Natural Groundwater Research Articles

In-situ oxidation of ammonia nitrogen to N2 in low temperature groundwater through Cl• − mediated peroxymonosulfate – Fe3O4 / chlorine process

The conventional ammonia in-situ treatment technology fails to achieve complete NH4+-N degradation, while the high concentration of native iron in groundwater further complicates its removal process, potentially leading to adverse environmental consequences. This study investigates the introduction of peroxymonosulfate (PMS) into groundwater containing high concentrations Fe2+ (Fe3O4 as a ferrous source), which can act as persistent catalysts, and Cl-, causing the degradation of ammonia through chlorine free radical-based advanced oxidation processes (PMS- Fe3O4/Cl-), and evaluates the advantages and limitations of employing the PMS- Fe3O4/Cl- system for ammonia treatment. The rapid reaction between SO4•- and Cl- resulted in the formation of Cl• as primary products. Cl• initiates a cascade of subsequent reactions with pH-dependent secondary active products. Under optimal conditions, the ammonia removal efficiency reached 97.44 % using the PMS- Fe3O4/Cl- system within 120 min of operation, which can be attributed to the selective oxidation of ammonia by chlorine reactive species. And this finding was substantiated by observations from experiments involving free radical quenching and EPR spectra coupled with DMPO. The HCO3– and humic acid (HA) in water can significantly affect the removal of ammonia, owing to their capability of quenching SO4•- and Cl•. Meanwhile, the levels of generated toxic chlorates in our system remain within acceptable limits. The PMS- Fe3O4/Cl- system exhibited outstanding transport capacity and stability in simulated columns, demonstrating excellent ammonia oxidation efficiency in natural groundwater, thereby confirming its promising practical potential. All experiments were executed at a temperature of 12 ℃, thereby verifying the remarkable efficacy of the PMS- Fe3O4/Cl- system in removing ammonia even under microtherm conditions.

Arsenic and fluoride adsorption from multielement solutions onto aluminium modified montmorillonite

Groundwater is the primary source of drinking water worldwide. However, it might be harmful to consumer's health due to the presence of trace elements, such as arsenic and fluoride, commonly found in Latin American. The main objective of this study was to investigate the adsorption parameters of arsenic (As) and fluoride (F) dissolved in multielemental solutions containing vanadium (V) and boron (B), on aluminium-modified montmorillonite. To achieve that, a new adsorbent was synthesised and characterised using X-ray diffraction spectroscopy (XRD), Scanning Electron Microscopy (SEM) coupled with Energy Dispersive X-Ray (EDX) and N2 adsorption/desorption isotherm techniques. Adsorption efficiencies for As and F were evaluated in multielement solutions considering the simultaneous occurrence of B and V, naturally present in groundwater. Kinetic and equilibrium adsorption experiments were carried out in batch conditions for both, mono and multicomponent solutions. The adsorbent characterization indicated an effective incorporation of Aluminium (Al) into the aluminosilicate layers and at the external surface of the montmorillonite. The adsorption process for multielement solutions took a short time and the As adsorption was not affected by the presence of V, B, or F in the solution while F adsorption parameters were enhanced by the co-occurrence of the other species in the solution. The maximum adsorption capacities were 21 and 68 mg g−1 for As and F, respectively, in the presence of B and V, at low adsorbent dosage. The new material was also tested for groundwater samples collected from Buenos Aires province (Argentina) that were naturally contaminated with As, V, B, and F. The removal of these elements was lower when compared to synthetic solutions. However, the material's efficiency in removing the ions from natural groundwater was approximately 50%. These results suggest that the material could be used to develop filters to remediate arsenic and fluoride from naturally contaminated groundwater.

Evaluation of the Permeability of Clay-Lime Mixtures for Hazardous Waste Insulation Barriers, Case of Southern Algeria (Adrar)

Containment of hazardous waste is one of the methods that can be used today for its disposal worldwide, especially in landfills. In order to preserve groundwater, landfills are constructed on a natural or reconstituted clay layer of low permeability, known as a passive safety barrier. This paper presents an experimental laboratory study that aims to upgrade local materials for use as a passive barrier in the bottoms of hazardous waste storage facilities (HWSCs). The basic materials are clays from the Adrar region in southern Algeria. An experimental study based on physical-chemical characterization and mechanical tests was performed on 2 samples of clayey soils (AA, Adrar clay, and AB, Bouda clay). Physico-chemical and mechanical characterization of Adrar clay (AA) mixtures with lime was conducted to minimize swelling and improve the studied soil. The permeability criterion allowed the adoption of an optimal mixture of Adrar clay + 6 % lime for a permeability lower than 10–12 m/s. HIGHLIGHTS Ideal solution to protect natural groundwater resources using local materials, clay and lime Large area exceeding 30 km2 of clay sources and including sources of oil pollution Noticeable improvement in clay properties thanks to the addition of lime to reduce swelling The treated clay has a very low permeability value, lower than 10−12 m/s and is ideal for hazardous waste storage centers GRAPHICAL ABSTRACT

A low-cost approach to map natural groundwater recharge potential zones of a tropical watershed with complex land occupation

Groundwater recharge is one of the components of the water cycle and is the most difficult parameter to estimate due to multiple factors that can influence the water percolation until it reaches the water table, such as land use/cover, slope, and soil texture, besides climatic conditions. Given that groundwater is Brazil's most widely exploited natural resource and its significance in sustaining ecosystems, apart from its role in guaranteeing the city's water security, mapping zones of recharge potential is a growing demand for water resources management. This work uses the GIS approach and the water balance (2010–2019) to map the groundwater recharge potential zones of the Adamantina Aquifer in Urânia (São Paulo State, Brazil) delimited on a local scale by the Córrego Comprido watershed. The results showed that 39% of the area has a recharge potential of 165 mm/year or 13% of the average annual precipitation (APPT) for the time, reflecting the gently undulating topography (2–7% slope) with sandy soil texture and shrubby herbaceous cover. Maintaining these same terrain characteristics and changing the land use/cover only, the presence of eucalyptus trees would decrease the recharge potential by 32% (111 mm/y; 9% of average APPT). As another example, the urban occupations would cause a reduction of 80% for the same parameter (33 mm/y; 3% of average APPT). Furthermore, in urban areas, a developing recharge potential value of only 7 mm/year (1% of average APPT) corresponding to sandy lands but with slopes of 7% was observed, demonstrating the primary control of land use/cover and topography in the estimates. The predominant recharge potential value of 165 mm/y correlated with the results of previous recharge studies conducted in Urânia. It demonstrated the versatility of this approach to extrapolate over large areas when required.

Decoding degassing modes of magma chamber of arc volcanoes: Insights from CO2/Cl and Cl/H2O ratios of magmatic fluids in groundwater

The H2O-CO2-Cl composition of the fluids released from the magma chambers for arc volcanoes was calculated based on the solubilities of H2O and CO2 in the silicate melt and the partition coefficient of Cl between the aqueous fluid and melt for the stages defined by a simple evolution model of the magma chamber. The degassing modes consisted of mafic bubbling (MB: first boiling) and felsic bubbling (FB: second boiling) releasing fluids as separate bubbles due to the mafic magma supply and felsic magma formation by differentiation, respectively, and felsic solidification (FS) releasing fluid due to felsic pluton formation. The variations in the CO2/Cl and Cl/H2O ratios of the fluids were examined for each degassing mode at pressures ranging from 150 to 400 MPa and were found to have very large variations at 0.00024–845 for CO2/Cl and 0.00043–0.041 for Cl/H2O. The CO2/Cl is concluded to be a good indicator of magma chamber conditions because each mode has a specific ratio distinguished from that of the other modes; i.e., CO2/Cl > 43 for MB, 0.027–23 for FB, and < 0.62 for FS.The alteration of magmatic composition of fluid during ascent was discussed considering the phase separation of fluid, CO2 bubbling in groundwater, dissolution, and deposition of minerals; furthermore, the limitation of the method when applied to natural groundwater systems were outlined. This method was tested for a natural volcanic system, the Kuju volcano in central Kyusyu, Japan, which is an active volcano complex composed of various magma types from rhyolitic to basaltic, replacing the eruption centers from west to east. Groundwater samples from springs and boreholes were collected and analyzed for chemical and isotopic compositions to determine the magmatic H2O, dissolved inorganic carbon (DIC), and Cl concentrations. The new approach to determine the magmatic CO2 concentration in groundwater using 3He concentration proposed herein cancelled the effect of carbonate deposition/dissolution, addition of DIC from organic matter, and bubbling of CO2. The estimated magmatic CO2/Cl ratios were 0.0009–14, which overlapped consistently with the modeled variation in the CO2/Cl ratio. The spatial variation of magmatic CO2/Cl in groundwater showed that higher-CO2/Cl are found near the central part of the volcanic complex which composed of felsic to mafic volcanoes, and low-CO2/Cl are only found around old felsic volcanoes. The CO2 bubbling springs were found to be associated with younger mafic volcanoes. The condition of the magma chambers, as shown by the spatial variation in CO2/Cl, were consistent with the record of the eruptive activities of the Kuju volcano. The CO2/Cl method proposed in this study using groundwater is useful for estimating magmatic conditions in chambers.

In-situ targeted removal of naphthalene from groundwater by peroxymonosulfate activation using molecularly imprinted activated carbon: Efficacy, mechanism and applicability

Efficient removal of low-concentration refractory polycyclic aromatic hydrocarbons (PAHs) pollutants is crucial for ensuring groundwater safety. In this study, surface molecularly imprinted catalyst (MIP@AC) was developed based on activated carbon (AC) and molecular imprinting technology, and then MIP@AC was introduced into the simulated permeable reaction barrier to evaluate the performance of MIP@AC activated peroxymonosulfate (PMS) in in-situ targeted remediation of naphthalene (NAP) contaminated groundwater. The results showed that the relative adsorption selectivity coefficient and relative degradation selectivity coefficient of the MIP@AC material relative to the non-imprinted material AC was as high as 31.47 and 10.88, respectively; that is, MIP@AC can better resist the interference of competitive pollutants and achieve efficient targeted removal of NAP. Additionally, the reactive oxygen species (ROS) yield was higher in the MIP@AC/PMS system compared to the AC/PMS system. The target pollutant NAP was precisely enriched in the imprinted cavity of the MIP@AC, realizing that ROS production and pollutant degradation occurred simultaneously in the MIP@AC imprinted cavity. Therefore, the spatial confinement effect of the imprinted cavity shortened the mass transfer distance between the ROS and NAP, thereby reducing the loss of ROS due to self-quenching. Besides, Cl- significantly promoted the targeted removal of NAP, while HCO3- had a slight inhibitory effect; humic acid had no effect because of its larger molecular structure, which does not fit into the small imprinted cavities preferred by NAP. Importantly, the MIP@AC/PMS system demonstrated effective anti-complex matrix interference ability and targeted removal performance for NAP under natural groundwater conditions. This study can promote further research on the surface molecularly imprinted catalyst/PMS system as a new strategy for in-situ targeted remediation technology of contaminated groundwater.

Hydrological and biogeochemical processes controlling riparian groundwater quantity and quality during riverbank filtration

Groundwater exploitation in a riparian zone causes water infiltration from the river into the aquifer. Owing to adsorption and redox reactions along the flow path, the quality of water flowing from the river to groundwater wells is variably altered. The riverbed composition often involves spatiotemporal differences due to frequent changes in hydrological conditions. These changes create uncertainties in the transport and removal of solutes in the river water. In this study, the hydrodynamic field associated with riparian groundwater, changes in the structure of riverbed sediments caused by erosion and deposition, fluctuations in surface water and groundwater levels, and the removal efficiency of pollutants from groundwater through pumping were investigated. This involved in situ monitoring and sample testing of the composition of the river water, riverbed sediments, riverbed pore water, and groundwater during dry and wet seasons. Implementation of field in situ column experiments and molecular biology evidences were conducive to identifying the main biogeochemical processes occurring in the riverbed. The findings indicated that riparian groundwater exploitation alters the natural groundwater flow field, while fine sand deposition and microbial adsorption can reduce river recharge to aquifers by diminishing riverbed hydraulic conductivity. Shallow sediments within 1 m depth mainly involve NO3− reduction and E. coli adsorption. Reductive dissolution of Mn dominates in the deeper sediments. Additionally, reductive dissolution of Fe and dissimilatory nitrate reduction to ammonium (DNRA) drive high Fe2+ and NH4+ concentrations in groundwater. The findings can improve the management of riparian groundwater and aid in the optimization of a plan for its exploitation.

Performance and optimization of diclofenac and ibuprofen adsorption onto activated carbon synthesized from sunflower seed shell (Helianthus annuus) in natural groundwater samples

Performance and optimization of diclofenac and ibuprofen adsorption onto activated carbon synthesized from sunflower seed shell (Helianthus annuus) in natural groundwater samples

Комплексные решения по управлению хвостовым хозяйством на Усольском калийном комбинате

Introduction. At enterprises engaged in the extraction and processing of mineral raw materials, the volume of production waste is usually much higher than the volume of a commercial product. At the same time, there is a tendency to decrease the metal content in ores while increasing the volume of waste rock extracted when accessing ores. According to various estimates, the annual volume of waste from mining enterprises is 7 billion tons per year. The proportion of waste (tailings) in some copper-containing ores can reach 98 % or higher. Gold mining enterprises process ores in which tailings amount to 99.9 % and which contain only a few grams of gold. This trend will continue, as the enterprises of the mineral processing industry have to increase the volume of processed products. Materials and methods. Tailings processing technology solutions include equipment and services that can be used in almost any tailings farm, while tailings thickening and paste thickening can be used. Just as in the case of surface tailings management solutions, the development of solutions for underground workings begins with consideration of the available storage space underground. Post and dry storage technologies combined with closed water circuits represent the best options available for saving water in processing plants. In traditional tailings systems, the source of process water is natural sources or groundwater from mine drainage. Results. The use of sludge dewatering technology has significant advantages in handling excess brines, because it allows you to separate the mother liquor, return it to the technology and thereby prevent discharge to the sludge storage. To enhance the effect of sludge dewatering, it is necessary to limit the supply of fresh water to the technological process beyond the level of irretrievable losses (for example, evaporation into the atmosphere) by using a mother liquor or recycled brine instead of water. Discussion. liquid phase entering the sludge storage, increase the efficiency of hydraulic transport, and increase the service life of tailings facilities. Scientific works confirm the possibility of using filtered sludge from potash factories as a meliorant for agriculture and restoration of forest soils after fires. When implementing integrated tailings management, it is necessary to take into account the existing conditions and limitations of the site, the requirements of the technological process of a particular enterprise. Conclusion. The article presents the results of research on the dehydration of sludge of potassium salts. It has been established that the sludge dewatering technology significantly reduces the volume of sludge entering the sludge storage, which will increase the efficiency of hydraulic transport, increase the service life of tailings facilities. Resume. The use of sludge dewatering technology can significantly improve the efficiency of the processing plant. The development of sludge dewatering technology will require a number of research projects on transportation, storage and logistics of meliorant.

Долгосрочная оценка режима минимального зимнего стока рек бассейна озера Севан при изменении климата

Introduction. Analysis and assessment of the statistically significant consequences of climate change for the long-term minimum 30-day winter runoff of rivers in the Lake Sevan basin is of significant interest to consumers and water resource management, being an important hydrological issue. The relevance of consideration of the issue is due to the fact that for Armenia Lake Sevan is a strategic reservoir of fresh water, a large water management complex, a source of water for hydropower and agricultural irrigation, an object of tourism and recreation. Issues of formation and calculation of the minimum runoff of rivers in the lake basin. Sevan were discussed in works, the analysis of the spatial-temporal distribution of the winter minimum decade-day, monthly and 30-day runoff can be found, for example, in works.In contrast to the listed works, in this study a technique for assessing the statistically significant consequences of climate change for the hydrological regime in relation to small foothill watersheds of the rivers of the Lake Sevan basin (Republic of Armenia) is considered. The values of the minimum 30-day water runoff within the study area can be used when calculating standards for permissible discharges into rivers, to assess natural groundwater resources, as indicators of the extremeness of river flow and in other water management calculations. Research methods and materials. The methodology is based on a probabilistic model of the formation of long-term river runoff, which is approximated by a system of linear equations for the initial statistical moments. As the source material were used the data of actual hydrometeorological observations (minimum 30-day winter river runoff, air temperature and precipitation) of the “Center for Hydrometeorology and Monitoring” of the SNCO of the Ministry of Environment of the Republic of Armenia. Research results. The results of approbation of the methodology on retrospective material are presented, taking into account possible climate change both towards warming and towards cooling.The conditions for the applicability of the methodology to small foothill watersheds for assessing the minimum 30-water winter river runoff are identified. The obtained satisfactory results made it possible to assess the impact of climate change for the minimum runoff using the IPCC climate scenarios. Three climatic scenarios are considered, the model of the Max Planck Institute with a monthly time resolution. Conclusions. As a result, watersheds of rivers in the basin of Lake Sevan were identified, in which significant deviations of the predicted average annual values of the minimum 30-day winter runoff and the coefficients of its variation from the actual ones in the implementation of the considered scenarios can be expected. An analysis of the obtained results is given from the point of view of taking possible preventive measures, including strategic planning of the use of water resources in winter low water, in case of climate change.

Mapping natural groundwater potential recharge zones using GIS-AHP in the Upper Cheliff alluvial aquifer, Algeria

Water scarcity is a big issue in arid and semi-arid regions. This challenge is particularly evident in the Upper Cheliff plain in Algeria, where the alluvial aquifer plays a vital role in drinking water supply and supporting irrigation. This aquifer faces high demand and quality issues. A study was conducted in this context, employing a cartographic approach to assess potential groundwater recharge from precipitation into the alluvial aquifer. The current study aimed at mapping zones with potential natural groundwater recharge zones by applying the Analytic Hierarchy Process (AHP) integrated within a Geographic Information System (GIS) environment, combining various factors that can influence recharge, such as rainfall, surface soil type, slope degree, land use and land cover, unsaturated zone, groundwater depth, and curve number. The map resulting from the analysis indicates that only 22% of the assessed area covers zones with very low and low potential recharge, 35% with moderate potential recharge zones, and 43% with high and very high potential recharge zones. This map reveals that the eastern region of the plain, from the cities of Djendel to Ain Soltane, is moderately to highly favorable for recharge. This is due to the natural recharge from rainfall and watercourse infiltration during dam release periods, excess irrigation water, and recharge from the Miocene sandstone aquifer in areas with direct aquifer contact. A validation process was performed using data from 66 wells distributed in this plain and it indicated that 48 wells exhibited good agreement with the resulting map, while 18 wells showed slight deviations. The results indicate an agreement of 72.72% between expected and exist number value of wells which confirming the good prediction of the AHP technique.

Enhancing groundwater recharge in drinking water protection zones in Flanders (Belgium): A novel approach to assess stormwater managed aquifer recharge potential

Study regionFlanders (Belgium) Study focusStormwater infiltration for managed aquifer recharge is increasingly recognized as a drought adaptation measure. Given the high degree of urbanization and imperviousness, stormwater infiltration has significant potential in Flanders (Belgium). This research presents a novel approach to quantify stormwater availability and its potential to enhance groundwater recharge. Stormwater volumes available for recharge are calculated based on the imperviousness level, yearly average precipitation volumes, and runoff coefficients. This study focuses on groundwater protection zones around drinking water wells to assess the role of increased infiltration for sustainable drinking water production. Calculated potential stormwater volumes for recharge are compared to natural groundwater recharge and pumping volumes for drinking water production to quantify the potential significance of stormwater infiltration for aquifer recharge. New hydrological insights for the regionResults show a high potential for stormwater infiltration in Flemish protection zones with an average of 17% (7%-33%) additional groundwater recharge from stormwater infiltration. Additionally, stormwater recharge could potentially compensate for 19% (8%-37%) of abstracted drinking water production from phreatic aquifers. Locally, higher groundwater recharge potentials were calculated, especially in protection zones around the city of Leuven. Therefore, stormwater harvesting for infiltration and groundwater recharge should be further encouraged throughout the region, with special attention to urban areas. However, further research is needed on stormwater quality to assess groundwater quality risks in this water quantity-quality balancing exercise.

Electrospinning Chitosan/Fe-Mn Nanofibrous Composite for Efficient and Rapid Removal of Arsenite from Water.

Efficient removal of extremely mobile and toxic As(III) from water is a challenging but critical task. Herein, we developed a functionalized sorbent of chitosan nanofiber with iron-manganese (Fe-Mn@CS NF) using a one-step hybrid electrospinning approach to remove trace As(III) from water. Batch adsorption studies were performed to determine the adsorption efficiency under a variety of conditions, including contact time, starting concentration of As(III), ionic strength, and the presence of competing anions. The experimental results demonstrated that the concentration of As(III) dropped from 550 to less than 1.2 µg/L when using 0.5 g/L Fe-Mn@CS NF. This demonstrates the exceptional adsorption efficiency (99.8%) of Fe-Mn@CS NF for removing As(III) at pH 6.5. The kinetic tests revealed that the adsorption equilibrium was reached in 2.6 h, indicating a quick uptake of As(III). The ionic strength effect analysis showed that the adsorbed As(III) formed inner-sphere surface complexes with Fe-Mn@CS NF. The presence of SO42- or F- had a negligible impact on As(III) uptake, while the presence of PO43- impeded As(III) absorption by competing for adsorption sites. The exhausted sorbent could be effectively regenerated with a dilute NaOH solution. Even after 10 cycles of regenerating Fe-Mn@CS NF, the adsorption efficiency of As(III) in natural groundwater was maintained over 65%. XPS and FTIR analyses show that the presence of M-OH and C-O groups on the sorbent surface is essential for removing As(III) from water. Overall, our study highlights the significant potential of Fe-Mn@CS NF for the efficient and quick elimination of As(III) from water.

Catchment-Wide Groundwater Budget for the Inkomati-Usuthu Water Management Area in South Africa.

In South Africa, approximately 98% of the predicted total surface water resources are already being used up. Consequently, the National Water Resource Strategy considers groundwater to be important for the future planning and management of water resources. In this case, quantifying groundwater budgets is a prerequisite because they provide a means for evaluating the availability and sustainability of a water supply. This study estimated the regional groundwater budgets for the Inkomati-Usuthu Water Management Area (Usuthu, Komati, Sabie-Sand, and Crocodile) using the classical hydrological continuity equation. The equation was used to describe prevailing feedback loops between groundwater draft, recharge, baseflow, and storage change. The results were coarser scale estimates which, beforehand, were derived from the 2006 study. In the years to follow, groundwater reliance intensified and there was also the historic 2015/2016 drought. This inevitably led to an increased draft while the rest of the components of the groundwater budgets experienced decreases. Both Crocodile and Sabie-Sand experienced groundwater storage depletion which led to reduced baseflow and groundwater availability, while groundwater recharge contrarily increased due to capture. Conversely, the other two catchments experienced relatively lower drafts with correspondingly higher groundwater availability and recharge while storage change was positive. The results highlighted the need for adaptive water management whose effectiveness relies on predictive studies. Consequently, future models should be developed to capture the spatial and temporal dynamism of the natural groundwater budget due to climate change, water demands, and population growth predictions.

Using L. minor and C. elegans to assess the ecotoxicity of real-life contaminated soil samples and their remediation by clay- and carbon-based sorbents

Toxic substances, such as polycyclic aromatic hydrocarbons (PAHs) and heavy metals, can accumulate in soil, posing a risk to human health and the environment. To reduce the risk of exposure, rapid identification and remediation of potentially hazardous soils is necessary. Adsorption of contaminants by activated carbons and clay materials is commonly utilized to decrease the bioavailability of chemicals in soil and environmental toxicity in vitro, and this study aims to determine their efficacy in real-life soil samples. Two ecotoxicological models (Lemna minor and Caenorhabditis elegans) were used to test residential soil samples, known to contain an average of 5.3, 262, and 9.6 ppm of PAHs, lead, and mercury, for potential toxicity. Toxicity testing of these soils indicated that 86% and 58% of soils caused ≤50% inhibition of growth and survival of L. minor and C. elegans, respectively. Importantly, 3 soil samples caused ≥90% inhibition of growth in both models, and the toxicity was positively correlated with levels of heavy metals. These toxic soil samples were prioritized for remediation using activated carbon and SM-Tyrosine sorbents, which have been shown to immobilize PAHs and heavy metals, respectively. The inclusion of low levels of SM-Tyrosine protected the growth and survival of L. minor and C. elegans by 83% and 78%, respectively from the polluted soil samples while activated carbon offered no significant protection. These results also indicated that heavy metals were the driver of toxicity in the samples. Results from this study demonstrate that adsorption technologies are effective strategies for remediating complex, real-life soil samples contaminated with hazardous pollutants and protecting natural soil and groundwater resources and habitats. The results highlight the applicability of these ecotoxicological models as rapid screening tools for monitoring soil quality and verifying the efficacy of remediation practices.

Electrochemical arsenite oxidation for drinking water treatment: Mechanisms, by-product formation and energy consumption

The mechanisms and by-product formation of electrochemical oxidation (EO) for As(III) oxidation in drinking water treatment using groundwater was investigated. Experiments were carried out using a flowthrough system, with an RuO2/IrO2 MMO Ti anode electrode, fed with synthetic and natural groundwater containing As(III) concentrations in a range of around 75 and 2 µg/L, respectively. Oxidation was dependent on charge dosage (CD) [C/L] and current density [A/m2], with the latter showing plateau behaviour for increasing intensity. As(III) concentrations of <0.3 µg/L were obtained, indicating oxidation of 99.9 % of influent As(III). Achieving this required a higher charge dosage for the natural groundwater (>40 C/L) compared to the oxidation in the synthetic water matrix (20 C/L), indicating reaction with natural organic matter or other compounds. As(III) oxidation in groundwater required an energy consumption of 0.09 and 0.21 kWh/m3, for current densities of 20 and 60 A/m2, respectively. At EO settings relevant for As(III) oxidation, in the 30–100 C/L CD range, the formation of anodic by-products, as trihalomethanes (THMs) (0.11–0.75 µg/L) and bromate (<0.2 µg/L) was investigated. Interestingly, concentrations of the formed by-products did not exceed strictest regulatory standards of 1 µg/L, applicable to Dutch tap water. This study showed the promising perspective of EO as electrochemical advanced oxidation process (eAOP) in drinking water treatment as alternative for the conventional use of strong oxidizing chemicals.

A sulphide resistant Ag|AgCl reference electrode for long-term monitoring.

Reference electrodes which demonstrate long-term potential stability are essential for many continuous monitoring applications and are commonly based on Ag|AgCl electrodes; however, these electrodes are susceptible to poisoning from aqueous sulphide species which are commonly present in wastewater and natural groundwater. This work presents a sulphide resistant solid-state reference electrode (SSRE) based on a composite material using suspended KCl electrolyte and sacrificial AgCl in a cross-linked polyvinyl acetate polymer matrix. Sulphidation of the sacrificial AgCl produces a stable Ag2S precipitate and prevents further ingress of the poisoning sulphide species through the composite material. A novel SSRE using this material is compared to a control SSRE without suspended AgCl and a typical liquid filled reference electrode. These three reference electrodes are studied using electrochemical impedance spectroscopy (EIS), and their application is also studied in potentiometric pH sensing and cyclic voltammetry (CV). The long-term sulphide resistance of the two SSREs is also studied with potentiometry, and cross-sections of these electrodes were examined using micro X-ray fluorescence (μXRF). Both SSREs demonstrated higher impedance than the liquid reference electrode but were similar to other SSREs reported in the literature. This impedance did not result a meaningful difference in potentiometric pH sensing or CV experiments done using typical scan rates. The KCl/AgCl SSRE exhibited remarkable sulphide resistance, with all samples demonstrating a stable potential without maintenance after ca. 120 days of continuous immersion in 1 g L-1 Na2S solution, whereas KCl SSRE samples all demonstrated significant drift before this time. μXRF sulphur maps revealed that suspended AgCl prevented sulphide ingress, thus protecting the embedded Ag|AgCl electrode. This work presents a reference electrode that could enable long-term monitoring in challenging sulphide solutions, and also highlights a novel approach for preventing reference electrode poisoning which could be more widely explored.

Final report for SIM.QM-S12: supplementary comparison for trace elements in natural water

Main textThe SIM Supplementary Comparison SIM.QM-S12 for Trace Elements in Natural Water was undertaken to assess and demonstrate the analytical capabilities of national metrology institutes (NMIs) and designated institutes (DIs) of SIM members (or other regions) for the accurate determination of trace elements in natural water at µg/kg levels.Evidence of successful participation in formal, relevant international comparisons is needed to document calibration and measurement capability claims (CMCs) made by NMIs and DIs.Seventeen NMIs and DIs participated. Participants were requested to evaluate the mass fractions, expressed in µg/kg, of arsenic, cadmium, lead and antimony in a natural mineral groundwater that was spiked with the respective elements. A variety of instrumental techniques including inductively coupled plasma mass spectrometry (ICP-MS), isotope dilution ICP-MS (ID-ICP-MS), inductively coupled plasma optical emission spectrometry (ICP-OES), electrothermal atomic absorption spectrometry (ETAAS) and hydride generation flame atomic absorption spectrometry (HG-FAAS) were used by the participants for the determination.The NIST decision tree was used to assign the SCRV estimate for the proposed measurands and to calculate the degrees of equivalence of each national measurement standard following the IAWG Guidance on Using NIST Decision Tree for Comparison Reporting from 30 June 2023.Successful participation in SIM.QM-S12 demonstrates measurement for determination of elements in water matrices. Considering the IAWG Core Capability Matrix, this material falls into the matrix challenge called "Water/aqueous", which corresponds to the CCQM amount-of-substance category fresh water, and so will support CMCs for the metalloids and semi-metals at mass fraction levels below 50 µg/kg (As and Sb measurements) and transition elements at mass fraction levels below 50 µg/kg (except Hg) (for Cd and Pb measurements).To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/.The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

GRAVITATIONAL GEOLOGICAL PROCESSES (KARST)

The article presents karsts, as one of the gravitational geological processes, developing in rocks (limestone, dolomite, gypsum, anhydrite, sodium and potassium salts) dissolving in natural surface and groundwater. For the first time, an attempt was made to study karsts, changes in hydrogeological conditions during their development and the influence on internal and external hazardous geological phenomena. The main purpose of this article is to draw attention to the need for further study of the Dvin earthquake source, associated with the possible collapse of underground voids (in this case, karst halls) characteristic of this territory.

Comparative study of natural and artificial groundwater recharge methods

Comparative study of natural and artificial groundwater recharge methods