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Groundwater pollution poses a significant threat globally, particularly in developing countries where inadequate sanitation facilities contribute to growing concerns about contamination from sewer leaks. Hence, the objective of this study is to present a comprehensive review, offering insights into diverse aspects of sewer leaks and their impacts on the urban groundwater system. This includes an exploration of leak sources, methods for leak detection, quantification approaches, analysis of contaminants in sewage along with their health effects, and strategies for mitigating both sewer leaks and groundwater contamination. This review addresses various factors leading to sewer infrastructure damage, emphasizing its importance in effective maintenance strategies. In this review, a range of contaminants released from sewer leaks were outlined, ranges from emerging contaminants to heavy metals that poses risk to the human health and environment. Further it evaluates various methods for detecting sewer leaks, emphasizing advancements in water quality analysis, visual, electromagnetic, and acoustics techniques. This research assesses diverse techniques for quantifying sewage leaks, including mass balance and wastewater balance and concludes pinpointing specific leak hotspots remains challenging. Furthermore, an appraisal of mitigation measures was also conducted, determining that rehabilitation serves as a more effective approach to stop leaks at their source. This paper delves into groundwater treatment methods, highlighting the difficulties in achieving optimal water quality and reveals that technologies such as Permeable Reactive Barrier and advanced oxidation processes exhibit potential in effectively removing trace-level pollutants. Overall, the review underscores the importance of understanding, detecting, and mitigating sewer leakage for the health and sustainability of groundwater systems. [ABSTRACT FROM AUTHOR]

The treatment of contaminated groundwater using integrated bone char and biochar beds has been studied. The bone char and biochar were made in a locally built double-barrel retort utilising cow bones, coconut husks, bamboo, neem trees, and palm kernel shells at 450 °C and were graded into 0.05- and 0.315-mm sizes. Eight groundwater treatment experiments (BF2-BF9) were performed in columns with bed heights of 8.5–16.5 cm to remove nutrients, heavy metals, microorganisms, and interfering ions from groundwater using bone char, biochar, and a combination of bone and biochar. The water samples were analysed for twenty-one water quality parameters including pH, total dissolved solids, conductivity, turbidity, fluoride, chloride, sodium, and potassium. The rest were total coliforms, faecal coliforms, total heterotrophic bacteria, Escherichia coli, manganese, and total iron. The effectiveness of the treatment processes was assessed using the Ghana standard authority and the World Health Organisation's recommended values for drinking water quality. The results were shared using a simplified single-factor index, Nemerow's pollution index, and a heavy metal pollution index with decision-makers as a technology for groundwater treatment in rural communities in Africa. Bone char was more effective in removing total heterotrophic bacteria than any of the other treatment agents tested. This is because of its compact nature and small particle size. The quality of water treated by BF3, BF5, BF6, BF7, BF8, and BF9 was fit for drinking based on the single-factor and heavy-metal pollution evaluation because they have the lowest level of pollution. However, Nemerow pollution analysis found only BF5 to be the most suitable for public use. [ABSTRACT FROM AUTHOR]

The present study deals with the utilization of waste biomass of Tectona plant refuse to synthesize the monometallic and bimetallic biochar and to examine their performance for As(III) removal from aqueous solution as well as from groundwater. The biochar materials were characterized using Scanning Electron Microscope (SEM), Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), Particle Size Analysis (PSA), zeta potential and pHZPC. The enhanced removal of As(III) was observed with Fe/Mn-TB (bimetallic) which was greater than Fe-TB (monometallic) biochar. The highest adsorption was 90.35 % and 84.85 % achieved with Fe/Mn-TB and Fe-TB, respectively, at 0.5 mg/L As initial concentration 0.5 mg/L. The adsorption capacity was found to be 0.91 mg/g and 1.89 mg/g, respectively, by Fe-TB and Fe/Mn-TB. The adsorption process of As(III) has good compliance with pseudo-second order kinetics as well as Freundlich isotherm model. As(III) was adsorbed by the Fe-TB and Fe/Mn-TB possibly by electrostatic attraction, H-bond formation and complexation mechanism. Both these materials successfully removed As(III) from aqueous solution as well as from groundwater thus it can be used for the eradication of As(III) from the affected areas by utilizing them as an adsorbent in continuous flow system. [ABSTRACT FROM AUTHOR]

Among the most common and problematic groundwater contaminants are iron and manganese compounds. Specific filter materials are of primary importance in removing them from groundwater. They can be based on natural or modified materials. Modification of the natural materials used for traditional water treatment is one of the factors determining the efficiency of the Fe and Mn removal process, because raw natural media do not effectively remove them from the water. For this reason, research has been carried out on the modification of selected natural materials with coatings that accelerate the removal of iron and manganese from water. In order to shorten the activation time, the coating process was supported with an electrolytic method. The research was conducted on sand and aluminosilicate, which were activated with a KMnO4 solution by reducing it with natural reducing agents – coffee and lemon juice. Conducted experiments let to achieve new catalytic masses for Fe and Mn removal from the water. All tested materials were covered with oxidation layer of MnO2. The best materials coated with precipitated MnO2 were aluminosilicates of both finer- and larger-grain size. The process of electrolysis allowed a significant reduction in a modification time. After filter columns backfilling with the new modified beds, both aluminosilicates showed the best efficiency in Fe and Mn removal from the water and the most stable MnO2 coating. Electrolysis support let to shorten the time of backwash. [ABSTRACT FROM AUTHOR]

A very low concentration of manganese (Mn) in water is a critical issue for municipal and industrial water supply systems. Mn removal technology is based on the use of manganese oxides (MnOx), especially manganese dioxide (MnO2) polymorphs, under different conditions of pH and ionic strength (water salinity). The statistical significance of the impact of polymorph type (akhtenskite ε-MnO2, birnessite δ-MnO2, cryptomelane α-MnO2 and pyrolusite β-MnO2), pH (2–9) and ionic strength (1–50 mmol/L) of solution on the adsorption level of Mn was investigated. The analysis of variance and the non-parametric Kruskal–Wallis H test were applied. Before and after Mn adsorption, the tested polymorphs were characterized using X-ray diffraction, scanning electron microscope techniques and gas porosimetry analysis. Here we demonstrated the significant differences in adsorption level between MnO2 polymorphs' type and pH; however, the statistical analysis proves that the type of MnO2 has a four times stronger influence. There was no statistical significance for the ionic strength parameter. We showed that the high adsorption of Mn on the poorly crystalline polymorphs leads to the blockage of micropores in akhtenskite and, contrary, causes the development of the surface structure of birnessite. At the same time, no changes in the surfaces of cryptomelane and pyrolusite, the highly crystalline polymorphs, were found due to the very small loading by the adsorbate. [ABSTRACT FROM AUTHOR]

The efficacy of a fine bubble (FB) diffuser in enhancing the performance of an attached biofilm hydrogenotrophic denitrification (HD) reactor was evaluated. HD reactors equipped with an FB diffuser (FB reactor) and an air stone (AS) diffuser that produced ordinary bubbles (AS reactor) were operated in parallel at different hydraulic retention times (HRTs) in a synthetic groundwater treatment experiment. A reduction in H2 consumption of approximately 77% was achieved using the FB diffuser to reach a gas-liquid mass transfer coefficient similar to that of the AS diffuser. The high gas dissolution efficiency of the FB diffuser resulted in an effective nitrogen removal rate (NRR) enhancement, requiring less H2 supply. The highest value of NRR at 53.0±9.8 g-N/m3/d was obtained in the FB reactor at a minimum HRT of 3 h, which was two-fold higher than the corresponding value from the AS reactor. The FB reactor also had the lowest requirement of H2 for denitrification reaching 0.1 m3-H2/g-N in this condition, which was ten-fold lower than that in the AS reactor. Furthermore, the suspended sludge concentration in the FB reactor was lower than that in the AS reactor, indicating that the application of the FB diffuser can minimize excess suspended sludge accumulation inside the HD reactor. Microbial community analysis showed the predominance of Thauera spp. reaching a relative abundance of 15.7–27.3% in the FB reactor, suggesting a contribution to the HD. This finding can provide insight into the application of the FB diffuser for optimizing nitrate-contaminated groundwater treatment technology by HD. [ABSTRACT FROM AUTHOR]

Global food security challenges have been burdened by a rapidly expanding population and its attendant food demands. Safer and higher-quality agriculture is one of the most essential solutions for addressing the growing problem. In agriculture that is safer, the quality of irrigation from a safer water source will boost food security. Groundwater is one of the most widely utilized water sources for agriculture. Safeguarding groundwater against contamination and preserving water resources is a rising global concern. Herein, previous literature studies were analyzed to determine the groundwater potential for food production of the various continents around the globe, as well as the various types of groundwater contamination, the sources of groundwater contamination, and the best methods for combating groundwater contamination in order to guarantee safe irrigation for agriculture and thus achieve food security. Consequently, the natural and anthropogenic activities that degrade the quality of the groundwater and transform it into contaminated water from harmful organisms, residues of organic and inorganic soluble and non-soluble salts of the groundwater from chemical, leachate from landfills, sewage systems, and biological contamination, are the major issues in safer agriculture, causing a number of problems in the growth of agricultural crops and leading to a negative impact on food production as well as on the health of the population. Proper identification of different sources of contamination and proper methods to prevent contamination from reaching groundwater, as well as governmental and institutional frameworks to combat contamination and treatment methods to treat contaminated groundwater, will contribute to the future achievement of food security by ensuring a safer irrigation method and agriculture. [ABSTRACT FROM AUTHOR]

Zeolite materials are among the relatively cheap and readily available materials for wastewater treatment. However, the performance of zeolite-based systems can be highly affected by the material properties. In this study, the treatment system based on natural zeolite materials from Chankanai mines in Kazakhstan was compared with a synthetic zeolite treatment system for the purification of groundwater. Water quality indices were also developed from a set of selected water quality parameters to further assess the state of water quality of raw groundwater and the effluents treated with natural and synthetic zeolite. The lowest removal efficiency of natural zeolite (30%) was observed with zinc, while the lowest removal efficiency (36%) of synthetic zeolite was observed with arsenic. With turbidity and beryllium, we observed the maximum removal efficiency (100%) of natural zeolite, whereas with turbidity, we observed the highest removal efficiency (100%) of synthetic zeolite. When the groundwater samples were put through the natural zeolite treatment system, removal efficiency of 50% and above was obtained with 27 (79.4%) out of the 34 water quality parameters examined. On the other hand, when the groundwater samples were put through the synthetic zeolite treatment system, more than 50% removal efficiency was attained with 30 (88.2%) out of the 34 water quality parameters studied. The aggregated water quality index of raw groundwater was 3278.24, falling in the "water unsuitable for drinking" category. The effluent treated with natural zeolite generated 144.82 as a water quality index, falling in the "poor water" quality category. Synthetic zeolite generated 94.79 as a water quality index, falling in the "good water" quality category. Across the board, it was shown that the synthetic zeolite treatment system outperformed the natural zeolite treatment system according to a number of water quality parameters. The findings of this study offer substantial knowledge that can be used to develop more efficient groundwater treatment technologies. [ABSTRACT FROM AUTHOR]

In the Netherlands, approximately 60% of drinking water is obtained from (generally anaerobic) groundwater. This requires aeration followed by rapid sand filtration (RSF) to remove iron, manganese, arsenic and ammonium. The mechanisms responsible for their removal or the clogging of RSFs and breakthrough of colloidal iron or manganese oxides have not been fully elucidated in previous studies. In this work, factors affecting iron precipitation have been studied in aerated, continuously stirred bench scale jar experiments to simulate the supernatant layer of submerged sand filters. Time series data of filtered iron concentration and precipitate size have been collected in experiments with synthetic groundwater with and without P, Si, HCO3 and Ca at neutral pH. We observed that precipitate growth is not influenced by different HCO3 concentrations but is reduced drastically when natural organic matter (NOM) is present in water and, to lesser extent, Si as well. The addition of P appears to hamper precipitate growth to some extent, but requires more research to fully understand the implications. We also observed that addition of Ca improved the growth of Fe precipitates in the presence of Si and especially NOM. These results have great significance for improving Fe removal efficiency of groundwater treatment plants in The Netherlands and abroad. HIGHLIGHTS Different HCO3 concentrations have no significant impact on the precipitation of Fe for typical groundwater conditions.; Silicate additions in the presence of HCO3 result in reduced Fe precipitation.; Addition of NOM in the presence of HCO3, hamper the precipitation growth of Fe.; The impact of Ca on precipitate growth is stronger for dissolved organic carbon-containing water compared to Si-containing water for typical concentration ranges.;

An electrocoagulation (EC) model is developed for hexavalent chromium reduction and precipitation, using iron electrodes. Parallel removal mechanisms such as adsorption of chromium on ferrihydrite and direct reduction at the cathode is assumed negligible due to low concentration of Cr(VI). The reaction model presented for batch system represents species complexation, precipitation/dissolution, acid/base, and oxidation-reduction reactions. Batch reactor simulation is verified using experimental data obtained by Sarahney et al. (2012), where the effect of initial chromium concentration, pH, volumetric current density, and ionic strength is considered (Sarahney et al., 2012). The model couples multicomponent ionic transport in MATLAB with chemical reaction model in PHREEQC, as a widely used computational programming tool and a geochemical reaction simulator with comprehensive geochemistry databases. The suggested current density is 0.05 − 0.3 mA / c m 2 and the surface to volume ratio in batch reactor is considered 0.017 1/cm. Design parameters are presented for operation of a flow-through hexavalent chromium removal using electrocoagulation by iron electrode to treat Cr(VI) in range of 10–50 mg/L. The operational parameters for a flow-through EC reactor for Cr(VI) removal is suggested to follow 0.05 mA / c m 2 ≤ 3 nFeQ c Cr VI inlet ≤ 0.3 mA / c m 2 . [Display omitted] • Modeling the anodic dissolution of iron during Electrocoagulation (EC) operation. • Simulating the EC operation for hexavalent chromium removal from water. • Design parameters for flow-through reactor to remove hexavalent chromium by electrocoagulation technique. • Operational parameters for efficient removal of hexavalent chromium from aqueous phase. [ABSTRACT FROM AUTHOR]

The groundwater system is one of the most important subsurface resources on Earth, which offers many important services to humankind, such as irrigated agriculture, household use, and manufacturing. However, the safety of groundwater resources is seriously threatened by contamination from human activities. The emulsion has been proposed as a potential solution for the removal of contaminants due to its high apparent viscosity. Here we reveal the pore-scale mechanism for the viscosity increase in decane-water emulsions by lattice Boltzmann simulations. We assess the effect of phase saturation, interfacial tension, and contact angle, on the apparent viscosity of decane-water emulsions in porous media. Our results show that the apparent viscosity of the emulsion reaches its maximum value when the decane saturation is around 20%. We also find that this maximum viscosity increases with interfacial tension, and it is larger in decane-wet or water-wet systems than it is in intermedia-wet media.

Elevated arsenic (As) contamination in water, especially groundwater, has been recognized as a major problem of catastrophic proportions. This work explores As(V) removal via the coagulation-flocculation process by use of ferric chloride coagulant and polyacrylamide k16 co-coagulant as a first time. The effects of major operating variables such as coagulant dosing (50, 125 and 200 mg/L), co-coagulant dosing (5, 12.5 and 20 mg/L), pH (6, 7and 8), fast mixing time (1, 2 and 3 min), and fast mixing speed (110, 200 and 300 rpm) on As(V) removal efficiency were investigated by a Box-Behnken statistical experiment design (BBD) and response surface methodology (RSM). According to factors F values, coagulant dosing, rapid mixing speed, pH, and co-coagulant dosing showed the most effect on As(V) removal efficiency, and the rapid mixing time factor indicated the slightest effect. The proposed quadratic model was significant with a p value < 0.0001 and has satisfactorily described the experimental data with R2 and adjusted R2 values of 0.9855 and 0.9738, respectively. Predicted model optimal conditions with target of complete As(V) removal were coagulant dosing = 197.63 ppm, co-coagulant dosing = 19.55 ppm, pH = 7.37, fast mixing time = 1.43 min and fast mixing speed = 286.77 rpm. The treatment of Nazarabad well water sample with an initial As(V) concentration of 5 mg/L under the optimal conditions removed 100% As(V) with the volume of produced sludge of 10.7 mL/200 mL. Increasing coagulant dosing, co-coagulant dosing, fast mixing time and fast mixing speed operation parameters from low-level to high-level values indicated 78%, 20%, 10.52% and 9.47% increases in volume of the produced sludge, respectively. However, a reduction of 13.63% in volume of the produced sludge resulted via pH increases. [ABSTRACT FROM AUTHOR]

In this work, neutron computed tomography (CT) is employed to investigate the dissolution of porous aluminum electrodes during electrocoagulation (EC). Porous electrodes were chosen in efforts to reduce electric power requirements by using larger surface-area electrodes, having both inner and outer surface, for the EC process. Neutron CT allowed 3D reconstruction of the porous electrodes, and image analysis provided the volume of each electrode vs. thickness, which can indicate whether the inner surface is effectively involved in EC reactions. For the anode, the volume decreased uniformly throughout the thickness of the electrode, indicating that both the outer and inner surface participated in electrochemical dissolution, while the volume of the cathode increased uniformly vs. thickness, indicating deposition of material on both the outer and inner surface. The attenuation coefficient vs. thickness, increased for both anode and cathode, indicating surface chemistry changes. For the anode, the attenuation coefficient increased slightly but uniformly, probably due to aluminum oxide formation on the surface of the anode. For the cathode, the attenuation coefficient increased more than for the anode and nonuniformly. The higher increase in the attenuation coefficient for the cathode is due to precipitation of aluminum hydroxide on the electrode surface, which added hydrogen. Image analysis also showed that, although the attenuation coefficient increased throughout the thickness of the electrode, most of the hydroxide deposition occurred on the outer surface. Energy analysis showed that porous electrodes can be used to reduce process energy requirements by as much as 4 times compared to solid electrodes.

This paper concerns the removal of arsenic and hydrated silica (HS) from groundwater (32.45 µg L−1 As, 5.70 mg L−1 F − , 155.5 mg L−1 HS, 30.0 mg L−1 SO 4 2-, 0.77 mg L−1 PO 4 3-, pH 8.36, and conductivity of 533 µS cm−1) by electrocoagulation (EC) using an up-flow continuous reactor. Iron electrodes were used as sacrificial anodes. The EC efficiency on pollutants removal at current densities from 4 to 8 mA cm−2 and mean linear flow velocities ranging from 1.1 to 4.5 cm s−1 were analyzed. The best EC trial was obtained at 8 mA cm−2 and 1.1 cm s−1, where the residual concentrations of As and HS were 1.1 µg L−1, and 33 mg L−1, respectively, giving values of electrolytic energy consumption (E cons) and overall costs (OC) of 1.96 kWh m−3 and 0.28 USD m−3. The proposed EC process agrees with the WHO guideline for the concentration of As (<10 μg L−1). XRF, SEM-EDS, XRD, FTIR, and Raman analyzes indicate that HS reacts with coagulant forming iron silicates. Arsenic was removed by adsorption on iron hydroxides, iron oxyhydroxides, and iron silicates flocs. Sulfate and phosphate are trapped and swept within the sedimentation of the flocs. The removal of fluorides (17%) is attributed to weak adsorption on the iron agglomerates. • Arsenic (As) and hydrated silica (HS) removal from groundwater by electrocoagulation (EC). • Iron plate sacrificial electrodes installed in an up-flow continuous EC reactor. • HS reacts with Fe(II) forming iron silicates, As was removed by adsorption on flocs. • EC meets the WHO guideline for arsenic (<10 μg L−1) and HS is eliminated. • Overall cost of 0.28 USD m−3, highlight the EC as an economical technology. [ABSTRACT FROM AUTHOR]

1,2,3-Trichloropropane (TCP), a suspected human carcinogen, is a widespread contaminant that leaches into groundwater, where it persists. This systematic review of studies examines treatment technologies for TCP contamination. A four-database search yielded 1,160 papers, 36 of which met the eligibility criteria for a full-text review. The three most-represented treatment technologies, such as biodegradation (13), zerovalent transition metals (8), and granular activated carbon (GAC) (4), are either fully deployed in water systems or in the field test stage. To meet TCP treatment goals, additional site-specific testing of well water is needed since source water chemistry and co-contamination influence treatment efficacy. Future studies should include standardized units for reporting degradation or sorption normalized to surface area, chemical input, and/or energy expenditures. Although GAC is the most common treatment for contaminated wells, this technology remains limited due to a low TCP adsorption capacity which requires frequent bed-volume replacement. Aerobic biodegradation, reduction with zerovalent iron, and Fenton's treatment produce byproducts that could limit their use. A geospatial analysis of TCP treatment studies reveals a dearth of knowledge about the extent of TCP contamination. TCP contamination is documented in at least nine countries on three continents, but there is little information about the rest of the world. HIGHLIGHTS First systematic review of 1,2,3-trichloropropane (TCP) treatment studies.; The most highly developed technologies are GAC, zerovalent zinc, and bioremediation.; Source water chemistry and co-contamination influence TCP treatment efficacy.; Studies need standardized TCP removal reporting units normalized to the surface area.; TCP contamination studied in only three continents, revealing wide knowledge gaps.;

This study proposes the use of an ultrasound-assisted adsorption system coupled to porous ceramic fragments to improve the removal of iron from FeSO4 aqueous solution. Ultrasound was applied using an ultrasound bath at a low frequency (37 kHz, 330 W). The optimized conditions for Fe removal were achieved by 7 g of adsorbent, 40 min of sonication, 20 mg L–1 of initial Fe concentration, and 30 °C of reaction temperature. After optimizing the conditions, the method was applied for the removal of iron in groundwater. A central composite design and response surface methodology were used to evaluate the degree to which different variables had a significant effect on iron removal. The efficiency of iron removal using the selected conditions for FeSO4 solution was near to 100%. However, for groundwater samples, the maximum iron removal efficiencies of the system with and without ultrasound were 80.7% and 51.1%, respectively, indicating that the adsorption with ultrasound was significantly higher than that without ultrasound. It was shown that the proposed ultrasound-assisted adsorption system can be used to enhance the removal of inorganic iron from groundwater. [ABSTRACT FROM AUTHOR]

Post pesticides production landfills are often a source of large uncontrolled contamination of groundwater. Therefore, there is a need to find suitable technologies to reduce the concentration and ecotoxicity of these pesticides. In this paper, both lab- and field-scale technology of permeable reactive barrier (PRB) for the treatment of hexachlorocyclohexanes (HCHs) and chlorobenzenes (CBs) at a site in Jaworzno, Poland are described. The results showed the high efficiency of the treatment process for hexachlorocyclohexane (90%) and chlorobenzenes (99%) in lab-scale which slowly decreased to 86% and 97%, respectively with the time of PRB operation (112 d). The efficiency of treatment of HCHs and CBs by PRB technology in pilot scale in the 8th day operation was ca. 82% and 60%, respectively during the first phase of operation and highly decreased after two months of operation due to the loss of sorption capacity of peat bed and the passivation process of iron chips. Base on the measured data, it could be determined that the treatment train in such barrier relies on subsequent reductive dehalogenation and adsorption. Therefore, the results obtained and presented in this paper could be useful for further design of full-scale permeable reactive barriers on sites with groundwater contaminated by similar organochlorine pesticides. [ABSTRACT FROM AUTHOR]

The article deals with simple methods of decontamination of groundwater from the vicinity of brownfields contaminated with organic and inorganic substances. In the literature, thousands of articles on this issue at various sophisticated levels of knowledge can be found. The articles are mostly suitable as an extension of scientific knowledge; however, regarding potential costs and respectively scale-up problems, the applications are limited. It turns out that the vast majority of contaminated water can be effectively decontaminated by simple methods, in a coagulation-sedimentation sequence → simple oxidation and reduction methods for separated water (Fenton reaction, photocatalysis, ozonation, reductive dehalogenation with zero metals) → adsorption of remaining pollutants on simple sorbents, eg on biochar → (possibly bioremediation or advanced physical methods such as membrane filtration) → final purification on activated carbon. Due to the usually limited volume loads of soils with pollutants in the vicinity of brownfields, it is not economically advantageous to build demanding decontamination units for water purification. Usually, the simplest solution is the system to pump-and-treat around the source of contamination, with the main emphasis on highly effective removal of pollutants from water that returns underground. Groundwater was taken from boreholes leading to the saturated zone in the vicinity of several selected industrial brownfields. The solutions are shown on individual typical cases.

A very low concentration of manganese (Mn) in water is a critical issue for municipal and industrial water supply systems. Mn removal technology is based on the use of manganese oxides (MnOx), especially manganese dioxide (MnO2) polymorphs, under different conditions of pH and ionic strength (water salinity). The statistical significance of the impact of polymorph type (akhtenskite ε-MnO2, birnessite δ-MnO2, cryptomelane α-MnO2 and pyrolusite β-MnO2), pH (2–9) and ionic strength (1–50 mmol/L) of solution on the adsorption level of Mn was investigated. The analysis of variance and the non-parametric Kruskal–Wallis H test were applied. Before and after Mn adsorption, the tested polymorphs were characterized using X-ray diffraction, scanning electron microscope techniques and gas porosimetry analysis. Here we demonstrated the significant differences in adsorption level between MnO2 polymorphs’ type and pH; however, the statistical analysis proves that the type of MnO2 has a four times stronger influence. There was no statistical significance for the ionic strength parameter. We showed that the high adsorption of Mn on the poorly crystalline polymorphs leads to the blockage of micropores in akhtenskite and, contrary, causes the development of the surface structure of birnessite. At the same time, no changes in the surfaces of cryptomelane and pyrolusite, the highly crystalline polymorphs, were found due to the very small loading by the adsorbate.

Zeolite materials are among the relatively cheap and readily available materials for wastewater treatment. However, the performance of zeolite-based systems can be highly affected by the material properties. In this study, the treatment system based on natural zeolite materials from Chankanai mines in Kazakhstan was compared with a synthetic zeolite treatment system for the purification of groundwater. Water quality indices were also developed from a set of selected water quality parameters to further assess the state of water quality of raw groundwater and the effluents treated with natural and synthetic zeolite. The lowest removal efficiency of natural zeolite (30%) was observed with zinc, while the lowest removal efficiency (36%) of synthetic zeolite was observed with arsenic. With turbidity and beryllium, we observed the maximum removal efficiency (100%) of natural zeolite, whereas with turbidity, we observed the highest removal efficiency (100%) of synthetic zeolite. When the groundwater samples were put through the natural zeolite treatment system, removal efficiency of 50% and above was obtained with 27 (79.4%) out of the 34 water quality parameters examined. On the other hand, when the groundwater samples were put through the synthetic zeolite treatment system, more than 50% removal efficiency was attained with 30 (88.2%) out of the 34 water quality parameters studied. The aggregated water quality index of raw groundwater was 3278.24, falling in the “water unsuitable for drinking” category. The effluent treated with natural zeolite generated 144.82 as a water quality index, falling in the “poor water” quality category. Synthetic zeolite generated 94.79 as a water quality index, falling in the “good water” quality category. Across the board, it was shown that the synthetic zeolite treatment system outperformed the natural zeolite treatment system according to a number of water quality parameters. The findings of this study offer substantial knowledge that can be used to develop more efficient groundwater treatment technologies.

Groundwater with increased ammonia concentration is a constant concern regarding the preparation of drinking water. The affinity of ammonia to be adsorbed on the surface of different solid materials significantly influences the selection of its removal process and has been the motivation for this investigation. Crystal-Right™ (CR-100) was used for the removal of ammonia from aqueous solution in batch adsorption procedure. The kinetics of adsorption followed the pseudo-second-order model. The Elovich model suggested that chemisorption rate decreased with the temperature increase. The liquid film diffusion and intra-particle diffusion models revealed that heterogeneous adsorbent surface energy had a particularly pronounced impact on the overall mass transfer rate. The Arrhenius and Eyring's equations suggested spontaneous and endothermic nature of complex adsorption/ion exchange removal process. The isosteric heat of adsorption revealed that with the increase in surface loading lateral interactions between the adsorbed molecules occurred. [ABSTRACT FROM AUTHOR]

Elevated arsenic (As) contamination in water, especially groundwater, has been recognized as a major problem of catastrophic proportions. This work explores As(V) removal via the coagulation-flocculation process by use of ferric chloride coagulant and polyacrylamide k16 co-coagulant as a first time. The effects of major operating variables such as coagulant dosing (50, 125 and 200 mg/L), co-coagulant dosing (5, 12.5 and 20 mg/L), pH (6, 7and 8), fast mixing time (1, 2 and 3 min), and fast mixing speed (110, 200 and 300 rpm) on As(V) removal efficiency were investigated by a Box-Behnken statistical experiment design (BBD) and response surface methodology (RSM). According to factors F values, coagulant dosing, rapid mixing speed, pH, and co-coagulant dosing showed the most effect on As(V) removal efficiency, and the rapid mixing time factor indicated the slightest effect. The proposed quadratic model was significant with a p value < 0.0001 and has satisfactorily described the experimental data with R2 and adjusted R2 values of 0.9855 and 0.9738, respectively. Predicted model optimal conditions with target of complete As(V) removal were coagulant dosing = 197.63 ppm, co-coagulant dosing = 19.55 ppm, pH = 7.37, fast mixing time = 1.43 min and fast mixing speed = 286.77 rpm. The treatment of Nazarabad well water sample with an initial As(V) concentration of 5 mg/L under the optimal conditions removed 100% As(V) with the volume of produced sludge of 10.7 mL/200 mL. Increasing coagulant dosing, co-coagulant dosing, fast mixing time and fast mixing speed operation parameters from low-level to high-level values indicated 78%, 20%, 10.52% and 9.47% increases in volume of the produced sludge, respectively. However, a reduction of 13.63% in volume of the produced sludge resulted via pH increases.

A sequential bed granular bioreactor was adapted to treat nitrate-polluted synthetic groundwater under anaerobic conditions and agitation with denitrification gas, achieving very efficient performance in total nitrogen removal at influent organic carbon concentrations of 1 g L-1 (80–90%) and 0.5 g L-1 (70–80%) sodium acetate, but concentrations below 0.5 g L-1 caused accumulation of nitrite and nitrate and led to system failure (30–40% removal). Biomass size and settling velocity were higher above 0.5 g L-1 sodium acetate. Trichosporonaceae dominated the fungal populations at all times, while a dominance of terrestrial group Thaumarchaeota and Acidovorax at 1 and 0.5 g L-1 passed to a domination of Methanobrevibacter and an unclassified Comamonadaceae clone for NaAc lower than 0.5 g L-1. The results obtained pointed out that the denitrifying granular sludge technology is a feasible solution for the treatment of nitrogen-contaminated groundwater, and that influent organic matter plays an important role on the conformation of microbial communities within it and, therefore, on the overall efficiency of the system. [ABSTRACT FROM AUTHOR]

Arsenic (As) poisoning in groundwater and rice paddy soil has increased globally, impacting human health and food security. There is an urgent need to deal with As-contaminated groundwater and soil. Biochar can be a useful remedy for toxic contaminants. This study explains the synthesis of pinecone-magnetic biochar (PC-MBC) by engineering the pinecone-pristine biochar with iron salts (FeCl 3.6H 2 O and FeSO 4.7H 2 O) to investigate its effects on As(V) adsorption and immobilization in water and soil, respectively. The results indicated that PC-MBC can remediate As(V)-contaminated water, with an adsorption capacity of 12.14 mg g−1 in water. Isotherm and kinetic modeling showed that the adsorption mechanism involved multilayer, monolayer, and diffusional processes, with chemisorption operating as the primary interface between As(V) and biochar. Post-adsorption analysis of PC-MBC, using FTIR and XRD, further revealed chemical fixing and outer-sphere complexation between As(V) and Fe, O, NH, and OH as the main reasons for As(V) adsorption onto PC-MBC. Recycling of PC-MBC also had excellent adsorption even after several regeneration cycles. Similarly, PC-MBC successfully immobilized As in paddy soil. Single and sequential extraction results showed the transformation of mobile forms of As to a more stable form, confirmed by non-destructive analysis using SEM, EDX, and elemental dot mapping. Thus, Fe-modified pine-cone biochar could be a suitable and cheap adsorbent for As-contaminated water and soil. [Display omitted] • Magnetic biochar was produced from pinecones via impregnation with iron-salts. • Biochar successfully remediated arsenic-contaminated groundwater and paddy soil. • Arsenic was chemically fixed with active functional groups on surface of biochar. • Mobility of arsenic in soil was highly reduced due to transformation to stable form. [ABSTRACT FROM AUTHOR]

The paper concerns experimental research related to the removal of color and permanganate index (CODMn) in the presence of iron and manganese from underground water by means of coagulation and ozonation. The tests were carried out on a laboratory and technical scale in the real underground water treatment system. Ozone, as a strong oxidizing agent, was used to reduce the color intensity and to convert the iron Fe2+ and manganese ions Mn2+ to Fe(OH)3 and MnO2, respectively. In order to optimally remove the color to a value below 15 mg/L, the ozone dose of 3 mg/L was sufficient, which also ensured proper removal of iron and manganese, respectively by 94% and 83%. Ozonation under these conditions, however, did not provide sufficient removal of organic compounds expressed as CODMn below the assumed value of 3 mg/L. The effect of aluminum sulfate and polyaluminum chloride (PAC) was also studied, as a result of which it was found that polyaluminum chloride proved to be more effective reagent. In the technical conditions of water purification at a dose of 16 mg/L coagulant, the efficiency of color removal was 65.2% and CODMn – 50.8%, which ensured adequate values of the tested indicators in purified water below the permissible level.

Arid areas often contain brackish groundwater that has a salinity exceeding 500 mg/L. This poses several challenges to the users of the water such as a salty taste and damage to household appliances. Desalination can be one of the key solutions to significantly lower the salinity and solute content of the water. However, the technology requires high energy inputs as well as managing waste products. This paper presents the fabrication of ultrafiltration heterogeneous ion exchange membranes for brackish groundwater treatment. Scanning electron microscopy (SEM) images showed a relatively uniform resin particle distribution within the polymer matrix. The mean roughness of the cation exchange membrane (CEM) and anion exchange membrane (AEM) surfaces increased from 42.12 to 317.25 and 68.56 to 295.95 nm, respectively, when resin loading was increased from 1 to 3.5 wt %. Contact angle measures suggested a more hydrophilic surface (86.13 to 76.26° and 88.10 to 74.47° for CEM and AEM, respectively) was achieved with greater resin loading rates. The ion exchange capacity (IEC) of the prepared membranes was assessed using synthetic groundwater in a dead-end filtration system and removal efficiency of K+, Mg2+, and Ca2+ were 56.0, 93.5, and 85.4%, respectively, for CEM with the highest resin loading. Additionally, the anion, NO3− and SO42− removal efficiency was 84.2% and 52.4%, respectively, for the AEM with the highest resin loading. This work demonstrates that the prepared ultrafiltration heterogeneous ion exchange membranes have potential for selective removal for of ions by ion exchange, under filtration conditions at low pressure of 0.05 MPa.

Iron oxidation and removal from groundwater is a necessary and costly process in drinking water production. In most cases, iron removal is done via aeration, succeeded by precipitation. Most systems for aeration are based on increasing the interfacial area via injecting air in the system or spraying. Both methods have disadvantages, like clogging and formation of aerosols. In this study, a new vortex-based flow-through reactor consisting of a cylindrical tank with an impeller located at the bottom was studied regarding its aeration and iron oxidation capabilities in groundwater. During the aeration experiments, the flow rate, impeller rotation and aerated volume were varied. A nondimensional constant α was proposed to relate the system’s physical characteristics and its aeration capabilities, expressed in dissolved oxygen and system volumetric mass transfer coefficient (KLa). Three distinct operational regimes were defined: formation, complete and bubble regime. These regimes showed very specific characteristics regarding the air–water interface structure and the area to volume ratio, resulting in different aeration capabilities and iron oxidation efficiency values. The system presented KLa values similar to commercially available aeration systems, especially inside the bubble regime. By using dimensionless coefficients, the presented analysis provided the basis for the design of continuous impeller aeration and oxidation systems of arbitrary size.

Zinc (Zn) removal by physically mixed particles of zero-valent iron (Fe) and iron sulfide (FeS) was investigated as one technology for Zn removal from waste groundwater. The effects of the Fe/FeS mass ratio, including a single Fe and FeS particles, and pH on changes in the concentrations of Zn, Fe, and S were examined by a batch test and column tests, and the mechanism of Zn elimination was discussed. Among all the mixing fractions of Fe and FeS, Zn was eliminated most effectively by 3Fe/7FeS (mass ratio of Fe/FeS = 3/7). The Zn removal rate decreased in the order of 3Fe/7FeS, FeS, and Fe, whereas the Fe concentration decreased in the order of Fe, FeS, and 3Fe/7FeS. The S concentration of FeS was larger than that of 3Fe/7FeS. The Zn removal rate by physically mixed 3Fe/7FeS particles was enhanced by a local cell reaction between the Fe and FeS particles. The electrons caused by Fe corrosion moved to the FeS surface and reduced the dissolved oxygen in the solution. Zn2+, Fe2+, and OH− ions in the solution were then coprecipitated on the particles as ZnFe2(OH)6 and oxidized to ZnFe2O4. Moreover, Zn2+ was sulfurized as ZnS by both the Fe/FeS mixture and the simple FeS particles. The Zn removal rate increased with increasing pH in the range from pH 3 to 7. From a kinetic analysis of Zn removal, the rate constant of anode (Fe)/cathode (FeS) reaction was almost the same as that of ZnS formation and slightly larger than that of Fe alone. [ABSTRACT FROM AUTHOR]

The high radon concentrations measured in the indoor air of groundwater facilities and the prevalence of the problem have been known for several years. Unlike in other workplaces, in groundwater plants, radon is released into the air from the water treatment processes. During the measurements of this study, the average radon concentrations varied from 500 to 8800 Bq m -3 . In addition, the indoor air of the treatment plants is filtered and there are no significant internal aerosol sources. However, only a few published studies on groundwater plants have investigated the properties of the radon progeny aerosol, such as the equilibrium factor ( F ) or the size distribution of the aerosol, which are important for assessing the dose received by workers. Moreover, the International Commission on Radiological Protection has not provided generic aerosol parameter values for dose assessment in groundwater treatment facilities. In this study, radon and radon progeny measurements were carried out at three groundwater plants. The results indicate surprisingly high unattached fractions ( f p = 0.27-0.58), suggesting a low aerosol concentration in indoor air. The corresponding F values were 0.09-0.42, well below those measured in previous studies. Based on a comparison of the effective dose rate calculations, either the determination of the f p or, with certain limitations, the measurement of radon is recommended. Dose rate calculation based on the potential alpha energy concentration alone proved unreliable., (Creative Commons Attribution license.)

Mixed plumes of chlorinated organics and oxidized metals are a common contaminant at many sites. The oxidized metals can be mediated by the establishment of moderately reducing conditions. The chlorinated organics have been demonstrated to be degradable by specific dechlorinating microrganisms in anaerobic environment such as Dehalococcoides sp. Enhanced biological dechlorination requires the presence of an effective electron donor to provide molecular hydrogen (H2) to completely degrade chlorinated ethenes. Distribution of the electron donor results in the biologically mediated establishment of highly reducing conditions in the treatment zone. This process also results in the reduction and precipitation of the oxidized metals via sulphate-reducing conditions. Peroxychem LLC has developed an innovative electron donor, ELS® Microemulsion Reagent (ELS) for in situ treatment of chlorinated organics and metals. This substrate has been successfully applied at numerous sites to address a variety of contaminants. ELS® is an organic electron donor composed of an easily fermentable organic substrate based on lecithin, and designed to enhance in situ anaerobic bioremediation aquifers contaminated by organochlorine compounds and heavy metals such as hexavalent chromium Cr[VI]. The product is easy to mix, dilute and inject into the subsurface. Once in the groundwater, indigenous microorganisms utilize ELS to rapidly generate highly reducing conditions, favoring biotic dechlorination reactions and the reduction of oxidized metals such as Cr[VI]. This innovative technology was successfully applied to a former manufacturing site in the center of Italy, where groundwater was historically contaminated with Tetrachloroethylene (PCE > 5.5 milligrams per Liter; mg/L), Trichloroethylene (TCE > 2 mg/L), 1,2-Dichloroethene (1,2-DCE > 1 mg/L) and, to a lesser extent, Vinyl Chloride (VC) and 1,2-Dichloropropane (DP). A pump-and-treat system (P&T) installed in the source was active as a source containment measure and to speed up the overall groundwater remediation. However, there was concern that the pumping could affect the ELS treatment effectiveness because of the increased groundwater flow velocity and the potential for removal of the injected bioremediation substrate. To mitigate this potential some wells were switched off the flow rates of others was adjusted to ensure compatibility with the planned product injection. In particular, an upstream low-flow-rate pump and treat system was maintained over the ELS® treatment period, primarily to delay the fast-downstream diffusion of the amendments in the aquifer, thus enhancing the source treatment. Following the calibration of the P&T system, approximately 4,900 kg of ELS® concentration was injected under high pressure at 51 locations into the source area. In about 12 months from injection of ELS® Microemulsion into the groundwater in the main source area, concentrations of PCE, TCE and the recognized catabolites, such as DCE and VC, rapidly reduced, compared to the pre-treatment concentrations, until they reached the statutory national limits (CSC D.lgs 152/06) in the main monitoring piezometers of the area, also highlighting the establishment of clear and enhanced biotic reducing conditions. No rebound effects have been observed in the next three years of monitoring.

The negative consequences of unintentional antibiotic exposure to humans and the ecosystem have raised wide concerns due to their presence in groundwater in large quantities. Recent research has focused on finding low-cost materials for the remediation of groundwater by removing unwanted antibiotics. In this study, Cement Kiln Dust (CKD), currently seen only as a waste by-product of the cement industry and environmental pollutant, has been tested for its potential in removing contaminants from water by way of PRB filtering. The results have been calculated using the Langmuir model, and have showed that at pH 7.0, 60 mg/g was the maximum adsorption capacity. CKD dosage and pH have affected the adsorption process significantly. The performance of PRB has been also affected by initial concentration, influent, and flow rate. The data have been also modelled using COMSOL Multiphysics 3.5a. This model has been integrated with the advection dispersion equation through the Langmuir isotherm. The integrated model has been found to be an effective and efficient tool for describing the migration of contaminants spatially and temporally in the experimental set-up, a one-dimensional packed column. A good agreement has been recognized between the predicted and the measured results of R2 ≥ 0.989 for the breakthrough curves. Finally, the predicted and the experimental results indicate that there is a high affinity of binding sites on CKD for meropenem. [ABSTRACT FROM AUTHOR]

• Fe-based co-precipitation of As is widely applied to remove As from groundwater. • This method is easy to deploy, but consists of complicated co-occurring reactions. • Synchrotron techniques have produced new molecular-scale insights in these reactions. • We critically review the reactions underpinning Fe-based co-precipitation of As. • Knowledge gaps are identified and future research directions are proposed. The co-precipitation of Fe(III) (oxyhydr)oxides with arsenic (As) is one of the most widespread approaches to treat As-contaminated groundwater in both low- and high-income settings. Fe-based co-precipitation of As occurs in a variety of conventional and decentralized treatment schemes, including aeration and sand filtration, ferric chloride addition and technologies based on controlled corrosion of Fe(0) (i.e., electrocoagulation). Despite its ease of deployment, Fe-based co-precipitation of As entails a complex series of chemical reactions that often occur simultaneously, including electron-transfer reactions, mineral nucleation, crystal growth, and As sorption. In recent years, the growing use of sophisticated synchrotron-based characterization techniques in water treatment research has generated new detailed and mechanistic insights into the reactions that govern As removal efficiency. The purpose of this critical review is to synthesize the current understanding of the molecular-scale reaction pathways of As co-precipitation with Fe(III), where the source of Fe(III) can be ferric chloride solutions or oxidized Fe(II) sourced from natural Fe(II) in groundwater, ferrous salts or controlled Fe(0) corrosion. We draw primarily on the mechanistic knowledge gained from spectroscopic and nano-scale investigations. We begin by describing the least complex reactions relevant in these conditions (Fe(II) oxidation, Fe(III) polymerization, As sorption in single-solute systems) and build to multi-solute systems containing common groundwater ions that can alter the pathways of As uptake during Fe(III) co-precipitation (Ca, Mg bivalent cations; P, Si oxyanions). We conclude the review by providing a perspective on critical knowledge gaps remaining in this field and new research directions that can further improve the understanding of As removal via Fe(III) co-precipitation. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Fe doping greatly enhanced the activity of NC catalysts toward Oxone activation. • Generation of Fe(IV)=O and 1O 2 were identified by experiments and DFT calculations. • Phenolic compounds were efficiently degraded with a notable decrease in biotoxicity. • The prepared Fe-3%@NC-700 catalyst had a long-term activity for Oxone activation. Iron-based catalysts are widely used in peroxysulfate-based AOPs but suffering from low catalytic performance at neutral pH conditions, which limits the application in groundwater remediation. Herein, this study investigated the efficacy, mechanism and long-term durability of Fe-doped nitrogen carbon (Fe@NC) armor catalysts toward peroxysulfate activation for the degradation of anthropogenic phenolics (APs) in groundwater matrices. The results showed that nonradical activation of Oxone (i.e., HSO 5 –) was obtained over the as-prepared Fe-3 % @NC-700 catalyst, high-valent Fe species (Fe(IV) O) and 1O 2 were identified as the dominant reactive species for the efficient degradation of APs by experiments and density functional theory (DFT) calculations. Notably, the DFT results indicated that HSO 5 – was favorably adsorbed on the Fe atoms owing to the electrostatic interaction, which transformed exothermically into SO 4 2– and 1O 2 over Fe 3 C, accompanied by the generation of Fe(IV) O. Additionally, the Fe-3 % @NC-700 catalyst displayed long-term activity for in situ activation of Oxone in groundwater matrices without pH adjustment, resulting in ΔAPs: ΔOxone stoichiometry efficiencies at 4.2–5.0 %. Wheat seeds germination tests revealed that the biotoxicity of the treated water was reduced notably by the present catalytic system, which holds large potential application in treatment of APs-contaminated groundwater. [ABSTRACT FROM AUTHOR]

According to the Health Regulations of 20 April 2010, the concentration of manganese in water must not exceed 0.05 mg/l. This condition forces underground water treatment and the required concentrations. For this purpose, popular filter materials are available on the domestic market. Authors in the study conducted experiments on two filter beds. The first was the G-1 catalytic mass, the second was the Crystal-Right. Thus, this paper presents the methodology of the study, the characteristics of the studied fields and the results of water tests, including the content of manganese in the process after filtration.

Fluoride contamination in groundwater is a major problem in many parts of the World. Several novel nano- and composite materials are produced and tested for removal of fluoride from water. However, not many of these techniques are applied in natural groundwater conditions that are contaminated with fluoride. Thus, in this study, the main focus is to study systematically the performance of the cerium impregnated activated carbon-based novel composite for fluoride removal from the contaminated groundwater. To achieve the objective, first, several groundwater samples that are contaminated with fluoride are collected from two different states in India for detail analysis. Then, fluoride removal efficiencies by the cerium-impregnated activated carbon composite under the groundwater conditions are evaluated, and the possible factors affecting fluoride removal are identified. Pre-treatment of groundwater by adding selected acid to adjust the pH level of natural water is adopted to enhance the fluoride removal efficiency by the composite. It is found that the fluoride concentration in groundwater is strongly associated with pH value, alkalinity and sodium ions in the groundwater. Furthermore, it is also observed that fluoride removal efficiency reduces significantly under the groundwater condition. The presence of excessive amount of bicarbonate and carbonate (or alkalinity) and the high value of pH are the major factors responsible for the reduction in the sorption capacity. Acid treatment, which resulted in a reduction in pH and alkalinity of groundwater, has improved the fluoride removal efficiency by the composite significantly. However, leaching of cerium is observed in a few cases, which is likely to be dependent on the initial fluoride concentration. [ABSTRACT FROM AUTHOR]

The paper concerns the experimental research related to the removal of color and permanganate index (CODMn) in the presence of iron and manganese from the underground water by means of coagulation and ozonation. The tests were carried out on a laboratory and technical scale in the real underground water treatment system. Ozone, as a strong oxidizing agent, was used to reduce the color intensity and to convert the iron Fe2+ and manganese ions Mn2+ to Fe(OH)3 and MnO2, respectively. In order to optimally remove the color to a value below 15 mg/L, the ozone dose of 3 mg/L was sufficient, which also ensured the proper removal of iron and manganese, by 94% and 83%, respectively. However, ozonation conducted under these conditions, did not provide sufficient removal of organic compounds expressed as CODMn below the assumed value of 3 mg/L. The effect of aluminum sulfate and polyaluminum chloride (PAC) was also studied, as a result of which it was found that polyaluminum chloride proved to be more effective reagent. Under the technical conditions of water purification at a dose of 16 mg/L coagulant, the efficiency of color removal was 65.2% and CODMn – 50.8%, which ensured that the values of the tested indicators in the purified water were maintained below the permissible level. [ABSTRACT FROM AUTHOR]

In the advanced oxidation processes, using persulfate (PS) as a radical precursor for pollutant degradation in groundwater has received increasing attention. In this study, zeolite supported nZVI composites (Z/nZVI) were synthesized through an ion exchange and borohydride reduction method to investigate their ability to activate PS for the TCE degradation. Based on preliminary screening of the PS activation by the Z/nZVI (PS-Z/nZVI) system in terms of TCE degradation, Z/nZVI composite with a zeolite to nZVI mass ratio of 1:1 (Z/nZVI (1)) was optimized as the best composition and chosen for further characterization and examination. Especially, for this PS-Z/nZVI system, PS concentration, solution matrix effects (i.e., solution pH, coexisting anions and natural organic matter) were studied. Characterization results revealed that the aggregation of nZVI particles was alleviated and they were good dispersed on the zeolite sheet with a large SSA (159.49 m2/g) compared to the unsupported nZVI (8.77 m2/g). The synthesized Z/nZVI (1) composite exhibited excellent activated ability towards PS (1.5 mM) and effectively degraded 98.8% of TCE at pH 7 within 120 min. The PS-Z/nZVI system was observed to operate effectively over a wide range of pH (i.e., 4–7) for TCE degradation. Moreover, the presence of nitrates (1 mM) and bicarbonates (10 mM) decreased the TCE degradation efficiency to 91.5% and 59.6%, respectively. Scavenger tests demonstrated that both sulfate and hydroxyl radicals participated in the TCE degradation. The ion chromatography analysis suggested the formation of oxalic acid and formic acid as the reaction intermediates during the TCE degradation process in the PS-Z/nZVI system. Unlabelled Image • Zeolite supported nZVI were synthesized and alleviated the nZVI aggregation. • Zeolite supported nZVI (1:1) composites showed excellent ability for PS activation. • PS-Z/nZVI system showed high TCE degradation ability at pH 4 to 7. • High nitrate and bicarbonate concentrations caused inhibition in TCE degradation. • Both SO 4 − and OH contributed to the TCE degradation in the PS-Z/nZVI system. [ABSTRACT FROM AUTHOR]

In this work, we combined macroscopic measurements of precipitate aggregation and chemical composition (Mn/Fe solids ratio) with Fe and Mn K-edge X-ray absorption spectroscopy to investigate the solids formed by co-oxidation of Fe(II) and Mn(II) with O 2 , MnO 4 , and HOCl in the presence of groundwater ions. In the absence of the strongly sorbing oxyanions, phosphate (P) and silicate (Si), and calcium (Ca), O 2 and HOCl produced suspensions that aggregated rapidly, whereas co-oxidation of Fe(II) and Mn(II) by MnO 4 generated colloidally stable suspensions. The aggregation of all suspensions decreased in P and Si solutions, but Ca counteracted these oxyanion effects. The speciation of oxidized Fe and Mn in the absence of P and Si also depended on the oxidant, with O 2 producing Mn(III)-incorporated lepidocrocite (Mn/Fe = 0.01–0.02 mol/mol), HOCl producing Mn(III)-incorporated hydrous ferric oxide (HFO) (Mn/Fe = 0.08 mol/mol), and MnO 4 producing poorly-ordered MnO 2 and HFO (Mn/Fe > 0.5 mol/mol). In general, the presence of P and Si decreased the crystallinity of the Fe(III) phase and increased the Mn/Fe solids ratio, which was found by Mn K-edge XAS analysis to be due to an increase in surface-bound Mn(II). By contrast, Ca decreased the Mn/Fe solids ratio and decreased the fraction of Mn(II) associated with the solids, suggesting that Ca and Mn(II) compete for sorption sites. Based on these results, we discuss strategies to optimize the design (i.e. filter bed operation and chemical dosing) of water treatment plants that aim to remove Fe(II) and Mn(II) by co-oxidation. Image 1 • Precipitates formed by co-oxidation of Fe(II) and Mn(II) were investigated. • Phosphate and silicate decreased the crystallinity and aggregation state of solids. • The Mn/Fe solids ratio varied with oxidant and solution composition. • Implications for water treatment are discussed. [ABSTRACT FROM AUTHOR]

Groundwater is essential for the provision of drinking water in many areas around the world. The performance of the groundwater-bearing aquifer relies on the ecosystem services provided by groundwater-related organisms. Therefore, if remediation of contaminated groundwater is necessary, the remediation method has to be carefully selected to avoid risk-risk trade-offs that might impact these ecosystems. In the present study, the environmental risk of the in situ remediation agent Carbo-Iron was performed. Carbo-Iron® is a composite of zero valent nano-iron and active carbon. Existing ecotoxicity data were complemented by studies with Daphnia magna (Crustacea), Scenedesmus vacuolatus (Algae), Chironomus riparius (Insecta) and nitrifying soil microorganisms. The predicted no effect concentration of 0.1 mg/L was derived from acute and chronic ecotoxicity studies. It was compared to measured and modelled environmental concentrations of Carbo-Iron applied in a groundwater contaminated with chlorohydrocarbons in a field study and risk ratios were derived. A comprehensive assessment approach was developed further based on existing strategies and used to identify changes of the environmental risk due to the remediation of the contaminated site with Carbo-Iron. With the data used in the present study, the total environmental risk decreased by approximately 50% in the heavily contaminated zones after the application of Carbo-Iron. Thus, based on the results of the present study, the benefit of remediation with Carbo-Iron seems to outweigh its negative effects on the environment. Unlabelled Image • Environmental concentrations for the nFe0 agent Carbo-Iron derived from field study. • Ecotoxicity data set for effects assessment was completed. • Standard risk assessment could be performed for a novel remediation agent. • Evaluation of benefit and risk of groundwater treatment for the environment. • Method applicable to identify environmental risks of other treatment techniques. [ABSTRACT FROM AUTHOR]

Abstract One of the challenges in the petroleum hydrocarbon contaminated groundwater remediation by oxygen releasing compounds (ORCs) is to identify the remediation mechanism and determine the impact of ORCs on the environment and the intrinsic groundwater microorganisms. In this research, the application of encapsulated magnesium peroxide (MgO 2) nanoparticles in the permeable reactive barrier (PRB) for bioremediation of the groundwater contaminated by toluene and naphthalene was studied in the continuous flow sand-packed plexiglass columns within 50 d experiments. For the biodiversity studies, next generation sequencing (NGS) of the 16S rRNA gene was applied. The results showed that naphthalene was metabolized (within 20 days) faster than toluene (after 30 days) by microorganisms of the aqueous phase. By comparing the contaminant removal in the biotic (which resulted in the complete contaminant removal) and abiotic (around 32% removal for naphthalene and 36% for toluene after 50 d) conditions, the significant role of microorganisms on the decontamination process was proved. Furthermore, the attached microbial communities on the porous media were visualized by scanning electron microscopy (SEM). Microbial community structure analysis by NGS technique revealed that the microbial species which were able to degrade toluene and naphthalene such as P. putida and P. mendocina respectively were stimulated by addition of MgO 2 nanoparticles. The presented study resulted in a momentous insight into the application of MgO 2 nanoparticles in the hydrocarbon compounds removal from groundwater. Graphical abstract Unlabelled Image Highlights • Magnesium peroxide is able to remove BTEX and PAH from groundwater. • Encapsulation of MgO 2 improves the groundwater remediation. • The intrinsic groundwater flora plays a key role in the bioremediation process. • Groundwater microbial structure is changed within the remediation according to NGS. [ABSTRACT FROM AUTHOR]

Subgrade biogeochemical reactors (SBGRs) are an in situ remediation technology shown to be effective in treating contaminant source areas and groundwater hot spots, while being sustainable and economical. This technology has been applied for over a decade to treat chlorinated volatile organic compound source areas where groundwater is shallow (e.g., less than approximately 30 feet below ground surface [ft bgs]). However, this article provides three case studies describing innovative SBGR configurations recently developed and tested that are outside of this norm, which enable use of this technology under more challenging site conditions or for treatment of alternative contaminant classes. The first SBGR case study addresses a site with groundwater deeper than 30 ft bgs and limited space for construction, where an SBGR column configuration reduced the maximum trichloroethene (TCE) groundwater concentration from 9,900 micrograms per liter (μg/L) to <1 μg/L (nondetect) within approximately 15 months. The second SBGR is a recirculating trench configuration that is supporting remediation of a 5.7‐acre TCE plume, which has significant surface footprint constraints due to the presence of endangered species habitat. The third SBGR was constructed with a new amendment mixture and reduced groundwater contaminant concentrations in a petroleum hydrocarbon source area by over 97% within approximately 1 year. Additionally, a summary is provided for new SBGR configurations that are planned for treatment of additional classes of contaminants (e.g., hexavalent chromium, 1,4‐dioxane, dissolved explosives constituents, etc.). A discussion is also provided describing research being conducted to further understand and optimize treatment mechanisms within SBGRs, including a recently developed sampling approach called the aquifer matrix probe. [ABSTRACT FROM AUTHOR]

This article reports the high performance of a solid polymer electrolyte cell, equipped with a Nafion® N117 membrane packed between a Nb/boron‐doped diamond (Nb/BDD) mesh anode and a Ti/RuO2 mesh cathode, to degrade the insecticide imidacloprid spiked at 1.2–59.2 mg L−1 into low conductivity groundwater by electrochemical oxidation. The natural water matrix was first softened using valorized industrial waste in the form of zeolite as reactive sorbent. Total removal of the insecticide, always obeying pseudo‐first‐order kinetics, and maximum mineralization degrees of 70 %–87 % were achieved, with energy consumption of 26.4±1.6 kWh m−3. Active chlorine in the bulk and.OH at the BDD surface were the main oxidants. Comparative studies using simulated water with analogous anions content revealed that the natural organic matter interfered in the groundwater treatment. Trials carried out in ultrapure water showed the primary conversion of the initial N and Cl atoms of imidacloprid to NO3− and Cl− ions, being the latter anion eventually transformed into ClO3− and ClO4− ions. 6‐Chloro‐nicotinonitrile, 6‐chloro‐pyridine‐3‐carbaldehyde, and tartaric acid were identified as oxidation products. Break new ground: a solid polymer electrolyte (SPE) cell with a Nb/boron doped diamond mesh anode, a Ti/RuO2 mesh cathode, and a Nafion® N117 membrane is used to effectively degrade and mineralize the drug imidacloprid spiked into softened groundwater with very low conductivity under galvanostatic conditions. [ABSTRACT FROM AUTHOR]

Abstract Arsenic (As) contamination in groundwater is a significant health and environmental concern worldwide because of its wide distribution and toxicity. The fate and mobility of As is greatly influenced by its interaction with redox-active mineral phases, among which green rust (GR), an FeII-FeIII layered double hydroxide mineral, plays a crucial role. However, the controlling parameters of As uptake by GR are not yet fully understood. To fill this gap, we determined the interfacial reactions between GR sulfate (GR SO4) and aqueous inorganic As(III) and As(V) through batch adsorption experiments, under environmentally-relevant groundwater conditions. Our data showed that, under anoxic conditions, GR SO4 is a stable and effective mineral adsorbent for the removal of As(III) and As(V). At an initial concentration of 10 mg L−1, As(III) removal was higher at alkaline pH conditions (~95% removal at pH 9) while As(V) was more efficiently removed at near-neutral conditions (>99% at pH 7). The calculated maximum As adsorption capacities on GR SO4 were 160 mg g−1 (pH 8–9) for As(III) and 105 mg g−1 (pH 7) for As(V). The presence of other common groundwater ions such as Mg2+ and PO 4 3− reduces the efficiency of As removal, especially at high ionic strengths. Long-term batch adsorption experiments (up to 90 days) revealed that As-interacted GR SO4 remained stable, with no mineral transformation or release of adsorbed As species. Overall, our work shows that GR SO4 is one of the most effective As adsorbents among iron (oxyhydr)oxide phases. Graphical abstract Unlabelled Image Highlights • GR SO4 is among the best performing Fe-bearing minerals for As removal. • Both pH and the presence of competing aqueous ions affect As removal efficiency. • Long term experiments showed that GR SO4 with As adsorbed onto its surface is stable for up to 90 days. • High-resolution electron microscopy revealed that As is preferentially adsorbed at the GR particle edges. [ABSTRACT FROM AUTHOR]