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Fuel components such as benzene, toluene, and methyl tertiary-butyl ether (MTBE) are frequently detected pollutants in groundwater resources. Ex-situ remediation technologies by activated carbon have been used for treatment for many years. However, due to high cost of these technology, more attention has been given to the in-situ remediation methods of contaminated groundwaters using liquid carbon adsorbents. Literature search showed limited studies on using adsorbents in liquid form for the removal of such contaminants. Therefore, this lab-scale study investigates the capacity of using raw biochar-based liquid activated carbon and iron-modified biochar-based liquid activated carbon to remove these pollutants. The adsorption efficiency of the synthesized liquid activated carbon and iron-modified liquid activated carbon mixed with sand, limestone, and 1:1 mixture of sand/limestone, was tested using batch suspension experiments. Adsorption by granular activated carbon was also investigated for comparison with liquid activated carbon. Results of the study revealed that mixing of liquid activated carbon or LAC-Fe on subsurface materials had not improved the removal efficiency of MTBE. At the same time, it showed a slight improvement in the adsorption efficiency of benzene and toluene. In all cases, the removal by GAC was higher with around 80% and 90% for MTBE and BT, respectively. Results also showed that benzene and toluene were better removed by liquid activated carbon and iron-modified liquid activated carbon (∼ 40%) than MTBE (∼ 20%). It is also found that water chemistry (i.e., salinity and pH) had insignificant effects on the removal efficiency of pollutants under the study conditions. It can be concluded that more research is needed to improve the capacity of biochar-based liquid-activated carbon in removing MTBE, benzene and toluene compounds that will lead to improve the utilization of liquid activated carbon for the in-situ remediation of contaminated groundwaters. [ABSTRACT FROM AUTHOR]

Zero valent iron (ZVI) is widely used in permeable reactive barriers (PRBs) for the remediation of contaminated groundwater. The hydraulic conductivity of ZVI can be reduced due to iron corrosion processes activated by water and its constituents including pollutants. To overcome this issue, ZVI particles can be mixed with granular materials that avoid a drastic reduction in the hydraulic conductivity over time. In light of the most recent studies concerning iron corrosion processes and recalling the basic principles of century-old chemistry of iron corrosion, we have revised the results of 24 long-term column tests investigating the hydraulic and reactive behavior of granular mixtures composed of ZVI and pumice or lapillus. From this analysis, we found a clear correlation between the reactive behavior, described by the retardation factor (i.e., the ratio between flow velocity and propagation velocity of the contamination front), and the hydraulic behavior, described by means of the permeability ratio of the reactive medium (i.e., the ratio between the final and initial value of hydraulic conductivity). In particular, the permeability ratio decreased with the increase in the retardation factor. Moreover, it was found that the retardation factor is a useful parameter to evaluate the influence of flow rate, contaminant concentration, and ZVI content on the reactive behavior of the granular medium. [ABSTRACT FROM AUTHOR]

With the economic growth of the world, sustainable development is a popular issue in recent years. Sustainable assessment is an important part of sustainable development. There are many previous scholars have used multiple-criteria decision-making (MCDM) to develop different evaluation frameworks in different fields. Elimination et Choix Traduisant la Realite II (ELECTRE II) is one of the most commonly used methods for MCDM. ELECTRE II uses alternatives, criteria, and criteria weighting from decision-makers to calculate the concordance and discordance indices. These two indices are used to rank the alternatives. The concordance and discordance indices in ELECTRE II are important because they are the key to make accurate decisions. Previous scholars have failed to make comprehensive calculations for these indices, nor make their units of measure comparable, which negatively affected their results. This study improved the approach in calculating these indices and illustrated it using three case studies: (1) university examination results, (2) a sustainability assessment of groundwater remediation and (3) an assessment of power generation technologies. This improved ELECTRE II method offers decision-makers an objective basis for decision-making. [ABSTRACT FROM AUTHOR]

The use of zinc dioxide (ZnO2) powder as a source of H2O2 in a modified Fenton reaction catalyzed with Fe(II) to destroy trichloroethylene (TCE) was investigated. The experimental results showed that the optimum molar ratio of ZnO2/Fe(II)/TCE in ZnO2/Fe(II)/TCE system was 20/20/1 with a TCE removal of up to 99.6%. TCE degradation was significantly inhibited by the low reaction temperature and influenced by the initial solution pH, in which ZnO2/Fe(II)/TCE system was suited for high temperature and low pH settings. Both Cl− and HCO3− anions showed a detrimental effect on TCE elimination with HCO3− being more significant. The addition of a high concentration (100 mg/L) of HA in solution inhabited TCE degradation performance, while the effect was negligible at low concentrations (1–10 mg/L). The tests with hydroxyl radical (HO·) scavengers elucidated that TCE was mainly degraded by HO· radicals in ZnO2/Fe(II)/TCE system. TCE degradation and the dechlorination proceeded simultaneously, but the final release of Cl− was less than the degraded TCE, indicating the occurrence of chlorinated intermediates in the reaction process. [ABSTRACT FROM AUTHOR]

The objective of this investigation involved the green synthesis of Graphene Sand Hybrid (GSH) using the sustainable carbon source provided from the pyrolysis of low-quality dates; it was evaluated for use as a cost-effective reactive material in permeable reactive barrier (PRB) technology for remediating lead-Pb(II) and tetracycline-TC contaminated groundwater. The GSH was proven to be composed of graphene structures on the inorganic support material (sand). The experimental experiments of this study were done using batch and continuous mode. In the batch experiments, different factors were studied, and the sorption data were explained using the Langmuir and Freundlich isotherm models, whereas the sorption kinetic was ascertained through the use of the three kinetic models (pseudo-first, second-orders, and intraparticle diffusion). The results evidenced that the Langmuir and the pseudo-second-order models show a better fit for the experimental data, with a maximum adsorption capacity of 55.4 mg/g and 46.4 mg/g for Pb(II) and TC, respectively. The continuous mode was performed employing a series of column experiments. Besides, the COMSOL Multiphysics software was used to solve a numerical model that was advanced to simulate the equilibrium one-dimensional contaminant's conveyance. The results depicted that the GSH was an efficient material in PRB technology to remediate contaminated groundwater. [ABSTRACT FROM AUTHOR]

Zerovalent iron nanoparticles (nZVI) are becoming one of the most widely recommended nanomaterials for soil and groundwater remediation. However, when nZVI are injected in the groundwater flow, the behavior (mobility, dispersion, distribution) is practically unknown. This fact generally results in the use of enormous quantities of them at the field scale. The uncertainties are on the effective volumes reached from the plume of nZVI because their tendency to aggregate and their weight can cause their settling and deposition. So, the mobility of nanoparticles is a real issue, which can often lead to inefficient or expensive soil remediation. Furthermore, there is another aspect that must be considered: the fate of these nZVI in the groundwater and their possible impact on the subsoil environment. All these considerations have led us to propose an application of nZVI simulating the permeation technique through a laboratory experience, finalized to have a better, or even simpler description of their real behavior when injected in a flow in the subsoil. A two-dimensional laboratory-scale tank was used to study the dispersion and transport of nZVI. A nZVI solution, with a concentration equal to 4.54 g/L, was injected into glass beads, utilized as porous medium. The laboratory experiment included a digital camera to acquire the images. The images were then used for calibrating a numerical model. The results of the mass balance confirm the validity of the proposed numerical model, obtaining values of velocity (5.41 × 10−3 m/s) and mass (1.9 g) of the nZVI of the same order of those from the experimental tests. Several information were inferred from both experimental and numerical tests. Both demonstrate that nZVI plume does not behave as a solute dissolved in water, but as a mass showing its own mobility ruled mainly from the buoyancy force. A simple simulation of a tracer input and a nZVI plume are compared to evidence the large differences between their evolution in time and space. This means that commercial numerical models, if not corrected, cannot furnish a real forecast of the volume of influence of the injected nZVI. Further deductions can be found from the images and confirmed by means the numerical model where the detachment effect is much smaller than the attachment one (ratio kd/ka = 0.001). From what is reported, it is worthwhile to pay attention on the localization of the contaminants source/plume to reach an effective treatment and it is important to go further in the improvement of solution for the limiting the nanoparticles aggregation phenomenon. [ABSTRACT FROM AUTHOR]

Determining the most suitable groundwater contamination remediation among multiple discrete alternatives is usually difficult for decision makers and of great significance to ensure the green development of ecological environment. This study proposed a novel multi-attribute preference model (MAPM) method by combining the trapezoidal fuzzy information, analytic hierarchy process (AHP) and entropy method for prioritizing the groundwater contamination remediation among a number of alternatives. This method has the advantages of (1) screening the most desirable remediation without introducing time-consuming nonlinear multi-objective optimization algorithms; (2) addressing uncertain attributes expressed as trapezoidal fuzzy information; (3) assessing priority orders of alternative remediation actions under uncertainty; and (4) being less affected by data inexactness and guaranteeing better environmental performance than MAPM. The method is applied to remediation design of practical naphthalene-contaminated aquifer located in Anhui. A total of 50 alternative remediation strategies with an attributes system which consists of ten attribute in three aspects has been proposed. Results indicate that the developed model is feasible and the priorities of groundwater cleanup systems are greatly different for four remediation schemes. The proposed method can be applied into other study area by modifying the relevant attributes appropriately in order to obtain customized remediation strategies. [ABSTRACT FROM AUTHOR]

It is a major problem to remediate the uranium contaminated groundwater at an acid in-situ leaching uranium mine. In this paper, phytic acid was hydrolyzed by the hydrothermal reaction to obtain phytic acid hydrolyzate, and the simulated uranium contaminated groundwater was prepared according to the physicochemical characteristics of uranium-contaminated groundwater at an acid in-situ leaching uranium mine. The effect of the amount of added phytic acid hydrolyzate and its pH value on the removal performance of U( VI) from the uranium contaminated groundwater was explored, and the concentrations of phosphate anion, calcium ion, total iron ion, manganese ion, zinc ion, and magnesium ion were monitored, and the mechanism for the remediation of uranium contaminated groundwater was analyzed by SEM, TEM, XPS and XRD. The results show that when the amount of the addied phytic acid hydrolyzate was 2 mL, the concentration of phosphate was 24.562 g/L, the initial pH value was 6, the amount of simulated uranium contaminated groundwater was 100 mL, its initial pH value was 3, its uranium concentration was 5 mg/L, and the reaction time was 12 h, the removal rate of uranium reached more than 99%, and the pH value was raised to 5.9. The current research verified that it is feasible to use phytic acid hydrolyzate to remediate the uranium contaminated groundwater at add in-situ leading uranium mine. Since phytic add is cheap and easy to obtain, it can be used as an economical phosphorus source to replace expensive phosphate compounds for the remediation of uranium-contaminated groundwater at the mine. [ABSTRACT FROM AUTHOR]

Zerovalent iron nanoparticle (nZVI) technology has been found to be promising and effective for soil and groundwater remediation. This paper shows the results of two batch tests (Test A and Test B) carried out to assess the capacity of nZVI to remediate arsenic (As)-contaminated water. Test A, performed with batches of tap water contaminated by arsenic, with a concentration equal to 10 mg ∗ L−1, showed a significant reduction of the As concentrations in solution, with a maximum removal rate up to 98% (Batch 3). Test A lasted 26 h. At the same time, Test B was performed with a sample of arsenic-contaminated sediment, with a concentration equal to 100 mg ∗ Kg−1 (ca). Test B lasted 72 h. Test B also confirmed an excellent reduction of the As concentrations in solution, up to a maximum removal rate of 99% (Batch 3). These results show the effectiveness of nZVI for the remediation of water contaminated by arsenic. However, as the As–nZVI interaction time increased, there was a decrease in the available sites for arsenic immobilization, and so the As concentrations in solution became constant. In fact, as the dose of nZVI (mnZVI) used in the batches increased, the mass concentration of residue As in the solution at the equilibrium decreased (cAse) and therefore the concentration of As absorbed (cAs0–cAse) on the nZVI increased due to the immobilization action of the nanoparticles. The results show concentrations of As absorbed (cAs0–cAse) on the nZVI with a range between 5.10 mg ∗ L−1 (mnZVI = 0.05 g) and 9.54 mg ∗ L−1 (mnZVI = 0.5 g) for Test A, and with a range between 0.029 mg ∗ L−1 (mnZVI = 0.05 g) and 0.058 mg ∗ L−1 (mnZVI = 0.7 g) for Test B. Therefore, these results underline the need to monitor As concentrations during applications in the field, in order to verify the demand for injecting new active nanoparticles for arsenic removal. [ABSTRACT FROM AUTHOR]

The novel iron-based reductive particles, functionalized with amino and carboxylic functional groups, were synthesized to remove Cr(VI) and Cd(II) ions from aqueous solutions. The morphological structure and surface functional groups of new composites were characterized with SEM, XRD, FTIR, BET, and other techniques. The influence of pH, initial concentration, adsorbent dosing, and temperature on removal efficiencies were explored by batch experiments. The adsorption capacity of Cr(VI) and Cd(II) increased by 159.95% and 76.60%, respectively, compared with Fe0, reaching 47.638 and 62.047 mg/g. EDS and XPS analysis showed most of Cr(VI) was reduced to Cr(III) and precipitated as ferrochrome oxide, and Cd(II) was mainly precipitated as hydroxide. Reduction-precipitation and complexation may predominate in the removal process of Cr(VI), which fitted well with Langmuir and Freundlich models and pseudo-second-order kinetics. While hydrolysis and complexation may prevail for Cd(II), which was suited with Langmuir model and pseudo-second-order kinetics. Having good magnetic properties, the A/C-Fe@SiO2 particles exhibited excellent reusable stability after four times regeneration experiments, promising a prospect for in-situ remediations of groundwater contaminated by Cr(VI) and Cd(II). [ABSTRACT FROM AUTHOR]

Inorganic pollution is widespread in groundwater, and sulfate pollution is one of the important types, which has an important impact on the ecological environment and human health. Elevated concentrations of sulfate ion pollutants often come from the sewage discharge of chemical plants. This study takes a sulfate-contaminated site in Dongying City, Shandong Province, China, as the research object. Nine boreholes were arranged along the sewage discharge ditches in the site to collect and analyze soil samples and groundwater samples in layers. The concentration of pollutants and the change with depths were determined; the maximum concentration of sulfate ion was 10,330 mg L−1 in groundwater, and the maximum pollution depth was no more than 8 m. A hydraulic barrier was carried out to cut off the pollution sources. Based on a comprehensive understanding of the hydrogeological conditions and pollution degree of the site, the hydraulic capture technique was used to control the water pumping and injection volume, so that the scope of the pollution plume was gradually reduced. The pumping wells were arranged in the polluted area, and the water injection wells were arranged at the outer edge of the pollution zone. According to the calculation of the single well water inflow and influence radius, 28 pumping wells and 66 water injection wells were needed to be arranged on the site. The treatment process was divided into four stages according to the following steps: water pumping, water injection, stoppage of water injection, stoppage of water pumping, collecting water samples after the water level recovered, and the completion stage of treatment. The above process was repeated twice. Chemical precipitation was employed in the last step. The results of the remediation showed that the sulfate concentrations in 54 percent of the samples decreased significantly to less than 100 mg L−1, and the rest were between 100 and 200 mg L−1 after the treatment process. Two pumping wells with serious pollution were selected as long-term monitoring wells, and two-year continuous monitoring results showed that sulfate concentrations in the monitoring wells ranged from 110 to 220 mg L−1, indicating that integrated groundwater remediation techniques are more effective and more reliable than one single technique. [ABSTRACT FROM AUTHOR]

BACKGROUND: A novel, original and green technology for the remediation of lead‐contaminated soil is proposed. The treatment strategy integrates two well‐known technologies: electrokinetic (EK) remediation and permeable reactive barriers (PRBs). The novelty of the present work is based on the use of cork granules, as reactive media, in the PRBs for interrupting Pb reaching groundwater. The cork barrier (treatment zone) was emplaced near the anodic compartment to favor the retention and sorption of Pb due to the migration/diffusion effects promoted from soil to the anode during EK remediation. For this purpose, NaNO3 (0.1 mol L−1) and citric acid (0.1 mol L−1) were tested as supporting electrolytes in the cathodic reservoir, while in the anodic compartment a solution of 0.1 mol L−1 NaNO3 was used. Additionally, the influence of direct current and reverse polarity approaches on EK efficiency was evaluated. RESULTS: Results clearly indicated that the novel cork‐based PRBs concept was efficient when coupled with EK. Nevertheless, pH conditions played a significant role in Pb sorption by cork granules as well as in the physical–chemical properties of cork under an electrical field. The transportation of Pb by EK, towards the PRB with cork granules, was favored through the use of citric acid in the catholyte and reverse polarity strategy. CONCLUSIONS: These approaches promote a better pH control in the soil and electrode wells, being able to reach near 80% Pb removal from soil, after 14 days of experiment. Therefore, this technology can be used for in situ remediation of Pb‐contaminated groundwater. © 2022 Society of Chemical Industry (SCI). [ABSTRACT FROM AUTHOR]

When using the simulation–optimization model to optimize groundwater extraction-treatment schemes, constructing a surrogate model for the numerical simulation model is an effective tool for overcoming the large computational load. However, the construction of a one-shot static-surrogate model has disadvantages, such as a large sample size, low accuracy, and the problem of losing the optimal solution. A construction strategy for a batch locally optimal solution-based adaptive dynamic kriging surrogate model is proposed here and applied to the optimal remediation of contaminated groundwater. First, the preliminary kriging surrogate model is established by the kriging method. Second, the adaptive dynamic kriging surrogate model is updated based on the batch locally optimal solutions method. Finally, when the accuracy of the adaptive dynamic kriging surrogate model reaches the convergence criterion, the update stops to obtain the convergent adaptive kriging surrogate model and the optimal remediation scheme. The results show that the optimal pumping wells based on the convergent adaptive kriging surrogate model are well 5, well 6, and well 9, with a remediation cost of ¥ 44,336.16. All pollutant concentrations meet the limit (6 mg/L). This remediation scheme has better effects and less costs than that based on the preliminary kriging surrogate model. Therefore, the batch locally optimal solution-based convergent adaptive kriging surrogate model can effectively avoid the risk of losing the optimal solution, which is of great importance for improving the computational efficiency and accuracy of solving the simulation–optimization model. [ABSTRACT FROM AUTHOR]

For efficient and environmentally friendly removal of nitrate from groundwater, biochar-based nanoscale zerovalent iron composites were prepared, where biochar was derived from pine sawdust at 4 different pyrolysis temperatures. The results show that biochar with different pyrolysis temperatures played a great role in both nitrate removal efficiency and nitrate conversion rate to nitrogen gas for the prepared composites. Specifically, the composite with biochar pyrolyzed at 500 °C, ZB12-500, showed the best performance in both nitrate removal and conversion to nitrogen gas. With an initial solution pH from 5 to 10, ZB12-500 maintained high removal efficiencies varying from 97.29% to 89.04%. Moreover, the conversion of nitrate to nitrogen gas increased with the initial nitrate concentration, and it reached 31.66% with an initial nitrate concentration of 100 mg/L. Kinetics analysis showed that the nitrate removal process fit well with a two-compartment first-order kinetic model. Meanwhile, the test of nitrate removal by ZB12-500 in synthetic groundwater showed that HCO3− and SO42− limited nitrate removal but improved nitrate conversion to nitrogen gas. Furthermore, the nitrate removal mechanism suggested that biochar could facilitate electron transfer from zero valent iron to nitrate, which led to high nitrate removal efficiency. In addition, the interaction of ferrous ions and the quinone group of biochar could increase the nitrate conversion to nitrogen gas. Therefore, this study suggests that ZB12-500 is a promising alternative for the remediation of nitrate-contaminated groundwater. [ABSTRACT FROM AUTHOR]

At present, groundwater nitrate pollution in China is serious. The use of microorganisms for biological denitrification has been widely applied, and it is a universal and efficient in situ groundwater remediation technique, but this approach is influenced by many factors. In this study, glucose was adopted as the carbon source, four different concentrations of 0, 2, 5 and 10 g/L were considered, and natural groundwater with a nitrate concentration of 300.8 mg/L was employed as the experimental solution. The effect of the carbon source concentration on the nitrate removal rate in groundwater was examined through heterotrophic anaerobic denitrification experiments. The results showed that the nitrate removal rate could be improved by the addition of an external carbon source in the process of biological denitrification, and an optimal concentration was observed. At a glucose concentration of 2 g/L, the denitrification effect was the best. [ABSTRACT FROM AUTHOR]

Groundwater is contaminated with chlorinated volatile organic compounds (CVOCs) including trichloroethene (TCE), tetrachloroethene (PCE), and their degradation products at a 230-acre formerly used defense site in Pennsylvania. Unconsolidated overburden materials ranging in thicknesses from 15 to 60 feet overlie two types of bedrock: quartzitic sandstone and phyllite on the eastern sloping hills and limestone and dolomite on the western flat-lying terrane. Karst is well developed in the carbonate rocks and is characterized by a pinnacle-and-cutter bedrock surface, solution-enlarged fractures/conduits at depths up to 450 feet below ground surface (bgs), caverns in tens of feet, and frequent occurrence of sinkholes. The PCE and TCE concentrations in groundwater samples suggest that dense non-aqueous phase liquid penetration extended to depths on the order of 400–450 feet bgs in the carbonate bedrock. A dye trace study was conducted to help refine the conceptual site model. The study consisted of five fluorescent dyes that were injected in five wells that encountered karst conduits/caverns at various depths from 32 to 216 feet bgs. The dyes were monitored at 40 monitoring wells and 16 points along a stream to the west of the site. The dye tracing results established positive dye detections at seven monitoring points in the stream. Field observations, infrared thermography imaging, and water quality survey confirmed that three of them, i.e., Spring-15, Spring-17, and Spring-26, are groundwater discharge points in the stream, i.e., submerged springs. Discovery of the submerged springs significantly contributed to the refinement of the conceptual site model and provided an opportunity to effectively remediate and manage the contaminated groundwater. These springs confirmed the exposure pathways that connect the site-impacted groundwater to surface water receptors, and the final remedy included measures to address potentially unacceptable risks to human beings and the environment in the stream and ensure that the state-regulated ambient water quality criteria are met for the site CVOCs at established compliance monitoring stations. These springs also helped optimize an existing pump and treat system that has been active since 1994. Shutdown and restart-up tests were conducted to evaluate the effectiveness of different extraction scenarios in the removal of the CVOCs at the springs under wet and dry seasons. The results led to a new configuration of the extraction wells by including a previously inactive extraction well CW-20. [ABSTRACT FROM AUTHOR]

Many practical applications, such as enhanced oil recovery or groundwater remediation, encounter the flow of viscoelastic fluids in porous media. Once the flow rate exceeds a critical value in such flows, an elastic instability with a fluctuating flow field is observed, which ultimately transits to a more chaotic and turbulence-like flow structure as the flow rate further increases. In this study, we present an extensive numerical investigation of the viscoelastic fluid flows in a model porous media consisting of a microchannel with many micropillars placed in it by considering both their initial staggered and aligned configurations. Within the present range of conditions encompassed in this study, we find that the geometric disorder always increases the chaotic fluctuations irrespective of the initial arrangement of micropillars. We propose that it is due to the formation of preferential paths or lanes and the formation of highly curved streamlines, which results in the local stretching of polymer molecules and, hence, significant origin in the local elastic stresses. We further show that this chaotic flow behavior strongly depends on the competitive influence between the strain-hardening and shear-thinning behaviors of a viscoelastic fluid, which again strongly depends on the polymer extensibility parameter, polymer viscosity ratio, and geometric disorder parameter. In particular, we show that the strain-hardening behavior of a viscoelastic fluid promotes these chaotic fluctuations, whereas the shear-thinning behavior tends to suppress these. Therefore, it is not a general phenomenon that can always be seen in the flows of a viscoelastic fluid in porous media. [ABSTRACT FROM AUTHOR]

Acid-polluted groundwater may cause many environmental problems due to its corrosivity. Pumping and injection technology is a commonly used remediation technology, and its main principles are displacement and neutralization. However, due to the high salinity in groundwater, blockage easily occurs and reduces the efficiency. The mechanism of pumping and remediation of strong acid–high salinity groundwater is unclear, and the mechanism and effect of pore blocking are unknown. In this paper, based on an actual polluted site, a field pumping test was carried out. Through groundwater monitoring and drilling core sampling, the process and mechanism of acid groundwater pumping–injection remediation were clarified, and the principle and impact of pore blockage are revealed. The results showed that increasing the injection pressure can effectively improve the repairing efficiency. When the pressure increased from 0.2 MPa to 0.3 MPa, the water injection efficiency per unit time was increased by more than 20%. The principle of pumping–injection remediation of acidic groundwater was mainly displacement, accounting for more than 93%, while neutralization only contributed less than 0.1%. Although the neutralization contribution was small, the neutralization interface of injected alkaline water and acidic groundwater was the main place for precipitation. The precipitation was mainly formed around the injection well, the amount of which decreases greatly with the increase in displacement distance. This was because the formation of precipitation required both an appropriate concentration of Fe and high pH (5.63). Affected by neutralization and dispersion, the pH of the acid–base water interface decreased and the necessary conditions for the formation of precipitation were not met. Therefore, in the actual pumping–injection restoration project, optimization can be carried out from two perspectives of appropriately increasing the injected water pressure and reducing the injected water pH. This study has important reference value for the control and remediation of such acid-polluted groundwater. [ABSTRACT FROM AUTHOR]

Strengthening the transmission uniformity of remedial amendments in heterogeneous porous media is important for improving in situ groundwater remediation efficiency. This study developed a characterization method to represent the improvement of transmission uniformity in heterogeneous media using the degree of difference in hydraulic conductivity of porous media between xanthan solution and pure water, which was defined as the transmission uniformity control coefficient U. Research results showed that U of medium sand/fine sand (2.44) was the most ideal among the three medium combinations tested when the concentration of xanthan solution was 100 mg/L. Then, factors that may influence U were analyzed, and the obtained results showed that xanthan's control ability is affected by permeability contrast (media combinations) and polymer concentration. Generally, when concentrations were in the range of 100~800 mg/L, Umf > Ucf > Ucm. Finally, the actual degree of polymer propulsion under different concentrations and media combinations was analyzed, and the obtained results showed that as different media were varied in permeability change degree, while the migration speed presented an overall decrease as the concentration increased, where the maximum migration front in the low-permeability zone (LPZ) was more obvious than that in the high permeability zone (HPZ). This was consistent with the results characterized by U. [ABSTRACT FROM AUTHOR]

Groundwater pollution remediation has always been a hot topic in the field of environment. Nano zero-valent iron material (nZVI) has been widely used in the treatment and remediation of halogenated organics and heavy metals in groundwater. In this paper, we briefly describe nZVI and its modification technologies, expounds the characteristics of nZVI and its modified materials in groundwater remediation, summarizes the influence of groundwater environment on the properties of nZVI materials, and summarizes the in situ remediation cases of groundwater halogenated organic matter and heavy metal pollution of nZVI and its modified materials. Finally, the author looks forward to the development of nZVI and its modified materials in the field of groundwater in situ remediation in the future, and puts forward some suggestions, such as establishing a simulation model to simulate nZVI modification technology and pollutant removal process, and carrying out the research on the environmental effects and fate of nZVI and its modified materials in the process of groundwater pollution remediation, in order to provide theoretical reference for the research of large-scale practical application of nZVI. [ABSTRACT FROM AUTHOR]

Groundwater in-situ chemical remediation is to inject remediation agents into groundwater through injection wells. The procedure includes groundwater flow, chemical oxidant transport, and soil deformation, which are coupled. Partial differential equations for soil equilibrium, groundwater continuity and mass transport were first constructed, then they were solved by COMSOL Multiphysics for a parameter sensitivity analysis and an actual case. Hydraulic conductivity, hydrodynamic dispersion, and injection pressure have significant effects on groundwater remediation, and their greater values result in a shorter time for reaching the remediation goal. The dissipation of the pore water pressure lags behind the injection stopping, which is conducive to further transport of remediation agents and improving remediation effects. Injection pressure can obviously cause soil displacement, especially in vertical direction, which is affected clearly by soil elastic modulus. It took 80 days for the entire site to meet the remediation requirement that the contaminant concentration was less than 0.6 mg/L. [ABSTRACT FROM AUTHOR]

Metallic iron (Fe0) has been increasingly used to remove toxics from water over the past three decades. However, the idea that metallic iron (Fe0) is not an environmental reducing agent has been vigorously refuted. Researchers presenting their findings in a scientific journal have to accept the burden of proving that their argument has any validity. This 30-year-lasting discussion within the Fe0 remediation community is alien to electro-chemists, as it is a century-old knowledge. Nevertheless, the peer-reviewed literature on "remediation using Fe0" seems to be dominated by evaluators thinking that Fe0 is a reducing agent. This communication challenges the view that Fe0 donates any electron to any dissolved species. The sole goal is to reconcile a proven efficient technology with its scientific roots and enable the design of better Fe0 remediation systems. [ABSTRACT FROM AUTHOR]

In situ remediation of contaminated groundwater often relies on the installation of a treatment zone (TZ) degrading the contamination. Zero‐valent‐iron (ZVI) is a type of reagent used for this purpose. Adequate delivery of ZVI in the whole target volume is particularly challenging and requires monitoring with high spatial resolution. We present a monitoring tool for imaging the dynamic spreading of ZVI and its associated ionic cloud, using cross‐borehole time‐lapse electrical resistivity tomography (ERT). This tool works in urban areas and is particularly suitable for achieving the required spatial resolution at the scale of the target volume. Groundwater and sediment samples show a consistent spatial and temporal distribution of the remediation cloud with cross‐borehole ERT. Yet, the 2D anomalies observed with cross‐borehole ERT provide a more spatially complete and rapid image of the remediation cloud distribution than if based solely on monitoring screens. At the study site, ZVI injection leads to uneven spreading, clearly documented by cross‐borehole ERT monitoring. The benefit of hydraulic conductivity (K) mapping by cross‐borehole induced polarization (IP) to understand unexpected injection paths (upstream leakage, spreading in preferred pathways) is investigated. A 2D, IP‐based, continuous, and coherent K‐distribution is obtained that compares well with estimations by grain size analyses from the TZ. However, the IP‐based K‐field fails at predicting injection paths, suggesting the creation of pathways during the high‐pressure injection of ZVI. Cross‐borehole time‐lapse ERT is the most promising geophysical tool for performance assessment of in situ remediation involving reagents with conductivity contrast. Key Points: Reagent injection leads to a heterogeneously distributed remediation cloud, imaged by 2D cross‐borehole electrical resistivity tomography (ERT) with high spatial resolutionChemical analyses are needed to understand which compounds affect the ERT response: Fe(diss), Ca2+, HCO3−, and most likely solid ironThe initial K‐distribution, inferred from ERT/induced polarization and grain size analyses, does not explain reagent spreading after high‐pressure injection [ABSTRACT FROM AUTHOR]

Green rust (GR) is an interlayer anion-containing Fe(II)/Fe(III) mineral material that is versatile in removing a series of ionic contaminants in water. Taking SeO 4 2- (Se(VI)) as the target contaminant, this study identified that the removal processes of Se(VI) by GR could be divided into three stages: initial rapid interlayer exchange, followed by a rebound, and finally slow removal. In addition, as the percentage of SO 4 2- in GR interlayer increased, the Se(VI) removal by GR gradually decreased. To mediate the SO 4 2- -induced rebound of Se(VI), the coupling of GR with iron nanoparticles (nFe 0 @GR) was proposed in this study and it was found that the removal efficiency of Se(VI) by nFe 0 @GR was 3.53 folds greater than that of GR. This study further revealed that the enhanced reactivity of nFe 0 @GR with Se(VI) could be attributed to the re-equilibration of SO 4 2- driven by the formed GR in situ. Since it had a weaker electrostatic repulsion with interlayer SeO 4 2- than pristine GR, the Se(VI) could be quickly removed by nFe 0 @GR without the rebound. Moreover, the nFe 0 @GR was demonstrated to be effective in immobilizing Se(VI) from simulated groundwater and has a great potential to reduce the risk of Se(VI) re-release into the environment., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

This study examines the efficacy and environmental impact of peracetic acid (PAA) activated by thermally modified activated carbon (AC600) for degrading antibiotics in actual groundwater. Laboratory-scale experiments evaluated the system's effects on contaminant degradation, ecological balance, and substance cycling in the hyporheic zone. Our findings demonstrated the effectiveness of the AC600/PAA system in removing sulfamethoxazole (SMX) from groundwater porous media. Additionally, the AC600/PAA system synergistically interacted with the in-situ microbiota of the hyporheic zone, producing more fragmented degradation products without increasing mixed toxicity. Bacterial abundance increased post-reaction, with notable alterations in the bacterial community and enhanced bacterial metabolism. Key genera such as Lysobacter thrived in the treated environment, playing critical roles in microbiota modification and SMX degradation. The pH remained stable before and after the reaction, while dissolved organic carbon content increased. Overall, our results highlight the promising potential of PAA activation by carbonaceous materials as a low-impact, ecologically friendly technology for in-situ remediation of organic pollutants in groundwater, characterized by high compatibility and biosynthesis., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Per- and polyfluoroalkyl substances (PFAS) are widespread contaminants with adverse environmental and public health effects. Anion exchange (IX) processes can effectively remove many PFAS from water. Objectives of this research were to (1) quantify the effects of PFAS structure and background water matrix constituents [dissolved organic matter (DOM) and major inorganic anions (bicarbonate, chloride, sulfate, and nitrate)] on PFAS uptake capacity of IX resins (K IX ), and (2) develop models that predict PFAS breakthrough in packed bed IX columns from PFAS structure and background water matrix characteristics. Rapid small-scale column tests were conducted with two IX resins and 18 water matrices to determine breakthrough curves and K IX values for 23 PFAS. A quantitative structure-property relationship (QSPR) was developed that predicts K IX for different PFAS from a newly developed concept, the normalized chain length (NCL). NCL for each PFAS was calculated using a group contribution method, in which the contributions of PFAS structural fragments to NCL were normalized to that of -CF 2 -, which was assigned a value of 1.00. Relative to -CF 2 -, contributions of the structural fragments -O-, -CH 2 -, >CF-CF 3 , -CHF-, and -SO 3 H to NCL for the purposes of K IX prediction were 0.34, -1.87, 1.70, 0.00, and 3.65, respectively. DOM and nitrate adversely impacted PFAS removal, while chloride, sulfate, and bicarbonate, when added at concentrations of up to 3 meq/L above native background levels, had negligible effects on K IX . Based on the obtained water matrix effects, pseudo-single solute models were developed for the two tested IX resins, with which PFAS breakthrough curves for fixed bed IX columns can be predicted using only the NCL and the total organic carbon and nitrate concentrations of the influent water., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

The over-pumping of freshwater makes shoreline aquifers susceptible to seawater intrusion. Most studies on aquifer homogeneity that are used to form management guidelines focus on salinization sensitivity. However, under certain extraction conditions, the geographic structure can be quite diverse, with low-permeability obstacles and preferred flow routes that affect circulation and saline transport mechanisms. Here, we used a laboratory-scale glass box apparatus of dimension 100 × 50 × 10 cm 3 to study intrusion in stratified layers under the influence of an inclined ocean-aquifer boundary with a mixed barrier as a remediation technique. The T L \H ratio ranged from 0.2 to 12.84 for all stratification conditions and remediation installed. There was a 40-48 % decrease in the extent of toe length after installation. With a mixed barrier installed, the height of the intrusion was reduced, resulting in an increase in the T L \H and a decrease in the potential for toe length. The intrusion was delayed by 86.67 % in parallel stratification and 28.22 % in perpendicular stratification after comparing the time frame for base case and the mixed barrier installed condition. A parabolic profile of intrusion was observed in the low-permeability layer, while a convex-outward profile was observed in the higher-permeability layers. Similar results are obtained after conducting the sensitivity analysis. The intrusion follows an increasing pattern of ratio with increasing interaction gap opening in parallel stratification, while for perpendicular stratification, with gap opening from 10 cm to 30 cm, there was a decreasing trend followed by an increasing trend, indicating an increase in magnitude with a similar pattern of intrusion. The results of this investigation shed light on the mixed barrier's suitability for use in realistically diverse coastal aquifers. Future research could explore the utilization of different combinations of new barriers, such as under-surface barriers, which work well for stratified layers, and already established barrier systems, to further improve the efficiency of mixed barriers., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier B.V.)

Density-modification remediation of dense nonaqueous phase liquid (DNAPL) using colloidal biliquid aphron (CBLA) is an efficient means of enhancing flushing and avoiding the risk of downward migration of DNAPL. However, the use of demulsifier is currently necessary for CBLA to achieve density modification. This leads to issues such as low modification efficiency and the risk of secondary contamination. In this work, we developed a self-demulsifying CBLA (PO-CBLA-S) for density-modification remediation of DNAPL, eliminating the need for external demulsifiers. The self-demulsification process exhibited pseudo-secondary reaction kinetics, achieving densities below 1 g/cm 3 for various DNAPLs. Groundwater chemistry parameters (pH, anions, cations, temperature, and humic acid (HA) content) were investigated for their impact on perchloroethylene (PCE) density modification. Cations were found to enhance PO-CBLA-S density modification more than anions. Both strong acidic and alkaline environments promote the density regulation of PCE by PO-CBLA-S, and temperature positively correlates with the efficiency of density modification. High concentrations of HA also have a favorable facilitating effect on the density modification. The mechanisms of self-demulsifying density modification were clarified at the microscale. Surfactant entanglement caused by internal surfactant-solvent interaction decreased the stability of PO-CBLA-S, leading to self-demulsification. This study addresses density modification challenges and provides a theoretical foundation for its groundwater remediation applications., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

ENVIRONMENTAL APPLICATIONS OF PERSULFATE: REMEDIATION OF CONTAMINATED GROUNDWATER AND SOILS. Environmental remediation represents a major technological challenge due to the complexity of the environmental matrices and the high treatment cost. In recent years, in situ chemical oxidation technologies (ISCO) have shown a good cost/benefit ratio, which has favored their use in the degradation of several relevant environmental pollutants. In this context, persulfate-mediated processes are of relevant importance once persulfate can be activated in situ, promoting the formation of highly oxidative radical species. Persulfate-based treatments have been frequently reported in environmental remediation studies because they guarantee the effective degradation of pollutants without producing significant changes in the remediated matrix. Given these statements, this study aims to discuss the main ways of activating persulfate and the relevant applications in the remediation of groundwater and soils contaminated with resistant organic pollutants.

As a widely employed method for in situ remediation of groundwater contamination, the pump-and-treat (PAT) system involves the management of water recirculation between the extraction and injection wells. The recirculation zone (RZ) of an extraction-injection well pair in a confined aquifer has been well known. However, PAT systems are more frequently used in unconfined aquifers with a natural regional flow and may not only include one injection well. We develop comparable analytical models for an unconfined aquifer treated by two different system settings, including an extraction well and one injection well (1e/1i system) or two injection wells (1e/2i system). The role of regional groundwater flow is highlighted. Analytical solutions of RZs and recirculation ratios are obtained using complex potential functions, with a new treatment of the jump of the stream function at a branch cut. Results indicate that the shape of RZs and the recirculation ratio nonlinearly depend on several dimensionless parameters linked to the pumping rate and direction of regional flow. Compared to the 1e/1i system, the two injection wells in the 1e/2i system may reduce the integrity of RZs and decrease the recirculation ratio; however, they lead to a higher allowable pumping rate in satisfying the limitations of the water table in wells. This study suggests a useful methodology for analyzing PAT systems with multiple injection wells and provides new insights into RZs between extraction and injection wells.

Metallic iron (Fe0) is a reactive material for treating polluted water. The effect of water salinity on the efficiency of Fe0-based remediation systems is not yet established. This work aims to clarify the reasons why Cl− ions are often reported to improve the efficiency of Fe0/H2O remediation systems. Quiescent batch experiments were carried out to characterize the effect of chloride (Cl−) ions on the efficiency of methylene blue (MB) discoloration in the presence of Fe0. Cl− was used in the form of NaCl at concentrations ranging from 0 to 40 g L−1. The MB concentration was 10 mg L−1, the Fe0 loading was 5 g L−1, and the duration of the experiment varied from 2 to 46 days. Four different Fe0 materials were tested in parallel experiments. Tests with different NaCl levels were performed in parallel with three other organic dyes: Methyl orange (MO), orange II (OII), and reactive red 120 (RR 120). The results clearly show that the presence of Cl− reduces the extent of dye discoloration in all systems investigated. The efficiency of the dyes increased in the order MB < MO < RR 120 < OII. In systems with varying NaCl concentrations, dye discoloration initially decreases with increasing NaCl and slightly increases for [NaCl] > 30 g L−1. However, the extent of dye discoloration for [NaCl] = 40 g L−1 remains much lower than for the system with [NaCl] = 0 g L−1. The results clearly demonstrate that the presence of Cl− fundamentally delays the process of contaminant removal in Fe0/H2O systems, thus improving the understanding of the contaminant interactions in Fe0-based remediation systems. These results also suggest that the effects of other inorganic anions on the efficiency of Fe0/H2O systems should be revisited for the design of field applications.

Although most of the studies focus on the nanoscale zero‐valent iron (nZVI), it still ineffective when comes to in situ utilization due to its intrinsic drawbacks such as rapid aggregation, biotoxicity, high cost, complex preparation process, and so forth. With advantages of lower health risk, lower cost, and simpler fabricate method, microscale zero‐valent iron (mZVI) shows more attractiveness for groundwater remediation than nZVI if its main problem, passivation, can be alleviated. In order to overcome the passivation of mZVI, (mZVI+AC)/CA was produced by encapsulating mZVI and activated carbon (AC) in spherical calcium alginate (CA) matrix in this study. The method effectively solved the passivation of mZVI and showed great long‐effective removal of Cr(VI). The Cr(VI) removal efficiency of (mZVI+AC)/CA could maintain 1.6–2.69 times as much as that of pure mZVI for 0–1500 pore volumes. The maximum Cr(VI) removal capacity reached 100.47 mg/g, which exceeded most of mZVI‐based materials and even some nZVI‐based materials. In addition, mechanism of Cr(VI) removal was revealed by X‐ray diffraction and X‐ray photo‐electron spectroscopy. The results showed that chemisorption, physisorption, reduction, oxidation, and precipitation were involved in the process. Pseudo‐second order model and Freundlich isotherm model were best fitted in kinetics and isotherm experiments, respectively. [ABSTRACT FROM AUTHOR]

Miscible viscous fingering occurs when a less viscous fluid displaces a more viscous one in porous media or a Hele–Shaw cell. Such flow instabilities are of particular interest in a variety of applications in flows and displacements in subsurface energy and environment systems. In this study, we investigate the miscible viscous fingering dynamics experimentally using water to displace glycerol in a sealed Hele–Shaw cell with two wells located in it instead of at the boundary or corners. We comprehensively examine the spatial and temporal variations of fingering dynamics, different flow regimes, and how they are affected by the water injection rate and control of pressure or rate at the outlet. Alongside the widely recognized diffusion-dominated and convection-dominated flow regimes, we identify three new regimes: a slow expansion regime prior to breakthrough, a rapid shrinkage regime immediately after breakthrough, and a uniform, slow expansion regime without fingering instability. Each regime is characterized by interesting flow dynamics, which has not been reported previously. The duration of each regime depends on the water injection rate and whether constant pressure or a constant production rate is applied at the outlet. The variations of swept area, interfacial length, and count of fingers are also quantitatively examined. This study provides new insights into the fundamental mechanisms for miscible fluid displacements in a variety of applications such as CO2 sequestration, hydrogen storage, enhanced oil recovery, and groundwater contaminate remediation. [ABSTRACT FROM AUTHOR]

The basic characteristics and production methods of MNBs, their applications in groundwater remediation, wastewater treatment, air flotation, enhanced biological activity and other fields, as well as their combination with other water treatment processes are reviewed. Finally, the future development trend and research focus of MNBs technology are summarized and prospected. [ABSTRACT FROM AUTHOR]

Groundwater contribution towards human health and livelihood depends on the contaminants level in groundwater. Many people in rural communities are being exposed to waterborne diseases resulting from drinking untreated contaminated groundwater. This study argues that the lack of implementation of available groundwater remediation methods and associated high costs are exposing rural communities to health risks. This study assessed 22 years of groundwater quality data from 12 boreholes and 2 springs to understand the contaminants level in the Soutpansberg region. A feasibility assessment of the application and design of a sustainable groundwater remediation technique was carried out based on individual- and community-based groundwater remediation types. The assessment considered groundwater management, cost and risk of theft and damage to infrastructure model for rural settings. This study determined that groundwater was not suitable for drinking purposes in some parts due to high concentration levels of NO3− and F−. The feasibility assessment indicated that community-based groundwater remediation schemes are more sustainable in rural areas when compared to individual household remediation. In this study, it is recommended that groundwater remediation plans must be included in any proposed water supply or drought intervention project in rural communities. [ABSTRACT FROM AUTHOR]

To combat groundwater pollution, in situ chemical oxidation (ISCO) has been extensively adopted to degrade groundwater pollutants. A critical factor associated with the success of ISCO is the stability (or persistence) of the chemical oxidant. A higher oxidant stability can result in a higher integrity and a sustained oxidation capacity for the oxidants. Both potassium permanganate (KMnO4) and persulfate (PS) are two most commonly employed chemical oxidants for ISCO operations. Although a number of experimental studies have been conducted to evaluate the persistence of these two oxidants, systematic investigations of the persistence of KMnO4 and PS and especially the impact of different subsurface materials on oxidant stability are still limited. To fill these knowledge gaps, the stability of both KMnO4 and PS oxidants has been systemically evaluated in this study. For each type of oxidant, the impact of solution pH and the presence of matrix anions on oxidant stability were evaluated. Furthermore, the persistence of these oxidants was examined in the presence of a number of soils and subsurface minerals with the natural oxidant demand value of each subsurface material being determined. It is found that KMnO4 can directly react with the reducing constituents in the soils via chemical oxidation where PS requires to be activated first in order to produce sulfate radical to react with reducing species. This study provides the essential information of the stability of KMnO4 and PS under different physiochemical conditions and in the presence of different subsurface materials for groundwater ISCO treatment. The conclusions from this study can substantially facilitate the ISCO operations by use of KMnO4 and PS in a more efficient and cost-effective manner. [ABSTRACT FROM AUTHOR]

Groundwater pollution is a significant threat to the public health and environment. Existing groundwater remedial approaches include ex situ treatment and conventional in situ chemical oxidation methods. Although these two methods are widely adopted for groundwater cleanup, continual treatment effectiveness is not satisfactory due to several physicochemical challenges, such as tailing, back diffusion, and concentration rebound. Moreover, these two methods require significant energy and chemical inputs. As an alternative to conventional approaches, controlled release materials are able to discharge chemical oxidants in a continual manner with a substantially prolonged release longevity and treatment time. Thus, these materials are characterized as cost-effective and low-maintenance. In this study, controlled release bead (CRB) materials composed of potassium permanganate (KMnO4)-paraffin were synthesized and evaluated for their performance in degrading alkylbenzene organics. Both batch and dynamic degradation studies indicate that the fabricated CRBs can gradually release KMnO4 into the aqueous phase to degrade alkylbenzenes and the eventual effectiveness in pollutant degradation is on par with the aqueous KMnO4 solution. Furthermore, KMnO4-cement CRBs were fabricated and tested for KMnO4 release kinetics from the CRB surface. It shows that system temperature can considerably influence KMnO4 release longevity and hence treatment lifetime. This study provides the essential information of the novel CRB materials for groundwater pollution remediation with a reduced energy and chemical consumption and a lower environmental footprint. This study expands our capacity in designing, laboratory testing, and modeling these novel materials to facilitate their potential field remedial application. [ABSTRACT FROM AUTHOR]

This study demonstrated that peroxymonosulfate (PMS) activated by Fe(II)/citric acid (CA) could effectively degrade trichloroethylene (TCE) in the presence of Tween-80 (TW-80) or sodium dodecyl sulfate (SDS). Significant TCE removal of 91.6% (90.1%) with 1.3 g L−1 TW-80 (2.3 g L−1 SDS) were achieved at the PMS/Fe(II)/CA/TCE molar ratio of 4/4/4/1 (20/20/20/1). TCE degradation could be greatly elevated by Fe(II) and CA addition, while the existence of surfactants restrained TCE removal and the inhibitory effect increased with the higher surfactant concentration. The tests of the electron paramagnetic resonance (EPR) and reactive radicals scavenging experiments proved that sulfate radical (SO4−•), hydroxyl radical (HO•), and superoxide radical (O2−•) were responsible for TCE degradation and SO4−• acted as the major one. The influences of initial solution pH and inorganic anions k(Cl− and HCO3−) on TCE removal were also investigated. Eventually, TCE removal in actual groundwater tests with surfactants confirmed that the PMS/Fe(II)/CA process has a huge potential of practical application in remediating the groundwater contaminated by TCE after the pretreatment by solubilization using surfactants. [ABSTRACT FROM AUTHOR]

Chlorinated solvents still represent an environmental concern that requires sustainable and innovative bioremediation strategies. This study describes the microbiome composition of a novel bioelectrochemical system (BES) based on sequential reductive/oxidative dechlorination for complete perchloroethylene (PCE) removal occurring in two separate but sequential chambers. The BES has been tested under various feeding compositions [i.e., anaerobic mineral medium (MM), synthetic groundwater (SG), and real groundwater (RG)] differing in presence of sulfate, nitrate, and iron (III). In addition, the main biomarkers of the dechlorination process have been monitored in the system under various conditions. Among them, Dehalococcoides mccartyi 16S rRNA and reductive dehalogenase genes (tceA, bvcA, and vcrA) involved in anaerobic dechlorination have been quantified. The etnE and etnC genes involved in aerobic dechlorination have also been quantified. The feeding composition affected the microbiome, in particular when the BES was fed with RG. Sulfuricurvum, enriched in the reductive compartment, operated with MM and SG, suggesting complex interactions in the sulfur cycle mostly including sulfur oxidation occurring at the anodic counter electrode (MM) or coupled to nitrate reduction (SG). Moreover, the known Mycobacterium responsible for natural attenuation of VC by aerobic degradation was found abundant in the oxidative compartment fed with RG, which was in line with the high VC removal observed (92 ± 2%). D. mccartyi was observed in all the tested conditions ranging from 8.78E C 06 (with RG) to 2.35E C 07 (with MM) 16S rRNA gene copies/L. tceA was found as the most abundant reductive dehalogenase gene in all the conditions explored (up to 2.46 E C 07 gene copies/L in MM). The microbiome dynamics and the occurrence of biomarkers of dechlorination, along with the kinetic performance of the system under various feeding conditions, suggested promising implications for the scale-up of the BES, which couples reductive with oxidative dechlorination to ensure the complete removal of highly chlorinated ethylene and mobile low-chlorinated by-products. [ABSTRACT FROM AUTHOR]

The article describes the remediation of contaminated groundwater during the ex situ remediation of coal tar contamination following the closure of a coking plant in the Moravian–Silesian Region (Czech Republic). The aim of the article is to point out the advantages of ex situ soil remediation via the excavation of the contaminated geological environment combined with thermal desorption, a method of removing contaminants both from soil and groundwater. Its advantage is the absolute qualitative and quantitative control over the contaminated soil with the possibility of precise segmentation into contaminated and non-contaminated soils. Next, all contaminated groundwater may be pumped off upon the construction of sealing walls to control groundwater flows. To excavate the soil, it is necessary to reduce the contaminated groundwater level inside the sealing walls and thus create conditions for the extraction of contaminated soils using standard machinery. In detail, the article describes the removal of the contaminated groundwater and compares the quality of the pumped and inflowing water before and after the remediation. The locality is characteristic of a high horizontal and vertical grain-size heterogeneity of gravel-sand, which led to a varying filtration coefficient affecting the capacities of pumped groundwater quantity during the remediation. At the start of the remediation process, the contaminant levels exceeded the limits by the Czech Environmental Inspectorate several times. The post-remediation monitoring showed that all the contaminant levels were below the limit. Surprisingly, the overall groundwater contamination amounted to 232.86 t of contaminants as non-aqueous phase liquids, and 6872.9 kg of dissolved contaminants. As much as 12,200 t of contaminants were removed from the soil. [ABSTRACT FROM AUTHOR]

Arsenic(As) is one of the most toxic elements commonly found in water and groundwater. Due to the limitation of anaerobic oxidation As(III) by traditional anaerobic treatment method, microbial fuel cells (MFCs) were applied to As(III) oxidation. A double chamber MFC with As(III) and sodium acetate(CH3COONa) as electron donors was constructed, the transformation and migration of As(III) in the anode chamber under the stimulation of micro-voltage and the evolution of microorganisms were monitored. The results indicated that simultaneous As(III) anaerobic oxidation with bioelectricity generation were achieved only when CH3COONa were required. The As(III) removal efficiency was 80% while the removal efficiency of traditional anaerobic treatment method was only 51% after a cycle of bioelectricity generation. The addition of As(III) with certain concentration could promote the power outputs of MFCs with itself being oxidized to less toxic As(V). Moreover, it was found that the migration of total As (including As(III) and As(V)) was from liquid phase to solid phase, and were enriched in sludge. It was also come to a conclusion that the activity of Acinetobacter and Pseudomonas with arsenic resistance was enhanced in the environment of longterm arsenic pollution by high throughput sequencing technology. This study offered a potential attractive method for remediation of arsenic-polluted groundwater. [ABSTRACT FROM AUTHOR]

Contamination of soil and groundwater by chlorinated solvents is an environmental issue of primary concern. Recently, electrically conductive iron particles have been proposed as a novel approach to accelerate anaerobic bioremediation processes. In fact, it was demonstrated that conductive particles facilitate the exchange of electrons between microorganisms via Direct Interspecies Electron Transfer (DIET) processes, thus enhancing the pollutant-degrading potential of the microbial community. However, the use of natural minerals in this context has not been reported so far. In this study, we applied, for the first time, natural magnetite and hematite to accelerate the reductive dechlorination of 1,2-dichloroethane by an enrichment culture in lab-scale anaerobic microcosms. After four feeding cycles, low magnetite-amended microcosms (13 mg/L) yielded the highest rate of 1,2-DCA reductive dechlorination and reduced methanogenic activity. By contrast, hematite did not display any apparent stimulatory effect. Surprisingly, in the presence of higher amounts of iron oxides, a weaker effect was obtained, probably because iron(III) present in the minerals competed for the electrons necessary for reductive dechlorination. For all microcosms, the concentration of the toxic byproduct vinyl chloride was negligible throughout the whole study. The SEM/EDS analysis confirmed the close interaction between the conductive iron oxide particles and the dechlorinating bacteria. This work opens the possibility of using natural conductive minerals for bioremediation applications as well as shedding light on the previously unrecognized role of such minerals in contaminated ecosystems. [ABSTRACT FROM AUTHOR]

Arsenic contamination of groundwater occurs due to both geogenic and anthropogenic processes. Conventional arsenic remediation techniques require extraction of groundwater into pump-and-treat systems, which are expensive and require long operational times. Hence, there is a need for cost-effective remediation. In this study, we assessed and validated the in situ remediation of arsenic contamination in groundwater resources using permeable reactive barriers (PRBs) made of injectable, colloidal iron oxide nanoparticles in the laboratory and in field-scale pilot tests. Sand-packed, flow-through column studies were used in order to assess the sorption behavior of the iron oxide nanoparticles using field materials (sand, groundwater) in the laboratory. The breakthrough curves were analyzed using a reactive transport model considering linear and nonlinear adsorption isotherms and were fitted best with a chemical nonequilibrium consideration. The results were used to design a pilot-scale field test. The injected 28 m3 of nanoparticles (ca. 280 kg dry weight of iron oxide) were successfully delivered to the aquifer via an injection well. No mobile iron was detected downstream, confirming that a stable in situ barrier was formed that did not move with the groundwater flow. Arsenic concentrations in groundwater were reduced to the aimed 50% of the background value, despite the relatively short contact time between arsenic and the iron oxide in the barrier, due to the high flow velocity of 1.21 m/day. We compared the results of the laboratory and field tests and concluded that the single-parameter models based on retardation factor and/or adsorption capacity fail to predict the longevity of the barrier and the evolution of arsenic breakthrough with time, most likely because they do not consider the chemical nonequilibrium effects. Therefore, we propose that upscaling the laboratory findings to field design must be carried out with care and be coupled with detailed reactive transport models. [ABSTRACT FROM AUTHOR]

The Ras Jebel aquifer (North Tunisia) is a typical Mediterranean overexploited coastal aquifer. Since 1966, the piezometric levels have decreased, and water quality has deteriorated. A piezometric dropdown correlated to high salinity is observed in the coastal part of the aquifer. The salinity was increased from 1.7 g.L−1 in 1966 to 4 g.L−1 in 1985. For groundwater remediation, and to combat seawater intrusion, the Tunisian Water Authorities (DGRE and CRDA Bizerte) have set up an artificial groundwater recharge program by surface water through an irrigation system since 1992. Until 2018, 9.21 Mm3 was injected into the aquifer. The work aims are to study and find out the impact of artificial recharge by surface water on the piezometric evolution and the water quality of the Ras Jebel aquifer in relation to the seawater intrusion risk. A multi-tracer approach was carried out in the Ras Jebel region in May 2015 and 2016, including piezometric, geochemical, and geophysical studies. The piezometric study was used to assess the piezometric evolution in relation to the recharge operations. The salinity data were used to characterize the groundwater salinity evolution. Four electrical tomography profiles of a 315 m length were executed between the recharge site and the coastline. Inverted apparent resistivity models have been developed. Electrical resistivity contrast between the recharge water infiltration, seawater intrusion, and groundwater shows the infiltration of recharge water in the direction of the piezometric depression. Consequently, a hydraulic barrier of 150 m larger was formed on the side of the sea. It resists seawater intrusion. [ABSTRACT FROM AUTHOR]