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: D.vanHalem@TUdelft.nl/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: D.vanHalem@TUdelft.nl/drinkwater.tudelft.nl