Quantification of - And determining factors affecting - Methane emissions from composting plants.

Methane is a potent greenhouse gas contributing to climate change. Reliable data for methane emissions from the waste management sector are paramount in terms of providing national methane budgets and developing climate mitigation efforts. This study quantified total methane emissions and characterised temporal as well as operational emission patterns at five commercial composting plants in Denmark. Methane emissions were measured over a one-year period, using the tracer gas dispersion method. The results show that methane emission rates ranged from 8.0 ± 0.1 to 42.5 ± 1.5 kg CH4 h-1 and were significantly affected by factors including the type of feedstock and composting technology, treated feedstock mass, operational patterns and season. The results indicate that the highest methane emission factors were obtained at the combined anaerobic digestion and open windrow composting plant (4.51-5.21 kg CH4 Mg-1 wet garden/park waste (GPW) and food waste), followed by open windrow plants co-composting GPW, sewage sludge and straw (3.49-3.76 kg CH4 Mg-1 wet feedstock). The lowest methane emission factors were found at open windrow composting plants treating GPW (1.56-3.24 kg CH4 Mg-1 wet feedstock). Emissions tended to be higher when measurements were performed during working hours, in comparison to when they were measured after the plant closed for the day. At one plant, emissions were measured monthly over one year, and emissions were about 50% higher in spring and summer in comparison to autumn and winter.

Methane emission rates averaged over a year from ten farm-scale manure storage tanks.

Methane (CH4) emissions from animal manure stored in outdoor tanks are difficult to predict because of several influencing factors. In this study, the tracer gas dispersion method (TDM) was used to quantify CH4 emissions from ten manure storage tanks, along with the collection of supporting information, in order to identify its emission drivers. The dataset included two tanks storing dairy cattle manure, six holding pig manure, and two with digestate from manure-based biogas plants. CH4 emissions from the tanks were measured six to 14 times over a year. Emissions varied from 0.02 to 14.30 kg h-1, or when normalised by the volume of manure stored, emission factors (EFs) varied from 0.05 to 11 g m-3 h-1. Annual average CH4 EFs varied greatly between the tanks, ranging from 0.20 to 2.75 g m-3 h-1. Normalised EFs are similar to literature values for cattle and digested manure, but at the high end of the interval for pig manure. The averaged manure temperature for all tanks varied from 10.6 to 16.4 °C, which was higher than reported in a previous Danish study. Volatile solids (VS) concentration was in average higher for cattle manure (ranging from 3.1 and 4.4 %) than pig manure (ranging from 1.0 to 3.6 %). CH4 emission rates were positively correlated with manure temperature, whereas this was not the case for VS concentration. Annual average EFs were higher for pig than for cattle manure (a factor of 2.5), which was greater than digested manure emissions (a factor of 1.2). For the pig manure storage tanks, CH4 emissions were higher for covered tanks than for uncovered tanks (by a factor of 2.3). In this study, manure storage tanks showed a large disparity in emission rates, driven not only by physical factors, but also by farm management practices.

The Danish national effort to minimise methane emissions from biogas plants.

In total, 69 biogas plants representing 59 % of Danish biogas production participated in a national effort to reduce methane (CH4) emission. Measurements in terms of total plant CH4 emissions, quantification of emissions from point sources, leak surveys and conceptual design plans to mitigate emissions were performed. Plant-level CH4 emission rates varied between 1.3 and 81.2 kg CH4 h-1, and CH4 losses expressed in percentages of production varied between 0.3 and 40.6 %. Agricultural plants generally had lower CH4 loss rates compared to wastewater treatment plants. Biogas plants with a smaller gas production emitted a larger fraction of their production compared to larger plants, which was partly explained by the absence of gas collection from digestate storage tanks at smaller plants. A very commonly observed source of emission was pressure relief valves, where this source of leakage was observed at 53 % of the plants. A national emission factor (sum of CH4 emissions/sum of CH4 productions) was determined at 2.5 % for the Danish biogas production, whereof it was 2.1 % for agricultural biogas production and 6.7 % for biogas production at wastewater treatment plants. Measurements of total CH4 emissions at six plants performed before and after implementation of mitigating actions showed that emissions were reduced by 46 % by carrying out relatively minor technical fixes and adjustments. An economic evaluation showed that, in some cases, mitigating actions could be economically beneficial for the biogas plant (positive net present value over a 10 year time frame), due to an increase in revenue.

Methane losses from different biogas plant technologies.

Biogas and biomethane production can play an important role in a fossil-fuel-free energy supply, provided that process-related methane (CH4) losses are minimized. Addressing the lack of representative emission data, this study aims to provide component specific CH4 emission factors (EFs) for various biogas plant technologies, enabling more accurate emission estimates for the biogas sector and supporting the identification of low emission technologies. Four measurement teams investigated 33 biogas plants in Austria, Germany, Sweden and Switzerland including mainly agricultural and biowaste treating facilities. For the first time, a harmonized measurement procedure was used to systematically survey individual on-site emission sources and leakages. Measurements revealed a large variability in technology specific emissions, especially for biogas utilization and upgrading. Median loss from combined heat and power (CHP) plants was 1.6 % for gas engines (n = 21), and 3.0 % for pilot injection units (n = 3) of the input CH4. Biogas upgrading units showed median CH4 slips of < 0.1 % (chemical scrubbers, n = 4), 0.1 % (after exhaust gas treatment, n = 3) and 2.9 % (water scrubbers, n = 2). Not-gastight digestate storage (n = 8) was identified as a major emission source with maximum 5.6 % of the produced CH4 emitted. Individual leakages (n = 37) released between 0.0 and 2.1 % (median 0.1 %) relative to the CH4 production. All measurement and secondary data are provided in a harmonized dataset (294 datapoints). A review of IPCC default EFs indicate an underestimation of emissions from biogas utilization (reported in the energy sector) while the impact of leakages on overall plant emissions (waste sector) may be overestimated for European biogas plants.

Methane emissions from five Danish pig farms: Mitigation strategies and inventory estimated emissions.

This study investigated whole-farm methane emissions from five Danish pig farms with different manure management practices and compared measured emission rates to international and national greenhouse gas inventory emission models. Methane emissions were quantified by using the tracer gas dispersion method. Farms were measured between five and eight times throughout a whole year. One of the farms housed sows and weaners (P1) and the others focused on fattening pigs (P2-P5). The farms had different manure treatment practices including biogasification (P3), acidification (P4-P5) and no manure treatment (liquid slurry) (P1-P2). Quantified methane emissions ranged from 0.2 to 20 kg/h and the highest rates were seen at the farms with fattening pigs and with no manure treatment (P2), while the lowest emissions were detected at farms with manure acidification (P4 and P5). Average methane emission factors (EFs), normalised based on livestock units, were 14 ± 6, 18 ± 9, 8 ± 7, 2 ± 1 and 1 ± 1 g/LU/h, for P1, P2, P3, P4 and P5, respectively. Emissions from fattening pig farms with biogasification (P3) and acidification (P4-P5) facilities were 55% and 91-93% lower, respectively, than from farm with no manure treatment (P2). Inventory models underestimated farm-measured methane emissions on average by 51%, across all models and farms, with the Danish model performing the worst (underestimation of 64%). A revision of model parameters related to manure emissions, such as the estimation of volatile solids excreted and methane conversion factor parameters, could improve model output, although more data needs to be collected to strengthen the conclusions. As one of the first studies assessing whole-pig farm emissions, the results showed the potential of the applied measuring method to identify mitigation strategy efficiencies and highlighted the necessity to investigate inventory model accuracy.

Mitigation of methane emissions from three Danish landfills using different biocover systems.

The establishment of biocover systems is an emerging methodology in reducing methane (CH4) emissions from landfills. This study investigated the performance of three biocover systems with different designs (biowindow and passively and actively loaded biofilters) in mitigating CH4 emissions from three landfills in Denmark. A series of field tests were carried out to evaluate the functionality of each system, and total CH4 emissions from relevant landfill sections or the entire landfill were measured before and after biocover implementation. Surface CH4 concentration screening and local CH4 fluxes showed generally low emissions from the biowindow/biofilters (mostly < 5 g CH4 m-2 d-1), although some hotspots were identified on two actively loaded biofilters. One passively loaded biofilter exhibited high CH4 emissions, mainly due to gas overloading into the system. Gas concentration profiles measured at different locations suggested uneven gas distribution in the biofilters, and significant CH4 oxidation occurred in both the gas distribution layer (when oxygen was fed into the system) and the CH4 oxidation layer. High CH4 oxidation efficiencies of above 95% were found in all systems except for one biofilter (55%). Whole-site emission measurements showed CH4 reduction efficiencies between 29 and 72% after implementing biocover systems at the three landfills, suggesting that they were efficient in reducing CH4 emissions. The most challenging task for the passively loaded biocover systems was to control gas flow and secure homogenous gas distribution, while for actively loaded biocovers, it might be more important to eliminate emission hotspots for better functionality.

Efficiency of gas collection systems at Danish landfills and implications for regulations.

Globally, landfills are an important source of anthropogenic methane emissions. Regulations require landfill gas be managed to reduce emissions, and some landfills have therefore installed gas collection systems to recover energy and mitigate methane emissions. However, the efficiency of such systems is seldom evaluated. This paper presents the gas collection efficiencies of 23 Danish landfills and suggests how these values could be used to regulate landfill methane emissions in Denmark. Methane emissions from all sites were measured using the tracer gas dispersion method, and gas collection efficiencies were calculated using the ratio of the methane collection rate to the sum of the collection and emission (and oxidation) rates. Gas collection efficiencies ranged between 13 and 86% with an average of 50% - a value lower than for Swedish (58%), UK (64%) and US (63%) landfills. Possible reasons for the inefficiency of gas collection systems in Denmark include shallow gas collection pipes, leakage from installations (e.g. leachate wells, gas engines), low gas recovery due to minimal gas production or a lack of gas collection in active waste cells. It is suggested to use gas collection efficiency to regulate landfills and help them reach a particular methane mitigation goal. Gas collection efficiency that falls below the target mitigation rate would in turn trigger actions to reduce landfill methane emissions. At sites where the quality of the collected gas is too low to operate a gas engine, the installed gas collection system could be retrofitted to a biocover system designed for methane oxidation.

Prediction of biochemical methane potential of urban organic waste using Fourier transform mid-infrared photoacoustic spectroscopy and multivariate analysis.

Biochemical methane potential (BMP) assays are widely used to assess feedsocks in oder to control the process of biogas production. However, the continuous evaluation of feedstocks using a BMP assay is expensive, time-consuming and challenging. In this study, Fourier transform mid-infrared photoacoustic spectroscopy (FTIR-PAS) was used to predict the BMP values of 87 urban organic waste (UOW) samples derived from different sources in Denmark. The developed model of BMP prediction showed a coefficient of determination (R2) of 0.86 and a root mean square error (RMSE) of 59.3 mL CH4/g VS in prediction. The interpretation of the regression coefficients used in the calibration showed a positive correlation with BMP for relatively easily degradable compounds, such as aliphatics, most likely lipids and amides most likely in proteins, while a negative correlation was found with lignin and hemicellulose.

Mitigation of methane and trace gas emissions through a large-scale active biofilter system at Glatved landfill, Denmark.

Biocover systems are a cost-effective technology utilised to mitigate methane (CH4) and trace gas emissions from landfills. A full-scale biofilter system was constructed at Glatved landfill, Denmark, consisting of three biofilters with a total area of 3950 m2. Landfill gas collected mainly from shredder waste cells was mixed with ambient air and fed actively into the biofilter, resulting in an average load of 60-75 g m-2 d-1 for CH4 and 0.15-0.21 g m-2 d-1 for trace gases (e.g., aromatics, chlorofluorocarbons (CFCs), aliphatic hydrocarbons). The initial CH4 surface screening showed uneven gas distribution into the system, and elevated surface concentrations were observed close to the gas inlet. Both positive and negative CH4 fluxes, ranging from -0.36 to 4.25 g m-2 d-1, were measured across the surface of the biofilter. Total trace gas emissions were between -0.005 and 0.042 g m-2 d-1, and the emission flux of individual compounds were generally small (10-8 to 10-3 g m-2 d-1). Vertical gas concentration profiles showed that the oxidation of CH4 and easily degradable trace compounds such as aromatics and aliphatic hydrocarbons happened in the aerobic zones, while CFCs were degraded in the anaerobic zone inside the compost layer. In addition, oxidation/degradation of CH4 and trace gases also occurred in the gas distribution layer, which contributed significantly to the overall mitigation efficiency of the biofilter system. Overall, the biofilter system showed mitigation efficiencies of nearly 100% for both CH4 and trace gases, and it might have the potential to work under higher loads.

Trace gas composition in landfill gas at Danish landfills receiving low-organic waste.

In 1997, the landfilling of biodegradable waste was banned in Denmark, and currently Danish landfills receive mostly non-combustible waste with a low-organic content. This study aimed to investigate trace gas composition in landfill gas (LFG) at modern Danish landfills. Landfill gas samples were taken from waste cells containing shredder, mixed and aged waste from four Danish landfills. The highest trace gas concentrations were found in shredder waste cells (average concentration of 103 mg m-3), which were comparable with conventional municipal solid waste landfills receiving organic waste. Aliphatic hydrocarbons and aromatics were dominant in the shredder waste cells, most likely released through direct volatilisation from disposed waste products. Abundant oxygenated compounds were found in the shredder waste cell in one of the landfills, thereby indicating a higher level of organic fraction biodegradation. Benzene, toluene, ethylbenzene and xylenes (BTEXs) were measured in high concentrations in all shredder waste cells, contributing to more than 75% of total aromatics. Considerably lower concentrations of trace gases were measured in the mixed and aged waste cells, which were dominated by hydrogen sulphide and several aliphatic hydrocarbons. A constant concentration ratio was established between aliphatic hydrocarbons together with aromatics and methane in shredder waste cells, which was then used in an LFG generation model to estimate trace gas production. The production rates of BTEXs from two landfills were estimated at 272 and 73 kg yr-1 in 2020, which were not considered to pose a significant risk to the environment or to human health.

Improving the analytical flexibility of thermal desorption in determining unknown VOC samples by using re-collection.

The thermal desorption (TD) technique has long suffered from the 'one-shot' problem, whereby the entire sample is consumed in a single analysis, and thus no sample remains for repeated analysis. Recent developments in TD equipment allow for the quantitative re-collection of split samples during thermal desorption, which can be utilised for archiving or immediate analysis. However, the performance of TD systems for re-collecting different volatile organic compounds (VOCs) has rarely been demonstrated. This study provides a systematic investigation into the re-collection efficiency for over 90 VOCs on a TD unit under different conditions. An analytical method was developed based on multi-sorbent tubes and TD-GC/MS, which could quantitatively measure 92 VOCs with good sensitivity (method detection limit between 0.01 and 2 ng) and precision (< 10%). Satisfactory re-collection performance (recoveries within 100% ± 20%) was found for over 70 compounds under different split modes for multiple times, and the single (outlet) split mode was preferred in this regard, in order to avoid significant uncertainties in the results. Thermal labile, polar or reactive compounds such as alcohols and ketones were generally not compatible with re-collection, as they were either lost due to thermal decomposition or formed as system artefacts. In addition, bromochloromethane should not be used as an internal standard when performing sample re-collection, since it will experience significant loss during repeated analysis and lead to overestimation for corresponding compounds. Finally, the re-collection was tested with low-concentration field samples to resolve the unexpected water problem in analysis. Although higher uncertainties were expected in the re-collected samples, the results provided good information on overall concentration variations at the sampling site, thereby instilling confidence in the results obtained from the primary analysis.

Trace gas emissions from municipal solid waste landfills: A review.

Trace gas emissions from municipal solid waste (MSW) landfills have received increasing attention in recent years. This paper reviews literature published between 1983 and 2019, focusing on (i) the origin and fate of trace gas in MSW landfills, (ii) sampling and analytical techniques, (iii) quantitative emission measurement techniques, (iv) concentration and surface emission rates of common trace compounds at different landfill units and (v) the environmental and health concerns associated with trace gas emissions from MSW landfills. Trace gases can be produced from waste degradation, direct volatilisation of chemicals in waste products or from conversions/reactions between other compounds. Different chemical groups dominate the different waste decomposition stages. In general, organic sulphur compounds and oxygenated compounds are connected with fresh waste, while abundant hydrogen sulphide, aromatics and aliphatic hydrocarbons are usually found during the methane fermentation stage. Selection of different sampling, analytical and emission rate measurement techniques might generate different results when quantifying trace gas emission from landfills, and validation tests are needed to evaluate the reliability of current methods. The concentrations of trace gases and their surface emission rates vary largely from site to site, and fresh waste dumping areas and uncovered waste surfaces are the most important fugitive emission sources. The adverse effects of trace gas emission are not fully understood, and more emission data are required in future studies to assess quantitatively their environmental impacts as well as health risks.

Model-based interpretation of methane oxidation and respiration processes in landfill biocovers: 3-D simulation of laboratory and pilot experiments.

Landfill biocovers are an efficient strategy for the mitigation of greenhouse gas emissions from landfills. A complex interplay between key physical and reactive processes occurs in biocovers and affects the transport of gas components. Therefore, numerical models can greatly help the understanding of these systems, their design and optimal operation. In this study, we developed a 3-D multicomponent modeling approach to quantitatively interpret experimental datasets measured in the laboratory and in pilot-scale landfill biocovers. The proposed model is able to reproduce the observed spatial and temporal dynamics of CH4, O2 and CO2 migration in biocovers under different operating conditions and demonstrates the importance of dimensionality in understanding the propagation of gas flow and migration of gas components in such porous media. The model allowed us to capture the coupled transport behavior of gas components, to evaluate the exchange of gas fluxes at the interface between the biocover surface and free air flow, and to investigate the effects of different gas injection patterns on the distribution of gas components within biocovers. The model also helps elucidating the dynamics and competition between methane oxidation and respiration processes observed in the different experimental setups. The simulation outcomes reveal that increasing availability of methane (i.e., higher injection flow rates or higher fractions of CH4 in the injected gas composition) results in progressive dominance of methane oxidation in the biocovers and moderates the impact of respiration.

Total methane emission rates and losses from 23 biogas plants.

Methane losses from biogas plants are problematic, since they contribute to global warming and thus reduce the environmental benefits of biogas production. Total losses of methane from 23 biogas plants were measured by applying a tracer gas dispersion method to assess the magnitude of these emissions. The investigated biogas plants varied in terms of size, substrates used and biogas utilisation. Methane emission rates varied between 2.3 and 33.5 kg CH4 h-1, and losses expressed in percentages of production varied between 0.4 and 14.9%. The average emission rate was 10.4 kg CH4 h-1, and the average loss was 4.6%. Methane losses from the larger biogas plants were generally lower compared to those from the smaller facilities. In general, methane losses were higher from wastewater treatment biogas plants (7.5% in average) in comparison to agricultural biogas plants (2.4% in average). In essence, methane loss may constitute the largest negative environmental impact on the carbon footprint of biogas production.

Stable isotopic determination of methane oxidation: When smaller scales are better.

Stable isotope measurements are an effective tool for evaluating methane (CH4) consumption in landfill soils. However, determining the extent of CH4 oxidation in soils using this approach can be inherently biased, depending on characteristics of the study site and the sampling strategy that is employed. In this study, we establish the unusual case that sampling at smaller scales captures a better representation of the degree of oxidation occurring in landfill cover soils. We did this by comparing three techniques (Plume, Probe, and Transect) that vary in the location of sampling within a site and in the areal footprint of each sample. The Plume method yielded estimates of CH4 oxidation that were 13-16% lower than the Transect and Probe methods, respectively. The Probe and Transect methods, two relatively small-scale and high resolution methods, the latter of which has not been previously described, are best suited to quantify CH4 oxidation in landfill soils as they demonstrably overcome the tendency of stable isotope methods to underestimate CH4 oxidation at the landfill scale. We recommend the use of these two sampling methods for monitoring the efficacy of landfill CH4 reduction strategies that are desired to help meet the goals of the Paris Agreement.

Quantity and quality of clothing and household textiles in the Danish household waste.

Despite the fact that studies have indicated that a large proportion of textiles is disposed in the waste, only few studies have looked at the content of textiles in waste, and even less have considered the quality of these textiles. However, it is crucial to know both quantity and quality, in order to assess the potential for improved reuse and recycling. Following a new method for assessing the quantity and quality of textile waste, this study assessed residual household waste from 17 areas and small combustible waste from six recycling stations throughout Denmark. The average contents of Clothing and Household textiles in residual household waste were 1.4 ±â€¯0.5% and 0.6 ±â€¯0.3%, respectively, whereas the content was 4.5 ±â€¯2.1% for Clothing and 2.6 ±â€¯1.2% for Household textiles in the small combustibles. On an annual basis each resident discards to 2.4 ±â€¯0.9 kg of Clothing and 1.1 ±â€¯0.5 kg/resident/year of Household textiles with the residual household waste. The quality assessments showed, that an average of 65 ±â€¯8.0% and 65 ±â€¯19.3% of the Clothing and Household textiles were reusable in the residual household waste, while in small combustibles it were an average of 69 ±â€¯5.8% and 66 ±â€¯9.6% of the Clothing and Household textiles. In addition, an average of 12 ±â€¯5.3% and 15 ±â€¯10.5% of the Clothing and Household textiles in residual waste, and an average of 14 ±â€¯3.9% and 16 ±â€¯8.7% of the Clothing and Household textiles in small combustibles, could be recycled. This emphasizes that there is good potential for improving textile waste management, as most of the identified Clothing and Household textiles were misplaced and little were actually waste.

Life cycle assessment of garden waste management options including long-term emissions after land application.

A life cycle assessment (LCA) was performed on five garden waste treatment practices: the production of mature compost including the woody fraction (MCIW), the production of mature compost without the woody fraction (MCWW), the production of immature compost without the woody fraction (ICWW), fresh garden waste including the woody fraction (GWIW) and fresh garden waste without the woody fraction (GWWW). The assessment included carbon sequestration after land application of the garden waste and composts, and associated emissions. The removed woody fraction was incinerated and energy recovery included as heat and electricity. The functional unit of the assessment was treatment of 1000 kg of garden waste generated in Denmark. Overall, the results showed that composting of garden waste resulted in comparable or higher environmental impact potentials (depletion of abiotic resources, marine eutrophication, and terrestrial eutrophication and acidification) than no treatment before land application. The toxicity potentials showed the highest normalised impact potentials for all the scenarios, but were unaffected by the different garden waste treatments. The choice of energy source for substituted heat and electricity production affected the performance of the different treatment scenarios with respect to climate change. The scenarios with removal of the woody fraction performed better than the scenarios without removal of the woody fraction when fossil energy sources were substituted, but performed worse when renewable energy sources were substituted. Furthermore, the study showed the importance of including long-term emission factors after land application of fresh and composted garden waste products since the greatest proportion of carbon and nitrogen emissions occurred after land application in three out of the five scenarios for carbon and in all scenarios for nitrogen.

Guidelines for landfill gas emission monitoring using the tracer gas dispersion method.

Landfill gas often containing 50-60% methane, is generated on waste disposal sites receiving organic waste. Regulation requires that this gas is managed in order to reduce emissions, but very few suggestions exist as to how management activities are monitored, what should be set up to ensure this management and how criteria should be developed for when monitoring activities are terminated. Methane emission monitoring procedures are suggested, based on a robust method for measuring total leakage from the site; additionally, quantitative measures, to determine the efficiency of the performed emission mitigation, are defined. The tracer gas dispersion measuring technique is suggested as the core emission measurement methodology in monitoring plans for methane emissions from landfills and a guideline for best practice measurement performance is presented. A minimum methane mitigation efficiency of 80% is suggested. Finally, several principles are presented on how criteria can be developed for when a monitoring program can be terminated. Three of the suggested principles result in comparable completion criteria of about 1-3 kg CH4/h for a small landfill (an area of 4 ha).

Treatment of landfill gas with low methane content by biocover systems.

Landfills are significant sources of anthropogenic atmospheric methane (CH4), which contributes to climate change. Large amounts of CH4 are emitted from landfills in dilute form due to mixing with air in leachate collection systems, or during lateral migration away from landfills. The objective of this study was to investigate the CH4 oxidation efficiency of a compost material subject to LFG diluted with atmospheric air resulting in CH4 concentrations of 5-10% v/v. CH4 oxidation rates and carbon dioxide (CO2) production were measured through batch and dynamic column experiments where two laboratory scale biofilters were constructed. The columns were run at increasing flow rates. Column gas concentration profiles for each of five flow campaigns were compared to each other. This showed that oxygen (O2) was present through the entire column and elevated CO2 concentrations throughout the biofilters were found. Moreover, the oxidation process tended to be centred in the lower parts of both columns. It was observed that the biofilters performed better once they had adapted to the increasing loads of CH4. In both columns, the maximum removal rate of CH4 was found to be 98-100%. Using CH4 mass balances the maximum oxidation rate was 238 g CH4 m-2 d-1 in Column 1 and 483 g CH4 m-2 d-1 in Column 2 (equal to the load). None of the biofilters reached their maximum CH4 oxidation capacity, hence they could have been exposed to a larger CH4 load. It was found that the retention time in the columns was not a factor limiting the oxidation process. High O2 consumption and carbon mass balances underlined the strong microbial activity in the biofilters and it was not suspected that the methane oxidising bacteria were O2 limited. The results of this study suggest that biofilters have great potential for reducing CH4 in diluted LFG.