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Enhanced Bioremediation Using
Sulfate and/or Nitrate
Ravi Kolhatkar and Davis Taggart
Environmental Technology
Remediation Management Technology Meeting
Warrenville
January 22, 2004
Overview
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• Why add sulfate (and/or nitrate)?
• What kinds of contaminants can be addressed?
• Why bother if anaerobic rates are slower than
aerobic rates?
• What about Hydrogen Sulfide?
• Application Guidance
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Hydrocarbon Biodegradation
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e- and C
Microbial Growth
Contaminant
(Electron donor)
e.g. BTEX
Energy
eElectron Acceptors
High
Energy
Yield
Low
Fast
Kinetics in lab
experiments
Slow
1.
2.
3.
4.
5.
6.
Oxygen
Nitrate
Fe(III)
Mn(IV)
Sulfate
None (fermentation)
Products
>>>
>>>
>>>
>>>
>>>
>>>
Water, CO2
Nitrogen, CO2
Fe(II), CO2
Mn(II), CO2
Sulfide, CO2
Methane, CO2
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Sulfate in Ground Water at Retail
Sites(BP-EPA Study)
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1600
16
Sulfate (mg/L)
Background
sulfate
1200
14
12
Sulfate in
plume
1000
10
800
8
600
6
400
4
200
2
0
0
1
11
21
31
41
51
61
Methane (mg/L)
Methane in plume
1400
71
Rank
Sulfate is absent in most of the plumes
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Why Sulfate?
Electron
Acceptor (EA)
Maximum
Concentration
(mg/L)
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Mass of
benzene
degraded per
unit mass of EA
Potential
Benzene
Degraded
Issues
(mg/L)
Oxygen (in air)
9 - 10
0.33
3.0 – 3.3
Pure Oxygen
60 - 70
0.33
19.8 – 23.1
•Limited solubility
•Numerous oxygen sinks
•Potential aquifer clogging
•Biofouling near injection
point
Sulfate
100 – 250*
0.22
22.0 – 55.0
•Hydrogen sulfide; never
documented as an issue in
the field
•Secondary MCL for sulfate
– 250 mg/L*
Nitrate
80 - 100
0.21
16.8 – 21.0
•DW concern
•Primary MCL – 10 mg/L
NO3-N (45 mg/L NO3)
Iron (III)
0-1
0.024
0 – 0.024
•Very low solubility
•Aquifer clogging
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Sulfate Does the Heavy Lifting!
Sulfate Reduction
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sulfate reduction
methanogenesis
nitrate reduction
aerobic oxidation
iron reduction
Based on median consumptions of
electron acceptors at 74 sites
Gasoline Release Sites
BP-EPA study
6
Field Data - Conclusions
•
Most hydrocarbon plumes are anaerobic and depleted of
sulfate
•
Sulfate reduction is important in ground water
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⇒ Adding sulfate to ground water will likely
stimulate BTEX degradation
¾ No solubility constraints (unlike oxygen)
¾ No chemical sinks (unlike oxygen)
¾ Can address “non-target” electron acceptor demand
enabling contaminants of concern (e.g. benzene) to
“see” oxygen
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Is Anaerobic Biodegradation Slower?
•
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Laboratory Experiments
– Electron acceptor supply (DO, nitrate,..) >> Electron Donor
(BTEX) demand
– Rate dictated by biodegradation
A > NR > IR > SR > M (rates follow same order)
•
Natural Field Setting
– Electron donor demand (BTEX) >> Electron acceptor supply (DO,
nitrate,..)
– Rate dictated by transport of electron acceptors
A ~ NR ~ IR ~ SR (rates are similar)
M (rate dictated by biodegradation)
No, rates are comparable in the field
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Data from Push-pull Tests
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Method
First order rate
constant (day-1)
Reference
Petroleum Impacted
Aquifer (PIA)
Flow path
0.02 to 0.08
Chappelle, 1996
PIA
Augmented
flow path
0.1
Cunningham et al.
2000
Petroleum and CHC
impacted aquifer
Push-pull
tests
4.32 to 6.48
McGuire et al.,
2002
PIA
Push-pull
tests
5.28
Schroth et al.,
1998
PIA
Augmented
flow path
0.1 to 0.6
Cunningham et al.
2000
Petroleum and CHC
impacted aquifer
Push-pull
tests
5.04 to 7.44
McGuire et al.,
2002
Environment
Sulfate Reduction
Nitrate Reduction
McGuire et al., Enviro. Sci. Technol., 36, 2693-2700, 2002
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Normal Alkanes
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McGuire et al., Enviro. Sci. Technol., 36, 2693-2700, 2002?????
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Normal Alkanes
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Townsend et al., Enviro. Sci. Technol., 37, 5213-5218, 2003
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PAH
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PAH
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Townsend et al., Enviro. Sci. Technol., 37, 5213-5218, 2003
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PAH in Sediments
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Rothermich et al., Enviro. Sci. Technol., 36, 4811-4817, 2002
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PAH in Sediments
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More complex PAH relatively difficult to degrade
Rothermich et al., Enviro. Sci. Technol., 36, 4811-4817, 2002
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PAH in Sediments
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Rothermich et al., Enviro. Sci. Technol., 36, 4811-4817, 2002
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Anaerobic Benzene
Biodegradation
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Naval Weapons Station, Seal Beach,
CA
•
Pilot study – Stanford University and NFESC
•
“Injection-extraction” cells to create 3 remediation zones
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– With sulfate
– With sulfate and nitrate
– No amendment (naturally methanogenic)
•
Sulfate and nitrate were quickly consumed Î supply of electron
acceptors was limiting under natural conditions
– Nitrate (0.1 to 0.6 d-1) and sulfate (0.1 d-1) were consumed at similar rates
– Nitrate effective at oxidizing sulfide back to sulfate
•
BTEX removal:
– Toluene preferentially degraded naturally over B, EB and X
– Sulfate preferentially stimulated removal of o-X, but not B, EB and m+p-X
– Nitrate stimulated removal of EB and m+p-X
– Benzene biodegradation was the slowest in all conditions, if at all
ESTCP Cost & Performance Report, December 1999
http://www.estcp.org/documents/techdocs/199522.pdf
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Application
ESTCP Cost & Performance Report, December 1999
http://www.estcp.org/documents/techdocs/199522.pdf
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BTEX Removal with Sulfate and
Nitrate
ESTCP Cost & Performance Report, December 1999
http://www.estcp.org/documents/techdocs/199522.pdf
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MTBE – Surface Water
Sediments
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TBA accumulation tendency increased with more anaerobic conditions
Bradley, P. et al., Enviro. Sci. Technol., 35(23), 4643-4647, 2001
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MTBE – Marine Sediment
Enrichments with Sulfate
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TBA accumulation
Somsamak, P. et al., FEMS Microbiol. Ecology., 37, 259-264, 200122
TBA – Surface Water Sediments
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Bradley, P. et al., Enviro. Sci. Technol., 36(19), 4087-4090, 2002
What About Hydrogen Sulfide?
•
Colorless gas with a strong odor of rotten eggs
•
Exposure limits
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– NIOSH: 10 ppmv (10 minutes)
– OSHA: 20 ppmv
– IDLH: 100 ppmv
•
Health Hazards
– Inhalation: irritation to eyes, conjunctivitis, affects CNS
– Ingestion: excitement, colored urine
– Contact: nausea, dizziness, suffocation, rapid breath
•
Explosive limits: 4% to 44%
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Most of Sulfide is Bound to Soil
Vadose
Zone (oxidized)
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Residual sulfide
oxidized to sulfate
Residual
Hydrocarbon
2−
H 2S (g) + 2O 2(g) → SO 4(s) + 2H
+
NAPL
Aquifer
(reduced)
−
2−
SO 4(aq) → HS (aq) + H 2S (aq) Sulfate reduction
Fe(II) on sediments
+
H 2S (aq) + Fe(II)(s) → FeS(s) + 2H (aq)
0
Sulfide sequestered as iron sulfides
FeS + S → Fe 2 S
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Soil Profile at Neodesha (SOW-9)
0
Depth (ft below grade)
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Soil TOC
(mg/kg)
Sulfate
(mg/kg)
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Fe(III)
(mg/kg)
10
15
Impacted
Zone
20
Water Table
25
30
1
10
100
1000
10000
100000
Soil Concentration
Plenty of iron to
Bind sulfide
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Refinery Site in Oklahoma
•
Operating refinery with an old benzene plume (max. 7.8 mg/L)
•
Hydrogeology:
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– Coarse sand (GW seepage velocity 2500 ft/y)
– DTW: 9-12 ft bgs
•
Sodium sulfate injection
– 40 one-inch wells in 2 rows
– Sulfate injected: 770 mg/L @ 0.14 gpm (total flow)
– Maximum sulfate detected in GW: 58 mg/L
– Sulfide not detected in GW
•
Benzene concentrations were reduced between 73% to 93% in
165 days (half life ~ 2 months)
Anderson and Loveley, Enviro. Sci. Technol., 34, 2261-2266, 200027
Benzene Reduction Following
Sulfate Addition
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Anderson and Loveley, Enviro. Sci. Technol., 34, 2261-2266, 200028
Nitrate for Enhanced Bioremediation
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Nitrate-N (mg/L)
35
Background
nitrate
30
25
20
15
10
Nitrate in
plume
5
0
1
11
21
31
41
51
61
71
Rank
Background nitrate concentrations are generally lower
and nitrate is depleted in plumes
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Nitrate for Enhanced Bioremediation
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Facts
•
Background levels are generally low
•
Primary MCL of 45 mg/L nitrate
•
Like oxygen, nitrate is utilized to oxidize reduced species (e.g. iron
sulfides), as well as other organic carbon
Observations from Field Studies in Literature
⇒ Most pilots and field applications have employed extraction-injection pairs
(“recirculation cell”)
⇒ Injection concentrations – 50 – 200 mg/L nitrate
⇒ Monitoring periods from 2 to 5 months
⇒ Required 10 to 100 times more nitrate over that required for BTEX
biodegradation. Nitrate known to oxidize sulfide back to sulfate.
⇒ TEX compounds degraded, but Benzene generally remained persistent
(total duration too short?). Recent evidence of benzene biodegradation
with nitrate.
⇒ Consider nitrate together with sulfate to increase the
electron acceptor pool
⇒ Naval weapons site, Seal Beach, CA data recommend the same
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Benzene and Nitrate Reduction
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Rothermich et al., Enviro. Sci. Technol., 36, 4811-4817, 2002
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Engineered Bioremediation of a
Diesel-impacted Aquifer
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•
Menziken, Switzerland
•
4.5 years
•
GW pumped from S2 or
KB12
•
Water aerated and
amended with KNO3
mg/L nitrate) and
ammonium phosphate
•
(84
Re-injected in S3 connected
to infiltration gallery
Hunkeler et al., J. Contam. Hydro., 59, 231-245, 2002 32
Natural Diesel Biodegradation
Following Engineered Bioremediation
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Hunkeler et al., J. Contam. Hydro., 59, 231-245, 2002 33
Applications
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• Dissolved Plume
– Addition of solution of sulfate salts (e.g. epsom, sodium sulfate)
– Design sulfate addition (concentration and flow rate) based on
sulfate demand for the mass flux of dissolved BTEX
• Continuous addition, Periodic slug addition
• Row of addition wells, infiltration gallery
• Gypsum socks in transect of wells
• Extract down-gradient, amend sulfate-nitrate and re-infiltrate upgradient
• Source Area (or hotspots)
– Agricultural gypsum amendment (up to 1% w/w) to source area
excavation backfill material as a long term source of sulfate
– Cost effective: ag gypsum ~ $ 19 to 150/t vs $16530/ton for ORC
– Site selection criteria and application procedure (Gypsum FAQs)
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Site Selection Criteria (Sulfate)
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•
Site with residual impact (“sheen” or high dissolved), but not with
“gross” free product impacts
•
Shallowest water table > 5 ft below grade
•
Distance to residence, surface water or private well > 100 ft
•
Distance to municipal DW well (100s of gpm) > 1250 ft
•
Analyze GW samples from “clean” and “impacted” wells for BTEX,
sulfate, sulfide, Fe(II), pH, Total Inorganic Carbon ( or total
alkalinity). Site suitable if
1. Sulfate in clean wells > 15 mg/L and
2. Sulfate depleted in impacted wells
3. Elevated Fe(II) in impacted wells
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Remedial Design Guidance
Data Input (in yellow highlighted cells)
Site Name
Hydraulic Conductivity Estimate (K)
Thickness of impacted saturated zone
Hydraulic gradient
Width of GW plume being addressed
Maximum BTEX concentration
Safety Factor for sulfate demand (over stoichiometric)
Injection Sulfate Concentration
Number of injection wells
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Comments/Basis
200
10
0.003
10
3.50
2
500
2
ft/d
ft
ft/ft
ft
mg/L
Preferablly based on slug test or pump test data
Estimate as length of screened interval of most impacted well
mg/L
Assume 2 to 4
Higher of sulfate in un-impacted water or 250 mg/L
Design choice
60
5945
0.22
27025
29
ft3/d
mg BTEX/d
(mg/mg)
mg sulfate/d
gal/d
Based on stoichiometry for benzene and sulfate
Lateral extent of proposed treatment (e.g. row of wells)
Calculations
Total groundwater volumetric flux (Q = KiA)
Mass flux of BTEX Through Treatment Zone
BTEX degraded/mass of sulfate
Stoichiometric Sulfate Demand
Total sulfate injection volume (w/ safety factor)
Design Choices for Liquid Sulfate Addition
Option 1: Continuous Addition
Solution Flow/well
Option 2: Addition in Slugs
Slug Addition Frequency
Required Slug Addition Rate
Slug volume/well/event
0.010 gpm/well
Adjust sulfate concentration to get reasonable flow
2 times/week
200 gal/week
50 gal
Chemical Requirements
Salt Used
Epsom salt (MgSO4.7H2O)
anhydrous Sodium Sulfate
MW
(gm)
120.37
142
Quantity Required
(gm/d)
68
80
Unit Cost
($/lb)
0.75
1.76
Chemical Cost
($/year)
41
113
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Summary
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•
Most plumes are anaerobic and depleted of soluble electron
acceptors (nitrate and sulfate)
•
Sulfate
– Sulfate is more efficient and stimulates existing anaerobic
conditions
– Suitable for a variety of hydrocarbons – gasoline, gas condensate,
alkanes, PAH, diesel…
– Sulfide not been an issue in studies (OK refinery, Seal Beach site,
other literature, closed BP refinery site)
– Expect some lag time after sulfate shows up at the wells (3 – 6
months)!
•
Nitrate
– Useful to oxidize iron sulfides to sulfate
– Useful to boost the total electron acceptor pool
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Pilot Layout
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35 gal of 500 mg/L sulfate, 100 mg/L bromide twice a week/well
SVP-2
11
9
10
6
7
8
20 ft
5
8 ft
SVP-2
Addition well
SAW-1
SAW-2
GW Flow
4
2
3
- 8 ft
- 20 ft
1
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795
794
600
793
400
792
200
791
5/
03
11
/2
/0
3
17
/
8/
28
/
6/
10
/6
03
790
03
3
9/
0
5/
03
3/
20
/
03
29
/
1/
12
/1
1/
02
0/
02
Sulfate and Bromide not detected
0
GW Elevation in SOW-1 (ft)
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800
10
/2
Benzene, Xylene (ug/ L)
Up-gradient Well (SOW-1)
Variations in B and X related to groundwater fluctuations
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11
/2
10
/6
8/
17
/
03
28
/
6/
9/
0
5/
3/
20
/
03
29
/
1/
12
/1
5/
03
0
10
0
/0
3
2000
30
20
03
50
40
3
4000
03
70
60
0/
02
6000
1/
02
90
80
Sulfate, Bromide (mg/ L)
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8000
10
/2
Benzene, Xylene (ug/ L)
20 ft Downgradient Well (SOW-10)
Significant decrease in B and X in presence of sulfate
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Sulfate and Bromide not detected
8000
40
6000
4000
20
2000
0
5/
03
11
/2
/0
3
10
/6
03
17
/
8/
6/
28
/
03
3
9/
0
5/
03
3/
20
/
03
29
/
1/
0/
02
12
/1
1/
02
0
Sulfate, Bromide (mg/ L)
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10000
10
/2
Benzene, Xylene (ug/ L)
20 ft Downgradient Well (SOW-11)
Decrease in B and X following arrival of sulfate
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Terminal in Minnesota
Ag gypsum in Excavation
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0.5% w/w ag gypsum in backfill
MW-51
MW-44
MW-43
MW-49
MW-50
MW-45
MW-48
MW-47
MW-52
MW-46
Excavated to 15 ft
10 ft
MW-53
100 ft
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Effect of Sulfate on BTEX and TPH
MW-49 Up-gradient of excavation
MW-45 Down-gradient of excavation
100000
10000
10000
1000
1000
ug/L
ug/L
100000
B
100
10
B
100
T
T
EB
EB
X
10
X
MTBE
MTBE
GRO
GRO
•Sulfate not present
•Groundwater impact stays
Sep-03
Jun-03
Mar-03
Dec-02
Oct-02
Jul-02
Apr-02
Jan-02
Oct-01
Jul-01
Sep-03
Jun-03
Mar-03
Dec-02
Oct-02
Jul-02
Apr-02
Jan-02
Oct-01
1
Jul-01
1
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•Sulfate upto 290 mg/L
•Groundwater cleans up!
44