Determination of environmental factors influencing methane oxidation in a sandy landfill cover soil

Effects of fir-wood biochar on CH4 oxidation rates and methanotrophs in landfill cover soils packed at three different proctor compaction levels

Application of biochar to landfill cover soils can purportedly improve methane (CH4) oxidation rates, but understanding the combined effects of soil texture, compaction, and biochar on the activity and composition of the methanotrophs is limited. The amendment of wood biochar on two differently textured landfill cover soils at three compaction levels of the Proctor density was explored by analyzing changes in soil physical properties relevant to methane oxidation, the effects on CH4 oxidation rates, and the composition of the methanotrophic community. Loose soils with and without biochar were pre-incubated to equally elevate the CH4 oxidation rates. Hereafter, soils were compacted and re-incubated. Methane oxidation rates, gas diffusivity, water retention characteristics, and pore size distribution were analyzed on the compacted soils. The relative abundance of methanotrophic bacteria (MOB) was determined at the end of both the pre-incubation and incubation tests of the packed samples. Biochar significantly increased porosity at all compaction levels, enhancing diffusion coefficients. Also, a re-distribution in pore sizes was observed. Increased gas diffusivity from low compaction and amendment of biochar, though, did not reflect higher methane oxidation rates due to high diffusive oxygen fluxes over the limited height of the compacted soil specimens. All soils, with and without biochar, were strongly dominated by Type II methanotrophs. In the sandy soil, biochar amendment strongly increased MOB abundance, which could be attributed to a corresponding increase in the relative abundance of Methylocystis species, while no such response was observed in the clayey soil. Compaction did not change the community composition in either soil. Fir-wood biochar addition to landfill cover soils may not always enhance methanotrophic activity and hence reduce fugitive methane emissions, with the effect being soil-specific. However, especially in finer and more compacted soils, biochar amendment can maintain soil diffusivity above a critical level, preventing the collapse of methanotrophy.

Transcriptional and metabolomic responses of Methylococcus capsulatus Bath to nitrogen source and temperature downshift

Methanotrophs play a significant role in methane oxidation, because they are the only biological methane sink present in nature. The methane monooxygenase enzyme oxidizes methane or ammonia into methanol or hydroxylamine, respectively. While much is known about central carbon metabolism in methanotrophs, far less is known about nitrogen metabolism. In this study, we investigated how Methylococcus capsulatus Bath, a methane-oxidizing bacterium, responds to nitrogen source and temperature. Batch culture experiments were conducted using nitrate or ammonium as nitrogen sources at both 37°C and 42°C. While growth rates with nitrate and ammonium were comparable at 42°C, a significant growth advantage was observed with ammonium at 37°C. Utilization of nitrate was higher at 42°C than at 37°C, especially in the first 24 h. Use of ammonium remained constant between 42°C and 37°C; however, nitrite buildup and conversion to ammonia were found to be temperature-dependent processes. We performed RNA-seq to understand the underlying molecular mechanisms, and the results revealed complex transcriptional changes in response to varying conditions. Different gene expression patterns connected to respiration, nitrate and ammonia metabolism, methane oxidation, and amino acid biosynthesis were identified using gene ontology analysis. Notably, key pathways with variable expression profiles included oxidative phosphorylation and methane and methanol oxidation. Additionally, there were transcription levels that varied for genes related to nitrogen metabolism, particularly for ammonia oxidation, nitrate reduction, and transporters. Quantitative PCR was used to validate these transcriptional changes. Analyses of intracellular metabolites revealed changes in fatty acids, amino acids, central carbon intermediates, and nitrogen bases in response to various nitrogen sources and temperatures. Overall, our results offer improved understanding of the intricate interactions between nitrogen availability, temperature, and gene expression in M. capsulatus Bath. This study enhances our understanding of microbial adaptation strategies, offering potential applications in biotechnological and environmental contexts.

Use of methanotrophically activated biochar in novel biogeochemical cover system for carbon sequestration: Microbial characterization

Biochar-amended soils have been explored to enhance microbial methane (CH₄) oxidation in landfill cover systems. Recently, research priorities have expanded to include the mitigation of other components of landfill gas such as carbon dioxide (CO₂) and hydrogen sulfide (H₂S) along with CH₄. In this study, column tests were performed to simulate the newly proposed biogeochemical cover systems, which incorporate biochar-amended soil for CH₄ oxidation and basic oxygen furnace (BOF) slag for CO₂ and H₂S mitigation, to evaluate the effect of cover configuration on microbial CH₄ oxidation and community composition. Biogeochemical covers included a biochar-amended soil (10% w/w), and methanotroph-enriched activated biochar amended soil (5% or 10% w/w) as a biocover layer or CH₄ oxidation layer. The primary outcome measures of interest were CH₄ oxidation rates and the structure and abundance of methane-oxidation bacteria in the covers. All column reactors were active in CH₄ oxidation, but columns containing activated biochar-amended soils had higher CH₄ oxidation rates (133 to 143 μg CH₄ g^-1 day^-1) than those containing non-activated biochar-amended soil (50 μg CH₄ g^-1 day^-1) and no-biochar soil or control soil (43 μg CH₄ g^-1 day^-1). All treatments showed significant increases in the relative abundance of methanotrophs from an average relative abundance of 5.6% before incubation to a maximum of 45% following incubation. In activated biochar, the abundance of Type II methanotrophs, primarily Methylocystis and Methylosinus, was greater than that of Type I methanotrophs (Methylobacter) due to which activated biochar-amended soils also showed higher abundance of Type II methanotrophs. Overall, biogeochemical cover profiles showed promising potential for CH₄ oxidation without any adverse effect on microbial community composition and methane oxidation. Biochar activation led to an alteration of the dominant methanotrophic communities and increased CH₄ oxidation.

Methane oxidation in a landfill biowindow under wide seasonally fluctuating climatic conditions

In the current study, a pilot biowindow was constructed in a closed cell of a Canadian Landfill, undergoing high seasonal fluctuations in the temperature from -30 in winter to 35 in summer. The biowindow was filled with biosolids compost amended with yard waste and leaf compost with the ratio of 4:1 as the substrate layer. Two years of monitoring of methane (CH₄) oxidation in the biowindow led to remarkable expected observations including a thick, solid winter frost cover affecting gas exchange in winter and temperatures above 45 ℃ in the biowindow in late summer. A high influx compared to the reported values was observed into the biowindow with an average value of 1137 g.m^-2.d^-1, consisting of 64% of CH₄ and 36% of carbon dioxide (CO₂) in the landfill gas. The variations in the temperature and moisture content (MC) of the compost layer in addition to the influx fluctuations affected CH₄ oxidation efficiency; however, a high average CH₄ oxidation rate of 237 g.m^-2.d^-1 was obtained, with CH₄ being mostly oxidized at top layers. The laboratory batch experiments verified that thermophilic methane-oxidizing bacteria (MOB) were active throughout the study period and oxidized CH₄ with a higher rate than mesophilic MOB. The methanotrophic potential of the compost mixture showed an average value of 282 µmol.g^-1.d^-1 in the entire period of the study which is in the range of the highest reported maximum CH₄ oxidation rates. The adopted compost mixture was suitable for CH₄ oxidation if the MC was above 30%. The significance of MC variations on CH₄ oxidation rate depended on the temperature range within the biowindow. At temperatures below 2 ℃, between 29 and 31℃, and above 45 ℃, MC was not a controlling factor for mesophilic CH₄ oxidation.

How do forest fires affect soil greenhouse gas emissions in upland boreal forests? A review

Wildfires strongly regulate carbon (C) cycling and storage in boreal forests and account for almost 10% of global fire C emissions. However, the anticipated effects of climate change on fire regimes may destabilize current C-climate feedbacks and switch the systems to new stability domains. Since most of these forests are located in upland soils where permafrost is widespread, the expected climate warming and drying combined with more active fires may alter the greenhouse gas (GHG) budgets of boreal forests and trigger unprecedented changes in the global C balance. Therefore, a better understanding of the effects of fires on the various spatial and temporal patterns of GHG fluxes of different physical environments (permafrost and nonpermafrost soils) is fundamental to an understanding of the role played by fire in future climate feedbacks. While large amounts of C are released during fires, postfire GHG fluxes play an important role in boreal C budgets over the short and long term. The timescale over which the vegetation cover regenerates seems to drive the recovery of C emissions after both low- and high-severity fires, regardless of fire-induced changes in soil decomposition. In soils underlain by permafrost, fires increase the active layer depth for several years, which may alter the soil dynamics regulating soil GHG exchange. In a scenario of global warming, prolonged exposition of previously immobilized C could result in higher carbon dioxide emission during the early fire succession. However, without knowledge of the contribution of each respiration component combined with assessment of the warming and drying effects on both labile and recalcitrant soil organic matter throughout the soil profile, we cannot advance on the most relevant feedbacks involving fire and permafrost. Fires seem to have either negligible effects on methane (CH₄) fluxes or a slight increase in CH₄ uptake. However, permafrost thawing driven by climate or fire could turn upland boreal soils into temporary CH₄ sources, depending on how fast the transition from moist to drier soils occurs. Most studies indicate a slight decrease or no significant change in postfire nitrous oxide (N₂O) fluxes. However, simulations have shown that the temperature sensitivity of denitrification exceeds that of soil respiration; thus, the effects of warming on soil N₂O emissions may be greater than on C emissions.

Effect of temperature on methane oxidation and community composition in landfill cover soil

Municipal solid waste (MSW) landfills are the third largest anthropogenic source of methane (CH₄) emissions in the United States. The majority of CH₄ generated in landfills is converted to carbon dioxide (CO₂) by CH₄-oxidizing bacteria (MOB) present in the landfill cover soil, whose activity is controlled by various environmental factors including temperature. As landfill temperature can fluctuate substantially seasonally, rates of CH₄ oxidation can also vary, and this could lead to incomplete oxidation. This study aims at analyzing the effect of temperature on CH₄ oxidation potential and microbial community structure of methanotrophs in laboratory-based studies of landfill cover soil and cultivated consortia. Soil and enrichment cultures were incubated at temperatures ranging from 6 to 70 °C, and rates of CH₄ oxidation were measured, and the microbial community structure was analyzed using 16S rRNA gene amplicon sequencing and shotgun metagenome sequencing. CH₄ oxidation occurred at temperatures from 6 to 50 °C in soil microcosm tests, and 6-40 °C in enrichment culture batch tests; maximum rates of oxidation were obtained at 30 °C. A corresponding shift in the soil microbiota was observed, with a transition from putative psychrophilic to thermophilic methanotrophs with increasing incubation temperature. A strong shift in methanotrophic community structure was observed above 30 °C. At temperatures up to 30 °C, methanotrophs from the genus Methylobacter were dominant in soils and enrichment cultures; at a temperature of 40 °C, putative thermophilic methanotrophs from the genus Methylocaldum become dominant. Maximum rate measurements of nearly 195 μg CH₄ g^-1 day^-1 were observed in soil incubations, while observed maximum rates in enrichments were significantly lower, likely as a result of diffusion limitations. This study demonstrates that temperature is a critical factor affecting rates of landfill soil CH₄ oxidation in vitro and that changing rates of CH₄ oxidation are in part driven by changes in methylotroph community structure.

Methane emissions from landfill: influence of vegetation and weather conditions

Vegetation plays an important role in CH₄ transport and oxidation in landfill cover soil. This study investigated CH₄ emission fluxes in two landfills with different surface coverage conditions and it found that the CH₄ emission fluxes presented spatial and temporal disparities. A significant discrepancy in CH₄ emission flux between day and night in areas covered with Kochia sieversiana indicated that enhanced diffusion induced by rising temperature was the main mechanism for CH₄ transport during daytime. A significant increase of CH₄ emission flux after the K. sieversiana and Suaeda glauca plants were cut indicated that these plants provide greater contributions to CH₄ oxidation than to CH₄ transport. Diel CH₄ emission flux was found closely correlated with the climatic conditions. Diffusion was determined as the main mechanism for CH₄ transport at daytime in bare area, mediated by solar radiation and air temperature. Diffusion and plant-mediated transport by convection was established as the main transport mechanism in areas covered with K. sieversiana. Our results further the understanding of both the CH₄ emission mechanism and the impact of vegetation on CH₄ oxidation, transport, and emission, which will benefit the development of a reliable model for landfill CH₄ emissions.

Activity and Identification of Methanotrophic Bacteria in Arable and No-Tillage Soils from Lublin Region (Poland)

Methanotrophic bacteria are able to use methane (CH₄) as a sole carbon and energy source. Photochemical oxidation of methane takes place in the stratosphere, whereas in the troposphere, this process is carried out by methanotrophic bacteria. On the one hand, it is known that the efficiency of biological CH₄ oxidation is dependent on the mode of land use but, on the other hand, the knowledge of this impact on methanotrophic activity (MTA) is still limited. Thus, the aim of the study was to determine the CH₄ oxidation ability of methanotrophic bacteria inhabiting selected arable and no-tillage soils from the Lublin region (Albic Luvisol, Brunic Arenosol, Haplic Chernozem, Calcaric Cambisol) and to identify bacteria involved in this process. MTA was determined based on incubation of soils in air with addition of methane at the concentrations of 0.002, 0.5, 1, 5, and 10%. The experiment was conducted in a temperature range of 10-30 °C. Methanotrophs in soils were identified by next-generation sequencing (NGS). MTA was confirmed in all investigated soils (in the entire range of the tested methane concentrations and temperatures, except for the arable Albic Luvisol). Importantly, the MTA values in the no-tillage soil were nearly two-fold higher than in the cultivated soils. Statistical analysis indicated a significant influence of land use, type of soil, temperature, and especially methane concentration (p < 0.05) on MTA. Metagenomic analysis confirmed the presence of methanotrophs from the genus Methylocystis (Alphaproteobacteria) in the studied soils (except for the arable Albic Luvisol). Our results also proved the ability of methanotrophic bacteria to oxidize methane although they constituted only up to 0.1% of the total bacterial community.

Biofiltration of methane

The on-going annual increase in global methane (CH₄) emissions can be largely attributed to anthropogenic activities. However, as more than half of these emissions are diffuse and possess a concentration less than 3% (v/v), physical-chemical treatments are inefficient as an abatement technology. In this regard, biotechnologies, such as biofiltration using methane-oxidizing bacteria, or methanotrophs, are a cost-effective and efficient means of combating diffuse CH₄ emissions. In this review, a number of abiotic factors including temperature, pH, water content, packing material, empty-bed residence time, inlet gas flow rate, CH₄ concentration, as well biotic factors, such as biomass development, are reviewed based on empirical findings on CH₄ biofiltration studies that have been performed in the last decades.

A Simulation model for estimating methane oxidation and emission from landfill cover soils

Quantification of methane (CH₄) oxidation and emission from landfill cover soils is important for evaluating measures to mitigate anthropogenic greenhouse gas emissions. In this study, a model that combines the multicomponent diffusive equation and Darcy's law, coupled with the dual Monod kinetic equation, was established to simulate CH₄ transport, oxidation and emission in landfill cover soils. Sensitivity analysis was performed to illustrate the influence of model parameters on CH₄ transport, oxidation and emission. The model was then applied to predict CH₄ emissions from several column experiments. The results of the sensitivity analysis showed that a high CH₄ oxidation rate can be obtained with a high V_max of cover soil, even for a low cover soil thickness, and that oxidation efficiency is constant when the thickness of the cover soil becomes greater than a threshold value. The simulated results fitted well with the measured values, confirming that the new model provides a reliable method for estimating CH₄ emissions from landfills.

A simulation model for methane emissions from landfills with interaction of vegetation and cover soil

Global climate change and ecological problems brought about by greenhouse gas effect have become a severe threat to humanity in the 21st century. Vegetation plays an important role in methane (CH₄) transport, oxidation and emissions from municipal solid waste (MSW) landfills as it modifies the physical and chemical properties of the cover soil, and transports CH₄ to the atmosphere directly via their conduits, which are mainly aerenchymatous structures. In this study, a novel 2-D simulation CH₄ emission model was established, based on an interactive mechanism of cover soil and vegetation, to model CH₄ transport, oxidation and emissions in landfill cover soil. Results of the simulation model showed that the distribution of CH₄ concentration and emission fluxes displayed a significant difference between vegetated and non-vegetated areas. CH₄ emission flux was 1-2 orders of magnitude higher than bare areas in simulation conditions. Vegetation play a negative role in CH₄ emissions from landfill cover soil due to the strong CH₄ transport capacity even though vegetation also promotes CH₄ oxidation via changing properties of cover soil and emitting O₂ via root system. The model will be proposed to allow decision makers to reconsider the actual CH₄ emission from vegetated and non-vegetated covered landfills.

Real-time monitoring of methane oxidation in a simulated landfill cover soil and MiSeq pyrosequencing analysis of the related bacterial community structure

Real-time CH₄ oxidation in a landfill cover soil was studied using automated gas sampling that determined biogas (CH₄ and CO₂) and O₂ concentrations at various depths in a simulated landfill cover soil (SLCS) column reactor. The real-time monitoring system obtained more than 10,000 biogas (CH₄ and CO₂) and O₂ data points covering 32 steady states of CH₄ oxidation with 32 different CH₄ fluxes (0.2-125mol·m^-2·d^-1). The kinetics of CH₄ oxidation at different depths (0-20cm, 20-40cm, and 40-60cm) of SLCS were well fit by a CH₄-O₂ dual-substrate model based on 32 values (averaged, n=5-15) of equilibrated CH₄ concentrations. The quality of the fit (R² ranged from 0.90 to 0.96) was higher than those reported in previous studies, which suggests that real time monitoring is beneficial for CH₄ oxidation simulations. MiSeq pyrosequencing indicated that CH₄ flux events changed the bacterial community structure (e.g., increased the abundance of Bacteroidetes and Methanotrophs) and resulted in a relative increase in the amount of type I methanotrophs (Methylobacter and Methylococcales) and a decrease in the amount of type II methanotrophs (Methylocystis).

Methane oxidation in a landfill cover soil reactor: Changing of kinetic parameters and microorganism community structure

Changing of CH₄ oxidation potential and biological characteristics with CH₄ concentration was studied in a landfill cover soil reactor (LCSR). The maximum rate of CH₄ oxidation reached 32.40 mol d^-1 m^-2 by providing sufficient O₂ in the LCSR. The kinetic parameters of methane oxidation in landfill cover soil were obtained by fitting substrate diffusion and consumption model based on the concentration profile of CH₄ and O₂. The values of [Formula: see text] (0.93-2.29%) and [Formula: see text] (140-524 nmol kg_soil-DW^-1·s^-1) increased with CH₄ concentration (9.25-20.30%), while the values of [Formula: see text] (312.9-2.6%) and [Formula: see text] (1.3 × 10^-5 to 9.0 × 10^-3 nmol mL^-1 h^-1) were just the opposite. MiSeq pyrosequencing data revealed that Methylobacter (the relative abundance was decreased with height of LCSR) and Methylococcales_unclassified (the relative abundance was increased expect in H 80) became the key players after incubation with increasing CH₄ concentration. These findings provide information for assessing CH₄ oxidation potential and changing of biological characteristics in landfill cover soil.

Effect of biomass concentration on methane oxidation activity using mature compost and graphite granules as substrata

Reported methane oxidation activity (MOA) varies widely for common landfill cover materials. Variation is expected due to differences in surface area, the composition of the substratum and culturing conditions. MOA per methanotrophic cell has been calculated in the study of natural systems such as lake sediments to examine the inherent conditions for methanotrophic activity. In this study, biomass normalised MOA (i.e., MOA per methanotophic cell) was measured on stabilised compost, a commonly used cover in landfills, and on graphite granules, an inert substratum widely used in microbial electrosynthesis studies. After initially enriching methanotrophs on both substrata, biomass normalised MOA was quantified under excess oxygen and limiting methane conditions in 160ml serum vials on both substrata and blends of the substrata. Biomass concentration was measured using the bicinchoninic acid assay for microbial protein. The biomass normalised MOA was consistent across all compost-to-graphite granules blends, but varied with time, reflecting the growth phase of the microorganisms. The biomass normalised MOA ranged from 0.069±0.006μmol CH4/mg dry biomass/h during active growth, to 0.024±0.001μmol CH4/mg dry biomass/h for established biofilms regardless of the substrata employed, indicating the substrata were equally effective in terms of inherent composition. The correlation of MOA with biomass is consistent with studies on methanotrophic activity in natural systems, but biomass normalised MOA varies by over 5 orders of magnitude between studies. This is partially due to different methods being used to quantify biomass, such as pmoA gene quantification and the culture dependent Most Probable Number method, but also indicates that long term exposure of materials to a supply of methane in an aerobic environment, as can occur in natural systems, leads to the enrichment and adaptation of types suitable for those conditions.

Evaluation and statistical optimization of methane oxidation using rice husk amended dumpsite soil as biocover

A laboratory scale study was conducted to investigate the effect of rice husk amended biocover to mitigate the CH4 emission from landfills. Various physico-chemical and environmental variables like proportion of amended biocover material (rice husk), temperature, moisture content, CH4 concentration, CO2 concentration, O2 concentration and incubation time were considered in the study which affect the CH4 bio-oxidation. For the present study, sequential statistical approach with Placket Burman Design (PBD) was used to identify significant variables, having influential role on CH4 bio-oxidation, from all variables. Further, interactive effect of four selected variables including rice husk proportion, temperature, CH4 concentration and incubation time was studied with Box-Behnken Design (BBD) adopting Response Surface Methodology (RSM) to optimize the conditions for CH4 oxidation. In this study, the maximum CH4 oxidation potential of 76.83μgCH4g(-1)dwh(-1) was observed under optimum conditions with rice husk amendment of 6% (w/w), 5h incubation time at 40°C temperature with 40% (v/v) initial CH4 concentration. The results for CH4 oxidation potential also advocated the suitability of rice husk amendment in biocover system to curb emitted CH4 from landfills/open dumpsite over conventional clay or sand cover on supplying CH4 and O2 to microbes on maintaining proper aeration.

Performance of green waste biocovers for enhancing methane oxidation

Green waste aged 2 and 24months, labeled "fresh" and "aged" green waste, respectively, were placed in biocover test cells and evaluated for their ability to oxidize methane (CH4) under high landfill gas loading over a 15-month testing period. These materials are less costly to produce than green waste compost, yet satisfied recommended respiration requirements for landfill compost covers. In field tests employing a novel gas tracer to correct for leakage, both green wastes oxidized CH4 at high rates during the first few months of operation - 140 and 200g/m(2)/day for aged and fresh green waste, respectively. Biocover performance degraded during the winter and spring, with significant CH4 generated from anaerobic regions in the 60-80cm thick biocovers. Concurrently, CH4 oxidation rates decreased. Two previously developed empirical models for moisture and temperature dependency of CH4 oxidation in soils were used to test their applicability to green waste. Models accounted for 68% and 79% of the observed seasonal variations in CH4 oxidation rates for aged green waste. Neither model could describe similar seasonal changes for the less stable fresh green waste. This is the first field application and evaluation of these empirical models using media with high organic matter. Given the difficulty of preventing undesired CH4 generation, green waste may not be a viable biocover material for many climates and landfill conditions.

Modeling the effects of vegetation on methane oxidation and emissions through soil landfill final covers across different climates

Plant roots are reported to enhance the aeration of soil by creating secondary macropores which improve the diffusion of oxygen into soil as well as the supply of methane to bacteria. Therefore, methane oxidation can be improved considerably by the soil structuring processes of vegetation, along with the increase of organic biomass in the soil associated with plant roots. This study consisted of using a numerical model that combines flow of water and heat with gas transport and oxidation in soils, to simulate methane emission and oxidation through simulated vegetated and non-vegetated landfill covers under different climatic conditions. Different simulations were performed using different methane loading flux (5-200 g m(-2) d(-1)) as the bottom boundary. The lowest modeled surface emissions were always obtained with vegetated soil covers for all simulated climates. The largest differences in simulated surface emissions between the vegetated and non-vegetated scenarios occur during the growing season. Higher average yearly percent oxidation was obtained in simulations with vegetated soil covers as compared to non-vegetated scenario. The modeled effects of vegetation on methane surface emissions and percent oxidation were attributed to two separate mechanisms: (1) increase in methane oxidation associated with the change of the physical properties of the upper vegetative layer and (2) increase in organic matter associated with vegetated soil layers. Finally, correlations between percent oxidation and methane loading into simulated vegetated and non-vegetated covers were proposed to allow decision makers to compare vegetated versus non-vegetated soil landfill covers. These results were obtained using a modeling study with several simplifying assumptions that do not capture the complexities of vegetated soils under field conditions.

Biodegradation of methane, benzene, and toluene by a consortium MBT14 enriched from a landfill cover soil

In this study, landfill cover soil was used as an inoculum source to enrich a methane, benzene, and toluene-degrading consortium MBT14. Under a single substrate, the maximum degradation rates of methane, benzene and toluene were 1.96, 0.15, and 0.77 mmole g-DCW(-1) h(-1), respectively. Although the coexistence of benzene and toluene inhibited the methane degradation rates, the consortium was able to simultaneously degrade methane, benzene and toluene. Methane had an insignificant effect on benzene or toluene degradation. Based on 16S rDNA sequencing analysis, Cupriavidus spp. are dominant in the consortium MBT14. The combined results of this study indicate that the consortium MBT 14 is a promising bioresource for removing CH(4), benzene, and toluene from a variety of environments.

Methane distribution surrounding closed landfill sites in China

Methane as a green gas has been a concern for a long time. The emission of landfill gas and the release of dissolved methane in water in contaminated sites surrounding the landfills are two main sources of methane contributing to surface air. The distribution of methane in leachate, air and groundwater around the closed Erfei Shan landfill was investigated and the effects of redox species in leachate plume on methane distribution were also discussed in this paper. The result showed a high concentration of dissolved methane was determined in raw leachate (up to 46.07 mg L(-1)) and in the shallow groundwater (up to 27.95 mg L(-1)) near the landfill. Methane was depleted where elevated concentrations of sulfate were observed at 7-10 m under ground level. The average methane concentrations by volume in the surface air surrounding the landfill for SA1, SA2, SA3 and SA4 were 55.09, 118.29, 14.01 and 87.22 mgL(-1), respectively. The surface methane concentrations were related to their emission sources and low levels of methane emissions can last a long time, even after the landfill is closed.

Methanotrophic communities in Australian woodland soils of varying salinity

Despite their large areas and potential importance as methane sinks, the role of methane-oxidizing bacteria (MOB) in native woodland soils is poorly understood. These environments are increasingly being altered by anthropogenic disturbances, which potentially alter ecosystem service provision. Dryland salinity is one such disturbance and is becoming increasingly prevalent in Australian soils. We used microarrays and analysis of soil physicochemical variables to investigate the methane-oxidizing communities of several Australian natural woodland soils affected to varying degrees by dryland salinity. Soils varied in terms of salinity, gravitational water content, NO(3)-N, SO(4)-S and Mg, all of which explained to a significant degree MOB community composition. Analysis of the relative abundance and diversity of the MOB communities also revealed significant differences between soils of different salinities. Type II and type Ib methanotrophs dominated the soils and differences in methanotroph communities existed between salinity groups. The low salinity soils possessed less diverse MOB communities, including most conspicuously, the low numbers or absence of type II Methylocystis phylotypes. The differences in MOB communities suggest niche separation of MOB across varying salinities, as has been observed in the closely related ammonia-oxidizing bacteria, and that anthropogenic disturbance, such as dryland salinity, has the potential to alter MOB community and therefore the methane uptake rates in soils in which disturbance occurs.

Limits and dynamics of methane oxidation in landfill cover soils

In order to understand the limits and dynamics of methane (CH(4)) oxidation in landfill cover soils, we investigated CH(4) oxidation in daily, intermediate, and final cover soils from two California landfills as a function of temperature, soil moisture and CO(2) concentration. The results indicate a significant difference between the observed soil CH(4) oxidation at field sampled conditions compared to optimum conditions achieved through pre-incubation (60 days) in the presence of CH(4) (50 ml l(-1)) and soil moisture optimization. This pre-incubation period normalized CH(4) oxidation rates to within the same order of magnitude (112-644 μg CH(4) g(-1) day(-1)) for all the cover soils samples examined, as opposed to the four orders of magnitude variation in the soil CH(4) oxidation rates without this pre-incubation (0.9-277 μg CH(4) g(-1) day(-1)). Using pre-incubated soils, a minimum soil moisture potential threshold for CH(4) oxidation activity was estimated at 1500 kPa, which is the soil wilting point. From the laboratory incubations, 50% of the oxidation capacity was inhibited at soil moisture potential drier than 700 kPa and optimum oxidation activity was typical observed at 50 kPa, which is just slightly drier than field capacity (33 kPa). At the extreme temperatures for CH(4) oxidation activity, this minimum moisture potential threshold decreased (300 kPa for temperatures <5°C and 50 kPa for temperatures >40°C), indicating the requirement for more easily available soil water. However, oxidation rates at these extreme temperatures were less than 10% of the rate observed at more optimum temperatures (∼ 30°C). For temperatures from 5 to 40°C, the rate of CH(4) oxidation was not limited by moisture potentials between 0 (saturated) and 50 kPa. The use of soil moisture potential normalizes soil variability (e.g. soil texture and organic matter content) with respect to the effect of soil moisture on methanotroph activity. The results of this study indicate that the wilting point is the lower moisture threshold for CH(4) oxidation activity and optimum moisture potential is close to field capacity. No inhibitory effects of elevated CO(2) soil gas concentrations were observed on CH(4) oxidation rates. However, significant differences were observed for diurnal temperature fluctuations compared to thermally equivalent daily isothermal incubations.

Effect of substrate interaction on oxidation of methane and benzene in enriched microbial consortia from landfill cover soil

The interaction of methane and benzene during oxidation in enriched methane-oxidizing consortium (MOC) and in benzene-oxidizing consortium (BOC) from landfill cover soil was characterized. Oxidation of both methane and benzene occurred in the MOC due to the coexistence of bacteria responsible for benzene oxidation, as well as methanotrophs, whereas in the BOC, only benzene was oxidized, not methane. Methane oxidation rates in the MOC were decreased with increasing benzene/methane ratio (mol/mol), indicating its methane oxidation was inhibited by the benzene coexistence. Benzene oxidation rates in the MOC, however, were increased with increasing benzene/methane ratio. The benzene oxidation in the BOC was not affected by the coexistence of methane or by the ratio of methane/benzene ratio (mol/mol). No effect of methane or benzene was found on the dynamics of functional genes, such as particulate methane monooxygenase and toluene monooxygenase, in association with oxidation of methane and benzene in the MOC and BOC.

Methanotrophs and methanotrophic activity in engineered landfill biocovers

The dynamics and changes in the potential activity and community structure of methanotrophs in landfill covers, as a function of time and depth were investigated. A passive methane oxidation biocover (PMOB-1) was constructed in St-Nicéphore MSW Landfill (Quebec, Canada). The most probable number (MPN) method was used for methanotroph counts, methanotrophic diversity was assessed using denaturing gradient gel electrophoresis (DGGE) fingerprinting of the pmoA gene and the potential CH(4) oxidation rate was determined using soil microcosms. Results of the PMOB-1 were compared with those obtained for the existing landfill cover (silty clay) or a reference soil (RS). During the monitoring period, changes in the number of methanotrophic bacteria in the PMOB-1 exhibited different developmental phases and significant variations with depth. In comparison, no observable changes over time occurred in the number of methanotrophs in the RS. The maximum counts measured in the uppermost layer was 1.5x10(9) cells g dw(-1) for the PMOB-1 and 1.6x10(8) cells g dw(-1) for the RS. No distinct difference was observed in the methanotroph diversity in the PMOB-1 or RS. As expected, the potential methane oxidation rate was higher in the PMOB-1 than in the RS. The maximum potential rates were 441.1 and 76.0 microg CH(4) h(-1) g dw(-1) in the PMOB and RS, respectively. From these results, the PMOB was found to be a good technology to enhance methane oxidation, as its performance was clearly better than the starting soil that was present in the landfill site.

Phylogenetic analysis of methanotrophic communities in cover soils of a landfill in Ontario

We examined the methanotrophs in the Trail Road Landfill soils, Ottawa, Ontario, through cultivation-independent molecular assay and the culturing approach. Denaturing gradient gel electrophoresis (DGGE) analysis of amplified methanotroph-specific 16S rDNA gene fragments revealed a more diverse type I (RuMP pathway) methanotrophic community than type II (serine pathway) in 17 soil samples taken along a 50 m transect. The type II methanotrophic community was less diverse, with the dominance of Methylocystis in almost all samples, and clustering with high similarity (85%–88%). Also, the results showed that the C/N ratio of soil organic matter could significantly affect the methanotrophic community structures. The DGGE results were supported by sequence analysis of cloned pmoA. Members of the genera Methylobacter (type I), Methylocaldum (type X), and Methylocystis (type II) appeared to be the dominant methanotrophs. From methanotrophic enrichments, we isolated type I Methylobacter sp., and 3 type II Methylocystis spp.,which appeared to be one of the dominant bacteria species in the soil sample from which isolates were obtained.

Microbial methane oxidation processes and technologies for mitigation of landfill gas emissions

Landfill gas containing methane is produced by anaerobic degradation of organic waste. Methane is a strong greenhouse gas and landfills are one of the major anthropogenic sources of atmospheric methane. Landfill methane may be oxidized by methanotrophic microorganisms in soils or waste materials utilizing oxygen that diffuses into the cover layer from the atmosphere. The methane oxidation process, which is governed by several environmental factors, can be exploited in engineered systems developed for methane emission mitigation. Mathematical models that account for methane oxidation can be used to predict methane emissions from landfills. Additional research and technology development is needed before methane mitigation technologies utilizing microbial methane oxidation processes can become commercially viable and widely deployed.

Estimation of mass transport parameters of gases for quantifying CH4 oxidation in landfill soil covers

Methane (CH(4)), which is one of the most abundant anthropogenic greenhouse gases, is produced from landfills. CH(4) is biologically oxidized to carbon dioxide, which has a lower global warming potential than methane, when it passes through a cover soil. In order to quantify the amount of CH(4) oxidized in a landfill cover soil, a soil column test, a diffusion cell test, and a mathematical model analysis were carried out. In the column test, maximum oxidation rates of CH(4) (V(max)) showed higher values in the upper part of the column than those in the lower part caused by the penetration of O(2) from the top. The organic matter content in the upper area was also higher due to the active microbial growth. The dispersion analysis results for O(2) and CH(4) in the column are counter-intuitive. As the upward flow rate of the landfill gas increased, the dispersion coefficient of CH(4) slightly increased, possibly due to the effect of mechanical dispersion. On the other hand, as the upward flow rate of the landfill gas increased, the dispersion coefficient of O(2) decreased. It is possible that the diffusion of gases in porous media is influenced by the counter-directional flow rate. Further analysis of other gases in the column, N(2) and CO(2), may be required to support this hypothesis, but in this paper we propose the possibility that the simulations using the diffusion coefficient of O(2) under the natural condition may overestimate the penetration of O(2) into the soil cover layer and consequently overestimate the oxidation of CH(4).

Transport of methane and noble gases during gas push-pull tests in variably saturated porous media

The gas push-pull test (GPPT) is a single-well gas-tracer method to quantify in situ rates of CH4 oxidation in soils. To improve the design and interpretation of GPPT field experiments, gas component transport during GPPTs was examined in abiotic porous media over a range of water saturations (0.0 < or = Sw < or = 0.61). A series of GPPTs using He, Ne, and Ar as tracers for CH4 were performed at two injection/extraction gas flow rates (approximately 200 and approximately 700 mL min(-1)) in a laboratory tank. Extraction phase breakthrough curves and mass recovery curves of the gaseous components became more similar at higher Sw as water in the pore space restricted diffusive gas-phase transport. Diffusional fractionation of the stable carbon isotopes of CH4 during the extraction period of GPPTs also decreased with increasing Sw (particularly when Sw > 0.42). Gas-component transport during GPPTs was numerically simulated using estimated hydraulic parameters for the porous media and no fitting of data for the GPPTs. Numerical simulations accurately predicted the relative decline of the gaseous components in the breakthrough curves, but slightly overestimated recoveries at low Sw (< or = 0.35) and underestimated recoveries at high Sw (> or = 0.49). Comparison of numerical simulations considering and not considering air-water partitioning indicated that removal of gaseous components through dissolution in pore water was not significant during GPPTs, even at Sw = 0.61. These data indicate that Ar is a good tracer for CH4 physical transport over the full range of Sw studied, whereas, at Sw > 0.61, any of the tracers could be used. Greater mass recovery at higher Sw raises the possibility to reduce gas flow rates, thereby extending GPPT times in environments such as tundra soils where low activity due to low temperatures may require longer test times to establish a quantifiable difference between reactant and tracer breakthrough curves.

Effect of temperature on composition of the methanotrophic community in rice field and forest soil

Temperature change affects methane consumption in soil. However, there is no information on possible temperature control of methanotrophic bacterial populations. Therefore, we studied CH(4) consumption and populations of methanotrophs in an upland forest soil and a rice field soil incubated at different temperatures between 5 and 45 degrees C for up to 40 days. Potential methane consumption was measured at 4% CH(4). The temporal progress of CH(4) consumption indicated growth of methanotrophs. Both soils showed maximum CH(4) consumption at 25-35 degrees C, but no activity at >40 degrees C. In forest soil CH(4) was also consumed at 5 degrees C, but in rice soil only at 15 degrees C. Methanotroph populations were assessed by terminal restriction fragment length polymorphism (T-RFLP) targeting particulate methane monooxygenase (pmoA) genes. Eight T-RFs with relative abundance >1% were retrieved from both forest and rice soil. The individual T-RFs were tentatively assigned to different methanotrophic populations (e.g. Methylococcus/Methylocaldum, Methylomicrobium, Methylobacter, Methylocystis/Methylosinus) according to published sequence data. Two T-RFs were assigned to ammonium monooxygenase (amoA) gene sequences. Statistical tests showed that temperature affected the relative abundance of most T-RFs. Furthermore, the relative abundance of individual T-RFs differed between the two soils, and also exhibited different temperature dependence. We conclude that temperature can be an important factor regulating the community composition of methanotrophs in soil.