This study aimed to evaluate the field scale potential of Microbially Induced Desaturation (MID) to improve the compactibility of silty sands. Conventional soil compaction techniques for saturated silty sands often require either high compaction effort or even fail to reach aspired relative densities. This thesis is a follow-up study based on the promising small scale results of Stals 2020. The proposed solution consists of a two-stage method in which, firstly, a soil sample was desaturated by means of Microbially Induced Desaturation (MID) through denitrification and, secondly, dynamically compacted. The objective of this, and previous, research was to assess whether biogenic gas formation could be used as a pretreatment to increase the effectivity of soil compaction techniques. Tests with a height of 1m and 2.5m were developed, opposed to the previous 15cm small scale tests. Series of tests were conducted on a silt-sand mixture of 16% fines. Each series was compacted with both a different compaction method and energy input. The investigated scale effects included: the desaturation stage, bubble growth, bubble distribution, gas migration and final degree of compaction. All treated soils were able to desaturate to, and even below the optimum water content. In this research the in-situ shear strength was linked to swelling and bubble production. Based on a qualitative inspection, the gas distribution in the sample was found to be homogeneous over depth. In order to estimate swelling and venting of the sample during the desaturation stage, a model was produced based on a saturation dependent gas conductivity. It was suggested that a continuous gas phase was responsible for the highest amounts of compactive strain. With a non-intrusive compaction method, more compactive energy led to faster, but not more, release of gas. All 2.5m tests ended with a residual amount of gas. A 1m test series, consisting of three tests resulted in higher degrees of compaction for the treated tests opposed to the untreated tests. The final relative density of the treated tests was at least two times higher than the final relative density of the untreated test. A 2.5m test, which included surcharge, had a final RD 2.8 times higher opposed to a similar untreated test without surcharge. Taking into account the uncertainties of the results, it was concluded that a field trial is feasible. A hypothetical field case was set up of 500 m3. The costs of the proposed method were a factor 2.2 times cheaper opposed to the current soil improvement for silty sands, namely a stone column vibroreplacement technique.

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.

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 construction of the new airport of Mexico City (NAICM) is challenging, as the subsoil at the site is very weak. The airport, which is under construction at the moment, is located on top of thick layers of Mexico Clay soils. These clayey layers consist of a mixture of both clay particles and pyroclastic volcanic materials. These unique soils are characterised by a high water content and compressibility. Upon loading, the soft soils will settle as a result of the consolidation process. This consolidation is defined as the dissipation of excess pore water as a result of an increase in stress. The rate of consolidation is governed by the hydraulic conductivity of the soil, which is in general very low in soft soils, and the drainage path. In order to speed up this time consuming process, vertical permeable elements can be installed in the soil. Upon installation of these elements, a reduction in drainage path is realised. This reduction in drainage path allows faster dissipation of excess pore water pressure, hence reducing the consolidation time. Due to the conditions at the site, the design of the runways is challenging. The differential- and residual settlements need to be within strict boundaries in order to keep the runways operational. Prior to the design of the runways, trial embankments have been constructed in order to measure the performance of different soil improvement techniques at this specific site. Based upon this field test results, prefabricated vertical drains (PVDs) were selected as the most efficient soil improvement technique. Besides the PVD trial, the sandpile trial also showed promising results. The PVDs and sandpiles both decrease the drainage path length inside the soft soil layers. The main difference is the relative high stiffness of the sandpiles, the stiffness of the PVDs is negligible. By installing stiff elements in the soft soil, the loads applied on the top of the soils are transferred to deeper and stiffer soils. Hence, the total settlements of the top soft soil layers are reduced. The sandpiles could therefore be feasible alternative to PVDs, applied at locations in which the total settlement needs to be limited. The investigation into the behaviour of sandpiles in Mexico Clay soils is performed in multiple stages. First, analytical models are used for gaining knowledge about the expected sandpile behaviour. In the second stage the FEM software Plaxis 2D is used for the numerical modelling of the sandpiles, using an axisymmetric model setup. The model is constructed in multiple steps, with increasing complexity. The first models simulate the material behaviour with the Mohr-Coulomb model, in the advanced models the Soft Soil Creep and Hardening Soil models are used. The final numerical model is verified by the measurement data obtained from the field trials. After fitting the numerical model to the field data, the verified model is used in the sandpile sensitivity analysis. In this analysis the sensitivity of the material properties and geometry of the sandpile on the performance are researched. The residual settlements or performance, which is defined as the difference in settlement after construction and over a period of 8 years, is affected by the length, radius and centre to centre (ctc) distance of the sandpile. Adjusting the pile stiffness has minimal effect on the performance of the sandpile. An optimum in performance is found by varying both the pile radius and ctc distance. A combination of a small pile diameter with a small ctc distance results in the best performance. When comparing the performance of both sandpile and PVD, the PVD is found to be more effective in terms of performance. The additional stiffness of the sandpile is not reducing the total settlements, on the contrary, the self-weight of the piles increases the total settlements by providing an additional load to the soft soil layers located underneath the pile tip. In conclusion the sandpiles have no additional benefit over the use of PVDs, therefore the application of sandpiles at the NAICM site is not a feasible alternative to the use of PVDs.

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. igskip 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.

Conceptual hydrological model parameters represent characteristics of a catchment. They are an integration of spatial heterogeneous parts of the system. Finding adequate parameter values based on field observations, which represents the heterogeneity of a catchment on the spatial resolution and scale of the model, is considered challenging since the scale of the observations do not meet the scale of the parameters. The objective of this thesis is to analyze the extent to which it is possible to make an estimation of parameter distributions based on field observations (the precipitation, evaporation and discharge) and a given hydrological model structure. The goal is to avoid the use of uninformed prior parameter distributions during calibration by using available field data to generate informed prior distributions. In this research, six different expert-knowledge inverse modelling methods are developed to find four parameter distributions. Each method uses sub-periods in the data and is coupled to the parameter of the model component representing that specific type of sub-period. To test the methods, the study was conducted in a synthetic environment, which made it easier to validate the parameter distributions obtained with the methods. In this synthetic experiment, discharge data was produced by a model driven by real rainfall data and potential evaporation data. All forms of uncertainty were excluded in this test. The effect of data uncertainty in the methods was investigated separately by conducting a sensitivity analysis. The same synthetic data was used; however the synthetic data was corrupted to simulate data uncertainty. Last, an application of the methods upon real measured data was completed. The performance of the methods to find parameter distributions can no longer be assessed since in the real world the “correct” parameter values are not known. However, a comparison of the informed prior parameter distributions of the methods with uninformed prior parameter distributions could be made with a Monte-Carlo sampling strategy calibration. In the synthetic experiment, all parameter distributions of the investigated model were correctly determined using the expert-knowledge inverse modelling methods. The sensitivity analysis revealed that the method to determine the maximum percolation rate parameter (Pmax) distribution was sensitive to data uncertainty. The determined Pmax parameter distributions did not include the original parameter of the corrupted synthetic data. However, this issue does not lead to other parameter distributions that do not include the original parameters. In real-world application, insight is gained into the performance of the developed methods to find parameter distributions. An uncertainty interval was constructed with the Generalized Likelihood Uncertainty Estimation (GLUE) method. The total area of the constructed uncertainty interval using the calibration results of the informed prior parameter distributions was less than half than the uncertainty interval constructed using the uninformed prior parameter distributions. The posterior parameter distributions of the informed parameter distributions was two to five times smaller than for the uninformed parameter distribution. The model performance of both calibrations did not deviate significantly, indicating a sufficient model structure for the catchment and an adequate performance of the methods to find parameters.

A considerable contribution to the greenhouse effect originates from landfills. This contribution originates from the degeneration of waste in the landfill. The gas which is created during the degeneration consists of 40 to 60% methane. One mole of methane has a global warming potential which is 28 times higher than that of carbon dioxide. Therefore, emissions of methane should be reduced. One method which can be used to reduce this emission is the oxidization of methane to carbon dioxide. This can be done by the construction of a cover soil with methanotrophic bacteria in the soil. These bacteria oxidize methane as their source of carbon and energy. This oxidation process discriminates against the heavier isotopes present in the gas, this shifts the isotope signature. A method to determine the oxidation efficiency of the methane is based on the evaluation of this change in isotope signature over the cover soil. Next to the fractionation of isotopes due to oxidation, fractionation also occurs due to diffusion. However, fractionation due to diffusion is generally assumed to be negligible. Mostly, this assumption is valid, since the dominant part of transport is advective; which does not discriminate against an isotope. In this thesis the effect of compaction and saturation on two sands are evaluated. Using this evaluation, the criteria during which diffusion becomes an important transport phenomena are determined. This is determined by a series of experiments, where the concentration of methane is monitored while the gas diffuses through a soil sample. In this thesis the effect of the soil matrix on the fractionation of methane is also evaluated. This is evaluated by performing isotope spectrometry on samples of gas, taken at different times during the experiments. These two aspects are combined to evaluate if the oxidation efficiency can still be determined using fractionation of stable methane isotopes when diffusion plays a considerable role in gas transport. During the experiments the decrease of methane in the chamber was measured. Spread over two soils, for a total of 18 variations in compaction or saturation the decrease of methane over time was measured. The results of the experiments show that for diffusion no distinction between variation in compaction and saturation needs to be made. Compaction and saturation can be described together for both soils using the air-filled porosity. The relation between the air-filled porosity and the effective diffusion coefficient is linear for both soils. Due to the large sand fraction the share of coarse pores is high for the whole range of compaction, meaning that no significant increase of tortuosity is visible in the relation between air-filled porosity and the effective diffusion coefficient. When the effective diffusion coefficients are compared to effective permeability values of these soils, it showed that the diffusion is more important for drier and more compacted soils. Thus, diffusive transport becomes important for gas transport over a cover soil when the pressures are lower, the soil is drier, and the soil is more compacted. The fractionation factors due to diffusion, which have been determined for a selection of experiments, showed no trend with any other measured parameters. The precision of the measured values from which the fractionation factors are determined is high. Thus, the confidence in the fractionation factors is high. The lack of a trend present means that in sand the soil matrix has no effect on the fractionation factor. This means that the fractionation factor due to diffusion in soil is the same as in free air. For the calculation of the oxidation efficiency with a relevant diffusive flux the ratio of diffusive to advective flux needs to be determined but the fractionation factor due to diffusion is constant. Before the oxidation efficiency can be calculated, first the load needs to be corrected for any loss through hot-spots. Next, the advective flux and diffusive flux are combined, this is done by adding the fluxes together. The fluxes can be added because there are no interdependent effects, each flux only increases the total flux. Thus, the oxidation efficiency can be calculated using the changes in isotope signatures, even when a significant diffusive flux is present.

"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.

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 퐷KL 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 퐷KL 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.

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.

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.

The management of sediment, soil and water in the Netherlands dates back to the first settlements in the lower Northern and Western parts of the Netherlands. Around 500 B.C. farmers constructed ‘terps’ (artificial dwelling mounds) to protect against floodwater. The Romans (50 B.C. – 250 A.C.) reshaped natural waterways, to improve transport by ship. This also meant that river embankments were constructed and waterways and harbours had to be dredged. With the construction of river dikes in the period 700 – 1200 A.C. the sediment challenge began. The peatlands behind the dikes dried out, creating land below the average sea level. Dikes and dike maintenance therefore became crucial and since 1255 A.C. the first official governmental bodies, public utility boards (waterschappen) were created. These public utility boards together with the Dutch government, provinces and cities are still responsible for sediment and water quantity and quality. With this timeframe in mind, the scope of this thesis, examining developments in sediment and water quality management in the Netherlands over the past 25 years (1993 – 2018) is relatively short. A critical focus during these past 25 years was the heritage of industrial pollution of waterways and sediments from the early twentieth century. During the past 25 years changes took place in the way risks of contaminants in sediment and water were evaluated, partly due to scientific progress on the ecotoxicological impact of contaminants. As important as the scientific progress were the policy and legislation changes. These changes are driven by a broader spectrum of societal needs, like safety against flooding, scarcity of public funds and the need to change to a more circular economy using sediment as a resource. The goal of this thesis is to help water managers to understand the mechanisms that change the ecotoxicological risks in their water and sediment systems, providing tools that go beyond the legislation requirements to assess these risks.@en

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.