Impact of phosphate, silicate and natural organic matter on the size of Fe(III) precipitates and arsenate co-precipitation efficiency in calcium containing water

Remediation of biochar-supported effective microorganisms and microplastics on multiple forms of nitrogenous and phosphorous in eutrophic lake

Lots of studies on eutrophication, but there is a lack of comprehensive research on the repair of multiple forms of nitrogen and phosphorus under combined heavy metals (HMs) pollution. This work investigated the various forms of nitrogen and phosphorus in the water-sediment systems of eutrophic lakes with the application of biochar, Effective Microorganisms (EMs) and microplastics, aiming to deliberate the repair behavior of multiple forms of nitrogen/phosphorus and the integrated repairment of these nutrients and HMs in different remediations. For amended-groups, the application of biochar-supported EMs (BE) achieved the most desirable remediation for removing nitrogen, phosphorus and HMs in water and improved their stability in sediment due to the improved microbial activity and the developed biofilm system created by biochar. The addition of aging microplastics (MP) obviously reduced the systematic levels of nitrogen, phosphorus and HMs due to the stimulation of microbial activity and the adsorption of biofilm/EPS, but its high movability also increased the Fe(II) and S(-II) levels and the pollutants' ecological risks in sediment. The co-application of BE and MP (MBE) destroyed the ecosystem and decreased the removal of nitrogen and phosphorus, while greatly removing HMs by the superfluous biofilms/EPS. The application of biochar (BC) preferentially adsorbed and degraded dissolved nitrogen and phosphorus, releasing HMs into water. From these amended-groups, it's also knew that the removal of nitrogen and phosphorus mainly came from the degradation/assimilation of NH3-N, SRP and dissolved matters, particularly those molecular weight below 3 kDa; the higher removal of phosphorus than nitrogen was attributed to the coprecipitation of Fe-S-P hydroxides and the adsorption of particulates; however, the colloidal (3-100 kDa) nitrogen and phosphorus had low accessibility and bioavailability, and it also showed the competitive adsorption with colloidal HMs, causing their relatively low removal in water. This study provides insight into the comprehensive repair of nitrogen, phosphorus and HMs in various forms by biochar-immobilized microbes and the influence of microplastics on nutrients and HMs in eutrophic lakes.

Hybrid method integrating adsorption and chemical precipitation of heavy metal ions on polymeric fiber surfaces for highly efficient water purification

A lot of research has been focused on increasing the specific surface area of adsorbents over a long period of time to remove heavy metal ions from wastewater using the adsorbent. However, porous adsorbents with high specific surface area have demonstrated drawbacks in water purification processes, such as high pressure drop and limitations in the adsorption capacity of heavy metal ions. In recent years, a mechanism-based convergence method involving adsorption/chemical precipitation has emerged as a promising strategy to surmount the constraints associated with porous adsorbents. The mechanism involves amine groups on chelating fibers dissociating OH- ions from water molecules, thereby raising the pH near the fibers. This elevated pH promotes the crystallization of heavy metal ions on the fiber surfaces. The removal of heavy metal ions proceeds through a sequence of adsorption and chemical precipitation processes. An adsorbent based on chelating fibers, integrating adsorption technology with chemical precipitation, demonstrates superior performance in removing significant quantities of heavy metal ions (ca. 1000-2000 mg/g for Cd2+, Cu2+ and Pb2+) when compared to developed porous adsorbents (ca. 50-760 mg/g for same ions). This review paper introduces advanced polymer fibers endowed with the capability to integrate hybrid technology, delves into the mechanism of hybrid technology, and examines its application in process technology for the effective removal of heavy metal ions. The versatility of these advanced fibers extends far beyond the removal of heavy metal ions in water treatment, making them poised to garner significant attention from researchers across diverse fields due to their broad range of potential applications. After further processes involving the removal of templates from chelating polymeric fibers used as supports and the reduction of precipitated heavy metal oxide crystals, the resulting heavy metal crystals can exhibit thin walls and well-interconnected porous structures, suitable for catalytic applications.

The redistribution process of As(Ⅲ) and Fe(Ⅱ) caused by As/Fe ratio, organic matter, and co-existing ions: Co-precipitation and co-oxidation

The contamination of arsenic (As) in aqueous environments has drawn widespread attention, and iron compounds may largely alter the migration ability of As. However, the stability of As(III) in Fe-As system with the intervention of organic matter (OM) remains unclear. Herein, we had explored the co-precipitation and co-oxidation processes of As-Fe system by using batch experiments combined with Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Photoelectron Spectroscopy (XPS) in this research. The precipitation quantity of As(III) increased (28.85-92.41 %) when the As/Fe ratio decreased, and increased (24.20-64.20 %) with pH increased. The main active substance for oxidizing As(III) was H2O2, which was produced in the As-Fe system. FTIR and XPS revealed that As(III) was first oxidized in neutral, and then absorbed and enteredthe interior of Fe(OH)3 colloids. But under alkaline conditions, As(III) was adsorbed by Fe (Oxyhydr) oxides firstly, and then oxidized. The intervention of OM would inhibit the redistribution process of As(III) in aqueous environments. Functional groups and unsaturation of the carbon chain were the dominant factors that affected the precipitation and oxidation processes of As(III), respectively. Co-existing ions (especially PO43-) also signally affected the precipitation quantity of As(Ⅲ) in the system and, when coexisting with OM, could exacerbate this process. The influence of co-existing ions on the redistributive process of As(III) in the As-Fe system with/without OM were as follows: PO43- > SO42- > mixed ions > SiO32-. Moreover, high concentration of OM and PO43- might lead to morphological alterations of As, acting as a threat to aqueous environments. In summary, the present findings were to further understand and appreciate the changes of As toxicity in the aqueous environments. Particularly, the coexistence of OM and As can potentially increase the risk to drinking water safety.

Eliminating the stabilizer antagonistic effects for efficiently stabilizing Pb and As co-contaminated soil by innovative stepwise steam flash heating

Chemical stabilization is frequently used to stabilize lead (Pb) or arsenate (As), but faces challenges in Pb-As co-contaminated soils because of the antagonistic reactions between chemical stabilizers and contaminants. In this work, we innovated an effective and cost-efficient stepwise steam flash heating (SSFH) strategy to simultaneously immobilize Pb and As, and unraveled the underlying mechanisms. The combination of 1.5% Ca(H2PO4)2 and 2% Fe2(SO4)3 only decreased 1.99% Pb by toxicity characteristic leaching procedure (TCLP-Pb) but increased 17.8% of TCLP-As due to the antagonistic effects. SSFH with Ca(H2PO4)2 in the first step and Fe2(SO4)3 in the second step achieved the minimal TCLP-Pb and TCLP-As of 0.778 and 0.327 mg/L, respectively. It also reduced 69.8% of leachable As in 100-year acid rain simulation, indicating a favorable long-term stabilization performance. Additionally, SSFH approach reduced 43.2% stabilizer dosage and 14.9% cost. X-ray absorption near edge structure (XANES) documented that the stepwise SFH promoted the transformation of Pb(NO3)2 and NaAsO2/NaAsO3/As2O3/As2O5 into stable Pb3(PO4)2 and FeAsO4, preventing the formation of AsO43- and FePO4. Our findings proved the state-of-the-art SSFH approach and unraveled its mechanisms to stabilize Pb and As co-contamination in soils, offering a green and sustainable remediation alternative for the management of heavy metal contaminated sites. ENVIRONMENTAL IMPLICATION: A novel stepwise SFH approach can be applied to overcome the stabilizer antagonist effects by separately immobilizing Pb and As in two sequential steps. It also decreased 43.2% of stabilizer dosage and 14.9% of cost comparing to conventional chemical stabilization. This approach can be used for other metal co-contaminated soils facing similar antagonistic challenges, and our work raises a state-of-the-art solution for cost-effective, green and sustainable remediation practices.

Influence of iron, phosphate, and silicate on arsenic removal from groundwater using a low-cost ceramic filter

The ceramic filter amended with iron (Fe) has proven to be a potential low-cost method for arsenic (As) removal from groundwater. The presence of Fe, phosphate (P), and silicate (Si) significantly affects the As removal efficiency of the ceramic filter, which has not been passably investigated. The present research aimed to examine the effect of Fe, P, and (or) Si presence as single or in combination on As (III) removal from synthetics groundwater by a low-cost iron amended ceramic filter (IACF). Laboratory-scale filtration experiments at different compositions of Fe, P, Si, and As (III) were conducted by the IACF fabricated with a ceramic candle and iron netting box. Fe (II) in synthetic groundwater positively impacted As (III) removal. At a concentration of 2 mg/L of Fe (II), the As levels in the effluent decreased to less than the maximum contamination level (MCL) of 50 μg/L. Groundwater P concentration needed less than 3 mg/L or Si concentrations required less than 35 mg/L to effectively reduce As (III) to below the MCL at 5 mg/L of groundwater Fe (II). The cumulative effect of P and Si on As removal was found to be more significant than distinct contributions. The presence of 2 mg/L P and 35 mg/L or higher Si in the groundwater cumulatively reduced the As removal performance from 92% to 63%, and the MCL was not met. The negative impact of P and Si on As (III) removal followed the order of (P + Si) > P > Si. P competed with As for adsorption sites during the process, while Si inhibited the Fe release and floc formation, significantly reducing As removal performance. The study findings can potentially contribute to optimizing IACF as a low-cost method for As removal from groundwater.

Arsenic (As) resistant bacteria with multiple plant growth-promoting traits: Potential to alleviate As toxicity and accumulation in rice

A currently serious agronomic concern for paddy soils is arsenic (As) contamination. Paddy soils are mostly utilized for rice cultivation. Arsenite (As(III)) is prevalent in paddy soils, and its high mobility and toxicity make As uptake by rice substantially greater than that by other food crops. Globally, interest has increased towards using As-resistant plant growth-promoting bacteria (PGPB) to improve plant metal tolerance, promote plant growth, and immobilize As to prevent its uptake and accumulation in the edible parts of rice as much as possible. This review focuses on the As-resistant PGPB characteristics influencing rice growth and the mechanisms by which they function to alleviate As toxicity stress in rice plants. Several recent examples of mechanisms responsible for decreasing the availability of As to rice and coping with As stresses facilitated by the PGPB with multiple PGP traits (e.g., phosphate and silicate solubilization, the production of 1-aminocyclopropane-1-carboxylate deaminase, phytohormones, and siderophore, N₂ fixation, sulfate reduction, the biosorption, bioaccumulation, methylation, and volatilization of As, and arsenite oxidation) are also reviewed. In addition, future research needs about the application of As-resistant PGPB with PGP traits to mitigate As accumulation in rice plants are described.

Enhanced immobility of Pb(II) during ferrihydrite-Pb(II) coprecipitates aging impacted by malic acid or phosphate

Metastable ferrihydrite is omnipresent in environments and can influence the fate of Pb(II) during ferrihydrite transformation. Ferrihydrite is rarely pure and often coexists with impurities, which may influence the mineralogical changes of ferrihydrite and Pb(II) behavior. In this work, we investigated the effect of malic acid or phosphate on Pb(II)-ferrihydrite coprecipitates (Fh-Pb) transformation and the subsequent fate of Pb(II) during the 10-day aging of Fh-Pb. Results showed that both malic acid and phosphate retarded Fh-Pb transformation and prevented the release of Pb(II) from Fh-Pb back into solutions. Pb(II) was beneficial to goethite formation by inhibiting hematite formation while both malic acid and phosphate inhibited goethite formation since they could act as templates of nucleation. Besides, malic acid and phosphate improved the proportion of non-extracted Pb(II) during Fh-Pb transformation, indicating that Pb(II) was incorporated into secondary minerals. Pb(II) could not replace Fe(III) within the crystal lattice due to its large radius but was occluded into pores and defect structures within the secondary mineral lattices. This work can advance our understanding of the influences of malic acid and phosphate on Pb(II) immobility during Fh-Pb aging.

A Simulation Experiment on Quality Dynamics of Reclaimed Water under Different Flow Exchanges

Reclaimed water plays an important role in maintaining urban aquatic ecosystems, especially in areas with water shortages. However, there is little information on water quality dynamics and its driving mechanism in reclaimed water bodies. The simulated experiments were conducted to investigate the effect of flow exchange on water quality dynamics and soil microbial diversity for 100% reclaimed water and mixed water (50% reclaimed and 50% stream water), and the exchange periods ranged from 2 to 40 days. The results showed that the degradation coefficients (K) of COD_Mn and NH₃-N were 0.015 d^-1 and 0.001 d^-1 for the mixed water, while their K values were negative for the reclaimed water. The flow exchange had little effect on water quality dynamics for the mixed water, which may be attributed to the relatively low concentration of TP in this reclaimed water. A small or great exchange period led to a relatively high fluctuation in K during the experimental period and corresponded to a worse soil microbial diversity. These results indicate that it is not recommended to fill an isolated urban lake with 100% reclaimed water and that a suitable flow exchange period of 5~10 days could help self-purify the water quality.

Effects of phosphate, silicate, humic acid, and calcium on the release of As(V) co-precipitated with Fe(III) and Fe(II) during aging

The effects of phosphate (P), silicate (Si), humic acid (HA), and calcium (Ca) on the release of As(V) co-precipitated with Fe(III) and Fe(II) during aging were investigated. As(V) in synthetic groundwater could be efficiently removed by both Fe(III) and Fe(II) processes. The addition of P remarkably decreased As(V) removal efficiency while no obvious release of As(V) during aging was observed. Si and HA reduced As(V) removal to a less extent than P but caused notable As(V) release during aging. FTIR spectra and particle size of the precipitates before and after aging indicated that As(V) release in the presence of Si was due to the serious structural transformation and particle aggregation of the precipitates during aging. While for HA, As(V) release was caused by sorption of HA on the precipitates and dissolution of the precipitates by HA. The addition of Ca partially counteracted the adverse impacts of P, Si, and HA and promoted As(V) removal efficiency but had limited inhibitory effect on As(V) release as it induced more serious particle aggregation during aging. The results demonstrated that the release of As(V) caused by Si and HA should be considered when using Fe coagulation for in-situ treatment of As(V) contaminated groundwater.

Freshwater suspended particulate matter-Key components and processes in floc formation and dynamics

Freshwater suspended particulate matter (SPM) plays an important role in many biogeochemical cycles and serves multiple ecosystem functions. Most SPM is present as complex floc-like aggregate structures composed of various minerals and organic matter from the molecular to the organism level. Flocs provide habitat for microbes and feed for larger organisms. They constitute microbial bioreactors, with prominent roles in carbon and inorganic nutrient cycles, and transport nutrients as well as pollutants, affecting sediments, inundation zones, and the ocean. Composition, structure, size, and concentration of SPM flocs are subject to high spatiotemporal variability. Floc formation processes and compositional or morphological dynamics can be established around three functional components: phyllosilicates, iron oxides/(oxy)hydroxides (FeOx), and microbial extracellular polymeric substances (EPS). These components and their interactions increase heterogeneity in surface properties, enhancing flocculation. Phyllosilicates exhibit intrinsic heterogeneities in surface charge and hydrophobicity. They are preferential substrates for precipitation or attachment of reactive FeOx. FeOx form patchy coatings on minerals, especially on phyllosilicates, which increase surface charge heterogeneities. Both, phyllosilicates and FeOx strongly adsorb natural organic matter (NOM), preferentially certain EPS. EPS comprise various substances with heterogeneous properties that make them a sticky mixture, enhancing flocculation. Microbial metabolism, and thus EPS release, is supported by the high adsorption capacity and favorable nutrient composition of phyllosilicates, and FeOx supply essential Fe.

Fe and As geochemical self-removal dynamics in mineral waters: evidence from the Ferrarelle groundwater system (Riardo Plain, Southern Italy)

A theoretical pattern for Fe and As co-precipitation was tested directly in a groundwater natural system. Several monitoring wells were sampled to identify the different endmembers that govern the hydrodynamics of the Ferrarelle Groundwater System in the Riardo Plain (Southern Italy). In agreement with recent investigations, we found a mix of a deep and a shallow component in different proportions, resulting in a specific chemical composition of groundwater in each well depending on the percentages of each component. The shallow component was characterized by EC ~ 430 µS/cm, Eh ~ 300 mV, Fe ~ 0.06 µmol/L and As ~ 0.01-0.12 µmol/L, while the deep component was characterized by EC ~ 3400 µS/cm, Eh ~ 170 mV, Fe ~ 140 µmol/L and As ~ 0.59 µmol/L. A general attenuation of As and Fe concentration that was not due to a simple dilution effect was observed in the mixing process. The oxidation of Fe(II) to Fe(III) produces solid precipitates which adsorb As from solution and then co-precipitate. The reactions pattern of Fe(II) oxidation and As adsorption gave a linear function between [As] and [Fe], where the angular coefficient depends on the [O₂]/[H⁺] ratio. Chemical data obtained from our samples showed a very good agreement with this theoretical relationship. The investigated geochemical dynamics represented a natural process of attenuation of Fe and As, two undesirable elements that usually affect groundwater quality in volcanic aquifers in central-southern Italy, which are exploited to supply drinking water.

From Adsorption to Precipitation of U(VI): What is the Role of pH and Natural Organic Matter?

We investigated interfacial reactions of U(VI) in the presence of Suwannee River natural organic matter (NOM) at acidic and neutral pH. Laboratory batch experiments show that the adsorption and precipitation of U(VI) in the presence of NOM occur at pH 2 and pH 4, while the aqueous complexation of U by dissolved organic matter is favored at pH 7, preventing its precipitation. Spectroscopic analyses indicate that U(VI) is mainly adsorbed to the particulate organic matter at pH 4. However, U(VI)-bearing ultrafine to nanocrystalline solids were identified at pH 4 by electron microscopy. This study shows the promotion of U(VI) precipitation by NOM at low pH which may be relevant to the formation of mineralized deposits, radioactive waste repositories, wetlands, and other U- and organic-rich environmental systems.

The Effect of High Selenite and Selenate Concentrations on Ferric Oxyhydroxides Transformation under Alkaline Conditions

Iron-based nanomaterials have high technological impacts on various pro-environmental applications, including wastewater treatment using the co-precipitation method. The purpose of this research was to identify the changes of iron nanomaterial's structure caused by the presence of selenium, a typical water contaminant, which might affect the removal when the iron co-precipitation method is used. Therefore, we have investigated the maturation of co-precipitated nanosized ferric oxyhydroxides under alkaline conditions and their thermal transformation into hematite in the presence of selenite and selenate with high concentrations. Since the association of selenium with precipitates surfaces has been proven to be weak, the mineralogy of the system was affected insignificantly, and the goethite was identified as an only ferric phase in all treatments. However, the morphology and the crystallinity of ferric oxyhydroxides was slightly altered. Selenium affected the structural order of precipitates, especially at the initial phase of co-precipitation. Still, the crystal integrity and homogeneity increased with time almost constantly, regardless of the treatment. The thermal transformation into well crystalized hematite was more pronounced in the presence of selenite, while selenate-treated and selenium-free samples indicated the presence of highly disordered fraction. This highlights that the aftermath of selenium release does not result in destabilization of ferric phases; however, since weak interactions of selenium are dominant at alkaline conditions with goethite's surfaces, it still poses a high risk for the environment. The findings of this study should be applicable in waters affected by mining and metallurgical operations.

Arsenic biogeochemical cycling in paddy soil-rice system: Interaction with various factors, amendments and mineral nutrients

Arsenic (As) contamination is a well-recognized environmental and health issue, threatening over 200 million people worldwide with the prime cases in South and Southeast Asian and Latin American countries. Rice is mostly cultivated under flooded paddy soil conditions, where As speciation and accumulation by rice plants is controlled by various geo-environmental (biotic and abiotic) factors. In contrast to other food crops, As uptake in rice has been found to be substantially higher due to the prevalence of highly mobile and toxic As species, arsenite (As(III)), under paddy soil conditions. In this review, we discussed the biogeochemical cycling of As in paddy soil-rice system, described the influence of critical factors such as pH, iron oxides, organic matter, microbial species, and pathways affecting As transformation and accumulation by rice. Moreover, we elucidated As interaction with organic and inorganic amendments and mineral nutrients. The review also elaborates on As (im)mobilization processes and As uptake by rice under the influence of different mineral nutrients and amendments in paddy soil conditions, as well as their role in mitigating As transfer to rice grain. This review article provides critical information on As contamination in paddy soil-rice system, which is important to develop suitable strategies and mitigation programs for limiting As exposure via rice crop, and meet the UN's key Sustainable Development Goals (SDGs: 2 (zero hunger), 3 (good health and well-being), 12 (responsible consumption and production), and 13 (climate action)).

Mitigating translocation of arsenic from rice field to soil pore solution by manipulating the redox conditions

Arsenic (As) is uptaken more readily by rice over wheat and barley. The exposure of As to humans being in the rice-consuming regions is a serious issue. Thus, an effective practice to reduce the translocation of As from soil to rice grain should be implemented. During a flooding period, the water layer greatly limits the transport of oxygen from atmosphere to soil, which provides favorable conditions for reduction of oxygen. The reduction of Fe in the soil during the flooding condition is closely related to the As mobility, which expedites the release of As to the soil pore solution and increases As uptake by rice plants. Therefore, the performance of oxygen releasing compounds (ORCs) was evaluated to lower the translocation of As from soil to soil solution. Specifically, in the simple system containing ORCs and water, the oxygen releasing capacity of ORCs was scrutinized. In addition, ORCs was applied to sea sand and arsenic bearing ferrihydrite to identify the contribution of ORCs to As and iron mobility. Especially, ORCs were introduced to the closed (completely mixed system) and open (static) systems to simulate the paddy soil environment. Introducing ORCs increased the DO in the aqueous phase, and CaO₂ was more effective in increasing DO than MgO₂. In the static system simulating a rice field, the dissolution of ORCs was inhibited. The pH increased due to the formation of hydroxide, but the increase was not significant in the soil due to the buffering capacity of the soil. Finally, the As concentration in the soil solution was lowered to 25-50% of that of the control system by application of ORCs in the static paddy soil system. All experimental findings signify that the application of ORCs can be an effective practice to lower the translocation of As from soil to pore solution.

Advanced application of nano-technological and biological processes as well as mitigation options for arsenic removal

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.

Groundwater As Removal by As(III), Fe(II), and Mn(II) Co-Oxidation: Contrasting As Removal Pathways with O2, NaOCl, and KMnO4

Effective arsenic (As) removal from groundwater is a pressing need in view of increasingly stringent As drinking water limits in some US states and European countries. In this study, we compared the addition of weak (O₂), intermediate (NaOCl), and strong (KMnO₄) groundwater oxidants on the fate of As during As(III), Fe(II), and Mn(II) co-oxidation. Experiments were performed with 50 μg/L As(III), 5 mg/L Fe(II), and 0.5 mg/L Mn(II) in solutions containing relevant groundwater ions, with the reaction products characterized by As K-edge X-ray absorption spectroscopy (XAS). Adding O₂ by aeration was the least effective method, unable to decrease As to below 10 μg/L, which was attributed to inefficient As(III) oxidation. Dosing NaOCl (55 μM) consistently removed As to <10 μg/L (and often <5 μg/L). The As K-edge XAS data of the NaOCl samples indicated complete As(III) oxidation and As(V) sorption to coprecipitated hydrous ferric oxide (HFO) in the binuclear, bridging (²C) complex. The most effective As removal was observed with KMnO₄ (40 μM), which completely oxidized As(III) and yielded residual As concentrations that were less than (by as much as 50%) or equal to the NaOCl experiments. Furthermore, the average As-metal bond length of the KMnO₄ solids (R_As-Fe/Mn = 3.24 ± 0.02 Å) was systematically shorter than the NaOCl solids (R_As-Fe/Mn = 3.29 ± 0.02 Å), consistent with As(V) sorption to both MnO₂ and HFO. These findings can be used to optimize groundwater As treatment to meet relevant drinking water guidelines, while considering the As uptake mode and characteristics of the particle suspension (i.e., colloidal stability and filterability).

Arsenic reduction to <1 µg/L in Dutch drinking water

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.