Theme: 07. Per- and Polyfluorinated Alkyl Substances (PFAS)

Topic Area: 7g. PFAS and Bugs: The Search Continues

Formatted Title:

Exploring Biostimulation of Acidimicrobium sp. Strain A6 in Selected PFAS-Impacted Sediments for PFAS Degradation

Background/Objectives:

Acidimicrobium sp. Strain A6 (A6 for short), which is capable of defluorinating perfluorinated compounds such as PFOA and PFOS in laboratory incubations, is an organism that has been shown to be present in many iron-rich acidic soils and sediments, where its growth can be stimulated via the addition of ammonium (the electron donor) and/or ferric iron (the electron acceptor). The objective of this work was to determine if this organism is present in iron-rich acidic sediments at PFAS-impacted sites, if its activity can be stimulated, and if so, how to supply a solid iron phase in a sediment/groundwater environment for the purpose of in situ biostimulation.

Approach/Activities:

Anoxic, 60-day incubations were conducted with iron-rich acidic PFAS impacted sediments from four DoD sites and relatively clean sediments from two of these sites for the following treatments: (i) deionized (DI) water, (ii) growth medium with ammonium and augmented with 10 mg/l PFOA and PFOS, (iii) growth medium with ammonium, ferrihydrite, and augmented with 10 mg/l PFOA and PFOS, and (iv) autoclaved control. Changes in A6 numbers, ammonium, fluoride, and PFOA/PFOS, the microbial community, as well as expression of genes for reductive dehalogenases were monitored. To study the delivery of ferric iron sources to a porous medium, column experiments were conducted with two of these sediments. Goethite was treated with polyacrylic acids to change the zeta potential from positive to negative, allowing the treated goethite to be transported in these columns. Three columns were run in parallel for each sediment: (i) DI water, (ii) growth medium with ammonium, and (iii) growth medium with ammonium and the PAA-treated goethite. Once goethite breakthrough was observed, columns were allowed to rest for 50 days, after which pumping was restarted and the effluent monitored for ammonium, fluoride, and PFOS. Columns were then taken apart and sediments extracted to quantify A6 numbers and total PFOS.

Results/Lessons Learned:

Results show that, except for one sediment for which the pH was 7.1, in all other sediments A6 could be stimulated via the addition of ammonium and ferrihydrite, resulting in a decrease in PFOA/PFOS concentration with a commensurate increase in fluoride, while no changes were observed in the autoclaved controls. Although A6 was also present in the uncontaminated sediments, the addition of PFOA/PFOS had a negative impact on its growth and little if any changes in PFOA concentrations were observed, indicating that some acclimatation period might be required. Stimulation of A6 in the contaminated sediments also resulted in a significant increase of the gene encoding a reductive dehalogenase in A6. Initial results from the column experiments, which are still ongoing, showed a significant decrease in ammonium in the porewater, increase of fluoride, and decrease in PFOS concentrations. Experiments spiked with C-13 labeled PFOS are under way. Overall, results to date indicate that there are sites where A6 might be stimulated to achieve PFAS defluorination. The degree to which this can be achieved and effects such as temperature, are currently being investigated.

Jinhee Park

Affiliation

Refine Results

(Group 2, Poster Board #87) Exploring Biostimulation of (ital)Acidimicrobium sp. Strain A6 in Selected PFAS-Impacted Sediments for PFAS Degradation