J. Gebert
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Journal article
(2025)
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Jelle A. Dercksen, Jan Willem Foppen, Astrid Blom, Krijn B. Trimbos, Julia Gebert, Thom A. Bogaard, Laura Maria Stancanelli
Organisms perpetually release genetic material in their surroundings, referred to as environmental DNA (eDNA), which can be captured and subsequently analyzed to detect biodiversity across the tree of life. In lotic, dynamic environments, little is known about the specific factors that affect the concentration of eDNA between release by the host and its dissemination into the environment. This gap in knowledge introduces significant uncertainty when applying eDNA as a monitoring tool. Our objective is to provide insight on the factors that affect the eDNA concentrations in ecosystems representative of rivers and streams. To this end, we conducted a series of laboratory experiments in a rotating circular (annular) flume, which allows for extended degradation experiments under conditions of flow. Here, we show that flow velocity impacts the observed eDNA concentration over time. Our results suggest that flow-induced transport keeps eDNA in suspension, reducing eDNA removal from the water column, which increased the observed concentration of eDNA. We observed a temporary increase in eDNA concentration over the early phase of the flume experiment with the highest flow velocity. This increase in eDNA concentration seems to be due to a combination of low eDNA degradation rates and high shear stress, which fragment and subsequently homogenize eDNA particles over the water column. The results of our study show the importance of better understanding and assessing the detection probability of eDNA, both in controlled laboratory and larger-scale environmental conditions.
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Organisms perpetually release genetic material in their surroundings, referred to as environmental DNA (eDNA), which can be captured and subsequently analyzed to detect biodiversity across the tree of life. In lotic, dynamic environments, little is known about the specific factors that affect the concentration of eDNA between release by the host and its dissemination into the environment. This gap in knowledge introduces significant uncertainty when applying eDNA as a monitoring tool. Our objective is to provide insight on the factors that affect the eDNA concentrations in ecosystems representative of rivers and streams. To this end, we conducted a series of laboratory experiments in a rotating circular (annular) flume, which allows for extended degradation experiments under conditions of flow. Here, we show that flow velocity impacts the observed eDNA concentration over time. Our results suggest that flow-induced transport keeps eDNA in suspension, reducing eDNA removal from the water column, which increased the observed concentration of eDNA. We observed a temporary increase in eDNA concentration over the early phase of the flume experiment with the highest flow velocity. This increase in eDNA concentration seems to be due to a combination of low eDNA degradation rates and high shear stress, which fragment and subsequently homogenize eDNA particles over the water column. The results of our study show the importance of better understanding and assessing the detection probability of eDNA, both in controlled laboratory and larger-scale environmental conditions.
Mud is a fine-grained cohesive material which contains mineral particles (predominantly clay and silt), organic (and inorganic) matter, and water. Understanding mud’s rheological and settling behaviour is critical for sustainable sediment management in ports [1, 2]. A systematic analysis of the effect of clay minerology on the rheological and settling behaviour of mud has been conducted previously [3, 4]. In contrast, literature on the impact of organic matter on physical properties of sediment is scarce. Our previous work [5] demonstrated the impact of microbial inactivation via gamma radiation, revealing a significant increase in settling rates. Current research incorporates chemical sterilization (NaN3) and organic matter removal (NaOCl), to systematically differentiate between effects of microbial activity and effects of organic matter on the physical properties of fluid mud (FM).
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Mud is a fine-grained cohesive material which contains mineral particles (predominantly clay and silt), organic (and inorganic) matter, and water. Understanding mud’s rheological and settling behaviour is critical for sustainable sediment management in ports [1, 2]. A systematic analysis of the effect of clay minerology on the rheological and settling behaviour of mud has been conducted previously [3, 4]. In contrast, literature on the impact of organic matter on physical properties of sediment is scarce. Our previous work [5] demonstrated the impact of microbial inactivation via gamma radiation, revealing a significant increase in settling rates. Current research incorporates chemical sterilization (NaN3) and organic matter removal (NaOCl), to systematically differentiate between effects of microbial activity and effects of organic matter on the physical properties of fluid mud (FM).
Increase of sea level and land subsidence necessitate heightening and strengthening of dikes and embankments, creating large material demands. On the other hand, maintenance of fairways, harbor basins, sluices, barrages and water reservoirs generate large volumes of dredged sediment. Physical and biogeochemical properties of freshly dredged, saturated sediment differ significantly from those of ripened, unsaturated soil. Beneficial use of sediment as earthen construction material therefore requires dewatering and further biogeochemical and physical ripening. If repurposed for dike construction, particularly the shrinkage potential of the material and hence its susceptibility to crack formation is of interest. Further, compactibility of the material determines key mechanical properties such as shear and tensile strength. Here, we investigate the effect of field ripening of partially dewatered dredged sediment (METHA material) on these parameters.
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Increase of sea level and land subsidence necessitate heightening and strengthening of dikes and embankments, creating large material demands. On the other hand, maintenance of fairways, harbor basins, sluices, barrages and water reservoirs generate large volumes of dredged sediment. Physical and biogeochemical properties of freshly dredged, saturated sediment differ significantly from those of ripened, unsaturated soil. Beneficial use of sediment as earthen construction material therefore requires dewatering and further biogeochemical and physical ripening. If repurposed for dike construction, particularly the shrinkage potential of the material and hence its susceptibility to crack formation is of interest. Further, compactibility of the material determines key mechanical properties such as shear and tensile strength. Here, we investigate the effect of field ripening of partially dewatered dredged sediment (METHA material) on these parameters.
Journal article
(2025)
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Julia Gebert, Stefanie Böhnke-Brandt, Florian Zander, Daniela Indenbirken, Lutgardis Bergmann, Ines Krohn, Mirjam Perner
The port of Hamburg represents a transition zone between upstream, shallow regions of high net primary production and downstream deep and more turbulent waters in the tidal Elbe River in northwestern Germany. Correspondingly, strong gradients of degradable organic matter (OM) on a distance of a few river kilometers had been identified. This study links microbial community composition using 16S metagenomic amplicons and extracellular polymeric substances (EPS) composition to the observed gradients of sediment OM lability. It was hypothesized that lability gradients caused by higher concentrations of biogenic, autochthonous OM upstream and greater share of already stabilized OM downstream reflect in gradients of microbial community composition, diversity and EPS characteristics.
Indeed, available OM was found to act as key driver regulating syntrophic microbial community composition and associated metabolic features, with location-specific overriding the effect of seasonal variations. Upstream sites with high available OM featuring lower bacterial but increased archaeal diversity and elevated methane and carbon dioxide fluxes, whereas lower OM lability downstream fostered a more diverse bacterial but decreased archaeal diversity. The ratio between microbial taxon richness and biomass correlated inversely with OM transformation rates. These patterns also reflected in increased EPS concentration produced in response to metabolic needs (i.e. polysaccharides and proteins), whereas structural components such as lipids, which can be more resistant under the prevailing anoxic conditions, remained more evenly distributed along the transect. Although bacterial relative abundances exceeded archaeal abundances (<1 %) by far, archaeal functional significance remained pivotal for the final release of carbon as methane and carbon dioxide under the mostly reducing conditions in the deposited sediment. ...
Indeed, available OM was found to act as key driver regulating syntrophic microbial community composition and associated metabolic features, with location-specific overriding the effect of seasonal variations. Upstream sites with high available OM featuring lower bacterial but increased archaeal diversity and elevated methane and carbon dioxide fluxes, whereas lower OM lability downstream fostered a more diverse bacterial but decreased archaeal diversity. The ratio between microbial taxon richness and biomass correlated inversely with OM transformation rates. These patterns also reflected in increased EPS concentration produced in response to metabolic needs (i.e. polysaccharides and proteins), whereas structural components such as lipids, which can be more resistant under the prevailing anoxic conditions, remained more evenly distributed along the transect. Although bacterial relative abundances exceeded archaeal abundances (<1 %) by far, archaeal functional significance remained pivotal for the final release of carbon as methane and carbon dioxide under the mostly reducing conditions in the deposited sediment. ...
The port of Hamburg represents a transition zone between upstream, shallow regions of high net primary production and downstream deep and more turbulent waters in the tidal Elbe River in northwestern Germany. Correspondingly, strong gradients of degradable organic matter (OM) on a distance of a few river kilometers had been identified. This study links microbial community composition using 16S metagenomic amplicons and extracellular polymeric substances (EPS) composition to the observed gradients of sediment OM lability. It was hypothesized that lability gradients caused by higher concentrations of biogenic, autochthonous OM upstream and greater share of already stabilized OM downstream reflect in gradients of microbial community composition, diversity and EPS characteristics.
Indeed, available OM was found to act as key driver regulating syntrophic microbial community composition and associated metabolic features, with location-specific overriding the effect of seasonal variations. Upstream sites with high available OM featuring lower bacterial but increased archaeal diversity and elevated methane and carbon dioxide fluxes, whereas lower OM lability downstream fostered a more diverse bacterial but decreased archaeal diversity. The ratio between microbial taxon richness and biomass correlated inversely with OM transformation rates. These patterns also reflected in increased EPS concentration produced in response to metabolic needs (i.e. polysaccharides and proteins), whereas structural components such as lipids, which can be more resistant under the prevailing anoxic conditions, remained more evenly distributed along the transect. Although bacterial relative abundances exceeded archaeal abundances (<1 %) by far, archaeal functional significance remained pivotal for the final release of carbon as methane and carbon dioxide under the mostly reducing conditions in the deposited sediment.
Indeed, available OM was found to act as key driver regulating syntrophic microbial community composition and associated metabolic features, with location-specific overriding the effect of seasonal variations. Upstream sites with high available OM featuring lower bacterial but increased archaeal diversity and elevated methane and carbon dioxide fluxes, whereas lower OM lability downstream fostered a more diverse bacterial but decreased archaeal diversity. The ratio between microbial taxon richness and biomass correlated inversely with OM transformation rates. These patterns also reflected in increased EPS concentration produced in response to metabolic needs (i.e. polysaccharides and proteins), whereas structural components such as lipids, which can be more resistant under the prevailing anoxic conditions, remained more evenly distributed along the transect. Although bacterial relative abundances exceeded archaeal abundances (<1 %) by far, archaeal functional significance remained pivotal for the final release of carbon as methane and carbon dioxide under the mostly reducing conditions in the deposited sediment.
Dredging produces large sediment volumes with organic matter (OM) from natural and industrial sources, which even in small amounts, can significantly affect sediment properties [1]. For beneficial use of dredged sediment, OM stability is paramount. Sediment ripening aims to reducing and stabilizing the organic fractions [2], [3]. This study examines OM degradation in mechanically dewatered dredged sediment (METHA plant, Hamburg, Germany) during ripening, analyzing sediment respiration and the Tea Bag Index [4]. Together, these methods provide a comprehensive understanding of the dynamics of organic matter transformation during biological ripening of dredged sediment.
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Dredging produces large sediment volumes with organic matter (OM) from natural and industrial sources, which even in small amounts, can significantly affect sediment properties [1]. For beneficial use of dredged sediment, OM stability is paramount. Sediment ripening aims to reducing and stabilizing the organic fractions [2], [3]. This study examines OM degradation in mechanically dewatered dredged sediment (METHA plant, Hamburg, Germany) during ripening, analyzing sediment respiration and the Tea Bag Index [4]. Together, these methods provide a comprehensive understanding of the dynamics of organic matter transformation during biological ripening of dredged sediment.
Soil Formation from Dredged Sediment
Evolution of Biochemical and Physical Properties
Using dredged material from ports and waterways in agriculture, forestry, and construction (e.g., dike building, habitat restoration) is gaining interest. For such applications, organic matter (OM) must be stable, which can be achieved through soil ripening—a process that transforms waterlogged, anoxic sediment into aerated, soil-like material via drainage and oxidation. This study examines the ripening of mechanically dewatered dredged sediment from the Elbe River around the port of Hamburg, deposited into nine stockpiles (1,000–2,200 m³) managed under different turning frequencies (none, 2×/year, 4×/year) and vegetation management (removed before turning or not). OM stability and microbial activity were assessed over two years using soil respiration, the Tea Bag Index (TBI), and Rock-Eval pyrolysis (RE7S). Proctor compaction tests were performed to ascertain the compactibility of the soil, and shrink-swell behavior was assessed using the Coefficient of Linear Extensibility (COLE). Samples from several decades’ old locations (‘historical sediment’), where dredged sediment had been applied for soil amendment, served to benchmark ripened material. Carbon release and decomposition rates (k) decreased over time (Fig. 1, left), whereas the stabilization factor (S) increased. These trends reflect the depletion of labile OM and a shift toward recalcitrant ones. Respiration in the top layers of stockpiled sediment was higher than in lower layers, reflecting enhanced exposition to atmospheric air, enabling advanced stages of soil ripening. Rock-Eval pyrolysis detected a relative increase in recalcitrant carbon and the Oxygen Index (OI), while the Hydrogen Index (HI), reflecting labile OM, decreased (Fig. 1, middle). Also, the soil physical parameters indicated significant changes in the material over the course of ripening. Proctor density (Fig. 1, right) increased by 13.64% in the control stockpile (SP4) from 1.10 g/cm³ in the initial material (HIP) to 1.25 g/cm³, and higher turning frequencies of the stockpiles led to higher compactibility. COLE values significantly decreased in all stockpiles to values below 0.14 at the latter part of the monitoring period, indicating progressively decreasing shrink–swell behavior. These findings reveal how the combined biological breakdown of organic matter (OM) and mechanical processing enhances the structural and functional properties of dredged sediment for use as an earthen construction material.
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Using dredged material from ports and waterways in agriculture, forestry, and construction (e.g., dike building, habitat restoration) is gaining interest. For such applications, organic matter (OM) must be stable, which can be achieved through soil ripening—a process that transforms waterlogged, anoxic sediment into aerated, soil-like material via drainage and oxidation. This study examines the ripening of mechanically dewatered dredged sediment from the Elbe River around the port of Hamburg, deposited into nine stockpiles (1,000–2,200 m³) managed under different turning frequencies (none, 2×/year, 4×/year) and vegetation management (removed before turning or not). OM stability and microbial activity were assessed over two years using soil respiration, the Tea Bag Index (TBI), and Rock-Eval pyrolysis (RE7S). Proctor compaction tests were performed to ascertain the compactibility of the soil, and shrink-swell behavior was assessed using the Coefficient of Linear Extensibility (COLE). Samples from several decades’ old locations (‘historical sediment’), where dredged sediment had been applied for soil amendment, served to benchmark ripened material. Carbon release and decomposition rates (k) decreased over time (Fig. 1, left), whereas the stabilization factor (S) increased. These trends reflect the depletion of labile OM and a shift toward recalcitrant ones. Respiration in the top layers of stockpiled sediment was higher than in lower layers, reflecting enhanced exposition to atmospheric air, enabling advanced stages of soil ripening. Rock-Eval pyrolysis detected a relative increase in recalcitrant carbon and the Oxygen Index (OI), while the Hydrogen Index (HI), reflecting labile OM, decreased (Fig. 1, middle). Also, the soil physical parameters indicated significant changes in the material over the course of ripening. Proctor density (Fig. 1, right) increased by 13.64% in the control stockpile (SP4) from 1.10 g/cm³ in the initial material (HIP) to 1.25 g/cm³, and higher turning frequencies of the stockpiles led to higher compactibility. COLE values significantly decreased in all stockpiles to values below 0.14 at the latter part of the monitoring period, indicating progressively decreasing shrink–swell behavior. These findings reveal how the combined biological breakdown of organic matter (OM) and mechanical processing enhances the structural and functional properties of dredged sediment for use as an earthen construction material.
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.
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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.
Purpose: The share of microbially degradable sediment organic matter (SOM) and the degradation rate depend, among others, on the intrinsic properties of SOM as well as on the type and concentration of terminal electron acceptors (TEA). Next to its role as TEA, molecular oxygen enhances SOM decay by oxygenase-mediated breakdown of complex organic molecules. This research investigated long-term SOM decay (> 250 days) under aerobic and anaerobic conditions to (1) provide a basis for sediment carbon flux estimates from the River Elbe estuary and (2) assess the potential for carbon burial in relation to redox conditions and dredging interventions. Methods: Long-term aerobic and anaerobic SOM decay in fluid mud, pre-consolidated and consolidated sediment layers was investigated over three years along a transect of ca. 20 km through the Port of Hamburg, starting at the first hydrodynamically determined hotspot of sedimentation after the weir in Geesthacht. Absolute differences between aerobic and anaerobic cumulative carbon mineralization were calculated, as well as their ratio. Findings were correlated to a suite of solids and pore water properties. Results: SOM decay followed first order multi-phase exponential decay kinetics. The ratio between C release under aerobic and anaerobic conditions ranged around 4 in the short-term, converging to a value of 2 in the long term. Strong gradients in absolute C release along the upstream–downstream transect did not reflect in a corresponding gradient of the aerobic-anaerobic ratio. C release was most strongly correlated to the water-soluble organic matter, in particular humic acids. Contact of anaerobically stabilized sediment with the oxygenated water phase induced significant release of carbon. Conclusion: SOM degradability in the study area exhibited strong spatial gradients in relation to the organic matter source gradient but was mainly limited by the high extent of organic matter stabilization. Under these conditions, molecular oxygen as TEA provides little thermodynamic advantage. Carbon-sensitive sediment management, considering SOM reactivity patterns in stratified depositional areas, is a powerful strategy to reduce environmental impacts of dredging measures.
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Purpose: The share of microbially degradable sediment organic matter (SOM) and the degradation rate depend, among others, on the intrinsic properties of SOM as well as on the type and concentration of terminal electron acceptors (TEA). Next to its role as TEA, molecular oxygen enhances SOM decay by oxygenase-mediated breakdown of complex organic molecules. This research investigated long-term SOM decay (> 250 days) under aerobic and anaerobic conditions to (1) provide a basis for sediment carbon flux estimates from the River Elbe estuary and (2) assess the potential for carbon burial in relation to redox conditions and dredging interventions.
Methods: Long-term aerobic and anaerobic SOM decay in fluid mud, pre-consolidated and consolidated sediment layers was investigated over three years along a transect of ca. 20 km through the Port of Hamburg, starting at the first hydrodynamically determined hotspot of sedimentation after the weir in Geesthacht. Absolute differences between aerobic and anaerobic cumulative carbon mineralization were calculated, as well as their ratio. Findings were correlated to a suite of solids and pore water properties.
Results: SOM decay followed first order multi-phase exponential decay kinetics. The ratio between C release under aerobic and anaerobic conditions ranged around 4 in the short-term, converging to a value of 2 in the long term. Strong gradients in absolute C release along the upstream–downstream transect did not reflect in a corresponding gradient of the aerobic-anaerobic ratio. C release was most strongly correlated to the water-soluble organic matter, in particular humic acids. Contact of anaerobically stabilized sediment with the oxygenated water phase induced significant release of carbon.
Conclusion: SOM degradability in the study area exhibited strong spatial gradients in relation to the organic matter source gradient but was mainly limited by the high extent of organic matter stabilization. Under these conditions, molecular oxygen as TEA provides little thermodynamic advantage. Carbon-sensitive sediment management, considering SOM reactivity patterns in stratified depositional areas, is a powerful strategy to reduce environmental impacts of dredging measures.
Purpose
Recirculation dredging is a port maintenance concept developed in the Port of Emden, Germany to create a navigable fluid mud layer. This study investigates the effects of recirculation on key sediment properties, including density, yield stress, and oxygen concentration.
Methods
Six field monitoring surveys were carried out at two locations at different times of the year to assess changes before and after recirculation. Bathymetry, bulk density, yield stress, and oxygen concentration profiles were measured in situ. The settling properties and oxygen concentration levels on collected fluid mud samples were analyzed in the laboratory.
Results
The investigation reveals minimal changes in the density of recirculated fluid mud. However, the post-recirculation measurements showed a decrease in yield stress, ranging from 18 to 51% at Große Seeschleuse (GS) and 36% to 52% at Industriehafen (IH). The yield stress and density vary depending on the frequency of dredging. After structural density (1166 kg m−3 in GS and 1173 kg m−3 in IH), the yield stress of fluid mud increased exponentially. Therefore, monitoring of the yield stress is important for recirculation. A slight increase in oxygen concentration was observed post-recirculation, especially during winter. Yet, the rapid decline in oxygen levels post-mixing in the laboratory showed that sustaining long-term elevated oxygenation levels is not feasible by recirculation dredging alone.
Conclusions
The findings highlight the effectiveness of the recirculation on the yield stress, density, and oxygen concentration of fluid mud and illustrate the importance of considering both density and yield stress in sediment management practices. Future research should address the temporal evolution of density, yield stress, and oxygen levels following a dredging intervention and the influence of extracellular polymeric substances (EPS) and organic matter decay on sediment behavior. ...
Recirculation dredging is a port maintenance concept developed in the Port of Emden, Germany to create a navigable fluid mud layer. This study investigates the effects of recirculation on key sediment properties, including density, yield stress, and oxygen concentration.
Methods
Six field monitoring surveys were carried out at two locations at different times of the year to assess changes before and after recirculation. Bathymetry, bulk density, yield stress, and oxygen concentration profiles were measured in situ. The settling properties and oxygen concentration levels on collected fluid mud samples were analyzed in the laboratory.
Results
The investigation reveals minimal changes in the density of recirculated fluid mud. However, the post-recirculation measurements showed a decrease in yield stress, ranging from 18 to 51% at Große Seeschleuse (GS) and 36% to 52% at Industriehafen (IH). The yield stress and density vary depending on the frequency of dredging. After structural density (1166 kg m−3 in GS and 1173 kg m−3 in IH), the yield stress of fluid mud increased exponentially. Therefore, monitoring of the yield stress is important for recirculation. A slight increase in oxygen concentration was observed post-recirculation, especially during winter. Yet, the rapid decline in oxygen levels post-mixing in the laboratory showed that sustaining long-term elevated oxygenation levels is not feasible by recirculation dredging alone.
Conclusions
The findings highlight the effectiveness of the recirculation on the yield stress, density, and oxygen concentration of fluid mud and illustrate the importance of considering both density and yield stress in sediment management practices. Future research should address the temporal evolution of density, yield stress, and oxygen levels following a dredging intervention and the influence of extracellular polymeric substances (EPS) and organic matter decay on sediment behavior. ...
Purpose
Recirculation dredging is a port maintenance concept developed in the Port of Emden, Germany to create a navigable fluid mud layer. This study investigates the effects of recirculation on key sediment properties, including density, yield stress, and oxygen concentration.
Methods
Six field monitoring surveys were carried out at two locations at different times of the year to assess changes before and after recirculation. Bathymetry, bulk density, yield stress, and oxygen concentration profiles were measured in situ. The settling properties and oxygen concentration levels on collected fluid mud samples were analyzed in the laboratory.
Results
The investigation reveals minimal changes in the density of recirculated fluid mud. However, the post-recirculation measurements showed a decrease in yield stress, ranging from 18 to 51% at Große Seeschleuse (GS) and 36% to 52% at Industriehafen (IH). The yield stress and density vary depending on the frequency of dredging. After structural density (1166 kg m−3 in GS and 1173 kg m−3 in IH), the yield stress of fluid mud increased exponentially. Therefore, monitoring of the yield stress is important for recirculation. A slight increase in oxygen concentration was observed post-recirculation, especially during winter. Yet, the rapid decline in oxygen levels post-mixing in the laboratory showed that sustaining long-term elevated oxygenation levels is not feasible by recirculation dredging alone.
Conclusions
The findings highlight the effectiveness of the recirculation on the yield stress, density, and oxygen concentration of fluid mud and illustrate the importance of considering both density and yield stress in sediment management practices. Future research should address the temporal evolution of density, yield stress, and oxygen levels following a dredging intervention and the influence of extracellular polymeric substances (EPS) and organic matter decay on sediment behavior.
Recirculation dredging is a port maintenance concept developed in the Port of Emden, Germany to create a navigable fluid mud layer. This study investigates the effects of recirculation on key sediment properties, including density, yield stress, and oxygen concentration.
Methods
Six field monitoring surveys were carried out at two locations at different times of the year to assess changes before and after recirculation. Bathymetry, bulk density, yield stress, and oxygen concentration profiles were measured in situ. The settling properties and oxygen concentration levels on collected fluid mud samples were analyzed in the laboratory.
Results
The investigation reveals minimal changes in the density of recirculated fluid mud. However, the post-recirculation measurements showed a decrease in yield stress, ranging from 18 to 51% at Große Seeschleuse (GS) and 36% to 52% at Industriehafen (IH). The yield stress and density vary depending on the frequency of dredging. After structural density (1166 kg m−3 in GS and 1173 kg m−3 in IH), the yield stress of fluid mud increased exponentially. Therefore, monitoring of the yield stress is important for recirculation. A slight increase in oxygen concentration was observed post-recirculation, especially during winter. Yet, the rapid decline in oxygen levels post-mixing in the laboratory showed that sustaining long-term elevated oxygenation levels is not feasible by recirculation dredging alone.
Conclusions
The findings highlight the effectiveness of the recirculation on the yield stress, density, and oxygen concentration of fluid mud and illustrate the importance of considering both density and yield stress in sediment management practices. Future research should address the temporal evolution of density, yield stress, and oxygen levels following a dredging intervention and the influence of extracellular polymeric substances (EPS) and organic matter decay on sediment behavior.
Journal article
(2024)
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J.M. van den Brink, H. Scharff, B. Steinert, S. Melchior, M. Hrachowitz, J. Heimovaara, J. Gebert
This study quantifies the field hydraulic performance of a dual-functionality landfill cover, combining microbial methane oxidation with water diversion using a capillary barrier. The investigated 500 m2 test field, constructed on a landfill in the Netherlands, consisted of a cover soil optimised for methane oxidation, underlain by a sandy capillary layer and a gravelly capillary block. Outflows from these layers were measured between 2009 and 2023. Average precipitation was 848 mm/a, evapotranspiration, diverted infiltration and breakthrough amounted to 504 (59.4 %), 282 (33.3 %) and 62 (7.3 %) mm/a, respectively. On average, the capillary barrier diverted 82 % of the inflow into the capillary layer. Breakthrough occurred mainly from October to March when evapotranspiration was low and the maximum water storage capacity of the cover soil was reached. During this period, inflow into the capillary barrier exceeded its diversion capacity, caused by the relatively high hydraulic conductivity of the cover soil due to its optimisation for gas transport. The diversion capacity declined drastically in the year after construction and increased again afterwards. This was attributed to suffusion of sand from the capillary layer into the capillary block and subsequent washout to greater depths or the influence of iron precipitates at the bottom of the capillary layer. The effect of a more finely grained methane oxidation layer on the hydraulic and methane oxidation performance should be investigated further. These measures could further improve the combined performance of the dual functionality landfill cover system under the given conditions of a temperate climate.
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This study quantifies the field hydraulic performance of a dual-functionality landfill cover, combining microbial methane oxidation with water diversion using a capillary barrier. The investigated 500 m2 test field, constructed on a landfill in the Netherlands, consisted of a cover soil optimised for methane oxidation, underlain by a sandy capillary layer and a gravelly capillary block. Outflows from these layers were measured between 2009 and 2023. Average precipitation was 848 mm/a, evapotranspiration, diverted infiltration and breakthrough amounted to 504 (59.4 %), 282 (33.3 %) and 62 (7.3 %) mm/a, respectively. On average, the capillary barrier diverted 82 % of the inflow into the capillary layer. Breakthrough occurred mainly from October to March when evapotranspiration was low and the maximum water storage capacity of the cover soil was reached. During this period, inflow into the capillary barrier exceeded its diversion capacity, caused by the relatively high hydraulic conductivity of the cover soil due to its optimisation for gas transport. The diversion capacity declined drastically in the year after construction and increased again afterwards. This was attributed to suffusion of sand from the capillary layer into the capillary block and subsequent washout to greater depths or the influence of iron precipitates at the bottom of the capillary layer. The effect of a more finely grained methane oxidation layer on the hydraulic and methane oxidation performance should be investigated further. These measures could further improve the combined performance of the dual functionality landfill cover system under the given conditions of a temperate climate.
Conference paper
(2023)
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Cristhian F. Andrade, Anne-Catherine Dieudonné, Julia Gebert, Timo Heimovaara
Nitrogen undergoes multiple biogeochemical transformations during waste degradation, which depend on speciation, prevailing geochemical boundary conditions, and waste surface properties. This study developed a waste biodegradation model with high flexibility in accommodating reaction pathways to assess different process dynamics. The model was applied to landfill simulator reactors operating anaerobically. Model results show that dilution with adsorption matches the experimental dissolved NH4+ concentration (C/N=25) at the early experimental stages. Also, NH4+ binding decreases
due to competition with Ca2+, and the model better captures the dissolved NH4+ behavior when CaSO4 is present in solution. Mass removal due to sampling and posterior dilution are the main mechanisms to reduce NH4+ concentration in the leachate. The model highlights the role of nitrogen sorption as the main
mechanism for nitrogen accumulation in the solid phase of municipal solid waste. ...
due to competition with Ca2+, and the model better captures the dissolved NH4+ behavior when CaSO4 is present in solution. Mass removal due to sampling and posterior dilution are the main mechanisms to reduce NH4+ concentration in the leachate. The model highlights the role of nitrogen sorption as the main
mechanism for nitrogen accumulation in the solid phase of municipal solid waste. ...
Nitrogen undergoes multiple biogeochemical transformations during waste degradation, which depend on speciation, prevailing geochemical boundary conditions, and waste surface properties. This study developed a waste biodegradation model with high flexibility in accommodating reaction pathways to assess different process dynamics. The model was applied to landfill simulator reactors operating anaerobically. Model results show that dilution with adsorption matches the experimental dissolved NH4+ concentration (C/N=25) at the early experimental stages. Also, NH4+ binding decreases
due to competition with Ca2+, and the model better captures the dissolved NH4+ behavior when CaSO4 is present in solution. Mass removal due to sampling and posterior dilution are the main mechanisms to reduce NH4+ concentration in the leachate. The model highlights the role of nitrogen sorption as the main
mechanism for nitrogen accumulation in the solid phase of municipal solid waste.
due to competition with Ca2+, and the model better captures the dissolved NH4+ behavior when CaSO4 is present in solution. Mass removal due to sampling and posterior dilution are the main mechanisms to reduce NH4+ concentration in the leachate. The model highlights the role of nitrogen sorption as the main
mechanism for nitrogen accumulation in the solid phase of municipal solid waste.
Degradability of organic matter in river sediments differs in relation to origin and age. In order to explain previously observed spatial patterns of organic matter degradability and stabilization, this study investigated sediment organic matter (SOM) properties along a tidal Elbe river transect using dissolved organic matter (DOM) fractions, density fractions, carbon stable isotopes and thermometric pyrolysis (Rock-Eval 6). These properties were linked to SOM decay rates and biological indicators such as chlorophyll a and silicic acid in the water phase, and sediment-bound extracellular polymeric substances (EPS), microbial biomass and oxygen consumption. Sediment source gradients were established using the concentration of Zn in the fraction < 20 μm as proxy. The specific Zn concentration showed that the most upstream location was nourished primarily by upstream fluviatile sediments while the other locations carried a downstream signature. The upstream location was also characterised by the highest concentrations of chlorophyll a, microbial biomass, silicic acid, EPS, humic acids and hydrophilic DOM, the most negative δ13C signature and by the highest oxygen consumption rate, with decreasing trends towards downstream locations. This trend was also evident in the decreasing SOM lability from upstream to downstream, an increasing share of total SOM found in the acid-base-extractable fractions and a
decreasing share of carbon in the light density fractions. Thermometric pyrolysis revealed the highest H-index(easily degradable SOM) for the most upstream location and the ratio of the I-index (immature SOM) to the R-
index (refractory SOM) to correlate positively with measured SOM decay rates. This study suggests that spatial patterns of SOM degradability can be explained by a source gradient, with young organic matter entering the system from upstream from predominantly biogenic sources, while down-stream sources (North Sea sediment) deliver more refractory SOM that is stabilized in organo-mineral associations to a higher extent. In the investigated sediments, dissolved organic matter represented 0.23–1.20% of the total organic carbon (TOC) from anaerobically degradable SOM, while 4.10–11.46% TOC was liberated as CO2 and CH4 after long-term incubation (250 days). Thermometric pyrolysis is shown to serve as a useful proxy for SOM degradability in river sediments, with the Hydrogen-Index (HI) correlating well with degradability and the relationship between the I-index and R-index changing consistently towards lower I-indices and higher R-indices with an increasing degree of SOM stabilization.
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decreasing share of carbon in the light density fractions. Thermometric pyrolysis revealed the highest H-index(easily degradable SOM) for the most upstream location and the ratio of the I-index (immature SOM) to the R-
index (refractory SOM) to correlate positively with measured SOM decay rates. This study suggests that spatial patterns of SOM degradability can be explained by a source gradient, with young organic matter entering the system from upstream from predominantly biogenic sources, while down-stream sources (North Sea sediment) deliver more refractory SOM that is stabilized in organo-mineral associations to a higher extent. In the investigated sediments, dissolved organic matter represented 0.23–1.20% of the total organic carbon (TOC) from anaerobically degradable SOM, while 4.10–11.46% TOC was liberated as CO2 and CH4 after long-term incubation (250 days). Thermometric pyrolysis is shown to serve as a useful proxy for SOM degradability in river sediments, with the Hydrogen-Index (HI) correlating well with degradability and the relationship between the I-index and R-index changing consistently towards lower I-indices and higher R-indices with an increasing degree of SOM stabilization.
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Degradability of organic matter in river sediments differs in relation to origin and age. In order to explain previously observed spatial patterns of organic matter degradability and stabilization, this study investigated sediment organic matter (SOM) properties along a tidal Elbe river transect using dissolved organic matter (DOM) fractions, density fractions, carbon stable isotopes and thermometric pyrolysis (Rock-Eval 6). These properties were linked to SOM decay rates and biological indicators such as chlorophyll a and silicic acid in the water phase, and sediment-bound extracellular polymeric substances (EPS), microbial biomass and oxygen consumption. Sediment source gradients were established using the concentration of Zn in the fraction < 20 μm as proxy. The specific Zn concentration showed that the most upstream location was nourished primarily by upstream fluviatile sediments while the other locations carried a downstream signature. The upstream location was also characterised by the highest concentrations of chlorophyll a, microbial biomass, silicic acid, EPS, humic acids and hydrophilic DOM, the most negative δ13C signature and by the highest oxygen consumption rate, with decreasing trends towards downstream locations. This trend was also evident in the decreasing SOM lability from upstream to downstream, an increasing share of total SOM found in the acid-base-extractable fractions and a
decreasing share of carbon in the light density fractions. Thermometric pyrolysis revealed the highest H-index(easily degradable SOM) for the most upstream location and the ratio of the I-index (immature SOM) to the R-
index (refractory SOM) to correlate positively with measured SOM decay rates. This study suggests that spatial patterns of SOM degradability can be explained by a source gradient, with young organic matter entering the system from upstream from predominantly biogenic sources, while down-stream sources (North Sea sediment) deliver more refractory SOM that is stabilized in organo-mineral associations to a higher extent. In the investigated sediments, dissolved organic matter represented 0.23–1.20% of the total organic carbon (TOC) from anaerobically degradable SOM, while 4.10–11.46% TOC was liberated as CO2 and CH4 after long-term incubation (250 days). Thermometric pyrolysis is shown to serve as a useful proxy for SOM degradability in river sediments, with the Hydrogen-Index (HI) correlating well with degradability and the relationship between the I-index and R-index changing consistently towards lower I-indices and higher R-indices with an increasing degree of SOM stabilization.
Conference paper
(2023)
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Tristan Rees-White, Merel Feenstra, Twan Kanen, Richard Beaven, Julia Gebert
The recirculation and infiltration of leachate in landfills may be carried out to facilitate the flushing of contaminants and accelerate the stabilisation of waste. Flushing contaminants through recirculation relies on the movement of fluids through the landfill body to basal drains, which will predominantly be driven by gravity. Leachate recirculation and infiltration measures commenced at de Kragge II landfill (Bergen op Zoom, The Netherlands) in March 2018. Up to 90 m3/day of treated leachate is recirculated into the top of a 20 m deep, 5 ha landfill cell through 14 horizontal drains installed at the surface. Poor connectivity between the waste and the basal drainage system has resulted in saturated conditions forming in the lower 7-8 m of the landfill. Knowledge about the leachate flow within the waste body is essential for evaluating the success of the stabilisation measures. To investigate the flow regime within the saturated waste, 22 Single Borehole Dilution tests were carried out in 13 piezometers at different depths, between 8.4 and 18.1 m below ground level, and locations across the landfill cell. Tests were repeated in a number of the piezometers to demonstrate repeatability. Flow was measured in all piezometers. Calculated Darcy flow velocities ranged between 0.01 and 1.02 m/day, with the highest velocities measured in the deepest piezometers. Four tests were carried out in one nest of piezometers installed at different depths, with the leachate recirculation system switched off for two days prior to and during the test. Although flows were somewhat higher in two of the piezometers, it was not possible to conclude whether the infiltration of leachate significantly influences flow.
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The recirculation and infiltration of leachate in landfills may be carried out to facilitate the flushing of contaminants and accelerate the stabilisation of waste. Flushing contaminants through recirculation relies on the movement of fluids through the landfill body to basal drains, which will predominantly be driven by gravity. Leachate recirculation and infiltration measures commenced at de Kragge II landfill (Bergen op Zoom, The Netherlands) in March 2018. Up to 90 m3/day of treated leachate is recirculated into the top of a 20 m deep, 5 ha landfill cell through 14 horizontal drains installed at the surface. Poor connectivity between the waste and the basal drainage system has resulted in saturated conditions forming in the lower 7-8 m of the landfill. Knowledge about the leachate flow within the waste body is essential for evaluating the success of the stabilisation measures. To investigate the flow regime within the saturated waste, 22 Single Borehole Dilution tests were carried out in 13 piezometers at different depths, between 8.4 and 18.1 m below ground level, and locations across the landfill cell. Tests were repeated in a number of the piezometers to demonstrate repeatability. Flow was measured in all piezometers. Calculated Darcy flow velocities ranged between 0.01 and 1.02 m/day, with the highest velocities measured in the deepest piezometers. Four tests were carried out in one nest of piezometers installed at different depths, with the leachate recirculation system switched off for two days prior to and during the test. Although flows were somewhat higher in two of the piezometers, it was not possible to conclude whether the infiltration of leachate significantly influences flow.
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.
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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.
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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.
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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.
Conference paper
(2023)
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L. Duarte Campos, T. Rees-White, R. Beaven, C. Osorio, H. Lammen, J. Gebert
This paper presents the preliminary results of field trials conducted to investigate the air permeability of waste at the Braambergen landfill located near the city of Almere, the Netherlands. Pressure variations were monitored in surrounding wells during air extraction tests using differential pressure transducers. The magnitude of the pressure response to gas abstraction indicates suitability of the method to investigate waste permeability and the swiftness of the pressure response indicated good connectivity within the investigated well field. The obtained air permeability values showed a trend where permeability decreased as the distance between two wells increased, suggesting higher permeability in closer proximity to a well. Although the values are comparable to those reported in other landfills, the differences can be explained by the influence of site-specific factors on permeability.
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This paper presents the preliminary results of field trials conducted to investigate the air permeability of waste at the Braambergen landfill located near the city of Almere, the Netherlands. Pressure variations were monitored in surrounding wells during air extraction tests using differential pressure transducers. The magnitude of the pressure response to gas abstraction indicates suitability of the method to investigate waste permeability and the swiftness of the pressure response indicated good connectivity within the investigated well field. The obtained air permeability values showed a trend where permeability decreased as the distance between two wells increased, suggesting higher permeability in closer proximity to a well. Although the values are comparable to those reported in other landfills, the differences can be explained by the influence of site-specific factors on permeability.
Journal article
(2023)
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Susan C. Yi, Anne Heijbroek, Luis Cutz, Stephanie Pillay, Wiebren de Jong, Thomas Abeel, Julia Gebert
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.
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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.
Abstract
(2023)
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Alex Kirichek, Atha Bampatzeliou, Julia Gebert, Claire Chassagne, Nino Ohle, Uli Schmekel