In situ iron removal, beneficial side effects

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 CONTACT D.vanHalem_at_TUdelft.nl/dri
nkwater.tudelft.nl
2
Lay-out of this presentation

• Introduction to subsurface iron removal
• Oasen drinking water company
• Subsurface arsenic removal
• Enhanced nitrification in biofilters

3
Subsurface or in-situ iron removal

• 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.

4
Subsurface or in-situ iron removal (contd)

• Subsurface treatment in short
• injection of aerated water into anaerobic
  aquifer
• (adsorbed) iron(II) is oxidized to iron(III)
• retardation of the oxygen front.

5
Subsurface or in-situ iron removal (contd)

• 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

6
Oasen Drinking Water Company, the Netherlands

• 750.000 customers
• 10 production stations
• Water use p.p.
• 45 m3/y 34 gallons p.d.
• Total Oasen annual
• 47 million m3
• 12 billion gallons

7
Oasen Drinking Water Company, the Netherlands
(contd)

• The Netherlands below see level
• Oasen fenland and reclamed marches

8
Oasen Drinking Water Company, the Netherlands
(contd)

• 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 (lt10 ug/L)
• - 1 volume injection of volume abstraction
• - duration of cycle approximately 1 month

9
Oasen Drinking Water Company, the Netherlands
(contd)

• 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.

10
Oasen Drinking Water Company, the Netherlands
(contd)
Table 1Water quality parameters in reference
wells around subsurface treatment well (LS-P08)
a average 1992-2006 b average 1994-2005 c average
2003-2005
11
Oasen Drinking Water Company, the Netherlands
(contd)
Start subsurface iron removal
12
Side effects

• Adsorption and co-precipitation of arsenic during
  subsurface iron removal
• -gt subsurface arsenic removal
• Enhanced nitrification in dry biofilters after
  subsurface treatment

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)

14
Arsenic occurrence and geochemistry (contd)
Note countries with very local arsenic problems
due to mining or geothermal influences are not
listed in this map

• Arsenic a worldwide problem!

15
Subsurface arsenic removal

• Oxidation-adsorption mechanism
• Arsenic adsorption onto iron hydroxides
• pH dependency
• competing anions (e.g. PO43-)
• high FeAs ratio required

Source Sharma (2001)
Source Dixit and Hering (2003)
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Subsurface arsenic removal (contd)
Source Oasen Drinking Water Company
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Subsurface arsenic removal (contd)
Does remobilization occur?
Source Oasen Drinking Water Company
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

19
Enhanced nitrification in biofilters

• Dry biofilters coarse river sand (fraction
  1.7-2.5 mm)
• Methane is effectively stripped before or during
  dry biofiltration by forced aeration.

20
Enhanced nitrification in biofilters (contd)
21
RT-PCR or Quantitative-PCRReal Time Polymerase
Chain Reaction

• Ammonia-oxidizing microorganisms
• Iron-oxidizing bacteria

22
Microbial growth in subsurface aerated well

• For more results on enhanced nitrification in
  biofilters is referred to the 430 presentation

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 D.vanHalem_at_TUdelft.nl/dri
nkwater.tudelft.nl