trichloroethylene (TCE) contamination presents a significant environmental challenge, necessitating efficient treatment solutions. This study aimed to develop an optimized immobilized bioreactor using methanotrophs for TCE degradation. Activated carbon fibres were identified as the optimal immobilization material, with an adsorption rate of 6–23 h – significantly faster than over 50 h for other materials – and the highest methane oxidation capacity of 0.970 mL·g−1·h−1. Adsorption kinetics indicated that activated carbon fibres followed a second-order kinetic model with a constant of 0.598 g·mg−1·h−1, suitable for low-concentration bacterial solutions. Thermodynamic analysis confirmed an exothermic process, favouring lower temperatures (288.15 K). The negative interaction energies, as per DLVO theory, suggested electrostatic attraction as a key mechanism. The bioreactor achieved 99% TCE removal within 1 h at an initial concentration of 10 mg·L−1, with visible microbial immobilization within 5 days. This research provides a novel and effective approach for using immobilized methane-oxidizing bacteria in TCE treatment, offering both theoretical and practical advancements for chlorinated hydrocarbon wastewater management.

In situ aerobic methane oxidation rates in a stratified lake

AbstractMicrobial aerobic methane oxidation is an important sink for aquatic methane worldwide. Despite its importance to global methane fluxes, few aerobic methane oxidation rates have been obtained in freshwater or marine environments without imposing changes to the microbial community through use of ex situ methods. A novel in situ incubation method for continuous time‐series measurements was used in Jordan Lake, North Carolina, during 2020–2021, to determine reaction kinetics for aerobic methane oxidation rates across a wide range of naturally varying methane (55–1833 nM) and dissolved oxygen (DO; 28–366 μM) concentrations and temperatures (17–30°C). Methane oxidation began immediately at the start of each of 21 incubations and methane oxidation rates were 1st order with respect to methane. The data density allowed for accurate calculation of 1st‐order rate constants, k, that ranged from 0.018 to 0.462 h−1 (R2 > 0.967). Addition of ammonium (20–45 μM) to natural concentrations ranging from 0.057 to 2.4 μM did not change aerobic methane oxidation rate kinetics, suggesting that the natural population of aerobic methane oxidizers in this eutrophic lake was not nitrogen limited. Values of k inversely correlated most strongly with initial DO concentrations (R2 = 0.82) rather than temperature. Values for k increased with Julian day throughout our sampling period, suggesting seasonal influences on methane oxidation via responses to geochemical changes or shifts in microbial community abundance and composition. These experiments demonstrate a high variability in the enzymatic capacity for 1st‐order methane oxidation rates in this eutrophic lake that is tightly and inversely coupled to oxygen concentrations. Measurements of in situ aerobic methane oxidation rate constants allow for the direct quantification and modeling of the microbial community's capacity for methane oxidation over a wide range of natural methane concentrations.

Selenium-Induced Enhancement in Growth and Rhizosphere Soil Methane Oxidation of Prickly Pear.

As an essential element for plants, animals, and humans, selenium (Se) has been shown to participate in microbial methane oxidation. We studied the growth response and rhizosphere methane oxidation of an economic crop (prickly pear, Rosa roxburghii Tratt) through three treatments (Se0.6 mg/kg, Se2.0 mg/kg, and Se10 mg/kg) and a control (Se0 mg/kg) in a two-month pot experiment. The results showed that the height, total biomass, root biomass, and leaf biomass of prickly pear were significantly increased in the Se0.6 and Se2.0 treatments. The root-to-shoot ratio of prickly pear reached a maximum value in the Se2 treatment. The leaf carotenoid contents significantly increased in the three treatments. Antioxidant activities significantly increased in the Se0.6 and Se2 treatments. Low Se contents (0.6, 2 mg/kg) promoted root growth, including dry weight, length, surface area, volume, and root activity. There was a significant linear relationship between root and aboveground Se contents. The Se translocation factor increased as the soil Se content increased, ranging from 0.173 to 0.288. The application of Se can improve the state of rhizosphere soil's organic C and soil nutrients (N, P, and K). Se significantly promoted the methane oxidation rate in rhizosphere soils, and the Se10 treatment showed the highest methane oxidation rate. The soil Se gradients led to differentiation in the growth, rhizosphere soil properties, and methane oxidation capacity of prickly pear. The root Se content and Se translocation factor were significantly positively correlated with the methane oxidation rate. Prickly pear can accumulate Se when grown in Se-enriched soil. The 2 mg/kg Se soil treatment enhanced growth and methane oxidation in the rhizosphere soil of prickly pear.

Reduction of soil methane emissions from croplands with 20–40 years of cultivation mediated by methane-metabolizing microorganisms

Reducing carbon emissions from cropland ecosystems is an important measure to achieve early carbon neutrality. However, how methane-metabolizing microorganisms affect methane emissions from cropland soils of different planting years is not known. In this study, we determined methane emissions from cropland soils of different tobacco-rice rotation years after rice harvesting. By mean of functional gene sequencing, we analyzed the relationship between methane-metabolizing microorganisms and methane emissions, and revealed the microbial mechanism of action for methane emissions from cropland soils. The results showed that the soil organic carbon content was higher (P < 0.05) and methane emissions were lower (P < 0.05) in cropland cultivated for 20–40 years (PY20). Soil methane emissions from PY20 cropland were reduced by 30.11% and 14.58% (P < 0.05) compared to cropland planted for 10–20 years and more than 40 years. The alpha diversity of methanogens communities was significantly lower in PY20 cropland soils, whereas the methanotrophs communities alpha diversity did not differ significantly between planting years. The methanogenic genus Methanocorpusculum was significantly and positively correlated with methane emissions. The relative abundance of Methanocorpusculum in PY20 cropland soil was lower (P < 0.05), and the relative abundance of Methylocystis, a type II methanotrophs with greater oxidizing capacity for methane, was higher (P < 0.05). Reducing PY20 cropland soil methane emissions by reducing methane production and enhancing methane oxidation. At the same time, more methanotrophs in PY20 cropland soil formed a molecular interactions network with methanogens. Planting years altered the diversity and composition of methane-metabolizing microbial communities and the interactions of different taxa, which in turn affected methane emissions. Cropland soils that have been cultivated for 20–40 years have lower methane production capacity and higher methane oxidation capacity, resulting in lower methane emissions. This study provides a scientific reference for the microbial action mechanism of soil methane emission from cropland under different planting years, with a view to contributing to carbon neutralization in cropland ecosystems.

A bio-augmented system with Methylosarcina sp. LC-4 immobilized on bio-carriers: Towards an integrated approach to mitigate and valorize methane emissions from landfills to biodiesel

Bio-augmented systems based on methanotrophs are indispensable in curbing anthropogenic methane emissions from engineered landfills or dumpsites to curtail rising levels of greenhouse gases. Using a defined methanotroph culture immobilized on an inert material-based bio-carrier makes it possible to harness these methane emissions for creating value-added products, thus contributing to the circular bio-economy. The methane oxidation capacity of the model methanotroph Methylosarcina sp. LC-4, a prospective organism for biodiesel production using methane present in landfill gas, immobilized on several inert bio-carriers, was evaluated to identify a bio-carrier that provided optimum conditions for the process.Among the several bio-carriers evaluated, perlite and vermiculite were selected due to their high specific surface area and superior water-holding capacity, which result in the retention of nutrients and biomass and higher methane elimination capacity. While perlite showed high biomass holding capacity and methane transport, vermiculite supported a high growth of methanotrophs. LC-4 immobilized on perlite and vermiculite as the bio-carrier showed maximum methane elimination capacity (MEC) of 291.3 g m−2 day−1 and 155.5 g m−2 day−1, respectively. The low bed height of only 0.13 m and a short start-up period of 2–4 days are promising for use as alternate daily cover in a landfill. The recovered biomass had 12% (w/w) fatty acid methyl ester (FAME), with a high fraction of (∼85%) of C14–C18 saturated and monounsaturated fatty acids, suitable for biodiesel production. The combination of perlite and vermiculite increased MEC and FAME content levels. The current study demonstrated a new bio-augmented system designed with a pure methanotroph for methane elimination with a short start-up time and the valorization of the assimilated methane.

Impact of temperature on the performance of compost-based landfill biocovers

Methane (CH4) emissions from landfills are a major contributor to global greenhouse gas emissions. Compost-based biocovers offer a viable approach to reduce CH4 emissions from landfills; however, the effectiveness in climates with varying temperatures is not well understood. The methane removal performances of two compost-based biocover materials (food and yard waste compost) were examined under different temperature conditions using laboratory column experiments. A reactive transport model was used to simulate the experimental results to develop a better quantitative understanding of the effect of temperature on overall methane removal efficiency. As expected, experimental results indicated that the oxidation rate was influenced by temperature, as it was reduced when the temperature decreased from 22 °C to 8 °C. However, some oxidation was observed at a lower temperature, which was confirmed by CO2 concentrations above the initial level and the observed temperatures above the exposure temperature along the height of biocover column. Furthermore, results showed that when the compost-based materials were subjected to 8 °C and then increased to 22 °C, methane oxidation within the material recovered quickly and returned to similar oxidation rates as observed before the temperature was reduced, suggesting that compost-based biocovers may not be affected by cyclic temperature variations when used in colder climates. Methane oxidation capacity was limited by the maximum oxidation rate, the biocover porosity, and the gas saturation profile that affects residence time and overall methane oxidation in the columns. The model results show that the CH4 oxidation rate was reduced by one order of magnitude when the temperature decreased from 22 °C to 8 °C. Therefore, the calculated Q10 values were 4.19 and 5.18 for the food and yard waste compost, respectively. Overall, compost-based landfill biocovers, such as food and yard waste compost, are capable of mitigate CH4 emissions from old and small landfills under different temperature conditions.

Characteristics of the methanotroph used in coalbed methane emission reduction: Methane oxidation efficiency and coal wettability

In the process of coal mining, a large amount of methane is emitted into the atmosphere every year, which enhances the greenhouse effect of the atmosphere. Microbial methane oxidation technology provides a new idea for methane emission reduction and methane control in coal mines. To improve the environmental adaptability of microorganisms, mixed methanotrophic consortia were selected from the natural environment. During the growth process, microorganisms grew most vigorously in the 4th–10th days and peaked on the 7th day. Affected by microbial metabolism, the pH (potential of hydrogen) of the solution increased, and the ORP (oxidation–reduction potential) decreased, both of which were negatively correlated. The selected mixed methanotrophic consortia have extremely strong methane-oxidizing ability, the volume of methane gas decreased by 71.19 %. It is particularly important that the microorganisms still have a certain methane oxidation capacity, after which the oxygen in the device is exhausted. The results showed that the mixed methanotrophic consortia adjusted the population structure to adapt to the changes in the surrounding environment and continued to exert methane oxidation ability. The contact angle between the bacterial solution and coal sample surface was far lower than that of pure water and culture medium. Microorganisms adsorbed onto the surface of the coal sample through self-movement, greatly improving the contact ability between the bacterial solution and the coal sample. The retention of microorganisms in the coal sample was affected by the flow velocity and the particle size of the coal sample. A low flow velocity and large contact area can improve the contact efficiency of microorganisms on the coal surface. Mixed methanotrophic consortia have high application value and feasibility in coal mine methane emission reduction and underground methane treatment.

The effect of barometric pressure changes on the performance of a passive biocover system, Skellingsted landfill, Denmark

This study investigated the performance of a passive biocover system at a Danish landfill. The overall methane oxidation efficiency of the system was assessed by comparing annual whole-site methane emissions before and after biocover installation. Annual whole-site methane emission predictions were calculated based on empirical models developed by a discrete number of tracer gas dispersion measurements. Moreover, a series of field campaigns and continuous flux measurements was carried out to evaluate the functionality of an individual biowindow. The results indicated that biocover system performance highly depended on barometric pressure variations. Under decreasing barometric pressure, estimated efficiency declined to 20%, while under increasing barometric pressure, nearly 100% oxidation was achieved. In-situ measurements on a specific biowindow showed a similar oxidation efficiency pattern in respect to barometric pressure changes despite the difference in spatial representation. Eddy covariance results revealed pronounced seasonal variability in the investigated biowindow, measuring higher methane fluxes during the cold period compared to the warm period. Results from the in-situ campaigns confirmed this finding, reporting a threefold increase in the biowindow’s methane oxidation capacity from April to May. The annual average oxidation efficiency of the system was estimated to range between 51% and 65%, taking into consideration the impact of changes in barometric pressure and seasonal variability. This indicated an annual reduction in landfill’s methane emissions between 24 and 35 tonnes. This study revealed the challenge facing current approaches in documenting accurately the performance of a passive biocover system, due to the short-term variability of oxidation efficiency, which is influenced by barometric pressure changes.

Enhanced Methane Oxidation Potential of Landfill Cover Soil Modified with Aged Refuse

Aged refuse with a landfill age of 1.5 years was collected from a municipal solid waste landfill with high kitchen waste content and mixed with soil as biocover material for landfill. A series of laboratory batch tests was performed to determine the methane oxidation potential and optimal mixing ratio of landfill cover soil modified with aged refuse, and the effects of water content, temperature, CO2/CH4, and O2/CH4 ratios on its methane oxidation capacity were analyzed. The microbial community analysis of aged refuse showed that the proportions of type I and type II methane-oxidizing bacteria were 56.27% and 43.73%, respectively. Aged refuse could significantly enhance the methane oxidation potential of cover soil, and the optimal mixing ratio was approximately 1:1. The optimal temperature and water content were about 25 °C and 30%, respectively. Under the conditions of an initial methane concentration of 15% and an O2/CH4 ratio of 0.8–1.2, the measured methane oxidation rate was negatively correlated with the O2/CH4 ratio. The maximum methane oxidation capacity measured in the test reached 308.5 (μg CH4/g)/h, indicating that the low-age refuse in the landfill with high kitchen waste content is a biocover material with great application potential.

Anaerobic methane oxidation in a coastal oxygen minimum zone: spatial and temporal dynamics

SummaryCoastal waters are a major source of marine methane to the atmosphere. Particularly high concentrations of this potent greenhouse gas are found in anoxic waters, but it remains unclear if and to what extent anaerobic methanotrophs mitigate the methane flux. Here we investigate the long‐term dynamics in methanotrophic activity and the methanotroph community in the coastal oxygen minimum zone (OMZ) of Golfo Dulce, Costa Rica, combining biogeochemical analyses, experimental incubations and 16S rRNA gene sequencing over 3 consecutive years. Our results demonstrate a stable redox zonation across the years with high concentrations of methane (up to 1.7 μmol L−1) in anoxic bottom waters. However, we also measured high activities of anaerobic methane oxidation in the OMZ core (rate constant, k, averaging 30 yr−1 in 2018 and 8 yr−1 in 2019–2020). The OPU3 and Deep Sea‐1 clades of the Methylococcales were implicated as conveyors of the activity, peaking in relative abundance 5–25 m below the oxic–anoxic interface and in the deep anoxic water respectively. Although their genetic capacity for anaerobic methane oxidation remains unexplored, their sustained high relative abundance indicates an adaptation of these clades to the anoxic, methane‐rich OMZ environment, allowing them to play major roles in mitigating methane fluxes.

树种多样性对土壤微生物群落结构和元素生物地球化学循环的影响研究进展

PDF HTML阅读 XML下载 导出引用 引用提醒 树种多样性对土壤微生物群落结构和元素生物地球化学循环的影响研究进展 DOI: 10.5846/stxb202101070073 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学面上项目(32071631)；国家自然科学基金青年基金项目(41907022)；福建省自然科学面上基金项目(2020J01138) Research progresses in the effects of tree species diversity on soil microbial communities and biogeochemical cycling of elements Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:森林是陆地生态系统的重要组成部分,其巨大的生产力和生态服务功能对人类的生存和发展至关重要。森林树种多样性增加能够显著提高森林生产力,关于树种多样性如何影响地下生物多样性及生态功能逐渐受到国内外学者的广泛关注。从土壤微生物及其介导的元素生物地球化学循环这一视角出发,综述了树种多样性对土壤细菌和真菌多样性、群落结构及功能的影响,提出需要进一步深入研究的方向。总体来说,树种多样性有利于增加土壤细菌生物量和多样性,是预测病原性真菌和菌根真菌多样性及群落结构的重要生物因子。树种多样性能增加土壤有机碳储量,增强森林土壤的甲烷氧化能力,并提高土壤磷周转速率及有效磷含量。关于树种多样性对森林土壤氮循环的影响需考虑多样性假说和质量比假说的相对贡献。今后应加强树种多样性对多个营养级之间相互作用的研究;关注树种多样性对生态系统多功能的影响;加强学科交叉,引入微生物种群动态模型和气候模型等模型预测方法,研究树种多样性对全球气候变化的应对机制,以期促进地上植物多样性与地下生态系统功能关系的研究,增强森林生态系统应对未来全球环境变化的能力。 Abstract:Forest is an important component of terrestrial ecosystems. Its high productivity and ecosystem services play a key role in anthropogenic survival and development. The increases in forest tree species diversity can significantly increase forest productivity. It has been widely concerned about how tree species diversity influences the belowground biodiversity and ecosystem functioning. From the perspective of soil microorganisms and their mediated biogeochemical cycling of elements, we reviewed the effects of tree species diversity on soil bacterial and fungal diversity, community structure and ecosystem functioning, and further proposed future research directions. In general, tree species diversity is beneficial to increase soil bacterial biomass and diversity. Tree species diversity is an important bio-indicator of the diversity and community structure of pathogenic fungi and mycorrhizal fungi. Tree species diversity can increase soil organic carbon storage, and enhance soil methane oxidation capacity, as well as facilitate soil phosphorus turnover and bioavailability. The relative contribution of diversity hypothesis and mass ratio hypothesis should be taken into consideration in terms of the effects of tree species diversity on the nitrogen cycling. In the future, we should devote great efforts to the influence of tree species diversity on interactions among multiple trophic levels. Meanwhile, more attention should be paid to the effects of tree species diversity on ecosystem multifunctionality. Interdisciplinary research and modelling prediction methods, such as microbial population dynamics model and climate model, should be incorporated to explore the mechanisms of tree species diversity in response to global environmental change. This aims to promote the study on the relationship between aboveground plant diversity and belowground ecosystem functioning, and thus enhance the capacity of forest ecosystem for dealing with future global environmental change. 参考文献 相似文献 引证文献

Impact of hydrogen sulfide on biochar in stimulating the methane oxidation capacity and microbial communities of landfill cover soil

Hydrogen sulfide (H2S) can influence methanotrophic activities and be adsorbed by biochar (BC); however, the impact of H2S on BC in stimulating the methane (CH4) oxidation capacity of landfill cover soil (LCS) has not been clarified. Thus, batch incubation experiments were conducted to observe the effect of H2S on the CH4 oxidation capacity of and microbial communities in BC-amended LCS. Three landfill gas conditions were considered: 5 % CH4 and 15 % oxygen (O2) (5 M), 10 % CH4 and 10 % O2, and 20 % CH4 and 5 % O2 (20 M) by volume, with H2S concentrations of 0, 100, 250, and 1000 ppm, respectively. Another series was conducted using LCS subjected to pre-H2S saturation under the 20 M gas condition. In the 5 M gas condition suitable for the dominant methanotroph Methylocaldum (type I), the BC retained its ability to stimulate the CH4 oxidation capacity of LCS (enhancement of 41–108 %) in the presence of H2S. Additionally, when H2S ≤ 250 ppm, the BC exhibited a relatively consistent impact of H2S on both CH4 oxidation capacity and microbial communities in LCS, independent of the CH4 or O2 concentrations. This result could be attributed to the different pathways of H2S metabolism for the LCS and BC-amended LCS. Furthermore, when saturated adsorption of H2S occurred for the LCS, the CH4 oxidation capacity for BC-amended LCS was higher than that for non-amended LCS, which demonstrated the ability of BC in alleviating the inhibition of H2S on CH4 oxidation due to its excellent H2S adsorption under even anoxic environments.

Validation and optimization of key biochar properties through iron modification for improving the methane oxidation capacity of landfill cover soil

Knowledge of various BC properties in stimulating the methane (CH4) oxidation capacity of landfill cover soil (LCS) is still limited, restricting the optimization of BC performance. To validate key BC properties and seek a feasible way for enhancing BC performance, this study prepared BCs with distinctly varying characteristics through iron (Fe) modification. Then, batch incubation experiments under different CH4 and oxygen concentrations were conducted. Pore volume, cation exchange capacity (CEC), and surface area of BC collectively accounted for 78.5% of the variances in the microbial community structures, with pore volume being the most important factor. These correlated well with the differences in the CH4 oxidation capacities among the different BC-amended LCS. At a low ratio of 15% (v/v) in LCS, BCs' pH not affected their performance but homogeneity could be a limiting factor. Fe modification proved a promising approach to more efficiently improve the three key BC properties (especially pore volume) and thus optimize BC performance than increasing pyrolysis temperature did. Fe-modified BCs encouraged a bacterial consortium (methanotroph, methylotrophs, and nitrogen-fixing bacteria) in the soil with significantly improved CH4 oxidation capacities by up to 26%–74% compared to that of pristine BC.

Metagenomic views of microbial dynamics influenced by hydrocarbon seepage in sediments of the\xa0Gulf of Mexico

Microbial cells in the seabed are thought to persist by slow population turnover rates and extremely low energy requirements. External stimulations such as seafloor hydrocarbon seeps have been demonstrated to significantly boost microbial growth; however, the microbial community response has not been fully understood. Here we report a comparative metagenomic study of microbial response to natural hydrocarbon seeps in the Gulf of Mexico. Subsurface sediments (10–15 cm below seafloor) were collected from five natural seep sites and two reference sites. The resulting metagenome sequencing datasets were analyzed with both gene-based and genome-based approaches. 16S rRNA gene-based analyses suggest that the seep samples are distinct from the references by both 16S rRNA fractional content and phylogeny, with the former dominated by ANME-1 archaea (~50% of total) and Desulfobacterales, and the latter dominated by the Deltaproteobacteria, Planctomycetes, and Chloroflexi phyla. Sulfate-reducing bacteria (SRB) are present in both types of samples, with higher relative abundances in seep samples than the references. Genes for nitrogen fixation were predominantly found in the seep sites, whereas the reference sites showed a dominant signal for anaerobic ammonium oxidation (anammox). We recovered 49 metagenome-assembled genomes and assessed the microbial functional potentials in both types of samples. By this genome-based analysis, the seep samples were dominated by ANME-1 archaea and SRB, with the capacity for methane oxidation coupled to sulfate reduction, which is consistent with the 16S rRNA-gene based characterization. Although ANME-1 archaea and SRB are present in low relative abundances, genome bins from the reference sites are dominated by uncultured members of NC10 and anammox Scalindua, suggesting a prevalence of nitrogen transformations for energy in non-seep pelagic sediments. This study suggests that hydrocarbon seeps can greatly change the microbial community structure by stimulating nitrogen fixation, inherently shifting the nitrogen metabolism compared to those of the reference sediments.

A finite-volume numerical model for temporal and spatial variability of methane oxidation in landfill covers

Abstract A multi-field model is proposed to study methane oxidation in landfill covers, especially its temporal and spatial variability. The proposed model consists of water-gas two-phase flow, multi-component gas flow, heat transfer, and biochemical reaction modules, and is solved using OpenFOAM based on the finite volume method. Applying this model, the coupled effect of gas diffusion, temperature and oxidation rate is studied, and the influence of water content on oxidation efficiency and capacity is quantified. The temporal variability of oxidation efficiency and capacity in landfill covers is illustrated by modelling a long-term field test. It is found that the CH4 removal rate can reach 40 g d−1 m−2 in the summers and drop to less than 10 g d−1 m−2 in the winters. A 3-D landfill cover cell with a cracked zone is applied to illustrate the spatial variability of oxidation, and a significant preferential flow can be observed when the cracked zone depth of a 1 m thick soil cover exceeds 0.8 m. The above studies demonstrate that the proposed model is able to predict temporal and spatial distributions of methane oxidation efficiency and capacity, and some results contribute to a better understanding of methane oxidation in landfill covers.

Screening methane-oxidizing bacteria from municipal solid waste landfills and simulating their effects on methane and ammonia reduction.

Municipal solid waste landfills are not only a crucial source of global greenhouse gas emissions; they also produce large amounts of ammonia (NH3), hydrogen sulfide, and other odorous gases that negatively affect the regional environment. Several types of methane-oxidizing bacteria (MOB) were proved to be effective in mitigating methane emission from landfills. Nevertheless, more MOB species and their technical parameters for best mitigating methane still need to be explored. In landfills, methane is simultaneously generated with ammonia, which may impede the CH4 bio-oxidizing process of MOB. However, very limited studies examined the enhancement of methane reduction by introducing ammonia-oxidizing bacteria (AOB) in landfills. In this study, two enriched MOB cultures were gained from a typical municipal solid waste landfill, and then were cultured with three strains of ammonia-oxidizing bacteria (AOB). The MOB enrichment culture used in this work includes Methylocaldum, Methylocystaceae, and Methyloversatilis, with a methane oxidation capacity of 43.6-65.0%, and the AOB includes Candida ethanolica, Bacillus cereus, and Alcaligenes faecalis. The effects on the emission reduction of both NH3 and CH4 were measured using self-made landfill-simulating equipment, as MOB, AOB, and a MOB-AOB mixture were added to the soil cover of the simulation equipment. The concentrations of CH4 and NH3 in the MOB-AOB mixture group decreased sharply, and the CH4 and NH3 concentration was 76.4% and 83.7% of the control group level. We also found that addition of AOB can help MOB oxidize CH4 and improve the emission reduction effect.

Comparison of the methane-oxidizing capacity of landfill cover soil amended with biochar produced using different pyrolysis temperatures

The in-situ mitigation of methane (CH4) in landfill gas using landfill cover soil (LCS) is a cost-effective approach, but its efficiency needs to be enhanced. In this study, we incorporated an enriched methane-oxidizing bacteria (MOB) consortium into LCS and established four biochar-amended LCS groups with biochar produced at 300 °C (BC300), 400 °C (BC400), 500 °C (BC500), and 600 °C (BC600). The purpose was to evaluate the CH4 oxidation capacity of biochar-amended LCS after inoculation with MOB and to investigate how the physicochemical properties of biochar that are influenced by the pyrolysis temperature affect the performance and microbial activity of biochar-amended LCS. It was found that a 15% volume ratio (representing a mass ratio of 2.49%–2.78%) for biochar amendment in LCS enhanced CH4 removal efficiency, with the highest removal observed to be 46% for BC400-amended LCS compared to 30% for the original LCS. In addition, CH4 adsorption by the biochar was not observed, and a 15% mass ratio for biochar in the LCS had no or a negative impact. Besides improving the water-holding capacity and gas permeability of LCS, other possible advantages of biochar amendment in terms of CH4 oxidization include greater retention of nutrients, electron acceptors, and exchangeable cations, as well as introducing iron ions. It was also found that CH4 oxidation capacity and the methanotroph activity of biochar-amended LCS did not continue to increase with higher pyrolysis temperatures, even though higher micropore volumes and surface areas were obtained at higher pyrolysis temperatures. From this study, BC400 was identified as the optimal choice for the best performance in terms of enhancing both the CH4 oxidation capacity of the amended LCS and the growth of type II methanotroph Methylocystaceae, which can possibly be attributed to having the highest cation exchange capacity of the four biochars.

Soil Methane Production, Anaerobic and Aerobic Oxidation in Porewater of Wetland Soils of the Minjiang River Estuarine, China

Wetlands are important sources of methane emission. Anaerobic oxidation, aerobic oxidation and production of methane as well as dissolved methane are important processes of methane metabolism. We studied methane metabolism and the soil influencing factors. Potential soil methane production, anaerobic oxidation and aerobic oxidation rates, and dissolved methane in soil porewater changed seasonally and the annual average was 21.1 ± 5.1 μg g−1d−1, 11.0 ± 3.9 μg g−1d−1, 20.9 ± 5.8 μg g−1d−1, and 62.9 ± 20.6 μmol l−1, respectively. Potential soil methane production and anaerobic and aerobic oxidation were positively correlated among themselves and with soil pH and negatively correlated with soil redox potential (Eh). Potential soil methane production and aerobic and anaerobic oxidation rates were negatively related to pore soil methane concentration. Thus, the more water-saturated the soil (the lower Eh), the higher its capacity to produce methane. The potential soil capacity for methane oxidation was higher both in the same anaerobic circumstances and when the soil was suddenly subjected to aerobic conditions. The results of this study suggested a buffer effect in the methane balance in wetland areas. The environmental circumstances favoring methane production are also favorable for anaerobic methane oxidation.

Methane oxidation capacity of methanotrophs isolated from different soil ecosystems

Methane is one of the potential greenhouse gases contributing to global climate change, with a global warming potential of about 25 times than that of carbon dioxide. Aerobic methane oxidation (methanotrophy) is the key process that counteracts emission of methane to atmosphere. In this study, methane oxidation capacity of different methane-oxidizing bacteria (methanotrophs) isolated from six different ecosystems was investigated. Methanotrophic consortium isolated from dumpsite proved to be most effective in oxidizing methane. Initially, methane oxidation rate was found to be 0.72 ± 0.036 mM/day; in course of the study consortium M5 showed an increase in methane oxidation rate up to 1.7 ± 0.016 mM/day. A maximum of 0.78 mol of CO2 production was found during methane oxidation in methanotrophs from dumpsite (M5). While varying temperatures, methane oxidation rate was in the range of 1.3–1.7 mM/day which has been found in the temperature range of 30–40 °C. Even at higher temperature (50 °C), 0.076 ± 0.14 mM of the methane was utilized per day. Methane oxidation was assessed by Michaelis–Menten kinetics. By varying the methane concentration, methane oxidation was studied and kinetic parameters such as V max and K m were derived using Lineweaver–Burk plot and found to be 1.497 mM/day and 2.23 mM, respectively. In methane mitigation approach, Methane soil sink is very essential because a balance between methane production by methanogens and consumption by methanotrophs plays an important role in methane emission reduction. Enhancing the methane soil sink will be a cost-effective method to cut down methane emission.

Bringing methanotrophy in rivers out of the shadows

AbstractMethane oxidation produces biomass that is a potential source of particulate carbon for consumers, and is in addition to photosynthetic production. We assessed methanotrophy and photosynthetic production under differing conditions of light and methane concentration. We measured methane oxidation and photosynthesis in gravel sediments from adjacent shaded and unshaded stretches of 15 chalk rivers in southern England, and also in 30 artificial channels in which we manipulated light and methane experimentally. The capacity for methane oxidation was 78% higher in the shade than unshaded areas, indicating a denser, or more active, methanotrophic assemblage on shaded riverbeds, and the difference was most pronounced when methane concentration was high. Across the 15 rivers, methanotrophic production ranged from 16 to 650 nmol C cm−2 d−1 and net photosynthetic production from 256 to 35,750 nmol C cm−2 d−1. The relative importance of methanotrophy to their total production (i.e., photosynthetic and methanotrophic) increased with methane concentration and ranged from 0.1–2.4% and 0.2–13% in unshaded and shaded areas, respectively. Over an annual cycle in one river, the response of the methanotrophs in the shade to a high summer methane concentration was ∼ five times greater than in the open; in winter, there was no effect of shading on methane oxidation. The response of methanotrophy to shading and methane concentration in the artificial channels resembled that found in the rivers. Methanotrophy makes a non‐negligible (here up to ∼ 13%) contribution to particulate carbon production in these streams, is disproportionately greater in the shade, and constitutes a distinct carbon pathway available for their food webs.