Vermelding onderdeel organisatie March 25, 2022 1 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
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Vermelding onderdeel organisatie
April 18, 2023
1
Modeling subsurface iron removalGeochemical modeling of subsurface aeration at Schuwacht Lekkerkerk
Harmen van der Laan
Faculty of Civil EngineeringMsc. Water ManagementSpecilization Drinking Water
April 18, 2023 2
Content
• Subsurface iron removal• Objective research• Results• Conclusions• Next steps & Recommendations
April 18, 2023 3
Content
• Subsurface iron removal• Objective research• Results• Conclusions• Next steps & Recommendations
April 18, 2023 4
Subsurface iron removal
O2
front
0
1
inje
cted
wat
er
O2
fro
nt
injected
water
Fe2+
front 0
1
Fe2+
front
Fe2+
front
0
1
0
1
Fe2+
front
inje
cted
wat
er
Injection Extraction
Measured data
5April 18, 2023
April 18, 2023 6
Measured data
Development final iron concentration
0
1
2
3
4
5
6
7
0 5 10 15 20 25 30 35
injection - extraction cycles
Fe (
mg/
L)
July 1998 – June 2000 March 2004 – June 2005
‘Original’ Model
7April 18, 2023
V/Vi
Expanded model
8April 18, 2023
main limitation original model
No explanation for the phenomena of the increasing spread of the (iron) front over the successive cycles
April 18, 2023 9
Content
• Subsurface iron removal• Objective research• Results• Conclusions• Next steps & Recommendations
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
10April 18, 2023
April 18, 2023 11
Content
• Subsurface iron removal• Objective research• Results• Conclusions• Next steps & Recommendations
April 18, 2023 12
Results
I. Goethite / FerrihydriteII. Ion exchange vs. AdsorptionIII.Transport modeling
April 18, 2023 13
Goethite vs. Ferrihydrite
FerrihydriteHfo, 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
Goethiteα-FeOOH
Stable Crystalline Spec. area ≈ 60 m2/g 2 - 10 sites / nm2 pHPZC 8.7 Solubility log K = -1
Observed by: Mettler (2002)
April 18, 2023 14
Surface complexation theory
OHOH
OHOH
OH + / - depends
on pH
Number of sites
Surface area
Fe2
+
Fe2
+
Fe2
+
April 18, 2023 15
Site density
April 18, 2023 16
Surface characterization
April 18, 2023 17
Goethite vs. Ferrihydrite ?
• Variations in site density and surface area only result in small bandwidth
• Differences between Goethite and Ferrihydrite not the main limitation
α-FeOOH
Ferrihydrite
‘solubility’ decreases in time
April 18, 2023 18
Results
I. Goethite / FerrihydriteII. Ion exchange vs. AdsorptionIII.Transport modeling
Exchange
April 18, 2023 19
Exchange
April 18, 2023 20
Exchange and adsorption hard to distinguish
Exchange capacity = lumped parameter
Empirical formula
does not give correct output
CEC (meq/kg) = 7 · (% clay) + 35 · (% C)
April 18, 2023 21
Results
I. Goethite / FerrihydriteII. Ion exchange vs. AdsorptionIII.Transport modeling
April 18, 2023 22
Retardation / Front spreading
April 18, 2023 23
Microdispersion Macrodispersivity
Injection well
April 18, 2023 24
Dispersion
Stagnant zones
April 18, 2023 25
Stagnant zones
April 18, 2023 26
April 18, 2023 27
Results
• Subsurface iron removal• Objective research• Results• Preliminary Conclusions• Next steps & Recommendations
Preliminary Conclusions
Objective is: Theoretical foundation and a better model
I. Many ‘flavors’, but I need too pick oneII. Model starts to describe the correct retardation
mainly because of dispersion / stagnant zones
April 18, 2023 28
April 18, 2023 29
Possible explanation
Ferric
iron
I. Kinetics: decrease SI in time / combination Ferrihydrite – Goethite
II. Stagnant zones III. Or:
Biological activity?Complexes? Change groundwater composition?
April 18, 2023 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
April 18, 2023 31
Questions?
Related Documents
