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Modeling subsurface iron removal

Modeling subsurface iron removal. Geochemical modeling of subsurface aeration at Schuwacht Lekkerkerk. Harmen van der Laan. Faculty of Civil Engineering Msc. Water Management Specilization Drinking Water. Content. Subsurface iron removal Objective research Results Conclusions

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Modeling subsurface iron removal

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  1. Modeling subsurface iron removal Geochemical modeling of subsurface aeration at Schuwacht Lekkerkerk Harmen van der Laan Faculty of Civil EngineeringMsc. Water Management Specilization Drinking Water

  2. Content • Subsurface iron removal • Objective research • Results • Conclusions • Next steps & Recommendations

  3. Content Subsurface iron removal Objective research Results Conclusions Next steps & Recommendations September 21, 2014 3

  4. Subsurface iron removal Injection Extraction O2 front injected water injected water injected water O2 front 1 1 1 1 C/C0 C/C0 C/C0 C/C0 Fe2+ front Fe2+ front 0 0 0 0 Fe2+ front Fe2+ front September 21, 2014 4

  5. Measured data September 21, 2014 5

  6. Measured data July 1998 – June 2000 March 2004 – June 2005 September 21, 2014 6

  7. ‘Original’ Model V/Vi September 21, 2014 7

  8. main limitation original model No explanation for the phenomena of the increasing spread of the (iron) front over the successive cycles Expanded model September 21, 2014 8

  9. Content Subsurface iron removal Objective research Results Conclusions Next steps & Recommendations September 21, 2014 9

  10. Objective The objective of this research project is to • Find a theoretical foundation to explain the development of the iron front over the successive cycles • Enhance the existing model to obtain a proper description of the measured iron concentrations September 21, 2014 10

  11. Content Subsurface iron removal Objective research Results Conclusions Next steps & Recommendations September 21, 2014 11

  12. Results Goethite / Ferrihydrite Ion exchange vs. Adsorption Transport modeling September 21, 2014 12

  13. Goethite vs. Ferrihydrite Ferrihydrite Hfo, FeOH3, Fe5HO8·4H2O Unstable, unstructured Amorphous / Aquaeous Spec. area ≈ 600 m2/g 2 sites / nm2 pHPZC 8.1 Solubility log K = 2 – 4.5 Observed by: KIWA Research Goethite α-FeOOH • Stable • Crystalline • Spec. area ≈ 60 m2/g • 2 - 10 sites / nm2 • pHPZC 8.7 • Solubility log K = -1 • Observed by: Mettler (2002) September 21, 2014 13

  14. Surface complexation theory Fe2+ Fe2+ Fe2+ OH OH OH OH OH + / - depends on pH Surface area Number of sites

  15. Site density

  16. Surface characterization

  17. Goethite vs. Ferrihydrite ? • Ferrihydrite • Variations in site density and surface area only result in small bandwidth • Differences between Goethite and Ferrihydrite not the main limitation • α-FeOOH ‘solubility’ decreases in time September 21, 2014 17

  18. Results Goethite / Ferrihydrite Ion exchange vs. Adsorption Transport modeling September 21, 2014 18

  19. Exchange

  20. Exchange • Exchange and adsorption hard to distinguish • Exchange capacity = lumped parameter • Empirical formula does not give correct output

  21. Results Goethite / Ferrihydrite Ion exchange vs. Adsorption Transport modeling September 21, 2014 21

  22. Retardation / Front spreading

  23. Macrodispersivity Microdispersion Injection well

  24. Dispersion

  25. Stagnant zones

  26. Stagnant zones

  27. Results Subsurface iron removal Objective research Results Preliminary Conclusions Next steps & Recommendations September 21, 2014 27

  28. Preliminary Conclusions Objective is: Theoretical foundation and a better model • Many ‘flavors’, but I need too pick one • Model starts to describe the correct retardationmainly because of dispersion / stagnant zones

  29. Possible explanation Ferric iron • Kinetics: decrease SI in time / combination Ferrihydrite – Goethite • Stagnant zones • Or:Biological activity?Complexes? Change groundwater composition? September 21, 2014 29

  30. Next steps & Recommendations Next steps Tracer in groundwater for dispersion? Implementation stagnant zones Influence conclusions on accumulation Finish model Recommendations Column experiments: separate transport model from geochemistry Research Ferrihydrite / Goethite September 21, 2014 30

  31. Questions? September 21, 2014 31

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