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Removal of Naturally Occurring Strontium by Nanofiltration/Reverse Osmosis from Groundwater
Open accessAbstract
Removal of naturally occurring strontium (Sr) from groundwater is vital as excessive exposure may lead to bone growth problems in children. Nanofiltration/reverse osmosis (NF/RO) is commonly used in groundwater treatment due to the high effectiveness and simple maintenance of these pressure driven membrane processes. In this research, a pilot-scale NF/RO system was used to desalinate a natural groundwater sample containing high Sr concentration (10.3 mg/L) and “old” groundwater organic matter (70.9 mg/L) from Esilalei in northern Tanzania to understand the removal of strontium by NF/RO. The impact of applied pressure (10–15 bar) and groundwater pH (3–12) on the membrane performance including permeate flux, strontium and total organic carbon (TOC) flux and removal was investigated. Increasing applied pressure was found to enhance the flux by increasing the driving force and enhance Sr and TOC removal by dilution effect (water flux higher than Sr passage). The alkaline pH caused severe flux decline likely due to membrane fouling and scaling, while it slightly enhanced Sr removal of RO membranes, but weakened the TOC removal. In contrast, acidic and neutral pH of groundwater enhanced TOC removal. These findings suggest that appropriately high applied pressure and acidic pH condition of groundwater are recommended to apply to the NF/RO membrane system in groundwater desalination to achieve better membrane performance.
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![Figure 1 (A) Schematic of hydration shells around strontium (Sr2+) ion. Inner and outer circles represent the first and second hydration shells; (B) basic speciation of strontium in water over a wide pH range (1–14) using Visual MINTEQ software (version 3.1, KTH, Sweden) (1 mg/L strontium chloride (SrCl2), typical Sr concentration in surface water [10], 25 °C).](/paper-figures/e6f86bd70b7641a99c9bad842f123418/removal-of-naturally-occurring-strontium-by-nanofiltration-reverse-osmosis-from-figure-1.jpg)


![Figure 4 Permeate flux of membranes as a function of applied pressure (10–15 bar) with groundwater sample 5, the pH was about 9, data adapted from [69]; light grey data points are pure water flux of membranes based on the pure water permeability in Table 2.](/paper-figures/671d98ba174a45049b1ecbf699d6f3fd/removal-of-naturally-occurring-strontium-by-nanofiltration-reverse-osmosis-from-figure-4.jpg)
![Figure 5 (A) Sr permeate concentration, (B) Sr flux and (C) strontium retention as a function of applied pressure (10–15 bar) with groundwater sample 5 (feed Sr concentration 10.3 mg/L). The pH was about 9, data adapted from [69].](/paper-figures/d43a69632ac441a78ca3d51040227878/removal-of-naturally-occurring-strontium-by-nanofiltration-reverse-osmosis-from-figure-5.jpg)
![Figure 6 (A) Total organic carbon (TOC) permeate concentration, (B) TOC flux and (C) TOC retention as a function of applied pressure (10–15 bar) with groundwater sample 5 (feed TOC concentration 70.9 mg/L). The pH was about 9, data adapted from [69].](/paper-figures/69a0647d177c4c60877542ee26ddabad/removal-of-naturally-occurring-strontium-by-nanofiltration-reverse-osmosis-from-figure-6.jpg)


![Figure 9 Permeate flux of three membranes as a function of pH (3–12) with groundwater sample 5. The grey area represents the pH range of groundwater 1–5. The applied pressure was 10 bar, data adapted from [69].](/paper-figures/ce06b0b9e7864cd18b97acd0882929a7/removal-of-naturally-occurring-strontium-by-nanofiltration-reverse-osmosis-from-figure-9.jpg)
![Figure 10 (A) Sr permeate concentration, (B) Sr flux and (C) Sr retention of three membranes as a function of the pH (3–12) of groundwater sample 5. The grey area represents the pH range of groundwater samples 1–5. The applied pressure was 10 bar. Data adapted from [69].](/paper-figures/65f5afc701614f3293cf7fa3ce74a778/removal-of-naturally-occurring-strontium-by-nanofiltration-reverse-osmosis-from-figure-10.jpg)
![Figure 11 (A) TOC permeate concentration, (B) TOC flux and (C) TOC retention as a function of the pH (3−12) of groundwater sample 5. The grey area is TOC removal at the pH range of groundwater samples 1−5. The applied pressure was 10 bar. Data adapted from [69].](/paper-figures/a0b69893b35347bc9011f25e2f474a45/removal-of-naturally-occurring-strontium-by-nanofiltration-reverse-osmosis-from-figure-11.jpg)
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In the citing paper
“Significant progress has been achieved in many nanomembrane methods, including ultrafiltration, nanofiltration, and reverse osmosis.172,173”
From Emerging nanotechnology approaches for sustainable water treatment and heavy metals removal: a comprehensive review (2025) · cites this paper as [172]
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Citations
Cites
Peer Reviewed: Characterizing Aquatic Dissolved Organic Matter
Leenheer, J. A., & Croué, J. (2003) · Environmental Science & Technology · doi:10.1021/es032333c · Cited by 5,785 · cited 1×
“The factors influencing the characteristics of NOM include location, pH, water chemistry, temperature, and biological processes [19].”
BackgroundCharacterizing aquatic dissolved organic matter.
Leenheer, J. A., & Croué, J.-P. (2003) · PubMed · Cited by 4,891
Phenomenological Theory of Ion Solvation. Effective Radii of Hydrated Ions
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Metal Ion Binding by Humic Acid: Application of the NICA-Donnan Model
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“The dissolved organic matter (DOC) of humic acid from a non-ideal competitive adsorption model combined with the Donnan-type model (NICA-Donnan model) [22] in the software was used as NOM.”
MethodNatural organic matter-cations complexation and its impact on water treatment: A critical review
Adusei-Gyamfi, J., Ouddane, B., Rietveld, L. C., Cornard, J. P., & Criquet, J. (2019) · Water Research · doi:10.1016/j.watres.2019.05.064 · Cited by 410 · cited 1×
“pH may affect these interactions by changing the charge and structure of NOM [21,24].”
BackgroundDielectric exclusion of ions from membranes
Yaroshchuk, A. E. (2000) · Advances in Colloid and Interface Science · doi:10.1016/s0001-8686(99)00021-4 · Cited by 396 · cited 1×
“The interactions of ions with the bound electric charges induced by ion interfaces between different media dielectric constants cause the dielectric exclusion [48].”
BackgroundPark, Y., Lee, Y.-C., Shin, W. S., & Choi, S.-J. (2010) · Chemical Engineering Journal · doi:10.1016/j.cej.2010.06.026 · Cited by 389
Factors affecting natural organic matter (NOM) and scaling fouling in NF membranes: A review
Al-Amoudi, A. S. (2010) · Desalination · doi:10.1016/j.desal.2010.04.003 · Cited by 351 · cited 1×
“Divalent cations can form complexes with chelating micelles, polymers, and NOM [53], enhancing the Sr removal by more open membranes.”
Background
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Shrestha, R., Ban, S., Devkota, S., Sharma, S., Joshi, R., Tiwari, A. P., Kim, H. Y., & Joshi, M. K. (2021) · Journal of Environmental Chemical Engineering · doi:10.1016/j.jece.2021.105688 · Cited by 961
Abidli, A., Huang, Y., Ben Rejeb, Z., Zaoui, A., & Park, C. B. (2022) · Chemosphere · doi:10.1016/j.chemosphere.2021.133102 · Cited by 194
Progress in Research and Application of Nanofiltration (NF) Technology for Brackish Water Treatment
Tian, J., Zhao, X., Gao, S., Wang, X., & Zhang, R. (2021) · Membranes · doi:10.3390/membranes11090662 · Cited by 84
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“172,173”
Metadata
- Authors
- Cai, Y.-H., Yang, X. J., & Schäfer, A. I.
- Affiliations
- Karlsruhe Institute of Technology (DE)
- Beijing University of Chemical Technology (CN)
- Corresponding author
- Schäfer, Andrea Iris
- Venue
- Membranes
- Publisher
- MDPI AG
- Published
- 2020-10-30
- Volume
- 10
- Issue
- 11
- Pages
- 321
- ISSN
- 2077-0375 (ISSN-L)
- PMC
- PMC7693364
- OpenAlex
- W3097766034
- Cited by
- 47
- References
- 67
- Citations by year
- 2026: 6 · 2025: 8 · 2024: 8 · 2023: 6 · 2022: 8 · 2021: 11
- FWCI
- 1.92
- Type
- journal article
- Language
- en
- Open access
- gold
- doi.org
- Licence
- Locations
- Membranes (publishedVersion, cc-by)
- PubMed Central (publishedVersion, cc-by)
- PubMed (publishedVersion)
- Repository KITopen (Karlsruhe Institute of Technology) (submittedVersion, cc-by)
- DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion, cc-by-sa)
- KITopen (cc-by)
- Funders
- Leverhulme Trust
- China Scholarship Council
- Université de Genève
- Beijing University of Chemical Technology
- Topics
- Physical Sciences › Environmental Science › Water Science and Technology › Membrane Separation Technologies
- Physical Sciences › Chemical Engineering › Filtration and Separation › Membrane-based Ion Separation Techniques
- Physical Sciences › Environmental Science › Waste Management and Disposal › Wastewater Treatment and Reuse
- Keywords
- strontium removal, nanofiltration, reverse osmosis, groundwater treatment, groundwater desalination, total organic carbon removal, membrane fouling, scaling, applied pressure, groundwater pH, permeate flux
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