subsurface iron removal for drinking water production: understanding the process and exploiting...
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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 Netherlands2 UNESCO-IHE Institute for Water Education, The Netherlands3 Oasen Drinking Water Company, The Netherlands
CONTACT: [email protected]/drinkwater.tudelft.nl
November 18, 2008
Lay-out of this presentation
Introduction to subsurface iron removal
Oasen drinking water company
Subsurface arsenic removal
Enhanced nitrification in biofilters
November 18, 2008
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.
November 18, 2008
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
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
November 18, 2008
Oasen Drinking Water Company, the Netherlands
750.000 customers10 production stations
Water use p.p. 45 m3/y = 34 gallons p.d.Total Oasen annual: 47 million m3 =12 billion gallons
November 18, 2008
Oasen Drinking Water Company, the Netherlands (cont’d)
OasenThe Netherlands: below see level
Oasen: fenland and reclamed marches
November 18, 2008
Oasen Drinking Water Company, the Netherlands (cont’d)
Drinking water treatment planti. operates “subsurface aeration” at multiple sites;ii. for enhancement of nitrification, so not for iron or arsenic
removal;iii. 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
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.
November 18, 2008
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)
2.2 5.1 2.9
Ironc mg L-1 Fe2+ 5.6 3.2 5.5
Manganesec mg L-1 Mn2+ 1.0 0.8 1.0
Phosphateb mg L-1 PO43- 0.8 0.9 1.0
Bicarbonateb mg L-1 HCO3- 265 222 282
TOCc mg L-1 C 2.3 2.2 2.8
Temperature °C 12 12 12
pH at 20°Cb - 7.2 7.4 7.2a average 1992-2006 b average 1994-2005 c average 2003-2005
November 18, 2008
Oasen Drinking Water Company, the Netherlands (cont’d)
0
1
2
3
4
5
6
7
8
1-7-1998 30-9-1998 30-12-1998
31-3-1999 30-6-1999 29-9-1999 29-12-1999
29-3-2000 28-6-2000
mg
/l F
e
Start subsurface iron removal
November 18, 2008
Side effects
Adsorption and co-precipitation of arsenic during subsurface iron removal
-> subsurface arsenic removal
Enhanced nitrification in dry biofilters after subsurface treatment
November 18, 2008
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
Arsenic occurrence and geochemistry (cont’d)
Arsenic: a worldwide problem!Note: countries with very local arsenic problems due to mining or geothermal influences are not listed in this map
November 18, 2008
Subsurface arsenic removal
Oxidation-adsorption mechanism
Arsenic adsorption onto iron hydroxides
pH dependency competing anions (e.g. PO4
3-) high Fe:As ratio required
Source: Dixit and Hering (2003)
Source: Sharma (2001)
November 18, 2008
Subsurface arsenic removal (cont’d)
0
1
2
3
4
5
19-12-2004
8-1-2005
28-1-2005
17-2-2005
9-3-2005
29-3-2005
18-4-2005
8-5-2005
28-5-2005
17-6-2005
Date
ug/L
As
0
0,2
0,4
0,6
0,8
1
mg/L
Fe o
r PO
4
Arsenic
Iron
Phosphate
Source: Oasen Drinking Water Company
November 18, 2008
0
2
4
6
8
10
12
1-1-1998 2-1-2000 2-1-2002 3-1-2004 3-1-2006
µg/L
As
0
1
2
3
4
5
6
7
8
mg/
L Fe
or
PO4
Arsenic
Iron
Phosphate
Stop periodic injection
Resume periodic injection
Subsurface arsenic removal (cont’d)
Does remobilization occur?
Source: Oasen Drinking Water Company
November 18, 2008
Ongoing arsenic research
(i) 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
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.
November 18, 2008
0,0
0,5
1,0
1,5
2,0
2,5
Oct-1997 Oct-2000 Oct-2003 Oct-2006
NH
4 in
wa
ter
(pp
m)
Enhanced nitrification in biofilters (cont’d)
Subsurfaceaeration
Subsurfaceaeration
No subsurfaceaeration
November 18, 2008
RT-PCR or Quantitative-PCRReal Time Polymerase Chain Reaction
• Ammonia-oxidizing microorganisms• Iron-oxidizing bacteria
http://www.mycometrics.com/images/image_pcr1.jpg©2005 by Steven M. Carr
(http://www.mun.ca/biology/scarr/Principle_of_RT-PCR.html)
November 18, 2008
Microbial growth in subsurface aerated well
1,0E+00
1,0E+01
1,0E+02
1,0E+03
1,0E+04
0 5 10 15 20 25 30 35Days from start of extraction
n (m
L-1)
AOB AOA
5,0E+01
1,9E+02
1,0E+01
1,0E+02
1,0E+03
1,0E+04
1,0E+05
1,0E+06
1,0E+07
0 5 10 15 20 25 30 35
Days from start of extractionn
(mL-
1)
G. ferruginea Reference PF07Z Reference PE99 A
For more results on enhanced nitrification in biofilters is referred to the 4:30 presentation
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 Netherlands2 UNESCO-IHE Institute for Water Education, The Netherlands3 Oasen Drinking Water Company, The Netherlands
CONTACT: [email protected]/drinkwater.tudelft.nl