Low-pH Fe(II) oxidation can improve

passive treatment of acid mine drainage

Bill Burgos

Civil and Environmental Engineering

Pennsylvania State University

Acknowledgements• John Senko, Melanie Lucas, Trinh DeSa,

Mickey Adelman (Lafayette) – Penn State University, Civil and Environmental Engineering

• Mary Ann Bruns, Pauline Wanjugi – Penn State University, Crop and Soil Sciences

Project Number PA DEP_AMD 42(0420)102.1NSF EMSI Program CHE-0431328

Research Objectives• study the microbial communities and mineral

precipitates associated with low-pH Fe(II) oxidation in Appalachian coal mine drainage

• transfer knowledge to the design and operation of more effective passive treatment systems

• engineer the system to produce minerals for industrial reuse

Presentation Outline

• Field chemistry

• Microbial characterizations

• Laboratory experiments

• Field implementation

Low-pH Fe(II) Oxidation Field Sites

Gum Boot:“high rate”Rapid Fe(II) oxidation

Fridays-2:“low rate”Little Fe(II) oxidation

Emergent water chemistry  Gum Boot Fridays-2

Al (µM) 52 4

Ca (µM) 344 232

K (µM) 82 18

Mg (µM) 313 103

Mn (µM) 51 BDL

Na (µM) 530 174

Si (µM) 436 129

Fe(II) (µM) 869 1150

Fe(III) (µM) 197 142

SO42- (µM) 987 3961

D.O. (µM) BDL BDL

pH 4.10 4.50

Temperature (oC) 12 10

Flow rate (gal/min) 13 35

To Gum Boot Creek

AMD Emergence

AMD Flow

X = sampling point

18 m

30 m

79 m

Gum BootAMD flows underground

AMD re-emerges

Gum Boot – view from bottom of hill

Gum Boot – top of “aeration terrace”

Creek Flow

AMD F

low

AMD Emergence

3 m

10 m

10 m

X = sampling point

X

X

X

X

X

XFridays-2

Fridays-2 – view upstream towards iron mound

SeasonalWater

Chemistry

Blue markers – winterRed markers – fallDark green – springLight green – summer

Arrows at Fridays-2 are upstream and downstream locations

downstream distance (m)

Presentation Outline

• Field chemistry

• Microbial characterizations

• Laboratory experiments

• Field implementation

Enumeration of Fe(II)-oxidizing bacteria

100 10-1 10-2 10-3 10-510-4 10-6 10-7

Serial dilution of a soil suspension

Spread on solid medium

Count number of colonies formedAssume 1 CFU = 1 cellSo, 20 colonies on 10-4 plate = 2 x 105 CFU/ml

AMD w/ Fe2+

Air

0

2.5

5

7.5

10

0 0.5 1 1.5 2

-2.5

-2

-1.5

-1

-0.5

0

0 0.5 1 1.5

Time (d)

Fe(

II)

(mM

)

ln(C

/Co)

Time (d)

y = -1.6x - 0.08R2 = 0.96

Determination of first-order rate constants for Fe(II) oxidation at Gum Boot and Fridays-2

Fridays-2 or Gum Boot sediment

Microbial Enumeratio

nand

Activity

Fe(II)OB most abundant in regions where most Fe(II)

oxidation is occurring

Fastest rates of Fe(II) oxidation at

Fridays-2 comparable to fastest rates at

Gum Boot

Iron mound sample with four different kinds of bacteria

Gumboot Fridays-2MWM

3000

2000

1500

1000

700

kbp 0 m

1

23

2 m

4

1

3

60 m

21

127 m

56

4

123

0 m

1

Upstream

4

123

3 m

123

10 m

123

Downstream

54

123

RIS

A p

rofi

les

After PCR, each kind of bacteria yields a differentband in the “communityDNA fingerprint”

Bacteriawith DNA

2

DNA fingerprint with four different bands

DNA bands

n = 34 n = 39

74% 59%

28%

6%3%

9% 6%2%

3%5%

2%

DNA-based bacterial community characterization

Microbial communities are distinctly different,yet potential for low-pH Fe(II) oxidation ~same.Therefore, relatively small fraction of community may be responsible for Fe(II) oxidation.

Presentation Outline

• Field chemistry

• Microbial characterizations

• Laboratory experiments

• Field implementation

20

Batch Reactor Experiments

Air out

500 mL synthetic AMD

25 grams sediment

Headspace purged with O2, CO2, and N2

Air in

Sampling Port

Septum

Gas Mix

Sediment

Air out

21

Batch Reactor Experimental Matrix

Varied partial pressure of O2

Varied partial pressure of CO2

Added organic C (glucose, mulch-ate)

Added nutrients – phosphate

Added nutrients – solid-phase N+P pellets

Add sand to AMD-only incubations

Batch Reactor Results

FR 10m sediments – 0.7% O2, 1.1% CO2, 98.2% N2

Batch Reactor Results – Gum Boot

Batch Reactor Results – Fridays-2

Enumeration of Fe(II) Oxidizing Bacteria

Rate Comparisons

Abiotic and Biological Fe(II)(aq) Oxidation

Rimstidt, 2004

27

Batch Reactor Experimental Matrix

Effect on rate of Fe(II) oxidation

Varied partial pressure of O2 direct +

Varied partial pressure of CO2 +/-

Added organic C (glucose, mulch-ate) none

Added nutrients – phosphate none

Added nutrients – solid-phase N+P pellets slight +

Add sand to AMD-only incubations direct +

Presentation Outline

• Field chemistry

• Microbial characterizations

• Laboratory experiments

• Field implementation

• Mine operators must meet effluent standards– Fe <7, Mn< 5, pH 6-9

• Two type of treatment– Active Treatment (chemical)– Passive Treatment (limestone)

CaCO3 + H+ = Ca2+ + HCO3-Ca(OH)2 + 2H+ = Ca2+ + 4H2O

Active Treatment Passive Treatment

Limestone ChannelPassive Treatment System

Fe Hydroxide Solubility

0.0001

0.001

0.01

0.1

1

10

100

1000

10000

2 3 4 5 6 7 8 9 10 11 12 13

pH

mg

/L

Fe(OH)3

Fe(OH)2

“emergent” AMDpH = 4.0Fe(II) = 100 mg/LDO = 0 mg/L

“aerated” AMDpH = 4.0Fe(II) remains Fe(II) in absence of bio-catalystDO > 2 mg/L

“aerated” AMDpH = 4.0Fe(II) Fe(III) via bio-oxidationDO > 2 mg/L

Spatial separation of iron oxidation/precipitation from alkalinity addition can improve performance

“aerated” AMDpH = 7.0Fe(II) Fe(III) rapid abiotic oxidationDO > 2 mg/L

Gum Boot – top of “aeration terrace”

Upstream overview of Fridays-2, February 2006.Mound flow disrupted May 2006 – Thanks Jon!

Upstream overview of Friday-2 05/09/07

mine pool

“Original” Flowpath

“Fresh” Flowpath new precipitates

since 05/06

Comparison of "original" and "fresh" AMD flowpaths at Fridays-2

0

0.2

0.4

0.6

0.8

1

1.2

0 5 10 15 20

Distance from Source (m)

So

lub

le F

e(I

I) C

on

c. (

mM

) Original Flowpath

Fresh Flowpath

All samples collected 05/09/07

October 2006

Hughes Borehole discharge:800 – 1,500 gallons per minute

October 2006

Hughes Borehole

October 2006

Hughes Borehole

April 2008

Hughes Borehole

May 2008

Hughes Borehole

May 2008

Hughes Borehole

Hughes Borehole

Sackett BuildingPenn State University

On-Mound Channels Laboratory “Gutter” Reactors

Construction of “Aeration Terraces”

• Design to mimic hydrologic characteristics of Gum Boot Run iron mound.

• Maximize aeration and surface area.• Maximize residence time (ca. 15 – 60 min?)

over iron mound sediments.• Construct as series of roughened steps.• Control system to produce minerals for

industrial reuse.

Thanks for your attention.