This doctoral research investigates the role of biological processes in arsenic removal during groundwater treatment. The study demonstrates that naturally occurring bacteria can effectively oxidise As(III) to As(V), enhancing arsenic adsorption onto iron and manganese oxides in sand filters. Laboratory and full-scale experiments showed that biological arsenic oxidation can substantially improve treatment performance without additional chemical dosing. The research also explores anoxic iron removal through mineral precipitation, demonstrating the potential to recover iron as vivianite and reduce sludge production. Together, the findings provide new strategies for more efficient, robust, and circular groundwater treatment. ... Read more

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. ... Read more

Decentralized drinking water production continues to face challenges in achieving acceptable standards for human consumption. This is mainly due to difficulty in developing treatments that can operate effectively in low-resource settings, either due to complications associated with providing the system in a decentralized context or overall unsatisfactory performance of the technology adopted. Electrochemical systems are emerging technologies within decentralized settings which provide many advantages to being adapted in resource-limited areas. This study focuses on understanding the mechanisms behind the electrochemical
disinfection for the treatment of surface water. Laboratory experiments were conducted to evaluate the performance of an RuO2/IrO2 and a Magneli-phase reactor for the disinfection of a bacteria species, Escherichia Coli, and a virus species, ΦX174. The two reactors are characterised in terms of distinct anodic properties and their performance is assessed by promoting different electrochemical reactions for the generation of various disinfectant agents within the electrochemical cell, with specific focus on the formation of chlorine and Reactive
Oxygen Species (ROS). Chlorine-based disinfection proved to be the primary agent in the removal of both pathogens; a 4 log removal for E. Coli was achieved at an energy use of 0.41 kWh/m3 for RuO2/IrO2 and of 0.31 kWh/m3 forMagneli, and a 5 log removal for ΦX174 was achieved at 2.88 kWh/m3 for RuO2/IrO2 and for 1.18 kWh/m3 for Magneli.
To further assess the viability for the treatment of surface waters in decentralized settings, the RuO2/IrO2 was also tested in a field setting in Ghana making use of different water types to compare the utility in using an electrochemical reactor to produce chlorine for disinfection as compared to traditional disinfection methods.  Seawater, lagoon and river water were tested, achieving an energy use per gram of produced chlorine of 0.007, 0.046 and 0.066 kWh/gchlorine for a produced chlorine dose of 35 mg/L for seawater and 5 mg/L for the lagoon and river water. With these results, chlorine can be produced from river water at an equivalent dosage to traditional chlorine tablets, and at a cost that is 40 times lower. ... Read more

Man made emergent contaminants are posing a big treat to the environment and human health. Their accumulation in water resources threatens the ecosystem equilibrium and challenges the current technologies to produce safe drinking water. This research explores anode oxidation (AO) using a Magnéli phase reactive electrochemical membrane (REM) flowthrough reactor as an alternative to treat reverse osmosis concentrate (ROC) water containing a broad list of organic micropollutants (OMPs). ROC water produced in two drinking water treatment facilities in the Netherlands was used to test the technology. This study searches for insights to manage ROC waste containing recalcitrant OMPs and safely discharge effluent to surface water.

Throughout laboratory experimentation, the effectivity of degrading OMPs (per- polyfluoroalkyl substances, pharmaceuticals, corrosion inhibitors, and synthetic dyes) was investigated. Main findings suggest that 100 mg/L Methylene blue (MB) spiked in an artificial water matrix is completely mineralized after an applied charge dosage (CD) of 22.56 kC/L. Additionally, pharmaceuticals spiked in artificial water matrix and ROC were degraded above 80% after applying a charge dosage of 5.64 kC/L. Finally, PFOA and PFOS degradation for drinking water utilities 1 & 2 resulted in an average of 49.5 and 76.90 % respectively after applying 120 kC/L.

Moreover, it was found that hardness in water inhibits the degradation capacity reducing the effective area of the anode with scaling deposition. Besides, the calcium and magnesium content slightly increases the energy consumption and the frequency of chemical cleaning required to maintain the reactor. The Magneli REM reactor has capabilities to degrade OMPs when treating ROC. Operational parameters such as flow rate, and CD can be adjusted to obtain better degradation rates. However, the treated water could contain byproducts with recalcitrant properties and high toxicity (for instance, ultra and, short chain PFAS, bromate, chlorates and perchlorates). For that reason, monitoring and further treatment is recommended to safely discharge back to surface water. ... Read more

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

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

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Drinking water production works well, but we can do better.

Anaerobic groundwater is an excellent drinking water source. It presents several advantages over its counterpart, surface water, such as constant quality and temperature, and it is considered to be microbiologically safe. The main contamination sources of anaerobic groundwater are the decomposition of natural organic matter and the dissolution of soil minerals. The first one produces compounds such as ammonia, while the second introduces manganese, iron, and trace metals. Iron, ammonia and manganese must be removed from groundwater to produce drinking water. For this purpose, humans have been using rapid sand filtration - preceded by an aeration step - for over a century.

The purpose of aeration is to strip out undesired gases and to introduce oxygen up to saturation levels. At this oxidation-reduction potential, iron, ammonia and manganese are oxidized by different physical-chemical and biological processes in the subsequent rapid sand filter. As a result, most contaminants precipitate, forming solids that are captured by the filter, and clean water is produced. Although widely used and robust, solid understanding of the intricacies of rapid sand filters is still missing. A high degree of complexity is hidden behind their seemingly simple working principles.

The main reason underneath this extraordinary complexity is the high oxygen load introduced during the aeration step. The saturation of anaerobic groundwater with oxygen onsets a series of simultaneous, interwoven and uncontrolled reactions whose nature and contribution to the overall process remains unknown and generally unpredictable. This process convolution precludes understanding and optimization of rapid sand filtration.

The overarching goal of this thesis is to gain knowledge to advance towards the design of high-flow, resource-efficient sand filters. To do so, we must be able to understand the mechanisms that govern which reactions take place, in which order they occur, and how they affect each other, which will ultimately allow us to predict and control i) microbial community assembly and performance and ii) the interplay between chemical and biological reactions. In the first part of this thesis, we focused on gaining mechanistic understanding of how current sand filters work using laboratory, pilot, and full-scale experiments. In the second one, we used this freshly acquired knowledge to design and test novel systems…
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This research explores the potential effect of Subsurface Iron removal (SIR) on the removal of organic micropollutants (OMPs). The presence of OMPs and their transformation products in the water environments globally, have raised concerns due to the potential environmental and human health risks they are posing. Recent technologies often fail to remove OMPs completely or require high energy levels and costs. Previous findings by Vitens water company have indicated that SIR application resulted in the attenuation of certain OMPs. Therefore, the effect of SIR as an alternative, cost-effective removal method of OMPs was investigated.

A continuous flow column experiment was conducted in order to simulate the processes which take place under oxic conditions at SIR for the removal of 5 targeted OMPs (bentazone, metformin, caffeine, carbamazepine and atrazine). Two columns were filled with iron oxides (FeOx) coated sand and manganese oxides (MnOx) coated sand respectively, in order to simulate the two precipitation zones created in the subsurface. The aim of the study was to investigate the removal efficiencies of the selected OMPs in both columns in order to understand if the SIR environment is favourable for the
removal of OMPs.

Results indicated that for most compounds there was removal observed after 65 pore volumes of continuous flow. Metformin was hardly removed (<10% removal rate) in both materials. A higher removal efficiency was observed at the FeOx column for bentazone (65%), caffeine (54%) and carbamazepine (29%), while atrazine was the only compound which had a greater affinity for MnOx, with a removal rate of 87%.

These findings suggest that SIR has a potential on the removal of certain OMPs. It is suggested that during SIR the OMPs existing in the subsurface, pass through the two precipitation zones and undergo removal processes within both zones. However, based on their respective affinities to each of these zones, their removal extents vary accordingly. Ultimately, the water extracted from the undergoing SIR exhibits a reduced concentration of OMPs, which is a result of the combined removal mechanisms operating within both precipitation zones. ... Read more

Groundwater is an essential source of drinking water, and it often contains contaminants in the form of dissolved metal ions that pose health risks and affect its suitability for consumption. Removal of these contaminants by conventional treatment methods, such as oxidation and filtration, results in additional treatment steps for managing sludge. New techniques are needed to prevent the formation of low-value sludge and provide better control over the drinking water treatment process. This study focused on understanding the mechanistics of electrochemical reduction for its utility as a groundwater treatment method. It was done by passing artificial groundwater containing dissolved metal ions Fe2+, Mn2+, and Al3+ through a stainless steel cathode in an electrochemical cell. It resulted in the removal of these ions through electrochemical reduction and the recovery of metals as deposits. The experiments were performed with very high metal ion concentrations (0.72 mmol/L) to obtain clear and noticeable results from their electrochemical reduction.
It was observed that while Fe2+ and Mn2+ were removed from the water and deposited on the cathode, Al3+ did not get electrochemically reduced. It was due to the system settings adopted for the study being unsuitable for Al3+ removal. It highlights the potential of electrochemical reduction as a selective treatment process that offers control by manipulating the system settings. Upto 51.4% removal was observed in Fe experiments, while for Mn experiments, up to 22.22% removal was observed. As the deposits grew with the volume of water treated during an experiment, the electrochemical reduction declined. The removal of metal ions from water became negligible when the volume of water treated reached 6.3 L. The decrease in the effective surface area of the cathode because of deposits and the changing water composition near the cathode, as the volume of the water treated was increasing, was detrimental to the transfer of electrons from the cathode to the dissolved metal ions. It was also observed that the voltage rises continuously as the water is treated due to increasing cell resistance.
Another observation was that the pH of the water matrix is an essential factor in the electrochemical reduction of the species, with cathodic depositions increasing as the pH increases. Fe depositions increased 5.8 times from 0.109 μm at pH 4 to 0.630 μm at pH 7, while Mn at pH 4 had negligible deposits, which rose to 0.213 μm at pH 7. As the pH decreases, the entropic barrier of H+ ions decreases, leading to H2 production and a decline in FE.
Further, it was observed that the electrochemical reduction performs better when a water matrix has only one type of metal ion (individual) instead of a water matrix with all three types of metal ions simultaneously (combined). The FE of Fe2+ ions in the individual case is 35.05% while it is 11.5% in combined, at pH 7. It is 14.90% for Mn2+ in individual and 1.75% in combined. This could be from the decreased availability of the free metal ions in the combined case - due to the formation of bonds between the ionic species and changes in the thermodynamic feasibility of electrochemical reduction resulting from changes in the water matrix composition.
Further investigations are required to check performance with natural groundwater samples, optimize the system settings and find cathode material that best fits the desired contaminant removal.
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Groundwater (GW) makes up roughly half of the global drinking water supply. Conventional iron removal in GW treatment produces approximately 10,000t/d of iron sludge. Iron sludge consists of low-density flocs with low to no commercial value and causes frequent energy intensive backwashing of the rapid sand filter. This study aimed to explore the novel concept of iron removal via iron sulfides formation. Iron sulfides are usually forming dense structures and offer a wider range of re-use applications.
To investigate this, an up-flow column reactor filled with pyrite seeding crystals was built and fed with iron and sulfide containing solutions. Flushed out formed solids were investigated with X-ray diffraction analysis and Raman spectroscopy. Seeding crystals were analyzed with scanning electron microscopy with energy dispersive X-ray spectroscopy.
This study observed rapid mackinawite formation after a few minutes. Mackinawite was likely retained by electrostatic adhesion on the pyrite seeding crystals. The molar ratio of removed iron to removed sulfide equaled up to 0.8 ± 0.2.
Mackinawite formation can present an interesting alternative to conventional iron removal, due to (i) its compact size, (ii) fast formation rates and (iii) possibly simple removal mechanism via electrostatic adhesion. Furthermore, in-situ formed mackinawite has the potential to simultaneously treat a wide range of pollutants ranging from toxic metals and metalloids such as arsenic over organic contaminants and nutrients such as nitrate and phosphate. Moreover, in-situ electrochemical dosing of sulfide by sulfate reduction might present a chemical-free solution for this approach. These potential synergies should be addressed in further investigations.
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This study analyses the removal of organic micropollutants (OMPs) through iron electrocoagulation in the presence of solar radiation. Methylene Blue (MB) dye has been considered as a contaminant which is removed by the action of highly reactive oxygen species (ROS) formed as intermediates during electrocoagulation (charge dosage, CD = 30 C/L and charge dosage rate, CDR = 5 C/L/min). The impact of pH on the removal rate is observed throughout the experiment. The effect of radiation (300-400 nm, 65 W/m2) on electrocoagulation has been further studied by performing iron electrocoagulation in a solar simulator (ECS) and comparing it with iron electrocoagulation in the air (EC), iron electrocoagulation with H2O2 – electro-fenton process (EF) and iron electrocoagulation with H2O2 in a solar simulator– photo-electro-fenton process in a solar simulator (PEF). The results of MB removal efficiency for each process can be deduced as: PEF = EF > ECS > EC; which conveys that combined electrocoagulation and solar radiation has synergies in the removal of OMPs, while there’s no impact of solar radiation in case of PEF when compared to EF. Further, the concentration removal capability in PEF and EF decline with the pH increasing from 3 to 9, while in case of EC and ECS, there’s is a slight improvement in the concentration removal from pH 6 to pH 8. ... Read more

Conventional groundwater treatment plants consist of aeration and rapid sand filtration steps, that are merely designed and optimized for iron (Fe), manganese (Mn) and ammonium (NH4+) removal. Understanding the various reduction-oxidation pathways, and interactions of manganese and iron, can play a major role in optimizing the performance of such filters. Interestingly, it is found that under certain conditions, mobilization of dissolved manganese can occur in such filters, which can be critical to the filter operation. Therefore, the main aim of this research is to dive deep into studying the possibilities of manganese reduction pathways occurring at the top layer of the filter media of a groundwater filter. Secondly, the research also focuses on knowing how the removal of manganese is related to the oxidation by MnO2+O2 systems, and also how these systems interact with each other under different pH conditions.
To do so, manganese dioxide (MnO2) coated sand grains were obtained from the second filtration unit of Vitens groundwater treatment plant situated in Holten. Various batch scale experiments were done under aerobic as well as anoxic conditions, in the presence of Mn(II) or Fe(II). Additionally, the influence of pH on manganese removal efficiencies as well as the rates of both manganese and iron oxidation was investigated.
It was found that the dissolved Mn was a reduction product of MnO2-Fe(II) system, where Mn(IV) got reduced to Mn(II), reaching an Fe(II) : Mn(II) molar ratio of 3.65:1 instead of 2:1, as there was a significant difference between the calculated theoretical values and the measured experimental values of both Mn(II) and Fe(II). There was mobilization of Mn(II) which took place from the MnO2 surface, when there was a presence of Fe(II) in the system, which simultaneously got partially oxidized to Fe(III). Also, it was observed that manganese could be removed by MnO2 under anoxic conditions, although under aerobic conditions the removal efficiency was high (93.32% vs 71.83%). Apart from oxidation, there is a possibility of adsorption over MnO2 due to its high sorption capacity towards cations like Mn2+, Mn3+ and Fe2+. This research also showed that a small fraction of Mn(II) reacts with Mn(IV) to form Mn(III) as a reaction product, enhancing the mobilization of Mn(II).
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With the rapid population growth and industrialization, water bodies are being infiltrated by a rising number of contaminants like metals, pharmaceuticals, pesticides and detergents, which requires the need for novel treatment technologies. Electrocoagulation (EC) is a water treatment technology where the coagulant is dosed electrochemically from a pure metal electrode. The performance of Fe-EC in a full water column using a continuous flow setup has had little to no attention yet. The aim of this proof of principle study is to determine the feasibility and the practical potential of Fe-EC during a continuous flow implementation, and to give insight to the general performance of the system in terms of water quality improvement.

Experiments were conducted in a continuous flow Fe-EC unit with descending flow. Two pairs of electrodes were used, evenly distributed along the length of the unit, and at the bottom an air diffuser was used to provide aeration. Operational configuration of the unit was needed as no prior experiments had been performed with this unit and the exact behavior of the electrodes, flow and aeration within the continuous flow system were unknown. Furthermore, experiments were conducted to evaluate the removal efficiency of Fe-EC on nutrients, organic micropollutants (OMPs), microbes and (heavy) metals, operating at a pH of 8 and 7.

The operational parameters were set to deliver an Fe dosage of 50 mg/L, flow rate of 7.5 L/h, and a current density of 15 mA/cm2. It was found that the system was able to achieve high removal of phosphorus up to 99% during all experiment sets. Highest removal of E. coli and coliphages was found when operating at a pH of 7, reaching 1.56 and 0.65 log removal respectively. Removal of OMPs was found to vary greatly among the compounds and measurements. More stable results were found when using increased OMP concentrations (around 50 µg/L), reaching removals varying from 7% to 25% at a pH of 8, and slightly lower removals from 1% to 15% at a pH of 7. No correlation was found between the observed removal and the acid dissociation constant (pKa) or the η–octanol–water partition ratio (Kow) of measured OMPs. Lastly, various heavy metals show affinity for removal during Fe-EC, such as arsenic, copper, zinc, manganese, chromium and vanadium. Using increased influent concentrations of the heavy metals (around 80 µg/L) resulted in removals above 85% for arsenic, zinc, chromium and vanadium.

The system has shown to have high removal potential on secondary effluent, even when contaminant concentrations reach high levels. Nevertheless, uncertainties and were found for the practical implementation of Fe-EC, and design and operational parameters first have to be optimized in order to fully utilize the potential that Fe-EC has. ... Read more

Dunea’s drinking water treatment plants (DWTPs) want to reach the new arsenic (As) companytarget of < 1 µg/L, due to uncertainties on toxicity at the current WHO, European and Dutch guideline of 10 µg/L. The aim of this research was to lower the As concentration in Dunea’s effluent
to < 1 µg/L by improving our system understanding and exploring novel techniques for As(III) oxidation. Fieldwork was performed to assess whether each well section contributed to the elevated As concentrations. In order to enhance As(III) oxidation at Dunea’s DWTP, the use of electrochemical advanced oxidation processes (eAOPs) with a RuO2/IrO2-coated anode was examined during laboratory experiments. Fieldwork results showed that in each monitoring point the measured As concentration was > 1 µg/L, indicating that each well section contributed to the elevated As concentrations. The combination of strongly fluctuating groundwater tables, infiltration of oxygenated water, the observed pH decrease and synchronous mobilisation of several TEs, indicated that As was most probably mobilised by pyrite oxidation. It was observed that the As-bearing layer was present between -2.5 and -8.5 m NAP. With an average filter depth from -1.6 to -7.4 m, water was being extracted from the As-bearing layer. Laboratory results showed complete As(III) oxidation by eAOPs at a current density (i) of 7.5 A/m2, with a corresponding charge dosage (q) and hydraulic retention time (HRT) of 30 C/L and 1.4 min, respectively. At the aforementioned condition, the energy consumption of the eAOP cell was 0.066 kWh/m3 with operational costs of 0.04 e/m3. Free chlorine formation was minimized by reducing q, HRT and i. During the optimal anodic configuration of 7.5 A/m2, the estimated cathodic OH− production was sufficient to replace the dosed chemicals for pellet softening (PS). However, it was not sufficient to buffer for the anodic pH decrease. It was proposed to implement the eAOP cell at Dunea’s DWTP after PS and before aeration and rapid sand filtration. ... Read more

Groundwater is a major source of drinking water containing various elements out of which arsenic(As) is one of the toxic elements present. It is present in the form of arsenite, Conventionally, As(III) can be effectively removed if it is pre-oxidized to arsenate, As(V), thereby not involving any chemical dosage. There are various techniques to remove arsenic from drinking water like membrane filtration, electro-coagulation, filtration, adsorption and ion exchange. Among these the iron electro-coagulation technique of arsenic removal is one such technique which can be done by electrochemically generating oxidizing compounds like
hydrogen peroxide, H2O2. Instead of dosing H2O2 anaerobically, it can be generated before the aeration step and can improve the As(III) oxidation with the groundwater native Fe(II).

The in-situ electrochemical generation of H2O2 was done by means of an air-cathode reactor setup, which reduces atmospheric oxygen O2 to H2O2, under anoxic water. This H2O2 then reacts with ferrous iron, Fe(II) to produce ferric iron Fe(III) and reactive oxidizing species(ROS)/intermediate products/fenton products. These ROS mainly form poorly ordered solids, which have higher adsorption capacities than the products of aeration. The oxidation of
As(III) is 4 times more by H2O2, than the oxidation by O2.

By varying the applied charge dosage (CD) and the rate of dosage (Charge Dosage Rate, CDR),the faradaic efficiencies of both Fe and H2O2 were analyzed. It was found that as the CDR increased, the overall faradaic efficiency of H2O2 generation also increased from 76.32% to 92.07%. However, there might have been discrepancies in the faradaic efficiencies of Fe due to acid & base dilutions, human errors or the difference in the operational values of the current. In theory, 1 mole of H2O2 oxidizes 2 moles of Fe(II), and in the absence of O2 the main Fe(II)-oxidant is the generated H2O2. ... Read more

Being one of the oldest water treatment systems in the world, slow sand filters (SSFs) have played a big role in the water treatment sector due to their reliability and their effective physico-chemical and biological purification capabilities. They are still widely used as a disinfection step in many countries, especially those that do not use chlorine for disinfection. SSFs are gaining popularity in recent times, especially due to their ability to deactivate pathogens like Giardia lamblia and Cryptosordidium parvum, which have been posing significant challenges to the public drinking water systems for years.
Over time, researchers have mainly focused on understanding the importance of the schmutzdecke layer of the SSFs, as it is understood that the schmutzdecke is essential for their functioning. This has limited the research done in the deeper layers of the sand bed, resulting in a lack of understanding of the activities here.
The aim of this study is to investigate the physico-chemical and biological functions happening in the deeper layers of the SSF, and to determine whether parameters like nitrate, turbidity, DOC, FEEM, ATP and particle cell counts can evaluate the ripening of a scraped bed. Furthermore, the ability of these parameters to sufficiently indicate biological stability of the sand bed is to be assessed.
In order to determine this, two full scale filters were sampled and analysed. One was a scraped bed and the other was a mature bed. They were also compared to judge how differently they behaved throughout the ripening phase.
The results of the tests showed that nitrate, turbidity and ATP are good indicators of ripening. ATP and particle cell counts, when used in parallel, are good assessors of biological stability. FEEM also serves as a useful method to determine why the DOC concentrations in the water samples were similar for both the filter beds. ATP tests conducted on the schmutzdecke sand samples provide evidence of ripening over time for the scraped bed. Further research using parameters like iron, manganese, ammonia and oxygen is required to strengthen the understanding of the workings of the deeper layers of the sand bed and the various physico-chemical and biological mechanisms happening within. ... Read more

In a global context of ever increasing population, climate change, and freshwater quality deterioration, water reclamation presents itself as a valid and valuable supplier of the resource. However, sewage and treated effluents remain important sources for waterborne pathogens, including Antibiotic Resistant Bacteria (ARB), a global emerging threat with potential to cripple our health systems and make us vulnerable once again to simple infections. Effluent disinfection thus becomes paramount to ensure suitable microbiological water quality and reuse applicability, although other water quality parameters critical for reuse applications (i.e. solid content, nutrients and organic matter) should also be addressed. Technologies developed for drinking water disinfection, such as chlorination, UV-irradiation, or ozone, usually fail to satisfy reclamation standards across all microbial groups, are not designed for nutrient or solid removal, and are known sources of hazardous disinfection by-products (DBPs). This research looks into a rather unknown water treatment technology, Iron Electrocoagulation (Fe-EC), as a suitable candidate for municipal effluent reclamation, based on its inactivation efficacy of a wide range of microorganisms, nutrient and solid removal, and absence of DBPs. The disinfection of ARB by Fe-EC and other processes is also described in detail, especially due to the shortage of literature regarding their inactivation, their general absence in water quality standards, and the health risk they pose to users. Significant efforts were made as to understand if indeed ARB are more resistant than other faecal indicator bacteria (FIB) when it comes to wastewater treatment, and if disinfection of both groups can be correlated... ... Read more

Groundwater arsenic (As) contamination is a severe drinking water quality problem and threatens human health in Bangladesh and other countries. Chronic exposure to As-contaminated drinking water has resulted in tens of millions of people suffering from skin lesions, hyperkeratosis, melanosis, skin cancer, and cancer of internal organs. The World Health Organization (WHO) recommends that As concentrations in drinking water should not be more than 10 μg/L. However, according to Bangladesh Drinking Water Standard (BDWS), the recommended value for As in drinking water is 50 μg/L. Nevertheless, groundwater in an extended area of Bangladesh contains As concentrations higher than those recommended values, and sometimes, it even exceeds 1500 μgAs/L. Various treatment technologies, including adsorption, chemical precipitation, ion exchange, membrane filtration, nanofiltration (NF), and reverse osmosis (RO) have been studied to remove As from water. However, these options are typically energy-intensive and/or consume chemicals that make the treatment methods expensive. In addition, commonly available treatment systems are complicated to operate and maintain, needing regular parts’ replacement and aftermarket services, and skilled personnel who may not be locally available. Consequently, these technologies are not sustainable on the long run in vulnerable communities. Therefore, there is a need for simple, economic, and energy-efficient alternatives, utilizing locally available materials and crafts without the need for chemical dosing... ... Read more

The presence of high levels of arsenic in groundwater, an otherwise preferred drinking water source, urges the need for innovative and highly efficient (in terms of chemical use and energy consumption) technologies to remove arsenic during drinking water treatment. This research focussed on embedding iron electrocoagulation (Fe-EC) within a biologically active rapid sand filter (RSF) by submerging horizontally perforated (Fe(0)) electrodes. These electrodes were designed in such a way that they could easily be submerged in the filter bed during backwashing. Based on As(V)/As(III) adsorption characteristics and iron removal mechanisms in a RSF it was hypothesized that the arsenic removal could be enhanced by placing the electrodes in the biologically active filter bed instead of in the supernatant. Iron to arsenic ratios (Fe:As) were reduced from 18.3 to 15.0 when the electrodes were placed in the filter bed instead of in the supernatant (for a charge dosage of 6.4 C/L and 150 µg/L As(III) in the influent), showing an improved arsenic removal efficiency. The arsenic oxidizing bacteria (AsOB) on top of the electrodes oxidized As(III) to As(V) (over 85 to 97% oxidation), which was subsequently removed by the iron that got released (by the embedded Fe-EC) and formed precipitates in the filter bed. The major drawback of embedding electrodes in the filter bed is the increase in energy consumption due to the increase in operating voltage. As(V) flowthrough experiments showed that the arsenic removal can be improved by lowering the pH from 8.0 to 7.0 and by increasing the charge dosage from 6.4 to 9.4 C/L. It was shown that besides arsenic removal efficiency, parameters as iron dosage, energy consumption, sludge production, and clogging have a significant relevance. Iron-As(V) experiments showed the flaws of the integrated system related to a partly homogeneous iron release and improper mixing, resulting in a decrease in the arsenic removal efficiency. Further, ways to potentially improve the design of the system are discussed and evaluated, pointing the way forward for future research. ... Read more

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

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

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

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

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