The basic science
of anaerobic bioremediation
Dan Leigh PG, CHG
June 4, 2013
Introduction: Dan Leigh
– Licensed geologist and hydrogeologist
– Walnut Creek, CA
– Applying bioremediation for > 25 yrs
– Applying anaerobic bioremediation of chlorinated
organics for >20 yrs
– Currently working on development of
biogeochemical processes occurring during
anaerobic bioremediation
– 925.984.9121
2 Basic Science of Anaerobic Bioremediation
FMC provides a wide range of products for
application of anaerobic bioremediation,
biogeochemical and abiotic degradation
Basic Science of Anaerobic Bioremediation 3
EHC-L ®
EHC®
EHC-M ®
ELS ®
Daramend ®
Solid organic substrate with microscale ZVI
Liquid organic substrate with soluble Fe(II)
EHC® with sulfur source for biogeochemical
metals treatment
Emulsified Lecithin Substrate for
enhancement of anaerobic bioremediation
Solid organic substrate with ZVI for
treatment of contaminated soils
http://environmental.fmc.com/solutions
Presentation outline
• Basic concepts of biological and geochemical processes
– Respiration, fermentation, co metabolism
– Electron donors and acceptors
– Biotic and abiotic anaerobic degradation pathways of chlorinated
ethenes
– Processes for stimulating anaerobic bioremediation of chlorinated
organics
• Significant site conditions not conducive to anaerobic
bioremedation and how to overcome them
– Inappropriate or insufficient bacteria
– High dissolved oxygen
– Low pH
– High sulfate concentrations
• Biogeochemical degradation
• Summary
4 Basic Science of Anaerobic Bioremediation
Contaminants that can be degraded
by anaerobic processes • Chlorinated solvents such as PCE, TCE, TCA, DCA,
CCl4, chloroform and methylene chloride
• Chlorobenzenes including di- and tri-chlorobenzene
• Energetic compounds such as TNT, DNT, HMX, RDX,
nitroglycerine and perchlorate.
• Most pesticides including DDT, DDE, dieldrin, 2,4-D and
2,4,5-T
• Nitrate compounds
• Petroleum hydrocarbons
This presentation focuses on biological and
geochemical processes that occur during the in situ
anaerobic degradation of chlorinated ethenes.
5 Basic Science of Anaerobic Bioremediation
Bioremediation is a natural and
sustainable remediation process.
Bioremediation utilizes the life processes of
organisms to reduce the concentration,
mass, mobility or toxicity of contaminants.
– Yeast, fungi, bacteria or plants are
stimulated to degrade toxic substances.
– The primary processes include
respiration and fermentation.
– Not a new technology –
• e.g. wastewater treatment
– Improvements to bioremediation
approaches are being developed.
6 Basic Science of Anaerobic Bioremediation
Basic concepts of biological and
geochemical processes
• Several biological processes occur during anaerobic
bioremediation including: – Respiration: Aerobic and Anaerobic
– Fermentation
– Co-metabolism
• Abiotic processes can be integrated, or occur naturally,
which enhance biological degradation processes.
• Biotic and abiotic anaerobic degradation processes
occur in distinct, identifiable pathways.
7 Basic Science of Anaerobic Bioremediation
Respiration processes
Aerobic
Respiration
Aerobic
Respiration
Eating and breathing Electron
Donor
Electron
Acceptor Organism Respiration
8 Basic Science of Anaerobic Bioremediation
Aerobic and anaerobic respiration
• Aerobic respiration
– Molecular oxygen (O2) is the only
electron acceptor used in the process
• Anaerobic respiration
– Any inorganic electron acceptor (other
than oxygen) is used in the respiration
process
• NO3, Mn(IV), As(V), Fe(III), SO4, CO2
• Cr(VI), ClO4
9 Basic Science of Anaerobic Bioremediation
Respiration Biologically Mediated Oxidation - Reduction
Electron Donor Electron Acceptor
Resistor
Positive Negative
Growth Protein Synthesis
Reproduction
CnHn Fe(II)
H2S
H2
O2
NO3
As(V)
Mn(IV)
SO4
CO2
Work Light bulb
Motors
As(III)
Mn(II)
Fe (III) Reduced Oxidized
HNO2
10 Basic Science of Anaerobic Bioremediation
Oxygen O2 + 4H+ + 4e- 2H2O (Eh0 = +820)
Nitrate 2NO3- + 12H+ +10e- N2(g) + 6H2O (Eh0 = +740)
De
cre
asin
g A
mo
un
t o
f En
erg
y R
ele
ase
d D
uri
ng
Elec
tro
n T
ran
sfe
r
Manganese (IV) MnO2(s) + HCO3 +3H + + 2e - MnCO3 (s) + 2H20 (Eh0 = +520)
Iron FeOOH(s) +HCO3 - + 2H+ e- FeCO3 + 2H2O (Eh0 = -50)
500
Aerobic
Anaerobic
1000
0
-250
Arsenic (V) H3AsO4 + 2H+ +2e- H3AsO3 + H2O (Eh0 = +559)
Chromium (VI ) Cr2O72- + 14H+ + 6e- 2Cr3++7H2O (Eh0 = +1330)
Anaerobic
Eh range for various electron acceptors
Redox Potential (Eh0) in Millivolts @ pH = 7
and T = 250C
Methanogenesis CO2 + 8H+ + 8e- CH4 + 2H2O (Eh0 = -240)
Sulfate SO4 2- + 9H+ + 8e- HS- + 4H2O (Eh0 = -220)
11 Basic Science of Anaerobic Bioremediation
Anaerobic respiration and chlororespiration
Anaerobic
Respiration
Chlororespiration
Electron
Donor
Electron
Acceptor Biota Respiration
Aerobic
Respiration
NO3
SO4
Fe(III)
CO2
Mn(IV)
12 Basic Science of Anaerobic Bioremediation
Range for Effective Chlorinated Ethene
Degradation (chlororespiration)
↓
Methanogenesis CO2 + 8H+ + 8e- CH4 + 2H2O (Eh0 = -240)
Sulfate SO4 2- + 9H+ + 8e- HS- + 4H2O (Eh0 = -220)
Iron FeOOH(s) +HCO3 - + 2H+ e- FeCO3 + 2H2O (Eh0 = -50)
Oxygen O2 + 4H+ + 4e- 2H2O (Eh0 = +820)
Nitrate 2NO3- + 12H+ +10e- N2(g) + 6H2O (Eh0 = +740)
De
cre
asin
g A
mo
un
t o
f En
erg
y R
ele
ase
d D
uri
ng
Elec
tro
n T
ran
sfe
r
Manganese (IV) MnO2(s) + HCO3 +3H + + 2e - MnCO3 (s) + 2H20 (Eh0 = +520)
Redox Potential (Eh0) in Millivolts @ pH = 7
and T = 250C
500
Aerobic
Anaerobic
1000
0
-250
Arsenic (V) H3AsO4 + 2H+ +2e- H3AsO3 + H2O (Eh0 = +559)
Chromium (VI ) Cr2O72- + 14H+ + 6e- 2Cr3++7H2O (Eh0 = +1330)
Anaerobic
Eh range for cholorinated ethene degradation
PCE TCE
TCE DCE
DCE VC
VC Ethene
13 Basic Science of Anaerobic Bioremediation
Many organisms generate energy by
fermentation rather than respiration • Fermentation refers to the conversion of sugar to acids,
gases and/or alcohol using yeast or bacteria.
• Fermentation does not use an electron transport chain
(e.g. O2, NO3, Mn(IV), SO4, CO2) as does respiration.
• Fermentation uses a reduced carbon source (e.g.,
cellulose, lecithin, lactose, sugars).
– to generate volatile fatty acids ((VFAs) e.g. lactic, acetic,
propionic, valeric, butyric acids)
– and gases (e.g. H2, CO2, CH4)
• H2 is used by dechlorinating bacteria to generate
energy by sequentially reducing chlorinated organics.
14 Basic Science of Anaerobic Bioremediation
A note about
co-metabolic oxidation The microbial breakdown of a contaminant in which the contaminant is
oxidized incidentally by an enzyme or cofactor that is produced during
microbial metabolism of another compound is called aerobic/anaerobic
co-metabolism.
– Co-metabolic oxidation applies respiration processes:
• Electron donor: (e.g., methane, ethane, ethene, propane, butane, toluene, phenol,
ammonia) PLUS: electron acceptor (e.g, O2, SO4)
– Enzymes generated to degrade food source also fortuitously degrades CEs or
other contaminants.
– The degrading organism does not gain energy from the contaminant degradation.
– The presence of electron donor may inhibit contaminant degradation.
Co-metabolism can be a challenge to apply.
– Often requires substantial engineering effort
– It is difficult to identify co-metabolic degradation in the aquifer
– May not be an efficient use of substrate
15 Basic Science of Anaerobic Bioremediation
Dechlorinating bacteria
• Several organisms capable of
partially dechlorinating
chlorinated organics.
• Only organism confirmed to
dechlorinate DCE and VC to
ethene is Dehalococcoides
(Dhc).
• Dhc uses H2 as the electron
donor in dechlorination process.
16 Basic Science of Anaerobic Bioremediation
Biological Reductive Dechlorination of Chlorinated Ethenes
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
H H H H H H
PCE PCE PCE TCE TCE TCE cis 1,2 -DCE trans 1,2 -DCE 1,1 -DCE
H H
H H H H H H H H H H
VC VC VC
H H
H H H H
Ethene Ethene Ethene
0
- 50
- 200
- 150
- 250
ORP
17 Basic Science of Anaerobic Bioremediation
C C C C C C
β elimination (abiotic) pathway
Cl
C
Cl
Cl
Cl Cl Cl
H
Cl
Cl
Cl
PCE TCE Dichloroacetylene Chloroacetylene Acetylene DCE
H H
Fe 0
II
Fe 0
II
Fe 0
II
C C C C C
Ethene Ethane
18 Basic Science of Anaerobic Bioremediation
Hydrogenation Hydrogenolysis
Acetylene
Some Hypothesized Reaction Pathways
Biotic Abiotic PCE
TCE
Cis 1,2-DCE Trans 1,2-DCE
VC
Ethene
Ethane
PCE
TCE
VC
Ethene
Ethane
Chloroacetylene
Acetylene
1,1-DCE, trans 1,2-DCE, cis1,2-DCE
Dichloroacetylene
Hydrogenolysis
β-elimination
α-elimination
Hydrogenation
CO2 , CH4 , H2O
CO2, CH4,H2O
19 Basic Science of Anaerobic Bioremediation
Concentr
ation
Time
Concentr
ation
Time
Biological and abiotic degradation processes appear
different when measuring standard analytical parameters
Biological Degradation
(Chlororespiration) Abiotic Degradation
PCE TCE DCE VC Ethene
(β elimination)
Anticipated change in CE molar concentration
Total
20 Basic Science of Anaerobic Bioremediation
Generating anaerobic
bioremediation processes Enhanced anaerobic bioremediation is conducted by providing
whatever is limiting the complete degradation process.
Need appropriate organism and electron donor (H2) to degrade CEs
Other supplements can be made to further enhance the anaerobic
process.
– Chemical reductants (e.g. ZVI, ferrous iron)
– Nutrients
Additional supplements can be made to enhance synergistic effects.
– Sulfate
– Iron
21 Basic Science of Anaerobic Bioremediation
Electron
Donor
Electron
Acceptor Organism Chlororespiration
Molasses
Starch
Cheese whey
Emulsified vegetable oil
Corn syrup
Lactose
Glucose
Ethanol
Methanol
Propanol
Lecithin
Glycerol, xylitol, sorbitol
Polylactate esters of fatty acids (e.g.., Glycerol tripolylactate)
Acetic acid and its salts
Lactic acid and its salts
Propionic acid and its salts
Citric acid and its salts
Benzoic acid and its salts
Oleic acid and its salts
Various Bean Oils (soy, guar)
Complex sugars
Food process byproducts including milk whey or yeast extract
Complex organic material such as wood chips (cellulose)
Draft General Waste Discharge
Requirements for
In Situ Groundwater Remediation –
Santa Ana Water Quality Control
Board CA, 2013
Only H2 has been
shown to be an
electron donor for
cis 1,2-DCE and
vinyl chloride
conversion to
ethene
Anaerobic reductive dechlorination is stimulated by
providing an electron donor to the organisms
Molecular Hydrogen (H2)
Various substrates used to generate H2 for dechlorination:
22 Basic Science of Anaerobic Bioremediation
Electron Acceptor Electron equivalents per mole
Oxygen (dissolved) 4
Nitrate (dissolved) 4
Sulfate (dissolved/solid) 8
Maybe carbon dioxide (dissolved) 8
Manganese (IV) (solid) 2
Ferric iron (III) (Solid) 1
PCE – tetrachloroethene (dissolved + adsorbed + NAPL) 8
TCE – trichloroethene (dissolved adsorbed + NAPL) 6
DCE – dichloroethene (dissolved + adsorbed) 4
VC – vinyl chloride (dissolved + adsorbed) 2
Most of the contaminant mass may be adsorbed to
aquifer matrix
Substrate requirements partially determined by amount
of hydrogen required to reduce electron acceptors and
contaminants
23 Basic Science of Anaerobic Bioremediation
Some electron acceptors
may be in solid form
• Solid electron acceptors
occur as: • oxides
• salts
• minerals
• Solid electron
acceptors are not
accounted for by
dissolved phase
analysis.
Some mineral electron
acceptors
• Barite – BaSO4
• Gypsum – CaSO4·2H2O
• Anhydrite – CaSO4
• Hannebachite – CaSO3 ·0.5H2O
• Anglesite (PbSO4)
• Magnetite (Fe2+Fe3+2O4 or Fe3O4)
• Hematite (Fe2O3)
Barite
(BaSO4)
24 Basic Science of Anaerobic Bioremediation
Substrate requirements partially determined by amount
of hydrogen generated during fermentation
Electron Donor Electron equivalent per mole
acetate 4
proprionate 3
lactate 2
fructose/glucose 12
sucrose/lactose 24
cellulose 24
linoleic acid 50
glycerol 7
lecithin 122 Most data derived from Fennel & Gossett (1998) and He, et al (2002)
Hydrogen equivalents produced by various electron donors
25 Basic Science of Anaerobic Bioremediation
Draft General Waste Discharge
Requirements for
In Situ Groundwater Remediation – Santa
Ana Water Quality Control Board CA, 2013
Ferrous Chloride
Ferrous Carbonate
Ferrous Gluconate
Sorbitol Cysteinate
Sodium Sulfide
Sodium Dithionite
Calcium Polysulfide
Zero-Valent Iron
Granular
Emulsified
Micro-scale
Nano-scale
Reducing/reductive degradation
enhancement compounds
26 Basic Science of Anaerobic Bioremediation
Undesired and unexpected results
Incomplete degradation (e.g. cis DCE or VC stall)
• No, or insufficient Dhc population
• Insufficient /too much substrate
• Inefficient distribution of substrate and culture
• Geochemical issues (e.g., sulfide toxicity)
• pH outside appropriate range
Contaminants disappear without generation of daughter products
• May be partitioning into substrate
• May be biogeochemical/abiotic degradation
Contaminants disappear but come back after substrate is gone. • Other source of contaminants
• DNAPL possible
• High adsorbed phase
• Matrix diffusion
27 Basic Science of Anaerobic Bioremediation
Anaerobic bioremediation may be applicable at
more sites than previously considered.
Some sites may not initially appear to be
appropriate for anaerobic bioremediation. Some of
these conditions include: • Inappropriate or insufficient dechlorinating bacteria
• High dissolved oxygen concentration
• Low pH
• Very high sulfate concentrations
Modifications may be made to alleviate these
conditions and allow use of anaerobic
bioremediation.
28 Basic Science of Anaerobic Bioremediation
At some sites biostimulation is sufficient, at
other sites bioaugmentation is required.
• Biostimulation is the
modification of the
environment to stimulate
existing bacteria capable
of bioremediation.
– Nutrients – e.g. nitrogen,
phosphorous, potassium
– Electron acceptors – e.g.
oxygen, nitrate,
manganese, ferric iron,
sulfate carbon dioxide
– Electron donors – e.g.
lactate, vegetable oil,
lecithin, cellulose, lactose
• Bioaugmentation is the
introduction of a group of
natural microbial strains
or genetically engineered
variants to achieve
bioremediation.
– Indigenous – native to site
– Exogenous - introduced
29 Basic Science of Anaerobic Bioremediation
Is bioaugmentation necessary?
• Dechlorinating organisms may not be present at
sufficient concentrations at many sites.
– > 1x107 Dhc cells/L considered necessary for dechlorination
• The indigenous organism may not be efficient at
dechlorination.
– Final step may be co-metabolic, which is slow
• Indigenous organisms (e.g. methanogenic bacteria) may
outcompete dechlorinators such as (Dhc) for H2.
www.mdsg.umd.edu/CQ/v05n1/main/
30 Basic Science of Anaerobic Bioremediation
Various organisms
approved for bioaugmentation
Dehalococcoides (Dhc)
Dehalobacter
Dehalogenimonas
Desulfuromonas
Desulfitobacterium
Desulfovbrio
Sulfurospirillum
Alcaligenes faecalis
Arthrobacter
Geobacter
Corynebacterium
Nitrosomonas
Nitrobacter
Rhodococcus
Pseudomonas fluorescens
Methylibium petroleiphilum
Methanotrophs
Methylosinus
31 Basic Science of Anaerobic Bioremediation
ETHENES LOOP 3 (BIOSTIMULATION, LACTATE ONLY)
0
50
100
150
200
0 30 60 90 120 150 180 210 240 270 300 330 360
Days
Co
nc
en
tra
tio
n (m
mo
l/L
)
Tetrachloroethene
Trichloroethene
1,2-Dichloroethene (total)
Vinyl Chloride
Ethene
Total umol/L
Biostimulation only
Bioaugmentation can increase degradation rates
32 Basic Science of Anaerobic Bioremediation
ETHENES LOOP 2 (BIOAUGMENTATION, LACTATE )
0
50
100
150
200
250
300
350
400
0 30 60 90 120 150 180 210 240 270 300 330 360
Days
Co
ncen
trati
on
(mm
ol/L
)
Tetrachloroethene
Trichloroethene
1,2-Dichloroethene (total)
Vinyl Chloride
Ethene
Total umol/L
Comparison of bioaugmentation to biostimulation
Biostimulation with Bioaugmentation
High total molar concentration
33 Basic Science of Anaerobic Bioremediation
Can anaerobic processes be applied in
aerobic aquifers?
• Aerobic aquifers are often not considered appropriate for
the application of anaerobic biological processes.
• Bioaugmentation is necessary to treat CE’s biologically in
aerobic aquifers.
• Substantial effort is considered necessary to bioaugment
in aerobic aquifers (i.e., several injection events required
to establish reducing conditions).
– Suggests anaerobic bio treatment not cost effective.
34 Basic Science of Anaerobic Bioremediation
Plan View
Cross Section
Inject 25% Substrate Inject Anaerobic Chase Water Inject Bioaugmentation Culture Inject Chase Water Inject 75% Substrate
Bioaugmentation methods applied to
overcome aerobic conditions
35 Basic Science of Anaerobic Bioremediation
Sites with high dissolved oxygen can be
appropriate for anaerobic bioremediation
• Dhc is an obligate anaerobe
– Anaerobes are organisms that are not able to use (consume)
molecular oxygen.
– Obligate: those that cannot grow in the presence of molecular
oxygen.
• Anaerobic bacteria can be:
– Oxyduric: those that are not killed by (i.e. tolerant of) molecular
oxygen.
– Oxylabile: Those killed in the presence of molecular oxygen.
– Aerotolerant: those able to grow in the presence of molecular
oxygen even though they do not use it.
36 Basic Science of Anaerobic Bioremediation
Bioaugmentation methods applied to
overcome aerobic conditions
Dhc exposed to oxygen in GW
37 Basic Science of Anaerobic Bioremediation
DO depletion in closed system after
addition of SDC-9* and e- donor
Time (minutes)
2
4
5
6
7
DO
Co
ncen
trati
on
(m
g/L
)
3
100 200 300 400 500 0 1
Temperature 15 ± °C
TSS 0.1 g/L
DHC Concentration 9E10 cells/L
*SDC-9 is a trademark of the CB&I/Shaw Corporation
38 Basic Science of Anaerobic Bioremediation
cDCE and VC degradation rates by SDC-9
exposed to air (with & without e- donor)
10 20 30 40 50 60 70 80 0 0
5
10
15
20
25
Air Exposure Time (Hours)
Deg
rad
ati
on
Rate
(m
g/L
xh
)
VC - Air Exposure
cDCE - Air Exposure
VC – e- donor - Air Exposure
cDCE – e- donor - Air Exposure
cDCE - Anaerobic Control No Air Exposure
VC - Anaerobic Control No Air Exposure
DHC 5E10 copies/L
Temperature 15±°C
Leigh, D.P., S. Vainberg, and R.Steffan, R., 2013, Can
Anaerobic Bioaugmentation Cultures be Applied Directly to
Aerobic Aquifers?: In situ and on Site Bioremediation
Symposium, 2013.
39 Basic Science of Anaerobic Bioremediation
0
1
2
3
4
5
6
7
8
-100 -50 0 50 100 150 200 250 300
mg
/L
Days (Day 0 = June 6, 2011)
CNWS - Dissolved Oxygen
Field analytical results
Dissolved Oxygen
40 Basic Science of Anaerobic Bioremediation
Groundwater analytical results after
bioaugmentation of anaerobic culture into an
aerobic aquifer
0
1
10
100
1000
10000
-100 0 100 200 300 400 500
µg
/L
Days (Day 0 = June 6, 2011)
Trichloroethene (TCE)
0
200
400
600
800
1000
1200
-100 0 100 200 300 400 500
Co
nc
en
tra
tio
n (µ
g/L
)
Days (Day 0 = June 6, 2011)
Total Dichloroethene (DCE)
0
1
10
100
1000
-100 0 100 200 300 400 500
Co
ncen
trati
on
( µ
g/L
)
Days (Day 0 = June 6, 2011)
Vinyl Chloride (VC)
0
20
40
60
80
100
120
-100 0 100 200 300 400 500
Co
nc
en
tra
tio
n( µ
g/L
)
Days (Day 0 = June 6, 2011)
Ethene
41 Basic Science of Anaerobic Bioremediation
Anerobic biodegradation can be
conducted only in a defined range of pH
• Dhc species are very sensitive to pH.
• Some other organisms (e.g.
methanogens/SRBs) are not as sensitive to
pH.
• SRB’s and methanogens outcompete
dechlorinators for available H2.
• Addition of organic substrates can generate
organic acids which cause pH drop.
• Addition of ZVI/buffers raises pH. 42 Basic Science of Anaerobic Bioremediation
Dechlorination rates by Dhc are affected by pH
6 5 10 7 8 9 pH
0
0.5
1.0
1.5
Vainberg, S., C.W. Condee, R.J. Steffan. 2009. Large scale production of Dehalococcoides sp.-
containing cultures for bioaugmentation. J. Indust. Microbiol. Biotechnol. 36:1189-1197.
43 Basic Science of Anaerobic Bioremediation
Dhc do not recover the
ability to dechlorinate after
extended exposure to low
pH water.
Elevated concentrations of sulfide can
inhibit anaerobic biodegradation
• Sulfate reduction stimulated
during anaerobic bioremediation
• Sulfate converted into HS-
• If ferrous iron is present, it will
precipitate as ferrous sulfide
species such as pyrite and
mackinawite
• If iron is insufficient, toxic levels
of HS- may accumulate.
Addition of iron can solve sulfide
toxicity issues.
44 Basic Science of Anaerobic Bioremediation
Example of sulfide toxicity
Bench tests – ambient conditions
Time (weeks)
1000
100
10
1
0.1
0.01
0.001
Concentr
ation (
mg/L
)
Sulfate
& S
ulfid
e C
oncentr
ation (
mg/L
)
1200
1000
800
600
400
200
0
0 4 8 12 16 20 24 28 32
e- donor
Addition
Week 8
Bioaugmentation Week 17
e- donor
Addition
Week 20
TCE DCE VC Ethene Sulfate Sulfide
45 Basic Science of Anaerobic Bioremediation
Time (weeks)
1000
100
10
1
0.1
0.01
0.001
Concentr
ation (
mg/L
)
Su
lfa
te &
Su
lfid
e C
on
cen
tra
tio
n (
mg
/L) 1200
1000
800
600
400
200
0
0 4 8 12 16 20 24 28 32
e- donor
Addition
Week 8
Bioaugmentation Week 17
e- donor
Addition
Week 20
TCE DCE VC Ethene Sulfate Sulfide
Example of sulfide toxicity
Bench tests – Fe-sulfide precipitation
46 Basic Science of Anaerobic Bioremediation
Anaerobic biogeochemical degradation
• Reactive iron sulfide minerals are produced
at sites containing bioavailble iron and
sulfate during anaerobic bioremediation.
• Degradation occurs by contact with reactive
minerals
• Biogeochemical degradation pathway are
the same as for ZVI (β elimination).
Biogeochemical degradation includes processes where
contaminants are degraded by abiotic reactions with naturally
occurring and biogenically-formed minerals in the
subsurface.
47 Basic Science of Anaerobic Bioremediation
Reactive iron sulfides minerals are formed during
anaerobic bioremediation processes
Pyrite (FeS2) Mackinawite (Fe(1+x)S
Euhedral pyrite (FeS2) Mackinawite (FeS)
pore coatings
Framboidal
Pyrite
(FeS2)
Mackinawite
coating
Pyrite
Framboids
48 Basic Science of Anaerobic Bioremediation
Other potential applications of
anaerobic bioremediation
• Sequential anaerobic/aerobic bioremediation can be applied
to treat some contaminants (i.e, chlorobenzenes/CEs).
• Sulfate generated during activated persulfate treatment can
be reduced to generate reactive iron sulfides.
• Biogeochemical processes occuring with anaerobic
bioremediation can be enhanced to sequester metals.
• Enhanced anaerobic bioremediation can be applied following
thermal treatment.
• Anaerobic bioremediation can be applied to supplement or
replace existing pump and treat systems.
49 Basic Science of Anaerobic Bioremediation
Presentation Summary
• Bioremediation uses natural and sustainable processes to
destroy contaminants rather than transfer to other media.
• The bioremediation process is effective because it enhances
the life processes of the organisms.
• Because this technology uses life processes organisms it can
be applied at sites with very high contaminant concentrations.
• Anaerobic bioremediation can be enhanced by adding abiotic
substrates (ZVI, soluble iron) and biogeochemical
amendments (sulfur sources) depending on site conditions.
• Anaerobic bioremediation can be conducted in aquifers
exhibiting low pH, high DO or high sulfate concentrations.
• Combined anaerobic biological, abiotic and biogeochemical
processes effectively treats a wide range of contaminants in
soil and groundwater.
50 Basic Science of Anaerobic Bioremediation
51 Basic Science of Anaerobic Bioremediation
925.984.9121