In order to improve the climate resilience and liveability of Curaçao’s Inner-City, various
interventions are proposed for Wilhelminaplein in Punda to mitigate the problem of heat stress, along with socioeconomic issues. This is done while keeping the problem of water scarcity in mind. Among various problem locations in the Inner-City, Wilhelminaplein was chosen as a development site because of its high potential and advantageous location. The main problems facing Wilhelminaplein are found to be extreme heat and lack of clear function, shade and maintenance.
Various possible solutions are proposed and discussed with experts, including a landscape architect and urban planner. Following this, the interventions are finalized and presented to various stakeholders, including representatives of relevant government agencies. Through a workshop, the stakeholders provided feedback on their preferred set of interventions.
The proposed interventions are subdivided into ’quick wins’, cool spots and additional interventions.
To quantify the effectiveness of the interventions, PET reductions of the proposed interventions are modelled using the modelling software RayMan. Along with the PET reduction, the initial cost, water usage, required level of maintenance and implementation time frame, are analysed for each proposed intervention.
To facilitate the practical implementation of the proposed interventions, an overview is given of which steps the relevant government agencies still need to take in terms of research, designs, and applying for permits.

For this thesis a hydrochemical groundwater survey was carried out on the Caribbean island of Curaçao in 2020 as part of the NWO SEALINK project. In order to be well-adapted against anthropogenic and natural pressures, Curaçao needs representative data, yet thorough hydrochemical datasets were only sparsely collected in the wet seasons of 1977 and 1992. The aim of this thesis was to determine the current chemical state of the groundwater and analyze for long-term pollution trends with an extended database spanning four decades, also including data that was collected in another fieldwork campaign in 2021.

Curaçao's coral reefs are subjected to a deteriorating momentum risking the health and therefore sustainability of this vital ecosystem. Despite the dependency of the Island's prosperity on the condition of the ecosystem, research suggests that wastewater management is likely to be a significant contributor to this effect. Incorporating both open literature results and information obtained from an extensive constructed research network, this study demonstrates essential aspects of the urban wastewater management system of Willemstad regarding the quantity and quality of the urban wastewater fluxes and their potential environmental implications. The system, which merely connects 33\% of Curaçao's population, is concluded to be outdated and insufficient with respect to capacity as well as treatment efficiency. Although it is solely designed for pure domestic wastewater, this study concluded and demonstrated the significant impact of illegal discharge onto this system by industrial sectors leading to both high contamination loading and increased wastewater volumes. The combination of these features is the major cause of wastewater discharge pathways into marine environments. Arising from the constructed urban wastewater flux model, which visualizes the wastewater management system, 14 discharge locations correlated to significant environmental contamination pathways are identified with Piscadera Bay, Rif Mangrove area, Playa Kanoa and Shut concluded as the utmost importance. Furthermore, the model revealed that the urban wastewater is predominantly directed towards the treatment plant Klein Hofje via either the northern trajectory (Bonam - Suffisant F - Garipitoweg - Argentianweg - Klein Hofje) or the southern one (SVB - Klein Hofje). Also, the quantity and quality of the fluxes are estimated based on the connected area and the potential industrial activities within it. However, validation of these estimations is recommended since no water quantity and quality analysis was performed or available for conducting the modelled estimations. Furthermore, since the system is partly a combined sewage system, hence harvesting stormwater fluxes as well, its effect is recommended to incorporate in the model and estimations for accuracy purposes. Lastly, the government reports that at least 90\% of all industrial wastewater is discharged either directly into the ocean or onto the sewer system. Since the actual ratio as well as the water quality remains unknown this is recommended for future research. Overall, this study enables tailored future research programs to overcome the discussed limitations and with that significantly contribute to eliminating the current existing white spot concerning the effect of urban wastewater fluxes on the marina ecosystem of Curaçao.

Urbanization has led to increased impermeable surfaces, disrupting the natural hydrological cycle and resulting in more frequent urban flooding and pollution. There is an urgent need for cost-efficient and effective stormwater management solutions to improve stormwater quality and facilitate its reuse. FieldFactors' BlueBloqs system integrates stormwater collection, water treatment in a biofilter, and aquifer recharge. The BlueBloqs system's biofilters are soil-plant systems with a submerged zone. Before being used to recharge an aquifer, the effluent from a biofilter must meet specific water quality standards. Improvements in water quality within the biofilter are achieved mainly through static optimization (changing media materials, the depth of layers, and plant species) and dynamic optimization (controlling hydraulic behavior). Some research found that retention time plays a crucial role in the operation of a biofilter, influencing both the quality and quantity of the effluent. The central challenge lies in operating the biofilter's retention time to maximize water recharge while ensuring optimal water quality.

The objective of this research is to determine the optimal retention time for the biofilter to achieve the best water quality while maximizing the total amount of water to be recharged by controlling the pump. This thesis includes water quality measurement and water quantity simulation. In the water quality part, the performance of the biofilter at different retention time (2, 6, 16, and 24 hours) is evaluated in terms of the removal efficiency of turbidity, nutrients (nitrate and phosphorus), dissolved and particulate metals (Mn, Ca, Mg, Ba, Zn), UV254 and DOC with two different influent types (surface water and stormwater). In the water quantity part, Cromvliet Park, with an 8000 m2 collection area, was modelled using Python and SWMM to operate the biofilter with various retention time under one year of rainfall data (total rainfall 731mm). This modelling was done to calculate the total water volume available for recharge. The sections on water quality and quantity were integrated by controlling and evaluating the biofilter based on the retention time.

The results indicate that the efficiency of the biofilter's pollutant removal is influenced by several factors. Turbidity (40-90%) is effectively removed by the filtration in the biofilter. Nitrate removal efficiency was 12-49% with short retention times (2-6 hours) but fluctuated with longer durations (16-24 hours), decreasing to -84-13% and then changing to -6-0%. Measurements of dissolved oxygen in the effluent indicated that an increase in nitrate removal efficiency due to nitrification happened with longer retention time. For dissolved zinc, removal efficiency ranged from 10-60% with stormwater influent and 0-100% with surface water because of the adsorption competition of metals. Combined with the water quantity calculations performed in SWMM, it is advisable to set the optimal retention time for the biofilter at 4–6 hours. This duration allows for the maximization of water reuse while maintaining high nitrate removal efficiency.

Leaching of phosphorus (P) from agricultural land is an important source of eutrophication in the Bollenstreek in the Netherlands. This is because floriculture has led to high P concentrations in the sandy soils with low organic carbon content, which are characterised by a low retention capacity for P. In this study, P concentrations in groundwater from three plots in the Bollensteek were found to exceed the water framework directive (WFD) by a factor of 40. The case study on a single plot showed a phosphate load of 5.5 kg/ha/year leached through the tile drains, which is an order of magnitude higher than fields outside the Bollensteek. To understand where phosphate comes from and how hydrological processes influence leaching, hydraulic and chemical measurements of soil, groundwater and tile drain outflow were taken in a field with regulated tile drainage, and two hydrological models were created to simulate wet winter and dry summer conditions. The results showed the flow paths from this plot under wet and dry conditions and illustrated how hydrological processes can influence phosphate leaching through the soil and tile drains.

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.

Urban water management is faced with upcoming challenges due to climate change, the deterioration of existing infrastructures and the depletion of water sources. Climate change brings about more intense rainfall events and longer periods of drought. On top of that, the deterioration of the piped network urges for investments in the existing system, to ensure that the provision of water services can be maintained. Furthermore, the depletion of water sources is raising awareness regarding the value of freshwater which gives rise to the re­use of water flows that have up to now often been considered as nuisance rather than viable resource. Examples of these flows are the wastewater and the stormwater flow.

The existing centralised infrastructure consists of three reliable systems. The first system supplies high­quality water, the second drains out stormwater and the third one discharges wastewater. These three systems operate separately from each other and follow a linear approach to
water management. In recent years, circular water management has become more prevalent. Instead of following a linear approach in the three separate systems, the re­use of water flows as viable sources are applied more often. New, often local, solutions can be designed to effectively complement existing systems in maintaining the high provision of water services that societies have consistently been using over the past decade. This circular approach can ensure that current water requirement levels can be met sustainably by the improved urban water systems.

By dealing with the upcoming challenges of high­intensity rainfall and long periods of drought– which both have a high spatial variability – local solutions are able to support the centralised infrastructure. This is done by both mitigating the pluvial flood risk, as well as by providing a high ­quality water source. An arguably ideal solution which addresses both the pluvial flood risk and also provides a high­quality water source, is the Bluebloqs system. The Bluebloqs system can help mitigate pluvial flood risk by the attenuation of flow, the result of implementing an attenuation tank in the stormwater drainage system. Also, the Bluebloqs system is able to filter and store this stormwater to provide a high­quality water source during water­scarce seasons.

Whether the Bluebloqs system is a viable solution which addresses both the mitigation of the pluvial flood risk as well as the provision of water challenge, is investigated in this research. The Bluebloqs system is a circular water solution that makes use of an attenuation tank, a bio­filter and an aquifer storage and recovery (ASR) system. The attenuation tank is physically connected to the drainage system and it consequently decreases the risk of surcharged pipes in the drainage network. From the attenuation tank, the water is pumped towards the bio­filter, where pollutants from the water are removed and the water is filtered to such an extent that it can be infiltrated into the aquifer. In the aquifer, the water is stored to overcome seasonal variations in
water availability. The Bluebloqs system has the objective to supply water in the dry season, even though its source is stormwater, which enters the system during the wet season. This research has analysed the performance of the Bluebloqs system for different dimensions and operations.

Within this thesis, a framework has been built that presents the performance of the Bluebloqssystem. This framework consists of three groups; the interactions with centralised infrastructure, the water quality indicators and the impact of the Bluebloqs system on its environment. These three have their own distinct performance indicators, which characterise the effectiveness of the Bluebloqs system in providing a specific water service. The group of the framework dealing with the interactions with the centralised infrastructure uses performance indicators for the volume of water lost in overflow events, and volume of water supplied through the Bluebloqs system as high­ quality water source to the end­user. The indicators for the other groups characterise the Bluebloqs system differently. Each group within the framework projects the performance of the Bluebloqs system for other interest groups. For example, the indicators regarding the impact of the Bluebloqs system on its environment are of interest to municipalities thinking about implementing the system.

The behaviour of the Bluebloqs system has been modelled. This model presents the physical processes taking place within the Bluebloqs system. The output of the model are the performance indicators of the framework. By running the model under different input parameters, the performance of the modelled Bluebloqs system is tested on the three groups of the framework.

The outcome of testing the model on the framework has shown that the Bluebloqs system can be improved. One of the suggested improvements is to work with feed cycles for the bio­filter. These feed cycles consist of the periodic saturation of the bio­filter. Once the bio­filter is saturated, the flow from the attenuation tank towards the bio­filter is interrupted, to let the water gradually filter through the bio­filter.
By applying feed cycles, the bio­filter is better capable of removing pollutants from the water. However, periodically interrupting the water flow from the attenuation tank towards the bio­filter negatively impacts the effective storage capacity of the attenuation tank. When having more feed cycles in a day, these interruptions last for a shorter period of time. Depending on the desired performance of the system, which is based on the performance indicators, these feed cycles should be aligned with the capacity of the attenuation tank and the discharge of the pump for the flow between the attenuation tank and the bio­filter.
Fitting the feed cycles to the seasonality of rainfall patterns can further increase the performance of the system in mitigating flood risks. Applying predictive control when overflow events occur is an additional control option that minimises the environmental impact of the system. Finally, the performance of the Bluebloqs system can be presented based on all the performance indicators included in the framework, and the model can be used to adjust the system dimensioning and operations to present the consequences of adjustments to the desired performance of the Bluebloqs system.

The frameworks’ performance indicators can be used to understand the Bluebloqs ideal configuration to deliver a specific desired performance. The desired performance of the system determines the dimensions and operations of the system. Co­designing the Bluebloqs system is thus crucial to its delivered performance.

In conclusion, the framework and model can be used to present the Bluebloqs system for different scenarios. The framework can generate a comprehensive overview of what can be expected of the Bluebloqs system when implementing it in a specific project site, in comparison to other solutions that may be considered, such as green roofs or storage tanks. Also, its use as circular solution being complementary to existing urban water infrastructure can be presented by the framework and model output. This will help in the transition of urban water systems in dealing with the upcoming challenges related to climate change, the deterioration of the piped infrastructure and the depletion of water sources.

In the winter of 2014 upon 2015 the Hondsbossche dike, between Petten and Camperduin in the Netherlands, has been transformed into a dune area through sand replenishment at the seaside of the dike. The area inland has been appointed as a Natura-2000 area because of the highly appreciated ecological value. A reduction of saltwater seepage would cause potential harm to the flora and fauna which is undesired. Two sectional models of the density dependent groundwater flow have been developed to map out the growth of a freshwater bubble forming beneath the Hondsbossche dunes and the corresponding decline of saltwater seepage to the polders inland. The two sections chosen are a section perpendicular to the coastline through the middle of a small lake De Putten and a section perpendicular to the coastline just south of a small lake Abtskolk. Both sectional models have been tested through a calibration process for the measurement data considering the freshwater head and geophysical properties of the groundwater. From the models the development of the groundwater regime for the coming 95 years has been calculated (100 years in total and 5 years until the present situation). Besides this the development of the groundwater regime in several sectional variations to the developed sectional models have been investigated. This has been done to investigate the impact of certain assumptions in the layout of the sectional models. These variations to the sectional models also are an indication of the range of possible changes to the groundwater regime for the whole area because elsewhere in the area these resulting sections could be present. Looking at the results of both sectional models and all model variations the conclusion can be drawn that the biggest reduction of saltwater seepage takes place in the years 2026 till 2056. Therefore it is advised to take action against the reduction of saltwater seepage before 2031. A sensible way of doing this is to firstly identify the most critical sections perpendicular to the sea in the area of interest. A good first step would be to identify the most permeable spots in the clay layer beneath the dunes. The results show that in these spots a faster spread of the freshwater bubble is expected. Besides this it has become apparent from the model results that the small lake De Putten attracts a bigger fraction of the seepage currents in comparison to the surrounding area. It would be a good idea to investigate where other hotspots for seepage are present in the area. In these areas the reduction of saltwater seepage would most likely be more intense. The identified critical sections would be the best places to start implementing measures against the decline of saltwater seepage. When actions are taken timely and precisely it is expected that the decline of saltwater seepage will remain small and the ecological value of the polders will remain.

Pressure on fresh water resources has led to water scarcity and increasing demand for alternative water resources, such as rainwater. Nevertheless, heavy metal contamination is a limiting factor for re-use of urban stormwater. This research focusses on the adsorption of heavy metal contaminants by biofiltration systems, specifically on the Bluebloqs Biofilter, to fulfil the water quality requirements for infiltration. The effect of various physical and chemical conditions on HM adsorption were assessed.A field experiment was built in the summer of 2019 and operated during 5 months. A range of low to high heavy metal concentrations was synthetically dosed to functional prototype of the Bluebloqs Biofilter, with the aim to characterise both the removal efficiency as well as geochemical processes in the filter media. Results showed that due to saturation of the filter media, Cd and Zn concentrations in the effluent rose above the Dutch infiltration standards after 74 bed volumes. Ni, Cd and Zn were most susceptible for bed saturation as average concentrations over biofilter depth increased by operation. Highest removal of all heavy metals happened in the top 5 cm of the filter bed. A surface complexation sorption model was developed in PHREEQC to evaluate adsorption of Cd, Cu, Ni and Zn. The model was established by calibration on batch adsorption experiment data of the same heavy metals. With this modelling tool, various physical and chemical conditions in stormwater could be easily simulated and extrapolated, as well as characteristics of filter media that could be modified. Surface complexation modelling showed a reasonable fit compared to the Freundlich isotherm.The order of adsorption to the filter media was Cu>Cd>Zn>Ni. Batch simulations showed that by raising solution pH, adsorption of each HM was increased for both quartz sand and iron oxide coated sand. For pH 7.0, the partition coefficient for iron oxide coated sand was 1.34, 16.8, 19.9 and 23.9 for Ni, Cd, Cu and Zn respectively. For pH 8.0, the partition coefficient rose to 12.9, 2.15*103, 282 and 698 in the same order. In the case of quartz sand and pH 7.0, partition coefficient was found 4.7 *10-2, 1.18, 1.41 and 14.8 for Ni, Zn, Cd and Cu respectively. When increased to pH 8.0, partition coefficients rose to 0.7, 34.0, 228 and 201 in the same order.To a lower extent, increase of ionic strength of the solution had a negative effect on the adsorption of Cu and Cd. By increasing the Zn and Cu proportion by a factor 5.0 in the influent stormwater, adsorption of Ni and Cd was negatively affected, but only for unrealistic high concentrations.One dimensional transport simulations were performed for the average stormwater compositions found at the field experiment. Ni showed first breakthrough in the filter due to lower affinity, followed by Zn, Cd and Cu. Increase of the pH from 7.0 to 8.0 delayed breakthrough by a factor 9.2, 15.8, 25.9 and 135.1 for Cu, Ni, Zn and Cd respectively, despite the type of media used in simulations. By changing the 20% of the top layer of the total filter length from quartz sand to iron oxide coated sand in the model, the adsorption capacity increased and delayed the breakthrough of heavy metals by a factor ±2.36 at all pH conditions.Comparison of the established sorption model with field experiment data showed underestimation of Ni adsorption, while Cd and Cu were overestimated. Zn adsorption showed the most similarity between model results and field data. The model cannot provide an accurate prediction on HM adsorption, but it can be used to compare in between HMs.For the first mature system of the Bluebloqs biofilter, operational in Spangen, Rotterdam since the summer of 2018, the first exceedance of the Zn for the infiltration standards was predicted after 410 bed volumes, due to saturation of filter media. This resulted in elevated Zn concentration in the effluent. Further improvement of the sorption model could be established by additional batch adsorption experiments to obtain more trustworthy results.

Biofilters are increasingly being implemented in urban environments to treat stormwater but knowledge on their pathogen removal capacity at field scale is limited. Adequate pathogen removal is, however, needed if treated water is reused. This research evaluates the fate of Escherichia coli, enterococci and Campylobacter in a field scale biofilter in Rotterdam. This biofilter is part of the Urban Waterbuffer Spangen that combines biofiltration with Aquifer Storage and Recovery (ASR) to provide irrigation water for Sparta’s sports field. Microbiological water quality was analysed to assess the removal capacity of the biofilter. To identify factors causing adverse treatment performance, system construction, and operation were investigated, water flows in the biofilter were assessed, and hydraulic conductivity was measured. Lastly, model simulations were used to investigate how short-circuiting and event frequency and duration affect microbiological outflow concentrations. Results showed leaching of enterococci and Campylobacter and minimal retention of Escherichia coli. Leaching is likely caused by secondary contamination with bird faeces and multiple design and operational choices lead to low microbial retention. Coarse filter media results in high hydraulic conductivity, and consequently, short hydraulic retention times. Electrical conductivity measurements revealed short-circuiting pathways between the inlet and outlet. Lastly, uneven distribution of feed water presumably reduced the effective reactor volume. It is recommended to upgrade biofilter design by incorporating small particles in the filter media and maximizing the distance between the inlet and outlet. Additionally, reintroduce a ponding zone and rearranging event frequency and duration to lower microbial outflow loads is advised. Model simulations suggest that short, frequent events are beneficial to control microbial loads. However, further work to clarify microbial decay rates is recommended. To conclude, results imply that the biofilter is currently unable to improve the microbiological water quality but can become a treatment barrier if design and operation are upgraded to tackle encountered problems.

This report contains the findings of a multidisciplinary project in Mozambique which ran from mid-November 2018 to mid-January 2019. This study is part of the IWACA-TECH project, which is an abbreviation for “Improved Water efficiency Control based on remote sensing TECHnologies. The goal is to increase water efficiency and crop yield without increasing the consumptive use of water, using remote sensing and Model Predictive Control (MPC). The structural water scarcity in the region points out the relevance of the IWACATECH project and with that this study. The research, carried out by students of Delft University of Technology, is of importance for both the company Tongaat Hulett and all inhabitants who are direct or indirect dependent on the water of the Incomati river. The study area on the plantation in Xinavane copes not only with inefficient irrigation water use but also suffers a sugarcane yield decline in recent years ??. Therefore, the overall aim of this report is to improve water efficiency and crop yield within Tongaat Hulett. To achieve this from a multidisciplinary perspective several research questions have been formulated. Although they all contribute to the overall aim, they do so from different angles and in varying degrees. Therefore, to increase the readability of the report, the research questions have been divided into three sections: (1) Irrigation Practices, (2) Field Assessment on Yield Variability and (3) Decision Support System. Fieldwork was conducted over a five week period in order to gather data. Groundwater levels were measured, water quality of irrigation, ground- and precipitation water samples was analysed and soil moisture content was measured. This led to further research of soil types and quality. Soil profiles along the edges of both fields were made revealing a shallow aquifer in the bad-performing field. Irrigation water quality seems to form no hazard, but ground water quality analyses revealed significantly high electrical conductivity levels and a high sodium adsorption ratio in areas without growth. These findings, combined with an analysis of the digital elevation map and socio-technical data revealed that evaporation of irrigation water seems to be a large contributor to the impaired crop growth. When excess water cannot run off, puddles are formed. When these puddles evaporate, salts can be taken up by the soil once the thickened irrigation water infiltrates. This process is strengthened by the clay soil layer and the shallow aquifer, which prevent water from infiltrating deeper into the ground. Results concerning remote sensing prove the relationship between soil moisture content and precipitation for meteo-station XNA-20. Combining spatial and temporal variability of soil moisture content with remote sensing can play an essential role in managing irrigation practices. For the decision support system, and in specific the controller part of the system, measurements have been done. It can be concluded that storage area and delay times can be considered insignificant, and that canals do not have to be modelled. This makes the controller significantly easier and thus more time and effort can be spend on other aspects of the controller.

To prepare for future challenges, such as possible upcoming organic micro pollutants in the source water, including traces of medicines, pesticides, and industrial by-products, it is expected that the conventional treatment does not ensure a reliable quality of drinking water. As a result, during the past few years, Oasen started to research a new treatment concept based on 100% reverse osmosis (RO) membrane filtration to provide an excellent barrier for organic micro pollutants. However, the water produced by the RO membranes, called permeate, is corrosive, bitter in taste and does not comply with the drinking water regulation standards in the Netherlands. Therefore, a certain degree of remineralisation is crucial to solve these problems and improve the water quality. A commonly used remineralisation process is to filter the desalinated water through a calcite contactor, providing the appropriate amount of bicarbonate and calcium in the water. In order to properly design and operate the calcite filters as well as to predict the final water quality, it is essential to understand the processes that occur in the filter.
The aim of this study was to find the best kinetic calcite dissolution model in order to understand the calcite grains dissolution behavior inside the filter and subsequently to adequately design and operate the calcite filter. Therefore, extensive pilot research was conducted to investigate the effect of various parameters on calcite dissolution such as the calcite grain size, velocity and carbon dioxide concentration. On top of that, the dissolution was modelled based on a successful empirical expression given by Yamauchi et al. (1987). However, it was found that the effect of the flow rate on the diffusion boundary layer around the calcite grains has not been taken into account in the study carried out by Yamauchi et al. (1987). Therefore, the effect of velocity on the calcite dissolution coefficient was investigated at five different velocity ,i.e., 5, 10,15,20,30 m/h. From there, a function was developed to describe the correlation between flow rate and the dissolution rate coefficient. In order to calculate the equilibrium concentration, the chemical reactions were simulated using PhreeqPython (Phreeqc built in Python).
The main difference of this study compare to previous investigations was the low temperature of the water (12 oC vs 22-40 oC) and the smaller grain size of the calcite (0.5-1.2 mm vs 1-2 and 2-3mm) which was tested. Besides that a high range of CO2 dosing (1.45- 9.5 mmol/l) was tested. As expected from theory, the dissolution rates was strongly affected by the varied parameters. It is concluded that the smaller grain size of 0.5-1.2 mm reduced the required empty bed contact time (EBCT) to15 min where operating the filter with the larger grain size of 1-2mm needs a minimum EBCT of 25 min to reach calcite equilibrium. The CO2 dosing is recommended to be less than 3 mmol/l, since the CO2 efficiency will drop under the 60% at higher CO2 concentrations.

Eventually, the optimal design will be introduced for the remineralisation process at Oasen treatment plant De Hooge Boom located in Kamerik. For this purpose various operational scenarios were compared on capital and operational cost. The overall cost including, both Capital expenses (CAPEX) and Operational expenses OPEX, was estimated between € 0.048 and 0.064 per m3 for different scenario’s where 71% consists of investment cost. The total treatment cost of this design is 0.057 €/m3 and the investment cost was found to be € 1.351.000 which is 32% less than price estimated by previous study done by Oasen.

This study introduces a new concept of ATES system, which is called ATEST system, to fulfill the transport function while crossing the barriers in water transmission and pipe replacements. Firstly, analytical models were used to help understand the physical process and range the working conditions of the ATEST system. Then numerical models were used to prove the feasibility and the value of this new conceptual system. Acceptable system performance that can meet the heat demand was iterated in case simulation; and the economical advantages were identified by comparing it with traditional ATES systems. The ATEST system showed a greater practical value than the ATES system in: 1) solving the discrepancy between heat service and heat demand in space, and 2) crossing barriers where pipes cannot be buried. However, the system should be further modified in operation to acquire better performance and avoid practical problems.

Standard conceptual hydrological models can rarely accommodate stream tracer dynamics at the catchmentscale. They rely on the generation of runoff through the propagation of a pressure wave and do not accountfor the actual advective movement of particles. Over the last years different model frameworks have beendeveloped to account for this shortcoming. The difference between the frameworks lies in whether they arebased on mixing coefficients or storage age selection functions. Both methods have shown their ability tocapture the stream chemistry response. It is however not clear how these distinct approaches compare toeach other and to reality.To provide more clarification in this matter, this research applied both frameworks separately to model thehydrological and stream water chemistry response for a specific catchment. The results are analysed usingthe concept of transit times, where information on the fluxes and states in all model components is used togenerate distributions that describe the age structure of water. By comparing the distributions generated byboth methods and by evaluating the overall model performances, more insight is gained on the two frame-works and on their ability to capture subsurface mixing dynamics.From the results of this research it is concluded that both frameworks show similar performance. They arehowever conceptually different, which might have implications for their ability to capture specific dynamics.These implications depend on the characteristics of the catchment of interest. It is still concluded howeverthat performance for each frameworks is likely to be similar. Because the model description of the MixingCoefficient framework is less complex, it is recommended to continue research with this framework.