Modeling subsurface iron removal

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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
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Content

• Subsurface iron removal
• Objective research
• Results
• Conclusions
• Next steps Recommendations

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Content

• Subsurface iron removal
• Objective research
• Results
• Conclusions
• Next steps Recommendations

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Subsurface iron removal
Injection
Extraction
injected water
Fe2 front
Fe2 front
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Measured data
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Measured data
July 1998 June 2000
March 2004 June 2005
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Original Model
V/Vi
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Expanded model
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Content

• Subsurface iron removal
• Objective research
• Results
• Conclusions
• Next steps Recommendations

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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

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Content

• Subsurface iron removal
• Objective research
• Results
• Conclusions
• Next steps Recommendations

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Results

• Goethite / Ferrihydrite
• Ion exchange vs. Adsorption
• Transport modeling

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Goethite vs. Ferrihydrite

• Ferrihydrite
• Hfo, FeOH3, Fe5HO84H2O
• 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
• a-FeOOH
• Stable
• Crystalline
• Spec. area 60 m2/g
• 2 - 10 sites / nm2
• pHPZC 8.7
• Solubility log K -1
• Observed by Mettler (2002)

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Surface complexation theory
Fe2
Fe2
Fe2
OH
OH
OH
OH
OH
/ - depends on pH
Surface area
Number of sites
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Site density
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Surface characterization
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Goethite vs. Ferrihydrite ?

• Variations in site density and surface area only
  result in small bandwidth
• Differences between Goethite and Ferrihydrite not
  the main limitation

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Results

• Goethite / Ferrihydrite
• Ion exchange vs. Adsorption
• Transport modeling

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Exchange
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Exchange
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Results

• Goethite / Ferrihydrite
• Ion exchange vs. Adsorption
• Transport modeling

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Retardation / Front spreading
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Macrodispersivity
Microdispersion
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Dispersion
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Stagnant zones
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Stagnant zones
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Results

• Subsurface iron removal
• Objective research
• Results
• Preliminary Conclusions
• Next steps Recommendations

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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

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Possible explanation
Ferric iron

• Kinetics decrease SI in time / combination
  Ferrihydrite Goethite
• Stagnant zones
• OrBiological activity?Complexes? Change
  groundwater composition?

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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

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Questions?
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