P.N. Meza Ramos
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Many landfills still pose significant emission and pollution risks because decomposition is incomplete, and contaminants persist. To mitigate these risks and reduce the duration of aftercare, in-situ stabilization techniques have been developed to accelerate waste degradation. Two methods have been tested in this context: recirculation of water to stimulate microbial activity and aeration to promote aerobic degradation. Both alter the composition of organic matter as readily degradable fractions are consumed, while more resistant components remain.
Although numerous projects worldwide have shown encouraging results, landfill stabilization remains challenged by the inherent heterogeneity of the waste body. This complexity limits uniform treatment and leaves uncertainties about the physical, chemical, and biological interactions at play. Addressing these knowledge gaps, this thesis investigates the effectiveness of aeration and water recirculation in three Dutch pilot landfills: Braambergen and Wieringermeer (aerated), and Kragge (water recirculation).
The pilots revealed that the effects of aeration are highly variable in space and time. At Braambergen, variability in aeration performance revealed the strong influence of site heterogeneity. Differences in water levels in aeration wells affected gas composition and flow, yet high water columns alone could not explain the observed contrast between compartments. Other factors, such as spatial variability in gas permeability within the waste body, also played a role. Where aeration was more effective, higher gas extraction, elevated temperatures, and greater settlement indicated enhanced microbial activity and carbon mineralization.
Beyond gas monitoring, stabilization was assessed by comparing the carbon generation of waste samples under aerobic and anaerobic conditions with model predictions and with carbon actually recovered on-site. The heterogeneity of the waste samples was reflected in the carbon potential and decay rate constants (k-values). Aerated pilots showed reduced aerobic carbon potential, reflecting advanced stabilization, while the recirculated pilot retained substantial degradable organic matter. These results highlight both the large potential of aeration to accelerate stabilization and the persistence of heterogeneity that complicates prediction and management.
A further focus was placed on building a comprehensive carbon and nitrogen balance across the solid, aqueous, and gas phases at field scale. Over seven years, aerated pilots exhibited higher organic matter degradation than the anaerobic pilot with a significant share of carbon and nitrogen released through the gas phase. In contrast, the recirculated pilot retained larger amounts of degradable carbon and poorly mobilizable nitrogen. Importantly, the analysis revealed that a substantial fraction of nitrogen remains fixed in solid or microbial pools, potentially delaying compliance with leachate emission targets.
Taken together, these findings advance understanding of how aeration and water recirculation influence landfill stabilization. They demonstrate the benefits of aeration for accelerating degradation while also underlining the challenges posed by spatial variability and persistent nitrogen pools. Such insights are crucial for improving the design and implementation of in-situ stabilization strategies and for reducing the long-term aftercare needs of landfills. ...
Although numerous projects worldwide have shown encouraging results, landfill stabilization remains challenged by the inherent heterogeneity of the waste body. This complexity limits uniform treatment and leaves uncertainties about the physical, chemical, and biological interactions at play. Addressing these knowledge gaps, this thesis investigates the effectiveness of aeration and water recirculation in three Dutch pilot landfills: Braambergen and Wieringermeer (aerated), and Kragge (water recirculation).
The pilots revealed that the effects of aeration are highly variable in space and time. At Braambergen, variability in aeration performance revealed the strong influence of site heterogeneity. Differences in water levels in aeration wells affected gas composition and flow, yet high water columns alone could not explain the observed contrast between compartments. Other factors, such as spatial variability in gas permeability within the waste body, also played a role. Where aeration was more effective, higher gas extraction, elevated temperatures, and greater settlement indicated enhanced microbial activity and carbon mineralization.
Beyond gas monitoring, stabilization was assessed by comparing the carbon generation of waste samples under aerobic and anaerobic conditions with model predictions and with carbon actually recovered on-site. The heterogeneity of the waste samples was reflected in the carbon potential and decay rate constants (k-values). Aerated pilots showed reduced aerobic carbon potential, reflecting advanced stabilization, while the recirculated pilot retained substantial degradable organic matter. These results highlight both the large potential of aeration to accelerate stabilization and the persistence of heterogeneity that complicates prediction and management.
A further focus was placed on building a comprehensive carbon and nitrogen balance across the solid, aqueous, and gas phases at field scale. Over seven years, aerated pilots exhibited higher organic matter degradation than the anaerobic pilot with a significant share of carbon and nitrogen released through the gas phase. In contrast, the recirculated pilot retained larger amounts of degradable carbon and poorly mobilizable nitrogen. Importantly, the analysis revealed that a substantial fraction of nitrogen remains fixed in solid or microbial pools, potentially delaying compliance with leachate emission targets.
Taken together, these findings advance understanding of how aeration and water recirculation influence landfill stabilization. They demonstrate the benefits of aeration for accelerating degradation while also underlining the challenges posed by spatial variability and persistent nitrogen pools. Such insights are crucial for improving the design and implementation of in-situ stabilization strategies and for reducing the long-term aftercare needs of landfills. ...
Many landfills still pose significant emission and pollution risks because decomposition is incomplete, and contaminants persist. To mitigate these risks and reduce the duration of aftercare, in-situ stabilization techniques have been developed to accelerate waste degradation. Two methods have been tested in this context: recirculation of water to stimulate microbial activity and aeration to promote aerobic degradation. Both alter the composition of organic matter as readily degradable fractions are consumed, while more resistant components remain.
Although numerous projects worldwide have shown encouraging results, landfill stabilization remains challenged by the inherent heterogeneity of the waste body. This complexity limits uniform treatment and leaves uncertainties about the physical, chemical, and biological interactions at play. Addressing these knowledge gaps, this thesis investigates the effectiveness of aeration and water recirculation in three Dutch pilot landfills: Braambergen and Wieringermeer (aerated), and Kragge (water recirculation).
The pilots revealed that the effects of aeration are highly variable in space and time. At Braambergen, variability in aeration performance revealed the strong influence of site heterogeneity. Differences in water levels in aeration wells affected gas composition and flow, yet high water columns alone could not explain the observed contrast between compartments. Other factors, such as spatial variability in gas permeability within the waste body, also played a role. Where aeration was more effective, higher gas extraction, elevated temperatures, and greater settlement indicated enhanced microbial activity and carbon mineralization.
Beyond gas monitoring, stabilization was assessed by comparing the carbon generation of waste samples under aerobic and anaerobic conditions with model predictions and with carbon actually recovered on-site. The heterogeneity of the waste samples was reflected in the carbon potential and decay rate constants (k-values). Aerated pilots showed reduced aerobic carbon potential, reflecting advanced stabilization, while the recirculated pilot retained substantial degradable organic matter. These results highlight both the large potential of aeration to accelerate stabilization and the persistence of heterogeneity that complicates prediction and management.
A further focus was placed on building a comprehensive carbon and nitrogen balance across the solid, aqueous, and gas phases at field scale. Over seven years, aerated pilots exhibited higher organic matter degradation than the anaerobic pilot with a significant share of carbon and nitrogen released through the gas phase. In contrast, the recirculated pilot retained larger amounts of degradable carbon and poorly mobilizable nitrogen. Importantly, the analysis revealed that a substantial fraction of nitrogen remains fixed in solid or microbial pools, potentially delaying compliance with leachate emission targets.
Taken together, these findings advance understanding of how aeration and water recirculation influence landfill stabilization. They demonstrate the benefits of aeration for accelerating degradation while also underlining the challenges posed by spatial variability and persistent nitrogen pools. Such insights are crucial for improving the design and implementation of in-situ stabilization strategies and for reducing the long-term aftercare needs of landfills.
Although numerous projects worldwide have shown encouraging results, landfill stabilization remains challenged by the inherent heterogeneity of the waste body. This complexity limits uniform treatment and leaves uncertainties about the physical, chemical, and biological interactions at play. Addressing these knowledge gaps, this thesis investigates the effectiveness of aeration and water recirculation in three Dutch pilot landfills: Braambergen and Wieringermeer (aerated), and Kragge (water recirculation).
The pilots revealed that the effects of aeration are highly variable in space and time. At Braambergen, variability in aeration performance revealed the strong influence of site heterogeneity. Differences in water levels in aeration wells affected gas composition and flow, yet high water columns alone could not explain the observed contrast between compartments. Other factors, such as spatial variability in gas permeability within the waste body, also played a role. Where aeration was more effective, higher gas extraction, elevated temperatures, and greater settlement indicated enhanced microbial activity and carbon mineralization.
Beyond gas monitoring, stabilization was assessed by comparing the carbon generation of waste samples under aerobic and anaerobic conditions with model predictions and with carbon actually recovered on-site. The heterogeneity of the waste samples was reflected in the carbon potential and decay rate constants (k-values). Aerated pilots showed reduced aerobic carbon potential, reflecting advanced stabilization, while the recirculated pilot retained substantial degradable organic matter. These results highlight both the large potential of aeration to accelerate stabilization and the persistence of heterogeneity that complicates prediction and management.
A further focus was placed on building a comprehensive carbon and nitrogen balance across the solid, aqueous, and gas phases at field scale. Over seven years, aerated pilots exhibited higher organic matter degradation than the anaerobic pilot with a significant share of carbon and nitrogen released through the gas phase. In contrast, the recirculated pilot retained larger amounts of degradable carbon and poorly mobilizable nitrogen. Importantly, the analysis revealed that a substantial fraction of nitrogen remains fixed in solid or microbial pools, potentially delaying compliance with leachate emission targets.
Taken together, these findings advance understanding of how aeration and water recirculation influence landfill stabilization. They demonstrate the benefits of aeration for accelerating degradation while also underlining the challenges posed by spatial variability and persistent nitrogen pools. Such insights are crucial for improving the design and implementation of in-situ stabilization strategies and for reducing the long-term aftercare needs of landfills.
The ratio of nitrogen (N2) to argon (Ar) in landfill gas was compared to the atmospheric gas ratio to quantify the balance between N2 generating (anaerobic ammonium oxidation, denitrification) and N2 consuming (nitrogen fixation) processes on three landfills undergoing in-situ stabilization. In the aerated landfills, as much as 22% of the extracted N2 could be explained by net denitrification, with coexisting aerobic and anaerobic domains fostering nitrification-dependent denitrification. Nitrogen fixation was also occasionally observed. Removal of nitrogen via the gas phase exceeded nitrogen removed via the leachate by up to a factor of 33. Contrastingly, the anaerobic landfill under leachate recirculation showed a net reduction of N2 in relation to Ar, indicating nitrogen fixation as the dominant mechanism, equivalent up to 28% of the nitrogen in the extracted landfill gas. The balance between denitrification and nitrogen fixation in the aerated sites varied seasonally, likely caused by increased evapotranspiration in the summer, allowing greater air intrusion through the cover soil, resulting in higher NO3– and NO2– availability for denitrification and anammox. No such variability was observed for the landfill under liquid recirculation. The nitrogen transforming microbial community comprised of species responsible for nitrification, ammonification, denitrification, and anammox, indicating all processes may coexist. The findings show aeration supports nitrogen removal through the gas phase, but also suggest that nitrogen fixation adds nitrogen to the waste body in anaerobic domains. This could delay reaching environmental compliance criteria for leachate nitrogen, both for in-situ treatment by aeration and by leachate recirculation.
...
The ratio of nitrogen (N2) to argon (Ar) in landfill gas was compared to the atmospheric gas ratio to quantify the balance between N2 generating (anaerobic ammonium oxidation, denitrification) and N2 consuming (nitrogen fixation) processes on three landfills undergoing in-situ stabilization. In the aerated landfills, as much as 22% of the extracted N2 could be explained by net denitrification, with coexisting aerobic and anaerobic domains fostering nitrification-dependent denitrification. Nitrogen fixation was also occasionally observed. Removal of nitrogen via the gas phase exceeded nitrogen removed via the leachate by up to a factor of 33. Contrastingly, the anaerobic landfill under leachate recirculation showed a net reduction of N2 in relation to Ar, indicating nitrogen fixation as the dominant mechanism, equivalent up to 28% of the nitrogen in the extracted landfill gas. The balance between denitrification and nitrogen fixation in the aerated sites varied seasonally, likely caused by increased evapotranspiration in the summer, allowing greater air intrusion through the cover soil, resulting in higher NO3– and NO2– availability for denitrification and anammox. No such variability was observed for the landfill under liquid recirculation. The nitrogen transforming microbial community comprised of species responsible for nitrification, ammonification, denitrification, and anammox, indicating all processes may coexist. The findings show aeration supports nitrogen removal through the gas phase, but also suggest that nitrogen fixation adds nitrogen to the waste body in anaerobic domains. This could delay reaching environmental compliance criteria for leachate nitrogen, both for in-situ treatment by aeration and by leachate recirculation.
In-situ stabilization of waste bodies can be achieved by the infiltration of water or recirculation of leachate into the landfill, which is thought to enhance the microbial degradation of waste organics by (re-)moisturizing dry zones and flushing out metabolic products of organic matter decay. The success of in-situ stabilization should reflect in initially accelerated and thereafter reduced rates of anaerobic waste organic matter decay rates. This paper compares the methane generation that was modelled using the Afvalzorg multiphase model without the added effect of leachate recirculation with actually extracted methane in the landfill and gas generation on sampled wastes following five years of leachate recirculation on a Dutch landfill. Laboratory incubations revealed a methane potential between 0.03 kg CH4/t dw and 15.8 kg CH4/t dw for 365 days. Clear trends with respect to depth, moisture content, total organic carbon or share in hard plastics did not emerge as overall waste heterogeneity was high and likely obfuscated the correlation analysis. The results showed a recovery efficiency of 30.4% for 2021, with 0.07 kg CH4/t dw for the recovered methane and 0.23 kg CH4/t dw for the predicted methane in compartment 3. The average methane potential measured in the laboratory was almost twice as high as the remaining methane potential predicted for the period of 2021-2093. The discrepancy could be due to (i) enhanced waste degradability as a result of five years of recirculation, (ii) enhancing effects of material perturbation during sampling and/or (iii) impeded on-site methane generation and gas and water transport limitations due to presence of plastics. Overall, the laboratory incubations demonstrate a significant potential for waste biodegradation still residing in the waste.
...
In-situ stabilization of waste bodies can be achieved by the infiltration of water or recirculation of leachate into the landfill, which is thought to enhance the microbial degradation of waste organics by (re-)moisturizing dry zones and flushing out metabolic products of organic matter decay. The success of in-situ stabilization should reflect in initially accelerated and thereafter reduced rates of anaerobic waste organic matter decay rates. This paper compares the methane generation that was modelled using the Afvalzorg multiphase model without the added effect of leachate recirculation with actually extracted methane in the landfill and gas generation on sampled wastes following five years of leachate recirculation on a Dutch landfill. Laboratory incubations revealed a methane potential between 0.03 kg CH4/t dw and 15.8 kg CH4/t dw for 365 days. Clear trends with respect to depth, moisture content, total organic carbon or share in hard plastics did not emerge as overall waste heterogeneity was high and likely obfuscated the correlation analysis. The results showed a recovery efficiency of 30.4% for 2021, with 0.07 kg CH4/t dw for the recovered methane and 0.23 kg CH4/t dw for the predicted methane in compartment 3. The average methane potential measured in the laboratory was almost twice as high as the remaining methane potential predicted for the period of 2021-2093. The discrepancy could be due to (i) enhanced waste degradability as a result of five years of recirculation, (ii) enhancing effects of material perturbation during sampling and/or (iii) impeded on-site methane generation and gas and water transport limitations due to presence of plastics. Overall, the laboratory incubations demonstrate a significant potential for waste biodegradation still residing in the waste.
Conference paper
(2023)
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Julia Gebert, Nathali Meza, Carmen Cruz Osorio, Hans Lammen
This study quantifies the share of aerobically produced carbon (aeration efficiency) during six years of a full scale landfill aeration project using the balance between methane and carbon dioxide in the bulk extracted gas. Aeration was realized by overextraction. Aeration enhanced carbon release in comparison to the anaerobic ‘base case’, as predicted by the Afvalzorg multiphase model, by a factor of 3.7. Aeration efficiency, averaging around 44%, varied seasonally, and was lower in periods of low or no evapotranspiration and hence higher moisture content in the landfill cover soil (winter). Higher aeration efficiencies were observed when evapotranspiration enables increased cover soil permeability (summer). Correspondingly, aeration efficiency was linearly related to the concentration of N2 in the bulk extracted gas. To a lesser extent, condensate and its removal also affected flow and hence the aeration efficiency. Except for the modulation by seasonal effects, the cumulative amount of extracted ‘aerobic carbon’ increased linearly over time, independent of changes in the blower pressure and flow. This suggests that below the cover soil, within the waste body, flow is chanelled in preferential pathways, limiting the intrusion of oxygen into the bulk waste. Aeration can hence only be enhanced by reducing well spacing. The blower efficiency, assessed by the ratio of flow to pressure, decreased markedly over time, likely indicating diminishing waste permeability as a result of waste consolidation.
...
This study quantifies the share of aerobically produced carbon (aeration efficiency) during six years of a full scale landfill aeration project using the balance between methane and carbon dioxide in the bulk extracted gas. Aeration was realized by overextraction. Aeration enhanced carbon release in comparison to the anaerobic ‘base case’, as predicted by the Afvalzorg multiphase model, by a factor of 3.7. Aeration efficiency, averaging around 44%, varied seasonally, and was lower in periods of low or no evapotranspiration and hence higher moisture content in the landfill cover soil (winter). Higher aeration efficiencies were observed when evapotranspiration enables increased cover soil permeability (summer). Correspondingly, aeration efficiency was linearly related to the concentration of N2 in the bulk extracted gas. To a lesser extent, condensate and its removal also affected flow and hence the aeration efficiency. Except for the modulation by seasonal effects, the cumulative amount of extracted ‘aerobic carbon’ increased linearly over time, independent of changes in the blower pressure and flow. This suggests that below the cover soil, within the waste body, flow is chanelled in preferential pathways, limiting the intrusion of oxygen into the bulk waste. Aeration can hence only be enhanced by reducing well spacing. The blower efficiency, assessed by the ratio of flow to pressure, decreased markedly over time, likely indicating diminishing waste permeability as a result of waste consolidation.
In the Netherlands, three full-scale pilots have been in operation for approximately five years to understand the effects of leachate recirculation or aeration on waste stabilisation. This study employs the ratio of N2 to Ar in the landfill gas in comparison to the ratio in atmospheric air to derive the share of N2 that originates from denitrification. We collected samples from the three pilot landfills from different gas wells, gas collector systems and from the total bulk extracted gas and measured its composition using gas chromatography. We estimated the aeration efficiency of the two landfills under in situ aeration based on the CO2/CH4 ratio as an indicator of aerobic processes. Denitrification dominated in the aerated landfills, with as much as 13% of N2 being explained by the net effect of denitrification, whereas the landfill under leachate recirculation showed a net ‘loss’ of N2, indicating N2 fixation to be a dominant mechanism. There was a seasonal variability of the balance between denitrification and N2 fixation in the aerated sites, likely caused by increased aeration efficiency and hence increased availability of NO3- for denitrification under summer conditions with lower moisture content in the cover soil, allowing for increased air ingress. No such variability was observed for the landfill under liquid recirculation. Future evaluation of the microbial community composition will further elucidate N transformation pathways in landfills under different in-situ stabilisation treatments.
...
In the Netherlands, three full-scale pilots have been in operation for approximately five years to understand the effects of leachate recirculation or aeration on waste stabilisation. This study employs the ratio of N2 to Ar in the landfill gas in comparison to the ratio in atmospheric air to derive the share of N2 that originates from denitrification. We collected samples from the three pilot landfills from different gas wells, gas collector systems and from the total bulk extracted gas and measured its composition using gas chromatography. We estimated the aeration efficiency of the two landfills under in situ aeration based on the CO2/CH4 ratio as an indicator of aerobic processes. Denitrification dominated in the aerated landfills, with as much as 13% of N2 being explained by the net effect of denitrification, whereas the landfill under leachate recirculation showed a net ‘loss’ of N2, indicating N2 fixation to be a dominant mechanism. There was a seasonal variability of the balance between denitrification and N2 fixation in the aerated sites, likely caused by increased aeration efficiency and hence increased availability of NO3- for denitrification under summer conditions with lower moisture content in the cover soil, allowing for increased air ingress. No such variability was observed for the landfill under liquid recirculation. Future evaluation of the microbial community composition will further elucidate N transformation pathways in landfills under different in-situ stabilisation treatments.
Journal article
(2022)
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Julia Gebert, Ties de Jong, Nathali Meza, Tristan Rees-White, Richard Paul Beaven, Hans Lammen
Within the framework of the Dutch sustainable landfill project iDS, four compartments of the Dutch landfill Braambergen have been treated by in-situ aeration since 2017. The aeration infrastructure comprises 230 wells with a spacing of 15 to 20 m, distrib-uted over an area of around 10 ha, intercepting a waste body of 1.2 × 106 t of contam-inated soils, soil treatment residues, bottom ashes and construction and demolition waste. The wells, used in an alternating fashion for air injection and gas extraction, can also be used to monitor water tables within the waste body. In order to describe the spatial variability of waste hydraulics, design a larger scale leachate pumping test and, eventually, support model predictions of the site’s water balance and emission potential, analyses of leachate composition and pumping tests on individual wells have been conducted. The spatial variability of leachate quality and water tables is very high with no geospatial relationship between the sampling points. Each sampling point is representative of itself only. Large differences prevail not only between and across the compartments, but also between directly neighbouring wells. Both the small scale differences in leachate tables as well as in leachate quality indicate a spatial pattern of zones with low horizontal connectivity within the waste body. Recovery rates of drawdown in the wells yielded preliminary estimates of horizontal waste hydraulic conductivity in the order of 1×10-7 to 6×10-4 m/s.
...
Within the framework of the Dutch sustainable landfill project iDS, four compartments of the Dutch landfill Braambergen have been treated by in-situ aeration since 2017. The aeration infrastructure comprises 230 wells with a spacing of 15 to 20 m, distrib-uted over an area of around 10 ha, intercepting a waste body of 1.2 × 106 t of contam-inated soils, soil treatment residues, bottom ashes and construction and demolition waste. The wells, used in an alternating fashion for air injection and gas extraction, can also be used to monitor water tables within the waste body. In order to describe the spatial variability of waste hydraulics, design a larger scale leachate pumping test and, eventually, support model predictions of the site’s water balance and emission potential, analyses of leachate composition and pumping tests on individual wells have been conducted. The spatial variability of leachate quality and water tables is very high with no geospatial relationship between the sampling points. Each sampling point is representative of itself only. Large differences prevail not only between and across the compartments, but also between directly neighbouring wells. Both the small scale differences in leachate tables as well as in leachate quality indicate a spatial pattern of zones with low horizontal connectivity within the waste body. Recovery rates of drawdown in the wells yielded preliminary estimates of horizontal waste hydraulic conductivity in the order of 1×10-7 to 6×10-4 m/s.
In-situ aeration of landfills accelerates biodegradation of waste organic matter and hence advances waste stabilization. The spatial outreach of aeration greatly affects stabilization efficiency. This study analyzed the spatial variability of gas composition and flow in 230 wells spread over four compartments of a Dutch landfill which is under in situ aeration since 2017, as well as the carbon extraction efficiency, tem-perature, and settlement. Flow rates and gas composition in the extraction wells varied strongly. The highest variability was observed in the compartment with the highest water tables with submerged filter screens for most wells, with low flow rates, and elevated ratios of CH4 to CO2, indicating predominance of anaerobic processes (compartment 11Z). The compartment with the most uniform distribution of gas flow rates, composition and lower ratios of CH4 to CO2, suggesting a significant share of aerobic carbon mineralization, also showed higher temperatures, a carbon extraction efficiency, and larger cumulative settlement, all indicative of enhanced microbial activity (compartment 11N). In this compartment, the amount of extracted carbon exceeded the carbon generation predicted from landfill gas modeling by the factor of 2 over the hitherto four years aeration. The effect of water tables on gas flow and the correlation between the flow, and the ratio of CH4 to CO2 appeared weak, indicating that also other factors than water tables influence gas concentration and flow. Future work includes stable isotope probing to analyze the significance of microbial respiration and microbial CH4 oxidation for the composition of the final extracted gas mixture.
...
In-situ aeration of landfills accelerates biodegradation of waste organic matter and hence advances waste stabilization. The spatial outreach of aeration greatly affects stabilization efficiency. This study analyzed the spatial variability of gas composition and flow in 230 wells spread over four compartments of a Dutch landfill which is under in situ aeration since 2017, as well as the carbon extraction efficiency, tem-perature, and settlement. Flow rates and gas composition in the extraction wells varied strongly. The highest variability was observed in the compartment with the highest water tables with submerged filter screens for most wells, with low flow rates, and elevated ratios of CH4 to CO2, indicating predominance of anaerobic processes (compartment 11Z). The compartment with the most uniform distribution of gas flow rates, composition and lower ratios of CH4 to CO2, suggesting a significant share of aerobic carbon mineralization, also showed higher temperatures, a carbon extraction efficiency, and larger cumulative settlement, all indicative of enhanced microbial activity (compartment 11N). In this compartment, the amount of extracted carbon exceeded the carbon generation predicted from landfill gas modeling by the factor of 2 over the hitherto four years aeration. The effect of water tables on gas flow and the correlation between the flow, and the ratio of CH4 to CO2 appeared weak, indicating that also other factors than water tables influence gas concentration and flow. Future work includes stable isotope probing to analyze the significance of microbial respiration and microbial CH4 oxidation for the composition of the final extracted gas mixture.