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Long-term consumption of groundwater containing elevated levels of arsenic (As) can have severe health consequences, including cancer. To effectively remove As, conventional treatment technologies require expensive chemical oxidants to oxidise neutral arsenite (As(III)) in groundwater to negatively charged arsenate (As(V)), which is more easily removed. Rapid sand filter beds used in conventional aeration-filtration to treat anaerobic groundwater can naturally oxidise As(III) through biological processes but require an additional step to remove the generated As(V), adding complexity and cost. This study introduces a novel approach where As(V), produced through biological As(III) oxidation in a sand filter, is effectively removed within the same filter by embedding and operating an iron electrocoagulation (FeEC) system inside the filter. Operating FeEC within the biological filter achieved higher As(III) removal (81 %) compared to operating FeEC in the filter supernatant (67 %). This performance was similar to an analogous embedded-FeEC system treating As(V)-contaminated water (85 %), confirming the benefits of incorporating FeEC in a biological bed for comparable As(III) and As(V) removal. However, operating FeEC in the sand matrix consumed more energy (14 Wh/m3) compared to FeEC operated in a water matrix (7 Wh/m3). The efficiency of As removal increased and energy requirements decreased in such embedded-FeEC systems by deep-bed infiltration of Fe(III)-precipitates, which can be controlled by adjusting flow rate and pH. This study is one of the first to demonstrate the feasibility of embedding FeEC systems in sand filters for groundwater arsenic removal. Such systems capitalise on biological As(III) oxidation in aeration-filtration, effectively eliminating As(V) within the same setup without the need for chemicals or major modifications., Sanitary Engineering

Slow sand filters (SSFs) are widely used in drinking water production to improve microbial safety and biological stability of water. Full-scale SSFs are maintained by scraping the biomass-rich top layers of sand. The period of downtime required for filter recovery after scraping is a major challenge due to limited knowledge of the re-stabilisation of purification processes. This study examined the recovery of microbial biomass, and removal of dissolved organic carbon (DOC) and ammonium (NH4+) in water phase and/or on sand along the depth of a scraped full-scale SSF. Scraping reduced microbial biomass on sand in the top layers, while the main prokaryotic taxa remained unaltered. Cellular ATP (cATP) and intact cell counts (ICC) in water sampled from the top layers increased, indicating a temporary disruption in functionality for 37 days. However, stable concentrations of cATP and ICC and similar microbial community composition in the effluent after scraping revealed that deeper layer biofilms offset any scraping effect. Consistent DOC and NH4+ removal after scraping showed that deeper layers effectively performed the role of the top layer. These findings highlight the resilience and robustness of microbial communities in mature full-scale SSFs and their contribution to water treatment efficiency after disturbances caused by scraping., Sanitary Engineering

Nitrate leaching from agricultural soils is increasingly found in groundwater, a primary source of drinking water worldwide. This nitrate influx can potentially stimulate the biological oxidation of iron in anoxic groundwater reservoirs. Nitrate-dependent iron-oxidizing (NDFO) bacteria have been extensively studied in laboratory settings, yet their ecophysiology in natural environments remains largely unknown. To this end, we established a pilot-scale filter on nitrate-rich groundwater to elucidate the structure and metabolism of nitrate-reducing iron-oxidizing microbiomes under oligotrophic conditions mimicking natural groundwaters. The enriched community stoichiometrically removed iron and nitrate consistently with the NDFO metabolism. Genome-resolved metagenomics revealed the underlying metabolic network between the dominant iron-dependent denitrifying autotrophs and the less abundant organoheterotrophs. The most abundant genome belonged to a new Candidate order, named Siderophiliales. This new species, “Candidatus Siderophilus nitratireducens,” carries genes central genes to iron oxidation (cytochrome c cyc2), carbon fixation (rbc), and for the sole periplasmic nitrate reductase (nap). Using thermodynamics, we demonstrate that iron oxidation coupled to nap based dissimilatory reduction of nitrate to nitrite is energetically favorable under realistic Fe3+/Fe2+ and NO3−/NO2− concentration ratios. Ultimately, by bridging the gap between laboratory investigations and nitrate real-world conditions, this study provides insights into the intricate interplay between nitrate and iron in groundwater ecosystems, and expands our understanding of NDFOs taxonomic diversity and ecological role., BT/Environmental Biotechnology, Sanitary Engineering

Iron (Fe)-based treatment methods are widely applied to remove carcinogenic arsenic (As) from drinking water, but generate toxic As-laden Fe (oxyhydr)oxide waste that has traditionally been ignored for resource recovery by the water sector. However, the European Commission recently classified As as a Critical Raw Material (CRM), thus providing new incentives to re-think As-laden groundwater treatment sludge. Before As recovery techniques can be developed for groundwater treatment waste, detailed information on its structure and composition is essential. To this end, we comprehensively characterized sludge generated from a variety of As-rich groundwater treatment plants in different geographic regions by combining a suite of macroscopic measurements, such as total digestions, leaching tests and BET surface area with molecular-scale solid-phase analysis by Fe and As K-edge X-ray absorption spectroscopy (XAS). We found that the As mass fraction of all samples ranged from ∼200–1200 mg As/kg (dry weight) and the phosphorous (P) content reached ∼0.5–2 mass%. Notably, our results indicated that the influent As level was a poor predictor of the As sludge content, with the highest As mass fractions (940–1200 mg As/kg) measured in sludge generated from treating low groundwater As levels (1.1–22 µg/L). The Fe K-edge XAS data revealed that all samples consisted of nanoscale Fe(III) precipitates with less structural order than ferrihydrite, which is consistent with their high BET surface area (up to >250 m2/g) and large As and P mass fractions. The As K-edge XAS data indicated As was present in all samples predominantly as As(V) bound to Fe(III) precipitates in the binuclear-corner sharing (2C) geometry. Overall, the similar structure and composition of all samples implies that As recovery methods optimized for one type of Fe-based treatment sludge can be applied to many groundwater treatment sludges. Our work provides a critical foundation for furthe, Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., Sanitary Engineering

Slow Sand Filtration is popular in drinking water treatment for the removal of a wide range of contaminants (e.g., particles, organic matter, and microorganisms). The Schmutzdecke in slow sand filters (SSFs) is known to be essential for pathogen removal, however, this layer is also responsible for increased head loss. Since the role of deeper layers in bacteria and virus removal is poorly understood, this research investigated the removal of E.coli WR1 and PhiX 174 at different depths of a full-scale SSF. Filter material from top (0–5 cm), middle (5–20 cm) and deep (20–35 cm) layers of an established filter was used in an innovative experimental set-up to differentiate physical-chemical and biological removal processes. In the analysis, we distinguished between removal by biological activity, biofilm and just sand. In addition, we modelled processes by a one-side kinetic model. The different layers contributed substantially to overall log removal of E.coli WR1 (1.4–1.7 log10) and PhiX 174 (0.4–0.6 log10). For E.coli WR1, biological activity caused major removal, followed by removal within biofilm and sand, whereas, removal of PhiX 174 mainly occurred within sand, followed by biofilm and biological activity. Narrow pore radii in the top layer obtained by micro-computed tomography scanner suggested enhanced retention of bacteria due to constrained transport. The retention rates of E.coli WR1 and PhiX 174 in top layer were four and five times higher than deeper layers, respectively (kret 1.09 min−1 vs 0.26 min−1 for E.coli WR1 and kret 0.32 min−1 vs of 0.06 min−1 for PhiX 174). While this higher rate was restricted to the Schmutzdecke alone (top 5 cm), the deeper layers extend to around 1 m in full-scale filters. Therefore, the contribution of deeper layers of established SSFs to the overall log removal of bacteria and viruses is much more substantial than the Schmutzdecke., Sanitary Engineering, Water Resources

Drinking water treatment plants (DWTPs) are designed to remove physical, chemical, and biological contaminants. However, until recently, the role of DWTPs in minimizing the cycling of antibiotic resistance determinants has got limited attention. In particular, the risk of selecting antibiotic-resistant bacteria (ARB) is largely overlooked in chlorine-free DWTPs where biological processes are applied. Here, we combined high-throughput quantitative PCR and metagenomics to analyze the abundance and dynamics of microbial communities, antibiotic resistance genes (ARGs), and mobile genetic elements (MGEs) across the treatment trains of two chlorine-free DWTPs involving dune-based and reservoir-based systems. The microbial diversity of the water increased after all biological unit operations, namely rapid and slow sand filtration (SSF), and granular activated carbon filtration. Both DWTPs reduced the concentration of ARGs and MGEs in the water by circa 2.5 log gene copies mL−1, despite their relative increase in the disinfection sub-units (SSF in dune-based and UV treatment in reservoir-based DWTPs). The total microbial concentration was also reduced (2.5 log units), and none of the DWTPs enriched for bacteria containing genes linked to antibiotic resistance. Our findings highlight the effectiveness of chlorine-free DWTPs in supplying safe drinking water while reducing the concentration of antibiotic resistance determinants. To the best of our knowledge, this is the first study that monitors the presence and dynamics of antibiotic resistance determinants in chlorine-free DWTPs., BT/Environmental Biotechnology, Sanitary Engineering

Rapid sand filters (RSF) are an established and widely applied technology for groundwater treatment. Yet, the underlying interwoven biological and physical-chemical reactions controlling the sequential removal of iron, ammonia and manganese remain poorly understood. To resolve the contribution and interactions between the individual reactions, we studied two full-scale drinking water treatment plant configurations, namely (i) one dual-media (anthracite and quartz sand) filter and (ii) two single-media (quartz sand) filters in series. In situ and ex situ activity tests were combined with mineral coating characterization and metagenome-guided metaproteomics along the depth of each filter. Both plants exhibited comparable performances and process compartmentalization, with most of ammonium and manganese removal occurring only after complete iron depletion. The homogeneity of the media coating and genome-based microbial composition within each compartment highlighted the effect of backwashing, namely the complete vertical mixing of the filter media. In stark contrast to this homogeneity, the removal of the contaminants was strongly stratified within each compartment, and decreased along the filter height. This apparent and longstanding conflict was resolved by quantifying the expressed proteome at different filter heights, revealing a consistent stratification of proteins catalysing ammonia oxidation and protein-based relative abundances of nitrifying genera (up to 2 orders of magnitude difference between top and bottom samples). This implies that microorganisms adapt their protein pool to the available nutrient load at a faster rate than the backwash mixing frequency. Ultimately, these results show the unique and complementary potential of metaproteomics to understand metabolic adaptations and interactions in highly dynamic ecosystems., BT/Environmental Biotechnology, Sanitary Engineering

Iron in anaerobic groundwater is commonly removed by oxidation followed by sand filtration. This produces large volumes of iron(III)(hydr)oxide sludge with little value. Our research investigates the novel concept of anaerobic iron(II) recovery from groundwater as the valuable mineral vivianite (Fe3(PO4)2 • 8 H2O) by the addition of phosphate to the water. We found that vivianite precipitated both in synthetic and natural groundwater when the saturation index (SI) was higher than 4. The SI can be increased by elevating the pH, which allows for iron removal at lower concentrations. Anaerobic iron removal reached 93.7% in natural groundwater, which increased further to 99.9% after a subsequent aeration step. Vivianite precipitation followed second order kinetics with a rate constant of 2.3 M−1s−1 and the sludge volume decreased by two third compared to iron oxidation. We therefore conclude that anaerobic iron removal is a promising new approach towards sustainable groundwater treatment., Sanitary Engineering, BT/Environmental Biotechnology

At wastewater treatment plants (WWTPs), additional steps are introduced for removal of organic micropollutants (OMPs) from the treated effluents, especially pharmaceutical residues. At the same time, a new concern is emerging: antibiotic resistance (AR). This research studied the effect of ozonation, coagulation and granular activated carbon (GAC) filtration applied as tertiary treatment for the removal of OMPs and nutrients, on AR removal. Bacterial culture methods in selective media were used to screen for four different microorganisms: two faecal indicators (Escherichia coli and Enterococci) as antibiotic sensitive bacteria (ASB), and a resistant strain of each of these bacteria, namely Extended-Spectrum Beta-lactamase producing E. coli (ESBL-E.coli) and Vancomycin Resistant Enterococci (VRE) as antibiotic resistant bacteria (ARB). At laboratory scale, ozonation experiments (ozone dose 0.4–0.6 g O 3/g DOC) and coagulation experiments using Polyaluminum chloride (PAX-214) and FeCl 3 (coagulant dose 0.004–1 mM/L) were performed using secondary effluent from two municipal WWTPs. In addition in a pilot plant and full-scale plant ozonation (ozone dose 0.4 g O 3/g DOC) and GAC filtration (empty bed contact time 15 min) were studied for AR removal. No significant differences were found between ARB and ASB removal for coagulation and ozonation which could indicate that ASB can be used as an initial proxy for ARB removal for these technologies. In the laboratory experiments, ozonation and coagulation showed a good removal of both ARB and ASB. However, the doses needed to reach 2–3 log removal were a factor 2.5–4 (ozonation) and 250 (coagulation) higher than applied for OMP removal (by ozonation) and phosphorus (P) removal (by coagulation). In the GAC filters, the risk of ARB enhancement occurred, especially in filters with a matured biology. Although these bacteria are not necessarily directly harmful, they can pass down their resistanc, Support Water Management, Sanitary Engineering

Groundwater contaminated with arsenic (As) must be treated prior to drinking, as human exposure to As at toxic levels can cause various diseases including cancer. Conventional aeration-filtration applied to anaerobic arsenite (As(III)) contaminated groundwater can remove As(III) by co-oxidizing native iron (Fe(II)) and As(III) with oxygen (O2). However, the As(III) removal efficiency of conventional aeration can be low, in part, because of incomplete As(III) oxidation to readily-sorbed arsenate (As(V)). In this work, we investigated a new approach to enhance As(III) co-removal with native Fe(II) by the anaerobic addition of hydrogen peroxide (H2O2) prior to aeration. Experiments were performed to co-oxidize Fe(II) and As(III) with H2O2 (anaerobically), O2 (aerobically), and by sequentially adding of H2O2 and O2. Aqueous As(III) and As(V) measurements after the reaction were coupled with solid-phase speciation by Fe and As K-edge X-ray absorption spectroscopy (XAS). We found that complete anaerobic oxidation of 100 µM Fe(II) with 100 µM H2O2 resulted in co-removal of 95% of 7 µM As(III) compared to 44% with 8.0-9.0 mg/L dissolved O2. Furthermore, we found that with 100 µM Fe(II), the initial Fe(II):H2O2 ratio was a critical parameter to remove 7 µM As(III) to below the 10 µg/L (0.13 µM) WHO guideline, where ratios of 1:4 (mol:mol) Fe(II):H2O2 led to As(III) removal matching that of 7 µM As(V). The improved As(III) removal with H2O2 was found to occur partly because of the well-established enhanced efficiency of As(III) oxidation in Fe(II)+H2O2 systems relatively to Fe(II)+O2 systems. However, the XAS results unambiguously demonstrated that a large factor in the improved As(III) removal was also due to a systematic decrease in crystallini, Sanitary Engineering, Water Management

Electrochemical water treatment is gaining increasing popularity due to its wide range of potential applications, its decreasing costs, and its suitability as a decentralized treatment alternative, but mainly due to it being considered a "green technology". In the field of municipal wastewater treatment, the use of iron electrocoagulation (Fe-EC) has been marginal and although disinfection has been reported, its underlying mechanisms are not fully understood, for which significant controversy remains. In this study, microbial inactivation during Fe-EC was evaluated as a two-component process, namely, physical removal by microbial floc sorption/entrapment, and inactivation by reactive oxygen species (ROS) produced by (semi)Fenton reactions. Using the fecal indicators Escherichia coli WR1 and somatic coliphage ØX174 suspended in a synthetic water matrix, the role of ROS and the role of flocculation were quantitatively evaluated. Fenton inhibitor TEMPOL was used to quench ROS production during Fe-EC. At circumneutral pH, ROS were found to be highly detrimental to E. coli, yet only mildly damaging for phage ØX174 (≈3.9 log10 and ≈0.8 log10 inactivation, respectively). Inactivation for both indicators increased under acidic conditions (pH 5.5), likely due to the formation of hydroxyl radicals (•OH), exceeding 5.1 log10 for E. coli and 1.5 log10 for phage ØX174. The ROS inactivation pathway is linked to the oxidation of ferrous iron (Fe2+), being independent of flocculation settings. Experiments involving different flocculation settings demonstrated that there is a strong positive correlation between orthokinetic-like flocculation conditions, floc sedimentation, and microbial removal, meaning that floc entrapment is a major removal pathway following Fe-EC. When compared to control experiments in which no proper flocculation stage was introduced, orthokinetic flocculation produced additional 3.1 log10 and 4.4 log10 removal for E. coli and phage ØX174, respectively. We c, Sanitary Engineering

Storage containers are usually used to provide a constant water head in decentralized, community groundwater treatment systems for the removal of iron (Fe) and arsenic (As). However, the commonly practiced aeration prior to storage assists in rapid and complete Fe2+ oxidation, resulting in poor As removal, despite sufficient native-Fe2+ in the source water. In this study, it was found that application of anoxic storage enhanced As removal from groundwater, containing ≥300 µg/L of As(III) and 2.33 mg/L of Fe2+ in an As affected village of Rajshahi district in Bangladesh. Although the oxidation of Fe2+ and As(III) during oxic storage was considerably faster, the As/Fe removal ratio was higher during anoxic storage (61–80±5 µgAs/mgFe) compared to the oxic storage (45±5 µgAs/mgFe). This higher As removal efficacy in anoxic storage containers could not be attributed to the speciation of As, since As(V) concentrations were higher during oxic storage due to more favorable abiotic (As(III) oxidation by O2 and Fenton-like intermediates) and biotic (As(III) oxidizing bacteria, e.g., Sideroxydans, Gallionella, Hydrogenophaga) conditions. The continuous, in-situ hydrous ferric oxide floc formation during flow-through operation, and the favorable lower pH aiding higher sorption capacities for the gradually formed As(V) likely contributed to the improved performance in the anoxic storage containers., Sanitary Engineering, Water Management

Excessive F- in drinking water due to natural and anthropogenic activities is a serious health hazard affecting humans worldwide. In this study, a comparative assessment was made of eight mineral-based materials with advantageous structural properties for F- uptake: layered-double-hydroxides (LDHs), geopolymers, softening pellets and struvite. These materials are considered low-cost, for being either a waste or by-product, or can be locally-sourced. It can be concluded that Ca-based materials showed the strongest affinity for F- (Ca-Al-CO3 LDHs, slag-based geopolymer, softening pellets). The Langmuir adsorption capacity of Ca-Al-CO3 LDHs, slag-based geopolymer and softening pellets was observed to be 20.83, 5.23 and 1.20 mg/g, respectively. The main mechanism of F- uptake on Ca-Al-CO3 LDHs, Mg-Al-Cl LDHs, slag-based geopolymers and softening pellets was found to be sorption at low initial F- concentrations (<10 mg/L) whereas precipitation as CaF2 is proposed to play a major role at higher initial F- concentrations (>20 mg/L). Although the softening pellets had the highest Ca-content (96-97%; XRF), their dense structure and consequent low BET surface area (2–3 m2/g), resulted in poorer performance than the Ca-based LDHs and slag-based geopolymers. Nevertheless, geopolymers, as well as struvite, were not considered to be of interest for application in water treatment, as they would need modification due to their poor stability and/or F- leaching., Sanitary Engineering, Materials and Environment, Water Management

Millions of people worldwide are exposed to excessive concentrations of fluoride (F−) from groundwater sources. Ca-Al-CO3 layered double hydroxides (LDHs) have shown promising defluoridation efficiency; however, defluoridation by Ca-Al-CO3 LDHs is highly pH sensitive. This study showed that simultaneous acidification by conventional acids, such as HCl and CO2 substantially increased the performance of Ca-Al-CO3 LDHs for F- removal at environmentally relevant concentrations (e.g., 10 mg/L) to below the WHO guideline value (1.5 mg/L), while, in comparison to other acids (HNO3, H2SO4, H3PO4), the use of HCl and CO2 does not lead to the introduction of potentially harmful or undesired anions. The addition of HCl and CO2 to LDHs suspensions did lead to changes to the LDHs structure. Leaching experiments, supported by PHREEQC modelling and characterization (SEM-EDX, XRD and FTIR), strongly suggest that the main mechanism of F- removal by Ca-Al-CO3 LDHs was F− adsorption or complexation onto/into various rehydrated mixed metal oxides which re-precipitated upon partial LDHs dissolution when acidifying., Sanitary Engineering

Generally, abstracted groundwater is aerated, leading to iron (Fe2+) oxidation to Fe3+ and precipitation as Fe3+-(hydr)oxide (HFO) flocs. This practice of passive groundwater treatment, however, is not considered a barrier for arsenic (As), as removal efficiencies vary widely (15–95%), depending on Fe/As ratio. This study hypothesizes that full utilization of the adsorption capacity of groundwater native-Fe2+ based HFO flocs is hampered by rapid Fe2+ oxidation-precipitation during aeration before or after storage. Therefore, delaying Fe2+ oxidation by the introduction of an anoxic storage step before aeration-filtration was investigated for As(III) oxidation and removal in Rajshahi (Bangladesh) with natural groundwater containing 329(±0.05) µgAs/L. The results indicated that As(III) oxidation in the oxic storage was higher with complete and rapid Fe2+ oxidation (2±0.01 mg/L) than in the anoxic storage system, where Fe2+ oxidation was partial (1.03±0.32 mg/L), but the oxidized As(V)/Fe removal ratio was comparatively higher for the anoxic storage system. The low pH (6.9) and dissolved oxygen (DO) concentration (0.24 mg/L) in the anoxic storage limited the rapid oxidation of Fe2+ and facilitated more As(V) removal. The groundwater native-Fe2+ (2.33±0.03 mg/L) removed 61% of As in the oxic system (storage-aeration-filtration), whereas 92% As removal was achieved in the anoxic system., Sanitary Engineering

Arsenic (As) is a toxic element present in many (ground)water sources in the world. Most conventional As removal techniques require pre-oxidation of the neutral arsenite (As(III)) species to the negatively charged arsenate (As(V)) oxyanion to optimize As removal and minimize chemical use. In this work, a novel, continuous-flow As removal system was developed that combines biological As(III) oxidation by bacteria with Fe electrocoagulation (EC), an Fe(0)-based electrochemical technology that generates reactive Fe(III) precipitates to bind As. The bio-integrated FeEC system (bio-FeEC) showed effective oxidation and removal of 150 µg/L As(III), without the need of chemicals. To remove As to below the WHO guideline of 10 µg/L, 10 times lower charge dosage was required for the bio-FeEC system compared to conventional FeEC. This lower Fe dosage requirement reduced sludge production and energy consumption. The As(III) oxidizing biomass was found to consist of bacteria belonging to Comamonadaceae, Rhodobacteraceae and Acidovorax, which are capable of oxidizing As(III) and are common in drinking water biofilms. Characterization of the As-laden Fe solids by X-ray absorption spectroscopy indicated that both bio-FeEC and conventional FeEC produced solids consistent with a mixture of lepidocrocite and 2-line ferrihydrite. Arsenic bound to the solids was dominantly As(V), but a slightly higher fraction of As(V) was detected in the bio-FeEC solids compared to the conventional FeEC., Sanitary Engineering

Cu and Ag have been used as bactericidal agents since ancient times, yet their antiviral capacity in water remains poorly understood. This study tested the effect of copper (Cu) and silver (Ag) on model RNA and DNA viruses MS2 and PhiX 174 in solution at pH 6–8. Cu caused MS2 inactivation with similar rates at pH 6 and 7 but was inert towards PhiX 174 regardless of pH. Ag inactivated both viruses, causing denaturation of MS2 and loss of capsid spikes in PhiX 174. Ag inactivation rates were pH dependent and increased with increasing pH. At pH 8, 6.5 logs of PhiX were inactivated after 3 h and 3 logs of MS2 after only 10 min. The combined use of Cu and Ag revealed synergy in disinfecting MS2 at pH ≥ 7. Although metal concentrations used were higher than the desired values for drinking water treatment, the results prove a promising potential of Cu and Ag combinations as efficient viricidal agents., Sanitary Engineering, BN/Stan Brouns Lab

Ceramic pot filters are household water treatment and safe storage (HWTS) systems designed to improve the microbial quality of drinking water. They yield high log reduction values (LRVs) for bacterial and protozoan pathogens but provide very little removal of viruses. This study investigated virus removal of ceramic filter discs (CFDs), using feed water with 3 different nutrient levels under extended continuous operation and limited cleaning frequency. The results show that filter use without cleaning resulted in biofilm growth and MS2 LRV values increased with increasing feed water nutrient content. Cleaning the filter surface by scrubbing led to a partial or total loss in improved LRVs, indicating the importance of this biological top layer to the removal of MS2. Overall, the removal capacity of a matured biofilm remained constant, regardless of its age. MS2 LRVs ranged between 0.9 ± 0.2 LRV for low nutrient (LN), 1.6 ± 0.2 LRV for medium nutrient (MN) and 2.4 ± 0.5 LRV for high nutrient (HN) biofilms. Interestingly, a change in feed conditions for the HN filters resulted in an unprecedented high LRV of >4 LRV, which supports further investigation of the mechanistic role of biofilms in virus removal., Sanitary Engineering

In this study, F− removal by Ca–Al–CO3 layered double hydroxides (LDHs) was investigated at environmentally-relevant concentration ranges (2–12 mg/L) to below the WHO guideline, with an emphasis on the effect of LDHs’ modification, as well as the effects of initial F− concentration, adsorbent dose, pH, temperature and co-existing ions. Ca–Al–CO3 LDHs, either untreated, calcined or microwave treated, showed affinity for the removal of F− from synthetic groundwater with capacities of 6.7–8.4 mg F−/g LDHs at groundwater-relevant pH, with a higher F− removal capacity at lower pH (<8) and lower temperature (12 °C, as compared to 25 °C & 35 °C). Since calcination and microwave treatment resulted in only marginal defluorination improvements, using untreated LDHs appears the practically most feasible option. For the untreated LDHs, competition with Cl− and NO3− was not observed, whereas at higher HCO3− and SO42− concentrations (>250 mg/L) a slight reduction in F− removal was observed. This study indicates the potential of Ca–Al–CO3 LDHs as a cost-effective F− removal technology, particularly when locally sourced and in combination with low-cost pH correction., Sanitary Engineering

This research evaluated the effect of different fluxes (16, 23 & 30 L/m 2 h) and temperatures (31,35 & 43 °C) on the rejection of As(V) during nanofiltration (NF) of natural geothermal influenced groundwater in Nicaragua. A NF pilot plant powered by solar panels was built and operated in rural community Telica, exposed to As-rich drinking water sources due to geothermal influences. The results showed that even at high temperatures it is possible to obtain high rejection of As(V) (0.87–0.9) during NF filtration (recovery 10%; flux 16 L/m 2 h) of geothermal influenced groundwater, with the additional advantage of requiring low operating pressures (1.2 bar ~ 12mwc). The permeate concentration (~5 μg/L) complied with the WHO guideline for drinking water and the concentrate (~55 μg/L) could be used by local villagers for daily activities (e.g., laundry and bathing). For all investigated fluxes and temperatures the order of rejection of As(V) (as HAsO 4 2− ), compared with the other anions, could be interpreted on the basis of its charge, hydrated radius and hydration free energy. At lower temperatures (31 and 35 °C) permeate quality improved slightly (~3 μg/L), but although an increased temperature had a negative effect on the As rejection, As concentrations in the permeate never exceeded 5 μg/L, while the required TMP dropped - depending on the flux - with 0.5 to 1 bar. This decrease in required pressure might be of huge benefit in deserted, rural locations where electricity is scarce, as with an overhead tank of 10–15 m a gravity-fed NF system would be feasible., Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., Sanitary Engineering

Several surveys have been conducted in Nicaragua between 1996 and 2015 confirming the presence of high levels of arsenic (>10 μg/L). In this paper, these peer-reviewed (n = 2) and non-peer reviewed sources (n = 14) have been combined to provide an extensive overview of the arsenic contamination of drinking water sources in Nicaragua. So far, arsenic contamination has been detected in over 80 rural communities located in 34 municipalities of the country and arsenic poisoning has been identified in at least six of those communities. The source of arsenic contamination in Nicaragua is probably volcanic in origin, both from volcanic rocks and geothermal fluids which are distributed across the country. Arsenic may have directly entered into the groundwater by geothermally-influenced water bodies, or indirectly by reductive dissolution or alkali desorption, depending on the local geochemical conditions., Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., Sanitary Engineering

In Nicaragua, a Central American country, geothermally influenced waters are frequently found to be contaminated with arsenic (as As(V)). This study investigated the effect of high-temperatures (25–50 °C), as found in geothermally influenced source waters, on the rejection of monovalent H2AsO4 - and divalent HAsO4 2- species (at pH 6,7 and 8) during NF membrane filtration of a multi-component solution containing Cl- and HCO3 -. In this multi-component solution, As(V) rejection was found to be enhanced at higher temperatures, which was in contrast to the previous assumption that temperature increase would have a negative effect on As(V) rejection. Previous studies were conducted with deionized waters, where pore size expansion and decreased viscosity drove As(V) rejection; however, in the presence of other anions such as those utilized in this study, As(V) rejection was promoted at higher temperatures. The enhancement of As(V) rejection at high temperature was associated with the presence of HCO3 - and Cl-, which are considerably more permeable than both As(V) species. An additional advantage of the higher temperature was the lower feed pressure (down to 1.5 bar) needed to operate these NF membranes, compared to colder waters. The lower energy consumption in combination with the improvement in As(V) rejection at higher temperatures shows the potential application of this technology for efficient treatment of As(V) contaminated, geothermally influenced waters for decentralised, rural drinking water production, in As-affected countries such Nicaragua., Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., Sanitary Engineering