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.

Manmade 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 flowrate, 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.

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.

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.

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.

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.

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).

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.

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.

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.

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.

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.

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.

Groundwater is an excellent source for the production of drinking water due to its low concentration of microorganisms and contaminants. The main contaminants present in groundwater are iron, ammonium and manganese, which are sequentially removed in rapid sand filters by a combination of biological and chemical processes. Currently, limited knowledge of the removal mechanisms challenges the design of new drinking water treatment plants (DWTPs). As a result, different treatment schemes are used to treat groundwater with a similar composition. We hypothesize that the difference in plant configuration does not affect the stratification of removal processes. In the present work, the spatial distribution of taxonomic and functional microbiological profiles and physical-chemical removal mechanisms were investigated in two DWTPs with similar incoming water but different treatment schemes. One plant employs a dual bed filter, while the other uses two sequential filters. Concentration profiles and composition of the coating on the sand showed sequential removal of iron and manganese, while ammonium removal was ubiquitous. Activity batch tests revealed section-specific manganese removal mechanisms: adsorption in the first section and oxidation in the second section. The latter is the dominant process in full-scale filters. Manganese oxidation capacity remained constant over the height of the second section. Contrarily, ammonia removal was highly stratified in there. The highest ammonium removal rates were observed at the top section of the filter. Furthermore, ammonium removal rates were higher in the second section compared to the first one. In accordance, metagenomic analysis revealed higher abundances of nitrifying organisms in the second sections. Besides, co-existence of nitrifiers and iron-oxidizers was observed in the top layer, in contrast to the common opinion that iron removal has to be complete before nitrification can start. We (i) conclude that similar distributions in removal mechanisms and genomic profiles were observed in both DWTPs, regardless of plant configuration, (ii) provide the first holistic quantitative analysis of the biological and chemical reactions in full-scale rapid sand filters and, (iii) to our knowledge, prove for the very first time that iron hydroxides on the sand grains adsorb manganese under aerobic conditions, using both adsorption and desorption tests.

The removal of iron from groundwater is essential to avoid aesthetic issues of the produced drinking water and to reduce maintenance cost of the system. The most applied iron removal method of oxidation and filtration produces large volumes of aqueous iron sludge of little value and the method is more likely to fail at high iron concentrations. This research investigates the novel concept of removing iron(II) anaerobically from groundwater by precipitation as vivianite (Fe3(PO4)2 ¢ 8 H2O) by dosing phosphate to the water. Natural groundwater was used to investigate the proposed method. A better understanding of the ironphosphate chemistry was obtained in experiments with a synthetic iron solution. To find a possible alternative to the limited resource phosphate, the possibility of removing iron by forming a compact mineral was also tested by dosing sulphate and carbonate. The chemical equilibriums and carried out experiments were evaluated by a geochemical model and the reaction products were analysed by X-ray diffraction. Up to 93% of iron removal by vivianite precipitation was obtained by dosing phosphate to anaerobic groundwater spiked with 100 mg Fe/L. An additional aeration step increased the efficiency to 99.9%, a higher total removal efficiency compared to the conventional aeration-filtration technique. The geochemical model showed that the anaerobic removal stopped when the saturation index (SI) of vivianite drops below 4, which explains why the last 7% were not removed anaerobically. Increasing the pH increases the SI of vivianite and can enhance further removal. Theoretically iron can be removed by vivianite precipitation starting from a concentration of 1 mg/L at a pH of 8.5. A second order kinetics was found for the removal of iron by vivianite precipitation at pH 7 with a rate constant of 2.27 M/s. The corresponding half life of iron is 4 minutes, while the half life of iron oxidation is 16 minutes at the same pH. Vivianite was the only crystalline end product detected and this decreased the sludge volume by a third compared to the sludge currently produced with oxidation and filtration. The total iron removal by sulphate addition only reached 73%, probably caused by the formation of iron(III)- sulphate complexes, and is therefore not a proper alternative to phosphate. The addition of carbonate reached an anaerobic removal of 59% and was increased to 99.9% by aeration. The formed sludge contained of a mixture of several oxidised compounds and the volume was almost 6 times higher compared to the currently produced aqueous iron sludge, which is why carbonate is not considered as an interesting alternative. The possibility of removing iron(II) anaerobically from groundwater by forming a compact mineral is successfully demonstrated. This method can increase the efficiency of drinking water production: higher throughput rates can be reached and a valuable end product with interesting reuse opportunities is created, provided that the phosphate can effectively be recovered from the water. It can decrease the operational costs of groundwater production substantially. The proposed novel method is a promising alternative to the conventional treatment method of oxidation and filtration, especially at plants where large iron sludge volumes are currently produced caused by elevated iron concentrations.

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

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.

Due to increasing water consumption and stress on natural water resources, enhanced treatment of wastewater and reuse of water are becoming more important. Treated municipal wastewater has potential to be used for irrigation purposes, but pathogens are a major concern to protect environmental and human health. Therefore, an advanced treatment step is required to reduce the levels of microorganisms, nutrients and suspended solids. This literature review focusses on electroflotation (EF) as disinfection method of secondary municipal wastewater treatment. EF is a combination of electrocoagulation (EC) and dissolved air flotation (DAF). In EC treatment, a sacrificial metallic anode releases metal ions (usually iron or aluminium) into the solution while hydroxyl ions and hydrogen gas are produced at the cathode. Coagulants are created in situ by the hydrolysis of these metal ions to hydroxides that can destabilize pollutants. DAF is an adsorptive bubble separation process where generated gas bubbles (of 10-100 µm) separate the impurities by flotation. This paper outlines the processes involved in EF technology and its applications in (waste)water treatment. Therefore, the processes of EC and DAF are discussed first. Influencing parameters such as electrode material, pH, retention time, charge dosage, charge dosage rate, bubble formation and size are discussed, as well as pollutant removal mechanisms. The main mechanisms responsible are charge neutralization, adsorption, sweep coagulation, microbial destruction by the electric field and deactivation by free radicals. The conclusion is drawn that the hybrid EF technique, which has been implemented in different water treatment processes, promises to increase removal efficiencies compared to single EC and DAF treatment, but the full potential of EF as a tertiary treatment step for secondary municipal wastewater effluent is yet to be fully realized. The process needs to be empirically optimized, a challenging task due to the involvement of complex chemical and physical processes.

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.

Additional master thesis