Search

Arsenic (As) removal studies were carried out through batch experiments to investigate the performance of the locally available calcined magnesite mineral rocks from Tanzania. Natural water from a stream source in Tanzania and the prepared synthetic water at the laboratory were used for the studies. Parameters such as initial As concentration, calcined magnesite dosage, contact time and pH were evaluated for As removal using an overhead reax2 shaker. Arsenic concentration was reduced from 5.3 to 1.1 mg/L As(V) at 180 min when 0.5 g/L calcined magnesite was applied to a synthetic water sample, whereas the concentration of 117 & mu;g/L As(V) and 5.2 & mu;g/L As(III) was reduced to below 0.1 & mu;g/L in natural water. An increase in calcined magnesite dosage resulted in increased As removal up to below 0.01 mg/L. The calcined magnesite raised the pH of the water sample from 6.8 to 10 when the applied dosage increased between 0.002 g/L and 0.05 g/L. The pH was constant at around 10 even when the amount of 0.05 g/L was added 2000 times. Despite the high pH, the amount of magnesium released in water was low. The calcination of magnesite at 500 degrees C increased surface area by 4 times as compared to the natural magnesite and X-ray diffraction showed presence of MgCO3 phase as the dominant phase at this temperature. The reaction kinetics of As removal on 0.5 g/L calcined magnesite fitted with the pseudo-second-order (R2 = 0.96). Reaction isotherm was strongly fitted with Freundlich isotherm (R2 = 0.98). Linear regression and artificial intelligence neural network showed the As removal was influenced by both contact time and pH. Arsenic can be removed from As water using calcined magnesite and will be suitable for water treatment around gold mining areas., QC 20230731

The presence of high levels of carcinogenic metalloid arsenic (As) in the groundwater system of Bangladesh has been considered as one of the major environmental disasters in this region. Many parts of Bangladesh have extensively reported the presence of high levels of arsenic in the groundwater due to both geological and anthropogenic activities. In this paper, we reviewed the available literature and scientific information regarding arsenic pollution in Bangladesh, including arsenic chemistry and occurrences. Along with using As-rich groundwater as a drinking-water source, the agricultural activities and especially irrigation have greatly depended on the groundwater resources in this region due to high water demands for ensuring food security. A number of investigations in Bangladesh have shown that high arsenic content in both soil and groundwater may result in high levels of arsenic accumulation in different plants, including cereals and vegetables. This review provides information regarding arsenic accumulation in major rice varieties, soil-groundwater-rice arsenic interaction, and past arsenic policies and plans, as well as previously implemented arsenic mitigation options for both drinking and irrigation water systems in Bangladesh. In conclusion, this review highlights the importance and necessity for more in-depth studies as well as more effective arsenic mitigation action plans to reduce arsenic incorporation in the food chain of Bangladesh.

The presence of high levels of carcinogenic metalloid arsenic (As) in the groundwater system of Bangladesh has been considered as one of the major environmental disasters in this region. Many parts of Bangladesh have extensively reported the presence of high levels of arsenic in the groundwater due to both geological and anthropogenic activities. In this paper, we reviewed the available literature and scientific information regarding arsenic pollution in Bangladesh, including arsenic chemistry and occurrences. Along with using As-rich groundwater as a drinking-water source, the agricultural activities and especially irrigation have greatly depended on the groundwater resources in this region due to high water demands for ensuring food security. A number of investigations in Bangladesh have shown that high arsenic content in both soil and groundwater may result in high levels of arsenic accumulation in different plants, including cereals and vegetables. This review provides information regarding arsenic accumulation in major rice varieties, soil-groundwater-rice arsenic interaction, and past arsenic policies and plans, as well as previously implemented arsenic mitigation options for both drinking and irrigation water systems in Bangladesh. In conclusion, this review highlights the importance and necessity for more in-depth studies as well as more effective arsenic mitigation action plans to reduce arsenic incorporation in the food chain of Bangladesh.

Chemical precipitation is one of the most widely known methods for treatment of industrial wastewaters with high sulphate content, where sulphate can be precipitated as practically insoluble ettringite (Ca₆Al₂(SO₄)₃(OH)₁₂·26H₂O). This treatment method is also widely recognised for solidifying hazardous components and toxic elements e.g. arsenic in wastewater. In the ettringite precipitation process, lime and aluminium salts are typically used as starting materials, in stoichiometric amounts to form ettringite from the sulphate-containing water, leading to a pH rise to ∼11.5 and ettringite precipitation. In the current study, for the first time, ye’elimite mineral (Ca₄Al₆O₁₂SO₄), also known as calcium sulfoaluminate (CSA) in cements, is used in order to investigate its suitability to form ettringite precipitate from sulphate and arsenic containing synthetic wastewater and industrial wastewater solutions. The dissolution of ye’elimite prior to dosing, optimal precipitation pH, and arsenic co-precipitation were studied. The effluent and precipitates were characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM-EDS) and inductively coupled plasma atomic emission spectroscopy (ICP-OES). The results showed that high percentage of sulphate removal (98% in the synthetic wastewater and 87% in the industrial wastewater) can be achieved using ye’elimite as the aluminium source in ettringite precipitation. Additionally, up to 95% arsenic removal was achieved in arsenic co-precipitation experiments from the synthetic wastewater. The current developed technology can be used as a novel ecological and cost-effective approach for removal of sulphate and toxic elements from wastewater.

The presence of high levels of carcinogenic metalloid arsenic (As) in the groundwater system of Bangladesh has been considered as one of the major environmental disasters in this region. Many parts of Bangladesh have extensively reported the presence of high levels of arsenic in the groundwater due to both geological and anthropogenic activities. In this paper, we reviewed the available literature and scientific information regarding arsenic pollution in Bangladesh, including arsenic chemistry and occurrences. Along with using As-rich groundwater as a drinking-water source, the agricultural activities and especially irrigation have greatly depended on the groundwater resources in this region due to high water demands for ensuring food security. A number of investigations in Bangladesh have shown that high arsenic content in both soil and groundwater may result in high levels of arsenic accumulation in different plants, including cereals and vegetables. This review provides information regarding arsenic accumulation in major rice varieties, soil-groundwater-rice arsenic interaction, and past arsenic policies and plans, as well as previously implemented arsenic mitigation options for both drinking and irrigation water systems in Bangladesh. In conclusion, this review highlights the importance and necessity for more in-depth studies as well as more effective arsenic mitigation action plans to reduce arsenic incorporation in the food chain of Bangladesh.

The presence of high levels of carcinogenic metalloid arsenic (As) in the groundwater system of Bangladesh has been considered as one of the major environmental disasters in this region. Many parts of Bangladesh have extensively reported the presence of high levels of arsenic in the groundwater due to both geological and anthropogenic activities. In this paper, we reviewed the available literature and scientific information regarding arsenic pollution in Bangladesh, including arsenic chemistry and occurrences. Along with using As-rich groundwater as a drinking-water source, the agricultural activities and especially irrigation have greatly depended on the groundwater resources in this region due to high water demands for ensuring food security. A number of investigations in Bangladesh have shown that high arsenic content in both soil and groundwater may result in high levels of arsenic accumulation in different plants, including cereals and vegetables. This review provides information regarding arsenic accumulation in major rice varieties, soil-groundwater-rice arsenic interaction, and past arsenic policies and plans, as well as previously implemented arsenic mitigation options for both drinking and irrigation water systems in Bangladesh. In conclusion, this review highlights the importance and necessity for more in-depth studies as well as more effective arsenic mitigation action plans to reduce arsenic incorporation in the food chain of Bangladesh.

The presence of high levels of carcinogenic metalloid arsenic (As) in the groundwater system of Bangladesh has been considered as one of the major environmental disasters in this region. Many parts of Bangladesh have extensively reported the presence of high levels of arsenic in the groundwater due to both geological and anthropogenic activities. In this paper, we reviewed the available literature and scientific information regarding arsenic pollution in Bangladesh, including arsenic chemistry and occurrences. Along with using As-rich groundwater as a drinking-water source, the agricultural activities and especially irrigation have greatly depended on the groundwater resources in this region due to high water demands for ensuring food security. A number of investigations in Bangladesh have shown that high arsenic content in both soil and groundwater may result in high levels of arsenic accumulation in different plants, including cereals and vegetables. This review provides information regarding arsenic accumulation in major rice varieties, soil-groundwater-rice arsenic interaction, and past arsenic policies and plans, as well as previously implemented arsenic mitigation options for both drinking and irrigation water systems in Bangladesh. In conclusion, this review highlights the importance and necessity for more in-depth studies as well as more effective arsenic mitigation action plans to reduce arsenic incorporation in the food chain of Bangladesh.

Arsenic (As) removal is a huge challenge, since several million people are potentially exposed (>10 μg/L World Health Organization guideline limit) through As contaminated drinking water worldwide. Review attempts to address the present situation of As removal, considering key topics on nano-technological and biological process and current progress and future perspectives of possible mitigation options have been evaluated. Different physical, chemical and biological methods are available to remove As from contaminated water/soil/wastes, where removal efficiency mainly depends on absorbent type, initial adsorbate concentration, speciation and interfering species. Oxidation is an important pretreatment step in As removal, which is generally achieved by several media such as O2/O3, HClO, KMnO4 and H2O2. The Fe-based-nanomaterials (α/β/γ-FeOOH, Fe2O3/Fe3O4–γ-Fe2O3), Fe-based-composite-compounds, activated-Al2O3, HFO, Fe-Al2O3, Fe2O3-impregnated-graphene-aerogel, iron-doped-TiO2, aerogel-based- CeTiO2, and iron-oxide-coated-manganese are effective to remove As from contaminated water. Biological processes (phytoremediation/microbiological) are effective and ecofriendly for As removal from water and/or soil environment. Microorganisms remove As from water, sediments and soil by metabolism, detoxification, oxidation-reduction, bio-adsorption, bio-precipitation, and volatilization processes. Ecofriendly As mitigation options can be achieved by utilizing an alternative As-safe-aquifer, surface-water or rainwater-harvesting. Application of hybrid (biological with chemical and physical process) and Best-Available-Technologies (BAT) can be the most effective As removal strategy to remediate As contaminated environments., QC 20210217

The presence of high levels of arsenic in groundwater, an otherwise preferred drinking water source, urges the need for innovative and highly efficient (in terms of chemical use and energy consumption) technologies to remove arsenic during drinking water treatment. This research focussed on embedding iron electrocoagulation (Fe-EC) within a biologically active rapid sand filter (RSF) by submerging horizontally perforated (Fe(0)) electrodes. These electrodes were designed in such a way that they could easily be submerged in the filter bed during backwashing. Based on As(V)/As(III) adsorption characteristics and iron removal mechanisms in a RSF it was hypothesized that the arsenic removal could be enhanced by placing the electrodes in the biologically active filter bed instead of in the supernatant. Iron to arsenic ratios (Fe:As) were reduced from 18.3 to 15.0 when the electrodes were placed in the filter bed instead of in the supernatant (for a charge dosage of 6.4 C/L and 150 µg/L As(III) in the influent), showing an improved arsenic removal efficiency. The arsenic oxidizing bacteria (AsOB) on top of the electrodes oxidized As(III) to As(V) (over 85 to 97% oxidation), which was subsequently removed by the iron that got released (by the embedded Fe-EC) and formed precipitates in the filter bed. The major drawback of embedding electrodes in the filter bed is the increase in energy consumption due to the increase in operating voltage. As(V) flowthrough experiments showed that the arsenic removal can be improved by lowering the pH from 8.0 to 7.0 and by increasing the charge dosage from 6.4 to 9.4 C/L. It was shown that besides arsenic removal efficiency, parameters as iron dosage, energy consumption, sludge production, and clogging have a significant relevance. Iron-As(V) experiments showed the flaws of the integrated system related to a partly homogeneous iron release and improper mixing, resulting in a decrease in the arsenic removal efficiency. Further, ways to pote, Water Management

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

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

The presence of high levels of arsenic in groundwater, an otherwise preferred drinking water source, urges the need for innovative and highly efficient (in terms of chemical use and energy consumption) technologies to remove arsenic during drinking water treatment. This research focussed on embedding iron electrocoagulation (Fe-EC) within a biologically active rapid sand filter (RSF) by submerging horizontally perforated (Fe(0)) electrodes. These electrodes were designed in such a way that they could easily be submerged in the filter bed during backwashing. Based on As(V)/As(III) adsorption characteristics and iron removal mechanisms in a RSF it was hypothesized that the arsenic removal could be enhanced by placing the electrodes in the biologically active filter bed instead of in the supernatant. Iron to arsenic ratios (Fe:As) were reduced from 18.3 to 15.0 when the electrodes were placed in the filter bed instead of in the supernatant (for a charge dosage of 6.4 C/L and 150 µg/L As(III) in the influent), showing an improved arsenic removal efficiency. The arsenic oxidizing bacteria (AsOB) on top of the electrodes oxidized As(III) to As(V) (over 85 to 97% oxidation), which was subsequently removed by the iron that got released (by the embedded Fe-EC) and formed precipitates in the filter bed. The major drawback of embedding electrodes in the filter bed is the increase in energy consumption due to the increase in operating voltage. As(V) flowthrough experiments showed that the arsenic removal can be improved by lowering the pH from 8.0 to 7.0 and by increasing the charge dosage from 6.4 to 9.4 C/L. It was shown that besides arsenic removal efficiency, parameters as iron dosage, energy consumption, sludge production, and clogging have a significant relevance. Iron-As(V) experiments showed the flaws of the integrated system related to a partly homogeneous iron release and improper mixing, resulting in a decrease in the arsenic removal efficiency. Further, ways to pote, Water Management

Die Adsorption von Arsen, einem toxischen Wasserinhaltsstoff in vielen Oberflächen- und Grundwasserressourcen, wird an zwei feinkörnigen Eisenoxyhydroxiden mittels Adsorptionstests untersucht. Die Arsenadsorption in einem durchmischten Schlammbettreaktor wird mit einer getauchten Mikrofiltrationsmembran (MF) kombiniert, um ein innovatives und kostengünstiges Wasseraufbereitungssystem zu entwickeln. Experimentell bestimmte Arsenentfernungsraten werden unter Verwendung eines entwickelten mathematischen Modells genutzt, um die Aufbereitungsleistung unter verschiedenen Betriebsbedingungen zu modellieren. Diese Arbeit bestätigt, dass feinkörnige Eisenoxyhydroxide als aktuelle Reststoffe der herkömmlicher Adsorbentienproduktion, erfolgreich in dem entwickelten Wasseraufbereitungssystem eingesetzt werden können, um so Trinkwassergrenzwerte von < 10 µg As/L zu erreichen, ohne dass es zu Fouling auf der MF-Membran kommt., The adsorption of arsenic, a toxic pollutant found in surface and groundwater resources, onto two micro-sized iron oxyhydroxides as adsorbents was investigated through batch adsorption tests. Moreover, arsenic adsorption in a slurry bed reactor was combined with a submerged microfiltration (MF) membrane unit to create an innovative and cost-effective water treatment system. Experimentally determined arsenic removal rates were modeled using a developed mathematical model. This work confirms that micro-sized iron oxyhydroxides, by-products of conventional adsorbent production processes, can successfully be employed in the proposed water treatment system to achieve a drinking water standard of < 10 µg As/L without fouling of the MF membrane, Deutscher Akademischer Austauschdienst (DAAD)

Arsenic (As) is a highly toxic element which naturally occurs in drinking water. In spite of substantial evidence on the association between many illnesses and chronic consumption of As, there is still a considerable uncertainty about the health risks due to low As concentrations in drinking water. In the Netherlands, drinking water companies aim to supply water with As concentration of <1 μg/L – a water quality goal which is tenfold more stringent than the current WHO guideline. This paper provides (i) an account on the assessed lung cancer risk for the Dutch population due to pertinent low-level As in drinking water and cost-comparison between health care provision and As removal from water, (ii) an overview of As occurrence and mobility in drinking water sources and water treatment systems in the Netherlands and (iii) insights into As removal methods that have been employed or under investigation to achieve As reduction to <1 µg/L at Dutch water treatment plants. Lowering of the average As concentration to <1μg/L in the Netherlands is shown to result in an annual benefit of 7.2–14 M€. This study has a global significance for setting drinking water As limits and provision of safe drinking water.

© 2020, The Author(s). Arsenic is among the major drinking water contaminants affecting populations in many countries because it causes serious health problems on long-term exposure. Two low-cost micro-sized iron oxyhydroxide-based adsorbents (which are by-products of the industrial production process of granular adsorbents), namely, micro granular ferric hydroxide (μGFH) and micro tetravalent manganese feroxyhyte (μTMF), were applied in batch adsorption kinetic tests and submerged microfiltration membrane adsorption hybrid system (SMAHS) to remove pentavalent arsenic (As(V)) from modeled drinking water. The adsorbents media were characterized in terms of iron content, BET surface area, pore volume, and particle size. The results of adsorption kinetics show that initial adsorption rate of As(V) by μTMF is faster than μGFH. The SMAHS results revealed that hydraulic residence time of As(V) in the slurry reactor plays a critical role. At longer residence time, the achieved adsorption capacities at As(V) permeate concentration of 10 μg/L (WHO guideline value) are 0.95 and 1.04 μg/mg for μGFH and μTMF, respectively. At shorter residence time of ~ 3 h, μTMF was able to treat 1.4 times more volumes of arsenic-polluted water than μGFH under the optimized experimental conditions due to its fast kinetic behavior. The outcomes of this study confirm that micro-sized iron oyxhydroxides, by-products of conventional adsorbent production processes, can successfully be employed in the proposed hybrid water treatment system to achieve drinking water guideline value for arsenic, without considerable fouling of the porous membrane.

Arsenic (As) is a highly toxic element which naturally occurs in drinking water. In spite of substantial evidence on the association between many illnesses and chronic consumption of As, there is still a considerable uncertainty about the health risks due to low As concentrations in drinking water. In the Netherlands, drinking water companies aim to supply water with As concentration of <1 μg/L – a water quality goal which is tenfold more stringent than the current WHO guideline. This paper provides (i) an account on the assessed lung cancer risk for the Dutch population due to pertinent low-level As in drinking water and cost-comparison between health care provision and As removal from water, (ii) an overview of As occurrence and mobility in drinking water sources and water treatment systems in the Netherlands and (iii) insights into As removal methods that have been employed or under investigation to achieve As reduction to <1 µg/L at Dutch water treatment plants. Lowering of the average As concentration to <1μg/L in the Netherlands is shown to result in an annual benefit of 7.2–14 M€. This study has a global significance for setting drinking water As limits and provision of safe drinking water., Geo-engineering

Ferric based coprecipitation-low pressure membrane filtration is a promising arsenic (As) removal method, however, membrane fouling mechanisms are not fully understood. In this study we investigated the effect of feed water composition and membrane pore size on arsenate [As(V)] removal and membrane fouling. We observed that As removal efficiency was independent of the membrane pore size because the size of the Fe(III) particles was larger than the pore size of the membranes, attributed to a high calcium concentration in the feed water. Arsenic coprecipitation with Fe(III) (oxyhydr)oxides rapidly reached equilibrium before membrane filtration, within 1 min. Therefore, As removal efficiency was not improved by increasing residence time before membrane filtration. The removal of As(V) was strongly dependent on feed water composition. A higher Fe(III) dose was required to reduce As(V) to sub-mu g/L levels for feed water containing higher concentration of oxyanions such as phosphate and silicate, and lower concentration of cations such as calcium. Cake-layer formation was observed to be the predominant membrane fouling mechanism., QC 20200525

Removal of arsenic (As) from water by co-precipitation with Fe(III) (oxyhydr)oxides is a widely used technique in water treatment. Nevertheless, As removal efficiency appears to be sensitive to the composition of the water matrix. The aim of this study was to gain a deeper understanding of the independent and combined effects of silicate (Si), phosphate (P), natural organic matter (NOM) and calcium (Ca) on arsenate [As(V)] co-precipitation efficiency and the size of Fe(III) precipitates. We found that, in complex solutions, containing multiple solutes and high levels of Ca, (variations in) Si and P concentrations reduce As(V) removal to some extent, mainly due to a decreased adsorption of As(V) onto Fe(III) precipitates. On the other hand, NOM concentrations reduced As(V) removal to a much greater extent, due to possible formation of mobile Fe(III)-NOM complexes that were difficult to remove by filtration. These findings have a great significance for predicting As(V) removal as a function of seasonal and process-related water quality changes at water treatment plants., QC 20200218

Arsenic (As) is a highly toxic element which naturally occurs in drinking water. In spite of substantial evidence on the association between many illnesses and chronic consumption of As, there is still a considerable uncertainty about the health risks due to low As concentrations in drinking water. In the Netherlands, drinking water companies aim to supply water with As concentration of < 1 mu g/L - a water quality goal which is tenfold more stringent than the current WHO guideline. This paper provides (i) an account on the assessed lung cancer risk for the Dutch population due to pertinent low-level As in drinking water and cost-comparison between health care provision and As removal from water, (ii) an overview of As occurrence and mobility in drinking water sources and water treatment systems in the Netherlands and (iii) insights into As removal methods that have been employed or under investigation to achieve As reduction to < 1 mu g/L at Dutch water treatment plants. Lowering of the average As concentration to < 1 mu g/L in the Netherlands is shown to result in an annual benefit of 7.2-14 M(sic). This study has a global significance for setting drinking water As limits and provision of safe drinking water., QC 20200103

The processing of fine metallurgical dust by pyrometallurgical methods leads to the accumulation of impurities and deterioration in the quality of blister copper. Fine dust contains copper, zinc, lead, arsenic and iron. A hydrometallurgical method for the separation of the main components into the following products is proposed: copper-zinc residue, iron-arsenic residue, lead residue. The hydrometallurgical scheme consists of three stages of leaching: neutral and using sulfuric and nitric acids. When processing metallurgical dust according to the proposed scheme, a solution containing copper, zinc, iron and arsenic is formed, as well as a lead containing precipitate. Arsenic and iron are removed from the solution in the form of iron (III) arsenate, after which zinc and copper are precipitated. Lead in sediment is in carbonated form. The developed technology allows the extraction of: 87% copper, 88% zinc, 83% iron, 83% arsenic, 99% lead in individual products.

One of the promising applications of nanomaterials is to use them as catalysts and sorbents to remove toxic pollutants such as nitroaromatic compounds and heavy metal ions for environmental protection. This work reports the synthesis of Cu/CuO-deposited composite track-etched membranes through low-temperature annealing and their application in catalysis and sorption. The synthesized Cu/CuO/poly(ethylene terephthalate) (PET) composites presented efficient catalytic activity with high conversion yield in the reduction of nitro aryl compounds to their corresponding amino derivatives. It has been found that increasing the time of annealing raises the ratio of the copper(II) oxide (CuO) tenorite phase in the structure, which leads to a significant increase in the catalytic activity of the composites. The samples presented maximum catalytic activity after 5 h of annealing, where the ratio of CuO phase and the degree of crystallinity were 64.3% and 62.7%, respectively. The catalytic activity of pristine and annealed composites was tested in the reduction of 4-nitroaniline and was shown to remain practically unchanged for five consecutive test cycles. Composites annealed at 140 °C were also tested for their capacity to absorb arsenic(III) ions in cross-flow mode. It was observed that the sorption capacity of composite membranes increased by 48.7% compared to the pristine sample and reached its maximum after 10 h of annealing, then gradually decreased by 24% with further annealing. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.

Threats due to insufficient, inadequate and costlier methods of treating contaminants such as arsenic have emphasized the significance of optimizing and managing the processes adopted. This study was aimed at the complete elimination of arsenic from an aqueous medium with minimum energy consumption using the electrocoagulation process. Arsenic removal around 95% was rapidly attained for optimized conditions having a pH of 7, 0.46 A current intensity, 10 mg/L initial concentration and only 2 min of applied time duration using the energy of 3.1 watt-hour per gram of arsenic removed. Low values of applied current for longer durations resulted in the complete removal of arsenic with low energy consumption. Various hydroxide complexes including ferrous hydroxide and ferric hydroxide assisted in the removal of arsenic by adsorption along with co-precipitation. Surface models obtained were checked and found with a reasonably good fit having high values of coefficient of determination of 0.933 and 0.980 for removal efficiency and energy consumption, respectively. Adsorption was found to follow pseudo-first-order kinetics. Multivariate optimization proved it as a low-cost effective technology having an operational cost of 0.0974 Indian rupees (equivalent to USD 0.0013) per gram removal of arsenic. Overall, the process was well optimized using CCD based on response surface methodology., Threats due to insufficient, inadequate and costlier methods of treating contaminants such as arsenic have emphasized the significance of optimizing and managing the processes adopted. This study was aimed at the complete elimination of arsenic from an aqueous medium with minimum energy consumption using the electrocoagulation process. Arsenic removal around 95% was rapidly attained for optimized conditions having a pH of 7, 0.46 A current intensity, 10 mg/L initial concentration and only 2 min of applied time duration using the energy of 3.1 watt-hour per gram of arsenic removed. Low values of applied current for longer durations resulted in the complete removal of arsenic with low energy consumption. Various hydroxide complexes including ferrous hydroxide and ferric hydroxide assisted in the removal of arsenic by adsorption along with co-precipitation. Surface models obtained were checked and found with a reasonably good fit having high values of coefficient of determination of 0.933 and 0.980 for removal efficiency and energy consumption, respectively. Adsorption was found to follow pseudo-first-order kinetics. Multivariate optimization proved it as a low-cost effective technology having an operational cost of 0.0974 Indian rupees (equivalent to USD 0.0013) per gram removal of arsenic. Overall, the process was well optimized using CCD based on response surface methodology.

Removal of arsenic (As) from water by co-precipitation with Fe(III) (oxyhydr)oxides is a widely used technique in water treatment. Nevertheless, As removal efficiency appears to be sensitive to the composition of the water matrix. The aim of this study was to gain a deeper understanding of the independent and combined effects of silicate (Si), phosphate (P), natural organic matter (NOM) and calcium (Ca) on arsenate [As(V)] co-precipitation efficiency and the size of Fe(III) precipitates. We found that, in complex solutions, containing multiple solutes and high levels of Ca, (variations in) Si and P concentrations reduce As(V) removal to some extent, mainly due to a decreased adsorption of As(V) onto Fe(III) precipitates. On the other hand, NOM concentrations reduced As(V) removal to a much greater extent, due to possible formation of mobile Fe(III)–NOM complexes that were difficult to remove by filtration. These findings have a great significance for predicting As(V) removal as a function of seasonal and process-related water quality changes at water treatment plants.

Ferric based coprecipitation–low pressure membrane filtration is a promising arsenic (As) removal method, however, membrane fouling mechanisms are not fully understood. In this study we investigated the effect of feed water composition and membrane pore size on arsenate [As(V)] removal and membrane fouling. We observed that As removal efficiency was independent of the membrane pore size because the size of the Fe(III) particles was larger than the pore size of the membranes, attributed to a high calcium concentration in the feed water. Arsenic coprecipitation with Fe(III) (oxyhydr)oxides rapidly reached equilibrium before membrane filtration, within 1 min. Therefore, As removal efficiency was not improved by increasing residence time before membrane filtration. The removal of As(V) was strongly dependent on feed water composition. A higher Fe(III) dose was required to reduce As(V) to sub-µg/L levels for feed water containing higher concentration of oxyanions such as phosphate and silicate, and lower concentration of cations such as calcium. Cake-layer formation was observed to be the predominant membrane fouling mechanism.

The maximal allowed concentration (MAC) for As(V) in water decreased from 50 to 10 μg/l, by considering the harmful effects of arsenic on the environment and human health. In order to achieve the established rigorous requirements, it is necessary to develop new materials and design new forms of adsorbents that can reduce the concentration of arsenic in drinking water. In this paper, the synthesized magnetite/3D-printed wollastonite hybrid sorbent was used to remove As(V) from aqueous solutions. 3D-printed wollastonite was obtained using the 3D-printing technique from methylhydrocyclosiloxane and calcium carbonate as precursors. Synthesis of adsorption material was carried out by depositing magnetite from an iron(II)-sulfate solution by potassium hydroxide on 3D-printed wollastonite. The adsorption properties of the hybrid adsorbent depend on the properties of magnetite and its porosity. This could be achieved by modifying the processes of depositing magnetite on the porous 3D-printed wollastonite. Characterization of the obtained material was performed using FTIR, SEM and TG-DTA. An investigation of the sorption properties of hybrid adsorbents was carried out for As(V) removal - one relative to the starting pH value of the solution, the adsorbent mass, the temperature and the adsorption time. Determination of adsorption parameters was performed by applying Langmuir, Freundlich and Dubinin- Radushkevich equations. Kinetics, using pseudo-first, pseudo-second and second order equations, as well as diffusion rate were determined using Veber-Moris and HSDM models. Determination of kinetics and adhesion parameters at three different temperatures enabled the calculation of thermodynamic and activation parameters of the adsorption process, which contributed to a better understanding of the adsorption mechanism.

Modified activated carbon cloth is prepared by mechanochemical modification of viscose rayon carbon cloth. The effects of different milling atmospheres, in the air and inert conditions, were investigated. Changes in kind and number of acidic and basic surface groups on the surface of activated carbon cloth, upon modification, as well as before and after the sorption of arsenic were determined. Higher number of basic groups responsible for the removal of arsenic ions was achieved by modification under inert conditions. Breakage and collapse of cylindrical fibers, decrease of particle sizes, change in the shape and consistency of the particles, as well as increase of microstructural disorder i.e. the loss of turbostratic structure occurred upon milling. pHPZC values increased from 4.46 to 5.04 and 5.77 after the air and inert milling, respectively. Adsorption followed pseudo second order kinetics with chemisorption as rate-controlling step. Langmuir isotherm best fit the equilibrium data and maximum adsorption capacity is 5.5 mg g−1 at a pH value close to 7.0, typical for groundwater. The mechanism of arsenic adsorption onto activated carbon cloth milled in inert atmosphere involved electrostatic and dispersive interactions between arsenic ions and carbon particles in wide pH range (from 2 to 10).

Modified activated carbon cloth is prepared by mechanochemical modification of viscose rayon carbon cloth. The effects of different milling atmospheres, in the air and inert conditions, were investigated. Changes in kind and number of acidic and basic surface groups on the surface of activated carbon cloth, upon modification, as well as before and after the sorption of arsenic were determined. Higher number of basic groups responsible for the removal of arsenic ions was achieved by modification under inert conditions. Breakage and collapse of cylindrical fibers, decrease of particle sizes, change in the shape and consistency of the particles, as well as increase of microstructural disorder i.e. the loss of turbostratic structure occurred upon milling. pHPZC values increased from 4.46 to 5.04 and 5.77 after the air and inert milling, respectively. Adsorption followed pseudo second order kinetics with chemisorption as rate-controlling step. Langmuir isotherm best fit the equilibrium data and maximum adsorption capacity is 5.5 mg g−1 at a pH value close to 7.0, typical for groundwater. The mechanism of arsenic adsorption onto activated carbon cloth milled in inert atmosphere involved electrostatic and dispersive interactions between arsenic ions and carbon particles in wide pH range (from 2 to 10).

The objective of this study was to investigate whether arsenic-oxidising bacteria (AsOB) will grow and survive in rapid sand filters. Additionally, the interdependence of other groundwater constituents (Fe(II), Mn(II), NH4) with biological As(III) oxidation was investigated. For this purpose As(III) oxidation was monitored in pilot-scale filter sand columns fed with raw groundwater, as well as treated groundwater (drinking water) with spikes of either As(III), Mn(II) or NH4. It was concluded that biological As(III) oxidation rapidly developed in the rapid sand filter columns. With a typical lag and log phase, decreasing As(III) and increasing As(V) concentrations in the effluent of the sand columns were observed in a timeframe of weeks. The growth of biomass in the sand columns was confirmed with ATP analysis. ATP concentrations on the sand grains increased from 0.7 ng/g to 16, 8 and 2 ng/g filter sand stratified from the top of the sand filter to the bottom, respectively. Additionally, a microbial community analysis (16S rRNA) showed a high relative abundance of α- and β-Proteobacteria; the same classes where most AsOB are phylogenetically placed. This study establishes that AsOB are able to grow and maintain their population on low As(III) concentrations, either in presence, or absence, of other common groundwater bacteria and mineral precipitates, directly leading to an increased As removal in the filter bed., Sanitary Engineering

The aim of this study is to investigate removal of low As concentrations from groundwater at a Drinking Water Treatment Plant (DWTP) in The Netherlands in order to achieve <1 µg L−1 As in produced drinking water. Two iron based emerging technologies, both relying on in-situ generated Fe(III) precipitates for As adsorption, were investigated. These include: 1) Advanced Oxidation-Coprecipitation-Filtration (AOCF) and 2) Coprecipitation prior to ultrafiltration (C-UF). We show that most of the As removal occurs in the top half of a Rapid Sand Filter (RSF) bed. In this part we also observe the conversion of As(III) into As(V). The mechanism of As(III) oxidation to As(V) in the RSF is still not understood, however we hypothesize that either the manganese oxides or the biological activity in the filter bed may be responsible for this conversion. In agreement with this observation, we also notice that drinking water only contains As(V) and that the levels of As(III) are negligible. The experiments have shown that both AOCF and C-UF are promising emerging technologies to reduce arsenic levels to below 1 µg L−1 which is the agreed target in The Netherlands between the Dutch water companies., QC 20211020

Drinking water companies in the Netherlands are actively investigating routes to reduce arsenic (As) to <1 µg L−1 in drinking water. Co-precipitation of As with iron during groundwater treatment is a promising method. When As(III) is present in raw water, permanganate (MnO4) can be dosed to oxidize As(III) to As(V) in order to improve As removal efficiency. The dosages of MnO4 and Fe(III) to achieve <1 µg L−1 As in the treatment effluents depend on the composition of raw water. The coprecipitation of As(III) and As(V) with ferrihydrite under variable raw water composition and redox environments, controlled by oxygen (O2) or MnO4 is modeled in this study by the generalized double layer model, and redox equilibrium reactions. Results show that the pH of the treatment process is critical to determine the As removal efficiency. At pH = 8 the highest As removal is obtained, followed by pH = 6 while pH = 7 gives the least removal. HCO3, PO4 and H4 SO4 hamper the adsorption of As(V). In future work, the model outcome will be assessed by experiments. Furthermore, the model will be extended with oxidation kinetics in case oxidation (by e.g. oxygen) occurs at a slower rate than the (mean) residence time of the water in the process., QC 20200616

The Dutch drinking water sector is actively investigating methods to reduce arsenic (As) to < 1 mu g/L in drinking water supply. We investigated (1) the effectiveness of sequential permanganate (MnO4-)-ferric (Fe(III)) dosing during aeration-rapid sand filtration to achieve < 1 mu g/L As (2) the influence of MnO4--Fe(III) dosing on preestablished removal patterns of As(III), Fe(II), Mn(II) and NH4+ in rapid sand filters and (3) the influence of MnO4--Fe(III) dosing on the settling and molecular-scale structural properties of the filter backwash solids. We report that MnO4--Fe(III) dosing is an effective technique to improve arsenite [As(III)] removal at groundwater treatment plants. At a typical aeration-rapid sand filtration facility in the Netherlands effluent As concentrations of < 1 mu g/L were achieved with 1.2 mg/L MnO4--and 1.8 mg/L Fe(III). The optimized combination of MnO4-and Fe(III) doses did not affect the removal efficiency of Fe(II), Mn(II) and NH4+ in rapid sand filters, however, the removal patterns of Fe(II) and Mn(II) in rapid sand filter were altered, as well as the settling behaviour of backwash solids. The characterization of backwash solids by Fe K-edge X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) showed that the changed settling velocity of backwash solids with MnO4-Fe(III) in place was not due to changes in the molecular-scale structure of Fe-precipitates that constitute the major portion of the backwash solids., QC 20181211

Phytofiltration of arsenic (As)-contaminated water could reduce As in irrigation and surface water. In a previous study, we found that the aquatic moss Warnstorfia fluitans efficiently removes arsenic from water contaminated with arsenate and arsenite. This work investigates how factors such as pH, temperature, and oxygenation influence As removal, since these factors vary in the environment. Plants were grown in a medium with 5 or 10 μM arsenite or arsenate and: 1) a pH of 2.5, 6.5, or 9.5; 2) a temperature of 12, 20, or 30 °C; and 3) oxygenation of <2 or 13 mg O2 L−1. Removal of As was monitored over 48–96 h, and the content and speciation of As were analysed in moss plants at the termination of the experiments. Results indicate that As removal was faster in arsenite than arsenate solutions. Arsenic removal from arsenite solution was the fastest, i.e., 80–90% within 2 h, at pH 6.5 and 9.5 and at 20 and 30 °C. At pH 2.5, plants were stressed and the net removal was low throughout the treatment period. Arsenic removal was more efficient at low than high oxygenation levels. Besides this, no As net efflux process was seen in the water system except after 48 h in arsenate-treated medium in high-temperature (30 °C) regimes. Regardless of As species added, usually only arsenite was found in the plants after treatment. Most internal As, i.e., 95% in the arsenate and 85% in the arsenite treatments, was firmly bound to the tissue. The study found that at 20 °C, neutral pH, and low oxygenation, this aquatic moss has great potential for As phytofiltration., QC 20170406

Phytofiltration of arsenic (As)-contaminated water could reduce As in irrigation and surface water. In a previous study, we found that the aquatic moss Warnstorfia fluitans efficiently removes arsenic from water contaminated with arsenate and arsenite. This work investigates how factors such as pH, temperature, and oxygenation influence As removal, since these factors vary in the environment. Plants were grown in a medium with 5 or 10 mu m arsenite or arsenate and: 1) a pH of 2.5, 6.5, or 9.5; 2) a temperature of 12, 20, or 30 degrees C; and 3) oxygenation of < 2 or 13 mg O-2 L-1. Removal of As was monitored over 48-96 h, and the content and speciation of As were analysed in moss plants at the termination of the experiments. Results indicate that As removal was faster in arsenite than arsenate solutions. Arsenic removal from arsenite solution was the fastest, i.e., 80-90% within 2 h, at pH 6.5 and 9.5 and at 20 and 30 degrees C. At pH 2.5, plants were stressed and the net removal was low throughout the treatment period. Arsenic removal was more efficient at low than high oxygenation levels. Besides this, no As net efflux process was seen in the water system except after 48 h in arsenate-treated medium in high-temperature (30 degrees C) regimes. Regardless of As species added, usually only arsenite was found in the plants after treatment. Most internal As, i.e., 95% in the arsenate and 85% in the arsenite treatments, was firmly bound to the tissue. The study found that at 20 degrees C, neutral pH, and low oxygenation, this aquatic moss has great potential for As phytofiltration.

This work investigates whether aquatic moss (Warnstorfia fluitans) originating from an arsenic (As) contaminated wetland close to a mine tailings impoundment may be used for phytofiltration of As. The aim was to elucidate the capacity of W. fluitans to remove As from arsenite and arsenate contaminated water, how nutrients affect the As uptake and the proportion of As adsorption and absorption by the moss plant, which consists of dead and living parts. Arsenic removal from 0, 1, or 10% Hoagland nutrient solution containing 0-100 mu M arsenate was followed over 192 h, and the total As in aquatic moss after treatment was analysed. The uptake and speciation of As in moss cultivated in water containing 10 mu M arsenate or arsenite were examined as As uptake in living (absorption + adsorption) and dead (adsorption) plant parts. Results indicated that W. fluitans removed up to 82% of As from the water within one hour when 1 mu M arsenate was added in the absence of nutrients. The removal time increased with greater nutrient and As concentrations. Up to 100 mu M As had no toxic effect on the plant biomass. Both arsenite and arsenate were removed from the solution to similar extents and, independent of the As species added, more arsenate than arsenite was found in the plant. Of the As taken up, over 90% was firmly bound to the tissue, a possible mechanism for resisting high As concentrations. Arsenic was both absorbed and adsorbed by the moss, and twice as much As was found in living parts as in dead moss tissue. This study revealed that W fluitans has potential to serve as a phytofilter for removing As from As-contaminated water without displaying any toxic effects of the metalloid.

Nano zero-valent iron (nZVI) is widely used in the arsenic (As) remediation of groundwater. During the remediation, nZVI reacts with As and then forms As-loaded nZVI. Unfortunately, some concerns occur regarding the release of As-loaded nZVI particles and their subsequent transport in aquatic environments, as well as the As release from As-loaded nZVI. This study investigated the fate and transport of the three types of As-loaded nZVI (As-loaded pristine, chitosan-modified and polyaniline-modified nZVI) at two levels of As loadings (low and high), under conditions related to practical groundwater remediation. In batch studies, the alkaline condition and the presence of humic acid were found to enhance the As release from all types of As-loaded nZVI. Ca2+ did not affect the As release from As-loaded pristine nZVI at both low and high As loadings, but affected the As release from both types of As-loaded nZVI (As-loaded chitosan-modified and polyaniline-modified nZVI) at high As loading. Surface modification and high As loading reduced the As release from the three types of As-loaded nZVI. In column studies, surface modification and high As loading enhanced the mobility of the three types of As-loaded nZVI. The As in the effluent was from the As release when nZVI was not detected. It was evident that the mobility of the three types of As-loaded nZVI particles were limited, at both As loadings. Thus, the As release, instead of As-loaded nZVI particles, can cause wide As contamination in groundwater. This study is the first time to systematically investigate the fate and transport of As-loaded nZVI in groundwater system. The findings could assess the potential risk caused by the As released from the As-loaded nZVI under different geochemical conditions and also provide guidelines for the selections of surface modification as well as the nZVI dosage regarding the As release in groundwater.

The Dutch drinking water sector is actively investigating methods to reduce arsenic (As) to <1 μg/L in drinking water supply. We investigated (1) the effectiveness of sequential permanganate (MnO4¯ )–ferric (Fe(III)) dosing during aeration–rapid sand filtration to achieve <1 μg/L As (2) the influence of MnO4¯ –Fe(III) dosing on pre-established removal patterns of As(III), Fe(II), Mn(II) and NH4 + in rapid sand filters and (3) the influence of MnO4¯ –Fe(III) dosing on the settling and molecular-scale structural properties of the filter backwash solids. We report that MnO4¯ –Fe(III) dosing is an effective technique to improve arsenite [As(III)] removal at groundwater treatment plants. At a typical aeration—rapid sand filtration facility in the Netherlands effluent As concentrations of <1 μg/L were achieved with 1.2 mg/L MnO4 ¯–and 1.8 mg/L Fe(III). The optimized combination of MnO4¯ –and Fe(III) doses did not affect the removal efficiency of Fe(II), Mn(II) and NH4 + in rapid sand filters, however, the removal patterns of Fe(II) and Mn(II) in rapid sand filter were altered, as well as the settling behaviour of backwash solids. The characterization of backwash solids by Fe K-edge X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) showed that the changed settling velocity of backwash solids with MnO4¯ –Fe(III) in place was not due to changes in the molecular-scale structure of Fe-precipitates that constitute the major portion of the backwash solids.

Nano zero-valent iron (nZVI) is widely used in the arsenic (As) remediation of groundwater. During the remediation, nZVI reacts with As and then forms As-loaded nZVI. Unfortunately, some concerns occur regarding the release of As-loaded nZVI particles and their subsequent transport in aquatic environments, as well as the As release from As-loaded nZVI. This study investigated the fate and transport of the three types of As-loaded nZVI (As-loaded pristine, chitosan-modified and polyaniline-modified nZVI) at two levels of As loadings (low and high), under conditions related to practical groundwater remediation. In batch studies, the alkaline condition and the presence of humic acid were found to enhance the As release from all types of As-loaded nZVI. Ca2+ did not affect the As release from As-loaded pristine nZVI at both low and high As loadings, but affected the As release from both types of As-loaded nZVI (As-loaded chitosan-modified and polyaniline-modified nZVI) at high As loading. Surface modification and high As loading reduced the As release from the three types of As-loaded nZVI. In column studies, surface modification and high As loading enhanced the mobility of the three types of As-loaded nZVI. The As in the effluent was from the As release when nZVI was not detected. It was evident that the mobility of the three types of As-loaded nZVI particles were limited, at both As loadings. Thus, the As release, instead of As-loaded nZVI particles, can cause wide As contamination in groundwater. This study is the first time to systematically investigate the fate and transport of As-loaded nZVI in groundwater system. The findings could assess the potential risk caused by the As released from the As-loaded nZVI under different geochemical conditions and also provide guidelines for the selections of surface modification as well as the nZVI dosage regarding the As release in groundwater.

Current groundwater treatment facilities, mostly relying on aeration-filtration configurations, aim at the removal of iron (Fe), ammonia (NH 4 + ) and manganese (Mn). However, recently water companies expressed the ambition to also reduce arsenic (As) concentrations in these rapid sand filters. The aim of this study was to investigate the effect of the Fe oxidation state entering a biological filter bed on As removal. By varying supernatant water level, either Fe(II) or Fe(III) in the form of hydrous ferric oxides (HFO) could be stimulated to enter the filter bed at alkaline groundwater pH (7.6). The experimental pilot column filters showed that once the As(III) oxidation stabilised in the top layer of the filter sand, As removal reached its maximum (±75% at 120 cm supernatant level and 1.5 m/h filtration velocity). The increase in supernatant level from 5 to 120 cm resulted in additional HFO production prior to rapid filtration (1.5, 5 and 10 m/h), i.e. homogeneous Fe(II) oxidation and flocculation, and subsequently, HFO ending up deeper into the filter bed (120 cm filter depth). At a low supernatant water level of 5 cm, Fe(II) oxidised heterogeneously and was removed within the top 20 cm of the filter bed. Consequently, filters with high supernatant levels removed As to lower levels (by 20%) than in filters with low supernatant water levels. The benefits of Fe(II) oxidation prior to filtration for As removal was confirmed by comparing Fe(III) to Fe(II) additions in the supernatant water or in the filter bed. Overall it is concluded that in biological groundwater filters, the combination of a higher supernatant level and/or Fe(III) addition with biological As(III) oxidation in the top of the filter bed promotes As removal., Sanitary Engineering

Nano zero-valent iron (nZVI) is widely used in the arsenic (As) remediation of groundwater. During the remediation, nZVI reacts with As and then forms As-loaded nZVI. Unfortunately, some concerns occur regarding the release of As-loaded nZVI particles and their subsequent transport in aquatic environments, as well as the As release from As-loaded nZVI. This study investigated the fate and transport of the three types of As-loaded nZVI (As-loaded pristine, chitosan-modified and polyaniline-modified nZVI) at two levels of As loadings (low and high), under conditions related to practical groundwater remediation. In batch studies, the alkaline condition and the presence of humic acid were found to enhance the As release from all types of As-loaded nZVI. Ca2+ did not affect the As release from As-loaded pristine nZVI at both low and high As loadings, but affected the As release from both types of As-loaded nZVI (As-loaded chitosan-modified and polyaniline-modified nZVI) at high As loading. Surface modification and high As loading reduced the As release from the three types of As-loaded nZVI. In column studies, surface modification and high As loading enhanced the mobility of the three types of As-loaded nZVI. The As in the effluent was from the As release when nZVI was not detected. It was evident that the mobility of the three types of As-loaded nZVI particles were limited, at both As loadings. Thus, the As release, instead of As-loaded nZVI particles, can cause wide As contamination in groundwater. This study is the first time to systematically investigate the fate and transport of As-loaded nZVI in groundwater system. The findings could assess the potential risk caused by the As released from the As-loaded nZVI under different geochemical conditions and also provide guidelines for the selections of surface modification as well as the nZVI dosage regarding the As release in groundwater.

Current groundwater treatment facilities, mostly relying on aeration-filtration configurations, aim at the removal of iron (Fe), ammonia (NH 4 + ) and manganese (Mn). However, recently water companies expressed the ambition to also reduce arsenic (As) concentrations in these rapid sand filters. The aim of this study was to investigate the effect of the Fe oxidation state entering a biological filter bed on As removal. By varying supernatant water level, either Fe(II) or Fe(III) in the form of hydrous ferric oxides (HFO) could be stimulated to enter the filter bed at alkaline groundwater pH (7.6). The experimental pilot column filters showed that once the As(III) oxidation stabilised in the top layer of the filter sand, As removal reached its maximum (±75% at 120 cm supernatant level and 1.5 m/h filtration velocity). The increase in supernatant level from 5 to 120 cm resulted in additional HFO production prior to rapid filtration (1.5, 5 and 10 m/h), i.e. homogeneous Fe(II) oxidation and flocculation, and subsequently, HFO ending up deeper into the filter bed (120 cm filter depth). At a low supernatant water level of 5 cm, Fe(II) oxidised heterogeneously and was removed within the top 20 cm of the filter bed. Consequently, filters with high supernatant levels removed As to lower levels (by 20%) than in filters with low supernatant water levels. The benefits of Fe(II) oxidation prior to filtration for As removal was confirmed by comparing Fe(III) to Fe(II) additions in the supernatant water or in the filter bed. Overall it is concluded that in biological groundwater filters, the combination of a higher supernatant level and/or Fe(III) addition with biological As(III) oxidation in the top of the filter bed promotes As removal., Sanitary Engineering

In the present study, several pre-polymerized coagulants of iron and aluminum were tested for their efficiency towards As(V) and As(III) removal from water sources. The results showed that the pre-polymerized coagulants of iron, such as poly-ferric sulfate and poly-ferric silicate chloride, were very efficient for As(V) removal. With regard to As(III) removal, among all examined coagulants, including the conventional ferric chloride, only the poly-ferric sulfate (PFS) was able to reduce As(III) to concentrations below the drinking water regulation limit of 10 μg/L. In contrast, all tested composite coagulants based on aluminum were not capable of removing efficiently both species of arsenic. PFS addition in water containing 4 mM of alkalinity and 25 μg/L of As(V) and As(III) (i.e., total arsenic concentration 50 μg/L) resulted in finished water with less than 5 μg/L arsenic, only by dosing 5 mg Fe-PFS/L at pH 7, whereas, simultaneously, the residual iron concentration was found well below its drinking water regulation limit of 200 μg/L. The use of PFS could provide a viable alternative for As(III) and As(V) removal at household treatment level for application in vulnerable communities, without the need of any additional treatment, such as oxidation of As(III) to As(V)., In the present study, several pre-polymerized coagulants of iron and aluminum were tested for their efficiency towards As(V) and As(III) removal from water sources. The results showed that the pre-polymerized coagulants of iron, such as poly-ferric sulfate and poly-ferric silicate chloride, were very efficient for As(V) removal. With regard to As(III) removal, among all examined coagulants, including the conventional ferric chloride, only the poly-ferric sulfate (PFS) was able to reduce As(III) to concentrations below the drinking water regulation limit of 10 μg/L. In contrast, all tested composite coagulants based on aluminum were not capable of removing efficiently both species of arsenic. PFS addition in water containing 4 mM of alkalinity and 25 μg/L of As(V) and As(III) (i.e., total arsenic concentration 50 μg/L) resulted in finished water with less than 5 μg/L arsenic, only by dosing 5 mg Fe-PFS/L at pH 7, whereas, simultaneously, the residual iron concentration was found well below its drinking water regulation limit of 200 μg/L. The use of PFS could provide a viable alternative for As(III) and As(V) removal at household treatment level for application in vulnerable communities, without the need of any additional treatment, such as oxidation of As(III) to As(V).

This work investigates whether aquatic moss (Warnstorfia fluitans) originating from an arsenic (As)-contaminated wetland close to a mine tailings impoundment may be used for phytofiltration of As. The aim was to elucidate the capacity of W. fluitans to remove As from arsenite and arsenate contaminated water, how nutrients affect the As uptake and the proportion of As adsorption and absorption by the moss plant, which consists of dead and living parts. Arsenic removal from 0, 1, or 10% Hoagland nutrient solution containing 0–100 μM arsenate was followed over 192 h, and the total As in aquatic moss after treatment was analysed. The uptake and speciation of As in moss cultivated in water containing 10 μM arsenate or arsenite were examined as As uptake in living (absorption + adsorption) and dead (adsorption) plant parts. Results indicated that W. fluitans removed up to 82% of As from the water within one hour when 1 μM arsenate was added in the absence of nutrients. The removal time increased with greater nutrient and As concentrations. Up to 100 μM As had no toxic effect on the plant biomass. Both arsenite and arsenate were removed from the solution to similar extents and, independent of the As species added, more arsenate than arsenite was found in the plant. Of the As taken up, over 90% was firmly bound to the tissue, a possible mechanism for resisting high As concentrations. Arsenic was both absorbed and adsorbed by the moss, and twice as much As was found in living parts as in dead moss tissue. This study revealed that W. fluitans has potential to serve as a phytofilter for removing As from As-contaminated water without displaying any toxic effects of the metalloid., This work was funded by Environment Foundation (Miljöfonden) of the Swedish Engineers’ Association.QC 20170406

In this work, selectrodialysis (SED) was used to separate arsenic (As(V)) from copper (Cu(II)) and (Zn(II)) of acidic metallurgical process streams by integrating non-selective and selective membranes. The separation process is determined by the chemical speciation of the involved elements. In this case, As(V) is mainly present as anionic species (H2AsO4-), while Cu(II) and Zn(II) are mainly present as cationic species although partially complexed as neutral complexes (CuSO4 and ZnSO4). A lab set-up was used to conduct the experimental tests with different type of standard and mono-selective ion-exchange membranes. The results obtained showed that by SED configuration it was possible to recover around 80±0.2 % of Cu(II), 87±0.2 % of Zn(II) and 95±0.3 % of As(V) from the feed solution to the rich-product streams with an energy consumption of 2.6±0.2 kWh/kg CuSO4+ZnSO4. Furthermore, a Cu/Zn-rich stream with a purity of both divalent cations of 99.8 % (0.02 % of As(V)) was achieved by means of SED. Overall, the results herein gathered suggest that SED is an efficient separation technology for Cu(II) and Zn(II) recovery from mining and metallurgical acidic streams., Peer Reviewed, Postprint (author's final draft)

Composite material Zr-doped TiO2, suitable for the removal of arsenic from water, was synthetized with fast and simple microwave-hydrothermal method. Obtained material, Zr-TiO2, had uniform size and composition with zirconium ions incorporated into crystal structure of titanium dioxide. Synthetized composite material had large specific surface area and well-developed micropore and mesopore structure that was responsible for fast adsorption of As(III) and As(V) from water. The influence of pH on the adsorption capacity of arsenic was studied. The kinetics and isotherm experiments were also performed. The treatment of natural water sample containing high concentration of arsenic with composite material Zr-TiO2 was efficient. The concentration of arsenic was reduced to the value recommended by WHO.

Composite material Zr-doped TiO2, suitable for the removal of arsenic from water, was synthetized with fast and simple microwave-hydrothermal method. Obtained material, Zr-TiO2, had uniform size and composition with zirconium ions incorporated into crystal structure of titanium dioxide. Synthetized composite material had large specific surface area and well-developed micropore and mesopore structure that was responsible for fast adsorption of As(III) and As(V) from water. The influence of pH on the adsorption capacity of arsenic was studied. The kinetics and isotherm experiments were also performed. The treatment of natural water sample containing high concentration of arsenic with composite material Zr-TiO2 was efficient. The concentration of arsenic was reduced to the value recommended by WHO.

Arsenic is a widely distributed element in the Earth’s crust with an average terrestrial concentration of about 5 g ton-1 . Arsenic is a persistent, bio-accumulative, toxic element. The United States Environmental Protection Agency (EPA) has implemented the discharge criterion of 10 µg L -1 for arsenic as the maximum acceptable level for ground water. During the past decades, several techniques have been developed for the removal of arsenic from the wastewater, including chemical precipitation, adsorption and ion exchange, membrane and biological removal processes, and so on. Because of the good arsenic removal efficiency and the low cost, adsorption is a more popular method. In this thesis research, two ranges of iron oxide nanocomposite adsorbents have been developed and studied for their performance properties towards arsenic removal. Novel iron oxide encapsulated carbon nanospheres (FeOx-CNS) with excellent arsenic adsorption performance has been successfully synthesized. CO2 activated carbon nanospheres material (A-CNS) with high surface area (2271 m²g -1 ) and high pore volume (5.18 cm³g -1 ) was selected as the porous matrix. After surface oxidation by ammonium persulfate (APS), iron oxide was loaded into the carbon nanospheres as the effective arsenic adsorbent. Transmission electron microscopy (TEM) and Braunauer–Emmett– Teller (BET) results indicate that iron oxide nanoparticles (7-60 wt%) are well-dispersed within the mesopores. In particular, FeOx-CNS-13 composite shows most optimum performance properties, with high arsenic adsorption capacities achieved for both As(III) (416 mg g−1 ) and As(V) (201 mg g−1 ). Another range of amorphous iron oxide-graphene oxide (FeOx-GO) nanocomposites having different graphene oxide (GO) content (36-80 wt%) was prepared by coprecipitation of ferrous sulfate heptahydrate and ferric sulfate hydrate on GO sheets. The composites have been thoroughly characterized and investigated for their performance towards arsenic remova

Composite material Zr-doped TiO2, suitable for the removal of arsenic from water, was synthetized with fast and simple microwave-hydrothermal method. Obtained material, Zr-TiO2, had uniform size and composition with zirconium ions incorporated into crystal structure of titanium dioxide. Synthetized composite material had large specific surface area and well-developed micropore and mesopore structure that was responsible for fast adsorption of As(III) and As(V) from water. The influence of pH on the adsorption capacity of arsenic was studied. The kinetics and isotherm experiments were also performed. The treatment of natural water sample containing high concentration of arsenic with composite material Zr-TiO2 was efficient. The concentration of arsenic was reduced to the value recommended by WHO.