Africa is the world’s second driest continent, supporting 15% of the global population with only 9% of the global renewable water resource. The 2015 to 2018 drought in the Western Cape of South Africa, where a Day-Zero scenario was narrowly avoided, highlighted the need to start looking at alternative water resources in conjunction with preserving the current water resources.

Globally, the water sector is moving towards a circular water economy - where all water sources, including wastewater, stormwater and rainwater are treated as a resource that can be used, recycled, and replenished into the system. Stormwater harvesting (SWH) has successfully been implemented in countries such as Australia, Israel, Singapore & South Africa.

The success of any SWH scheme depends on effective site selection. Yet, there is little guidance available, and site choices have traditionally relied on the subjective judgment of urban water managers. This demonstrates the need for an objective, data-driven approach that integrates multiple spatial datasets to identify optimal SWH locations.

This research develops such a method: an integrated hydrological and GIS-based screening tool that identifies high yield (hotspot) SWH sites using publicly available datasets in Africa. The collection models showed that high yielding stormwater harvesting sites can be identified with publicly available data, with all 4 weightings consistently pointing out the top 8 stormwater harvesting sites.

The storage and distribution models showed that with a storage facility that has a capacity of 10x the maximum daily demand, high reliability figures can be achieved in excess of 80% in terms of volume and time-based reliability. The storage and distribution models also showed that if the storage capacity can be increased, the reliability and resilience of the facility can also be increased.

The study also has some limitations and intrinsic uncertainties, and the framework should be used as a screening tool.

This study places focus on stormwater harvesting as an integral part of sustainable management of urban water and presents a robust, adaptable and scalable tool that can support urban areas across Africa to address the growing water demand challenges.

Access to clean and safe drinking water is essential for public health and sustainable development. Drinking water treatment plants (DWTPs) ensure water quality, but fluctuating raw water characteristics, particularly turbidity, challenge efficient coagulation and dosing control. Traditional strategies like jar tests and feed-backward control are limited by delayed results, making timely adjustments difficult. Short-term predictive tools based on machine learning (ML) offer a solution by forecasting water quality variations and enabling proactive control. This study develops several different ML models for short-term turbidity prediction at the Lekkanaal DWTP, addressing three questions: (1) which parameters influence turbidity, (2) which feature combinations yield optimal predictions, and (3) how far in advance turbidity can be reliably forecasted.

Historical water quality and hydrological data were collected from Waternet, KNMI, and Rijkswaterstaat, followed by preprocessing for reliable inputs. Candidate features were selected using Spearman correlation and Self-Organizing Maps (SOMs). Three regression models—AutoRegressive Integrated Moving Average (ARIMA), Random Forest (RF), and Long Short-Term Memory (LSTM)—were trained for different horizons, and feature importance analyzed using greedy selection and visualization tools. An RF classifier evaluated the feasibility of predicting peak turbidity events.

Results showed turbidity was driven by hydrological and physicochemical factors. Upstream discharge and turbidity strongly correlated with local measurements, highlighting the Lek River as a primary contributor, while EC and temperature showed negative correlations, reflecting dilution and seasonal sediment mobilization. SOMs confirmed high turbidity coincides with northward flows from the Lek River into the Amsterdam-Rhine Canal.

Feature analysis indicated univariate models using recent sensor\_turbidity outperformed multivariate models; additional features introduced noise. The last three hours of turbidity dominated predictions across ARIMA, RF, and LSTM.

All models provided reliable short-term forecasts, with RF outperforming ARIMA and LSTM for 3- and 6-hour horizons. Extreme peaks were systematically underestimated, and RF classification detected fewer than 16\% of peak events. Short-term forecasts up to six hours are feasible, but high-magnitude events remain challenging, emphasizing the need for enhanced monitoring and tailored strategies.

Pharmaceuticals in wastewater are an urgent environmental concern. Many emerging technologies, such as advanced oxidation processes (AOPs), are being explored for their removal. One promising AOP is Photoelectrocatalysis (PEC), which combines photocatalysis with electrochemistry to enhance pollutant degradation by suppressing electron-hole recombination. Bismuth vanadate (BiVO₄) is a promising visible-light-responsive photoanode material due to its narrow bandgap and chemical stability. However, its overall performance is limited by poor charge mobility and rapid recombination of photogenerated electrons and holes. To overcome these limitations, surface modification strategies have been applied, including the use of surfactants to alter and enhance its surface properties. Quaternary ammonium compounds (QACs), widely used for their surfactant properties and structural flexibility, have shown potential in enhancing the photoelectrocatalytic performance of BiVO₄. This study evaluated the effect of six commonly used QACs on BiVO₄ photoanodes. The modified photoanodes were synthesized and comprehensively characterized using several techniques: X-ray Diffraction (XRD) to determine crystal structure, Scanning Electron Microscopy (SEM) to examine surface morphology, Energy Dispersive X-ray Spectroscopy (EDX) for elemental composition, X-ray Photoelectron Spectroscopy (XPS) to analyze surface chemical states, Ultraviolet-Visible (UV-Vis) spectroscopy to assess optical absorption, and Linear Sweep Voltammetry (LSV) to evaluate electrochemical behaviour.
Photoelectrocatalytic degradation experiments were performed using real secondary treated effluent collected from the Horstermeer Wastewater Treatment Plant (WWTP), which was spiked with 20 pharmaceutical compounds. The QAC-modified BiVO₄ photoanodes were tested under simulated solar irradiation. Characterization results confirmed that the monoclinic phase of BiVO₄ was preserved after QAC modification, with minor shifts indicating changes in surface properties. SEM images showed that the structural integrity of BiVO₄ was maintained, while EDX and XPS results revealed an increase in oxygen vacancies, suggesting improved charge transport characteristics. LSV confirmed that photocurrent generation occurred only under illumination, as expected in PEC systems. Among the modified electrodes, the BiVO₄ photoanode modified with DADMAC C18 exhibited the highest pharmaceutical degradation efficiency over a 120-minute PEC run, outperforming even the unmodified BiVO₄ electrode. The ATMAC C18 variant demonstrated rapid initial degradation within the first 15 minutes, while the BAC C18 variant showed relatively poor performance. Kinetic analysis indicated that sulfamethoxazole was the most persistent compound in the pharmaceutical mixture, with the longest half-life. To assess real-world application potential, full-scale PEC reactor designs were reviewed. A circular reactor configuration with annular electrodes was identified as the most suitable due to its balanced light distribution, effective photoelectrocatalytic surface area, and ease of operation. A conceptual full-scale design was proposed to replace the existing UV oxidation system at WWTP Horstermeer, targeting a treatment capacity of 25,000 cubic meters per day. Based on preliminary calculations, the estimated treatment cost was €0.24 per cubic meter, highlighting the potential economic feasibility of implementing PEC technology in municipal wastewater treatment.

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.

Stringent industrial wastewater discharge regulations and rising energy costs demand industries to shift to sustainable water treatment technologies. The conventional physical-chemical wastewater treatment processes struggle to separate inorganic ions and emulsions. While polymeric membranes have limited mechanical, thermal and chemical stability. Ceramic membranes, and in particular silicon carbide (SiC) membranes, have emerged as promising alternatives due to their mechanical strength, thermal resilience, resistance to fouling, low isoelectric point, and super hydrophilicity. However, fabricating both SiC membrane supports and the selective layers require sintering temperatures of ca. 2100°C, with consequent high energy consumption. Additionally, preparing a SiC selective layer requires multiple coating and sintering cycles, which hinder precise pore size control and economic feasibility. To address these limitations, this thesis explores low-pressure chemical vapor deposition (LPCVD) as a route to coat commercially available alumina (Al2O3) supports by SiC at moderate temperatures to replace full SiC membranes...

This thesis examines the feasibility of Selectrodialysis as an innovative and efficient technology for nutrient recovery from greenhouse wastewater. The study aims to address the critical challenges of water quality degradation and Na+ accumulation in greenhouse operations, where the selective recovery of ions such as Na⁺, Ca²⁺, and Mg²⁺ is essential for maintaining optimal plant health and agricultural productivity.

The research evaluates the performance of SED by investigating the effects of various operational parameters, particularly voltage, and the presence of competing cations on ion transport efficiency. Experimental analysis revealed that SED could effectively achieve selective ion separation at an optimal voltage of 9V, which maximizes ion fractionation and migration rates while maintaining moderate energy consumption. However, higher voltages resulted in increased energy demands, water dissociation, and concentration polarization, which adversely impacted the selectivity of specific ions, particularly Na⁺.

The presence of competing cations, such as Ca²⁺ and Mg²⁺, was shown which significantly impacts the Na⁺ transport by reducing its migration rate and recovery efficiency. These effects are primarily due to competitive interactions and increased membrane resistance caused by concentration polarization, particularly at higher concentrations of divalent cations. Understanding these interactions is crucial for optimizing the recovery process and energy efficiency in systems where competing cations are prevalent.

The study also highlights the economic implications of implementing SED compared to conventional methods like RO. While SED demonstrates technical advantages in terms of selective ion recovery and reduced chemical usage, its broader adoption is constrained by significantly higher capital and operational costs. The total capital cost for SED was found to be over 13 times higher than that of RO, primarily due to the specialized membranes required for selective ion transport and the additional electrical components necessary for ion migration. Additionally, operational costs for SED are elevated due to higher energy consumption, which is more than double that of RO, and increased maintenance expenses resulting from the complexity of the system.

Despite its technical feasibility, the economic analysis suggests that SED may be better suited for niche applications where selective ion recovery is critical, such as in high-value greenhouse operations where precise nutrient control is essential. To improve the economic viability of SED, future research should focus on integrating renewable energy sources, experimenting with new membrane materials, and exploring different operational modes to reduce energy consumption and overall costs.

This research explores the feasibility of implementing ceramic microfiltration (CMF) treatment in Maputo, Mozambique, to reclaim wastewater for industrial reuse, addressing the city's pressing water scarcity challenges. As rapid urbanization increases Maputo's reliance on potable water for industrial and agricultural needs, this study evaluates reclaimed wastewater as a sustainable alternative to alleviate demand on the city's limited freshwater resources. Using a CMF pilot plant, the project tested wastewater from the recently upgraded Infulene Wastewater Treatment Plant (WWTP) to assess whether CMF treatment could achieve quality standards suitable for applications such as cooling, concrete production, car washes, agricultural irrigation, and municipal park irrigation. Furthermore, the opportunity of scalability was tested through a water balance, while relevant stakeholders were interviewed and costs estimated to complete the feasibility assessment.

Laboratory results indicated that CMF treatment effectively reduces turbidity, chemical oxygen demand (COD), and biological pollutants like E. coli and coliforms. However, dissolved particles and heavy metals were not removed, limiting its efficacy for high-specification uses. While the treated effluent met quality standards for lower-specification applications, such as local car washes and park irrigation, it did not reach the stricter requirements needed for cooling water or concrete production. This underscores a need for process optimization, particularly through coagulation, to expand CMF's application range.

To assess sustainable water availability, a water balance analysis of the Infulene WWTP considered seasonal flows and local agricultural demands. The findings suggest that although the current water supply is insufficient during dry months, full capacity utilization and improved sewer network connections in the future could support CMF-based water reuse consistently across seasons, with potential scalability for additional users.

Economic analysis compared CMF's capital and operational costs with revenue from reclaimed water sales, showing that while considerable initial investment is required, direct piping could potentially make CMF-treated water competitively priced against potable supplies under the condition of reaching maximum treatment capacity at a scaled up CMF plant. High costs associated with truck-based delivery, however, present a barrier to adoption for potential users. Stakeholder interest was strong across industrial users and developers, though contingent on achieving cost parity with the existing water network.

This study concludes that, while integrating CMF technology into Maputo's water management strategy offers promise, challenges remain in achieving quality standards for certain industrial applications and in lowering costs. Addressing these technical and economic barriers could open avenues for CMF's broader adoption, especially with future assessments that include alternative suppliers and configurations.

Growing concerns about elevated nitrate levels in natural springs on the southern slope of the Irazu Volcano, Cartago province in Costa Rica, were the driving force for a multi-disciplinary study on the problem. The region is characterized by its high agricultural output and steep slopes. More than sixty springs located in the area are managed by a large number of local water authorities, ASADAS. The study focused on determining the main sources of nitrate pollution. Anthropological activities such as agricultural practices and domestic actions are found to contribute the most. A multivariate polynomial regression model was used with a large set of parameters. From the results it can be seen that human activities within the by law determined 200 meter radius protection zone around the springs, are most influential on high nitrate concentrations in the springs. Furthermore a stakeholder analysis, fieldwork, financial analysis of alternatives and farmer interviews were performed to produce a comprehensive list of recommendations for the various stakeholders. The recommendations are compiled to ensure a future with clean drinking water for all the citizens in the region.

Water scarcity, population growth, and climate change are causing a shortage of water resources globally. Industries are turning to the reclamation and reuse of wastewater, including oily wastewater, which is a major byproduct of oil and gas extraction. The small droplet size of oil-in-water emulsions, however, makes them difficult to remove using traditional methods like coagulation and flocculation, gravitational settling, dissolved air flotation, hydrocyclone, and adsorption.
Membrane separation has emerged as one of the most promising techniques to deal with oil-in-water emulsions due to its high removal efficiency and small footprint. The main challenge for the wider adoption of membrane technology for oily wastewater treatment is membrane fouling. Membrane fouling is a pervasive problem in water purification membranes. It could cause serious negative effects, such as a decline in water production, higher operational pressure and associated higher energy consumption.
Ceramic membranes, particularly SiC membranes, are a promising method for removing small oil droplets from water. They are physically and chemically stable and have high fouling resistance to oil droplets. SiC membranes have better permeability and lower fouling tendency compared to other ceramic membranes. However, their high cost limits their widespread application in the market.
In this research, extensive literature reviews were first performed (Chapters 2 and 3) and then we proposed a new method, low-pressure chemical vapor deposition (LPCVD), to prepare SiC-deposited ceramic membranes for oily wastewater treatment. With LPCVD, a layer of SiC was deposited on alumina supports at a lower temperature (750 ˚C), compared to 2000 ˚C for commercial SiC preparations. Due to the low water contact angle (< 5˚) and negatively charged surface, these SiC-deposited alumina ceramic membranes are expected to be more fouling resistant to oil emulsions than the pristine alumina membranes. The performance of deposited membranes is influenced not only by the coated SiC layer but also by the filtration modes used for evaluation. As a result, we respectively used constant pressure and constant flux filtration to assess the fouling of ceramic membranes with and without SiC deposition. Additionally, the emulsion chemistry, such as surfactant concentration, pH, salinity, and Ca2+, plays a crucial role in the interactions between oil droplets and the membrane surface, which can cause membrane fouling. Understanding these mechanisms can be a crucial step towards the feasibility of using LPCVD to prepare SiC membranes for treating oily wastewater with lower fouling.
First, novel SiC-deposited ceramic membranes were developed by LPCVD at a relatively low temperature (750 ˚C) (Chapter 4). Different deposition times varying from 0 to 150 min were used to tune membrane pore size. The pure water permeance of the membranes only decreased from 350 L m-2 h-1 bar-1 to 157 L m-2 h-1 bar-1 when the deposition time was increased from 0 to 120 min. Correspondingly, the membrane pore size was narrowed down from 71 to 47 nm. Increasing the deposition time from 120 to 150 min mainly resulted in the formation of a thin, dense layer on top of the support instead of in the pores. Notably, the SiC layer rendered the pristine membrane surface more hydrophilic and negatively charged, effectively reducing membrane fouling during oil emulsion filtration.
Next, the fouling of SiC-deposited ceramic membranes and the pristine alumina membrane was respectively compared at constant pressure and constant flux filtration conditions (Chapter 5). The threshold flux of the membranes was first determined by flux-stepping experiments. Afterwards, membrane filtration was respectively conducted at below and above the threshold flux. In single cycle constant flux filtration experiment, the fouling tendency of the membranes was consistent with the results of threshold flux experiments. However, the inclusion of backwash in constant flux experiments led to a change in the fouling tendency, which was also dependent on the permeate flux. The improved surface hydrophilicity and charge made backwash more efficient for the modified membranes while extensive modification has a negative effect on membrane fouling resistance due to the huge loss in membrane permeance. In contrast, constant transmembrane pressure experiments showed that the order of membrane fouling was only related to membrane permeance, and no effect of surface properties was observed. Therefore, constant flux filtration experiments with backwash are recommended to be applied to evaluate the performance of the membranes with and without modification.
Finally, the impact of emulsion chemistry and operational parameters on the fouling of alumina membranes with and without a SiC deposition was systematically studied under constant flux filtration mode with backwash (Chapter 6). The results showed that the SiC-deposited membrane had a lower reversible and irreversible fouling when permeate flux was below 110 Lm-2h-1. In addition, a higher permeance recovery after physical and chemical cleaning was observed, as compared to the alumina membranes. The fouling of both membranes was decreased with the increase of sodium dodecyl sulphate (SDS) concentration in the feed, but to a higher extent in the alumina membranes. Increasing the pH of the emulsion could reduce the fouling of both membranes due to the enhanced electrostatic repulsion between oil droplets and membrane surface. Under high salinity conditions (100 mM NaCl), the screening of surface charge resulted in only a small difference in irreversible fouling between the alumina and SiC-deposited membranes. The presence of Ca2+ in the emulsion led to high irreversible fouling of both membranes, because of the compression of diffusion double layer and the interactions between Ca2+ and SDS. The low fouling tendency and/or high cleaning efficiency of the SiC-deposited membranes indicated their potential for oily wastewater treatment.
Overall, this dissertation shows that the fouling of SiC-deposited ceramic membranes is lower than that of the pristine alumina membranes towards oil-in-water emulsion treatment. Although there are still limitations, these SiC-deposited membranes show the potential for further development.

A novel activated carbon-iron composite material has been developed as an adsorbent for water treatment. Due to its activated carbon (AC) content, the material could be used to remove pollutants such as organic micropollutants (OMP). Fast AC bed exhaustion makes adsorption a cost-intensive solution. Regeneration of AC is done off-site and requires transport and high energy consumption for heat treatment. Due to the iron and graphite content of the novel adsorbent, catalytic regeneration could allow for in-situ regeneration. This property would present a major advantage over common AC. Regeneration could potentially be realized by applying an electric current across an exhausted bed of this adsorbent. Such a setup is called a “particle electrode”, where electrically conductive particles are placed between an anode and cathode. Upon application of an electric current across an exhausted bed of adsorbent, two mechanisms are hypothesized to result in the restoration of adsorption capacity: (1) desorption and (2) degradation of the pollutant. This study evaluated the adsorption capacity and rate constants for 17 OMP on two different versions of this partly graphitized carbon (with and without iron content) as an alternative to conventional AC for drinking water treatment. By batch adsorption experiments, the adsorption properties of this novel carbon were investigated. Oxidation of zero-valent iron on the iron containing version of carbon resulted in yellowish water. This version was therefore considered not appropriate for general drinking water treatment, and the remaining experiments were conducted only with the version without iron. The material adsorbed a great variety of OMP, including different charges and hydrophobicity. Its graphite content probably promoted the adsorption of neutral compounds. A negatively charged layer formed by NOM accumulation on adsorbent surfaces assisted positively charged compounds adsorption. Investigation of regeneration efficiency was conducted with alternative cycles of adsorption and regeneration with high OMP concentration solutions. This material could be electrochemically regenerated. Reverse adsorption could be achieved on neutral, positively and negatively charged compounds in multiple cycles of regeneration. Electrodesorption is probably the major mechanism responsible for regeneration. Permanent and partial loss of adsorption capacity was recorded, probably due to poor NOM desorption and change in surface chemistry. Regeneration efficiency was not positively correlated with elevating applied current. Increasing cell voltage is not always beneficial to the electrochemical process. Prolonged treatment time improved the regeneration efficiency, but the marginal benefit was considered to be uneconomical. Poor NOM regeneration was responsible and more concerning for the loss of adsorption capacity. Long-chain PFAS regeneration was achieved over cycles of regeneration. Short-chain PFAS regeneration was unfavorable due to blockage of micropores.

Interest in biogas has increased due to natural gas shortages and the energy transition. Most digesters in the EU have internal heating for process stability. Unheated reactors could potentially lower costs, but have decreased kinetics due to low operational temperatures, especially in winter. This raises the question how seasonal temperature fluctuations effect biogas production. If this effect could be incorporated in current models such as the Anaerobic Digestion Model no.1 (ADM1), scenarios could be compared to investigate when heating is worthwile. In this thesis, an extension is created to the ADM1 in Python to predict the operational temperature and its effects on the anaerobic digestion process. To lower the stiffness of the ADM1, different pH calculation methods were compared. These methods and the used Python version of the model were validated by digestion of the Benchmark Simulation Model 2 (BSM2) ADM1 influent. It was found that the combination of the Differential Algebraic Equation (DAE) with the Radau numerical solving method produced the smallest errors with the lowest computational burden. A heat-transfer model was included, which calculates bulk liquid temperature as a function of weather data, digester design and some operational factors. A One-At-a-Time (OAT) sensitivity analysis showed the dependence of yearly temperature fluctuations on several design and operational parameters. The calculated operational temperature is coupled to the ADM1 through several temperature inhibition functions for biochemical processes. Furthermore, the dependency of the liquid-gas transfer coefficient was investigated. It was found that this last step in biogas production could potentially become rate-limiting at temperatures lower than 30 °C, but this result was not validated. The coupled heat transfer - ADM1 model is used to study the case of an unheated fixed-dome reactor for the co-digestion of spent wort and Waste Activated Sludge (WAS) of the La Trappe brewery in the Netherlands. The influent substrate concentrations were determined by a biochemical fractionation procedure, and the model was able to simulate methane production curves found in Biochemical Methane Potential (BMP) experiments. Simulations of digestion for the La Trappe case showed seasonality in biogas production, increasing in summer and decreasing in winter. The extent of the effect was found to be dependent on substrate composition, with lipid-rich substrates being affected more than carbohydrate- or protein-rich substrates. Furthermore, the simulation showed seasonality in rate limiting step, with hydrolysis in summer and methanogenesis in winter. This caused the pH to lower with winter, and it was found that higher base dosage is needed in colder winters to prevent acidification. Higher influent temperatures improved process stability, lowered amounts of base needed and increased biogas production. Furthermore, the relation between temperature and volume showed that washout of methanogens and consequent VFA accumulation is dependent on the absolute temperature inhibition function for acetoclastic methanogens. Simulation of the digestion of BSM2 influent showed that the maximum Organic Loading Rate (OLR) increased with temperature till 30 °C, but decreased above this point as free ammonia inhibition starts to limit methanogenic metabolism. For La Trappe, OLR determines the needed base dosage, allowing smaller volumes if more base is added. Lastly, internal heating with the produced biogas was investigated, and optimal heating for biogas production was found. The found results from the model were used to asses the costs and benefits of several design and operational options for the digester at La Trappe. This digester will be used in future research for validation of the model.

To eliminate organic micropollutants (OMPs) from (surface) water, activated carbon adsorption is a cost-effective technology to remove a broad range of OMPs without producing any byproducts. However, co-existing dissolved organic matter (DOM), at much higher concentrations (mg C/L) than OMPs (ng/L-μg/L), inducing adsorption competition, can interfere with OMP removal. Direct site competition and pore blocking are two DOM competition mechanisms, and low molecular weight (LMW) DOM has been recognized as the major competitor in the site competition against OMPs. However, the insights into DOM molecular properties are limited with regard to DOM competition. Therefore, the objective of this research was to relate (LMW) DOM properties to the competitiveness against OMPs, clarify the mechanism of direct site competition, and explore a useful DOM surrogate to predict DOM competitiveness.
Model DOM compounds (mDOMs) could be described individually and more accurately with molecular properties than a complex, real DOM matrix in water. To elucidate the impact of LMW DOM characteristics (hydrophobicity/polarity and aromaticity) on DOM competitiveness, fifteen model compounds (mDOM), differed in functional groups (hydroxyl, phenol, carboxyl groups, etc.), were used to represent several elemental structures of LMW DOM. By temporarily occupying adsorption sites prior to OMPs, LMW mDOM was found to be more competitive to inhibit OMP adsorption kinetics than OMP adsorption equilibrium. Although OMPs were more preferentially adsorbed onto activated carbon than mDOM, the large concentration asymmetry (~500 μg DOC/μg OMP) made a few mDOM compounds exert strong competition against OMPs. The mDOM competitiveness increased when compounds were more hydrophobic and more aromatic, whereas π-π interactions were more important to determine mDOM competitiveness than hydrophobic interaction for LMW mDOM compounds. As an integrated indicator, mDOM adsorbability, defined by mDOM adsorption capacity, was considered better to associate with mDOM competitiveness than hydrophobicity and aromaticity individually. The competition was found to be strong between strongly adsorbable mDOM and weakly adsorbable OMPs, where weakly adsorbable mDOM could even co-adsorb with strongly adsorbable OMPs with little to no competition.
To relate DOM adsorbability to competitiveness in natural waters, a two-stage adsorption procedure was designed to differentiate the adsorption of DOM fractions and OMPs by removing variously adsorbable DOM fractions with activated carbon pretreatment and analyzing the competitiveness of the remaining DOM fractions. Our results demonstrated that adsorbable (LMW) DOM was not necessarily competitive against OMPs. In addition, an increasing amount of DOM competitors was observed against the weaker adsorbable OMPs, compared to their stronger adsorbable counterparts. Similarly, more DOM competitors were identified at high initial OMP concentrations, due to the increased loading of OMPs on activated carbon, highlighting the variable roles (varying competitiveness/ complementary adsorption) of differently adsorbable DOM fractions in competition.
To elucidate the role of molecular weight (MW), polarity and aromaticity in DOM competition from a natural DOM with a complex molecular composition, activated carbon and anion exchange resin (AER) pretreatment served for differentiating competitive DOM from natural DOM. Ultrahigh-resolution Fourier transform mass spectrometry was employed for the DOM analysis at the molecular level. A large percentage of molecular formulas in untreated DOM was PAC-absorbable (97.8% for 40 mg PAC/L), while ~75% of PAC-absorbable formulas were considered poorly competitive, since these molecular formulas were not detected in DOM remaining after AER pretreatment that was highly competitive. The semi-quantitative analysis revealed that aromaticity was the dominant factor for LMW DOM adsorbability and competitiveness. In contrast, with higher MW, the competitiveness of an increasing number of aromatic DOM compounds was diminished due to strong dissociation induced by relatively high polarity.
Finally, the interference of ozone-modified NOM with the adsorption of 2-methylisoborneol (MIB, an odorous OMP) was studied in three natural waters and one standard humics solution in order to study how ozonation influences the competitiveness of DOM with different MW distributions. In the three natural waters, it was found that reducing NOM competition against MIB was found to coincide with increasing ozone consumption. The cleavage of the macromolecules in a standard humics solution, with larger molecular weight and higher aromaticity than the humics in natural waters, only induced a slightly stronger competition under low/moderate ozone consumptions. Overall, the declined aromaticity outweighed the produced LMW DOM in the competitiveness of DOM against MIB in ozonated natural waters. The UV absorbance of the LMW DOM was better correlated with the competitiveness of ozonated/non-ozonated waters than the LMW DOM concentration itself, underlining the role of LMW hydrophobic aromatics in competitive adsorption prediction.
From this thesis, it could thus be concluded that the DOM competition against OMPs is not ubiquitous for all (adsorbable, LMW) DOM fractions. The amount of DOM competitors, as well as their competitiveness, strongly varies with to OMP adsorbability and the initial OMP concentrations (i.e., the concentration asymmetry). For LMW DOM, aromaticity was a key characteristic to promote DOM competitiveness, while the high polarity reduced the DOM competitiveness by DOM dissociation (and thus high hydrophilicity/polarity). To project the competitiveness of ozonated DOM of which the hydrophobicity and aromaticity were simultaneously diminished, LMWUV can then be a handy DOM surrogate instead of LMW DOM concentration itself.

Colloidal fouling has attracted increasing interest in the membrane field. Oil and water (O/W) emulsion droplet and Extracellular polymeric substance (EPS) are significant colloids in produced water and surface water, respectively. Oily wastewater is produced in many industrial processes such as oil and gas extraction processes, and can take a product, a by-product or a waste stream. In this study, silicon carbide (SiC) membranes were employed to separate oil droplets from O/W emulsion. The effect of ionic strength, pH, surfactant concentration on threshold flux of commercially SiC MF using O/W emulsion stabilized by the sodium dodecyl sulfonate (SDS) were investigated. The results indicated that the threshold fluxes, determined by both the TMPavg method and fouling rate method, increased with an increase of SDS concentration, but decreased with the salinity when using commercial SiC MF membrane filtering 400 mg/L O/W emulsions. Besides, a higher threshold flux was observed for emulsions with a higher pH. Moreover, the high absolute value of zeta potential of O/W emulsion could alleviate fouling. In the end, we produced SiC UF membrane by depositing SiC layer on the alumina supports by low pressure vapor deposition (LPCVD) due to its low fabrication cost. We investigated the anti-fouling abilities of pristine Al2O3 UF membrane and SiC-UF membrane by using sodium alginate as foulant (SA) solution in multi-stage experiments. When fouling experiments operated with pure SA solution or SA solution with a low calcium ion concentration, SiC UF membrane has a better anti-fouling ability compared with pristine Al2O3 UF membrane due to a lower reversible and irreversible fouling resistance and a slower increase of TMP.

A reverse osmosis (RO) membrane followed by a packed tower aerator and rapid sand filter are used by an agricultural company in Emmen to treat brackish groundwater to supply water for growing crops and cleaning purposes. The iron removal by the treatment plant is sufficient most of the time throughout the year. However, the farmer periodically (once per year) reported yellowish treated water, indicating insufficient iron removal. Nevertheless, it is still not clear what is the cause of the insufficiency of the iron removal. This thesis aimed to investigate the iron removal in the water treatment plant in Emmen and propose a solution to improve the iron removal. The iron removal of the treatment plant was investigated through a set of batch iron oxidation, flocculation, and filtration experiments. The pH of the water was the main parameter that influenced the oxidation of Fe(II). It was found that within the retention time that was available in the treatment plant’s tower aerator and the rapid sand filter (20 minutes), the Fe(II) was not fully oxidized and flocculated. At pH of the permeate in the range of 6 – 7, only <11.5% of the initial Fe(II) was oxidized in 20 minutes. Increasing the pH to 8 accelerated the oxidation of Fe(II), and the Fe(II) was completely oxidized within 30 minutes.Although removal of iron that is dominated by floc filtration was not achieved, the treatment plant also removed the iron through adsorption on iron hydroxide deposit in the packed tower aerator and sand particle. However, the Fe(II) adsorption capacity of adsorbents was low at low pH. The regeneration of the adsorption capacity was achieved through oxidation of the adsorbed Fe(II) which is also influenced by pH. COMSOL model showed that without regeneration, the adsorption capacity of new sand and iron oxide-coated sand was exhausted after 24 hours and 230 hours, respectively.When the concentration of CO2 in the permeate is in equilibrium with air, the pH of the permeate should be in the range of 7.9 – 8. However, the maximum pH of the permeate was 7 after aeration because the contact time of the tower aerator was not sufficient to completely strip the CO2. The tower aerator was also clogged by iron deposits that reduces the airflow and causes short-circuiting that decrease the CO2 stripping efficiency over time.Installation of a bubble column reactor was proposed to improve the CO2 stripping and increase the pH of the permeate. The Phreeqc model showed that the CO2 could be stripped until approx. 1 mg/L within 4 minutes, and the pH also increased to approx. 7.9. Moreover, the bubble column reactor will provide additional retention time for Fe(II) oxidation, and approx. 20 – 30% of the initial Fe(II) concentration can be oxidized within 4 minutes. The bubble column was considered preferable compared to the packed tower aerator because it was not susceptible to clogging by iron deposits and requires lower maintenance.

Many cities in Sub-Saharan Africa struggle to access reliable and adequate quantities of potable water for diverse water requirements. Under pressure of climatic change, urbanization and economic development, freshwater resources are becoming scarcer. These pressures combined with outdated infrastructure, pose a giant challenge to the Greater Maputo Region to meet their water demand in 2050. This report aims at identifying and analyzing pathways, using stakeholder preferences, that support SUWM and bear the potential to close the supply-demand gap in 2050.

This report utilizes population and demand forecasting to determine the gap between future supply and demand. Hereafter, alternative technical, social, and environmental methods to augment the Greater Maputo Region’s water supply are identified through a literature study. Furthermore, two distinct methods are used to develop scenario’s that augment the supply demand gap. The first being a technical analysis using multi-criteria decision analysis and the second a serious game that is to be played with stakeholders. At last, these scenarios are used to develop a framework that is technically feasible and approved by stakeholder opinions in the serious game.

It was found that the population of the Greater Maputo Region will grow from 2,8 million in 2017 to 6,9 people in 2050. Furthermore, under the pressure of economic development, population growth and urbanization, water demand increased from 9 million m3/day in 2017 to 22 million m3/day in 2050. This increase in demand, in the case of a business-as-usual scenario, amounts to a deficit of 1,2 million m3/day in 2050. The sector that consumes most water is agriculture, followed by industries and households. Furthermore, under climate change precipitation decreases over time whereas temperatures increase. Especially during the dry period, more evaporation and less rainwater is expected, highlighting the need for alternative water supply methods to ensure a steady availability of water.

Alternative methods that support SUWM such as dams, stormwater harvesting, rainwater harvesting, wastewater reuse and desalination were found to be most suitable approaches to augment the Greater Maputo Region’s water supply. However, it was also found that these approaches are not very efficient without the right urban context and socio-political and economic measures. Economic and social-political measures should incentivize water savings and fair distribution.

Two distinct methods were used to create scenarios to close the Greater Maputo Region’s supply demand gap. The first, multi-criteria decision analysis showed that that in the case of a high weight attributed to the cost of approaches, rainwater harvesting, stormwater harvesting, and dams are the most suitable options given the selected criteria and their respective rank. Whereas in the case of a low weight of the cost, wastewater reuse, stormwater harvesting, and rainwater harvesting are the most suitable. The second, a serious game that mimics the WASH situation in the Greater Maputo Region which showed that players focus on sustainable, circular, solutions, but that they are hard to implement because of financial limitations.

Ultimately, this report indicates that both decision analysis and serious gaming provide valuable insights for enhancing water supply in an urban context. In this report, both methods indicate that there is a preference for circular (sustainable) approaches. Such an ideal, circular, and sustainable, water system in the Greater Maputo Region, was found to be supported by decentralization of the water sector. In this case, decentralization of the water sector to a neighbourhood scale shapes niches for sustainable water supply approaches and within these niches, the local context of the neighbourhood determines the type of water supply infrastructure that is most suitable. Furthermore, the technical approaches are to be supported by socio-political and economic measures. Altogether, a combination of SUWM supporting approaches supported by political and socio-economic measures can close the supply-demand gap in 2050.

Irmão is a beach restaurant located in the region of Lisbon in Portugal and has been taken over by the new owners one year ago. Since the takeover, the owners of Irmão have been trying to work in a sustainable way, but there is always room for improvement. In addition, Irmão may have to move 100 metres inland due to a possible change in local regulations. Because of the uncertainty in the course of events, this report is written as guideline in order to make the current restaurant more sustainable and as a guideline during the design of the new beach restaurant, should the restaurant have to be relocated.

The aim of the report is therefore to provide beach restaurant Irmão with a consult on how to establish and operate a more sustainable beach restaurant, in present or future times. The study, executed at Irmão, focused on three main themes; the water system, waste management and the energy system. The level of sustainability in these areas is quantified in three ways, namely: the use of resources such as fossil fuels and groundwater; the emission of greenhouse gases CO2, NOx and CH4; the pollution of the direct environment, for example waste that ends up in nature or polluted waste water that flows into the soil. The present and future times refer to the two different scenarios used to implement sustainable solutions. If the restaurant is allowed to stay at its current location, it is referred to as the Improved Irmão Scenario. If the location has to be changed, it is referred to as the Future Irmão Scenario. For the Improved Irmão Scenario, the boundaries and limits of the current restaurant are taken into account and the design is carried out within these limits. For the Future Irmão Scenario on the other hand, these limits are loosened and the design is carried out from scratch.

To provide Irmão with a consult how to establish and operate a more sustainable beach restaurant, three steps were taken. First, the current situation of the three subjects is analysed to get a clear understanding of the current situation. This is done to have a baseline against which the final improvements can be compared. Secondly, different solutions to make Irmão more sustainable, within the three main topics, are compared using a multi¬criteria analysis to determine the most promising solutions. Thirdly, the final solutions are elaborated for the Improved Irmão Scenario and for the Future Irmão Scenario.

Regarding the Water system, the analysis showed that the water consumed at Irmão partly originates from the water grid and partly from the borehole in the dunes. The water use is estimated to cause an emission of 182 kg CO2 annually, leaving little room for improvement in emission reduction as this is a relative low amount. However, the water system is currently not water-efficient because it does not contain any water circularity and the water system does not contain any water saving equipment. Improvements regarding water usage are therefore possible. Regarding waste management, the analysis showed that currently, only residual waste is not recycled. Therefore, the section on waste management focused on making residual waste more sustainable. Regarding the energy system of Irmão, it became clear from the analysis that Irmão currently consumes propane gas and electricity from the local electricity grid. Both the consumption of propane gas and electricity from the local grid contribute to an emission of 26.8 tonnes of CO2 annually. From all processes carried out during the operation of Irmão, only the consumption of propane gas leads to an emission of NOx, namely 382 kg NOx annually…

The aim of the research is to aid selection of Household Water Treatment and Storage (HWTS) technologies. By creating an overview of important criteria for choosing between HWTS in a certain context, information on trade-offs is gathered. To do so, an explorative assessment is made of HWTS preferences in various contexts.

Ceramic nanofiltration (NF) is a newly developed technology for municipal sewage reclamation for drinking water production, agricultural and industrial utilisation, but organic fouling limits it to pilot-scale application. Herein, Fenton-based cleaning catalysed by FeOCl pre-coat was performed on ceramic NF membrane to clean persistent gel-like fouling. FeOCl pre-coating on ceramic NF membrane was conducted by pressure-driven filtration. Gel-like fouling was simulated by Ca-alginate. The compact fouling layer was proposed to impede the diffusion of H2O2; therefore, NaCl was introduced to perform Na-Ca ion exchange to relax the fouling layer and improve the mass transfer in Fenton-based cleaning. The cleaning efficiency of Fenton cleaning and NaCl treatment were evaluated individually, and their synergistic effect was determined by a mixture of NaCl/H2O2. In pre-coating, the iron loading could be controlled by permeate flux. Moreover, the iron loading on the membrane had a linear relationship with FeOCl dosage. The pre-coated FeOCl layer slightly decreased membrane permeability (by 4%), presumably because the porous FeOCl pre-coat provided abundant channels for water permeation. NaCl pre-treatment displayed high efficiency in the removal of the reversible fouling layer, which contributed to 50% of flux decline. The FeOCl pre-coat catalysed Fenton-based cleaning, which achieved a complete flux recovery in 1 hour. The addition of tert-butanol (an ∙OH scavenger) in Fenton-based cleaning system decreased the cleaning efficiency, which confirmed the participation of ∙OH in Fenton-based cleaning. No remarkable synergistic effect was observed between NaCl induced fouling layer swelling and Fenton oxidation. It was likely due to the effect of turbulent flush on improving the diffusion of H2O2 in Fenton-based cleaning, which surpassed the effect of fouling layer swelling induced by NaCl treatment.

Cape Town is a city with over four million people and a growing population. Due to three consecutive dry summers as a result of climate change, a growing population and an increased per capita water demand, the city’s main water supply was nearly depleted. Cape Town depends for 98% on surface water stored in dammed reservoirs, which is replenished by rainfall. There is a temporal mismatch between water availability and peak demand, and thus harvesting rainfall can be potentially become an additional source of water. Cape Town’s urban drainage system has 737 detention ponds, which are used to attenuate flooding in case of heavy rain events. These ponds can be used to harvest the stormwater and store it in the Cape Flats aquifer using managed aquifer recharge for seasonal availability. The complexity of retrofitting stormwater ponds into infiltration ponds calls for a systematic approach. This research offers a retrofitting framework for the context of Cape Town. The framework can be used to determine suitable detention ponds to allow managed aquifer recharge via infiltrating stormwater, and to retrofit these detention ponds into infiltration ponds. The framework consists of three phases; spatial assessment, physical assessment and conceptual design. It is highly flexible in usage due to the fact that every phase can be used separately. Additionally, the framework can be extended to include important socio-economic aspects. Following the framework standardizes the procedure of obtaining data on individual ponds, which allows for objective comparison in assessing their suitability for infiltration.

Arsenic in groundwater can constitute a persistent nuisance for water treatment facilities when it exceeds the admissible limit of 10 μg/L. Recently, a stricter limit has been set as a new challenging target by many companies in the Netherlands, which is below 1 μg/L. However, most of the groundwater treatment plants have been conventionally designed solely for the removal of the most common undesirable groundwater constituents, namely iron, manganese and ammonium. The current research aimed at the investigation of the operational conditions facilitating As removal in biological rapid filters simultaneously with the required Fe removal. This improved As retention should be correlated with an extended length where its adsorption takes place, thus with the deeper Fe penetration inside the bed. Therefore, this was attempted in this research. The process water used throughout the experimental tests contained As(III) and Fe(II) in order to simulate a typical anoxic groundwater quality. For the most part, a triple-layer filter bed was used, consisted of anthracite, sand and garnet. The different settings under examination involved a range of pH values (7.8, 7.1 and 6.4), two filtration velocities (2.5 m/h and 5 m/h) as well as the recirculation of the filtrate back to the feed stream. Finally, the multimedia bed was compared with a single-layer sand filter.
The results of the conducted pilot column filter experiments revealed that high pH values were accompanied with high oxidation rates and thus with the creation of Fe flocks, already in the supernatant water. Due to this, at pH 7.8 and 7.1 lower Fe concentrations were detected in the effluent, denoting a higher Fe retention as compared to pH 6.4. Interestingly enough, a relatively deep Fe penetration was observed for every pH value tested. Regarding As removal, it was evidently favored by high pH values owing to the oxidation-floc formation removal mechanism of Fe (homogeneous reaction), which prevailed under those conditions. On the other hand, at pH 6.4 the adsorption-oxidation mechanism was predominant (heterogeneous reaction), which obstructed the AsOB activity. As far as the tested filtration velocities is concerned, they didn’t seem to significantly impact both Fe spread over the bed as well as As removal at the higher pH levels. Nonetheless, this was not the case for pH 6.4, in which the slow flow rate enabled the generation of more and larger Fe flakes (due to sufficient residence time in the supernatant water), which were then retained in the top part of the bed. The high flow rate on the other hand allowed Fe to reach deeper in the filter. Surprisingly, As removal seemed to be improved at 2.5 m/h, despite the Fe flocks accumulation in the upper layers. Possibly, the short experimental times not allowing equilibrium to be reached could comprise a reasonable explanation of this unexpected result. Furthermore, the filtrate recirculation stream didn’t seem to positively influence As removal. The induced dilution effect resulted in a relatively large dispersion of Fe inside the filter bed, however the essentially halved incoming Fe concentration was not sufficient to adsorb the oxidized As(V). Finally, the comparison between the multimedia bed with the single-layer filter reveals a considerably wider Fe dispersion over the bed height in the former case, which in its turn promotes a more efficient As removal. The overall conclusion of the current study is that triple-layer bed filters facilitate a more gradual Fe removal and its deeper penetration in the bed as compared to single-layer filters. This fact stimulates As removal and additionally allows for longer filter run times. Moreover, heterogeneous Fe removal seems to obstruct As oxidation by AsOB and therefore homogeneous reaction can be considered as more favorable in terms of As removal. This specific removal mechanism becomes predominant at pH levels above 7, when sufficient oxygen is available. Lastly, the operational setting of filtrate recirculation back to the filter inlet, displays a negative impact regarding As removal.