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Konadu-Amoah B, Hu R, Ndé-Tchoupé AI, Gwenzi W, Noubactep C. Metallic iron (Fe 0)-based materials for aqueous phosphate removal: A critical review. JOURNAL OF ENVIRONMENTAL MANAGEMENT 2022; 315:115157. [PMID: 35526394 DOI: 10.1016/j.jenvman.2022.115157] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/24/2022] [Revised: 04/06/2022] [Accepted: 04/22/2022] [Indexed: 06/14/2023]
Abstract
The discharge of excessive phosphate from wastewater sources into the aquatic environment has been identified as a major environmental threat responsible for eutrophication. It has become essential to develop efficient but affordable techniques to remove excess phosphate from wastewater before discharging into freshwater bodies. The use of metallic iron (Fe0) as a reactive agent for aqueous phosphate removal has received a wide attention. Fe0 in-situ generates positively charged iron corrosion products (FeCPs) at pH > 4.5, with high binding affinity for anionic phosphate. This study critically reviews the literature that focuses on the utilization of Fe0-based materials for aqueous phosphate removal. The fundamental science of aqueous iron corrosion and historical background of the application of Fe0 for phosphate removal are elucidated. The main mechanisms for phosphate removal are identified and extensively discussed based on the chemistry of the Fe0/H2O system. This critical evaluation confirms that the removal process is highly influenced by several operational factors including contact time, Fe0 type, influent geochemistry, initial phosphate concentration, mixing conditions, and pH value. The difficulty in comparing independent results owing to diverse experimental conditions is highlighted. Moreover, contemporary research in progress including Fe0/oxidant systems, nano-Fe0 application, Fe0 material selection, desorption studies, and proper design of Fe0-based systems for improved phosphate removal have been discussed. Finally, potential strategies to close the loop in Fe0-based phosphate remediation systems are discussed. This review presents a science-based guide to optimize the efficient design of Fe0-based systems for phosphate removal.
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Affiliation(s)
- Bernard Konadu-Amoah
- School of Earth Science and Engineering, Hohai University, Fo Cheng Xi Road 8, Nanjing, 211100, China.
| | - Rui Hu
- School of Earth Science and Engineering, Hohai University, Fo Cheng Xi Road 8, Nanjing, 211100, China.
| | - Arnaud Igor Ndé-Tchoupé
- School of Earth Science and Engineering, Hohai University, Fo Cheng Xi Road 8, Nanjing, 211100, China.
| | - Willis Gwenzi
- Biosystems and Environmental Engineering Research Group, Department of Agricultural and Biosystems Engineering, University of Zimbabwe, P.O. Box MP167, Mount Pleasant, Harare, Zimbabwe.
| | - Chicgoua Noubactep
- School of Earth Science and Engineering, Hohai University, Fo Cheng Xi Road 8, Nanjing, 211100, China; Centre for Modern Indian Studies (CeMIS), University of Göttingen, Waldweg 26, 37073, Göttingen, Germany; Department of Water and Environmental Science and Engineering, Nelson Mandela African Institution of Science and Technology, Arusha P.O. Box 447, Tanzania; Faculty of Science and Technology, Campus of Banekane, Université des Montagnes, P.O. Box 208, Bangangté, Cameroon.
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Konadu-Amoah B, Ndé-Tchoupé AI, Hu R, Gwenzi W, Noubactep C. Investigating the Fe 0/H 2O systems using the methylene blue method: Validity, applications, and future directions. CHEMOSPHERE 2022; 291:132913. [PMID: 34788675 DOI: 10.1016/j.chemosphere.2021.132913] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/03/2021] [Revised: 11/12/2021] [Accepted: 11/13/2021] [Indexed: 06/13/2023]
Abstract
An innovative approach to characterize the reactivity of metallic iron (Fe0) for aqueous contaminant removal has been in use for a decade: The methylene blue method (MB method). The approach considers the differential adsorptive affinity of methylene blue (MB) for sand and iron oxides. The MB method characterizes MB discoloration by sand as it is progressively coated by in-situ generated iron corrosion products (FeCPs) to deduce the extent of iron corrosion. The MB method is a semi-quantitative tool that has successfully clarified some contradicting reports on the Fe0/H2O system. Moreover, it has the potential to serve as a powerful tool for routine tests in the Fe0 remediation industry, including quality assurance and quality control (QA/QC). However, MB is widely used as a 'molecular probe' to characterize the Fe0/H2O system, for instance for wastewater treatment. Thus, there is scope to avoid confusion created by the multiple uses of MB in Fe0/H2O systems. The present communication aims at filling this gap by presenting the science of the MB method, and its application and limitations. It is concluded that the MB method is very suitable for Fe0 material screening and optimization of operational designs. However, the MB method only provides semi-quantitative information, but gives no data on the solid-phase characterization of solid Fe0 and its reaction products. In other words, further comprehensive investigations with microscopic and spectroscopic surface and solid-state analyses are needed to complement results from the MB method.
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Affiliation(s)
- Bernard Konadu-Amoah
- School of Earth Science and Engineering, Hohai University, Fo Cheng Xi Road 8, Nanjing 211100, China.
| | - Arnaud Igor Ndé-Tchoupé
- School of Earth Science and Engineering, Hohai University, Fo Cheng Xi Road 8, Nanjing 211100, China.
| | - Rui Hu
- School of Earth Science and Engineering, Hohai University, Fo Cheng Xi Road 8, Nanjing 211100, China.
| | - Willis Gwenzi
- Biosystems and Environmental Engineering Research Group, Department of Agricultural and Biosystems Engineering, University of Zimbabwe, P.O. Box MP167, Mount Pleasant, Harare, Zimbabwe.
| | - Chicgoua Noubactep
- Centre for Modern Indian Studies (CeMIS), Universität Göttingen, Waldweg 26, 37073 Göttingen, Germany; Department of Applied Geology, University of Göttingen, Goldschmidtstraße 3, D-37077 Göttingen, Germany; Department of Water and Environmental Science and Engineering, Nelson Mandela African Institution of Science and Technology, P.O. Box 447, Arusha, Tanzania; Faculty of Science and Technology, Campus of Banekane, Université des Montagnes, P.O. Box 208, Bangangté, Cameroon.
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Noubactep C. Should the term 'metallic iron' appear in the title of a research paper? CHEMOSPHERE 2022; 287:132314. [PMID: 34600924 DOI: 10.1016/j.chemosphere.2021.132314] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/25/2021] [Revised: 09/06/2021] [Accepted: 09/19/2021] [Indexed: 06/13/2023]
Abstract
Over the past three decades, groundwater remediation using permeable reactive barriers (PRBs) has proven to be effective. The majority of installed PRBs uses metallic iron (Fe(0)) as a reactive material. However, the success of implemented Fe(0) PRBs is yet to be rationalized as Fe(0) is a generator of iron oxides (contaminant scavengers) and secondary reducing agents (e.g. Fe(II), Fe3O4, H2, green rust), This communication demonstrates that Fe(0) is not an environmental reducing agent. Therefore, more science-based investigations are needed to optimize the operation of Fe(0) PRBs. In particular, Fe(0) PRBs and Fe(0)-based water filters should be regarded as particular cases of "metal corrosion in porous media". A key feature of such systems is that the extent of Fe0 corrosion temporally depends on the residual porosity (capillarity). Thus, the functionality of any Fe0 PRB should be monitored in a way that the time-dependent variation of the kinetic of iron corrosion is discussed.
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Affiliation(s)
- Chicgoua Noubactep
- Centre for Modern Indian Studies (CeMIS), Universität Göttingen, Waldweg 26, 37073, Göttingen, Germany; Faculty of Science and Technology, Campus of Banekane, Université des Montagnes, P.O. Box 208, Bangangté, Cameroon; Department of Water and Environmental Science and Engineering, Nelson Mandela African Institution of Science and Technology, P.O. Box 447, Arusha, Tanzania; School of Earth Science and Engineering, Hohai University, Fo Cheng Xi Road 8, Nanjing, 211100, China; Department of Applied Geology, University of Göttingen, Goldschmidtstraße 3, D-37077, Göttingen, Germany.
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Cao V, Ndé-Tchoupé AI, Hu R, Gwenzi W, Noubactep C. The mechanism of contaminant removal in Fe(0)/H 2O systems: The burden of a poor literature review. CHEMOSPHERE 2021; 280:130614. [PMID: 33940455 DOI: 10.1016/j.chemosphere.2021.130614] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/25/2020] [Revised: 03/14/2021] [Accepted: 04/15/2021] [Indexed: 06/12/2023]
Abstract
The global effort to mitigate the impact of environmental pollution has led to the use of various types of metallic iron (Fe(0)) in the remediation of soil and groundwater as well as in the treatment of industrial and municipal effluents. During the past three decades, hundreds of scientific publications have controversially discussed the mechanism of contaminant removal in Fe(0)/H2O systems, with the large majority considering Fe(0) to be oxidized by contaminants of concern. This view assumes that contaminant reduction is the cathodic reaction occurring simultaneously with Fe0 oxidative dissolution (anodic reaction). This view contradicts the century-old theory of the electrochemical nature of aqueous iron corrosion and hinders progress in designing efficient and sustainable remediation Fe(0)/H2O systems. The aim of the present communication is to demonstrate the fallacy of the current prevailing view based on articles published before 1910. It is shown that properly reviewing the literature would have avoided the mistake. Going back to the roots is recommended as the way forward and should be considered first while designing laboratory experiments.
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Affiliation(s)
- Viet Cao
- Faculty of Natural Sciences, Hung Vuong University, Nguyen Tat Thanh Street, Viet Tri, 35120, Phu Tho, Viet Nam.
| | - Arnaud Igor Ndé-Tchoupé
- School of Earth Science and Engineering, Hohai University, Fo Cheng Xi Road 8, Nanjing, 211100, China.
| | - Rui Hu
- School of Earth Science and Engineering, Hohai University, Fo Cheng Xi Road 8, Nanjing, 211100, China.
| | - Willis Gwenzi
- Biosystems and Environmental Engineering Research Group, Department of Soil Science and Agricultural Engineering, University of Zimbabwe, P.O. Box MP167, Mt. Pleasant, Harare, Zimbabwe.
| | - Chicgoua Noubactep
- Department of Applied Geology, University of Göttingen, Goldschmidtstraße 3, D-37077, Göttingen, Germany; Centre for Modern Indian Studies (CeMIS), Universität Göttingen, Waldweg 26, 37073, Göttingen, Germany; Department of Water and Environmental Science and Engineering, Nelson Mandela African Institution of Science and Technology, P.O. Box 447, Arusha, Tanzania; Faculty of Science and Technology, Campus of Banekane, Université des Montagnes, P.O. Box 208, Bangangté, Cameroon.
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Universal Access to Safe Drinking Water: Escaping the Traps of Non-Frugal Technologies. SUSTAINABILITY 2021. [DOI: 10.3390/su13179645] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
This communication is motivated by recent publications discussing the affordability of appropriate decentralized solutions for safe drinking water provision in low-income communities. There is a huge contrast between the costs of presented technologies, which vary by a factor of up to 12. For example, for the production of 2000 L/d of treated drinking water, the costs vary between about 1500 and 12,000 Euro. A closer look at the technologies reveals that expensive technologies use imported manufactured components or devices that cannot yet be locally produced. In the battle to achieve the United Nations Sustainable Development Goal for safe drinking water (SDG 6.1), such technologies should be, at best, considered as bridging solutions. For a sustainable self-reliance in safe drinking water supply, do-it-yourself (DIY) systems should be popularized. These DIY technologies include biochar and metallic iron (Fe0) based systems. These relevant technologies should then be further improved through internal processes.
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Application of the Kilimanjaro Concept in Reversing Seawater Intrusion and Securing Water Supply in Zanzibar, Tanzania. WATER 2021. [DOI: 10.3390/w13152085] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
There is escalating salinity levels on small islands due to uncontrolled groundwater extraction. Conventionally, this challenge is addressed by adopting optimal groundwater pumping strategies. Currently, on Unguja Island (Zanzibar), urban freshwater is supplied by desalination, which is expensive and energy-intensive. Hence, desalinization cannot be afforded by rural communities. This study demonstrates that the innovative Kilimanjaro Concept (KC), based on rainwater harvesting (RWH) can remediate seawater intrusion in Unguja, while enabling a universal safe drinking water supply. The reasoning is rooted in the water balance of the whole island. It is shown that if rainwater is systematically harvested, quantitatively stored, and partly infiltrated, seawater intrusion will be reversed, and a universal safe drinking water supply will be secured. Water treatment with affordable technologies (e.g., filtration and adsorption) is suggested. The universality of KC and its suitability for small islands is demonstrated. Future research should focus on pilot testing of this concept on Unguja Island and other island nations.
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Cao V, Alyoussef G, Gatcha-Bandjun N, Gwenzi W, Noubactep C. The key role of contact time in elucidating the mechanisms of enhanced decontamination by Fe 0/MnO 2/sand systems. Sci Rep 2021; 11:12069. [PMID: 34103590 PMCID: PMC8187491 DOI: 10.1038/s41598-021-91475-x] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2021] [Accepted: 05/26/2021] [Indexed: 11/20/2022] Open
Abstract
Metallic iron (Fe0) has shown outstanding performances for water decontamination and its efficiency has been improved by the presence of sand (Fe0/sand) and manganese oxide (Fe0/MnOx). In this study, a ternary Fe0/MnOx/sand system is characterized for its discoloration efficiency of methylene blue (MB) in quiescent batch studies for 7, 18, 25 and 47 days. The objective was to understand the fundamental mechanisms of water treatment in Fe0/H2O systems using MB as an operational tracer of reactivity. The premise was that, in the short term, both MnO2 and sand delay MB discoloration by avoiding the availability of free iron corrosion products (FeCPs). Results clearly demonstrate no monotonous increase in MB discoloration with increasing contact time. As a rule, the extent of MB discoloration is influenced by the diffusive transport of MB from the solution to the aggregates at the bottom of the vessels (test-tubes). The presence of MnOx and sand enabled the long-term generation of iron hydroxides for MB discoloration by adsorption and co-precipitation. Results clearly reveal the complexity of the Fe0/MnOx/sand system, while establishing that both MnOx and sand improve the efficiency of Fe0/H2O systems in the long-term. This study establishes the mechanisms of the promotion of water decontamination by amending Fe0-based systems with reactive MnOx.
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Affiliation(s)
- Viet Cao
- Faculty of Natural Sciences, Hung Vuong University, Nguyen Tat Thanh Street, Viet Tri, Phu Tho, 35120, Vietnam
| | - Ghinwa Alyoussef
- Angewandte Geologie, Universität Göttingen, Goldschmidtstraße 3, 37077, Göttingen, Germany
| | - Nadège Gatcha-Bandjun
- Department of Chemistry, Faculty of Science, University of Maroua, BP 46, Maroua, Cameroon
| | - Willis Gwenzi
- Biosystems and Environmental Engineering Research Group, Department of Agricultural and Biosystems Engineering, University of Zimbabwe, P.O. Box MP167, Mt. Pleasant, Harare, Zimbabwe
| | - Chicgoua Noubactep
- Angewandte Geologie, Universität Göttingen, Goldschmidtstraße 3, 37077, Göttingen, Germany.
- Centre for Modern Indian Studies (CeMIS), Universität Göttingen, Waldweg 26, 37073, Göttingen, Germany.
- Department of Water and Environmental Science and Engineering, Nelson Mandela African Institution of Science and Technology, P.O. Box 447, Arusha, Tanzania.
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Cao V, Alyoussef G, Gatcha-Bandjun N, Gwenzi W, Noubactep C. Characterizing the impact of MnO 2 addition on the efficiency of Fe 0/H 2O systems. Sci Rep 2021; 11:9814. [PMID: 33963252 PMCID: PMC8105408 DOI: 10.1038/s41598-021-89318-w] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2021] [Accepted: 04/21/2021] [Indexed: 11/23/2022] Open
Abstract
The role of manganese dioxide (MnO2) in the process of water treatment using metallic iron (Fe0/H2O) was investigated in quiescent batch experiments for t ≤ 60 d. MnO2 was used as an agent to control the availability of solid iron corrosion products (FeCPs) while methylene blue (MB) was an indicator of reactivity. The investigated systems were: (1) Fe0, (2) MnO2, (3) sand, (4) Fe0/sand, (5) Fe0/MnO2, and (6) Fe0/sand/MnO2. The experiments were performed in test tubes each containing 22.0 mL of MB (10 mg L−1) and the solid aggregates. The initial pH value was 8.2. Each system was characterized for the final concentration of H+, Fe, and MB. Results show no detectable level of dissolved iron after 47 days. Final pH values varied from 7.4 to 9.8. The MB discoloration efficiency varies from 40 to 80% as the MnO2 loading increases from 2.3 to 45 g L−1. MB discoloration is only quantitative when the operational fixation capacity of MnO2 for Fe2+ was exhausted. This corresponds to the event where adsorption and co-precipitation with FeCPs is intensive. Adsorption and co-precipitation are thus the fundamental mechanisms of decontamination in Fe0/H2O systems. Hybrid Fe0/MnO2 systems are potential candidates for the design of more sustainable Fe0 filters.
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Affiliation(s)
- Viet Cao
- Faculty of Natural Sciences, Hung Vuong University, Nguyen Tat Thanh Street, Viet Tri, Phu Tho, 35120, Vietnam
| | - Ghinwa Alyoussef
- Angewandte Geologie, Universität Göttingen, Goldschmidtstraße 3, 37077, Göttingen, Germany
| | - Nadège Gatcha-Bandjun
- Faculty of Science, Department of Chemistry, University of Maroua, BP 46, Maroua, Cameroon
| | - Willis Gwenzi
- Biosystems and Environmental Engineering Research Group, Department of Agricultural and Biosystems Engineering, University of Zimbabwe, P.O. Box MP167, Mt. Pleasant, Harare, Zimbabwe
| | - Chicgoua Noubactep
- Angewandte Geologie, Universität Göttingen, Goldschmidtstraße 3, 37077, Göttingen, Germany. .,Centre for Modern Indian Studies (CeMIS), Universität Göttingen, Waldweg 26, 37073, Göttingen, Germany. .,Department of Water and Environmental Science and Engineering, Nelson Mandela African Institution of Science and Technology, P.O. Box 447, Arusha, Tanzania.
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Characterizing the impact of pyrite addition on the efficiency of Fe 0/H 2O systems. Sci Rep 2021; 11:2326. [PMID: 33504819 PMCID: PMC7841150 DOI: 10.1038/s41598-021-81649-y] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2020] [Accepted: 12/31/2020] [Indexed: 01/30/2023] Open
Abstract
The role of pyrite (FeS2) in the process of water treatment using metallic iron (Fe0) was investigated. FeS2 was used as a pH-shifting agent while methylene blue (MB) and methyl orange (MO) were used as an indicator of reactivity and model contaminant, respectively. The effect of the final pH value on the extent of MB discoloration was characterized using 5 g L-1 of a Fe0 specimen. pH variation was achieved by adding 0 to 30 g L-1 of FeS2. Quiescent batch experiments with Fe0/FeS2/sand systems (sand loading: 25 g L-1) and 20 mL of MB were performed for 41 days. Final pH values varied from 3.3 to 7.0. Results demonstrated that MB discoloration is only quantitative when the final pH value was larger than 4.5 and that adsorption and co-precipitation are the fundamental mechanisms of decontamination in Fe0/H2O systems. Such mechanisms are consistent with the effects of the pH value on the decontamination process.
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Validating the Efficiency of the FeS2 Method for Elucidating the Mechanisms of Contaminant Removal Using Fe0/H2O Systems. Processes (Basel) 2020. [DOI: 10.3390/pr8091162] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
There is growing interest in using pyrite minerals (FeS2) to enhance the efficiency of metallic iron (Fe0) for water treatment (Fe0/H2O systems). This approach contradicts the thermodynamic predicting suppression of FeS2 oxidation by Fe0 addition. Available results are rooted in time series correlations between aqueous and solid phases based on data collected under various operational conditions. Herein, the methylene blue method (MB method) is used to clarify the controversy. The MB method exploits the differential adsorptive affinity of MB onto sand and sand coated with iron corrosion products to assess the extent of Fe0 corrosion in Fe0/H2O systems. The effects of the addition of various amounts of FeS2 to a Fe0/sand mixture (FeS2 method) on MB discoloration were characterized in parallel quiescent batch experiments for up to 71 d (pH0 = 6.8). Pristine and aged FeS2 specimens were used. Parallel experiments with methyl orange (MO) and reactive red 120 (RR120) enabled a better discussion of the achieved results. The results clearly showed that FeS2 induces a pH shift and delays Fe precipitation and sand coating. Pristine FeS2 induced a pH shift to values lower than 4.5, but no quantitative MB discoloration occurred after 45 d. Aged FeS2 could not significantly shift the pH value (final pH ≥ 6.4) but improved the MB discoloration. The used systematic sequence of experiments demonstrated that adsorption and coprecipitation are the fundamental mechanisms of contaminant removal in Fe0/H2O systems. This research has clarified the reason why a FeS2 addition enhances the efficiency of Fe0 environmental remediation.
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