Synthetic Groundwater Research Articles

A low‐cost treatment system for underground water using Moringa oleifera seeds and Musa cavendish peels for remote communities

AbstractBACKGROUNDNemours plant‐based biomass exhibit higher removal capacities in comparison to chemical treatment methods. The present study aimed to investigate the potential of Moringa oleifera (MO) seeds and Musa cavendish (MC) peel biomass pre‐treated by HNO3 (1 N) and NaOH (0.1 M) for removing nickel (Ni), lead (Pb) and cadmium (Cd) ions from synthetic groundwater. It further aimed to establish the design and test the efficiency of an individual domestic groundwater treatment system with low‐cost using local materials. The batch tests with biomass (MC, MO and MC + MO) were conducted at pH 7. Adsorption was investigated using Freundlich and Langmuir models for single elements, and the Sheindorf–Rebhun–Sheintuch (SRS) model for multicontaminant elements. By contrast, the simulation of actual groundwater quality was studied using a Monte Carlo simulation model.RESULTSThe adsorption results fitted with the Freundlich model revealed that ≈91%, 98% and 84% of groundwater samples met WHO standards for Pb2+, Ni2+ and Cd2+, respectively. The FTIR analysis of MC, MO and MC + MO revealed that CC, CO and NH were the main functional groups playing roles in the removal of heavy metals from the water samples. The mechanism of adsorption took place by chemisorption and physisorption. The total cost of the water treatment system with a capacity of 50 L was US$17, and considered suitable for remote, lower income communities.CONCLUSIONThe MC + MO biomass was efficient in adsorbing heavy metal ions from water samples owing to the presence of abundant functional groups.

Water Treatment Plant Prototype with pH Control Modeled on Fuzzy Logic for Removing Arsenic Using Fe(VI) and Fe(III)

This study proposes a fuzzy control strategy embedded in a Siemens IoT2040 gateway developed for removing inorganic arsenic from synthetic underground water in a treatment plant prototype. The prototype is used to dose a constant flow of Fe(VI) to maintain an oxide-reduction potential to guarantee the oxidation of arsenite into arsenate, while the fuzzy logic embedded in the IoT control manages the addition of Fe(III) to achieve a proper pH adjustment and efficient arsenate removal. The tests used synthetic Bangladesh groundwater enriched with 200 µg/L of arsenite and 200 µg/L of arsenate. The results revealed that the plant prototype yielded an effective treatment of the water. Arsenate was decreased to an average value of 6.66 µg/L and, the arsenite concentration decreased to 1.01 µg/L or less. These values were lower than the limit of 10 µg/L deemed by the World Health Organization as safe for human consumption.

Aqueous Film-Forming Foams Exhibit Greater Interfacial Activity than PFOA, PFOS, or FOSA.

Perfluoroalkyl acids spontaneously concentrate at air-water and non-aqueous phase liquid (NAPL)-water interfaces, which can influence their retention during subsurface transport. This work presents measurements of air- and NAPL-water interfacial tension for synthetic groundwater containing perfluorooctanoic acid (PFOA), perfluorooctanesulfonic acid (PFOS), perfluorooctanesulfonamide (FOSA), or aqueous film-forming foam (AFFF) formulations at concentrations ranging from 0.1 to greater than 1000 mg/L. The NAPLs tested included dodecane, tetrachloroethylene, and jet fuel. AFFF formulations were less efficient at lowering interfacial tension than PFOA, FPOS, or FOSA substances below 100 mg/L, while above 100 mg/L, these formulations were more effective, achieving tensions of less than 3 mN/m. Infiltration of solutions with such low tension could lead to mobilization of residual NAPL. Equations based on interfacial tension measurements show that concentrations of PFOA, PFOS, and FOSA at the air-water interface were from 2 to 16 times greater than at the NAPL-water interface below 100 mg/L and were 10-50 times greater for AFFF below 20 mg/L. Calculations for unsaturated soil estimate that up to 87% of PFOS mass was at the air-water interface and less than 4% at the dodecane-water interface for bulk-water concentrations below 1 mg/L.

Design of up-flow aerated filters for the removal of iron from groundwater

Abstract Groundwater contains iron (Fe) that can be difficult to remove by singular physical–chemical methods. The aim of this presented study was to investigate the suitability of up-flow aerated filters as an upgrading step for the removal of total Fe from groundwater. Granular activated carbon (GAC) was applied as a pollutant carrier and compared with Bio-Pac media (BPM) by conducting a column test to treat synthetic groundwater (SGW). Initially two adsorption kinetic studies were done for GAC. The effect of influent Fe concentration, hydraulic retention time (HRT) and air supply to the system were investigated using a column experiment. The sorption result follows pseudo-second-order kinetics with an adsorption amount of 1.36 mg/g. The column experiment results show that around 99% and 70% Fe removal efficiency can be achieved for the best condition of 3 mg/L influent Fe concentration with seven hours HRT for GAC and BPM respectively. The air supply into the column did not show any improvement in Fe removal efficiency. The performance of GAC is found to be much better than that of BPM. All over, the new combined treatment method of aeration followed by filtration was demonstrated to be an effective technique for Fe removal from groundwater and also satisfied the World Health Organization (WHO) drinking water standard for Fe concentration.

Changes in Geochemical Composition of Groundwater Due to CO2 Leakage in Various Geological Media

This study evaluated the effects of CO2 leakage on the geochemical composition of groundwater in various geological media through long-term column experiments. Four columns were set up with soil representing a silicate aquifer; clean sand; a sand and limestone mixture; and alluvium soil, respectively. The experiments were conducted under the same experimental conditions for approximately one year. As the CO2-saturated synthetic groundwater was introduced into the columns, a decrease in pH and increases in electrical conductivity (EC), alkalinity, and concentrations of cations and trace elements were observed in all geological media. However, different patterns of changes were also observed depending on the mineralogical and physico-chemical characteristics of each material. As the column operation continued, while the pH decreased and low alkalinity values were more evident in the silicate soil and clean sand columns, the carbonate column continued to show high alkalinity and EC values in addition to high concentrations of most cations. The alluvium soil showed distinctive cation-exchange behaviors during the initial introduction of CO2. The results indicate that changes in the geochemical composition of groundwater will depend on the characteristic of the geological medium such as pH buffering capacity and cation exchange capacity. This study can be useful for monitoring and managing the impacts of CO2 leakage in various aquifer environments.

Three-dimensional hydraulic tomography analysis of long-term municipal wellfield operations: Validation with synthetic flow and solute transport data

This study proposes the utilization of municipal well records as an alternative dataset for large-scale heterogeneity characterization of hydraulic conductivity (K) and specific storage (Ss) using hydraulic tomography (HT). To investigate the performance of HT and the feasibility of utilizing municipal well records, a three-dimensional aquifer/aquitard system is constructed and synthetic groundwater flow and solute transport experiments are conducted to generate data for inverse modeling and validation of results. In particular, we simultaneously calibrate four groundwater models with varying parameterization complexity using five datasets consisting of different time durations and periods. Calibration and validation results are qualitatively and quantitatively assessed to evaluate the performance of investigated models. The estimated K and Ss tomograms from different model cases are also validated through the simulation of independently conducted pumping tests and conservative solute transport. Our study reveals that: 1) the HT analysis of municipal well records is feasible and yields reliable heterogeneous K and Ss distributions where drawdown records are available; 2) accurate geological information is of critical importance when data density is low and should be incorporated for geostatistical inversions; 3) the estimated K and Ss tomograms from the geostatistical model with geological information are capable in providing robust predictions of both groundwater flow and solute transport. Overall, this synthetic study provides a general framework for large-scale heterogeneity characterization using HT through the interpretation of municipal well records, and provides guidance for applying this concept to field problems.

Stress-related ecophysiology of members of the genus Rhodanobacter isolated from a mixed waste contaminated subsurface

This work examines the physiologic basis of stress tolerance in bacterial strains of the genus Rhodanobacter that dominate in the acidic and highly metal contaminated near-source subsurface zone of the Oak Ridge Integrated Field Research Challenge (ORIFRC) site. Tolerance of R. denitrificans to levels of different stresses were studied in synthetic groundwater medium and R2A broth. Two strains of R. denitrificans, strains 2APBS1T and 116–2, tolerate low to circumneutral pH (4-8), high Uranium (1 mmol/L), elevated levels of nitrate (400 mmol/L) and high NaCl (2.5%). A combination of physiologic traits, such as growth at low pH, increased growth in the presence of high organics concentration, and tolerance of high concentrations of nitrate, NaCl and heavy metals is likely responsible for dominance of Rhodanobacter at the ORIFRC site. Furthermore, extended incubation times and use of low carbon media, better approximating site groundwater conditions, are critical for accurate determination of stress responses. This study expands knowledge of the ecophysiology of bacteria from the genus Rhodanobacter and identifies methodological approaches necessary for acquiring accurate tolerance data.

Groundwater pollution containing ammonium, iron and manganese in a riverbank filtration system: Effects of dynamic geochemical conditions and microbial responses.

Bench-scale experiments were conducted to investigate the effect of hydraulic loadings and influent concentration on the migration and biotransformation behavior of three groundwater pollutants: ammonium (NH4 +), iron (Fe2+) and manganese (Mn2+). Columns packed with aquifer media collected from a river bank filtration (RBF) site in Harbin City, NE China were introduced synthetic groundwater (SGW) or real groundwater (RGW) were at two different constant flow rates and initial contaminant concentrations to determine the impact of system conditions on the fate of the target pollutants biotransformation. The results showed that the biotransformation rate of Fe2+ Mn2+, and NH4 + decreased by 8%, 39% and 15% under high flow rate (50 L d-1) compared to low flow rate (25 L d-1), which was consistent with the residence-time effect. While the biotransformation rate of Fe2+ Mn2+, and NH4 + decreased by 7%, 14% and 9% under high influent concentration compared to original groundwater. The 16S rRNA analysis of the aquifer media at different depths after experiments completion demonstrated that the relative abundance of major functional microbes iron oxidizing bacteria (IOB) and manganese oxidizing bacteria (MnOB) under higher flow rate and higher influent concentration decreased 13%, 14% and 25%, 24%, respectively, whereas the ammonium oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) exhibited minimal change, compared to the lower flow rate. Above all results indicated that both high flow rate and high concentration inhibit the biotransformation of NH4 +, Fe2+ and Mn2+. The biotransformation of Fe2+ and Mn2+ occurs primarily in the 0-40 cm and 20-60 cm depth intervals, respectively, whereas the NH4 + biotransformation appears to occur relatively uniformly throughout the whole 110cm column. The biotransformation kinetics of NH4 + in RGW and SGW, Mn2+ in RGW at different depths accords with the first order kinetics model, while Fe2+ in RGW and SGW, Mn2+ in SGW presented more complicated biotransformation process. The results should improve understanding of the transport and fate of common groundwater pollutants in riverbank filtration and other groundwater recharge environments.

Immobilized algae-based treatment of herbicide-contaminated groundwater.

Scenedesmus species, immobilized on alginate gel, was found effective in removing nitrate, atrazine, magnesium, phosphorus, zinc, oxadiazon, and triallate from groundwater in a continuous flow reactor. The laboratory-scale experiments with synthetic groundwater, made of 8.8mg/L NO3 -N and 90µg/L atrazine, were performed at a hydraulic retention time of 7days and the temperatures of 20 and 35°C. The highest uptake of nitrate and atrazine was observed at 20°C (97% and 70%, respectively). When tested in actual groundwater, 92% of nitrate, 100% of magnesium, 99.9% of phosphorus, and 92% of zinc were successfully removed at the end of 29days' treatment operations. The algal beads removed 100% of oxadiazon and triallate in the first 10days, but some of the herbicides diffused back into the solution toward the end of the treatment process. PRACTITIONER POINTS: Immobilized algae-alginate beads can remove nitrate, atrazine, oxadiazon, and triallate from groundwater in continuous flow reactor. The uptake rate of nitrate and atrazine is higher in room temperature (20°C). Same algae beads could be reused for herbicide uptake for the average of 10days. The immobilized system is a natural sustainable alternative that can be used in groundwater pump and treat.

Chromate fate and effect in bioelectrochemical systems for remediation of chlorinated solvents

A continuous-flow bioelectrochemical reactor was developed in a previous study to address the bioremediation of groundwater contaminated by trichloroethene (TCE). The present report investigated the applicability of the same system in the presence of Cr(VI) and its possible inhibitory effect on dehalorespiring bacterial populations. Preliminary batch tests were performed at the optimal cathodic reducing potential for the reductive dechlorination (RD) of TCE (-0.65 V vs. the standard hydrogen electrode) with two different dechlorinating microorganism consortia. The results demonstrated that Cr(VI) removal efficacy was increased by microorganisms that had been previously acclimatised to Cr(VI). Specifically, Cr(VI) was completely reduced only in the presence of acclimated microorganisms. The presence of chromate negatively affected RD performance, by either (i) limiting the TCE transformation to cis-dichloroethene at lower concentrations, or (ii) completely inhibiting RD at higher concentrations. In contrast, after the acclimation period, RD was extended down to vinyl chloride, which is the main TCE daughter product. Finally, the continuous flow reactor was fed by synthetic groundwater contaminated with TCE (50 μM) and Cr(VI) (45 μM), and the experimental results showed that Cr(VI) was completely reduced under RD conditions. Moreover, TCE removal was complete, with vinyl chloride and ethene as the main intermediates, thus indicating that chromate inhibition was decreased by Cr(VI) removal.

New insight into CO2-mediated denitrification process in H2-based membrane biofilm reactor: An experimental and modeling study

The H2-based membrane biofilm reactor (H2−MBfR) is an emerging technology for removal of nitrate (NO3−) in water supplies. In this research, a lab-scale H2−MBfR equipped with a separated CO2 providing system and a microsensor measuring unit was developed for NO3− removal from synthetic groundwater. Experimental results show that efficient NO3− reduction with a flux of 1.46 g/(m2⋅d) was achieved at the optimal operating conditions of hydraulic retention time (HRT) 80 min, influent NO3− concentration 20 mg N/L, H2 pressure 5 psig and CO2 addition 50 mg/L. Given the complex counter-diffusion of substrates in the H2−MBfR, mathematical modeling is a key tool to both understand its behavior and optimize its performance. A sophisticated model was successfully established, calibrated and validated via comparing the measured and simulated system performance and/or substrate gradients within biofilm. Model results indicate that i) even under the optimal operating conditions, denitrifying bacteria (DNB) in the interior and exterior of biofilm suffered low growth rate, attributed to CO2 and H2 limitation, respectively; ii) appropriate operating parameters are essential to maintaining high activity of DNB in the biofilm; iii) CO2 concentration was the decisive factor which matters its dominant role in mediating hydrogenotrophic denitrification process; iv) the predicted optimum biofilm thickness was 650 µm that can maximize the denitrification flux and prevent loss of H2.

Conditioning Multi-Gaussian Groundwater Flow Parameters to Transient Hydraulic Head and Flowrate Data With Iterative Ensemble Smoothers: A Synthetic Case Study

Over the last decade, data assimilation methods based on the ensemble Kalman filter (EnKF) have been particularly explored in various geoscience fields to solve inverse problems. Although this type of ensemble methods can handle high-dimensional systems, they assume that the errors coming from whether the observations or the numerical model are multivariate Gaussian. To handle existing nonlinearities between the observations and the variables to estimate, iterative methods have been proposed. In this paper, we investigate the feasibility of using the ensemble smoother and two iterative variants for the calibration of a synthetic 2D groundwater model inspired by a real nuclear storage problem in France. Using the same set of sparse and transient flow data, we compare the results of each method when employing them to condition an ensemble of multi-Gaussian groundwater flow parameter fields. In particular, we explore the benefit of transforming the state observations to improve the parameter identification performed by one of the two tested algorithms. Despite the favorable case of a multi-Gaussian parameter distribution considered, we show the importance of defining an ensemble size of at least 200 to obtain sufficiently accurate parameter and uncertainty estimates for the groundwater flow inverse problem considered.

Characterization of basin-scale aquifer heterogeneity using transient hydraulic tomography with aquifer responses induced by groundwater exploitation reduction

This study exploits aquifer responses to the reduction of pumping rates at different locations in a synthetic groundwater basin as basin-scale hydraulic tomography (HT) surveys to estimate transmissivity (T) and storage coefficient (S) fields. This experiment mimics the situation of groundwater exploitation reduction in a pilot area of groundwater-overexploitation control in the North China Plain. The results of the study show that taking advantage of the groundwater exploitation reduction as HT surveys is a viable approach for basin-scale parameter estimations. Results also suggest that HT analysis should use accurate mean values of T and S for geological zones as initial guesses for the inversion of parameters. Further, we show that the T and S fields estimated from HT yield accurate predictions of the groundwater flow velocities and breakthrough curves (BTCs). However, the BTCs based on kriged and zonal mean fields are inaccurate. The predicted BTCs using homogeneous fields fail to capture the true trend of solute concentration over time. We advocate that utilizing aquifer responses induced by groundwater exploitation reduction could be a new paradigm for basin-scale aquifer characterization.

Indicator-based data assimilation with multiple-point statistics for updating an ensemble of models with non-Gaussian parameter distributions

Ground-water flow and the transport of contaminants in groundwater systems are strongly controlled by geologic heterogeneities. Because, the data available to model these subsurface heterogeneities are generally sparse, the observed groundwater flow, piezometric head at well locations, or the concentration profile of solutes provide valuable additional information about these complex subsurface systems. Regardless, there is likely to be considerable uncertainty associated with the predictions of the subsurface heterogeneities. This has motivated the development of several ensemble-based schemes for assimilating flow response data into predictions of subsurface heterogeneities. Most ensemble-based data assimilation methods including ensemble Kalman filter (EnKF) or indicator-based data assimilation (InDA), used for assimilation of dynamic data into geologic models, utilize statistics in the form of covariances calculated using the ensemble of models to perform model updates. These covariance based updates do not preserve the complex spatial characteristics of geologic structures that are better represented using multiple-point statistics. Additionally, in EnKF, the mismatch between the observed and the simulated values are assumed to be linearly related to the parameter updates, and the distribution of the state variable is assumed to be multi-Gaussian. The spatial distribution of the primary variables like facies can be non-Gaussian because of the spatial continuity exhibited by channel facies (sands) and non-channel facies (clay), that have distinctly different properties. Also, the relationship between the mismatch and the parameter updates can be strongly non-linear. In indicator-based data assimilation (InDA) method the indicator transforms of parameter and mismatch variables are used, which affords the treatment of these variables as bi-variate non-Gaussian. Furthermore, in the indicator transformed space, restrictive linear assumption can also be lifted as the indicator transform is invariant under non-linear transformations. However, the updates are still governed by the bivariate interactions between the state variables. A multiple-point extension of InDA is proposed in this paper which utilizes existing multiple-point simulation algorithms like single normal equation simulation (SNESIM) in combination with InDA, to preserve the spatial characteristics of the geologic model while at the same time honor the observed flow or transport response. The proposed method is applied to a synthetic groundwater system with complex channel distributions. The channel features of the final updated ensemble of models is shown to converge towards the reference model and the ensemble flow responses are also shown to match the reference flow response.

A Comparison of Extremal Optimization, Differential Evolution and Particle Swarm Optimization Methods for Well Placement Design in Groundwater Management

When designing a well field for efficiently extracting groundwater or petroleum, it is common for designers to rely on computational optimization methods to determine the optimal placement of wells. The goal of these methods is to find a well-field solution that maximizes the value of a defined objective function, and to do so while utilizing the least amount of computational effort. To achieve this, researchers have developed algorithms based on a wide range of heuristics. Within groundwater management, popular methods include particle swarm optimization (PSO) and genetic algorithms such as differential evolution (DE). This study seeks to investigate a recently developed method called Extremal Optimization for Well Placement Problems (EO-WPP), and to compare its performance with established methods like PSO and DE. EO-WPP is an optimization method based on the extremal optimization (EO) algorithm. EO optimizes by iteratively identifying and modifying the least effective components of a solution. By following this heuristic, the EO algorithm has the potential to quickly find optimal solutions while requiring minimal computational effort. To test this, the performance of DE, PSO and EO-WPP was compared on four benchmark problems. Two of these are the Rastrigin and the Rosenbrock benchmark functions. These functions were used because of their quick evaluation and their popularity in optimization literature. The third benchmark is a synthetic groundwater model, built to test the methods under the context of groundwater management. The final benchmark is a field problem using the Aberdeen groundwater model in South Dakota. The results reveal that EO-WPP was able to outperform DE and PSO on all tested benchmarks. EO-WPP is an effective and efficient optimization tool for well placement design in groundwater management.

Comparison of the colloidal stability, mobility, and performance of nanoscale zerovalent iron and sulfidated derivatives

Nanoscale zerovalent iron (nZVI) and sulfidated nanoscale zerovalent iron (S-nZVI) have been increasingly studied for heavy metal removal in the subsurface. However, a comprehensive comparison of the effectiveness of the technologies and the stability of derived metal-adsorbed composites is lacking. In this study, we evaluated the colloidal stability and transport of nZVI, S-nZVI and S-nZVI modified with nanosized silica (FeSSi). Furthermore, we monitored the metal immobilization performance of the three nanoparticles (NPs) under anoxic conditions in synthetic groundwater for 30 days. The NP-metal composites were thereafter discharged into a river water and metal remobilization was monitored for 20 days. Sulfidation improved the colloidal stability of nZVI in both simple media and in natural waters, although a lower initial agglomeration rate constant (ka) was observed in unmodified nZVI at acidic pH. The transport of nZVI in saturated soil column was enhanced with sulfidation due to decreased electrostatic attraction between the NPs and sand. The three NPs sequestered more than 80 % of Cu2+, Zn2+, Cd2+ and Cr2O72− from groundwater. Among the three NPs tested, S-nZVI had a slightly higher removal capacity for metals than nZVI in synthetic groundwater and the chemical stability of metal-S-nZVI composites upon discharge into river water was the highest.

Sulfur-based autotrophic biosystem for efficient vanadium (V) and chromium (VI) reductions in groundwater

Vanadium and chromium co-exist commonly with elevated levels in groundwater at vanadium smelting sites. While bioremediation has been recognized promising for this co-contamination treatment in aquifer, interactions during vanadium (V) [V(V)] and chromium (VI) [Cr(VI)] bio-reductions under autotrophic condition remain largely unknown. In this study, efficient reductions of V(V) and Cr(VI) from synthetic groundwater were realized simultaneously in a continuous flow autotrophic sulfur-based biosystem, with more than 85% overall removals under hydrochemical and hydrodynamic fluctuations during 276-d operation. Soluble Cr(VI) was reduced to insoluble Cr(III) preferentially, while reduction of soluble V(V) to insoluble V(IV) was easily inhibited. Elemental sulfur [S(0)] was bio-oxidized to sulfate. Analyses of carbon isotope, microbial community and metabolic pathway revealed the synergetic mechanisms. Autotrophs (e.g., Sulfuricurvum) utilized energy released from S(0) oxidation to synthesize volatile fatty acids (VFAs), which were consumed by heterotrophic V(V) and/or Cr(VI) reducers (e.g., Geobacter). Functional genes responsible for S(0) oxidation and reduction of V(V) and Cr(VI) were detected. V(V) and Cr(VI) reductions were catalyzed by both cytochrome c and nicotinamide adenine dinucleotide. VFAs were also transformed to glycogen in cells to store energy. Robust remediation strategy is thereby proposed for aquifer co-contaminated by V(V) and Cr(VI).

Hydrothermal Interaction of Wyoming Bentonite and Opalinus Clay

AbstractMost investigations into clay-mineral stability and new mineral formation within engineered barrier system (EBS) materials for geologic repositories of nuclear waste have focused on temperatures <100°C. In response to the United States Department of Energy’s interest in disposing of waste packages with higher thermal loads, higher temperature (200–300°C) and pressure (~150 bar), long-term (6-week to 6-month), hydrothermal experiments were conducted to evaluate the interaction of Opalinus Clay (wall rock) and Wyoming bentonite (clay buffer) with synthetic Opalinus Clay groundwater. Experiments were conducted in autoclaves using a flexible gold reaction cell with water:rock ratios between 6:1 and 9:1. Run products were characterized in terms of mineralogy and geochemistry. Montmorillonite remained stable at 200 and 300°C; traces of illite-smectite interstratified minerals were observed. Clay minerals in Opalinus Clay experienced significant changes at 300°C, including the formation of illite, illite-smectite, and chlorite-smectite. Montmorillonite illitization within the Wyoming bentonite EBS material was likely limited by the bulk chemistry of the system (i.e. low potassium) and newly formed illite was likely limited to the Opalinus Clay fragments, nucleating on pre-existing illite in the clay rock. Zeolite minerals with compositions between analcime and wairakite formed at 300°C along edges of Opalinus Clay fragments and within the bentonite matrix, but not at 200°C. Aqueous fluids remained undersaturated with respect to quartz in Opalinus Clay ± Wyoming bentonite 300°C experiments, and dissolution and re-precipitation of phases such as kaolinite, calcite, and smectite likely contributed to zeolite formation. These results can be applied to understanding zeolite formation, clay-mineral phase stability, and silica saturation within EBS materials of a high-temperature repository.

Synthesis of MgO micro-rods coated with charred dextrose and its application for the adsorption of selected heavy metals from synthetic and real groundwater.

MgO micro-rods supported on porous carbon were synthesized by an economical method and applied for the adsorption of three different heavy metals ions (As (III), Cd (II) and Pb (II)). Here, we used dextrose as the source of carbon during the synthesis. The synthesized material has been characterized by different techniques like XRD, TEM, FE-SEM, BET and FT-IR for the determination of various physical properties. Compared with MgO synthesized without dextrose, the carbon-supported MgO or C-MgO demonstrated consistent rod-shaped morphology, higher surface area and better absorptivity. The adsorption data were analysed using various isotherm models and the Freundlich isotherm model seemed to provide the best fit to the data. The adsorption kinetics data on the other hand was well explicated by the pseudo second-order kinetic model. The maximum adsorption capacity of C-MgO was 508.47mgg-1 for As (III), 566.01mgg-1 for Cd (II) and 476.19mgg-1 for Pb (II), respectively after 6h of reaction. To check the real-life usability and efficiency of C-MgO, it was added to a groundwater sample which had 169.55ppb of As (III) and within 20min it was adsorbed with 99% efficiency. Reusability studies reveal that C-MgO could be used up to 6 times with more than 60% efficiency. This study shows that C-MgO has high adsorptive ability, is an economic and non-toxic material with versatile applications and can be used for groundwater remediation in real life.

Portable and rapid arsenic speciation in synthetic and natural waters by an As(V)-selective chemisorbent, validated against anodic stripping voltammetry

Inorganic arsenic speciation, i.e. the differentiation between arsenite and arsenate, is an important step for any program aiming to address the global issue of arsenic contaminated groundwater, whether for monitoring purposes or the development of new water treatment regimes. Reliable speciation by easy-to-use, portable and cost-effective analytical techniques is still challenging for both synthetic and natural waters. Here we demonstrate the first application of an As(V)-selective chemisorbent material for simple and portable speciation of arsenic using handheld syringes, enabling high sample throughput with minimal set-up costs. We first show that ImpAs efficiently removes As(V) from a variety of synthetic groundwaters with a single treatment, whilst As(III) is not retained. We then exemplify the potential of ImpAs for simple and fast speciation by determining rate constants for the photooxidation of As(III) in the presence of a TiO2 photocatalyst. Finally, we successfully speciate natural waters spiked with a mix of As(III) and As(V) in both Indian and UK groundwaters with less than 5 mg L−1 dissolved iron. Experimental results using ImpAs agreed with anodic stripping voltammetry (ASV), a benchmark portable technique, with analysis conditions optimised here for the groundwaters of South Asia. This new analytical tool is simple, portable and fast, and should find applications within the overall multi-disciplinary remediation effort that is taking place to tackle this worldwide arsenic problem.