In the near future, the demand for drinking water could do nothing but increase, leading to the necessity of investigating new sources of freshwater, in addition to the frequently used groundwater and surface water. Brackishwater, occurring at the interface between fresh and seawater, represents a potential source of freshwater and is often treated with reverse osmosis due to its high salinity. The waste stream of this treatment, usually discharged into the sea after proper treatment, represents a potential additional source of freshwater that could be treated by sand filtration.

The aim of this study is to assess the viability of adopting sand filtration as a treatment method against ammonium and manganese for the reverse osmosis concentrate. Sand filtration has proven to be effective for waters characterized by a relatively low salt content; hence, the influence of salinity on the removal of the two aforementioned contaminants needs to be evaluated. This is done by comparing sand filtration in two different conditions: fresh and saline water, where the composition of the latter is taken from the concentrate of the reverse osmosis from Dunea's Freshman Project.

The results showed that manganese removal characterized the initial period in both systems; nevertheless, it became inhibited by the subsequent onset of nitrification. In the freshwater system, this occurred naturally, while in the saline one, nitrification needed to be enhanced by the addition of sludge coming from a SWWTP, as the natural onset turned out to be delayed. A strong correlation between the two processes relies on the effect that nitrite presence in the water has on the release of adsorbed manganese from the sand medium, a behaviour that was observed in both systems and therefore independent of water salinity. By the end of the experiments, ammonium was successfully removed in both systems. In the freshwater one, nitrification and manganese oxidation were complete, unlike the saline one, where nitrite was detected in the effluent and manganese removal didn't recover since the onset of nitrification.

Overall, the findings suggest that salinity has a delaying effect on the development of the biological processes involved in the removal of manganese and ammonium. Over time, the sand medium proved to increase its performance and potentially promote the growth of the necessary bacteria, indicating that manganese removal might also recover. By investigating how these processes respond to changing salinity conditions, this study aims to contribute to a better understanding of the potential application of sand filtration for the treatment of brackish groundwater reverse osmosis concentrate.

Slow sand filters (SSFs) are essential for ensuring microbial quality and biological stability of drinking water in the Netherlands. However, gaps exist in understanding of removal processes of dissolved organic carbon (DOC) and ammonium and the effects of grain size, loading rate, and backwashing on removal in SSFs.
Four lab-scale SSF columns filled with fine (0.4-0.6 mm) and coarse (0.85-1.25 mm) sand were constructed and operated in two phases with a total of 165 days. In phase I, SSFs operated at a flow rate of 0.5 m/h to investigate the influence of grain size. After stabilization, higher loading rate of 2 m/h and backwashing procedure (20% expansion for 5 min) was applied during the phase II experiment. Various physicochemical and biological parameters, including DOC, ammnoium, phosphate, and ATP were analyzed in water along the filter depth. Additionally, biomass development on sand was quantified suing ATP measurement.
Results showed the stable SSF operation after 90-100 days, removing 100% of dosed 1.5 mg/L of DOC and 1.0 mg/L of ammonium. Compared with fine sand, coarse sand had similar removal performance but better backwashing effectiveness and lower clogging risk. Increased loading rate led to faster microbial growth, reducing operational lifespan, and poor removal performance. Backwashing showed minimal impact on DOC and ammonium removal capacity and microbial activity, which were recovered after backwashing within 7-14 days, indicating the potential for backwashing to prolong SSF’s operational lifespan.
This research investigated the DOC and ammnoium removal processes and the influence of grain size, loading rate, and backwashing on filter performance. Providing insights for optimized SSF design and operation. Future studies could delve into mechanisms using isotope analysis or metagenomics, along with more comprehensive sand sample analysis.

The United Nations (UN) Sustainable Development Goal (SDG) \#6 reads that by 2030 universal and equitable access to safe and affordable drinking water is achieved for all In order to achieve this goal, proper and complete monitoring, capturing all the facets of safe water access, is essential. In this thesis it is argued that the current monitoring techniques come with limitations and subsequently solutions are presented to come to a more complete picture of water access.

Monitoring safe water access happens primarily through household health surveys. These surveys are often incomplete, not covering entire nations, focus on only the primary water source and are often spatially aggregated for privacy reasons. Besides, health surveys almost never include questions on consumed water volumes while that is an important indicator for proper hygiene (WELL, 1998), and something that, at the same time, should be in balance with the natural available water resources. Next to this survey based monitoring, there is the Water Point Data Exchange (WPDx) that monitors safe access by providing a platform at which the exact location and type of water access points (such as boreholes, springs, etc.) are registered. This does give more insight into the presence and usage of a variety of sources, but also the WPDx is often incomplete: not covering entire nations.

In this thesis we present a dual methodology that gap-fills the incompleteness of the WPDx database through modeling and in parallel, researches the complex local dynamics of water access, the variety of water sources used by households and the relationships between access and water consumption by means of a household survey.

By improving a machine learning biological species modeling technique (called MaxEnt), successful predictions on the number of presences of eight different water access types across Uganda were made, also into areas that have little presence in the WPDx data. It was found that population density, precipitation, elevation, poverty and groundwater storage are important indicators for the (non)presence of water access points.

Next to modeling, a survey campaign was executed in Bushenyi-Ishaka municipality, a mid-sized town in the South West of Uganda comprising a mixture of both urban and rural areas. This was done in collaboration with Makerere University (Kampala). The survey results showed that water consumption increases with education and wealth, but also with higher number of water point presences predicted by the model. It was also found that households in Bushenyi make use of an average of two different water sources on a regular basis and often express preference for sources off premises compared to on premises (piped) for both cost and perceived quality reasons.

Lastly, modi operandi were suggested for the results to improve water access such as prioritising areas with poor(est) water access and investing in rainwater harvesting, infrastructure and education.

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

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

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

Due to the quick growth in human population and subsequently a high rate of urbanization, fresh water sources are under pressure. Estimated 1.8 billion people drink water from potentially sewage-contaminated sources and also the presence of antibiotic resistant bacteria in sewage has made the improper treatment of wastewater effluent an emerging problem. Iron electrocoagulation (Fe-EC) has shown to be successful in reducing pathogen concentration, although to different extent for types of pathogens. Besides, the water quality was found to be of influence on the effectiveness. This study therefore aimed to determine the removal mechanism for both bacteria and virus as well as assess the effect of wastewater components on the Fe-EC treatment process. EC experiments were conducted in an aerated beaker with a volume of 1L, continuously stirred. pH and current were kept stable at 7.5 and 200mA, respectively. The total charge dosage was 180 C/L. After electrolysis the samples were left to settle. Blank measurements were conducted in a 230 mg/L NaCl solution. Wastewater components were added in concentration of 4.0 mg/L for phosphate, 60 mg/L calcium, and 10 mg/L humic acids. E. coli WR1 and 휙X174 were used as indicator organisms. Contributing disinfection mechanisms for E. coli were inactivation and physical removal. During electrolysis a log removal of 3.8 log units was found, ascribed to inactivation. Further increase in removal to 6.0 log units was observed after settling. In the presence of TEMPOL only 0.3 log units removal were observed during electrolysis, but removal after settling still amounted 5.5 log units. For 휙X174 removal reactive species were not effective. Disinfection after settling equaled 4 log units, when settling was complete. Settling was found to be dependent on mixing conditions, and removal was correlated as well. Extended mixing promoted the formation of larger flocs and thereby enabled sweep flocculation for phage removal. Phosphate decreased attenuation of E. coli either for inactivation, 2.0 log units as for physical removal, 4.7 log units. Phosphate has high affinity for iron and competes with bacteria for iron surface. Calcium as well inhibited abatement of E. coli. Inactivation only amounted for 1.4 log units and removal after settling equaled 2.1 log units. Calcium is expected to complex bacteria surface, increasing repulsive forces between E. coli and iron. The effect of carbonate was only seen during electrolysis, 1.3 log units. The formation of the carbonate radical is suggested as explanation for the decrease in effectiveness. The effect of NOM on E. coli attenuation was unclear. Inactivation was inhibited to only 1.4 log units, but no effect was found on the total removal. Therefore, it can be concluded that NOM does not successfully compete with bacteria for iron surface. 휙X174 attenuation was not effected by addition of phosphate, calcium, or carbonate. On the other hand, the addition of NOM inhibited phage removal, only 0.6 log units in comparison to 4.0 log units for the blank. Adsorption of NOM onto iron surface is expected to negatively change the surface charge, inhibiting association between iron and virus.

This MSc thesis is a contribution to the African Water Corridor (AWC) project that gains insight into the future of water supply systems in the Sub-Saharan African small towns. The future water demand in these areas constitute a great challenge in the effort to provide safe water for everyone. Unfortunately, there are high uncertainties in the future posed by unforeseen changing factors such as global climate change and urbanization which makes it a challenge for decision-makers to develop strategies for these water supply systems in the long-term planning. The concept of resilience is introduced by many studies to address those uncertainties The objective of this thesis is to provide an approach for decision-makers to develop a resilience water supply system in small towns for long-term decision planning to answer the following research question: ‘How can a water supply system in a small African town be resilient and provide sufficient water in the future?’ This thesis presents a methodology that is resilience-based and develops reduced future supply and increased future demand scenarios for the small town in a period of 30 years. To analyze the water supply systems in small towns, Moamba has been used as a case study..

Groundwater use has seen a significant increase in the rapidly urbanising city of Kumasi, Ghana, due to its reliability, general good quality, and low-cost development. Conversion of vegetated to urban land along with the challenges of growing groundwater abstraction has put the groundwater system at risk. This study aims to assess how the urbanisation trends in Kumasi affect the availability of groundwater resources. Sustainability is investigated by comparing (multi-)annual groundwater withdrawals to long-term average annual replenishment. Groundwater recharge is estimated in Google Earth Engine using a water-balance approach and remote-sensing datasets to bridge the hydrological data gap. Runoff is determined using the Soil Conservation Service Curve-Number (SCS-CN) method requiring soil and land-cover maps. Land-cover maps are created for 1986, 2013, and 2020 using Sentinel-2 and Landsat 8 surface reflectance products. Evapotranspiration is derived from the MODIS evapotranspiration product and precipitation is retrieved from CHIRPS. Results indicate that groundwater recharge decreased by 80% from 1986 to 2020 (124Mm3 to 28.9Mm3) attributed to a loss of permeable land (63 percentage point decrease) and intensification of urbanisation. Domestic and non-domestic groundwater consumption in 2020 is estimated to be 28.4Mm3 and 2.7Mm3 respectively. For 2020, long-term average groundwater recharge (28.9Mm3) is less than the annual abstraction (31.1Mm3) indicating current urbanisation trends are unsustainable for future groundwater availability. Under a "business as usual" scenario, population growth presents the largest challenge for the future by causing an estimated four-fold increase in groundwater consumption by 2050. Climate change and land-cover changes under the same scenario may reduce groundwater recharge by 10% and 55% respectively. This requires the implementation of policies to properly manage the groundwater resource, such as promoting low-impact development, monitoring groundwater use, and monitoring changes in the groundwater system. This study should be seen as a preliminary investigation into the components affecting groundwater sustainability. Further research is needed to assess the exact state of the groundwater system and its response to future challenges.

https://code.earthengine.google.com/b4ebac49f28c93a633eb7bd4806f409b (groundwater recharge)
https://code.earthengine.google.com/ad1a0a88240e75e3dd727a6a350edb18 (land cover changes)

To validate rainfall intensity in urban areas measured by satellite a first prototype proof of concept is introduced and tested. Using low-cost electronics an umbrella is converted into a mobile acoustic rain gauge which can be used in urban areas to measure rainfall intensities. A reed switch is placed in the umbrella to measure whether the umbrella is open or closed. Using a piezoelectric sensor and a Sparkfun sound detector rain droplets are detected and using a Pycom WiPy send over Bluetooth to an application which saves it on an online server. Tests during a laboratory experiment to see how the output data evolves shows that the data collected have an output range of about 10 % compared to its mean value. During field evaluation, to compare its output data with rainfall intensities as measured with radar, it is shown that the output data follows the radar measurements within acceptable bounds.

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.

With the growing population and economic development, there is more stress on natural water resources. Additionally, current and future water shortages, increasing environmental concerns and stringent discharge standards demand high-quality treated water. In this scenario, it is crucial to recover water and wastewater resources for reuse, reducing the dependency on new resources. While aiming for water reclamation, the influence of wastewater quality parameters on human health is given foremost attention in recent times. Enteric pathogens are a major concern when reclaiming municipal wastewater. Electrocoagulation (EC) process that introduces coagulants by electrochemical means has been successfully employed for the treatment of groundwater, industrial and municipal wastewater. EC has been widely accepted over other physicochemical processes due to its process design and lowcost material. In this research, EC has been thoroughly investigated as a tertiary treatment technology for water reclamation from municipal wastewater. This research is focused on determining the efficiency of low voltage iron EC for the removal of enteric pathogen indicators and antibiotic-resistant bacteria from secondary wastewater effluent. The effect of operational parameters: charge dosage (C/L) and charge dosage rate (C/L/min) on pollutant reduction was evaluated in different water matrices: demineralized water, synthetic wastewater effluent and real wastewater effluent. EC operated at 400 C/L, 7.2 C/L/min and natural pH allowed > 3.5 log units removal for E. coli and Enterococci, > 2.5 log units for ESBL E. coli and VRE and > 2 and 2.7 log units for Somatic coliphages and Clostridium perfringens spores respectively in real wastewater effluent. Furthermore, a significant reduction of phosphorous, COD and the true color was observed at 400 C/L and 36 C/L/min. Pollutant reduction was influenced by sedimentation and floatation mechanisms observed at varying charge dosage rates. A marginally higher removal rate constant of pathogen indicators as a function of charge dosage at low charge dosage rate showed slow iron dosing to improve microbial adsorption and increase contact time with iron precipitates. The reduction of pathogen indicators was associated with physical removal mechanisms like adsorption, sweep coagulation and entrapment within the flocs, charge neutralization and aggregation based on literature. The effective removal of physical, chemical and microbiological parameters in real wastewater effluent was achieved at 400 C/L and 7.2 C/L/min at an operating cost of 0.17 €/m3 indicating EC to be a cost-effective treatment in comparison to alternative technologies like ozone, UV, activated carbon and reverse osmosis.

Blockages in irrigation during bioleaching operation cause additional production costs and might negatively influence metals yield. The main research question was to find out if the lifetime of the irrigation system can be extended. Production process was investigated from various angles in search of causes and patterns of solution flow blockages due to calcium sulfate precipitation which was identified as the main reason of clogging. Large number of process data was statistically analyzed. Clear correlation between the PLS temperature and calcium concentration in the solution was drawn and it was found that it is far different from any other research presented. Calcium solubility was experimentally tested – solution was cooled down to approx. 4 °C and agitated daily. Results were unclear, however, on average, calcium concentration decreased by approx. 100 mg/L. The ambiguity of the initial solubility trials led to designing a new experiment. Investigation of the system pointed out critical points and allowed for the formulation of clogging control strategy. Primary calcium sources were found within the ore and metals recovery plant; sulfate is produced during bioleaching process and added to the solution with sulfuric acid – pH control. Forced precipitation of gypsum was proposed as the most viable solution. Conceptual precipitation pond was proposed based on seeded batch crystallization of gypsum. Moreover, clogging was found more prominent in areas with lower pressure head thus redesigning of the irrigation system was suggested along with implementing pulsating pressure. The outcomes of this study set a new direction for the company to counter calcium precipitation problem.