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Abiotic Treatment Technologies for In-Site Remediation of Persistent
Perfluoroalkyl Acids
Linda S. Lee1,2*, Saerom Park2,3, and Jenny Zenobio2,3
1Professor of Environmental Chemistry, Agronomy2Interdisciplinary Ecological Sci. & Engineering Graduate Program, Program Head
3PhD Students
June 26, 2015NICOLE Workshop
Manchester, UK
ER-2426Office of the
Vice President
US Military big user of AFFFs, which are a primary source of PFAAs and likely present at > 550 sites.
Additional, many other military sites due to use/releases of AFFFs to extinguish hydrocarbon fires or industrial activities, etc.
PFAAs are persistent, bioaccumulative, and relatively mobile.
● Currently, no viable in-situ technology has been successfully demonstrated for the entire suite of PFASs, particularly linear PFOS, or PFAA precursors.
● Provisional health advisory levels are well below what is expected at military sites
*Moody and Field, 1999; Moody et al., 2003; Schultz et al., 2004
** *
Aqueous Film-Forming Foam (AFFF) Sources
Telomer-based fluorinated surfactants
Electrofluorination-based fluorinated surfactants
Perfluorocarboxylic acidsPFCAs (PFOA pKa < 4)
Perfluorosulfonic acidsPFSAs (PFOS pKa < 0)
Terminal microbial end products
Σ = PFAAs = perfluoro alkyl acids
PFASs in Aqueous Film Forming Foams (AFFFs)(Place & Field, EST, 2012)
B, C & D
Fenton’s Reagent◦ Thermodynamic studies indicate not effective◦ PFOS not degraded with an aggressive treatment.
Ultraviolet reactions◦ Successful for only PFOA◦ Conditions not applicable in situ
Permanganate ◦ some success with PFOS at ≥ 65 ºC & low pH (Liu et al, 2012)
Sonolysis◦ Good results for PFOA and PFOS◦ Not applicable for in situ
Persulfate◦ UV and heat activation established successful for PFOA (Hori et
al., 2005; Lee et al, 2012; Liu et al., 2013)
Initial Approach: Chemical Oxidative Treatment
*Choice of activation mode dependent on effectiveness and efficiency for a given environment, e.g., in-situ versus ex-situ.
-↔
PFOA/PFOA-
PFOS-
6:2 FTS (6:2 Fluorotelomer sulfonate)
Temperature (20 ~ 60 °C)
Unbuffered pH
Persulfate (Na2S2O8) Conc. (0 ~ 20,000 mg/L, 84.00 mM)
PFACs conc. (50 ~ 2,500 µg/L, 0.12 µM ~ 6 µM)
Fuel co-contaminants (BTEXs up to 1,000 µg/L)
Aquifer
Experimental Variables
Heat-activated Persulfate for 3 Representative PFASs
Varying Temperature[Na2S2O8 ] =- 10,000 mg/L Varying [Na2S2O8 ], T = 50 ºC
Heat-Activated Persulfate(100 µg/L PFOA)
Removal rate ↑ with ↑ temperature and ↑ [Na2S2O8] Linear Arrhenius Plots (right graph) Unbuffered pH (pH decreases with reaction) Same for PFCA range tested: 50 ~ 2,500 µg/L (0.12 µM ~ 6 µM)
0.0
0.2
0.4
0.6
0.8
1.0
0 50 100 150 200 250 300 350
Ct/C
o
Time (h)
20 C 30 C 40 C 50 C
-8
-6
-4
-2
0.0028 0.003 0.0032 0.0034 0.0036
ln (k
1, h-
1 )
1/(T, K)
This Study (unadjusted pH)Lee et al. (2012) pHo=2.5Lee et al. (2012) pHo=7.1Lee et al. (2012) pHo=11Liu et al. (2012) pHo=7.1
0.00
0.05
0.10
0.15
0.20
0.25
0 10 20 30 40 50 60 70 80 90
-k1
(h-1
)
Na2S2O8 (mM)
~100 µg/L M) (0.241 µM) PFOA ~100 µg/L (0.215 µM) 6:2 FTS
Heat (50 ºC) - Activated Persulfate[Na2S2O8] – 10,000 mg/L, 50 ºC
PFOA and 6:2 FTS unzipped to smaller PFCAs Eventually complete abiotic mineralization (F- and CO2) Co-contaminants (@ 1000 mg/L) - PFAS degradation NOT
affected
• PFOS unaltered at 90 C with 60.5 mM Na2S2O8 as well as at 90 C with 84 mM Na2S2O8
• PFOA & PFOS will coexist in groundwater, thus technologies that can remediate both are needed
Heat-Activated PersulfatePFOS (100 µg/L)
0.0
0.2
0.4
0.6
0.8
1.0
0 20 40 60 80 100
PFO
S (µ
M)
Time (h)
60.5 mM NaS2O8No Oxidant Contorl
Persulfate Oxidation - Yang et al. (2013)100,000 µg/L PFOS (0.2 mM)
• High PFOS concentration (0.2 mM PFOS = 3.4 mM Fluoride)• High persulfate concentration and no controls presented• Hydrothermal (HT) – high temperature and pressure• Other literature: Kingshott (2008) Thesis – probing using reactant
concentrations approaching solubility limits
doi:10.1371/journal.pone.0074877.g006
Accurately quantify target parent PFAS (and isomers)◦ High extraction efficiencies of all phases◦ Reliable chromatographic separation and detection
Accurately quantify fluoride and sulfonate metabolites◦ Above background noise◦ Optimize nanocomposite synthesis to minimize background ◦ Minimize analytical matrix effects ◦ High extraction efficiencies and appropriate analytical methods
Identify organic metabolites and quantify if possible◦ TOF, MS/MS probing of aqueous and extractants◦ Headspace sampling (requires airtight reaction vessel)
Analytical methods are treatment technique dependent
Method DevelopmentApproach for successful exploration requires:
UV (254 nm) photolysis- generated aquated electrons (eaq-) from
iodide (Eo= -2.9 V) (Park et al., 2009) ◦ PFOS degraded faster than PFOA (under argon atmosphere)◦ Not applicable for in situ
Vitamin B12 (Ochoa-Herrera et al., 2008)
◦ Successful for only branched PFOS isomers, but not linear chain Boron Doped Diamond Electrode (Carter and Ferrell, 2008)
◦ Some success for PFOS◦ Very expensive ◦ Not applicable for in-situ
Zero Valent Iron (ZVI) (Eo = -0.447 V) (Hori et al., 2005; 2008)
◦ Degraded PFOS at high T & high pressure (→ near supercritical) Electrochemical (Schaefer et al., 2015, J Hax. Materials)
Theoretical and experimental evidence: PFOS is amenable to reduction. Need: Enhance reactivity and delivery
Reductive Approaches: Literature
What extent of reductive transformation especially of linear PFOS can be achieved with the primary reductive techniques proposed?
What are the intermediates of PFCAs and PFSAs defluorination using the proposed reductive techniques?
How is reductive transformation affected by various solution parameters (pH, electrolyte composition, redox potential) and co-contaminants likely to be associated with AFFF-contaminated groundwater at military sites?
How does the presence of porous media affect defluorination potential and reductant reactivity?
How amenable are intermediates to other remediation processes (treatment train potential)?
Our Current Research Questions
Metals◦ nZVI – not successful by itself◦ nZVI/Pd as a function of % Pd, initial pH, temperature◦ nZVI/Pd/Al◦ nZVI/Ni with GO or GAC◦ Mg/Pd
Enhanced delivery◦ Fe3O4 composites◦ Deposit reactive metals within clay layers◦ Organo-bentonite
Vitamin B12 with◦ Ti-citrate◦ Cu◦ n-ZVI◦ n-ZVI/Pd
Reductive Approaches Probed to Date
→F- + SO3
2- + per/poly-fluoroalkanes +Poly-fluoroalkyl sulfonates
Any sulfite generated expected to rapidly convert to sulfate:
Consistent with Literature: Sulfite oxidation rate = 0.009 /h (Shizuo Tsunogai , 1971)
Expected Inorganic Metabolites
PFOS Isomers in Technical Grade PFOS & Formuations
Linear 65-75% 4-PFOS
5-PFOS
6-PFOS
dm-PFOS3-PFOS
1-PFOS
2-PFOS
HPLCZorbac C8
Isomer Separation and Response Optimization
• Standard analyses – all isomers elute in one peak• Ascentis F5 allows for isomer separation• Selexion allows for enhanced response to each isomer
ZVI is a potent reductant (Eo = -0.447 eV) Nano-sized ZVI (nZVI) - high surface area (40~60 m2/g) Cost-effective (low installation and operation cost) Low environmental impact and low toxicity nZVI can be doped with a catalyst such as Pd, Pt, Cu, Ni and Ag to
improve the reactivity. Successful for dehalogenation of chlorinated alkenes, alkanes, and
PCBs
Mechanisms of contaminants (e.g. chlorinated solvent) removal
a) Direct electron transfer b) Hydro-defluorinationonto the catalyst surface
c) Hydro-defluorinationonto the nZVI surfaceGunawardana et al, 2011
Why nZVI Systems?
Effect of %Pd and Mass of Bimetal
• For Pd/Fe ≥ 0.043, no significant difference on PFOS removal.
• [PFOSo] = 1,487 µg/L, unbuffered pH, T=25°C for 6 d (% Pd/Fe g).
2331 32 29
0
5
10
15
20
25
30
35
40
1 2 3 4
PFO
S re
mov
al %
0.014(0.43%/0.3 g)
0.043(0.43%/0.1 g)
0.05(1.0%/0.2 g)
0.175(1.75%/0.1 g)
a a a
b
• [PFOS]o = 1,570 µg/L• No pH adjustment• Initial pH = 5.57• Final pH after reaction:
→ 6.53, 6.45, 4.99, 6.26• T= 22o C for 6 d
Pd/nZVI wt/wt ratio
Effect of Initial pH with Pd/nZVI
• Acidic and basic initial pH had highest and similar PFOS removal.• Removal lowest at near neutral pH condition.
• [PFOS]o = 1,570 µg/L • 1% Pd/0.2 g nZVI • pH adjusted with HCl or NaOH• T= 22 °C for 6 d37
3239
05
1015202530354045
1 2 3
PFO
S R
emov
al %
[pH]o=3.6[pH]f=4.26
[pH]o=6.3[pH]f=4.99
[pH]o=12.5[pH]f=12.4
aa
b
Temperature Effect with Pd(1%)/nZVI (0.2 g)
Role of temperature not clear
22 °C 50 °C 70 °C
T-P
FOS
rem
oval
%
0
10
20
30
40
50
a
a*a
32 37 35
T (°C) [PFOS]o(µg/L)
Initial pH
Final pH
22 1,570 6.29 4.99
50 1,570 6.29 4.15
70 3, 460 5.62 7.29
~ 0.4 mol F- generated per mole PFOS lost~ 0.3 mol SO4
2- per mole PFOS lost
• [PFOS]o = 880 µg/L • 1% Pd/0.5g of Fe/Al • pH adjusted with HCl/NaOH• Base added at 0, 24, and 48 h• T= 22 °C• Reacted for 6 d
pH Effect with Pd/Fe/Al Trimetal
36 32
14
28 27
0
5
10
15
20
25
30
35
40
45
Acid-PFOS Neutral-PFOS Base-0-PFOS Base-24-PFOS Base-48-PFOS
Rem
oval
%
aa,b
bb
c
% P
FOS
Rem
oved
• Initial high pH slowed/reduced PFOS removal likely due to Al(OH)4‒ formation
• Reaction appeared complete by 24 h
• Ni content over Fe0 was 1.8 wt%. • Batch experiments were carried out in
triplicates for: Ni/FeNi/Fe-Graphene (NiFe-GO)Ni/Fe-Activated Carbon (NiFe-AC)
• 0.2 gr was added to each replicate and matrix. Both were mixed for 3 days.
• A blank containing 10 mL of PFOS (2 ppm) was carrying out together with all the samples.
• 4 extractions using ethyl acetate.
• pH shifts during reaction:
Method
ID NiFe NiFe-GO NiFe-ACMatrix Day 0 7.21 7.71 7.70Matrix Day 3 8.62 8.90 8.65
Day 0 7.39 7.17 7.95Day 3 10.18 10.61 10.28
Ni-nZVI
ID-Extract#% relative to
Sum recoveredNiFe-AC-E1 86NiFe-AC-E2 9.7NiFe-AC-E3 2.8NiFe-AC-E4 1.6
0%
10%
20%
30%
40%
50%
60%
NiFe NiFe-GO NiFe-AC
%R
emov
al
• 51% to 57% PFOS not recovered so assume ‘transformed’• Four extractions was found sufficient for PFOS from nZVI
particles• Apparent higher loss for Ni-nZVI on activated carbon may be
extraction efficiency issue – now using 5 extractions
baa
Ni-nZVI
• More associated with NiFe-AC particles (~85%).• Significant differences were observed on NiFe-AC compared
to NiFe (P < 0.0001) and NiFe-GO (P < 0.0001)
% Extracted from Ni/nZVI particlesversus in Aqueous Phase
0%
20%
40%
60%
80%
100%
NiFe NiFe-GO NiFe-AC
Rel
ativ
e %
on
nano
-par
ticle
sb
aa
9.2 9.3 9.4 9.5 9.6 9.7 9.8 9.9 10.0 10.1 10.2 10.3 10.4 10.5 10.6 10.7 10.8 10.9 11.0 11.1 11.2 11.3 11.4 11.5 11.6
Time, min
0.0e0
1.0e4
2.0e4
3.0e4
4.0e4
5.0e4
6.0e4
7.0e4
8.0e4
9.0e4
1.0e5
1.1e5
1.2e5
1.3e5
1.4e5
Inte
nsi
ty
11.12
10.70
10.42
10.149.98
TIC from NiFe-AC-R1.wiff (sample 1) - NiFe-AC-R1, Experiment 3, -TOF MS^2 of 499.0 (50 - 600)
TIC from NiFe-Stock.wiff (sample 1) - NiFe-Stock, Experiment 3, -TOF MS^2 of 499.0 (50 - 600)
TIC from NiFe-R1.wiff (sample 1) - NiFe-R1, Experiment 3, -TOF MS^2 of 499.0 (50 - 600)
TIC from NiFe-GO-R1.wiff (sample 1) - NiFe-GO-R1, Experiment 3, -TOF MS^2 of 499.0 (50 - 600) L-PFOS
6-PFOS
1-PFOS
0%
25%
50%
75%
NiFe NiFe-GO NiFe-AC
% R
emov
al
Branched PFOS
0%
20%
40%
60%
NiFe NiFe-GO NiFe-AC
% R
emov
al L-PFOS
Isomer-specific Removal
• Vitamin B12 (cyanocobalamin) is produced by anaerobic bacteria contains a corrin ring that coordinates a cobalt atom• Cobalt center of V-B12 can exist in 3 oxidation states (B12a, B12r, B12s) • Electrons transferred from reduced metal (Ti exemplified below but also assessed with other metals) to the contaminant
Reduced Ti (III) Citrate
Oxidized Ti (IV) Citrate
2e–
B12a↓
B12r↓
B12S
2e–
Some degradation of branched PFOS, not linear PFOS
70 C, pH=9 (Ochoa et al., 2008)
Unknown intermediates +
FluorideMost nucleophilic
Why Vitamin B12 Systems?
Vitamin B12 (0.4 mM) + n-ZVI (0.2 g)
• Similar PFOS removal in both systems• Inorganic metabolite production varies• Organic metabolites also appear different
16.12
0.921.05 0.3102468
1012141618
1 2m
ol/m
ol
B12-FePd-Fe
F– or SO42- / PFOS removed
(Comparing 2 systems)
Fluoride SO42-
Effect of Temperature and Initial pH for B12+ Ti System
• Heat enhanced only PFOA removal• At T=70 °C, PFOS removal increased with increase in initial pH
17
43
16 16
32
0
5
10
15
20
25
30
35
40
45
50
1 2 3
Rem
oval
%
PFOA PFOS
At 22 °C, pH not adjusted
At 70 °C, pH not adjusted
At 70 °C, at pH 9.54
• [PFOS]o= 4,655 µg/L • [B12]= 0.4 mM• [Ti-citrate]= 45 mM• pH adjusted with NaOH• T= 70 °C for 5 d
• [PFOA]o= 609 µg/L• [PFOS]o= 358 µg/L • [B12]= 0.5 mM• [Ti-citrate]= 35 mM• Unadjusted pH• T= 22 or 70 °C for 5 d
B12-Fe B12-Fe-Pd B12-Ti-Cu B12-Ti-Fe B12-Ti
T-P
FOS
rem
oval
%
0
10
20
30
40
50
22
9
2334 32
Effect of Cu°, Pd ° or Fe° in B12 - Ti system[PFOS]o = 4,655 µg/L, T = 70 °C, Reaction = 5 d
Treatment [pH]o [pH]f
B12-Fe 10.41 8.03B12-Pd/Fe 10.41 7.61B12-Ti-Cu 9.54 6.86B12-Ti-Fe 9.54 9.23
B12-Ti 9.54 6.03
• Addition of Fe° (as an electron donor) to B12+Ti systemt did not enhance PFOS removal.• Addition of Cu° or Pd°(as a catalyst) to B12-Ti-citrate system decreased PFOS removal.• In Ti-system, high Cl– concentration interfered with F– quantitation. • B12+Fe system, F- and SO4
2- were detected indicating partial reduction.
10-14 mol F- generated per mole PFOS lost~ 0.7 mol SO4
2- per mole PFOS lost
B12 + Fe Fe/Pd Ti-Cu Ti-Fe Ti
22°C at 21 day70°C at 21 day
70°C at 5 day
T-P
FOS
rem
oval
%
0
10
20
30
40
Col 5: 14.7 Col 5: 18.27
B12-Fe
B12-PFOS (NO Fe)
Effect of Temp. in B12 (0.4 mM) + nZVI (0.2 g) System
• PFOS removal increased with temperature .• At 70 °C, PFOS removal continued to increase from 5 to 21 days.• Most degraded PFOS is branch-PFOS.• PFOS removal in only Vitamin B12 (no metals to enhance electron shuttle) unexpected.
PFOS isomers Chromatographs in B12-Fe at 70 °C (in Aqueous phase)→ Stock, D-14, and D-21
Sample ID [pH]o [pH]f
22 °C at 21 d 10.51 9.8970 °C at 21 d 10.51 6.6770 °C at 5 d 10.41 8.03B12-PFOS
(no Fe)10.51 9.14 (22 °C)
7.52 (70 °C)
20
15
32
1622
Isomer-Specific Peak Comparison for B12-nZVI
L-PFOS 22C70C
D-5 D-7 D-11 D-14 D-21Stock D-1 D-2 D-31 2 3 4 5 6 7 8 9
6-PFOS 22C70C
D-5 D-7 D-11 D-14 D-21Stock D-1 D-2 D-3
1 2 3 4 5 6 7 8 9
5-PFOS 22C70C
D-5 D-7 D-11 D-14 D-21Stock D-1 D-2 D-31 2 3 4 5 6 7 8 9
3&4-PFOS 22C
70C
D-5 D-7 D-11 D-14 D-21Stock D-1 D-2 D-3
1 2 3 4 5 6 7 8 9
Other isomers 22C
70C
D-5 D-7 D-11 D-14 D-21Stock D-1 D-2 D-3
TIME (d)
REL
ATIV
E to
STO
CK
• LC/MS-ESI/TOF (and GC/MS Orbitrap forthcoming)• Several metabolites produced not in controls• Expect some perfluoroalkyl alkane/alkenes• Currently using a mass defect approach to identify metabolite• Example: Peaks in Ni/nZVI Treatment Systems:
• Positive Mode• 4 similar peaks observed in all systems• One additional peak in graphene oxide (GO) system
• Negative Mode• 1 peak observed in all• Peak was different in activated carbon (AC) system
Organic Metabolitess
Many combinations have been used in field applications◦ ZVI-type treatment zone coupled to natural or enhanced anaerobic
treatment zone◦ ISCO treatment zone coupled to enhanced or natural aerobic
degradation◦ Aerobic degradation treatment zone coupled to an anaerobic
abiotic (ZVI) or bioremediation (biowall) treatment zone One treatment can ‘soften’ a compound to be amenable to natural
anaerobic or aerobic degradation and/or to a subsequent chemical treatment.
At many of the sites where PFASs exist, redox conditions may already be depleted in O2 (redox range-100 to -250 mV) due to degradation of fuel and other easily biodegradable contaminants.
Order and placement of treatment train for PFASs depends on proximity to source and contaminants present – precursor oxidation will lead to increased concentration of PFAAs.
NRC (2013); IRTC (2011)
Treatment Train Potential
Used for Cl-methanes, ethanes, and ethenes, chlorinated phenols, PCBs, hexachlorocyclohexanes, munitions, metals, nitrates, perchlorate
Permeable Reactive Barriers (PRBs) Reductions in the target zone of typically 50 to 90 percent ◦ Treatment Trains◦ In-situ Injection
Barrier Media Superfund Industrial US Gov. International TotalZVI 5 36 26 16 83Non-Fe reactive materials 1 6 1 1 9Bio-barrier 0 6 5 4 15Combo/Sequenced (* ZVI) 0 4 2 0 6 (5*)
NRC (2013); IRTC (2011)
Enhancing ZVI-based techniques Nano-ZVI (nZVI) - pilot & full-scale tests with nZVI1 shows 50-90%
conc. reduction Surface coated/encapsulated nZVI-type particles (enhanced for in-situ
injection) Carbon/ZVI, C-rich organic/iron combinations (PRBs) Emulsified ZVI, ZVI-clays, organophilic-ZVI clays (PRBs, in-situ
injection)
Current Use of Reductive Technologies in the Field
Take Home Messages
No magic bullet! PFOS is the big challenge - more about steric hindrances Reductive approaches showing some promise for ‘softening’
PFOS (partial transformation) Linear PFOS remains the primary challenge – energetically
the most stable and ~75% of what is in the environment Many published studies lack sufficient recovery efficiencies
and background issues We are not ready for any field-scale attempts for in-situ
remediation due to◦ Increasing PFAAs due to aerobic transformation of
precursors – increased mobility◦ Unknown metabolites◦ Toxicity potential unknown or unclear for metabolites
Co-investigatorsDr. Linda S. Lee (PI)
Purdue UniversityEnvironmental Chemist; per/polyfluoro alkyl chemical fate expertise
Dr. Loring NiesPurdue UniversityEnvironmental engineering, biodegradation, nanoparticle
Dr. Victor MedinaU.S. Army Engineering Research & Development CenterChemical/metal remediation experience with military
Drs. Marc Mills & Kavitha Dasu*U.S. EPA, NRMRLFate/remediation expertise; * PFAS fate/ analytical expertise (with PI)
Dr. Hongtao YuJackson State UniversityChemistry/biochemistry; NSF-funded NMR Center
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