Reductive Bio-Modification of Sediment Reductive Bio-Modification of Sediment Contaminants: An Contaminants: An In SituIn Situ, Molecular Hydrogen , Molecular Hydrogen

Formation Approach.Formation Approach.

NATO/CCMS Pilot StudyPrevention and Remediation In Selected Industrial Sectors:

Sediments. Ljubljana, Slovenia. June 17-22, 2007

Guy W. Sewell, Ph.D.Guy W. Sewell, Ph.D.Professor of Environmental Health SciencesProfessor of Environmental Health Sciences

Robert S. Kerr Endowed ChairRobert S. Kerr Endowed Chair

Executive Director IESERExecutive Director IESER

East Central UniversityEast Central University

East Central UniversityAda, Oklahoma~4000 Students

Ada is Home to the US-EPAsGround Water Research Center

Assumption: Dredging may be necessary but it is not desirable.

• Efficacy Questions

• Ecological Impacts

• Sustainability Questions

Can we treat in situ effectively?

Sediments: System Management Factors

• Dynamic System Solution Transport Rate Particulate Transport Rate

Contaminant Transport Rate is a Function of BothPrediction of Contaminant Distribution DifficultControl of Treatment/Residence Time Difficult

• Mixture of ContaminantsSink for Multiple SourcesPoint and Non-Point linear source

• Concentration vs Mass Loading (mass flux)Descrete Receptor-More likely than most mediaDo we manage for the media or the receptor?

Redox gradients, flood plain, reversing hydraulic gradient, velocity profiles, baseflow, storm flow

Is in situ Biotreatment an Option?

Bioaugmentation: Addition of microbes• Sediments contain significant native populations• Challenges: GW-transport, Sediment-dispersal

Biostimulation: Addition of nutrients, electron donor/acceptors• Relatively organic rich• Often oxygen limited• Dispersal issue

Biodegradation Triangle

Active M

icroorganisms

Redox Couple

Activity

Reductive Bio-transformations

• Oxygen Limited Conditions• Fermentation

– substrate is both oxidized and reduced, (Ethanol, CO2)

• Anaerobic Oxidation– Discrete electron donor and acceptor (not O2)

• Hydrogen is the Energy Currency in Anaerobic Consortial Systems

• Applicable to a Wide Variety of Chlorinated Organics (PCBs, PCE, PCP, HCB, CT) , inorganics (Nitrate) and metals (CrVI).

Electron AcceptorsElectron Donors

OrganicCompound

H2

PartiallyOxidized

Compound(s)

CO2

NO3-

SO4=

Fe3+

HCO3-

R-Clx

N2(NH4+)

H2S

Fe2+CH4

R-Clx-1

ANAEROBIC OXIDATION-REDUCTION

SEWELL, '95

Reduced Electron Acceptors

sewell

[H2]

Reducing Equivalent Flow inAnaerobic Biotransformations

Complex Substrate

Organic Acids

Acetate

Nitrate Reduction

Metal Reduction

Sulfate Reduction

Methanogenesis

+CO2?

ReductiveDehalogenation

How do We Stimulate Reductive Biotransformations?

• Hydrogen limiting bio-reactant

• Metabolic Formation– Complex substrate addition (bio-stimulation)– HRC

• Direct Injection– Low solubility– Hazardous

Metal Surface

H+

SO4=S=

SRBFe2+

Feoelectrondelocalization

Fe2+ Fe[-]HHHH

Metal Surface

H+C2Cl4HC2Cl3

?Fe2+

e-Feoelectronrich

Fe2+ Fe[-]HHHH

Electrolytic ReductiveDechlorination

AnaerobicCorrosion

Figure 2. Bottom: Microbial consortia operating at the surface of corroding iron, transferring electrons from removed hydrogen, and reducing sulfate. Top: Microbial consortia operating at the surface of metal that is electrolytically generating hydrogen and transferring electrons to chlorinated hydrocarbons.

The story of The story of Postgate’s nailPostgate’s nail

0

2

4

6

8

10

12

0 50 100 150

Time (days)

FIGURE 1. Environmentally benign products production from PCE degradationand concurrent methane formation with cathodic hydrogen as electron donor(Ο control; l enrichment only; s iron B (5 g/L) only; Δ enrichment + iron B (5g/L))

Metal Surface

H+

SO4=S=

SRBFe2+

Feoelectrondelocalization

Fe2+ Fe[-]HHHH

Metal Surface

H+C2Cl4HC2Cl3

?Fe2+

e-Feoelectronrich

Fe2+ Fe[-]HHHH

Electrolytic ReductiveDechlorination

AnaerobicCorrosion

Figure 2. Bottom: Microbial consortia operating at the surface of corroding iron, transferring electrons from removed hydrogen, and reducing sulfate. Top: Microbial consortia operating at the surface of metal that is electrolytically generating hydrogen and transferring electrons to chlorinated hydrocarbons.

The story of The story of Postgate’s nailPostgate’s nail

Reducing Equivalent Flow inAnaerobic Biotransformations

Nitrate Reduction

Metal Reduction

Sulfate Reduction

Methanogenesis

[H2]+CO2

ReductiveDehalogenation

Complex Substrate

Organic Acids

Acetate

[>4nM]

[1-3nM]

[1nM]

[0.5nM]

Hydrogen Generation vs. Applied Potential

0

50

100

150

200

0 20 40 60

Time (min)

H2

(nM)

at 50 mV

at 100 mV

at 200 mV

at 300 mV

at 400 mV

Figure 7. Hydrogen production versus applied potential.

2H+ (aq) + 2e- (induced potential) -> 2H. (surface) <-> H2 (aq)

(Not electrolysis, proton reduction)

.

Hydrogen EvolutionExperimental conditions: 150 mL water, Na2SO4 3500mg/L, headspace150mL, mild steel electrode, 0.18 g each, diameter 0.83mm, 40mmlong, distance between cathode and anode 40mm, voltage 0.03 V

0

50

100

150

200

250

0 30 60 90 120 150 180 210 240

Time (min)

Hydrogen(ppm)

0

2

4

6

8

10

12Hydrogen

Control

Current

Current (µA)

Figure 6. Quantification of evolved hydrogen at a constant applied potential of 0.03V

CH4

Profiles for the Electrode Reversal Test

0

0.2

0.4

0.6

0.8

1

0 2 4 6 8

Time (day)

Methane (mM)

Control at 0 V (Protein content 7.5 micro-g/L)

Continuous electricity at 0.4 V

8 hr/day & 1 switching/10 min at 0.4 V

Figure 14. Methane concentration profiles for the systems tested at 0 V, 0.4 V continuous, and 0.4 V with reversal.

.

Injection Cathode,E3E-10'E3E-12'

E1 E2Anode

Row 1 Row 2 Row 3 Row 4 Row 5 Row 6

A

B

C

D E

A AB B

C C

D D

EWells

NWells are represented by

Wells are designated by Lane, Row, Letter (when applicable), and depth (when applicable).For example, E4A, E3E-12', etc. Distance between wells within rows ≈ 1 ft.Note: Row 3 wells C, D, and E are out of sequence with Row 4 and 5 wells.

Ground Water Flow Cathode to Anode Distance

5' 5' 2.7' 2.6' 2.7' 5' 5' 2.6'

5'

10'

15.3'

4.2'

30'

Figure 16. Lane E map showing the anode, cathode, installed monitoring wells and physical dimensions.

5 ft

(Row

1)

7.7 ft

(Row

2)

10.3 ft

(Row

3)

13 ft

(Row

4)

18 ft

(Row

5)

23 ft

(Row

6)

E

D

C

B

A

0

10

20

30

40

50

60

70

80

90

100

110

120

H2

(nM)

Row

Well

Hydrogen Concentration Profile in Lane E

(Fallon, NV, 10/29/98)

E D C B A

Figure 17. Fallon, NV, pilot test Lane E hydrogen profile on October 29, 1998.

5 ft

(Row

1)

7.7 ft

(Row

2)

10.3 ft

(Row

3)

13 ft

(Row

4)

18 ft

(Row

5)

23 ft

(Row

6)

E

D

C

B

A

0

20

40

60

80

100

120

H2

(nM)

Row

Well

Hydrogen Concentration Profile in Lane E

(Fallon, NV, 12/3/98)

E D C B A

Figure 19. Fallon, NV, pilot test Lane E hydrogen profile on December 3, 1998.

0

10

20

30

40

50

60

70

0 10 20 30 40 50 60

Time (day)

Influent Effluent-Enrichment only

Effluent-Enrichment+Electric Potential Effluent-Iron Only

Effluent-Iron+Enrichment

Column 3 Electric Potential: 0.8V 5.0V 0.0V 2.5V

Effluent

Influent

Syringe Pump

Anode

Cathode

Packings

-

+

Power

Supply

Solution

Reservoir

NO3- NO2

- N2

2NO3- + 5H2

N2 + 4H2O + 2OH-

Guy W. Sewell

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.QuickTime™ and a

TIFF (Uncompressed) decompressorare needed to see this picture.

Great Eastern 1860’s

Cable laying is a proven technology

Line-Electrode Characteristics:

• Ferrous based• Maximize surface area• Nutrient-biomass delivery• Sample collection

Power Characteristics:

• Low power requirements• Solar panel• Battery

• Low Hazard

BioLance Application to Sediments

BioLance Advantages• In situ application• Ease of installation• Low cost installation and

operation • Can be easily applied

where needed to intercept the plume or source

BioLance Disadvantages• Requires electricity source• Hydrogen is potentially

hazardous• Electrodes may need

replacement• There is a lack of

performance data due: ROI, rates

• Attenuation rates may be very slow

Summary• BioLance may be applicable to sediments• Low cost in situ technology• Appropriate for ex situ applications also• Ecologically Benign• Enhances Native Processes• Applicable to a variety of bio-reducible

contaminants

Next Step: Field Trials