1. Subsurface iron removal for drinking water production: understanding the process and exploiting beneficial side effects
ir. Doris van Halem1,2 ir. Weren de Vet1,3 prof. dr. Gary Amy1,2 prof. ir. Hans van Dijk1
1 Delft University of Technology, The Netherlands
2 UNESCO-IHE Institute for Water Education, The Netherlands
3 Oasen Drinking Water Company, The Netherlands
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2. Lay-out of this presentation
Introduction to subsurface iron removal
Oasen drinking water company
Subsurface arsenic removal
Enhanced nitrification in biofilters
November 18, 2008

3. Subsurface or in-situ iron removal
periodical
alternating
Numerous applications in Europe:
Van Beek, 1983; Rott and Friedle, 1985; Braester and Martinell, 1988; Rott and Lamberth, 1993; Mettler et al., 2001; Appelo et al. 1999; etc.
November 18, 2008

4. Subsurface or in-situ iron removal (cont’d)
Subsurface treatment in short
injection of aerated water into anaerobic aquifer;
(adsorbed) iron(II) is oxidized to iron(III);
retardation of the oxygen front.
November 18, 2008

5. Subsurface or in-situ iron removal (cont’d)
Subsurface treatment in short
iron (oxy)hydroxides promote iron(II) adsorption;
abstraction of groundwater with decreased iron levels;
also: adsorption of anions such as arsenic and phosphate
Emphasize co precipitation and adsorption of P and As, not iron removal
November 18, 2008

6. Oasen Drinking Water Company, the Netherlands
customers
10 production stations
Water use p.p.
45 m3/y = 34 gallons p.d.
Total Oasen annual:
47 million m3 =
12 billion gallons
The Netherlands small, densly populated country, 8 times more population on 8 times smaller land area.
Oasen rural area near Rotterdam
Water consumption in NL relative low
Annual production 12 billion gallons
Closer look Oasen area: polders
November 18, 2008

7. Oasen Drinking Water Company, the Netherlands (cont’d)
The Netherlands: below see level
Oasen: fenland and reclamed marches
Oasen
The Netherlands half under sea level (blue) =>“The low lands”
Oasen in this area
November 18, 2008

8. Oasen Drinking Water Company, the Netherlands (cont’d)
Drinking water treatment plant
operates “subsurface aeration” at multiple sites;
for enhancement of nitrification, so not for iron or arsenic removal;
a single well for injection and abstraction.
in short:
- arsenic concentrations very low (<10 ug/L)
- 1% volume injection of volume abstraction
- duration of cycle: approximately 1 month
November 18, 2008

9. Oasen Drinking Water Company, the Netherlands (cont’d)
Subsurface aeration: less intensive form of subsurface iron removal (i.e. less water is injected into the aquifer)
Abstracted water is mixed with other groundwater sources before treatment.
Injection water volume is only 6% of the abstracted volume from well 8 and
1% of the total abstracted volume of the whole well-field;
Yet this limited amount has a high effect on nitrification in the production biofilters
November 18, 2008

10. Oasen Drinking Water Company, the Netherlands (cont’d)
Table 1Water quality parameters in reference wells around subsurface treatment well (LS-P08)
Reference wells
LS-P02
LS-P07
LS-P11
Ammoniuma
mg L-1 NH4+-N
1.1
1.3
2.2
Arsenicb
µg L-1 As (total)
5.1
2.9
Ironc
mg L-1 Fe2+
5.6
3.2
5.5
Manganesec
mg L-1 Mn2+
1.0
0.8
Phosphateb
mg L-1 PO43-
0.9
Bicarbonateb
mg L-1 HCO3-
265
222
282
TOCc
mg L-1 C
2.3
2.8
Temperature °C 12
pH at 20°Cb -
7.2
7.4
a average b average c average
November 18, 2008

11. Oasen Drinking Water Company, the Netherlands (cont’d)
Start subsurface iron removal
November 18, 2008

12. Side effects
Adsorption and co-precipitation of arsenic during subsurface iron removal
-> subsurface arsenic removal
Enhanced nitrification in dry biofilters after subsurface treatment
Bron: Wikipedia
Arsenicosis: chronic arsenic poisoning from drinking water
Effects include changes in skin color, formation of hard patches on the skin, skin cancer, lung cancer, cancer of the kidney and bladder, and can lead to gangrene. The World Health Organization recommends a limit of 0.01 mg/L (10ppb) of arsenic in drinking water. This recommendation was established based on the limit of detection of available testing equipment at the time of publication of the WHO water quality guidelines. More recent findings show that consumption of water with levels as low as mg/L (0.17ppb) over long periods of time can lead to arsenicosis.
November 18, 2008

13. Arsenic occurrence and geochemistry
Arsenate (V)
typically in aerobic water (surface water)
negatively charged
Arsenite (III)
typically in anoxic water (groundwater)
uncharged
more mobile and toxic than As(V)
November 18, 2008

14. Arsenic occurrence and geochemistry (cont’d)
Note: countries with very local arsenic problems due to mining or geothermal influences are not listed in this map
Arsenic: a worldwide problem!
November 18, 2008

15. Subsurface arsenic removal
Oxidation-adsorption mechanism
Arsenic adsorption onto iron hydroxides
pH dependency
competing anions (e.g. PO43-)
high Fe:As ratio required
Source: Sharma (2001)
Source: Dixit and Hering (2003)
November 18, 2008

16. Subsurface arsenic removal (cont’d)
Source: Oasen Drinking Water Company
November 18, 2008

17. Subsurface arsenic removal (cont’d)
Does remobilization occur?
Source: Oasen Drinking Water Company
November 18, 2008

18. Ongoing arsenic research
Simulation in the laboratory: regeneration of the iron surface
(ii) Arsenic remobilization from accumulated iron precipitates
(iii) Field study in rural Bangladesh
November 18, 2008

19. Enhanced nitrification in biofilters
Dry biofilters: coarse river sand (fraction mm)
Methane is effectively stripped before or during dry biofiltration by forced aeration.
November 18, 2008

20. Enhanced nitrification in biofilters (cont’d)
Subsurface
aeration
No subsurface
aeration
Subsurface
aeration
Effectiveness of SA on nitrification shown in graph
Different treatment plant, same patron, vertical axis NH4 in effluent; in = 2,1 for this filter
First period little removal
After start of SA almost complete
Relapse when SA stopped
Total nitrification when restarted
November 18, 2008

21. RT-PCR or Quantitative-PCR Real Time Polymerase Chain Reaction
©2005 by Steven M. Carr (
Ammonia-oxidizing microorganisms
Iron-oxidizing bacteria
Erfelijk materiaal bestaat uit dubbelstrengs DNA moleculen, opgebouwd uit de nucleotiden A (adenosine), C (cytosine), T (thymine) en G (guanine). G bindt met C, A met T.
De volgorde A,C, T en G is uniek voor ieder organsime!
Vermenigvuldiging van een kenmerkend deel van het DNA met met PCR (‘Polymerase Chain Reaction’)
November 18, 2008

22. Microbial growth in subsurface aerated well
For more results on enhanced nitrification in biofilters is referred to the 4:30 presentation
November 18, 2008

23. Thank you for your attention!
ir. Doris van Halem1,2 ir. Weren de Vet1,3 prof. dr. Gary Amy1,2 prof. ir. Hans van Dijk1
1 Delft University of Technology, The Netherlands
2 UNESCO-IHE Institute for Water Education, The Netherlands
3 Oasen Drinking Water Company, The Netherlands
CONTACT: