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.

Variable density groundwater models are essential for managing coastal groundwater resources. However, their practical applicability can be questioned due to limited validation opportunities on long timescales associated with the development of fresh-saline distributions. This study addresses this challenge by applying upscaled metamodeling techniques to a state-of-the-art variable density groundwater model (the original model) for the Meijendel-Berkheijde drinking water reservoir. Model validation is performed using a Hydrochemical Facies Analysis (HyFA) conducted by Stuyfzand (1993) in the same area. The primary objective of this study is to enhance validation techniques for variable density groundwater models by incorporating the HyFA. Unlike traditional snapshot-based validation, the HyFA enables validation of groundwater pathways calculated by the model. The applied metamodeling approach significantly reduces calculation times by implementing an upscaled horizontal grid size, parameter rescaling, and linear boundary conditions, thereby enhancing computational efficiency. Although the original model lacks long-term salinity validation, it has not been invalidated based on the similarity of metamodel outputs to the HyFA. However, in the northern part of the study area, a potentially excessive conductance term may result in higher infiltration rates. Incorporating the HyFA into the metamodel is straightforward by adding a "species" dimension in the SEAWAT structure. This validation technique proves valuable for assessing variable density groundwater models on shorter timescales, particularly in areas affected by extensive human interventions. This study contributes to collaborative efforts by Dunea, Deltares, and Arcadis (2021), aimed at advancing efficient modeling for the coastal groundwater reserve of Meijendel-Berkheijde. Transparent documentation of detailed model scripts ensures reproducibility and provides a valuable resource for future research. The insights gained from this study have implications for global advancements in coastal groundwater management. Keywords: Hydrochemical Facies Analysis, variable density groundwater modeling, upscaled metamodeling, coastal groundwater management.

Over the years, modelling frameworks have been proposed to describe and predict the degradation of municipal solid waste in landfills. These frameworks, however, fail to couple the kinetic solutions to the real-time equilibrium state of the system. Because of this, fundamental processes such as pH changes, NH4+ adsorption to the waste surface and changes to the fluid composition are often not (or inadequate) taken into account. In this study, we propose a degradation model that couples a kinetic solver to the chemical equilibrium software, ORCHESTRA. For this, a tool is developed that allows seamless operability between ORCHESTRA and the Python environment. The modelling framework is used to simulate the degradation of solid organic matter in a batch reactor following a simplified, but comprehensive, reaction network. Reaction rates are based on Monod kinetics that includes a wide variety of inhibition functions. The Freundlich equation is used to capture NH4+ adsorption to the waste surface. Results from various case studies show that the modelling framework is suitable for coupling real-time landfill chemistry to degradation kinetics. We found that NH₄⁺ concentrations play a dominant role in the presented model. While low NH₄⁺ concentrations limit biomass growth by substrate inhibition, high concentrations (>0.002 4
mol/L) affect the hydrolysis rate by toxicity inhibition. This translates to a model that is sensitive to a variety of input parameters such as the initial C/N ratio, the Kd (degree of adsorption) value and the initial organic fraction. A comparison with literature studies, however, implies that the model lacks fundamental processes such as gas and fluid transport or changes in volume and temperature. In addition to this, we discuss that the Freundlich isotherms may be inappropriate to capture adsorption in a coupled framework as no ion exchange is taken into account. Models that do so, such as the NICA-Donnan model, could improve the model results significantly.

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.

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.

The services that society extracts from urban ecosystems are becoming increasingly important with increasing urbanization. A potentially crucial ecosystem service is soil carbon (C) storage, as negative soil C balances have the potential to offset some of the anthropogenic greenhouse gas emissions mitigating climate change. This research studied the soil C storage in the urban greenspaces of 2 districts in a typical Dutch city (The Hague districts’ City Centre and Scheveningen, 21 km2 , 37% greenspace) as a case study. The following research question was addressed: ‘What is the carbon storage potential of urban soils in The Hague?’ Soil samples were collected along a transect going from the suburban seaside towards the city centre of The Hague. The transect crossed a toposequence from sandier dune soils to peaty inland soils. Besides soil C densities, several soil-quality characteristics were measured namely dissolved organic C levels, pH, electrical conductivity, nitrogen, phosphorus, and sulphur levels, calcium carbonate, the water-holding capacity of the soil and the degradability of soil organic C.

Although urban soil can be highly disturbed or altered by anthropogenic activities, the high C densities in The Hague suggested that its potential to store C appeared unaffected. Along the transect, a mean C density of 88 t/ha, of which 82 t/ha was considered organic C, was detected, which was higher than the values currently assigned to urban soils in national C inventories. The urban soil C storage was dependent on the type of vegetation, urbanization extent and land ownership. The hypothesized links between land use and soil type were not apparent in this case study, suggesting that processes driving soil C storage are controlled by different factors.

The total soil C storage of the upper 30 cm of the greenspaces in The Hague was estimated at 18.8 kt of C. The use of high spatial resolution GIS data with a scale of 10 x 10 m enabled the inclusion of small patches in the total soil C storage of The Hague, which proved to be significant as the smaller urban greenspaces, which are typical for dense urban centres, contained similar soil C density as the larger urban greenspaces, such as urban forests.

Soil C storage in urban ecosystems is highly variable. How generalizable these results are across other Dutch cities requires further research. Moreover, to translate current soil C stocks to annual C fluxes further research is required. This study found that urban soil C stocks are underestimated, which potentially also is the case for urban soil sequestration rates that are currently applied in C modelling studies.

The control of infiltration and seepage of water is one ofthe most challenging tasks in water management and civil­-engineering and, inan attempt to control this, methods for forming a water­impermeable layer inthe soil have been widely practised in soil engineering (Laumann et al., 2018;Proto et al., 2016). The use of natural processes to modify the engineeringproperties of the subsurface could help to develop cost-­effective, robust andsustainable engineering technologies and is attracting increasing attentionfrom the industry (Zhou, 2020). This research aims to reduce the permeabilityby using aluminium (Al) and organic matter (OM) precipitates mixed ex­-situwith porous media to create a horizontal barrier. The Al­-OM precipitates wereexpected to clog the pore space with a reduction in permeability and hydraulicconductivity as result. To find out if it is feasible to use Al­-OMprecipitates mixed ex­-situ with porous media for a permeability reductivelayer, the Al­-OM precipitates and the permeability of the medium wereresearched.  To characterise the flocculation reaction, experiments onthe flocculation were performed. The yield of the reaction was obtained byadding certain amounts of Al and OM solutions to form particular amounts of drymass of flocs. This experiment confirmed the hypothesis that 85% of the addedmass of OM will result in dry mass of flocs. The concept of a critical metal tocarbon ratio (M/C­-ratio), indicating flocculation regardless of the inputconcentrations, was tested by measuring the pH over an increasing M/C-­ratio.From this titration curve, the found critical M/C ratio is between 0.023­0.031,and the pH stabilises at a level lower than pH 4. This result proves theconcept behind the numerical scenarios describing the titration of OM solutionswith Al3+, with a critical molar M/C ratio independent of the inputconcentrations (Veerkamp, 2018; Zhou, 2020). After determining the yield of thereaction and concluding that the concentration of Al and OM was not ofinfluence, the by-products of the Al­-OM reaction were quantified. The ionicstrength of the supernatant of an increasing density of flocs in solution wasdetermined by measuring the electrical conductivity (EC). The results showedthat the ionic strength increased linearly with an increasing density of flocs.The relationship between the ionic strength and the density of flocs was coupledto the linear relationship between concentrations potassium chloride (KCl) andits EC. From the results, the measured EC can be used as a tracer since the K+and Cl­ are non­reactive.  The hydraulic conductivity measurements were conducted by afalling head test to be able to make an indication of the change inpermeability when adding the Al­-OM precipitates to the sand. To find theoptimal method to mix the Al, OM and porous media, the influence of differentmethods of producing, adding and mixing the materials on the permeabilityreduction is explored. In the first mixing method, the Al and OM were added insolution, the solution containing Al-­OM precipitates was centrifuged until thereduced ionic strength was at an EC value less than 700 µm/cm. The hydraulicconductivity measurements were used to obtain the relationship between thehydraulic conductivity reduction over an increasing concentration of flocsretained by one kilogram of sand. The hydraulic conductivity was reducedexponentially over an increasing concentration of flocs up to a magnitude of 3.The results imply a large variability in the achieved reduction dominated bythe amount of retained flocs. The second method is using Al and OM in powderformat and adding them to the dry sand and adding 500 ml of water to thismixture. This mixing method resulted in a completely different floc structure.The flocs produced by mixing in solution have a shear dependency feature, whiledry mixing created particles that have a constant size. For this method, theincrease of the reduction is linear over an increase of concentration of flocsretained by the soil. The highest reduction for this method was found to be ofa magnitude of two, measured at 50 grams of flocs retained by one kilogram ofsand. Finally, this research gave proof of principle of using Al­-OMprecipitates mixed directly with sand could reduce the permeability up to amagnitude of 3. These results present a new road to research on this Al-­OM­-sandmixture’s strength parameters and compaction over time over an increasing flocdensity, since these parameters are critical for using the layer in practice.  

Eternal aftercare for landfills is the standard in Dutch waste management policy after a law came into effect in 1996, meaning eternal waste management from potentially hazardous substances. A prescription of this policy is the application of watertight barriers on top of the wastebody. The policy also prescribes the renewal of the packing materials every 75 years. The wastebody is dried out, and the degradation has stopped so the wastebody does not change. The 'dry tomb' stays hazardous, thus eternal aftercare is implied.

The project 'introductie Duurzaam Stortbeheer (iDS) aims to create aftercare with an ending, or finite aftercare. It is looking for possibilities to stabilise the landfill mass, i.e. to eliminate the threat of pollutants by treating the wastebodies.

The goal of the CURE project is to develop fundamental insight into landfill processes in order to research the feasibility of wastebody stabilisation. To predict behaviour of landfills, and to monitor the processes, as much information as possible needs to be gathered through measurements. These consist of measurement of gas concentration and production rates together with the variation in leachate quality and volumes, as well as many more. This research, as part of the CURE project, presents the applicability of settlement as and addition to these measurements.

The main goal of waste body stabilisation is to actively reduce the amount of organic matter in a landfill. Uncontrolled landfills produce considerable methane emissions as well as high concentrations of nitrogen and heavy metals in the leachate, leading to groundwater hazards in the environment.

McDougall (2007) introduced the fundamental conceptual model upon which this research is based. This model is not publicly available, so one of the goals of this research is to provide a fundamental conceptual model. The relation between degradation and settlement has been studied and implemented in a 1D model which allows for hydrological systems, oxygen penetration, degradation and cell strain. The outcome is a relation between mechanics, biochemistry and hydrology. A few assumptions and simplifications were made to make the model versatile and adjustible, but also easy to read. For instance, the model uses oxygen as absolute limiting factor in degradation, neglecting all processes concerning anaerobic degradation. The model also assumes that at the beginning of the simulation, each cell has the same composition, because there is no conclusive data about the distribution of waste types. The model has been created in one dimension, thereby neglecting all multi-dimensional processes and limitations.

In the final scenario, the main limitation to degradation is the availability of dissolved oxygen. As irrigation provides infiltration of 5 mm water per day with 10 mg dissolved oxygen per liter, the daily reduction of oxygen demand is 50 mg. The total modelled oxygen demand of the landfill is over 9600 kg, which concludes that a different tactic needs to happen in order to stabilise the wastebody. To increase the degradation rate, more oxygen needs to be applied. An approximation of the effect of applying a partial vacuum above the water table in the landfill to attract air from the environment is modelled, giving the oxygen more transfer area into unsaturated water. An increase by a factor 10^{4} is applied to the effect of oxygen on organic matter to model this enhanced irrigation system. The results are modeled over 100 years, after which approximately 26.17% of the degradation has happened. This shows that aerobic degradation over a wastebody takes too long with conventional degradation, and the unsaturated voids might help the process.

The model shows credible results for an unspecified landfill with deterministic parameters. Settlement has been brought in relation to a simplified form of biodegradation. The need for further research, with a spatial fluctuation of these parameters and detailed multidimensional water flow is needed to predict landfill behaviour in more detail. \pagebreak

The continuous accumulation of solid waste has posed a great threat to the environment of our future generations. A novel approach that is currently under development is to treat the waste collected in an engineered landfill in order to reduce the emission potential to an environmentally acceptable level. The main topic for this research is to improve the understanding of how leachate is distributed throughout the landfill Kragge and how this distribution varies in time. This is important for identifying the long-term behavior of the landfill and for managing landfill waste.

At the start of this project, we have a number of water level measurements obtained from various wells in the landfill. Straightforward spatial interpolation of this data leads to unexpected results. Most likely this is caused by the highly complex heterogeneity in this porous system. For this reason, this research aims to apply Electrical Resistivity Tomography (ERT) technology to explain the water distribution variations between wells. The apparent resistivity along several lines are measured over depth using different arrays. Some scripts written in Python with 'pyBERT' and 'pyGIMLi' packages are used to get electrical resistivity inversion results from the apparent resistivity. It is known that the decrease in the water content leads to a significant increase in the resistivity. Therefore, the possible existence of saturated and unsaturated blocks in the waste body can be visualized from the inversion maps.

Initially, the interface between the saturated and unsaturated zones is expected to be identified from Laplacian edge detection, while the results indicate that this technique fails to represent the area boundaries under highly-heterogeneous situations. Subsequently, Archie's law and van Genuchten equation are coupled to give a relation between the resistivity and water pressure head. Archie's law is used to compute the resistivity from water content and van Genuchten equation is used to compute the water content from the water pressure head. There are two hypotheses during this analysis: (a) where the resistivity is 20(ohm-m) gives the interface of dry and wet zones; and (b) the landfill leachate is under hydrostatic condition. Then the water pressure head is the distance from the interface, which can be read from the inversion maps. By selecting a certain range of empirical parameters, the computed resistivity-pressure head curves provide relatively good fits to the measured results.

This thesis aimed to elucidate the effects of dissolved organic matter on the applicability of electrocoagulation (EC) with iron electrodes for per- and polyfluorinated alkyl substances (PFAS) removal from landfill leachate. The research methodology consisted of an experimental and a computational part. Galvanostatic EC experiments were conducted in an aerated beaker with 500 mL working volume, using iron electrodes with a surface area of 8 cm2. The pH, voltage and current were measured continuously for 50 minutes. Blank measurements were conducted in a 2 g/L NaCl solution. PFAS removal was tested from 0.25 mmol/L perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) solutions at current densities of 12.5 and 25 mA/cm2, as well as from solutions with a commercial humic acid (HA) source added at 25 mA/cm2. The removal of HA was also tested separately. Eventually, the removal from real leachate samples was examined. A computer model was constructed in PHREEQC (pH Redox Equilibrium Calculation), a program for modelling chemical processes in water. The model simulates the removal of all tested pollutants based on electrostatic adsorption to a continuously forming surface, associated with the precipitating ferrihydrite. Model rate constants for O2 and CO2 dissolution and Fe(II) oxidation were determined from the results of the blank experiments. Good model fits were obtained for these datasets. HA could be removed completely within 50 minutes at all tested current densities and initial concentrations. PFOA removal was unsuccessful with and without HA as co-solute, with a maximum removal of 17 %. PFOS removal reached 81 % at 25 mA/cm2, but the removal essentially stagnated after 5 minutes treatment time. The presence of HA did not significantly affect the PFOS removal. Instead, HA removal was retarded by the presence of PFOS. For the real leachate samples, no significant removal of PFAS occurred. Conversely, approximately 20 % PFAS removal was observed after 5 minutes treatment of a leachate sample spiked with 0.15 mmol/L PFOA, perfluorobutane sulfonic acid (PFBS) and perfluorobutanoic acid (PFBA). However, this removal reversed during the remaining treatment time. The adsorption equilibrium constants were the most important model parameters. These parameters were determined for HA, PFOA and PFOS based on the experimental data. The model fits were good for HA and PFOA removal, indicating that these were indeed mainly removed by electrostatic adsorption. Contrarily, PFOS removal could not be represented accurately by the current model. Instead of stagnating after five minutes, the simulated removal continued to completion. The poor model fit may indicate that the mechanism of PFOS removal extends beyond strict electrostatic adsorption. Instead, charge neutralization of PFOS molecules causing their aggregation or mass transfer limitations in the vicinity of the electrodes could be involved. Further research is needed to explore these possibilities and determine improved equilibrium constants for the relevant adsorption reactions. In conclusion, this research did not confirm the high PFAS removal efficiency as observed in previous studies. Instead, significant removal of PFOA did not occur and removal of PFOS did not exceed 81 %. Competition effects were not observed in the simultaneous treatment of PFOA and HA. The presence of PFOS impeded the removal of HA, indicating that PFOS was removed preferentially under the current experimental conditions. The established model could simulate most experimental results accurately.

Research on sustainable landfill management has been studied since 30 years ago in the Netherlands, the principle of which is to reduce the emission of harmful substances from the landfill to the surrounding soil and groundwater. As for this purpose, the active treatment is applied on Wieringermeer landfill, meanwhile, the long-term monitoring of substance concentration is of great importance. The measurement frequency of chemical concentration is twice per month, which costs around 48000 / year. To save money by reducing the measurement frequency, SARIMAX model is studied as a tool of data interpolation. For this analysis, we currently focus on the concentration
measurements of chloride and ammonium. By comparing the SARIMAX interpolated data and the data with reduced size, the results indicate that directly dropping half of the measurements can be regarded as an acceptable way to reduce the measurement frequency, as the data properties are well preserved and the errors in estimating the mass of substances leaching out are in the acceptable range. However, interpolating using SARIMAX model doesn’t have significant improvements in preserving the data properties. Further quartering the data can lead to large deviations in data properties.

Aerobic granular sludge (AGS) is a revolution in the water treatment field, since it enables to simultaneously remove carbon, nitrogen, and phosphorus. Recently, the AGS studies mostly focus on the formation of granules, and the factors that influence the AGS morphology, like temperature and substrate type. In domestic wastewater, 85 % of total chemical oxygen demand (COD) are particulate COD (PCOD), which are likely to be mostly captured in anaerobic phase in AGS systems. These particles can have a negative impact on granules’ morphology. However, there are few studies about the AGS performance on particle capture in anaerobic phase. Hence, the major research objective was to investigate to what extent can particles in the influent be captured by the AGS bed in the anaerobic feeding period. There were three possible mechanisms attributing to particle capture in the anaerobic phase, which were filtering effect, adsorption, and protozoa consumption. The contribution of protozoa was investigated with a theoretical approach. Furthermore, A model was built up for studying the influence of particle transport mechanism on particle capture. A lab-scale plug-flow experiment in a column was conducted for investigation of AGS bed performance on particles in different size ranges, and the influence of duration on particle capture. The result of the laboratory work found that the particle capture efficiency was 95 %, 84 %, and 23 % for particles in the range of 45-100 μm, 10-45 μm, and 0.45-10 μm, respectively. The 1-10 μm particles were hard to be captured. Besides, the particle capture efficiency was constant with the duration of 2 hours. Anaerobic feeding duration will have limited influence on particle capture without negatively affecting the phosphorus and nitrogen removal. Towards to the role of protozoa, they are unlikely to contribute to wastewater particle capture and removal in anaerobic period. Additionally, the AGS system in anaerobic phase can act as granular filtration system and the filtration model can be applicable in AGS research. Overall, anaerobic phase most likely contributes little on particle removal for whole AGS system.

The goal of this bachelor thesis is to compare different datasets of precipitation from the Royal Netherlands Meteorological Institute for the purpose of modelling municipal solid waste landfills. It is essential to develop after-care methods for landfills so the future generations do not have to cope with the burden of the emission potential of the contaminants. Due to the complex and inhomogeneous nature of the landfill systems modelling is an essential part of understanding the process and predicting the behaviour of the emissions in the future. To model the mass balance an estimate of the precipitation is needed which can be retrieved from two datasets; rain gauges and the precipitation radar. The precipitation radar dataset has a higher resolution and might provide another, and maybe better, estimate for the modelling of the landfills. To see whether this is the case first a comparison for the daily scale is made, second a statistical analysis is performed to determine the difference in distributions between the datasets and third the datasets are compared as a result of the model of the landfills. The results of these comparisons and test show that the radar precipitation data gives a more accurate estimation on a daily basis but the trend in rainfall between the radar precipitation and the automatic rain gauge system is similar. The thesis concludes that the input of the radar dataset in the model creates a better model of the landfill on both a daily basis as on the long-term.

Controlling subsurface flow is crucial to prevent: the spreading of contaminants, the failure of dikes or any undesirable water flow. Subsurface flow can be controlled by changing the soil permeability. In order to change soil permeability rigid structures are often installed (for example the installation of sheet pile walls into dike bodies), however, these solutions are costly and disrupt the environment. Alternatively, the SoSEAL project aims to provide an in-situ solution to reduce the permeability of highly permeable soil layers in an ecological friendly and cost-effective way. The SoSEAL project is inspired by podzolization, which is a soil formation process. It reduces soil permeability via the precipitation of metal-organic matter complexes in the pore space. During earlier practices a need has arisen for a cheap, environmentally friendly and naturally available aluminum source. Accordingly, the goal of this research is to investigate if gibbsite can be used as the aluminum source to form metal-organic matter precipitates.

A literature study was conducted to investigate the interplay between gibbsite and dissolved organic matter (DOM). Four processes are primarily studied in this research, they are: the release of free Al via dissolution of gibbsite; the complexation between free Al and DOM; the protonation and subsequently precipitation of DOM and the adsorption of H⁺/DOM onto the gibbsite surface. Thereafter the following hypotheses were formulated:

•The extent of gibbsite dissolution is larger at low pH. However, due to its low solubility and slow dissolution kinetics, a low concentration of free Al is expected.
•The organic matter (OM) source used in this study is a humic acid, therefore it is expected to become completely insoluble when the pH is below two.
•The contradicting pH dependency of gibbsite dissolution and OM solubility leads a narrow transitional pH range, that is favourable for the occurrence of complexation between free Al and DOM.

These hypotheses are tested by performing experiments in the laboratory, where the pH varies from 2 to 8 and the aluminum/carbon (mol/mol) ratio is 0; 0.05; 0.1; 0.3 and 1. A synthesized crystalline gibbsite powder and a potassium humate are used.
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The results are subdivided into three pH ranges in which similar behaviour was found. In the low pH range (pH = 2 - 2.5), the protonation and subsequently precipitation of DOM is the dominant process in short term. However, when considering the long term behaviour, gibbsite dissolution is the dominant process as the DOM has precipitated. Due to the difference in time scale, there is very little complexation between free Al and DOM. In the transitional pH range (pH = 3 - 3.5), the competition for H⁺ between DOM and gibbsite is profound. This increases the solubility of DOM and slows the dissolution of gibbsite down. As a consequence, this favours the gradual complexation between free Al and DOM. Nevertheless, due to the ambiguity of free Al measurement method used in this research, it is difficult to quantify the complexation. In neutral to high pH range (pH = 4 - 8) DOM undergoes protonation over time but stays soluble. The release of free Al via the dissolution of gibbsite is negligible in this pH range. Therefore complexation between free Al and DOM should not be expected.

The results presented in this research indicate that gibbsite may not be suitable as the aluminum source to form precipitates with organic matter in engineering solutions that require fast soil permeability reduction. However, the slow release of free Al from gibbsite in combination with the gradual formation of precipitates with organic matter might be interesting for robust problems that require a self-healing ability. For efficiency concern, another OM source that is rich in fulvic acids (higher solubility at low pH than humic acid) and a natural gibbsite source (higher solubility than synthesized gibbsite) should be investigated.

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.

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.

The industrial site of Vosdonk Noord at Etten-Leur in the Netherlands consists of a large soil contamination in combination with highly heterogenic shallow subsurface soil characteristics. In this report, we study the groundwater flow and solute transport behaviour at this project location. Throughout this process, knowledge is gathered about the interpretation of the shallow subsurface heterogeneity with a main focus on the hydraulic conductivities. It is interesting to look at the subsurface heterogeneity because of the challenge to implement it inside a model and its uncertainty in characteristics. This means the subsurface heterogeneity is part of the problem to be solved. A comparison of groundwater flow and solute transport results were made using kriging as an interpolation method to implement subsurface cone penetration test data directly into the model. This generated a cell by cell implementation of the subsurface characteristics. To include the possible variability of the subsurface and to increase the reliability of the results, random simulations were implemented. In practice, the “pancake” method characterises the subsurface in a commercial software like Visual Modflow. This “pancake” method uses continuous horizontal subsurface soil layers. The gathered knowledge is useful to try and tackle the in practice used “pancake” method in case of a highly heterogenic subsurface.

Blockages in irrigation during bioleaching operation cause additional production costs and might negatively influence metals yield. The main research question was to find out if the lifetime of the irrigation system can be extended. Production process was investigated from various angles in search of causes and patterns of solution flow blockages due to calcium sulfate precipitation which was identified as the main reason of clogging. Large number of process data was statistically analyzed. Clear correlation between the PLS temperature and calcium concentration in the solution was drawn and it was found that it is far different from any other research presented. Calcium solubility was experimentally tested – solution was cooled down to approx. 4 °C and agitated daily. Results were unclear, however, on average, calcium concentration decreased by approx. 100 mg/L. The ambiguity of the initial solubility trials led to designing a new experiment. Investigation of the system pointed out critical points and allowed for the formulation of clogging control strategy. Primary calcium sources were found within the ore and metals recovery plant; sulfate is produced during bioleaching process and added to the solution with sulfuric acid – pH control. Forced precipitation of gypsum was proposed as the most viable solution. Conceptual precipitation pond was proposed based on seeded batch crystallization of gypsum. Moreover, clogging was found more prominent in areas with lower pressure head thus redesigning of the irrigation system was suggested along with implementing pulsating pressure. The outcomes of this study set a new direction for the company to counter calcium precipitation problem.

Aftercare of sanitary landfills represents a burden for future generations, for emission potential of leachate and gases remains for hundred of years. Treatment methods have to be developed in order to accelerate waste degradation and reduce emission potential preferably within the time-span of one generation. Aeration seems a promising treatment method but as yet has to be proven effective as a methodology to enhance waste degradation at full scale. Water content plays a crucial role in evaluating aeration, but the highly heterogeneous nature of a landfill body poses a big uncertainty in quantifying it and therefore also quantifying the effectiveness of aeration in reducing emission potential. To improve understanding of water within a waste body, Electrical Resistivity Tomography ERT is to be used to indirectly measure water content by obtaining electric resistivity information. However, full scale landfills have large areas and therefore a protocol needs to be developed for generating an optimum survey strategy, so that high resolution information is obtained while covering a large area. This thesis presents such a protocol consisting of four parts. First, optimum spread and spacing are defined by building a Pareto front with resolution and covered area as objective criteria. Second, array is designed in the previously defined grid, with standard and non-standard four-electrode configurations, by using a goodness function applied to multiple channel acquisition systems. Third, array design is tested with synthetic models showing that smooth resistivity models are well captured by data inversion, but array design performs poorly in a sharp resistivity model. Finally, practical aspects namely injection time, polarization effects and unstable configurations which are usually overlooked, are shown to have significant influence in data quality. This protocol is intended as a systematic approach to generate an optimum ERT survey strategy which could be extended to other geophysical methods.

Additional master thesis