August 27, 2008

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


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


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


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


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)


Fe0 = 70 ml (181 g)

SR Biofilm = 53 ml (6 g VSS)

Compost Reactor

Compost-ZVI Reactor

27

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

28

Influent

effluentBiogas

Com

pos

t o

nly

Influent

EffluentBiogas

Com

pos

t +

Fe0

R4 R5Cu0

29


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


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)


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


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


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


R6 Filling:

Inoculum:

Compost = 526 ml ( 78 g)

Sawdust = 272 ml ( 24 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


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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August 27, 2008