21 November 2008
Biogeochemical cycling ofBiogeochemical cycling ofarsenic in sedimentary basin ofarsenic in sedimentary basin of
southwestern Taiwansouthwestern Taiwan Wang, Sheng Wei
Department of Bioenvironmental Systems Engineering
National Taiwan University
Department of Bioenvironmental Systems Department of Bioenvironmental Systems Engineering NTUEngineering NTU
Introduction
Arsenic is carcinogenic, and can cause other human health effects
As(III), inorganic species in anaerobic environment, is generally considered more mobility and toxic than As(V), the primary form in aerobic environment
Most frequently found in groundwater As released from natural sources to groundwater is
the dominant cause
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Introduction
As contamination in groundwater of the world As contamination in groundwater of the world
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Introduction
As in Bangladesh As in Bangladesh
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C h o u sh u i r iv e r
Ta i
wan
Str
a it
Cen
tra l
Mou
n ta i
n
3
2 175
2 98 1 31 1 73 22 39 3 7
3 02 62
3 63 51 91 56
3 9
2 8
2 4
2 21 4
4 4 03 4
4 13 83 32 71 8
1 61 011
3 12 52 01 2
1
23 4
56
789
1 0
111 21 31 41 5
1 6
1 7 1 8
1 92 0 2 1
2 22 3
2 4 2 52 6 2 7
2 82 9 3 0
3 13 23 3
0 1 0 2 0 k m
S ou th ern C h ou sh u i r iver a llu v ia l fan
C h ian an p la in
P e ik an g riv e r
P ach an g r iv e r
T sen g w en riv e r
E rn jen r iv e r
T a iw a n
Introduction
High As in deep wells of depth 60-300m has been proved to
be associated with blackfoot
disease of the Chianan plain
High As in shallow wells of
depth 30-40m have been found in the southern Choushui river alluvial fan (Yun-Lin county)
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Aquaculture water
High As content groundwater
Effect human health
Sediment
Food
Fish/ShellfishBioaccumulation
Ingestion
Aquaculture Ecosystem
Drinking
As
As As
Introduction
Exposure pathway of As in southwest TaiwanExposure pathway of As in southwest Taiwan
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-350
-300
-250
-200
-150
-100
-50
0
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
As (mg/L)D
epth
(m
)
-300
-250
-200
-150
-100
-50
0
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
As (mg/L)
Dep
th (
m)
High As
High As
High As
High As
Chianan plain Chianan plain
Choushui river alluvial fan Choushui river alluvial fan
The vertical distribution of As in groundwater in Taiwan The vertical distribution of As in groundwater in Taiwan
Department of Bioenvironmental Systems Department of Bioenvironmental Systems Engineering NTUEngineering NTU
Study areasC h o u sh u i r iv e r
Ta i
wan
Str
a it
Cen
tra l
Mou
n ta i
n
3
2 175
2 98 1 31 1 73 22 39 3 7
3 02 62
3 63 51 91 56
3 9
2 8
2 4
2 21 4
4 4 03 4
4 13 83 32 71 8
1 61 011
3 12 52 01 2
1
23 4
56
789
1 0
111 21 31 41 5
1 6
1 7 1 8
1 92 0 2 1
2 22 3
2 4 2 52 6 2 7
2 82 9 3 0
3 13 23 3
0 1 0 2 0 k m
S o u th ern C h o u sh u i r iv er a llu v ia l fa n
C h ia n a n p la in
P e ik an g riv e r
P ach an g riv e r
T sen g w en riv e r
E rn jen r iv e r
A A '
B
B '
The southern Choushui
river alluvial fan 41 hydrological stations 107 monitoring wells
The Chianan plain 33 hydrological stations 100 monitoring wells
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Chianan plain
Chianan plain
Choushui river alluvial fan
Choushui river alluvial fan
Hydrogeological profile
Hydrogeological profile
Study areas
Department of Bioenvironmental Systems Department of Bioenvironmental Systems Engineering NTUEngineering NTU
Topic
11Where is the As in ground water from ?Where is the As in ground water from ?
33Have the As problemsalready been solved ? Have the As problemsalready been solved ?
22How dose the As releaseinto groundwater ?How dose the As releaseinto groundwater ?
Characterization of groundwater quality
Composition of sedimentary deposits
Department of Bioenvironmental Systems Department of Bioenvironmental Systems Engineering NTUEngineering NTU
Characterization of groundwater quality
Taiwan Sugar Company (2003; 2004) As concentrations of groundwater
0.12±0.14 mg/L in the southern Choushui river alluvial fan
0.30±0.35 mg/L in the Chianan plain
Monitoring wells of that As > 0.01 mg/L 70% in the southern Choushui river alluvial fan> 95% in the Chianan plain
Department of Bioenvironmental Systems Department of Bioenvironmental Systems Engineering NTUEngineering NTU
Factor analysis Liu et al. (2003): The Choushui river alluvial fan 33 hydrological stations, 100 monitoring wells of the Chianan
plain 3 layers: 0-70m, 70-170m, and >170m EC, Eh, pH, TDS, Alk, TOC, NH4
+, SO42-, Cl-, Ca2+, Mg2+, Na+,
K+, As, Fe
Characterization of groundwater quality
Department of Bioenvironmental Systems Department of Bioenvironmental Systems Engineering NTUEngineering NTU
Factor analysis
Factor EigenvaluePercentageof variance
Cumulative percentageof variance
1 7.55 50.34 50.34
2 2.79 18.62 68.96
3 1.28 8.56 77.52
4 0.79 5.24 82.75
5 0.68 4.51 87.27
6 0.48 3.18 90.45
7 0.42 2.77 93.22
8 0.31 2.08 95.30
9 0.27 1.83 97.12
10 0.20 1.33 98.45
11 0.12 0.80 99.25
12 0.08 0.52 99.76
13 0.03 0.17 99.93
14 0.01 0.04 99.98
15 0.00 0.02 100.00
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Variable Factor 1 Factor 2 Factor 3
EC 0.85 0.02 0.14
Eh -0.42 -0.67 0.15
pH -0.09 0.37 -0.79
TDS 0.98 0.02 0.09
Alk -0.14 0.82 -0.07
SO42- 0.89 -0.12 -0.05
Cl- 0.97 0.04 0.13
Ca2+ 0.79 -0.18 0.23
Mg2+ 0.93 -0.12 0.01
Na+ 0.97 0.05 0.10
K+ 0.95 -0.06 0.02
As -0.19 0.68 0.07
Fe 0.18 0.40 0.72
TOC 0.00 0.91 0.09
NH4+ 0.61 0.18 0.38
Loadings for three-factors Loadings for three-factors
As enrichment factorAs enrichment factorSalinization factorSalinization factor
Factor analysis
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Redox zoning
Redox zoning Chen and Liu (2003): The Choushui river alluvial fan Definition of redox zones were same with Chen and Liu (2003) zone 1: Eh >0, and DO or NO3
->0.5 mg/L
zone 2: Eh <0, and with detectable dissolved sulfide zone 3: Eh <0, and without detectable dissolved sulfide
Department of Bioenvironmental Systems Department of Bioenvironmental Systems Engineering NTUEngineering NTU
Redox zoning
1 5 0 0 0 0 1 6 0 0 0 0 1 7 0 0 0 0 1 8 0 0 0 0 1 9 0 0 0 0 2 0 0 0 0 02 5 3 0 0 0 0
2 5 4 0 0 0 0
2 5 5 0 0 0 0
2 5 6 0 0 0 0
2 5 7 0 0 0 0
2 5 8 0 0 0 0
2 5 9 0 0 0 0
2 6 0 0 0 0 0
2 6 1 0 0 0 0
1
234 5
7891 0 111 2
1 3 1 41 5
1 6 1 7
1 8 1 9 2 02 1
2 22 3
2 42 52 6 2 7
2 8 2 93 0
3 1
3 2
1 5 0 0 0 0 1 6 0 0 0 0 1 7 0 0 0 0 1 8 0 0 0 0 1 9 0 0 0 0 2 0 0 0 0 02 5 3 0 0 0 0
2 5 4 0 0 0 0
2 5 5 0 0 0 0
2 5 6 0 0 0 0
2 5 7 0 0 0 0
2 5 8 0 0 0 0
2 5 9 0 0 0 0
2 6 0 0 0 0 0
2 6 1 0 0 0 0
3 3
3 1
3 0 2 92 8
2 7 2 5
2 3 2 22 1
2 01 9
1 61 5
1 411
9 8 7
64 3
1
1 5 0 0 0 0 1 6 0 0 0 0 1 7 0 0 0 0 1 8 0 0 0 0 1 9 0 0 0 0 2 0 0 0 0 02 5 3 0 0 0 0
2 5 4 0 0 0 0
2 5 5 0 0 0 0
2 5 6 0 0 0 0
2 5 7 0 0 0 0
2 5 8 0 0 0 0
2 5 9 0 0 0 0
2 6 0 0 0 0 0
2 6 1 0 0 0 0
1
4 5
891 0 111 2
1 31 5
1 6 1 7
1 8 1 9 2 02 1
2 22 3
2 5
2 8 2 93 0
3 23 3
1 7 0 0 0 0 1 8 0 0 0 0 1 9 0 0 0 0 2 0 0 0 0 0 2 1 0 0 0 0 2 2 0 0 0 0
2 6 0 0 0 0 0
2 6 1 0 0 0 0
2 6 2 0 0 0 0
2 6 3 0 0 0 0
2 6 4 0 0 0 0
2 6 5 0 0 0 0
2 6 6 0 0 0 0
2 6 7 0 0 0 0
3
2 175
2 98 1 31 1 73 22 39 3 7
3 02 62
3 63 51 91 56
3 9
2 8
2 4
2 21 4
4 4 03 4
4 13 83 32 7
1 8
1 61 011
3 12 52 01 2
1 7 0 0 0 0 1 8 0 0 0 0 1 9 0 0 0 0 2 0 0 0 0 0 2 1 0 0 0 0
2 6 0 0 0 0 0
2 6 1 0 0 0 0
2 6 2 0 0 0 0
2 6 3 0 0 0 0
2 6 4 0 0 0 0
2 6 5 0 0 0 0
2 6 6 0 0 0 0
2 6 7 0 0 0 0
3
2 175
2 98 1 31 1 73 22 39 3 7
3 02 62
3 63 51 91 56
3 9
2 8
2 4
2 21 4
4 4 03 4
4 13 83 32 7
1 8
1 61 011
3 12 52 01 2
1 7 0 0 0 0 1 8 0 0 0 0 1 9 0 0 0 0 2 0 0 0 0 0 2 1 0 0 0 0
2 6 0 0 0 0 0
2 6 1 0 0 0 0
2 6 2 0 0 0 0
2 6 3 0 0 0 0
2 6 4 0 0 0 0
2 6 5 0 0 0 0
2 6 6 0 0 0 0
2 6 7 0 0 0 0
3
2 175
2 98 1 31 1 73 22 39 3 7
3 02 62
3 63 51 91 56
3 9
2 8
2 4
2 21 4
4 4 03 4
4 13 83 32 7
1 8
1 61 011
3 12 52 01 2
0-70 m 70-170 m >170 m
Zone 1
Zone 2
Zone 3
Distribution of redox zones at different depths Distribution of redox zones at different depths
Zone 1 Eh >0 DO or NO3
->0.5 mg/LZone 2 Eh <0 with sulfideZone 3 Eh <0 without sulfide
Aquifer 1 Aquifer 3Aquifer 2
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Composition of sedimentary deposits
13 drilling stations 655 samples
3 m intervals, <100m 10 m intervals, >100m
Analysis AAS+HG
11
32
1
5
1012
7
9
13
6 8
4
0 1 0 2 0 3 0
C h o u sh u i R iv e r
P e ik ang R iv e r
Tai
wan
Str
a it
Cen
tra l
Mou
n ta i
n
Y u n -L in co u n ty
T a iw a n
k m
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Composition of sedimentary deposits
As distribution of core samples
As distribution of core samples
Log-normaldistribution
Log-normaldistribution
Geometric mean: 2.27±1.43 mg/kg
Max: 590 mg/kg
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0 5 0 1 0 0 1 5 0 2 0 0 2 5 0 3 0 0-3 0 0
-2 5 0
-2 0 0
-1 5 0
-1 0 0
-5 0
0
Dep
th(m
)
-0 .2
0 .7 5
0 .8 6
6 7 8 9 1 0 11 1 2 1 3
lo g (A s(m g /k g ))
D is tan ce (x 1 0 0 m )
0 5 0 1 0 0 1 5 0 2 0 0 2 5 0 3 0 0
D is tan ce (x 5 0 m )
-3 0 0
-2 5 0
-2 0 0
-1 5 0
-1 0 0
-5 0
0
Dep
th(m
)
-0 .2
0 .7 5
0 .8 6
lo g (A s(m g /k g ))
1 2 3 4 5 6
Composition of sedimentary deposits
Log CAs(mg/kg) distributions in the west-east and north-south cross section Log CAs(mg/kg) distributions in the west-east and north-south cross section
11
32
1
5
1012
7
9
13
6 8
4
0 1 0 2 0 3 0
C h o u sh u i R iv e r
P e ikang R iv e r
Ta i
wan
Str
a it
Cen
tral
Mou
n tai
n
Y u n -L in co u n ty
T a iw a n
k m
Department of Bioenvironmental Systems Department of Bioenvironmental Systems Engineering NTUEngineering NTU
Station Depth (m) As (mg/kg)
1 54 590.00
3 162 117.00
3 180 107.50
8 130 102.60
1 63 76.80
1 6 75.35
10 39 75.08
10 272 74.64
10 152 67.48
11 30 61.88
10 21 56.55
8 12 54.90
1 60 52.35
ShallowShallow
DeepDeep
BothBoth
Tabulate CAs > 50 mg/kg of different drilling stations and depths Tabulate CAs > 50 mg/kg of different drilling stations and depths
Department of Bioenvironmental Systems Department of Bioenvironmental Systems Engineering NTUEngineering NTU
non-marine sequence 1 (<3,000 years B.P.)
marine sequence 1 (3,000-9,000 years B.P.)
non-marine sequence 2 (9,000-35,000 years B.P.)
marine sequence 2 (35,000-50,000 years B.P.)
non-marine sequence 3 (>50,000 years B.P.)
UnknownClaySandGravel
11
32
1
5
1012
7
9
13
6 8
4
0 .0 0 0 1 0 0 0 0 .0 0 0 2 0 0 0 0 .0 0 0 3 0 0 0 0 .0 0 0
C h o u -S h u i R iv e r
Y u n -L in co u n ty
T a iw a n
100 20 30km
Plain view of the marine and non-marine sequences distribution (Huang, 1996)
Plain view of the marine and non-marine sequences distribution (Huang, 1996)
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SandSiltClay
log(
As
Con
cent
rati
on)
3.0
2.5
2.0
1.5
1.0
.5
0.0
-.5
□﹕75% and 25%□﹕50%┬﹕non-outlier Max┴﹕non-outlier Min○﹕outlier 1.5~3 × box*﹕ extremes >3 × box
Composition of sedimentary deposits
Box-plot of log CAs of clay, silt and sand types of core samples Box-plot of log CAs of clay, silt and sand types of core samples
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Station Depth (m) Age (year) As (mg/kg)1 108.4 >52000 5.32
3 32.7 2931±81 29.34
3 48.9 8819±99 51.35
3 117.9 43900±1500 13.16
5 157.8 >45000 5.43
6 39.4 3936±64 11.31
7 23.0 5364±89 4.83
7 42.7 8440±90 8.27
7 111.4 39900±1100 110
7 129.6 >50000 1.71
8 91.6 >50000 34.04
9 25.1 7370±100 10.89
9 25.1 7620±80 10.89
9 48.8 9230±60 2.61
9 68.6 36400±500 6.63
9 105.1 >50000 17.22
13 38.2 8330±60 11.51
13 38.8 7920±70 11.51
13 55.0 7090±60 3.37
13 60.0 7850±60 3.01
13 99.0 43300±130 4.61
Geological dating v.s. CAs of core samples Geological dating v.s. CAs of core samples
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R2 = 0.51
0.0
0.5
1.0
1.5
2.0
2.5
-2.0 -1.5 -1.0 -0.5 0.0
log (As) in groundwater (mg/L)
log
(As)
of c
ore
sam
ples
in a
quita
rds
(mg/
kg)
As of core samples in aquitards v.s. As of ground water
As of core samples in aquitards v.s. As of ground water
As of core samples in aquifers v.s. As of ground water
As of core samples in aquifers v.s. As of ground water
R2 = 0.21
0.0
0.5
1.0
1.5
2.0
2.5
-2.0 -1.5 -1.0 -0.5 0.0
log (As) in groundwater (mg/L)
log
(As)
of co
re s
ampl
es in
aqui
fers
(mg/
kg)
Department of Bioenvironmental Systems Department of Bioenvironmental Systems Engineering NTUEngineering NTU
Composition of sedimentary deposits
Smedley and Kinniburgh (2002) Extreme As concentrations in natural water are rare, but are most
frequently observed in groundwater
Welch et al. (2000); Nordstrom (2002) Release from natural sources is the dominant cause of elevated As in
groundwater
Edmonds and Francesconi (1997); Francesconi et al. (1998) High As in the marine formation may be attributed to the
bioaccumulation and biotransformation of As in the sea organisms
Department of Bioenvironmental Systems Department of Bioenvironmental Systems Engineering NTUEngineering NTU
Topic
22
11Where is the As in ground water from ?Where is the As in ground water from ?
33Have the As problemsalready been solved ? Have the As problemsalready been solved ?
How dose the As releaseinto groundwater ?How dose the As releaseinto groundwater ?
Department of Bioenvironmental Systems Department of Bioenvironmental Systems Engineering NTUEngineering NTU
As release to groundwater
Mandal et al. (1996); Loeppert (1997); Wilkie and Hering (1998) The oxidation of As-bearing pyrite minerals
Nickson et al. (2000); McArthur et al. (2001) Reductive dissolution of As-rich Fe oxy-hydroxides
Acharyya et al. (1999) Competitive exchange of adsorbed As on aquifer minerals with
phosphate ions that migrate into aquifers from the application of
fertilizers to surface soil
Harvey et al. (2002); Smedley and Kinniburgh, (2002) Reductive dissolution of Fe oxy-hydroxides under reducing conditions
is the most probable reason of As accumulation in groundwater
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Geochemical modeling
Geochemical calculation: PHREEQC Chemical speciation Saturation index (SI)
SI<0: the potential for dissolution SI>0: the potential for precipitation
3 monitoring wells of 3 layers of the Chianan plain and the southern Choushui river alluvial fan pH, Eh, temperature, DO, Alk, SO4
2-, Cl- , Ca2+, Mg2+, Na+, K+, As, Fe, Mn, NH4
-, NO3- and HS-
Department of Bioenvironmental Systems Department of Bioenvironmental Systems Engineering NTUEngineering NTU
Geochemical modeling
1 7 0 0 0 0 1 8 0 0 0 0 1 9 0 0 0 0 2 0 0 0 0 0 2 1 0 0 0 0
2 6 0 0 0 0 0
2 6 1 0 0 0 0
2 6 2 0 0 0 0
2 6 3 0 0 0 0
2 6 4 0 0 0 0
2 6 5 0 0 0 0
2 6 6 0 0 0 0
2 6 7 0 0 0 0
3 8
2 66
1 7 0 0 0 0 1 8 0 0 0 0 1 9 0 0 0 0 2 0 0 0 0 0 2 1 0 0 0 0 2 2 0 0 0 0
2 6 0 0 0 0 0
2 6 1 0 0 0 0
2 6 2 0 0 0 0
2 6 3 0 0 0 0
2 6 4 0 0 0 0
2 6 5 0 0 0 0
2 6 6 0 0 0 0
2 6 7 0 0 0 0
4 12 7
6
1 7 0 0 0 0 1 8 0 0 0 0 1 9 0 0 0 0 2 0 0 0 0 0 2 1 0 0 0 0
2 6 0 0 0 0 0
2 6 1 0 0 0 0
2 6 2 0 0 0 0
2 6 3 0 0 0 0
2 6 4 0 0 0 0
2 6 5 0 0 0 0
2 6 6 0 0 0 0
2 6 7 0 0 0 0
4 1
2 3
6
150000 160000 170000 180000 190000 2000002530000
2540000
2550000
2560000
2570000
2580000
2590000
2600000
2610000
1 2
2 1
2 8
150000 160000 170000 180000 190000 2000002530000
2540000
2550000
2560000
2570000
2580000
2590000
2600000
2610000
1 9 2 0
2 7
150000 160000 170000 180000 190000 2000002530000
2540000
2550000
2560000
2570000
2580000
2590000
2600000
2610000
1 6
2 83 0
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Geochemical modeling
Chemical species of groundwater in 3 layersChemical species of groundwater in 3 layers
Department of Bioenvironmental Systems Department of Bioenvironmental Systems Engineering NTUEngineering NTU
Geochemical modeling
Saturation index of groundwater in 3 layersSaturation index of groundwater in 3 layers
Department of Bioenvironmental Systems Department of Bioenvironmental Systems Engineering NTUEngineering NTU
Step Extractant Target phaseMg 1M MgCl2 Ionically bound As
PO4 1M NaH2PO4 Strongly adsorbed As
HCl 1N HCl Coprecipitated with AVS, carbonates, Mn oxide
Ox 0.2M ammonium oxalate/oxalic acid Coprecipitated with amorphous Feoxyhydroxides
Ti 0.05M Ti( )-citrate-EDTA-Ⅲbicarbonate
Coprecipitated with crystalline Feoxyhydroxides
HF 10M HF As oxides and As coprecipitated withsilicates
HNO3 16N HNO3
Coprecipitated with pyrite andamorphous As2S3
hot HNO3 16N HNO3+30% H2O2Orpiment and remaining recalcitrant
As minerals
Sequential extraction
Surface analysesSurface analyses X-ray diffractometer (XRD) X-ray fluorescence (XRF) High resolution x-ray photoelectron spectrometer (HR-XPS)High resolution x-ray photoelectron spectrometer (HR-XPS) Scanning electron microscope (SEM-EDS)Scanning electron microscope (SEM-EDS)
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Oremland and Stolz (2003)
Bacteria-mediated mobilization of As into groundwater Bacteria-mediated mobilization of As into groundwater
As release to groundwater
Department of Bioenvironmental Systems Department of Bioenvironmental Systems Engineering NTUEngineering NTU
Islam et al. (2004) Reduction of ferric iron took place
before the As release to groundwater The iron-reducing bacteria played a
major role in the subsequent reduction
and release of As The delivery of surface - drived organic
carbon into subsurface communities
may have a dramatic role in As mobility
As release to groundwater
Department of Bioenvironmental Systems Department of Bioenvironmental Systems Engineering NTUEngineering NTU
Herbel and Fendorf (2006)
The effects of bacterial processes on arsenic mobilityin iron (hydr)oxide systems
The effects of bacterial processes on arsenic mobilityin iron (hydr)oxide systems
As release to groundwater
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Groundwater of YL7 was collected for IRB enrichment Geometric mean of As: 360.57 ppb
C h o u sh u i r iv e r
Y L 7
0 1 0 2 0 k m
S ou th ern C h ou sh u i r iv er a llu v ia l fa n
P e ik an g r iv e r
T a iw a n(R O C )
screen
-25
-5
-10
-15
-20
0
gravalsilty sandclay
As release to groundwater- Batch experiments of IRB
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Inject 1 ml groundwater into 10 ml autoclaved IRB
medium H2 or acetate or citrate + Fe3+ → HCO3
- + Fe2+ + H+
Orange →colorless (about 10 days) Transfer 4 times
As release to groundwater- Batch experiments of IRB
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Lu (2007) Amorphous Fe (hydr)oxides (HFO) are the primary Fe
mineral and correlate well with the As of core samples 0.5M NaOH was dropwised to 100ml of 0.05M Fe(NO3)3
until pH=7.5-8 HFO reducing experiments (anaerobic condition)
A: HFO+citrate+IRB B: HFO+citrate C: HFO+acetate+IRB D: HFO+acetate
As release to groundwater- Batch experiments of IRB
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As(V) reducing experiments E: As(V)+citrate+IRB F: As(V)+citrate G: As(V)+acetate+IRB H: As(V)+acetate
[As(V)-HFO] reducing experiments I: [As-HFO]+citrate+IRB J: [As-HFO]+citrate K: [As-HFO]+acetate+IRB L: [As-HFO]+acetate
As(III) and As(V) were analyzed by AAS+HG Fe(II) was measured colorimetrically by ferrozine method
As release to groundwater- Batch experiments of IRB
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HFO reducing experiments
0
50
100
150
200
250
0 5 10 15
Time (days)
Fe(
Ⅱ)
(mg/
l)
HFO+IRB+citrateHFO+citrateHFO+IRB+acetateHFO+acetate
As release to groundwater- Batch experiments of IRB
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(a)0
5
10
15
20
25
30
0 5 10 15 20
Time (days)
As
(mg/
l)
As (Ⅲ )
As (Ⅴ )
Total As
(c)0
5
10
15
20
25
30
0 5 10 15 20
Time (days)
As
(mg/
l)
As (Ⅲ )
As (Ⅴ )
Total As
As(V) reducing experiments
(b)0
5
10
15
20
25
30
0 5 10 15 20
Time (days)
As
(mg/
l) As (Ⅲ )
As (Ⅴ )
Total As
(d)0
5
10
15
20
25
30
0 5 10 15 20
Time (days)
As
(mg/
l)As (Ⅲ )
As (Ⅴ )
Total As
As(V) + citrate + IRB
As(V) + citrate + IRB
As(V) + acetate + IRB
As(V) + acetate + IRB
As(V) + citrate As(V) + citrate As(V) + acetate As(V) + acetate
As release to groundwater- Batch experiments of IRB
Department of Bioenvironmental Systems Department of Bioenvironmental Systems Engineering NTUEngineering NTU
Results and disscusions
Direct enzymatic microbial reduction of As(V) (arsC)
Detoxification pathway (arsC pathway)
Respiratory pathway (arrA pathway)
As(V)-reducing bacteria are simultaneously cultured of the enrichment experiments
Plausible microbial-mediated processes of As(V) reduction
Department of Bioenvironmental Systems Department of Bioenvironmental Systems Engineering NTUEngineering NTU
Results and disscusions
[As(V)-HFO] reducing experiments
(a)0
2
4
6
8
10
12
0 5 10 15 20
Time (days)
As
(mg/
l)
0
50
100
150
200
250
Fe(Ⅱ
) (m
g/l)
As (Ⅲ )As (Ⅴ )Total AsFe (Ⅱ )
(b)
0
2
4
6
8
10
12
0 5 10 15 20
Time (days)
As
(mg/
l)
0
50
100
150
200
250Fe
(Ⅱ) (
mg/
l)
As (Ⅲ )As (Ⅴ )Total AsFe (Ⅱ )
(c)
0
1
2
3
4
5
0 5 10 15 20
Time (days)
As
(mg/
l)
0
20
40
60
80
100
Fe(
Ⅱ)
(mg/
l)
As (Ⅲ )As (Ⅴ )Total AsFe (Ⅱ )
(d)
0
1
2
3
4
5
0 5 10 15 20
Time (days)
As
(mg/
l)
0
20
40
60
80
100
Fe(Ⅱ
) (m
g/l)
As (Ⅲ )As (Ⅴ )Total AsFe (Ⅱ )
[As(V)-HFO] + citrate + IRB
[As(V)-HFO] + citrate + IRB
[As(V)-HFO] + acetate[As(V)-HFO] + acetate[As(V)-HFO] + citrate[As(V)-HFO] + citrate
[As(V)-HFO] + acetate + IRB
[As(V)-HFO] + acetate + IRB
Department of Bioenvironmental Systems Department of Bioenvironmental Systems Engineering NTUEngineering NTU
Microbial reduction ofAs(V) by IRB
Reduction of As-rich Feoxy-hydroxides
Biogeochemical processes for As release
As(V) reduction took place after Fe(III) reduction and As(V)desorption, because IRB reduce aqueous As(V) following the
consumption of Fe(III) mineral
Direct enzymatic Indirect processes
Results and disscusions
Department of Bioenvironmental Systems Department of Bioenvironmental Systems Engineering NTUEngineering NTU
This reduction reactions are promoted by IRB Mobilization:
Citrate: desorption of As from the surface of HFO is the
main process of As release Acetate: As release caused by reductive dissolution of HFO
via IRB driven
Transformation: Some IRB have the ability to reduce aqueous As(V) after the
reduction of Fe(III) minerals
As release to groundwater- Batch experiments of IRB
Department of Bioenvironmental Systems Department of Bioenvironmental Systems Engineering NTUEngineering NTU
Topic
33
11Where is the As in ground water from ?Where is the As in ground water from ?
Have the As problemsalready been solved ? Have the As problemsalready been solved ?
22How dose the As releaseinto groundwater ?How dose the As releaseinto groundwater ?
Department of Bioenvironmental Systems Department of Bioenvironmental Systems Engineering NTUEngineering NTU
Future works
amorphous iron hydroxide (HFO)
Fe(III) Fe(III)
As(V) As(V)
Fe(II) (decrease As(V) sorption sites)
As(V)
As(III)
macromoleculeorganic carbon
degradatedorganic carbon
decrease of sorption sites
e- donor
Mobilization: desorption
aquifer
aquitardanaerobic environmentlow Eh
e- donor
Transport
:competitive desorption :reductive dissolution by IRB
competition of sorption sites
Transformation: reduced by IRB
Conceptual model of As mobilization and transformation in groundwaterConceptual model of As mobilization and transformation in groundwater
Department of Bioenvironmental Systems Department of Bioenvironmental Systems Engineering NTUEngineering NTU
21 November 2008
Thanks for your attention