Post on 13-Dec-2015
transcript
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
2
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
3
Acid Mine or Acid Rock Drainage
acid
heavy metals
sulfates
iron
H+
Cu2+Fe2+
SO42-
4
Acid Rock Drainage with Copper
5
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
6
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
7
Fe0 as an Electron Donor for Sulfate Reduction
Fe0
Fe2+ + H2
SRB
SO42-
H2S
SRB
Fe0
Fe2+SO42-
H2S
indirect
direct
8
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
9
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
10
Fe0 + Cu2+ Fe2+ + Cu0abiotic
Hypotheses: Benefits of Fe0 for Sulfate Reducing PRB (continued)
Direct abiotic reduction heavy metals by Fe0
11
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
12
Batch Experiment: Fe0 as E-donor SRB
endogenous
uninoculated
treatment
13
Continuous Column Experiments
14
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-)
15
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
16
Continuous Column 1st Experiments
Column Set Up
R1 (SO42-) R2 (no SO4
2-), R3 (SO42-),
*
17
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
18
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
19
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
20
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
21
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
22
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
23
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
24
Results R3: SEMS-EDS
25
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
26
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
29
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+
30
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+
31
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+
32
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
33
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
34
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
35
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
36
Continuous Column 3rd Experiments
Limestone Reactor, Pretreatment Column (0.7 L)
LR Filling: Limestone = 623 ml
HRT: 24 h
37
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
38
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
39
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
40
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
41
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
42
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