Remediation
of groundwater impacted by per- and polyfluoroalkyl
substances (PFAS) is particularly challenging due to the resistance
of the molecule to oxidation because of the strength of the carbon–fluorine
bond and the need to achieve low nanogram per liter drinking water
targets. Previous studies have shown that activated carbon is an effective
sorbent for removal of perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic
acid (PFOS) in conventional water treatment systems. The objective
of this study was to evaluate the in situ delivery and sorptive capacity of an aqueous
suspension containing powdered activated carbon (PAC) stabilized with
polydiallyldimethylammonium chloride (polyDADMAC). Batch reactor studies
demonstrated substantial adsorption of PFOA and PFOS by polyDADMAC-stabilized
PAC, which yielded Freundlich adsorption coefficients of 156 and 629
L/g–n
, respectively. In columns
packed with 40–50 mesh Ottawa sand, injection of a PAC (1000
mg/L) + polyDADMAC (5000 mg/L) suspension created a sorptive region
that increased subsequent PFOA and PFOS retention by 3 orders of magnitude
relative to untreated control columns, consistent with the mass of
retained PAC. Experiments conducted in a heterogeneous aquifer cell
further demonstrated the potential for stabilized-PAC to be an effective
in situ treatment option for PFAS-impacted groundwater.
The environmental fate of per- and polyfluoroalkyl substances
(PFAS)
in aqueous film-forming foams (AFFFs) remains largely unknown, especially
under the conditions representative of natural subsurface systems.
In this study, the biotransformation of 8:2 fluorotelomer alcohol
(8:2 FTOH), a component of new-generation AFFF formulations and a
byproduct in fluorotelomer-based AFFFs, was investigated under nitrate-,
iron-, and sulfate-reducing conditions in microcosms prepared with
AFFF-impacted soils. Liquid chromatography–tandem mass spectrometry
(LC–MS/MS) and high-resolution mass spectrometry (HRMS) were
employed to identify biotransformation products. The biotransformation
was much slower under sulfate- and iron-reducing conditions with >60
mol % of initial 8:2 FTOH remaining after ∼400 days compared
to a half-life ranging from 12.5 to 36.5 days under nitrate-reducing
conditions. Transformation products 8:2 fluorotelomer saturated and
unsaturated carboxylic acids (8:2 FTCA and 8:2 FTUA) were detected
under all redox conditions, while 7:2 secondary fluorotelomer alcohol
(7:2 sFTOH) and perfluorooctanoic acid (PFOA) were only observed as
transformation products under nitrate-reducing conditions. In addition,
1H-perfluoroheptane (F(CF2)6CF2H)
and 3-F-7:3 acid (F(CF2)7CFHCH2COOH)
were identified for the first time during 8:2 FTOH biotransformation.
Comprehensive biotransformation pathways for 8:2 FTOH are presented,
which highlight the importance of accounting for redox condition and
the related microbial community in the assessment of PFAS transformations
in natural environments.
Per-and polyfluoralkyl substances (PFAS) are known to accumulate at interfaces, and the presence of nonaqueous-phase liquids (NAPLs) could influence the PFAS fate in the subsurface. Experimental and mathematical modeling studies were conducted to investigate the effect of a representative NAPL, tetrachloroethene (PCE), on the transport behavior of PFAS in a quartz sand. Perfluorooctanesulfonate (PFOS), perfluorononanoic acid (PFNA), a 1:1 mixture of PFOS and PFNA, and a mixture of six PFAS (PFOS, PFNA, perfluorooctanoic acid (PFOA), perfluoroheptanoic acid (PFHpA), perfluorohexanesulfonate (PFHxS), and perfluorobutanesulfonate (PFBS)) were used to assess PFAS interactions with PCE-NAPL. Batch studies indicated that PFAS partitioning into PCE-NAPL (K nw < 0.1) and adsorption on 60−80 mesh Ottawa sand (K d < 6 × 10 −5 L/g) were minimal. Column studies demonstrated that the presence of residual PCE-NAPL (∼16% saturation) delayed the breakthrough of PFOS and PFNA, with minimal effects on the mobility of PFBS, PFHpA, PFHxS, and PFOA. Breakthrough curves (BTCs) obtained for PFNA and PFOS alone and in mixtures were nearly identical, indicating the absence of competitive adsorption effects. A mathematical model that accounts for NAPL−water interfacial sorption accurately reproduced PFAS BTCs, providing a tool to predict PFAS fate and transport in cocontaminated subsurface environments.
Perfluoroalkyl acids (PFAAs) have been shown to inhibit
biodegradation
(i.e., organohalide respiration) of chlorinated ethenes. The potential
negative impacts of PFAAs on microbial species performing organohalide
respiration, particularly Dehalococcoides mccartyi (Dhc), and the efficacy of in situ bioremediation
are a critical concern for comingled PFAA-chlorinated ethene plumes.
Batch reactor (no soil) and microcosm (with soil) experiments, containing
a PFAA mixture and bioaugmented with KB-1, were completed to assess
the impact of PFAAs on chlorinated ethene organohalide respiration.
In batch reactors, PFAAs delayed complete biodegradation of cis-1,2-dichloroethene (cis-DCE) to ethene.
Maximum substrate utilization rates (a metric for quantifying biodegradation
rates) were fit to batch reactor experiments using a numerical model
that accounted for chlorinated ethene losses to septa. Fitted values
for cis-DCE and vinyl chloride biodegradation were
significantly lower (p < 0.05) in batch reactors
containing ≥50 mg/L PFAAs. Examination of reductive dehalogenase
genes implicated in ethene formation revealed a PFAA-associated change
in the Dhc community from cells harboring the vcrA gene to those harboring the bvcA gene.
Organohalide respiration of chlorinated ethenes was not impaired in
microcosm experiments with PFAA concentrations of 38.7 mg/L and less,
suggesting that a microbial community containing multiple strains
of Dhc is unlikely to be inhibited by PFAAs at lower,
environmentally relevant concentrations.
The effects of nanoscale silver (nAg) particles on subsurface microbial communities can be influenced by the presence of biosurfactants, which have been shown alter nanoparticle surface properties. Batch and column...
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