august 27, 2008
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August 27, 2008 Treatment of Heavy Metals and Elimination of Sulfur with a Novel Sulfate Reducing Permeable Reactive Barrier Containing ZVI Dr. Jim Field Dept. Chemical and Environmental Engineering University of Arizona. - PowerPoint PPT PresentationTRANSCRIPT
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August 27, 2008
Treatment of Heavy Metals and Elimination of Sulfur with a Novel Sulfate Reducing Permeable Reactive Barrier Containing ZVI
Dr. Jim FieldDept. Chemical and Environmental Engineering
University of Arizona
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Dept. Chemical and Environmental Engineering
University of Arizona
Elimination of Heavy Metals and Sulfur with Zero Valent Iron as an Electron
Donor for Sulfate-Reduction
R. Sierra, B. Howard, A. Luna, L. J. Mendoza & J. A. Field
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Acid Mine or Acid Rock Drainage
acid
heavy metals
sulfates
iron
H+
Cu2+Fe2+
SO42-
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Acid Rock Drainage with Copper
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Stratergy: Sulfate Reduction for Acid Drainage
Reactions of Sulfate Reducing Bacteria
Promote Activity of the Sulfate Reducing Bacteria
Increase pH: a strong acid (sulfuric) is transformed into a weak acid (hydrogen sulfide)
Reactivity: sulfide for the precipitation of metals
Provide substrate that degrades slowly for the filling of the reactive barriers
e.g. sawdust, compost, straw
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How do Sulfate Reducing Bacteria Precipitate Metals?
Biomineralization
HS- + CO2
HS- H+ + S2-
M2+[aq]
+ S2-
SO42- + organics
biotic
abiotic
dissociation
MS[s]
Ksp = 10-24 to 10-53
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Fe0 as an Electron Donor for Sulfate Reduction
Fe0
Fe2+ + H2
SRB
SO42-
H2S
SRB
Fe0
Fe2+SO42-
H2S
indirect
direct
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Fe0 as an Electron Donor for Sulfate Reduction
Reaction of Fe0 (Anoxic Corrosion)
8H+ + 4Fe0 4H2 + 4Fe2+ G’ = -20.1 kJ/4 mol Fe0
Reaction of Autotrophic Sulfate Reduction
2H+ + 4H2 + SO42- H2S + 4H2O G’ = -152.2 kJ/mol SO4
2-
indirect
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Hypotheses: Benefits of Fe0 for Sulfate Reducing PRB
SO42- reduced and removed, no discharge of sulfides
FeS higher Ksp than heavy metal sulfides (Fe2+ doesn’t outcompete with precipitation of heavy metals)
Long term source of electron donating equivalents
Can treat very acid drainage
Additional metal removal mechanisms with hydroxides
Fe2+ formed attenuates excess sulfides
Oxidation of Fe0 forms high levels of alkalinity
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Fe0 + Cu2+ Fe2+ + Cu0abiotic
Hypotheses: Benefits of Fe0 for Sulfate Reducing PRB (continued)
Direct abiotic reduction heavy metals by Fe0
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Batch Experiment: Fe0 as E-donor SRB
medium + SO42-
sludge granules
head space
Fe0
N2/CO2
medium + SO42-
sludge granules
head spaceN2/CO2
endogenous control treatment
medium + SO42-
sludge granules
head spaceN2/CO2
uninoculated control
Fe0325 mesh47 g/L
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Batch Experiment: Fe0 as E-donor SRB
endogenous
uninoculated
treatment
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Continuous Column Experiments
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Continuous Column 1st Experiments
Laboratory Scale PRB Columns (0.41 L)
R1 Filling:
R2, R3 Filling:
Inoculum:
Sand = 300 ml (495 g)
Sand = 200 ml (331 g)
Fe0 = 100 ml (281 g)
SR Biofilm = 53 ml (6 g VSS)
Control Reactor (SO42-)
R2: Methanogenic Reactor (no SO42-)
R3: Sulfate Reducing Reactor (SO42-)
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Continuous Column 1st Experiments
Column Set Up
Inoculum: Sulfate reducing granular sludge from Twaron Reactor (The Netherlands)
Medium: basal inorganic nutrients
pH: variable 7.2 to 2.5
Sulfate: 1000 mg/L SO42- for R1 & R3; 0 mg/L R2
HRT: 24 h
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Continuous Column 1st Experiments
Column Set Up
R1 (SO42-) R2 (no SO4
2-), R3 (SO42-),
*
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Continuous Column 1st ExperimentsR1 R2 R3
Periods
I No MetalsII 10 ppm CuIII 25 ppm CuIV 50 ppm Cu
V50 ppm Cu + 7.5 ppm Ni &
Zn
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Results R3: Sulfate Data
600
800
1000
1200
0 50 100 150 200 250 300 350 400
Time (Days)
Su
lfat
e C
on
cen
trat
ion
(m
g/L
)
R3: sulfate reducing reactor (sand:ZVI)
influent
effluent
I II III IV V
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Results R1: Sulfate Data
R1: control sulfate reducing reactor (sand only)
600
800
1000
1200
0 50 100 150 200 250 300 350 400
Time (Days)
Su
lfat
e C
on
cen
trat
ion
(m
g/L
)
effluent
influent
I
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Results R2 & R3: pH
2.0
4.0
6.0
8.0
10.0
12.0
0 50 100 150 200 250 300 350 400
Time (d)
pH
Influent R3
effluent R3
Influent R2
effluent R2
I II III IV V
R3: sulfate reducing reactor; R2 methanogenic (sand:ZVI)
pH lowered
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Results R2 & R3: Copper Data
50
60
70
80
90
100
II (10) III (25) IV (50) V (50+ZnNi)
Period (Cu ppm infl)
To
t. C
op
per
Re
mo
val
(%
)
R2R3
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Results R2 & R3: Ni & Zn Data
50
60
70
80
90
100
Ni (7.5) Zn (7.5)
Additional Metal in Period V
To
t. N
i or
Zn
Re
mo
val
(%
)
R2R3
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Results R1 & R3: S-Balance (day 29-175)
0
20
40
60
80
R1 R3
Reactor
S c
on
vert
ed
(m
g/L
)
SO4-SH2S-S
no sequestering H2S
H2S sequestered
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Results R3: SEMS-EDS
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Results R2 & R3: MPN SRB
Nail in test tube method
Most Probable Number: Sulfate Reducing Bacteria
R2 methanogenic PRB
R3 sulfate reducing PRB
1.0 102
1.2 104
Reactor cells/ g dwt fill
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Continuous Column 2nd Experiments
Laboratory Scale PRB Columns (0.41 L)
R4 Filling:
R5 Filling:
Inoculum:
Compost = 210 ml (135 g)
Sand = 125 ml (191 g)
Limestone = 18 ml ( 26 g)
Compost = 210 ml (135 g)
Sand = 55 ml ( 82 g)
Limestone = 18 ml ( 26 g)
Fe0 = 70 ml (181 g)
SR Biofilm = 53 ml (6 g VSS)
Compost Reactor
Compost-ZVI Reactor
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Continuous Column 2nd Experiments
Column Set Up
Inoculum: Sulfidogenic granular sludge from Twaron Reactor (The Netherlands)
Medium: basal inorganic nutrients
pH: variable 7.2 to 3.0
Sulfate: initially 1000 mg/L SO42- (50 days);
remainder operation 250 mg/L SO42-
HRT: 24 h
Cu: Period A = 10, B = 25, C = 50, D = 20 ppm
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Influent
effluentBiogas
Com
pos
t o
nly
Influent
EffluentBiogas
Com
pos
t +
Fe0
R4 R5Cu0
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Results R4: Sulfate Data
0
100
200
300
400
0 50 100 150 200 250 300 350 400 450
Time (days)
Su
lfat
e C
on
c. (
pp
m)
influent
effluent
10 ppm Cu2+ 25 50 ppm Cu2+ 20 ppm Cu2+
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Results R5: Sulfate Data
influent
effluent
0
100
200
300
400
0 50 100 150 200 250 300 350 400 450
Time (days)
Su
lfat
e C
on
c. (
pp
m)
10 ppm Cu2+ 25 50 ppm Cu2+ 20 ppm Cu2+
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Results: Sulfide Data
0
10
20
30
40
50
60
0 50 100 150 200 250 300 350 400 450
Time (days)
S2-
Pro
du
cti
on
(p
pm
)
R4
R5
10 ppm Cu2+ 25 50 ppm Cu2+ 20 ppm Cu2+
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Results: S Balance (days 125-185)
0
10
20
30
40
50
R4 R5
Reactor
SO
4-S
Re
mo
va
l; H
2S
-S F
orm
ati
on
(p
pm
)
SO4-SH2S-S
no sequestering H2S
H2S sequestered
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Results: pH
R5 pH Effluent
R5 pH Influent
R4 pH Effluent
R4 pH Influent
2
3
4
5
6
7
8
9
10
11
0 50 100 150 200 250 300 350 400 450
Time (Days)
pH
10 ppm Cu2+ 25 50 ppm Cu2+ 20 ppm Cu2+
pH lowered on purpose
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Results: Total Cu Removal (%)
50
60
70
80
90
100
A (10) B (25) C (50) D (20)
Period
To
tal
Co
pp
er
Re
mo
va
l (%
)
R4R5
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Continuous Column 3rd Experiments
Laboratory Scale PRB Columns (1.3 L)
R6 Filling:
Inoculum:
Compost = 526 ml ( 78 g)
Sawdust = 272 ml ( 24 g)
Limestone = 45 ml ( 73 g)
Mix Biofilm = 108 ml ( 14 g)
Compost-ZVI Reactor
ZVI = 14 ml ( 36 g)
HRT: 48 h
SO42-: 250 mg/L
Cu: 10, 30, 75, 150, 300, 75 ppm
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Continuous Column 3rd Experiments
Limestone Reactor, Pretreatment Column (0.7 L)
LR Filling: Limestone = 623 ml
HRT: 24 h
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Results R6: Sulfate Data
I II III IV V VI VII
0
50
100
150
200
250
300
50 150 250 350 450
Time (days)
SO
4 (
mg
/L)
influent
effluent
effluent LR
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Results R6: pH DataII III IV V VI VII
2
3
4
5
6
7
8
9
10
50 150 250 350 450
Time (days)
pH
I
effluent
effluent LR
influent
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Results R6: Soluble Cu Data
II III IV V VI VII
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
50 150 250 350 450
Time (days)
Co
pp
er C
on
cen
trat
ion
(m
g/L
) 10 30 75 150 30300
influent
effluent
effluent LR
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Summary Chart
Reactor ZVI Comp LS Sand
% dwt
SO42- pH incr. Cu rem.
mg/Lr.d %
R3
R4
R6*
46
0
16
0
38
45†
0
7
6
32
54
53
19
0
33
29£
33
4.3
3.8
5.4*
99.8
99.0£
99.7
99.9*
(89.5)*preceded by limestone reactor
R5 42 31 76 6.8
efficiency post treatment polishing in PRB
†includes sawdust
£decreased when compost biodegradability was exhausted after day 270
Average performance from day 175 to day 240
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Conclusions
Fe0 increases the removal of sulfate
Fe0 prevents the discharge of excess sulfur
Fe0 increases the alkalinity
Compost and the mixture of compost/Fe0 are good substrates for sulfate reducing bacteria
Elimination of Total Copper: 99.5%
Drops in R4 to 72% when SO42- reduction ceased
(exhaustion of compost biodegradability)
Prolonged supply of electron equivalents
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