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. ... Read more

Low-pressure aeration is a sustainable landfill management technique in which atmospheric air is introduced to the waste body with the aim of promoting aerobic respiration and thereby speeding up waste stabilization. This strategy has been implemented at Braambergen, a pilot landfill in the Netherlands, for several years. Landfill operators and regulators are eager to determine the efficacy of this intervention. In this thesis, several novel testing methods were implemented to characterize the gas flow properties of the pilot landfill and evaluate the significance of preferential pathways, which are considered a limiting factor in landfill aeration. The test methods were also evaluated for their utility in landfill monitoring.

Pressure field tests (PFTs) were used in combination with two gas flow models to quantify the gas permeability of the waste body. Partitioning gas tracer tests (PGTTs) were used to evaluate the saturation of the waste body. Additionally, a dual porosity model was applied to estimate the immobile gas fraction, gas velocity, dispersion coefficient, and mass transfer rate. Finally, gas push-pull tests (GPPTs) were used to calculate the oxygen consumption rate.

The results showed that PFTs could be used to estimate gas permeability anisotropy and monitor the high-permeability pathways, but the method did not capture the differences between aerobic and anaerobic regions of the waste body. PGTTs seemed to better represent these differences, but there were major problems with the quality of the data and the applicability of the dual porosity model. If these issues are resolved, the method could be of great use to landfill operators. GPPTs were successfully used to estimate respiration rates,
but the methodology needs improvement. Not enough successful GPPTs were performed to determine their relationship to other test methods. ... Read more

The growing demand for sustainable construction materials has prompted interest in reusing dredged sediments as an alternative to traditional raw materials in dike construction. Before they can be reused, sediments must undergo the lengthy ripening process, during which they are transformed into stable soil. Accelerating this transformation could significantly improve the feasibility of sediment reuse. This study investigates whether biochar amendment can enhance the biophysicochemical ripening of dredged sediments, focusing on the influence of biochar application rate and particle size.

Dredged material from the port of Hamburg, Germany, that was dewatered and processed at the METHA plant, was mixed with biochar produced by Bio Energy Netherlands from the gasification of wood waste at 800-1000°C for 90-120 minutes. The mixtures contained biochar with varying application rates (2%, 4%, 6%) and particle sizes (<2 mm, 2-5 mm, >5 mm). Over the course of 15 weeks of field ripening, the sediment-biochar mixtures were exposed to natural weather conditions and turned weekly. Biochar amendment introduced additional porosity which increased water holding capacity by 33-72% compared to the control after 15 weeks of ripening, resulting in values of 24-72% DW. The oven-dried COLE, ranged from of 2.2 to 5.4% which represents a decrease of up to 54% relative to the unamended sediments. This improvement can be attributed to the non-plastic behavior of biochar and explains the decreasing shrinkage observed with an increasing application rate. Increasing particle size was correlated to decreasing shrinkage (p <0.05) which could be due to the interrupting effect of coarse biochar particles on tensile load propagation in the rods. A qualitative assessment of the structure development of the experimental variants suggests an acceleration of structure formation with higher biochar application rate and larger particle size when combined with weekly turning. This resulted in a faster breakdown of the dense and platy METHA material into smaller and more aerated aggregates. Overall, the physical ripening of the dredged material was improved with the addition of biochar at increasing application rates and particle size, which promoted a faster stabilization of sediment aggregates and enhanced physical properties beneficial for construction applications.

The occurrence of sulfur oxidation, the main chemical ripening reaction, was evidenced by a loss in the total sulfur content of samples and an increasing electrical conductivity during dry periods. The pH was expected to decrease as a result of the release of protons from this reaction, however this was not observed. Instead, increasing biochar application rates was correlated to a higher pH (p <0.05) and was evidence of the material's buffering capacity which can be attributed to its high functional group and mineral content. The total sulfur content reduced on average by 5% and 22% in the amended samples and the control, and this smaller decrease compared to the control could be explained either by a slower chemical ripening in amended sediments or by measurement limitations. Furthermore, the evolution of electrical conductivity over the 15 weeks of field ripening evidenced the accumulation of chemical reaction products in dry periods.

The influence of biochar on sediment physical and chemical properties, including the increased pore structure, water holding capacity, aeration and buffering capacity, all contributed to creating conditions favorable to microbial activity. A priming effect of biochar application could be observed in the first six weeks of ripening, with high respiration rates, high decomposition rates, and decreasing stabilization of organic matter. In this period, total organic carbon content decreased on average by 30\% in amended samples, compared to only 6% in the control. At the same time, nitrogen content decreased on average by 13% in the samples with biochar, further confirming the high microbial activity. This was followed by a period of decreasing microbial activity until the end of the experiment, which was marked by 14-32% lower respiratory carbon release of the amended samples compared to the control, decreasing decomposition rates and increasing stabilization of organic matter. Thus, biochar application accelerated the decomposition of labile carbon and enhanced the biological stabilization of organic matter in sediments.

These findings suggest that biochar amendment can significantly improve sediment ripening processes and can result in a material with properties desirable for dike construction. ... Read more

Rising sea levels, combined with land subsidence, have heightened the concerns for safeguarding the coast and waterways of Europe. This effort will require a large amount of strained resources, such as marsh soil, which is becoming increasingly difficult to source. A promising alternative is utilizing the vast amount of dredged sediments extracted by ports each year. Studies have already been conducted on the feasibility of using such a material in dike construction and reinforcements, and guidelines have been developed. Treatment of the material is recommended before application, usually through stockpiling. Although this is widely accepted as a suitable method to treat sediments, the potential for optimizing it has been a subject of few studies. Therefore, focusing on physical ripening, this thesis set out to investigate the evolution of tensile strength and crack formation over time under different stockpile management practices. This research was motivated by the observation that unripened material tends to develop shrinkage cracks when applied in a dike, which creates preferential channels for water to flow through. An important factor influencing the formation of cracks is the material’s tensile strength. Other aspects investigated were the Coefficient of Linear Extensibility (COLE) , which characterizes the shrinkage behavior, and the Atterberg limits. The latter is an important parameter to determine the suitability of a material to be used in dikes. This thesis investigated mechanically de-watered dredged sediments processed in the METHA plant in Hamburg. After processing, the sediments were stockpiled (1,000-2,200 m3) with varying turning rates (none, 2x per year, and 4x per year) and vegetation management (removed before turning or not). Samples were collected over approximately two years, covering ripening times from six months to two and a half years. The results showed that tensile strength increased significantly after one turning event to around 105% of the original material, likely due to aeration improving structural stability. However, subsequent turning events led to a drop in tensile strength. SP7 and SP9 (4x turning per year) exhibited tensile strength 30 % lower than the original material after two years of ripening, suggesting that the repeated mechanical breakdown degraded soil structure. At the end of the investigated period, tensile strength was found to be highest in the control stockpile, where no turning was applied and vegetation was allowed to grow. Higher turning frequency, however, greatly benefited the compactability of the samples. When tensile strength tests were carried out compacting the samples to 95 % of their Proctor density, an increase in tensile strength of 430 % was found in the sample with the highest Proctor density (SP-9). In comparison, SP-4 (control) exhibited an increase of 280 % at 95 % Proctor density. COLE values stabilized after two years to values approximately half of the original material. This indicates reduced shrinkage potential and, therefore, a lower tendency for crack formation in ripened sediments. Crack formation experiments exhibited no consistent pattern across different stockpiling methods and ripening periods. Instead, the most influential factor appeared to be the reduction in shrinkage due to ripening. Crack Intensity Factor (CIF) and average crack width results were consistently lower in the stockpiled material than in the unripened original material. This was likely caused by the reduced shrinkage behavior observed in COLE tests. Finally, the results of the Atterberg limits determination showed that the material is unsuitable for use in the top layer of a dike, but is still appropriate for use as core material. Overall, the findings highlight that limited turning preserves tensile strength, while higher turning frequencies improve compactability. Under field conditions, however, the improved compactability also greatly benefits tensile strength, outweighing the structural instability caused by mechanical breakdown. Ripening also significantly reduces shrinkage potential, thereby decreasing crack formation behavior. These insights suggest a higher turning frequency is the best method for managing dredged sediment, when only tensile strength and crack formation are concerned. ... Read more

In the Port of Emden, maintenance of the nautical depth is carried out by continuous re-circulation of sediment, creating a navigable fluid mud layer in the water and thereby facilitating safe navigation for ships. The sediment naturally contains organic matter, which to a certain extent is degradable by sediment microorganisms. Depending on the availability of oxygen, the degradation process generates carbon dioxide only (aerobic conditions) or methane and carbon dioxide (anaerobic conditions). This thesis aims to quantify the production of carbon dioxide and methane from fluid mud in the Port of Emden and analyze its seasonal variability to support carbon footprinting of sediment management activities. In this thesis, an experiment was carried out to determine the carbon production of Emden samples at different temperatures. Results were used and, based on the fluid mud temperatures throughout the year, monthly carbon production was calculated. These values were adjusted for seasonal variations in organic matter availability and finally extrapolated to give the total monthly carbon production for the port. Using data from previous research, upper and lower bounds for this production were found. The findings indicate that carbon production in the Port of Emden, due to micro-organisms in the fluid mud layer, varies significantly over the year. Specifically, the generated carbon was found to differ between 243 tons in February and 958 tons in August, with the upper bound being 7.2 times greater than these values and the lower bound 1.3 times smaller. From April until October, carbon generation was found to be considerably higher than from November until March, due to higher water temperatures and likely a greater availability of organic matter. Finally, the carbon production under aerobic conditions was found to be 2.7 to 2.8 times greater than under current conditions, with similar seasonal variability. Limitations of this thesis include assumptions about uniform seasonal scaling of organic matter availability and incomplete data on fluid mud temperature variations across the year. Future research could address these limitations by gathering and incorporating more data on these parameters. Finally, future studies should focus on applying the findings of this thesis to explore strategies for reducing the carbon footprint of sediment management activities. ... Read more

The long-term environmental management of closed landfills presents significant challenges due to persistent uncertainty regarding residual contamination and pollutant release processes. While conventional aftercare practices, such as those mandated by the European Landfill Directive, focus on emission monitoring and maintenance of engineered barriers, they often overlook the complex subsurface dynamics of pollutant mobility within landfill waste bodies. Accurately quantifying the internal releasable pollutant content, referred to as the emission potential, is essential for developing realistic and scientifically-grounded aftercare strategies.
In this dissertation, I present an integrated framework to estimate and predict landfill emission potentials by combining stochastic modeling, Bayesian uncertainty quantification, data assimilation, and hydrogeophysical measurements. The research introduces a stochastic Lagrangian-based travel time modeling approach to simulate the heterogeneous water flow and solute transport within landfill bodies. This method, unlike traditional grid-based models, captures preferential flow phenomena and accommodates the spatial variability inherent in landfill waste structures.
The model calibration is performed using Bayesian inference, employing long-term observational data of leachate production and quality from the Braambergen landfill in the Netherlands. This probabilistic calibration explicitly quantifies uncertainties in model parameters and outputs, providing more credible risk assessments and long-term predictions of leachate emissions.
Recognizing the risk of error accumulation in history-matching methods, I further implement data assimilation techniques, notably the Weakly Coupled Particle Filter (WCPF) and a hybrid Particle Filter–Markov Chain Monte Carlo (PF-MCMC) method. These approaches enable sequential updating of model parameters and system states as new data become available, improving the predictive performance and reducing uncertainty over time. The PF-MCMC method, in particular, can estimate parameters and hidden processes, which is very helpful for understanding the dynamics in the landfill.
To further enhance the accuracy of emission potential estimations, the framework integrates hydrogeophysical data obtained through Electrical Resistivity Tomography (ERT). Using a Bayesian evidential learning approach, resistivity measurements are directly mapped into probabilistic water storage estimates within landfill waste bodies. This additional constraint strengthens the characterization of subsurface hydrological conditions, distinguishing between leachable and isolated water fractions.
The dissertation is structured across six chapters, beginning with an overview of the landfill aftercare problem, followed by the development of the stochastic modeling framework, the application of particle filtering and PF-MCMC, the incorporation of ERT data through Bayesian evidential learning, and concluding with a synthesis of findings and recommendations for future research.
Overall, this work advances the scientific understanding of landfill emission dynamics by offering a unified methodological framework that integrates stochastic modeling, data assimilation, and hydrogeophysical surveying. The contributions herein support the development of more robust, data-driven, and cost-effective strategies for landfill aftercare, ensuring long-term environmental protection and sustainability. ... Read more

Sewage sludge production poses a significant global challenge, with anaerobic digestion (AD) being the most widely employed method to manage this issue. However, since hydrolysis is the rate-limiting step in AD, pretreatment of sludge can aid in enhancing the process.
The current study aimed to evaluate sludge solubilization and gas production—particularly bio-hydrogen (bio-H₂) production—following low-temperature thermal pretreatment (LTTP) at 55°C. This thesis replicates the full-scale setup of the Themista® system, which employs a two-stage thermal pretreatment process with 55°C and 70°C as the heating stages, operating in a semi-continuous mode. Four distinct pretreatment experiments were conducted to assess sludge solubilization and gas production: LTTP , LTTP with H₂O₂ at 55°C, LTTP with FeCl₂ at 55°C, and LTTP with both H₂O₂ and FeCl₂ at 55°C.
The results demonstrated that both thermo-chemical and thermal pretreatments exhibited similar soluble chemical oxygen demand(sCOD) release patterns. A shift from tightly bound to more soluble fractions of extracellular polymeric substances (EPS) was observed post-pretreatment. Gas production was noted only at 55°C across all conditions, with bio-H₂ being produced under each pretreatment. Notably, thermal pretreatment with FeCl₂ resulted in an average H₂ COD/tCOD ratio that was 24 times higher than that of thermal pretreatment alone. However, the average sludge to gas COD percentage for all pretreatments remained below 0.06%, with the highest of 0.1% observed in the thermal treatment with FeCl₂. Additionally, significant increases in BMP and a sludge COD to CH₄ conversion percentage of 75% were observed post-treatment with thermal pretreatment combined with FeCl₂ ... Read more

The Limpopo Lipadi Reserve has the difficult task of restoring its natural ecosystems and protecting them from future challenges. The increasing occurrence of droughts due to climate change and the historical use of this land for cattle farming contribute to concerns about the future availability of water for animals, vegetation and staff, as well as the overall health of the soil. By establishing a water balance and investigating soil health, conclusions could be drawn about the current state of the Reserve’s soil and water resources and recommendations made for future research. The parameters of the water balance were defined by combining the literature and the results of field experiments. A climate change model was applied to the water balance to assess how the Reserve will be affected by changes in precipitation and temperatures. Soil sampling was also undertaken at four characteristic sites in the Reserve to assess the impact of bush clearing on soil health and aquifer recharge through changes in physical, biological and hydraulic properties.
The results of the water balance and the different simulated scenarios show that: 1) the aquifers can currently be accounted as reliable when considered as a total available resource for the entire area of the Reserve; 2) when the bush clearing scenario was simulated, it was found that doubling the amount of clearing has a minor impact and only when 50 % of the reserve is cleared the impact becomes significant; 3) due to climate change and its impact on ecosystems, it was found that there will be an intensification of the hydrological cycle (wetter, hotter summer) with an increased seasonality. However, the results of this scenario indicated that there will be no drastic changes in the main pattern of water dynamics in the next 25 years and therefore no immediate threat to the available groundwater storage.
In carrying out the soil characterisation tests, it was noted that 8 different soil types were being studied, which would certainly include a wider range of values for soil properties. However, looking at the effects of bush clearing and considering the different types of soil, the results showed that there was indeed an outcome in the treated areas. For most of the studied sites, it was consistently found that bulk density had increased in the cleared areas, while porosity levels, soil moisture and organic matter decomposition rate had decreased. It was also discovered that as a side effect of bush clearing, insects such as termites were present, which played a role in some of the soil processes. Furthermore, no clear relationship with clearance status could be observed for hydraulic conductivity. These results were then used in a multi-criteria analysis to assess the health of the soils studied. This assessment showed that, overall and for the specific purpose of the research undertaken, all the soils analysed could be classified as ’healthy’ to sustain the current environmental practices of the Reserve, even after clearing was performed.
Although the results presented in this report take into account the current status of the Reserve, it is noted that there may be differences when different time frames are considered. The results provide valuable insights based on the highlights found and, based on these, recommendations that will impact the future environmental management and land use practices of the Reserve are provided.
Further analysis is recommended to gain a complete understanding of the possible effects of bush clearing on water dynamics and to compare the results presented in this research. It must also be
borne in mind that there may be discrepancies in the results obtained due to lack of equipment and time constraints. ... Read more

Capillary barrier systems (CBSs) have been demonstrated to be effective in deviating infiltration in a landfill cover. However, their performance when combined with a cover soil optimised for methane oxidation had not been tested in the field yet. This study aimed to describe the water balance of a test field where such a configuration was built, located on the landfill in the Wieringermeer area, the Netherlands, over the period from 2009 to 2023.
During that time period breakthrough and deviated infiltration were measured. A one-dimensional finite difference model was built to model evapotranspiration and storage in the cover soil as well as the moisture retaining layer (capillary layer; CL). This model performed well in describing overall seasonal trends but generally overestimated evapotranspiration in spring and outflow in autumn, consequently underestimating the storage in these seasons.
The results show that the annual precipitation ranges between 770 and 990 mm. On average, 59% (494 mm) of this precipitation is evaporated, 33% (281 mm) is diverted by the CBS and 7% (63 mm) breaks through. Compared to other test fields and design standards, this breakthrough is high. A weakened functioning of the CBS by construction errors or the ingress of sand could be a reason for that. Another factor might be the coarse grain size distribution of cover soil, necessary for the efficient oxidation of methane. This type of soil has a relatively high hydraulic conductivity which does not control infiltration rates into the CBS as well as cover soils in other studies.
Furthermore, the results suggest that storage in the cover soil and CL is the main determinant for breakthrough to occur. Major breakthrough only occurred at a storage larger than the storage in the soil associated with field capacity, both on a seasonal and daily time scale. The available storage is mainly affected by the evapotranspiration which shows a seasonal cycle. Consequently, outflows for the CL and breakthrough occur mostly when evapotranspiration is low (autumn, winter). The relation of breakthrough with precipitation is less straightforward as a high rainfall does not necessarily lead to breakthrough on a seasonal or daily scale, depending on the available storage in the system. The distribution of precipitation can matter however. On a seasonal scale, precipitation in late summer can result in high storage in the beginning of autumn, potentially leading to breakthrough. Furthermore, a precipitation amount uniformly distributed over a day leads to less breakthrough than more concentrated precipitation.
Overall, with some adjustments regarding the design of the CBS and the cover soil, this landfill cover design is a promising alternative for the current standard.
... Read more

As part of the Dutch sustainable landfill project iDS, two compartments of the Dutch landfill Wieringermeer have been treated by in-situ aeration since 2017. The chosen method of aeration is over-extraction, where suction pressure is created causing ambient air to intrude into the landfill. Aeration induces enhanced settlement due to the acceleration of aerobic degradation of the waste. The aeration infrastructure comprises 110 wells, separated by around 10 to 15 m, covering an area of approximately 5 ha. This study analysed the spatial and temporal variability of settlement of the landfill, and aimed to correlate this with the carbon extracted by the wells. In order to quantify the settlement of the landfill various remote sensing methods have been utilised and compared. The methods include an Aerial Laser Scanner (ALS), Terrestrial Laser Scanner (TLS) and Global Navigation Satellite System (GNSS) measurements from a rover. In total 11 GNSS surveys, 4 TLS point clouds, and 2 ALS point clouds were available to this study.

Ground settlement plates have been measured using the GNSS rover since the start of aeration, showing a maximum settlement of ∼1.17 m on the western slope from August 2017 to June 2022. The slopes of the landfill experience more settlement than the top of the landfill, as a plate installed on the top only
experienced ∼ 0.09 m over this same time period. This is due to the increased surface area of the landfill exposed to the outside air at the slopes. The UAV-based ALS and TLS point clouds were able to measure spatial and temporal variations in settlement. Whereas the trends in settlement are consistent between the methods, the absolute values show notable variance. The ALS and TLS data contain significant uncertainty due to the effect of vegetation on the landfill, to which this variance can almost entirely be attributed. At its peak the vegetation contributed to a difference of 0.95 m in settlement, compared to the GNSS measured settlement. Several processing steps were taken to help negate the effect, but these were not able to fully filter vegetation out. ALS data was impacted to a lesser extent due to the high angle of incidence of its laser
signals as it flies overhead, because of this the signals generally penetrated the vegetation to a deeper depth than the TLS.

The aeration wells extracted 2583 tonnes of carbon from August 2017 to March 2022. Both visually and through the Pearson Correlation Coefficient clear correlations were observed between the variability of settlement and carbon extraction by the wells. The highest correlation coefficient reached was 0.503 using GNSS and gas data from August 2021 to March 2022, signifying a strong correlation.
... Read more

Recirculation and infiltration of leachate in landfills are performed to accelerate the process of stabilizing organic matter in waste. At landfill De Kragge (Bergen op Zoom, the Netherlands), leachate recirculation and infiltration measures started in March 2018. This research aims to provide insight related to leachate flow throughout the landfill. Knowledge about the leachate flow is essential for evaluating the success of the stabilization measures. In this research, uniform and point borehole dilution tests were conducted to investigate the horizontal and vertical flow velocities. In addition, measured leachate levels throughout the landfill were analyzed.

The leachate levels indicated perched leachate zones: above the basal drainage system and below the injection drains at the top. Leachate injected through the infiltration drains cannot efficiently infiltrate the waste body, and the effects of the infiltration events were not picked up in the wells and piezometers throughout the landfill, implying little hydraulic connectivity.

The results of the dilution tests indicated horizontal and vertical flow within the landfill. Vertical velocities measured in the wells were estimated to be considerably higher (77 - 225 m/d) than the average horizontal velocities (0.02 - 1.0 m/d). The wells provide a path for vertical flow. Apart from the highest horizontal velocities measured in deeper sections of the landfill (15-18 m below ground level), velocities varied without a clear relation to landfill depth, indicating preferential flow paths. Uniform dilution tests performed with the infiltration drains turned off suggested that leachate infiltration does not increase the horizontal velocities. This research suggests that waste stabilization through recirculation is not optimal at De Kragge.

\noindent Due to an overall lack of understanding about the well and filter pack installation and the high spatial heterogeneity of the waste, the calculated velocities are uncertain. Further research into possible error sources (e.g., the borehole correction factor) is recommended. Additional tracer tests, including tests on the neighboring compartment without stabilization measures, are recommended to further assess the effectiveness of the recirculation system. ... Read more

Organic matter plays a major role in global ecosystems and has several functions in terrestrial and marine environments. As organic matter impacts, among others, the rheological behaviour and settling rates of mineral sediment particles, it is of great relevance to the definition and maintenance of the nautical depth in ports and waterways. The microbial decay of organic matter leads to the emission of climate forcing gases like CO2 and CH4. In this theses it will be provided fundamental insight in the behaviour of sediment organic matter in the aquatic river system. It presents analyses of field and laboratory experiments using sediment samples taken during 21 sampling campaigns between 2018 and 2020 in the Port of Hamburg, Germany. The focus lay on sampling locations with high sedimentation rates. It is investigated chemical, physical and biological parameters and their variability in space and over time. It quantifies the share of anaerobically and aerobically degradable sediment organic matter in a depth profile and along a transect of about 30 km within the tidal Elbe river. Sediment organic matter at upstream and downstream locations is mainly allochthonous as it comes from the catchment (upstream) or from North Sea (downstream). Young organic matter, entering the system from upstream, has predominantly biogenic sources. Upstream organic matter originates from the catchment, containing plankton-derived and more easily degradable components. It was shown that the most upstream location was nourished primarily by upstream fluviatile sediments. This location was characterised by the highest concentrations of chlorophyll a, microbial biomass, silicic acid, EPS, humic acids and hydrophilic organic matter, the most negative δ13C signature and by the highest oxygen consumption rate, with decreasing trends towards downstream locations. At downstream locations, organic matter is mainly of allochthonous origin, entering the harbour mainly with the tidal flood current from the direction of the North Sea. The organic matter degradability was the lowest at downstream locations and organic matter was stabilised in organo-mineral associations. It is elucidated that spatial patterns of organic matter degradability can be explained by a source gradient. It was found that sediment organic matter lability is inversely linked to its stabilisation in organo-mineral complexes. The degradability gradient could be explained by different organic matter quality in relation to its origin. A fast, medium, slowly and non-degradable pool (pool 1 to pool 4) were identified based on the measured organic matter lability. Temporal and spatial variabilities (gradient and depth) were observed as well as seasonal changes of degradable organic matter pools. An age gradient was found with easily degradable material in top layers and increasing stabilization of organic matter in organo-mineral compounds with depth. The degradability was larger in upper sediment layers. It was also larger under aerobic conditions but the differences between aerobic and anaerobic decay decreased from upstream to downstream. The investigation area mostly comprised stabilised organic matter. On average around 20 % of TOC was anaerobically degradable and around 30% of TOC was aerobically degradable. Thermometric pyrolysis was shown to serve as a useful proxy to predict organic matter degradability in river sediments, with the Hydrogen-Index (HI) correlating well with degradability. Further, it will be demonstrated that the sediment organic matter decay has a biological, chemical and physical effect on the shear strength. Degradation of organic matter significantly affects sediment strength, especially under the anaerobic conditions. The formation of gas bubbles under anaerobic conditions added an additional physical component to the effect of biological organic matter decay. The susceptibility of the sediment to yield stress changes might depend on the availability of easily XIV degradable organic matter. Pronounced spatial trends were found with higher changes in yield stress at upstream locations and lower yield stress changes at downstream locations. Finally, this thesis will demonstrate the metamorphosis of sediment properties and sediment organic matter from its state in suspension to being part of the settled and consolidated sediment as well as from upstream to downstream. Temporal and spatial gradients were found for aerobic and anaerobic carbon fluxes as well as for potentially degradable organic carbon. A first draft of a carbon flux estimate originating from the microbial decay of organic matter from the investigation area is presented which can be used for future carbon foot printing assessments, for example for port maintenance activities. ... Read more

"Landfills form the final stage in waste processing and are sources of multiple environmentally harmful emissions. Due to the biodegradation of organic material, methane, a strong greenhouse gas, is released into the air and soluble pollutants, like ammonium or heavy metals, are flushed out of the landfill waste. In modern landfills, the waste body is isolated from the environment by an impermeable liner and both the gas and the leachate fluxes are collected and treated. However, sealing the landfill reduces the emissions on the short term but gives no sustainable solution as eternal active aftercare is needed and the emission potential is not reduced. The goal of the CURE project is to develop methods to enable the sustainable management of Dutch landfills. One of these methods is piloted at the Braambergen landfill, which is the in-situ aeration of the waste body with the goal of speeding up the biological degradation of organic matter to reduce the emission potential relatively quickly below the values in the Dutch regulations, such that the eternal active aftercare is not required anymore. The issue that the landfill operator, Afvalzorg, is facing is that in compartment 11Z of the landfill the aeration efficiency is poor due to ponding leachate. The objective of this thesis is to quantify the relation between the water level in the landfill and the efficiency of aeration, and to research the spatial and temporal variability of the water levels, leachate composition and hydraulic conductivity of the waste body to investigate the nature of the water and to find a suitable solution to mitigate the reduced aeration efficiency. To reach this goal, multiple types of field and lab measurements have been performed and the results of a water balance model have been used for a numerical evaluation. In the field, water tables have been measured as well the magnitude and composition of landfill gas extracted by the aeration wells. Pumping tests have been performed on the wells to assess the hydrological behaviour of the leachate surrounding the wells and to determine the horizontal hydraulic conductivity of the waste. Leachate samples from all the wells have been collected and analysed in the lab on pH, redox potential, electrical conductivity, DOC and ammonium concentration. Also were CTD-divers installed in some of the wells to monitor the response to rainfall and the medium long term behaviour of the water level and the electrical conductivity. The general conclusion of this thesis is that the studied compartment 11Z is homogenous in its heterogeneity. With all the different measurement types performed it was in some way the objective to see whether the behaviour or the properties of the landfill and the leachate can be grouped spatially, but this was not the case. Therefore can be concluded that the only scale for which a measurement can be representative for the entire compartment is on the scale of the compartment itself. This is in line with the expectations of large heterogeneity in landfills and the unique situation of aeration system on the Braambergen made it possible to proof this. The efficiency of the aeration system is particularly low in compartment 11Z because the conditions are unfavourable for both water and gas flow. The conditions in compartments 12 and especially 11N are more favourable because the waste, especially at the bottom of the compartments, is more permeable. Even if the amount of water in 11Z is reduced and the gas flow increases, the total amount of extracted LFG will not reach the same level as for the other compartments. ... Read more

Water injection is widely used in the petroleum industry for the increase of hydrocarbon recovery or disposal of wastewater. Water production and injection are the primary mechanisms in Geothermal Energy. Both include injecting water into a porous formation under matrix injection conditions. While maintaining water injection is vital in these branches in the industry, so is the occurrence of formation damage (FD) due to suspended contaminants or brine incompatibility. Suspended particles in injection water are retained or deposited due to the creation of an External Filter Cake (EFC) or Internal Filter Cake (IFC) impairing the permeability. Consequently, FD results in Water Injectivity Decline (WID). In most cases, the negative impact on injectivity translates into operational and economic targets not being met. WID, as a result of FD, is highly connected to the Water Quality (WQ) of the injection water. A new approach to water quality (WQ) testing is proposed which suffices as a bridging application of membrane filtration and core flooding. To establish a foundation for this method, tests are conducted by performing particle-laden suspension injection experiments with porous outcrop sandstone 8 mm thin discs utilizing the ‘Con-vergence Hydra’. An experimental study is conducted investigating the effect of water quality (WQ) on formation damage, using dilute (20-100 mg/l) Baracarb2 (CaCO3) particle suspension as a model contaminant. Baracarb2 is tested for particle size distribution, mineral content and stability within synthetic brine (resembling Seawater). Subsequently, suspension flow experiments are conducted on porous thin discs (Bentheimer & Berea sandstone) as well as membrane filters (MF0.45μm). As performing suspension injection test with porous thin disc test utilising the Hydra has not been done before, reproducibility of the experiments is tested. The reproducibility of performing experiments utilising the Hydra is high, with very little difference between the experimental outcomes.Varying WQ within each different porous media type illustrates remarkably similar trends. Moreover, it is demonstrated that by performing a similarity curve collapse, a master curve is obtained for each porous medium type which scales with suspension concentration for Baracarb2. The damage mechanisms explaining this master curve all demonstrate a linear permeability impairment in the early part of the experiments. Subsequently, a linear impedance trend is observed where it is assumed that cake filtration is dominant. The latter is demonstrated by calculating the Modified fouling Index (MFI), which shows a linear dependency with suspension concentration. SEM imaging and Micro-CT scan images substantiate the damage mechanisms hypothesized from the pressure and rate data.The Con-vergence Hydra utilising porous thin discs has great potential for on-site testing which allows fast and reliable results on permeability impairment, i.e. formation damage. Subsequently, monitoring of the water quality can be done by performing MFI analysis during cake filtration.  ... Read more

In riverine environments under anaerobic conditions, methane and carbon dioxide are produced as a result of biological activity, causing degradation of organic matter. Under aerobic conditions, the bacteria present degrade the organic matter, whereby the concentration of dissolved oxygen may be lowered. Thus, issues experienced in the investigation area (the Port of Hamburg) are hindered construction operations, increased greenhouse gas emissions and the echo-sounding equipment used for sonic-depth finding for ships possibly showing an erroneous depth. The purpose of this investigation was to find out how gas generation and respiration relate to the basic sediment properties and what mathematical model with the highest accuracy can predict gas generation and respiration (separately), while maintaining within a given (precision) error (1%). Gas pressure was measured at the TU Delft for an incubation period of 100 days, which was later used to calculate the gas generation (mg C/g DW) with the use of the ideal gas law. Statistical methods used to analyze the data were: Pearson’s correlation coefficient, multiple regression analysis, adjusted coefficient of determination and error analysis. The results show that both gas generation and respiration have the highest Pearson’s correlation coefficient with TOC. Furthermore, in the multiple linear regression, gas generation had the highest coefficient of determination in a regression between TOC as the primary parameter and iron content (in solids) as the secondary parameter (푅2=0.91495). For respiration, it was displayed in a regression between TOC (as the primary parameter) and copper content in the solids (as the secondary parameter) (푅2=0.881). This concludes that organic matter degradation is driven by the quantity of organic matter. The residual sum of squares showed a decrease from the linear (and non-linear) model to the multiple linear regression model. The prob>|t| value (which determines the probability of error for the multiple linear regression) was much lower than 1% for all parameters in both the gas generation and respiration model, so it can be deduced that the variables are contributing to the model in a statistically significant way. Together with the previously mentioned highest coefficient of determination, the most accurate model for both gas generation and respiration found in this investigation was the multiple linear regression model, although the model for gas generation presented little difference to that of the simpler non-linear model. The exponential nature of the optimal fit for the data suggests that there is a threshold. In areas with low organic matter content, the organic matter present is much less degradable, falling into the “slow” pool category. It is recommended to investigate other mathematical models further. There is a possibility of a more accurate model (possibly a combination of a linear and non-linear model) for both gas generation and respiration which can model the parameters even better (higher coefficient of determination while still remaining within the permitted range of error). Furthermore, it is recommended to find out why the samples listed in tables 6 and 10 deviate more than accepted from the calculated value. ... Read more

Due to microbial activities, the anaerobic degradation of organic matter happens in the sediments and leads to considerable gas production. Especially for low flow areas gas production is more easily fostered. To prevent the potential problems caused by gas production from the riverine sediments, this study focuses on magnitude of gas formation and its relation with soil properties. Nine locations of known at Port of Hamburg were sampled; for each location the fresh sediment samples were collected at different depths and on different seasons. Samples were stored and transported to several institutes for various analyses, including analysis on sediment standard properties, and on gas production by incubation.

Being part of the BIOMUD project, this study analyzed data from several research institutes. A strong correlation was found between magnitude of gas production and some of the soil properties including content of TOC, TN, ratio of TOC/P, TOC/S, density fractionation, and content of various types of metal elements. A clear relationship was found between magnitude of short-term and long-term gas production, providing possibilities for estimation work on gas formation in the future. The modified Afvalzorg multi-phase model was applied in analyzing gas production on the timeline, which played a key role in describing and predicting gas production in the long-term. The total gas potential of the river sediments at the Port of Hamburg was then predicted as 105.3 mg C/g TOC on average, relating to 10.5% of the organic matter being degraded. By temperature experiment a Q10 value of 2.06 was determined for assessing the sensitivity of gas production to temperature. Gas composition inside the bottles was also measured after four months’ incubation in the temperature experiment, with the results of CH4/CO2 ratio ranged from 0.92 to 1.86 for different temperature conditions. Parts of the results acquired from the experiments mentioned above were also compared with the results from previous studies made by other researches. ... Read more

The goal of this study is to examine the feasibility of this solution, from a water quality and hydraulic point of view. Firstly, the current state of the three water bodies was investigated and a stakeholder analysis was conducted to look into the social and political context. Secondly, the effect of the solution on the water quality in the WL and TLR was researched. The most important water quality parameters were qualitatively discussed and after that, the quantitatively changes in the WL were modelled. A convection-diffusion model was set up for different parameter concentrations in R. The initial parameter concentrations were gathered by field measurements and extensive online research. The water quality assessment shows that the Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD), turbidity and Total Suspended Solids (TSS) concentrations in the RR have a better value than in the WL. The model itself shows for every parameter that after 100 days of mixing the water is not completely mixed in the WL. The water in the TLR is flushed with WL water and its quality is therefore more or less equal to WL water. It is concluded that the proposed solution improves the water quality in the WL and the TLR. However, long and frequent mixing is necessary for the WL water to reach the RR water quality level. Thirdly, a hydraulic analysis was carried out by investigating the hydrological and geometrical characteristics of the three water bodies. Thereafter, the hydraulic impact was examined by comparing six different flushing scenarios.The flow, water depth and sediment transport rates for different time intervals were modelled in R over the distance of the TLR. A Multi Criteria Analysis was done to interpret the results on the consequences in the TLR. The outcome of the optimum scenario is when the gate has an opening height of 5%. The total transported sediment volume is significantly larger in this scenario, which is beneficial. From a hydraulic perspective the proposed solution is feasible for all water bodies. However, more extensive research on for example the impact on the hydraulics in the TLR is needed to get more conclusive results. As a spin-off, our project (co-)developed educational tools that can be used within the HUNRE curriculum and as awareness raising activities in Hanoi with citizens, schools and the like. Fieldwork with Vietnamese students was conducted to start with building a data base on water quality of the water bodies in Hanoi. The tools that are created are manuals, instruction videos and an introduction lecture. Furthermore, the database, that is built, can be extended with more fieldwork in the future. The extent to which the educational tools and the database integrate in the study program of HUNRE remains unsure, however the awareness among Vietnamese students on the importance of water quality has increased. Furthermore, the OKP project strives to realize the integration of the educational tools in the future. Therefore, this research objective is expected to be achieved. ... Read more

English:
Landfills have been indicated as a major methane source. Methane oxidation systems are `low technology' systems that can treat these methane emissions. Yet, methane oxidation systems are herein still sub-optimal and leave room for improvement. A numerical model was established to research the effective gas permeability ratio between the gas distribution layer and the methane oxidation layer, and the centre-to-centre distance of the gas inlet points, necessary to achieve a spatial homogeneous methane load. In order to relate the permeability ratio to the design choice for the materials, laboratory experiments were performed to asses the influences of compaction level, hydraulic conditions and physical properties of a soil on the effective permeability of that soil. Overall, it is concluded that the effective permeability is predominantly influenced by the compaction level and soil texture. The water saturation only has a significant influence at near saturated levels. This means that the choice of suitable material and adequate construction practice has more effect on the effective permeability than seasonal changes in saturation levels in moderate climates. Furthermore, it is concluded that there are two parameters that govern the spatial homogeneity of the methane fluxes from the gas distribution layer into the methane oxidation layers: the permeability ratio between these layers, and the centre-to-centre distance between the inlet points. The required permeability ratio increases quadratically with an increasing centre-to-centre distance.

Nederlands:
Stortplaatsen zijn aangeduid als een belangrijke bron van methaanemissies. Methaanoxidatiesystemen zijn technisch simpele systemen die het stortgas kunnen saneren. Op dit moment zijn de bestaande methaanoxidatiesystemen nog weinig efficiënt en is het noodzakelijk om de homogeniteit van de laterale distributie van het stortgas te optimaliseren. Er is een numeriek model gegenereerd om inzicht te geven in de benodigde ratio tussen de effectieve permeabiliteit voor gas van de gasdistributielaag en van de methaanoxidatielaag, en in de maximale hart-op-hartafstand tussen de gasinlaatpunten om deze lateraal homogene methaan distributie te bereiken. Om de effectieve permeabiliteitsratio te relateren aan de materiaalselectie zijn er laboratoriumexperimenten uitgevoerd, die de invloeden van het compactieniveau, de hydraulische condities en de fysieke grondeigenschappen op de effectieve permeabiliteit voor gas vaststellen. Al met al kan worden geconcludeerd dat de effectieve permeabiliteit hoofdzakelijk wordt beïnvloed door het compactieniveau en de grondtextuur. Het watergehalte blijkt alleen significante invloed te hebben onder bijna verzadigde omstandigheden. Dit betekent dat een geschikte materiaalkeuze en adequate constructie de effectieve permeabiliteit voor gas meer beïnvloeden dan de seizoensgerelateerde veranderingen in het watergehalte in gematigde klimaten. Daarnaast kan worden geconcludeerd dat twee parameters bepalend zijn voor de laterale homogeniteit van de methaanstroom van de gasdistributielaag naar de methaanoxidatielaag: de ratio tussen de effectieve permeabiliteit voor gas tussen deze twee lagen, en de hart-op-hartafstand van de gasinlaatpunten. De benodigde permeabiliteitsratio neemt kwadratisch toe bij een toenemende hart-op-hartafstand. ... Read more

Landfills are full of contaminated material, which could be harmful for the environment. To reduce the risks of pollutants entering the environment, a watertight base layer and an impermeable cover layer isolate the waste. These layers have to be maintained eternally, which is very costly. To move towards a more sustainable landfill aftercare, Dutch landfill operators have started three demonstration projects, to reduce leachate concentration in 10 years. At one of the projects, this is attempted by recirculation of leachate, which in the long term, reduces the concentrations of pollutants in the leachate. During the project the reduction of emissions via leachate is measured, but in order to make this project successful, it also has to be proofed that the emissions are reduced permanently. To proof that the emission via leachate is permanently reduced a model is required which enables to predict how remaining mass in the landfill will be emitted via leachate, based on time series of leachate quantity and quality. 
This research focuses on adapting the prediction models, created for two demonstration projects, to describe the water balance for the third demonstration field at De Kragge II in Bergen op Zoom. Compared with the other two projects, the water balance for this field is a bit more complicated, since it has a different layout of the drainage system and lateral flow to and from adjacent fields is possible. The aim of this research is to model the water dynamics in the landfill with minimal uncertainty.

Available input and output data are: rainfall, evaporation potential, leachate levels and leachate outflow, available for the pilot field and the adjacent compartment. The leachate outflow is controlled by valves, level meters and pumps in the flow system, also the operator has influence on which compartment is drained. Another complication with the outflow data is that the data from weighed trucks transporting the leachate indicate that sometimes leachate was directly pumped from the landfill, herewith bypassing the flowmeter.

The model consists of three layers, a recultivation-, waste- and drainage layer. In the recultivation layer infiltration into the waste layer is calculated by balancing rainfall, evapotranspiration and storage. The water volume infiltrating the waste layer is distributed stochastically, according to a travel time distribution, that discretizes the infiltrated water to faster and slower moving regimes. In the drainage layer model, the balance of water inflow, leachate outflow, sideflow and storage is calculated. Resulting
in a volume of water ex-filtrating the landfill. To evaluate model uncertainty, visual and quantative criteria are used. The fits of modelled on measured data is used as a visual check. The quantitative analysis consists of evaluating the Kullback-Leibler divergence and the marginalized likelihood. The Kullback-leibler divergence estimates how much information is gained from the parameters, while the marginalized likelihood determines the balance between information content and complexity. 
In order to find a model that describes the water dynamics with minimal uncertainty, three different model implementations were evaluated. In the first approach both leachate level and outflow were used for calibration with measured data. Evaluation of the model performance showed that the outflow could not be determined with acceptable error. This was indicated by large standard deviations of the model and measurement error with respect to outflow measurements. Likely the reason for this is the gap in the water balance and the erratic patterns in the outflow data. A second approach was therefore modelled in which only the leachate levels were fitted with measured data and the outflow data was given as input. This increased the leachate level fits slightly, also the quantitative criteria showed that approach 2 is better than approach 1. Some of the parameters of approach 2 had large uncertainty and the model is quite complex given the available measured data. Therefore a third, simpler and faster model was implemented. In this model the waste layer calculations were simplified using the circular convolution function of MATLAB. This function calculates the travel time distribution continuously instead of discretizing the function over given retention times, which was done in the first two approaches. This model approach gave the best leachate level fits. The Kullback-leibler divergence indicated higher information content compared to approach 2.

In addition, each approach was evaluated with different model scenarios in which the waste compartments where either coupled or uncoupled. For each approach the uncoupled models performed visually and quantitatively better than the coupled models. 
Approach 2 gave the best insight in the water dynamics given its complexity, shown by the higher values for the marginalized likelihood. Approach 3 gave the best fits, of the leachate levels, the highest 퐷_KL values and is the fastest model. From these results it would be advised to use approach 3 to analyse the water dynamics of the landfill. Given the results of the different scenarios, it would be advised to use the uncoupled models for the analysis of water dynamics inside the landfill, since these models showed the best fits, highest 퐷_KL and marginalized likelihood values. 
Based on the obtained results, the following insights could be drawn about the landfill dynamics. The sideflow between the two compartments is about 5 to 25 m3/day. The model showed that water in the landfill, flows fast from the cover layer to the drainage layer. The infiltration flux of the recultivation layer model seemed to be dominated by rainfall and evaporation. Therefore this model could be simplified by omitting water storage and flow through the layer. ... Read more

The city of Guayaquil suffers from regular floods. During the wet season, typically from late December until late April or early May, multiple floods per week can occur. Mainly the excessive rainfall in combination with high tide penetrating into the city results in a high flood risk, but some flood-prone areas can also flood in case of spring tide only.
The main objective of this research is to investigate the possibility of reducing pluvial and coastal flooding in urban areas by constructing a (semi-permanent) barrier in a sea branch, which retains the incoming tide and creates storage for excessive rainfall. In addition, local storage areas spread over the city are considered to delay stormwater runoff into the sea branches. Based on a system analysis and by numerical modelling, several closure locations and their effects are assessed.
Temporary storage of stormwater behind a barrier in a sea branch is a suitable solution to prevent both coastal and pluvial flooding. Based on the results of this research and possible locations of the barriers, a combination of three selected barriers is most opportune, because all catchment areas adjacent to a sea branch can drain their stormwater in a closed-off part behind one of these barriers. In order for these barriers to be effective, they must be closed during low tide prior to heavy rainfall. All three barriers are able to withhold the stormwater volume from their corresponding catchment areas during a 10-year design rainfall event. Even in the event of the highest possible water level during low tide, being neap tide in combination with the storm surge of El Niño, the storage capacities are sufficiently large. Besides the large-scale and small-scale solutions that are currently considered by the local authorities, they are advised to also consider the intermediate-scale solution presented in this study.
Local stormwater storage in the form of water squares in parks and playgrounds is a small-scale solution to reduce pluvial flooding. The storage capacity of these areas is much smaller than the storage capacity behind a barrier, but it is a solution for low-lying urban areas that are not adjacent to a sea branch or river. When the storage capacity of parks and playgrounds in some catchment areas is not sufficient, underground storage basins can also be considered as local storage areas.
The local authorities are advised to set up regulations on return periods for designing flood risk-reducing structures and to assess the economic losses of floods in urban areas, in order to be able to estimate the acceptable cost of these structures.
... Read more