This thesis presents a comprehensive investigation into the optimization of Slow Sand Filter (SSF) performance through data driven modeling, with a focus on bacterial (E. coli, Coliform) and viral (Enterovirus, Adenovirus, Bacteriophage MS2) removal efficiencies. Combining an extensive literature review, exploratory data analysis (EDA), and machine learning modeling using XGBoost, this research provides new insights into the complex interactions between design parameters and SSF performance, ultimately contributing to the development of more efficient and sustainable SSF configurations. The study began with a systematic literature review of 135 experimental studies, identifying key design parameters and operational conditions of SSFs, including Filtration Rate (FR), Hydraulic Retention Time (HRT), Effective Grain Size (D10), Total Bed Height (T.B.H.), and Schmutzdecke characteristics. The literature review was supplemented with Exploratory Data Analysis (EDA) techniques such as scatterplots and correlation matrices to uncover trends and potential relationships between design parameters and removal efficiencies for bacteria and viruses. While the scatterplots and correlation matrices revealed limited linear relationships, they highlighted the complexity of the interactions, indicating the need for advanced modeling techniques capable of capturing nonlinear patterns. To address these complexities, XGBoost, a powerful machine learning model known for its ability to handle nonlinear relationships and parameter interactions, was developed and applied to the dataset. The model’s predictive capabilities were evaluated using performance metrics such as R², Mean Squared Error (MSE), and cross-validation results. Additionally, feature importance analysis was conducted using the XGBoost model, which provided insights into which design parameters and operational conditions had the most significant influence on removal efficiencies. A key contribution of this research was the development of interactive tools, such as feature contribution sliders and interactive heatmaps, which enabled dynamic exploration of how changes in design parameters affect removal efficiencies. These tools facilitated the simulation of design scenarios, offering an intuitive understanding of parameter impacts and guiding the formulation of new design paradigms. The model outputs were used to propose optimized parameter ranges that improve bacterial and viral removal while maintaining operational efficiency. The thesis further explored the robustness and reliability of the XGBoost models, discussing the results from controllable and uncontrollable design parameters and operational conditions and comparing the model’s predictive performance for bacterial and viral removal. In conclusion, this research highlights the effectiveness of XGBoost modeling for both predicting and explaining SSF performance. The insights gained provide a foundation for developing more efficient SSF design paradigms, enabling targeted adjustments to parameters based on model predictions. Additionally, the interactive tools created in this study offer practical resources for engineers to simulate different design configurations and optimize SSF performance. Overall, this thesis emphasizes the potential of machine learning to revolutionize the design and operation of SSFs, providing a foundation for future advancements in sustainable and effective water treatment technologies.

This thesis presents a collection of novel methods for the circularity and efficiency assessment of resource recovery solutions related to the water treatment sector. The resource recovery solutions pertain to the drinking water and wastewater treatment plants and include the recovery of nutrients, cellulose, treated wastewater, energy, sewage sludge, and calcite from drinking water softeners. The thesis also contains a new water-food-energy nexus framework which is used to compare the conventional centralized approach to wastewater treatment with a decentralized source separation one.@en

The necessity for sustainable industrial processes and solutions has been intensified by climate change, which has led to an increased focus on enhancing resource efficiency and reducing greenhouse gas emissions. In accordance with the principles of the circular economy, the implementation of improved water-smart solutions and enhanced water management processes, including the reuse and recycling of wastewater and the recovery of resources such as water, energy and nutrients, represents a pivotal strategy for addressing challenges such as climate change and water pollution.
This dissertation examines novel bio-composite materials derived from resources recovered from the water sector. These materials incorporate natural fibres derived from untreated wastewater (i.e., cellulose fibres) or surface water management (i.e., reed and grass fibres), as well as fillers such as calcite derived from drinking water softening processes or agricultural waste (i.e., coconut shells, olive powder, and food residue). Bio-based resins, such as polyester with a reduced styrene content or furan resin, containing furfuryl alcohol, serve as binders.
The presence of a wide range of pollutants has a significant impact on water resources as a result of human activities. It is therefore imperative that comprehensive testing is conducted to ensure that the utilisation of recovered resources does not result in any adverse effects on human health or the environment. It is crucial to emphasise that, because of their derivation from recycled raw materials, the utilisation of the novel bio-composite materials should not be assumed to be intrinsically risk-free. It is therefore imperative that a comprehensive risk assessment of the environmental and human health risks associated with the production and application of the new bio-composite materials is conducted.
The overall aim of this research project is to develop an approach for the evaluation of potential risks to human health and the environment that may result from the production and application of the new bio-composite materials. In line with this, four research questions have been formulated to conduct this study:
- What are the main risks and related hazards associated with the production of new resource recovery-based bio-composite materials and their applications and how are these interlinked?What existing methods can be potentially used (and with what modifications) and which new ones need to be developed to assess these risks?
- What is the best approach to define and quantify the human health risks involved in the production of bio-composite materials?
- What is the environmental risk associated with the use of the new bio-composite materials in the aquatic environment? More specifically, what is the risk in case of canal bank protection elements made from these new materials?
- What is the environmental risk associated with the use of new bio-composite materials based building façade elements and how does the weathering of these elements affect this risk?

Above research questions have been addressed and answered in Chapters 2 – 5 of this dissertation. Below, a summary of the work done in order to address the formulated research questions is provided.

A comprehensive literature review, detailed in Chapter 2, was conducted at the outset of this work to identify the principal hazards and associated risks involved in drinking water and wastewater treatment plants, water reuse, and water-based resources recovery. The literature study identified potential microbial and chemical contaminants of the raw materials used to produce the new water-based resource recovery bio-composite materials. These contaminants may pose a risk to human health and the environment. Nevertheless, it was found that no risk assessment methodologies have yet been used to assess the potential human health and environmental risks associated with the production and application of the new bio-composite materials.

The novel human health risk assessment framework, which is described in Chapter 3, employed a qualitative risk analysis as the initial step, followed by a quantitative risk analysis. The Hazard and Operability (HAZOP) method identified the principal hazards during the production, and the qualitative Event Tree Analysis (ETA) methodology created a corresponding risk map. The results of the qualitative risk assessment indicated that the main risks of new bio-composite materials are caused by chemical and microbial contamination, which can have a negative impact on human health and the environment. A quantitative human health risk assessment was conducted on four alternative new bio-composite materials, employing both Quantitative Chemical Risk Assessment (QCRA) and Quantitative Microbial Risk Assessment (QMRA) methodologies, with deterministic and stochastic approaches. The results of the chemical risk assessment indicated that the cancer risk from styrene and furfuryl alcohol exceeded the established safety threshold. Similarly, the microbial risk assessment identified significant concerns with E. coli in cellulose fibres, with the risk exceeding safety limit. The assessments were conducted under the most unfavourable circumstances, without the use of personal protective equipment (PPE) or safety protocols. Furthermore, the assumption of maximum exposure to contaminants was made due to the limited availability of input data, which resulted in an overestimation of the overall risk.

The presence of chemical contamination in raw materials used for the production of new bio-composite materials gave rise to concerns not only for human health but also for potential negative environmental impact. In order to assess the environmental risks involved, two applications of these new materials were considered in this study: (a) canal bank protection elements, which prevents soil from collapsing into the water and (b) façade building elements as decorations panels.

To assess the environmental risks of chemical release, from the bio-composite materials used as canal bank protection, laboratory column leaching tests were conducted. This preliminary step provided data for an approximate environmental risk assessment in real-world conditions. The environmental risk assessment framework, developed in accordance with European guidelines, as detailed in Chapter 4, showed that the concentration of chemicals leached into surface water was within safety threshold. However, styrene and furfuryl alcohol contained in the resins may still pose a concern to environmental risk. It is crucial to acknowledge that the interpretation of these results should be approached with caution, given the absence of on-site data and the numerous assumptions made, including instantaneous mixing of the leaching chemicals and the absence of Brownian motion. Furthermore, the background concentrations in freshwater and the fate and degradation of chemicals in surface water were not considered. Also, the leaching process was evaluated over time, with the observation of a plateau indicating a significant slowdown in the leaching process accompanied by a reduction in the driving force, thereby providing a better understanding of the leaching behaviour.

Bio-composite materials utilised as façade construction elements are more susceptible to adverse weather conditions than those used for canal bank protection. Chapter 5 presents an analysis of potential leaching from bio-composites on a real-world building of a pumping station in the Netherlands. Two bio-composite alternatives were tested, and two samples per material were used: one new sample (as the initial application) and one UV-treated sample (as the long-term application after weathering) per material, for a total of four samples. The samples were subjected to leaching tests simulating two rainfall events of a duration of one hour. The risk assessment demonstrated that no leached chemicals exceeded the safety threshold, with no detection of styrene or furfuryl alcohol in the leaching effluent samples. However, these findings should be interpreted with caution due to the limited input data and the assumptions made, including the lack of on-site data and the focus on a single rain event rather than analysing leaching over a longer time period. The weathering treatments affected the materials in different ways based on their resin composition. Material M3 (made of polyester resin) exhibited aesthetic changes, while Material M4 (made of furan resin) demonstrated increased roughness, reduced water resistance and fibre detachment. Microscopic examination revealed significant wrinkling in M4, indicating that environmental exposure significantly affects these materials.

Overall, it can be concluded (Chapter 6) that both microbial and chemical risks are inherent in the production and applications of new bio-composite materials considered in this thesis. These risks originate from the utilization of specific raw materials, including calcite from drinking water, cellulose derived from wastewater, reed and grass sourced from surface water management conducted by water boards, as well as the resins and additives employed in new materials. The framework developed in this research, which includes laboratory testing, modelling and risk assessment methods, has been validated as applicable to the case studies used in this work. Being generic in nature, the framework also shows potential for human health and environmental risk assessments associated with different future applications of new bio-composite materials.@en

Per- and polyfluoroalkyl substances (PFAS) have remained persistent environmental contaminants since the 1950s, despite ongoing efforts to curb their production and find alternatives. Most health studies have focused on Perfluorooctanoic acid (PFOA) and Perfluorooctane sulphonic acid (PFOS), leaving limited data on other PFAS compounds in water. The European Union, particularly the Netherlands, has implemented stringent measures to control PFAS in drinking water due to their uncertain health impacts on
humans. Recently, the Dutch Institute for Public Health and Environment (RIVM) proposed a new guideline of 4.4 ng PFOA equivalent (PEQ) per litre for PFAS in drinking water, a substantial reduction from the current European Drinking Water Directive standards of 100 ng/L for the sum of PFAS and 500 ng/L for total PFAS.

While improving drinking water quality is expected to have positive health outcomes, the advanced treatment technologies required to meet this new guideline can be harsh, potentially releasing emissions that may cause negative health effects. This research, centred on the Leiduin drinking water treatment plant operated by Waternet in the Netherlands, investigates whether the health benefits of the new guideline outweigh the potential harms caused by the treatment processes necessary to achieve it.

To explore this, the study first calculated the Disability-Adjusted Life Years (DALYs) lost due to PFAS exposure from drinking water at the current concentrations, exceeding the 4.4 ng PEQ/L guideline, using a literature review to link guidelines with PFAS health effects. The second step involved conducting a Life Cycle Assessment (LCA) of the treatment system at the Leiduin plant, focusing on the treatment steps necessary to meet the new guideline, and calculating the DALYs lost due to the environmental impact of achieving the 4.4 ng PEQ/L standard. These DALYs were then compared to assess whether adhering to the new guideline is justified in terms of health impacts.

The results indicate that the DALYs associated with the current and proposed guidelines fall within similar ranges, showing limited health benefits. Specifically, the health benefits (in DALYs) gained from implementing the new guideline range from 0.4 to 4 per year, while the DALYs lost due to the treatment technologies required at the Leiduin plant range from 1.55 to 3.25 per year for the population receiving drinking water from the Leiduin site, depending on the type of activated carbon used in the treatment process.

These findings suggest that the potential health benefits of stricter PFAS regulations in drinking water maybe counterbalanced by the negative health impacts of the treatment technologies required to achieve
these lower concentrations

Slow sand filtration is one of the oldest water treatment technology widely applied globally across various scales from centralised systems to point-of-use treatment. The major functions of these filters include turbidity removal, disinfection and production of biologically stable drinking water. SSFs operate on the principle of percolation of water through a fine sand bed at low rates of 0.1-0.3 m/h without backwashing. This fosters the growth of a thick biofilm layer called the Schmutzdecke on the filter surface, and thinner biofilms in the remaining filter bed.

SSFs to date are operated as “black boxes” with limited understanding of the underlying processes contributing to treatment. This research aimed to unravel the physical-chemical and biological processes involved in disinfection and removal of biological stability parameters (dissolved organic carbon (DOC) and ammonium (NH4+) and by contributing to the development of new design rules for modern SSFs. Moving beyond the traditional focus on the Schmutzdecke, considerable attention was given to understanding the role of the entire filter system in removing enteric pathogens, DOC and NH4 +. The insights from the depth-specific investigation in both full-scale SSFs at a Dutch drinking water utility and experimental filters in the laboratory yielded two main conclusions.....

@en

UV disinfection is an efficient way to inactivate chlorine resistant protozoan pathogens such as Cryptosporidium parvum and Giardia muris. In the United States, regulatory UV disinfection credit is typically granted when turbidity is <1 NTU. However, studies show turbidity does not correlate well with UV dose responses and partial inactivation when turbidity is > 1 NTU should be considered to avoid certain violations while still protecting public health. The objective of this study was to examine the impact of worst-case scenarios at drinking water treatment plants on UV disinfection. Indigenous spores from unfiltered source water and samples taken during the flocculation and softening steps at the Dublin Road Water Treatment Plant in Columbus, Ohio were exposed to Low-Pressure mercury UV254 disinfection from July 2019 to January 2020. Raw source water and softened water had similar dose responses despite significantly different water quality parameters. Flocculated water had the worst dose response: significantly lower maximum inactivation rate and higher residual population density than the other two water types despite having a lower turbidity than softened water. The modeled Geeraerd-tail maximum inactivation rates (k¬max) were 0.027, 0.021, and 0.030 cm²/mJ for raw source, flocculated, and softened water, respectively. The modeled Geeraerd-tail residual population density values (N¬res) were 1.168, 7.081, and 0.216 SFU/mL for raw source, flocculated, and softened water, respectively. Relationships between water quality parameters and modeled UV inactivation parameters were analyzed to determine and compare other potential indicators for UV disinfection to turbidity. Particle size and particle properties that govern the degree of particle-associated microorganisms best explained the differences in dose response between flocculated water and the other two water types. Larger particles are worse for UV disinfection. Microorganisms associated with particles are harder to disinfect with UV and lead to tailing. Climate change impacts on types, consistency, quantity, and quality of source waters for drinking water treatment make it especially important to understand UV disinfection kinetics under challenging scenarios. Informing regulatory changes to properly account for disinfection when turbidity is > 1 NTU could be especially useful for small or aged utilities that may not be as equipped to handle highly variable water qualities.

In the recent decade, a wide range of emerging contaminants (ECs) has been regularly detected in the wastewater treatment plants (WWTPs) effluent, surface water and even groundwater. Among all these ECs, organic micropollutants (OMPs) are receiving increasing attention due to their characteristics of low concentration, difficulty in degradation and their harmful effects on humans and the environment. Nineteen OMPs have been included on the contaminant watch list of the European Union Water Framework Directive since 2015 and efficient and reliable methods to eliminate them are researched worldwide. Therefore, in this study, five of these 19 OMPs (benzotriazole (BTA), carbamazepine (CBZ), diclofenac (DIC), ketoprofen (KET) and caffeine (CAF)) were selected as target OMPs. And the research objective is to fabricate a ternary composite photoanode and to investigate its photoelectrocatalytic degradation performance for all five target OMPs.

BiVO₄/(TiO₂/graphene oxide (GO))_mix ternary composite thin films were successfully deposited on fluorine-doped tin oxide (FTO) glass substrates using ultrasonic spray paralysis (USP) method to form a ternary heterojunction structure and to improve the photoelectrocatalytic performance for degradation of the five target OMPs. The morphology, crystal phase, surface chemical composition, optical and electrochemical properties of this ternary composite photoanode were analyzed by scanning electronic microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), X-Ray photoelectron spectroscopy (XPS), UV-vis spectroscopy, incident photon-to-electron conversion efficiency (IPCE), linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS), respectively. The results of these analyses showed that TiO₂ P25 nanoparticles and GO sheets were distributed uniformly on the brain-shaped BiVO₄ structure which indicated that the ternary heterojunction structure was formed successfully. From the UV-vis analysis, it could be estimated that the band gap energy for BiVO₄/(TiO₂/GO)_mix ternary composite photoanodes is 2.43 eV. Further, the LSV and EIS analysis showed that the photocurrent of the ternary composite photoanodes is lower than pure BiVO₄ photoanodes.
The degradation experiments were divided into five stages. The optimal photoanode type was first determined in the pre-experiment stage using methylene blue (MB) as indicator organic pollutant and then the effect of initial concentrations of target OMPs and initial pH on the degradation efficiency were studied in stage II and III, respectively. The highest removal efficiency of the five target OMPs was obtained with initial OMPs concentration at 10 μg·L^-1 and initial pH range of 3.5-4.0. The degradation experiments were triplicated under this optimal condition in stage IV. It was noticed from the results that the degradation efficiency of different OMPs after 3 hours of reaction time varied from 31.1 % to 99.5 %. To further confirm that there is competition between the five target OMPs during the photoelectrocatalytic degradation process, experiments were carried out in which individual OMPs were degraded independently. The reusability and stability of the photoanodes were evaluated in stage V. Trapping experiments using scavengers were also included in this stage, which showed that superoxide anions was the most active species during the degradation process.

As industrialization advances rapidly in pursuit of refining the quality of human life, there has been a release of organic micropollutants (OMPs) such as pharmaceuticals into various water reserves. This has endangered the ecosystem and the possibilities of water recovery. Commonly used tertiary wastewater treatment technologies have proven to, not under all conditions, be less effective in OMP removal. Hence, Advanced Oxidation Processes (AOPs) have gained attention in the recent past due to their production of reactive oxidative species (ROS) that unselectively degrade OMPs. Photocatalysis (PC), an AOP that uses solar radiation to produce ROS, has been investigated earlier, but shows low efficiency due to fast electron-hole recombination. Photoelectrocatalysis (PEC) is a modified version that additionally uses electrical energy, thereby reducing the recombination and improving the OMP removal efficiency. Bismuth vanadate (BiVO4) photocatalyst has gained importance due to its narrow band gap of 2.4 eV and hence, efficient absorption in visible light spectrum. Thus, this research focused on investigating PEC using BiVO4 electrodes for the removal of OMPs in aqueous solutions. The BiVO4 electrodes were fabricated using dip-coating from 1 to 5 layers, and electrodeposition at -0.2 V and -0.4 V, each at durations of 2, 5, 7, 10 and 15 minutes. They were then characterized using analytical techniques to investigate their structural, optical and optoelectronic properties. Subsequently, all the BiVO4 electrodes were used for the photoelectrocatalytic degradation of Acetaminophen (ACT). The electrodes fabricated by dip-coating were shown to achieve superior degradation efficiencies of ACT of over 99% in 5 hours, due to optimum surface morphology and band gap. It was seen that their varied surface structures played an important role in improving OMP degradation, and compensated for their low average quantum efficiency at 7%, as compared to that of electrodeposition at 14%. Next, the photoelectrocatalytic degradation of multiple OMPs in a solution was studied, and it was determined that although the ROS unselectively targeted all the OMPs, some were degraded quicker than others due to their chemical structure. Scavenging experiments were also carried out that affirmed the role played by ROS in the photoelectrocatalytic degradation of the OMPs. Eventually, the degradation of OMPs in secondary wastewater treatment effluent was conducted to test its usage in purification applications. Overall, PEC using BiVO4 electrodes was found to be feasible and successful in OMP degradation, and has the potential to be developed for usage in environmental remediation strategies like water treatment and recovery.

Bromate is a possible human carcinogen that does not naturally exist in surface or groundwater bodies. Its formation mostly results from ozonating bromide-containing water during wastewater treatment or drinking water production. Bromate is difficult to remove from water due to its high solubility and low reactivity in the aqueous environment; however, some bacteria showed the ability to reduce bromate to bromide, but the mechanism is unknown. Previous studies postulated a cometabolic pathway of biological bromate reduction, a side reaction of denitrification using the same enzymes. This study investigates the biological bromate reduction mechanism with a focus on its relationship with the denitrification process.

Wastewater and biologically active granular activated carbon (BAC) from a methanolsupplemented pilot filter called O3 -STEP in the wastewater treatment plant (WWTP) Horstermeer, the Netherlands, were used for research. This study first measured the crucial water quality parameters at eight different heights in the filter to investigate the redox condition’s influence on biological bromate removal. After that, batch experiments were conducted to validate the findings. The filter showed the ability to remove bromate as it lowered the bromate concentration from 2.7 to 0.9 µg/L. Bromate reduction happened at all depths including the supernatant, although the redox conditions significantly changed. Decreasing nitrate and dissolved oxygen (DO) concentrations did not change the bromate reduction rate in the filter. The batch experiments confirmed that nitrate did not affect bromate reduction. However, a DO concentration of 8 mg/L led to a 50% reduced bromate reduction rate compared to anoxic conditions. Experiments with varying chemical oxygen demand (COD, in the form of methanol) concentrations showed an extensive accelerating effect on bromate reduction. This explained why the bromate reduction rate was not lower at high DO levels in the filter, as the high COD concentration promoted bromate reduction. Nitrate reduction was found to have a high positive correlation with bromate reduction in both filter and batch experiments, indicating similarities in their mechanisms. Nitrate reduction happened under highly oxic conditions. The intensive mixing of the granules in the filter may have provided alternating aeration and anoxic conditions for the enrichment of aerobic denitrifiers.

This study is the first study to observe simultaneous nitrate and bromate reduction under oxic conditions. Taken together, biological bromate reduction is likely to be a synergetic cometabolic process of aerobic denitrification. The robustness of the biological bromate reduction under high DO and nitrate conditions enables the O3 -STEP ® filter to steadily produce bromate-free effluents under more extreme influent conditions.

In the context of climate change and urbanization, sustainable urban drainage systems (SUDS) are widely adopted measures to manage stormwater in the city on-site. However, their performance in practice often differs from modelled and laboratory-scale predictions due to the variability in properties of real sediments (in terms of size, shape, density and coagulation) compared to the silicate standard Millisil®W4. Clogging is a common source of failure. 
The SediSubstrator L is a decentralized stormwater treatment device installed as a pre-treatment step to mitigate clogging in a storage and infiltration system on the Rooseveltlaan in Amsterdam. It consists of a sedimentation pipe with a flow-separating grate, the SediPipe, and a filter-adsorbent, the SediSorp+. It is purported to remove 80 % of TSS by DiBT (the technical authority in the German construction sector) test principles that use Millisil®W4 to simulate real sediments. The full-scale unit was monitored in the city throughout May-September 2022 to assess its performance. 
The stormwater runoff discharged from the catchment had high concentrations of lead (54 μg/L) and zinc (790 μg/L), likely due to contact with gutters and old roofing material, amplified by the relative contribution of these roofs to the total catchment discharge (accounting for 50 % of the area contributing to runoff). The sediment (TSS) concentration was low, equivalent to 20 mg/L on average. The sediments were also light and fine—with an organic fraction of 66 % and with 78 % of diameter smaller than 63 μm.
In the SediSubstrator L, the TSS removal efficiency was 34 % on average. This corresponds to an estimated caught load of 2.7 kg for this period. The removal efficiency was shown to increase with an increasing stormwater TSS concentration, with longer antecedent dry periods and with lower TSS organic fractions. Turbidity dynamics in the system suggest that while a net sequestration of solids occurs in the SediPipe, there is a resuspension of fine solids. This was observed in a camera inspection to occur from solids which settle on or near the grate. In an extreme rainfall event on September 28th 2022, water collected on the section of the street connected to the SediSubstrator, the cause of which is still subject to speculation. The observed SediSorp+ filter resistance across the summer was not indicative of gradual clogging, but an inspection showed signs of decayed organic matter throughout the full length of the filter bedas well as traces of cement in two of the four cartridges. It is possible that these two effects together with turbulent inflows prompted the acute clogging behavior.

There is interest in using the SediSubstrator beyond the city of Amsterdam to reduce phosphorus loadings in the road runoff discharged to sensitive nature areas. On the Rooseveltlaan, the average total phosphorus removal efficiency was 18 % (50 % for dissolved, readily bioavailable ortho-phosphate). Interactions with settled sediments generated ortho-phosphate in the SediPipe, and fine particulate and colloidal organic phosphorus was shown remobilized in both the SediPipe and SediSorp+. The removal of ortho-phosphate in theSediSorp+ in natural rainfall was good (on average 50 %) and was shown to be consistent at different contact times (approximately 10-30 minutes). 
The installed unit should be monitored over a longer time period of two years for statistical significance and to capture seasonal variation in loads. Nevertheless, the removal efficiency observed on site is consistent with the results of a sedimentation model developed according to Ferguson & Church (2004), using a stormwater sediment particle density as measured at another location in the city. Design adaptations are recommended to improve the SediSubstrator L to the conditions observed in Amsterdam: namely, better site selection, a longer SediPipe section (24 m) and a second filter stage to better capture the fine suspended solids.

Magnesium is one of the most critical natural resources and 96% of magnesium used in Europe is imported. The present study investigated possible ways of implementing circularity in the magnesium cycle within the borders of Waternet, a water utility in the Netherlands. The wastewater treatment plant at Amsterdam-West produces struvite from anaerobic digestate. The production of struvite requires 4400 tons of 32% MgCl2 annually. At the same time, a reverse osmosis (R.O.) process treating brackish groundwater for drinking water production produces a concentrate rich in magnesium ions. This R.O. concentrate, after being treated by aeration and filtration to remove iron and ammonium, is considered for use in the wastewater struvite recovery process. Technologies for recovering magnesium from this R.O. concentrate were investigated in this study. After analyzing the constraints of the magnesium dosing system, the struvite reactor, and the R.O. concentrate composition, two technologies were selected for the study of Mg2+ recovery: Nano-filtration (N.F.) and Ion exchange. The present study investigated both these processes via software simulations and laboratory experiments. The study revealed that while the N.F. process is not viable, the cation exchange using a weak chelating resin AmberLite IRC747 in Na+ form (regeneration with H2SO4 and NaOH) is possible when the resin is saturated with divalent cations. The regenerant stream (produced via acid regeneration) is a sodium-free stream having gypsum precipitates. After gypsum separation, the process created an Mg2+ dose with a concentration of 4.45 g/l. This study developed a 1 step process for extracting Mg2+ from RO concentrate.

The presence of organic micro-pollutants (OMPs) in water bodies has become a major hindrance to protecting water quality in recent years. One of the main sources of OMPs is wastewater treatment plant (WWTP) effluents. One of the most recent Advanced Oxidation Processes (AOPs) technology is photo-electrocatalysis (PEC), which can produce radicals to oxide OMPs in an aqueous medium driven by solar energy and an external bias potential. In this study, ultrasonic spray pyrolysis was determined as a proper method to fabricate the ZnO/BiVO4 heterojunction. Then, the prepared photoanodes were characterised by X-ray Photoelectron spectroscopy (XPS), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), UV-vis and Incident Photo-to-electron Conversion Efficiency (IPCE). The results demonstrated the ZnO/BiVO4 heterojunction was successfully fabricated on the Fluorine-Tin-Oxide (FTO) glass. Moreover, the LSV and EIS analysis were carried out in this study to analyse its photo-electrochemical properties. The PEC degradation experiments were carried out in 10 μg/L of 11 OMPs spiked in MiliQ and in real WWTP effluent under simulated solar illumination at 1 V potential bias for three hours. Nine and four of 11 OMPs had achieved more than 70 % degradation efficiency when ZnO/BiVO4 photoanode was conducted to degrade spiked MiliQ and spiked real WWTP effluent. Except for diclofenac and sotalol, the real effluent showed inhibition to the degradation efficiencies and kinetic coefficient of the other nine OMPs. The concentrations of TOC, COD and NO3-N increased after the PEC process. The increase was found to be related to the disintegration of the carbon stick cathode. To further enhance the PEC process, the ZnO@GD/BiVO4 photoanode and adding persulfate were conducted the PEC degradation experiments separately in spiked real WWTPs effluent. Both two approaches showed an enhancement of the PEC process and improved degradation efficiencies. The results obtained in the present work reveal that the PEC process has excellent potential for the removal of OMPs from WWTPs effluent.

“Access to safe drinking water is a fundamental human need and, therefore, a basic human right. Contaminated water jeopardizes both the physical and social health of all people”: such is the importance of safe drinking water, as stated by Kofi Annan, former Secretary-General of the United Nations, on World Water Day 2001. While some countries are still struggling to protect their citizens from well-known drinking water contaminants, potential new drinking water risks from newly-identified chemical and microbial aquatic contaminants are appearing globally. The increasing detection of these emerging contaminants has been advanced by a combination of social, technological, regulatory, climatological and demographic developments. Recent examples of emerging contaminants are perfluoroalkyl and polyfluoroalkyl substances (PFAS), sapoviruses, pharmaceuticals and colistin resistant bacteria. Whether emerging aquatic contaminants are a concern for drinking water safety depends on their exposure and hazard potential, which is influenced by a range of various determinants, including their mobility, toxicity and persistence in the environment, the severity and duration of the health effects caused by the contaminant, and the possibility for, and efficacy of, protective measures. Evidence, however, of these determinants is often limited. The challenge of protecting public health from emerging drinking water contaminants, therefore, does not only relate to identifying emerging contaminants as soon as possible, but also to prioritising the impact on human health which these contaminants have when evidence on their exposure and hazard potential is limited. Once identified and assessed, the challenge of effective risk communication under uncertainty needs to be dealt with as well. In this dissertation, an integrated approach to facilitate the early warning of, and communication on, emerging chemical and microbial drinking water contaminants has been developed...@en

As antibiotics now save millions of human and animal lives annually, the World Health Organisation (WHO, 2019) declared Antibiotic Resistance (AR) as the number five most dangerous risk to global health. Several researchers mention WWTPs to be an important source for AR as the growth of bacteria is stimulated in an environment with a selective pressure facilitated by a relatively high concentration of antibiotics.

Tertiary treatment steps are implemented primary to polish the effluent and reduce the OMP load of the effluent. The O3-STEP filter is an innovative example of such a tertiary treatment combining the oxidative effects of ozone with the adsorption effects of a Granular Activated Carbon (GAC) filter. In addition to these effects, a coagulant is dosed for the removal of Phosphorus (P). The implications for AR are still unknown. In literature varying results are found on the disinfecting effects of ozone, GAC and coagulation and nothing is found on the combination of these treatment steps yet. The purpose of this document is to present how effective the treatment with ozone and coagulation is in the removal of antibiotic resistant bacteria (ARB) in comparison with antibiotic sensitive bacteria (ASB).

Agar growth media are used to test four different microorganisms: two faecal indicators (E. coli and Enterococci) and a resistant strain of each of these bacteria (ESBL E. coli and Vancomycin Resistant Enterococci (VRE)). Several experiments are conducted in the laboratory to test disinfection of ozone and coagulation on these microorganisms.

In confirmation of the hypothesis, ozonation and coagulation disinfect ARB as well as ASB. However, as both treatment steps are not aiming at the removal of microorganisms but at the removal of OMPs and phosphorus respectively, the microorganism removal is limited (with 0.7 log on average). Increasing the coagulant and ozone dosage showed promising results in the laboratory. Dosing the coagulant above the optimum sweep coagulation dosage is not favourable because the increase in removal stagnated above this concentration whilst the residual coagulant concentration in the supernatant water increased.
In the GAC of the O3-STEP filter and its backwash water, an increase of VRE is found relative to Enterococci in comparison with the ozonated water but not over the complete O3-STEP filter. This was different for the 1-STEP filter which showed the worrying result that VRE increased in the same amounts as Enterococci decreased. As the 1-STEP filter is a filter with a matured biology, where O3-STEP was recently started, the O3-STEP filter might increase the absolute and relative amount of ARB in long term as well.

In case the aim for the O3-STEP filter is to remove AR as well, several suggestions are made. As ozone and coagulation both potentially remove ARB, an increase in these concentrations is a no-regret possibility. Furthermore, ultrafiltration (UF) and the combination of ultraviolet (UV) and O3 are proposed as possible alternatives. Using a multicriteria analysis (MCA), increasing the ozone dosage with the existing bypass is recommended.

Research towards aquathermal energy solutions is still in a pioneering phase. Especially in urban environments, these solutions could potentially form the missing connection between heating supply and demand. This study focuses on the application of these solutions in the city canal waters in the largest city of the Netherlands, Amsterdam . Currently, these so-called Surface Water Heat (SWH) systems have not been implemented at all in the inner city canals of Amsterdam. One of the reasons for this can be found in a lack of knowledge about natural water temperature variations in these types of waters and the unknown thermal effects related to SWH systems. This study is an answer to this knowledge gap and an attempt is made to provide insight in the thermal effects of SWH on a city canal. The Amsterdam city canals form a unique water system in open connection with larger waterways and they are part of a hydrodynamically complex interaction between sea and the river Rhine. Until date, such a study towards SWH system effects, not being restricted to the boundaries of the respective water body, is scarce or even non-existent.\\ The case study location is situated at the Jacob van Lennepkanaal in Amsterdam, where a collective of civilians has recently started the exploratory phase for installation of the first SWH city canal system for heating of their own district. To respond to this societal development, this specific case study location was chosen. To be able to model the SWH system for this neighborhood, the first part of this thesis focuses on system layout and related system characteristics. It was found that open-loop SWH systems are often applied at district level. Secondly, a reference surface water temperature model without SWH systems was built and validated upon meteorological forcing with local water temperature measurements. The third part of the followed method was to apply the modelled SWH system to this validated three-dimensional thermodynamic model. For this purpose, the Delft3D model was chosen, which computes the RANS equations under the hydrostatic assumption. Several scenarios were calculated with varying temperature difference through the SWH heat exchanger and varying distance between system intake and outfall. The modelling results for the Jacob van Lennepkanaal case show that SWH systems used for heating purposes, thereby cooling the surface water, produce a negatively buoyant flow, causing the discharged cold water plume to sink to the bottom. Existing thermal stratification in the city canals is enhanced and hydrodynamic mixing processes are not strong enough to disturb this stratification built-up. Further away along the plume, in the far-field, a combination of buoyant spreading and the process of passive diffusion mix the water column and the temperature decrease, induced by the SWH system, becomes uniformly spread over the entire water column. Currently, steady state one-dimensional models are often used for assessment of SWH thermal effects. It was demonstrated that these models are useful and accurate, provided that the right heat exchange coefficient is used and near-field mixing at the outfall is represented correctly. These models can be used to study for example the time-averaged extent of the cold water plume, but fail to provide insight in time-varying and spatial characteristics of the canal. Local changes in bed level height, attraction of ambient water by the intake and intersections with lateral canals also influence the thermal profile. For a study towards these effects in greater detail, three-dimensional modelling or 2DV-modelling are preferred. Also, in case of a study towards application of multiple systems, these are the models of choice.

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.

This thesis proposes a novel design approach for a monitoring system that can detect hidden leaks in intermittent water supply (IWS) systems. Cities with IWS conditions in their drinking water network, such as Nairobi and Harare, often have a high percentage of non-revenue water (NRW) in their system. Estimations of the amount of NRW in these cities range from 40% to 50%, of which a large part is due to a leaky infrastructure. Intermittency of water supply is usually caused by a shortage of available supply, making it extra poignant to notice that these areas lose significant volumes of water. The leaks are also important locations for contaminant intrusion, which deteriorate the quality of drinking water. Additionally, intermittency of supply results in people using storage to fulfill themselves with their weekly water demand, which provides new challenges when constructing hydraulic models. Hidden leaks, which are leaks that do not appear at the surface, can be noticed in continuously supplied areas through reports of pressure deficiencies or the absence of supply. As these are regular circumstances in IWS areas, these hidden leaks are seldom noticed. Therefore, methods that are applicable in IWS systems need to be developed to detect these hidden leaks. This thesis proposes a new approach to detect hidden leaks in IWS areas with a smart hydraulic monitoring system. The approach optimizes the design of such a system in a district metered area (DMA) with IWS conditions in sub-Saharan Africa, by balancing information density and investment costs. By using as little equipment as possible, this optimization study aims to be not only scientifically and practically relevant, but also cost-effective. The methodology that was used to design the monitoring system makes use of a similar concept as the Dynamical Bandwidth Monitor (DBM), which is a smart hydraulic monitoring system that has been applied regularly in networks with continuous supply. The monitoring system consists of sensors that continuously measure flow or pressure and it compares these measurements to a range of expected values, attributing deviations from these expected values to a potential leak. A case study of Ashdown Park, a DMA with IWS conditions in Harare, was used to assess the performance of the design. The flow into this DMA and the pressure at its inlet had been monitored for one year. Two designs of the monitoring system were made, one which mainly consisted of flow sensors and one with mostly pressure sensors, to showcase which type of sensor could best be used in Ashdown Park. A hydraulic model was constructed for the DMA using pressure dependent outflow modelling. Daily demand patterns were constructed from analyzing the inflow measurements and used to calibrate the hydraulic model. The proposed calibration method assumes linear relationships between the demands and inlet pressure on one side and the pressure at a specific node and flow at a specific pipe on the other side. The range of expected flows and pressures within the DMA was calculated by Monte Carlo analyses, during which demand realizations were modelled by using a novel method which made use of a random weighted choice of demand, based on the outflow from a single tap. The ability of the monitoring system to detect leaks during different demand realizations was stored in a three-dimensional Boolean matrix, which was then used to determine the optimal sensor placement. A social and financial analysis, summarized in a business model canvas, shows more practical challenges and opportunities that could arise from implementing the monitoring system. The lessons learnt from this thesis were used to showcase whether the monitoring system could be applicable for IWS systems around the globe. Several conclusions can be drawn from the results of this thesis. The daily demand patterns in Ashdown Park showed a different pattern than in continuously supplied systems, showing less strong peaks. This could be due to a constant water demand for filling storage, leaks in the system or different consumer behaviour. The calibration method made it possible to model flows and pressures at the DMA inlet which were comparable to the measurements. The novel method to model demand realizations with a random weighted choice and a single tap capacity, showed promising results since the spread of the modelled inflow was well comparable to the spread of the inflow measurements. This standard tap capacity is especially suitable for IWS areas, since most people in IWS areas usually only have one tap directly connected to the water supply system and water end-use devices are not directly connected to the network. Furthermore, it was found that the water use behaviour of inhabitants of Ashdown Park had been more constant than the supply behaviour of the water utility. This irregular supply behaviour of the utility increased the difficulty of designing a pressure monitoring system. Using a flow monitoring system to detect leaks showed a better performance (leaks could be found on a daily basis in 25% of the pipes in the DMA) than using a monitoring system with pressure sensors (leaks could be found in 1% of the pipes). Making the monitoring system with pressure sensors dependent on the inlet pressure increased its performance (from 1% to 8.3%). Branched parts of the system were more favorable locations to place sensors and sensors at the DMA inlet were crucial for calibrating the hydraulic model. Practical barriers that were identified during this thesis were irregular operational schemes, unknown demand patterns and incomplete GIS data. Furthermore, costs can be saved as soon as leaks are detected, making the financial profitability very dependent on the performance of the system and the occurrence of leaks. The applicability of the monitoring system in IWS areas around the globe is determined by the priorities of a local water utility, its network characteristics and the ability of the local utility to overcome implementation barriers. The main limitations in this research are due to making some simplified assumptions, such as assuming a constant flow-rate from the tap in all households in Ashdown Park, and due to a lack of understanding of the local situation, since this research was performed in the Netherlands. To validate assumptions and get better understanding of the local situation, it is advised to conduct follow-up research at the location of interest. Especially a pilot project of the proposed monitoring system would likely find more practical barriers and limitations than could be thought off in this thesis and therefore bring more valuable information for the implementation of a smart hydraulic monitoring system. If prioritized, properly installed and operated, the proposed smart hydraulic monitoring system could generate substantial water savings and provide many social benefits, such as an increased access to clean drinking water and employment opportunities. Above all, it can assist a local utility with fulfilling their responsibility: supplying people with the basic need of drinking water.

Though slow sand filtration is one of the oldest and effective means of drinking water treatment, the mechanisms contributing to bacteria and viruses removal are not well understood. The lack of understanding of actual removal potential and different mechanisms occurring in the filter bed has limited the development of new filter design and operation. This research aims at assessing the bacteria and viruses removal capability of filter material in different depths from the top 40 cm of full-scale slow sand filter (SSF) operated for 436 days. In addition, the focus is to identify the key removal mechanisms that aid bacteria and viruses removal in the schmutzdecke.
The results show that three depths: 0-5, 5-20 and 20-35 cm contribute to E. coli removal of 0.55, 1.3 and 1.04 logs, PhiX174 removal of 0, 0.30 and 0.14 logs. The log reduction value of E. coli and PhiX174 is rather similar in different layers, even though the schmutzdecke is considered to be the critical component for E. coli removal. It indicated that the deeper layers are also important in a well-established SSF. No removal of PhiX174 was observed in 0-5 cm with a thick biofilm, which indicates that the thickness of a certain level would impact the performance of virus removal.
To determine mechanisms, filter material from 0-5 cm was operated under three conditions: active, inactive, and ignited condition. The results show E. coli removal of 0.68, 0.74, and 0.43 logs, PhiX174 removal of 0, 0, and 0.28 logs for active, inhibited, and ignited sand, respectively. Contrary to previous studies, no function of microbial mechanisms is observed for E. coli removal. That key mechanism might change with the different maturity levels of SSFs might be a possible reason. In addition, this may ascribe to incomplete microbial active inhibition. On the other hand, despite evidence that virus removal enhances with filter maturation, schmutzdecke did not improve PhiX174 removal. Poor virus removal may be attributed to higher interstitial velocity along with higher shearing forces caused by abundant biofilm within the schmutzdecke.

Intensive urbanisation enhances warming of cities’ ambient and subsoil environment. The local drinking water distribution system (DWDS) is likewise affected. Hotspots of anthropogenic heating were perceived to influence drinking water temperature and pose a threat for microbial drinking water quality. Information on temporal and spatial relation between drinking water temperature and microbial indicating parameters was however scarce. This is especially the case for a full scale unchlorinated DWDS in a metropolitan area. Therefore, this research aimed to explore the spatial and temporal relation between drinking water temperature and microbial indicating parameters Aeromonas and Heterotrophic Plate count (HPC). 11 Years of sample data from the DWDS in the metropole of Amsterdam was explored, with the objective to possibly draw conclusions beyond this DWDS. This DWDS consists of two interconnected subsystems. Each subsystem is fed by its own treatment facility. Areas with repetitive exceedance of threshold temperature (14 oC) for accelerating Aeromonas growth, were not inextricably tied to repetitive exceedance of the Aeromonas standard for safe drinking water. Areas with repetitive exceedance of the Aeromonas standard were often linked to prolonged residence time. For regions on the outskirt of observed DWDS it was suggested that the influence of residence time was more important than the absolute water temperature to explain Aeromonas concentrations.