This study investigated the possibility of enhancing immobilization of heavy metals in hazardous fly ashes by mineral carbonation. The research initially investigated five different fly ashes for their chemical composition and carbonation potential. The highest lime content resulted in the highest carbonation potential, but mineral carbonation occurred also in other fly ashes with very limited free lime. One of the municipal solid waste incineration (MSWI) fly ash (FA) with a high heavy metal content and the highest carbonation potential was selected for further carbonation and immobilization investigations.
The selected MSWI FA was carbonized following the first three out of four possible different routes:

1.Pre-carbonation of fly ash and casting with binder
2.Pre-carbonation of fly ash-binder mixture and casting after carbonation
3.Curing of the sample in the carbonation chamber
4.Carbonation of fresh mixture during mixing

The materials were tested for their crystalline composition before and after curing as well as for effective carbon-uptake. The second route resulted in the highest effective carbonation for the MSWI FA but also in the lowest compressive strength. The third route showed an increase in strength compared to the reference sample and effective reduction of final pH on the leachate and electrical conductivity. A fast shake leaching test was used to determine the leachability of relevant anions and cations from the mix designs. The results were compared with a reference sample prepared following a procedure used in industrial-scale applications and with the Dutch Soil Quality Decree and Regulation (Ministerie van Infrastructuur en Waterstaat, 2022).
The leaching tests resulted in an increased immobilization of lead, copper, and zinc for both a MSWI FA and a biomass (BM) FA also selected for its high carbonation potential. The highest total immobilization was reached for the MSWI FA through pre-carbonation of fly ash-binder mixture as the high reduction of pH of the sample cured in the carbonation chamber increased the solubility of other heavy metals. The immobilized BM FA through carbon-curing resulted in the optimal immobilization solution, followed by the pre-carbonation of the mixture of binder and fly ash. For both tested materials, the addition of carbonation outperforms the reference samples.
The comparison with the Dutch soil decree showed promising outcomes for future development of mineral carbonation for immobilization of hazardous materials. The carbonized specimens met most of the requirements for construction materials, which were expected to be more stringent than those for landfill use. The materials were evaluated under a worst-case scenario, showing the effective reduction of lead leachability. The carbonation of hazardous materials offered potential for application in highly lead-polluting waste streams to reduce carbon emissions and contribute to a cleaner environment.

On the 14th of July 2013, a methane peak was observed in the Gale crater. This methane peak has been investigated in a non-biological context before. This study applies exoplanet research strategies and knowledge about biological methane production on Earth to investigate the biological context. Bayes formula is the foundation of the Bayesian framework approach as proposed by Walker et al. [53]. This Bayesian framework allows for separate investigation of biotic and abiotic methane production pathways to assess the likelihood that one of these pathways is responsible for the methane observation. Before probability is investigated, the viability of biotic methane production is gauged by Thermodynamic calculations. These calculations use the Gibbs free energy and show methanogenesis and sulfate reduction as viable catabolic reactions under Martian temperature and chemical soil and atmosphere compositions. Mars analogue Experiments were conducted into the kinetics of methane and hydrogen sulfide gas production under the influence of Martian Regolith analogue and Martian atmospheric analogue. The seed organisms were gathered from the Belgian Boom clay layer in the HADES lab because the Boom clay layer has strong mineralogical similarities to the Martian regolith. The experiments show that both methane and hydrogen sulfide gas production is not significantly affected by the introduction of modified Phylosilicate Martian Regolith Analog (P-MRA) and Martian Atmosphere Analog (MAA). Comparison with the ADM1 kinetic model shows that only methane gas production is comparable within one standard deviation between all experiments and the model. Biomass growth and sulfur gas production are inconsistent between experiments and the kinetic model. To quantify the probability of biotic methane production, a modified ADM1 model was used for Monte Carlo (MC) analysis of the correlation between the Martian observed methane peak and the kinetic model output for varying initial chemical conditions and virtual reactor volumes. Based on this, 78% of the simulations showed a significant correlation. Using Bayes formula, the posterior probability of the methane peak being biological in origin is higher than the prior probability of an anaerobic community being active around the Gale crater. However, this misses the crucial information on the chance of this methane peak occurring in abiotic conditions.

To limit global warming to 2 °C or below, the IPCC emphasizes the need for large-scale carbon dioxide removal (CDR) alongside emissions reductions. There is a growing recognition of ocean-based CDR techniques and expanded research is needed. This thesis investigated the long-term (>100 years) carbon sequestration potential of enhancing the biological carbon pump by ocean nitrogen fertilization, a research domain which so far has received little attention. The objective was to make an initial rough quantification of the (cumulative) CDR potential of one-off ocean nitrogen fertilization achieved within 5 years after the fertilization, to evaluate its potential as a global CDR technique and for commercial implementation.
An idealized one-dimensional vertical (1DV) model framework, coupling a marine ecosystem model with a vertical eddy diffusion physical model, was established to simulate ocean nitrogen fertilization, incorporating essential processes of ocean productivity and the biological carbon pump. Half of the ocean was excluded from the framework since these regions are incompatible with 1DV modelling. Additionally, regions where nitrogen is not the first limiting nutrient were excluded. Various fertilization simulations were performed in which the nitrogen limitation in the mixed layer of the remaining ocean areas was replenished by a one-off addition. Long-term carbon sequestration resulting from fertilization was assessed by comparing these simulations with baseline simulations of the biological carbon pump. An aggregated global outcome, forming the basis for feasibility assessment, was derived by averaging over simulations, while excluding hexagons with low sequestration efficiency as they contribute insignificantly to CDR.
In principle, the one-off nitrogen fertilization shows an effective carbon sequestration efficiency (2.95 kg CO2 per kg N). However, the high and challenging-to-reduce carbon footprint of current urea production, coupled with challenges in collecting manure and the priority of utilising it in agriculture rather than directing it for carbon removal, leads to a low overall global carbon sequestration potential. Nevertheless, it is demonstrated that implementing one-off nitrogen fertilization at a location with high sequestration efficiency using manure can be commercially viable. The cost per net tonne of CO2 sequestered is lower than the current market price of a carbon credit, considering the transportation is conducted with vessels that would have navigated the route regardless.
Based on the findings of this study, it is concluded that nitrogen fertilization has very limited potential to serve as a large-scale global carbon dioxide removal strategy, but can be effectively employed on company-level using surplus manure without agricultural purpose. The initial quantification, despite inherent limitations such as the use of a 1DV modelling approach, serves as a valuable addition to the scarcity of research in the domain of ocean nitrogen fertilization. Further more detailed research into strategic nitrogen fertilization for company-level CDR is justified, with this study providing valuable guidance on optimal research locations.

The geo-technical quest to couple technical, environmental, and economic innovation, has increased recent attention towards bio-inspired soil strengthening techniques. This thesis presents a proof-of-concept for a coupled clay inhibition and bio-cementation treatment tested in sand-bentonite, referred to as Bio2Cementation. Fine particles are first aggregated using a nitrogen based compound. By binding the electrical double layer of clay minerals, the aggregates become chemically and physically stable. Thereafter, bio-cementation treatments hydrolyze urea to precipitate calcium carbonate crystals within the pore space. The crystals bind the mineral particles, increasing the strength and stiffness of the soil.
State of the art considerations regarding enzyme induced calcite precipitation and guanidinium hydrochloride research are used as the theoretical foundation for the treatment’s design. A diverse sand-bentonite matrix is tested, comprised of 10% and 30% bentonite, to evaluate the applicability limits of the technique. The implementation is tested in flow-cells, whereby soils are injected with Bio2Cementation treatments. Experiments show the dominant role of guanidine for stabilizing clay particles – the matrix aggregates, hydraulic conductivity improves by two orders of magnitude, surface charge interactions are minimized, and swelling is halted irreversibly. Hydraulic conductivity calcultations, unconfined compressive strength tests, image analysis of Micro-CT scans, and scanning electron microscope imaging evidence to notably improved bio-cementation following guanidine injections. Consistently, the optimized enzyme induced calcite precipitation was found to crystallize vigorously in 10% bentonite samples, but less successfully in optimally compacted 30% bentonite soils. The concept of Bio2Cementation is proven to work within certain limitations.
Future research should explore the role of different clay minerals such as kaolinite, in view of better defining the treatment’s engineering applicability in-situ. Additional strength testing, soil-structure interaction analyses and environmental impact studies are also recommended

The nautical bottom is defined as the level where physical characteristics of the bottom reach a critical limit beyond which contact with a ship’s keel causes either damage or unacceptable effects on the controllability and manoeuvrability of ships. The nautical bottom is usually assessed using the density of the bottom fluid mud layer as a criterion. However, for navigability purposes, rheological properties of bottom layers (and in particular yield stress), rather than density, are key parameters. The rheological properties of fluid mud depend on both the density and composition of mud and this composition can vary over time, owing to organic matter degradation.
In this study, the influence of organic matter degradation on the rheological properties of mud is investigated. A total of 129 samples from different locations and mud layers (depths) from the Port of Hamburg were analysed. They were degraded in the laboratory under aerobic and anaerobic conditions for 250 days. The rheological properties of these samples were analysed before and after degradation using a rotational rheometer (HAAKE MARS I).
The rheological properties of the samples before and after anaerobic degradation were significantly dissimilar. On average, the fluidic yield stress decreased by 26 %. This percentage had a strong positive correlation with the total organic carbon contents and degradabilities of the samples under consideration. In contrast, the seasonal variability of the samples did not show any correlation with the rheological properties.
After degradation, the decrease in total organic carbon content is small and could not be correlated to yield stress changes. This leads to conclude that the structural breakdown of organic matter and/or the breakdown of organic bridges between organic matter and clay particles are the reasons for the decrease in strength.
The fluidic yield stresses of the aerobically degraded samples increased by 2 %. The difference with their anaerobically degraded counterparts is suspected to be caused by oxidation, which could add cohesion to the mud. From this study, it can be concluded that intentional organic matter degradation during dredging operations could be very effective in making the mud navigable.

Climate change, population growth and urbanisation contribute to an increasing demand for freshwater resources. In order to face this challenge, stormwater harvesting for aquifer storage and recovery has gained interest over the past decades. However, pollutants from various surfaces are transported with the runoff, posing a threat for receiving groundwater upon aquifer infiltration. Biofiltration is a low-cost and low-energy technology that uses natural processes to improve the stormwater quality. Heavy metals are a contaminant of concern, because of their lack of degradability and toxicity at low levels. So far, removal potential has been shown in lab and column tests, but field research is limited. Furthermore, most biofiltration studies focused on removal of total metals, whereas dissolved metals are known to have higher bioavailibilities and thus toxicities. This research aims to gain more insight in the processes in field scale biofilters, by monitoring and analysing the concentrations of metals (Fe, Mn, As, Co, Cr, Cu, Ni, Pb, Zn) in the inlet and the outlet of a stormwater biofilter in Spangen, Rotterdam. In the analysis, a distinction was made between the total metal concentrations, consisting of dissolved and suspended metals, and dissolved metal concentrations. The main chemical water composition was also monitored, to get a better picture of the conditions in which the biofilter was operated. This information was used to identify how the design and operation of the system can be improved with regards to metal removal. Additionally, a transport model in PHREEQC was used to estimate the lifetime of the biofilter before breakthrough occurs, and how operational choices affect this lifetime. Preferential flows and short-circuiting as a result of design- and operational choices were uncovered by analysis of the electrical conductivity. Heterogeneous distribution of water on the filter and the inlet located closely to the outlet contributed to this. A great variation in hydraulic conductivity supported these observations. The hydraulic conductivity was generally much higher than is recommended for biofilters. Additionally, the system was irrigated with recovered water from the aquifer to avoid a foul smell of extracted water and keep the biofilter wet during longer dry periods. This means that the system was not only fed with stormwater, but also with water from the aquifer. Feeding of two different water sources with different compositions lead to the increase of total and dissolved concentrations of As, Co, Cu, Ni \& Pb in the outlet, as well as higher dissolved Zn concentrations. Phoshate, ammonium, and total and dissolved concentrations of Fe, Mn, and Cr on the other hand decreased. The effect of mixing of two different waters was accounted for, by estimating the expected concentration of each pollutant if mixing was the only mechanism effecting their concentration. This was done using mixing fractions based on the electrical conductivity. Differences in estimated and measured concentrations showed that the release and removal of various pollutants was not a mere result of mixing only. The change in water composition and subsequent competition for sorption spots was found to be the main mechanism involved. The transport model showed that preferential flows resulted in C/C0 = 0.8 breakthrough of metals occurring much faster than in a plug flow. These observations show that the current design and operation of the biofilter do not provide adequate removal of metals in the biofilter.

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 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.

Study of self-sealing and self-healing in clay is a fascinating topic which can be applied in many fields namely in construction sector or as the underground nuclear waste repository. However, lack of references still hinders the advancement of such field. Meanwhile, more advance researches are available for self-sealing and self-healing in concrete. Therefore, this project is held to find whether any valuable lessons from extensive researches of self-sealing and self-healing in concrete which can be applied to the development of the study in clay. This research is a comparative literature study of self-sealing and self healing mechanism between clay and concrete based on four aspects i.e. hydraulic, thermal, chemical and mechanical which based on the published papers from scientific journals and books. In terms of hydraulic aspect, hydraulic gradient plays an important role for sealing and healing mechanism in both clay and concrete. For thermal aspect, hydraulic conductivity is not affected by the temperature increased in clay while sealing and healing rate are improved for the similar condition in concrete. In chemical aspect, high pH environment increases sealing rate of concrete while high salinity decreases the capacity of sealing and healing of clay. For mechanical aspect, both concrete and clay experience a decreasing hydraulic conductivity under increasing confining stress. All of the results showed that both clay and concrete experience self-sealing and self healing mechanism with different influences by each aforementioned aspect.

Land subsidence is a complicated phenomenon, relevant in the Holocene coastal-plain of the Netherlands, that can be triggered by many different mechanisms and components. To cope with the effects of land subsidence, detailed information on which mechanisms are causing subsidence and its variation over time and space are needed. Subsidence studies predominantly focus on grass and agricultural areas with organic soils above the groundwater level. In this study, subsidence is also evaluated for dikes and the urban environment. It is attempted to model subsidence behaviour of four different projects, grass plots within the Krimpenerwaard polder, locations along the N3 Dordrecht, an embankment constructed for the A5 Badhoevedorp and locations along the Markermeerdikes, and to verify these model results with subsidence measurements available. Existing one-dimensional models for different subsidence components are used in the evaluations. For grass and agricultural areas it is found that subsidence behaviour could be modelled and the results lie within the range of uncertainty of the subsidence measurements used. However, the equations used are often empirical and do not include all relevant influencing factors and couplings. Compression by degradation of organic material as a response to drainage of organic soil is the main subsidence component in these areas. Anaerobic degradation of organic material is also included in the modelling approach, a component that is often neglected in other subsidence studies. Two infrastructure related projects provided insight to subsidence components in the urban environment. Compression by loading is the main subsidence component relevant in this area type, and thus settlement models are suitable to approximate the subsidence behaviour. However, a slight underestimation of creep shows that the existence of a small additional subsidence component for a situation with soft soil layers pushed below the water table could not be excluded. Unravelling subsidence behaviour from dikes showed to be more complicated, where an interplay between different components is relevant. Based on the evaluation in this study compression by loading and compression by an oxidation or shrinkage component are indicated the main subsidence components. Many uncertainties and assumptions used in this evaluation influenced the results. For all area types disentangling subsidence into contributions of separate components based on a total measured subsidence signal causes large uncertainties, as modelled subsidence contributions for individual components could not be verified.

To cope up with the rapid industrialization, urbanization and population it is very important to make use of sustainable water treatment technologies to reuse the processed water. Now a days, with technological advancements in anaerobic digestion (AD) process it is possible to recover some of the resources. AD can be coupled with the membrane to provide the complete biomass retention ensuring the growth of slow growing bacteria. Considering these aspects an innovative configuration of Anaerobic Membrane Bioreactor (AnMBR) with limited aeration is developed aiming to improve the reactor performance. This AnMBR is tested, comparing its performance before and after aeration to assess the impact of subjected aeration especially on the activity of methanogens monitoring the biogas production and its composition. Results show that limited aeration helped in achieving significantly lower overall COD removal without adversely affecting the biogas production as well as composition. It also improved the biodegradability of less biodegradable ovalbumin (protein).Furthermore, limited aeration might improve the biotransformation of some of the recalcitrant micropollutants (MPs) possibly by activating mono-oxygenase enzymes of micro-organisms. They might convert the aromatic hydrocarbons into less recalcitrant phenolic intermediates, whose degradation process could occur anaerobically. From the group of available MPs, diclofenac (DCF), metoprolol (MPT), sulphamethoxazole (SMX), trimethorprim (TMP) are selected based on different characteristics. All the selected MPs are analysed for their removal through biodegradation and adsorption under anaerobic conditions. MPs are tested from liquid phase in dissolved form through liquid chromatography coupled with mass spectroscopy (LC-MS) technique while MPs sorbed onto the sludge surface are not analysed because of complex extraction process.Results shows that SMX and TMP are removed more than 99% through AD while DCF is removed with removal efficiency of more than 90%. Adsorption is found to be a major contributor for the removal of DCF, MPT and TMP while SMX is mainly removed through biodegradation. DCF and TMP are adsorbed well (>90%) compared to SMX and MPT (around 30%) onto the sludge contributing to overall removal. Octanol water coefficient (Kow) which defines the hydrophobicity of compound, is the key parameter deciding the extent of adsorption. Additionally, sludge retention time (SRT) and compound structure play major role in deciding the fate of MPs through biodegradation. Different aerations had not shown any significant impact on the removal of DCF, SMX and TMP. While in case of metoprolol effect of aeration was not completely understood. Considering the overall removal, DCF was found to be bio-degraded more with increased concentration. Granular activated carbon (GAC) used for adsorption removed all the four MPs with more than 90% efficiency. Further studies can be conducted on possibilities of adding GAC to the reactor so that they get adsorbed and later on degraded.

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.

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.