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 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.

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.

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.

The implementation of new agricultural technologies is considered a key component of Malawi’s agricul- tural development strategy. However, successful technology adoption has proven to be difficult, affecting both farmers and small businesses introducing the technology. With a primary focus on farmers interested in adopting the technology, common factors influencing farmers’ adoption habits are determined by con- ducting interviews and observations. Survey results indicate that from a farmers perspective; market ac- cess, information access, education, and affordability are key factors helping facilitate adoption, while lack of these factors hinder adoption. Insight into these factors could provide business knowledge on how to better facilitate technology adoption. For this purpose, literature factors affecting a SME’s success are compared with an active agricultural technology company. These factors include experience, communication, man- agement and technology performance. Using both farmers needs and business developmental factors, this study hopes to provide insights for new companies starting a business in a developing country.

In drinking water production, natural organic matter (NOM) is sometimes removed using ion exchange (IEX) resin. This treatment method has a limitation based on the exchanging capacity on the resin. Therefore, the resin needs to be regenerated when it is saturated with adsorbed NOM which leads to the production of brine. In general, NaCl is used to regenerate the resin, hence, the brine will contain NOM, high sodium and chloride concentrations. Moreover, some other anions are also found in the IEX brine, such as sulphate that is usually present in surface water and ground water. Because of its salinity, the disposal of IEX brine is not possible to be done conventionally due to its impact on the environment and high cost. Therefore, separating chloride from the brine is an interesting alternative that can be reused for the regeneration of the IEX in the later process.

Ceramic nanofiltration (NF) emerges to be an interesting alternative for water treatment. Compared to polymeric membranes, this type of membrane offers great mechanical robustness and can be operated under extreme conditions, and tolerates high-pressure backwash, chemical cleaning, and high-temperature sterilization, which leads to longer periods of reliable performance. Moreover, ceramic NF membranes are potentially capable to separate multivalent ions from monovalent ions. Hence, this method could be applicable to treat IEX brine. Alternatively, chemical precipitation using barium and calcium is widely used to remove sulphate from water which is more straight forward than membrane filtration. The precipitates can be mechanically separated from the supernatant for further treatment or use.

Combination of chemical precipitation and ceramic NF membrane (later called as integrated sulphate removal) was investigated to remove sulphate from IEX brine. Along with that, investigation using synthetic brines consisting of Na2SO4 and NaCl for a binary salt solution and only Na2SO4 for a single salt solution was also conducted to build the understanding in treating the IEX brine. Barium salt was proved to efficiently remove sulphate due to its very low solubility. However, calcium salt was not as effective as barium salt. The treatment was followed by NF using a ceramic membrane with MWCO of 900 Da. In the end, the integrated approach was able to remove 86% of the sulphate and 85% of NOM from IEX brine. Furthermore, the precipitation stage was also modelled in PhreeqC by using Pitzer database.

Barium salt (BaCl2.2H2O) was preferred in this research for precipitating the sulphate. However, due to its toxicity, alternative precipitation was desired. Ettringite (calcium sulfoaluminate) precipitation was considered since the involving salts were not toxic. The efficacy of this method was predicted through modelling in PhreeqC to give some insight to alternatively removing sulphate from IEX brine. Eventually, a comparison using cost estimation and Life Cycle Assessment (LCA) were performed to obtain some considerations to implement the treatment alternative in a full-scale application.

Human exposure to the toxic element arsenic due to consumption of arsenic contaminated water is still a global issue worldwide. Conventional treatment techniques are not very efficient at removing arsenite, which is the predominant species of arsenic in raw groundwater. Biological oxidation of arsenite by arsenic oxidizing bacteria (AsOB) has shown potential to effectively oxidize arsenite to arsenate without use of any chemicals. Arsenite is then effectively removed by adsorption or separation technologies. Iron Electrocoagulation (Fe-EC) is also emerging as an influential technique for arsenic removal that involves in-situ generation of iron coagulants using iron electrodes by electrolytic oxidation of anode. The main advantage of Fe-EC is that it does not require dosage of chemical coagulants so can be beneficial to communities with better access to electricity than chemicals.
This research work is done to combine the two techniques: biological oxidation of arsenite and Fe-EC, for better removal of arsenite from water. Batch studies on Fe-EC were performed in the laboratory to investigate the effects of charge dosage, charge dosage rate, initial arsenic concentration, arsenic oxidation state and different water matrices on the rate and extent of arsenic removal. Also, growth of AsOB on suitable bio-carrier was performed by continuous dosing of 150 μg/L arsenite-spiked water over a period of 49 days. The AsOB grown on the bio-carriers performed 90 % oxidation of 150 μg/L arsenite after a period of 35 days. Finally, two continuous flow system were developed one containing arsenite oxidation step by AsOB followed by Fe-EC and rapid sand filtration whereas the other contained only Fe-EC and rapid sand filtration. The system containing biological oxidation followed by Fe- EC removed arsenite below the WHO standard (10 μg/L ) from an initial arsenite concentration of 150 μg/L at a low iron dosage compared to the system where only Fe-EC was applied.

For all pressure driven membranes, one of the main problems which hinders the membrane practical application is the permeate flux reduction due to the solute accumulation on the membrane surface. The most popular explanation for the flux decline supported by Bhattachajee &Bhattacharya (1993), contains two mechanisms: concentration polarization(CP) and fouling. The influence of CP is noteworthy in ceramic nanofiltration system. On the one hand, CP can influence the performance of membrane separation by decreasing the retention of the molecules. On the other hand, CP could have a desirable effect which can be used for membrane surface modification. In the past three or four decades, several different models have been used to verify the existence of CP or cake-enhanced CP(CECP) effect and try to quantify it. However, all these methods or models have their own limitations. Therefore, it is essential to build a new model or adjust the constants in the empirical model according to the practical situation. The flux decline behaviour of a ceramic nanofiltration membrane in the presence of polyethylene glycols (PEGs) and silica was investigated to examine the control factor in flux decline and calculate the CP factor in the filtration. The control factor in flux decline for PEGs is CP, while for silica, both CP and fouling are important. Based on the reversibility of CP and fouling, the Gel-polarization model together with the corresponded filtration method generated the modified Gel-polarization model which is suitable for calculating the fouling resistance and the osmotic pressure on the membrane. Sherwood formula is appropriate for calculating CP factor with calibrated constants. The flux decline behaviour, as well as the CECP model developed in this work, was used to investigate the possible CP&CECP during ceramic nanofiltration for phosphate retention. CECP model based on Sherwood relation can be used to investigate the influence of the fouling layer on CP with measured permeate flux, fouling mass, and an assumed/measured porosity of the fouling layer. Based on the CECP model analysis, lower crossflow velocity and cake layer porosity, larger permeate flux and fouling mass can produce a higher CECP factor. The change of permeability in phosphate retention can be used to calculate CP factors, however, the adsorption and electroviscous effect had influence on the accuracy of the results. CECP factor is not able to be measured by the change of permeability since the unstable fouling layer can influence the discovery of permeability decrease. The presence of calcium has a serious negative impact on phosphate retention probably due to the lower electrostatic repulsion of phosphate.

The primary goal of a drinking water company is to produce safe drinking water that meets the quality standards defined in national and international guidelines. Depending on the source water, one or multiple treatment steps are required to produce safe drinking water. Generally, the drinking water treatment plants (WTP) are very robust and over-sized and, as a result, have not required stringent advanced control based on the incoming water quality. However, water companies are facing increased challenges due to changes in feed water qualities and increased (micro-) pollution loads. When the source water originates from surface water an extensive treatment system is required, since surface water can be characterized by seasonal variations influenced by temperature, algae blooms, rain-fall run-off containing pathogens, solids and pesticides, environmental spills upstream and, since recently, the increased threat by endocrine disrupting compounds. This continuous changing source water requires improved monitoring and operation of the WTP, anticipating on the disturbances in the process. THESIS OBJECTIVE: Improved monitoring and operation of ozonation and biological activated carbon (BAC) filtration for the removal of pathogens and organic matter, for the optimisation of drinking water production from surface water. Ozonation and BAC filtration processes are susceptible to changes in the feed water quality. Besides, these processes have several control options and interaction between the two processes exists. The main objective for ozonation is disinfection and oxidation of organic matter, which results in an increase in the biodegradability of the natural organic matter (NOM). The main objective for BAC filtration is the removal of organic micropollutants and biodegradation of NOM to ensure the production of biologically safe and stable drinking water. In this thesis, pilot plant research was carried out at Waternet, water cycle company for Amsterdam and surrounding areas, location Weesperkarspel, the Netherlands. Easily assimilable organic carbon (AOC) is frequently used for the assessment of biological stability of drinking water, which is an important consideration in the control of bacterial growth in distribution networks. The first AOC bioassay was developed in 1982 and is based on growth of two bacterial strains (Psuedomonas fluorescens P17 and Spirillum spp. NOX) in drinking water relative to their growth on acetate. Since the original developed method, several new methods for the determination of AOC have been published with the aim of being faster, more reliable and cheaper. Application of these assays raises legitimate questions about the comparison of AOC data from different studies. In this thesis, a round-robin test was performed to evaluate the correlation between three established AOC methods. A total of 14 water samples covering a wide range of AOC concentrations were analysed with the original “van der Kooij” method, the “Werner & Hambsch” method and “Eawag” method. Good correlations were found between AOC concentrations measured with the various methods. The data suggest an acceptable compatibility between different AOC methods, although deviations between the methods call for careful interpretation and reporting of AOC data. The results from the round robin test emphasized the need to understand which measurement method was used to obtain the reported concentration, since the method gives insight in the actual meaning of the results. Sampling of the drinking water is carried out on a regular (almost daily) basis, to ensure the produced drinking water meets the quality standards. There is a trade-off between having a high probability of detecting a deviation while minimizing the measuring effort. In order to determine which measurements should be put in place, in this thesis, a seven step design methodology was developed. This enabled the determination of the required water quality monitoring strategy around ozonation and BAC filtration. It was shown how the previous on-line monitoring program of the treatment plant Weesperkarspel was optimised. Evaluation of on-line water quality sensors showed that the parameters typically measured to show compliance with the WHO standards were commonly available. Direct measurement of the more complex parameters such as AOC and bromate were not available on-line. It was shown that real-time information on the actual Ct value, the bromate and AOC concentration was necessary for continuous optimization of the applied ozone dosage. To address this gap, algorithms were developed for the on-line estimation of the Ct value and the formation of bromate and AOC during ozonation, based on the measured change in UV-Vis spectrum before and after ozonation. It was shown that these algorithms allow for the calculation of the optimal ozone dosage and provide a reliable indication of the amount of bromate and AOC formed during ozonation. Besides using these soft-sensors as surrogate sensors for parameters currently not available on-line, they also provide a cost effective alternative when used to determine multiple parameters through one single instrument. BAC filters are frequently used in the production of drinking water for the removal of organic micro- pollutants and organic matter, especially when produced from (humic rich) surface water. Differences in filter feed water quality are the result of differences in pre-treatment steps (coagulation/flocculation, ozonation and phosphate addition) commonly applied in the production of drinking water. Understanding of how BAC filters react to a change in feed water quality helps to identify where the focus in operating the BAC filters should be on. In this thesis, the immediate response of the BAC filters to a rapid change in feed water quality was investigated as well as the long term effects. The immediate response showed that all filters were able to mitigate a sudden change in feed water quality, either through improved adsorption or increased activity of the biomass on the filter. As a result of this resilience against sudden changes, it was therefore concluded that there is no direct need for very stringent on-line monitoring and continuous adjustments of the feed water quality of the BAC filters. Only the pressure drop and the pH and oxygen concentration in the effluent should be measured. The long term effects of changes in feed water quality were compared to previously published research and confirmed the need for sufficient nutrients (readily available carbon and phosphate) in the feed water for optimal performance. The addition of phosphate resulted in the lowest dissolved organic carbon (DOC) concentration in the effluent of the BAC filters. In this study the influence of intact cells in the feed water on the performance of the BAC filters was shown to be limited. One parameter in the BAC filters that requires enhanced control and understanding is the clogging of the filters, especially when the water temperature starts to increase in spring and summer time. In the BAC filters clogging takes place as a result of the physical, chemical and biological processes occurring in the filters. A simplified model, based on retention and mass balances, to predict the filter run times was developed. Results showed that clogging in the BAC filters was a combination of chemical and biological mechanisms. Already small concentrations of AOC resulted in the development of a biofilm. This biofilm caused the formation of a cake layer and accounted for the majority of the pressure build up in the BAC filters. The simplified model was able to accurately predict the head loss development. The model subsequently allowed for optimising the process control of the full scale BAC filters in terms of predicting the pressure drop and subsequently optimising the backwash sequence, saving 32% backwash water. In this thesis it was shown that the current monitoring strategy of ozonation-BAC filtration could be improved through implementation of the established design methodology in combination with the developed algorithms allowing for on-line estimation of AOC, bromate and Ct value around ozonation, based on the measured change in UV-Vis spectrum. The operation of BAC filters could be improved through a better understanding of the direct response of the BAC filters to a change in feed water quality and the use of simplified models to optimise the operational strategy around backwashing of BAC filters. At Waternet, location Weesperkarspel, some of the findings from this and previous studies have been taken and tested at full scale. As a result, on-line monitoring of ozonation was extended with UV/Vis sensors before and after ozonation and with ozone in water sensors in the influent of the first ozonation contact chambers.@en

The quality of treated drinking water in the distribution network might deteriorate even though the quality of water leaving the treatment plant has been set to be at the highest level. Regrowth of microorganisms or known as microbiological instability is found to be one of the responsible causes for the change of the water quality. This instability might also occur in household connections due to the higher temperature, longer residence time, and the possibility of mixing with contaminated water from the household. However, chlorination is not desired to be applied in the treatment process, especially in the Netherlands. Moreover, the Dutch future heating system will be replaced with a heat pump system where the temperature of the water will be estimated at around 40°C, as it is a comfortable temperature for showering. Whilst, the hot water supply system in current situation heats the water until around 60°C and then is combined with cold water until it reaches the comfortable temperature. The future heating system will enhance the risk of microbial contamination since the temperature is within the range where Legionella can survive. Ultrasound disinfection emerges as a solution as it offers a physical disinfection method, which does not change the quality of the water chemically. According to this opportunity and the risk of bacterial regrowth in the household connection, an investigation on the efficacy of ultrasound disinfection in microbial growth control in the household is desired. At the end of this research, an experimental set-up and research plan are established to investigate the efficacy of ultrasound disinfection for microbial growth control in household water system provide water of 40°C.