A NEW METHOD FOR IN-SITU REMEDIATION OF PFAS IN SOIL AND GROUNDWATER Anders G. Christensen, M.Sc, Expertise Director Jacqueline A. Falkenberg, PhD NIRAS A/S, ALLERØD, DENMARK Ian Ross, PhD & Jake Hurst, M.Sc, Allan Hornemann, PhD ARCADIS UK & USA 17-03-2016 Renare Mark Vårmöte 2016
Ian Ross, PhD & Jake Hurst, M.Sc, Allan Hornemann, PhD ARCADIS UK & USA 17-03-2016 Renare Mark Vårmöte 2016 A NEW METHOD FOR IN-SITU REMEDIATION OF PFAS IN SOIL AND GROUNDWATER Anders G. Christensen, M.Sc, Expertise Director Jacqueline A. Falkenberg, PhD NIRAS A/S, ALLERØD, DENMARK
AGENDA Background Scope of the work Laboratory work using the TOP Assay Laboratory test with the ScisoR method Results Conclusions & Outlook
PFAS CHARACTERISTICS PFAS: A large family of compounds Perfluorooctane sulfonate (PFOS) Perfluorooctanoic acid (PFOA) Other PFAS ranging from 2 to 16 carbon chains Precursors compounds exist as Dark Matter C6 chemistry generally replacing C8 PFAS Fluorotelomers replace PFOS/PFOA but some form PFOA, PFHA etc. Unique surface-active properties bind to organic carbon, clays, silts Transition to air water interface stratify in solution Non-reactive, stable, persistent Bioaccumulative Some evidence of causing endocrine disruption Extreme persistence
AEROBIC BIOTRANSFORMATION PFAA S AS DEAD END DAUGHTER PRODUCTS
PFAS SOIL REMEDIATION Currently options are limited to excavation (no final solution, concentrated in another phase) Landfilling introduces challenges since PFAS will become constituents of leachate (landfill leachate is not typically being evaluated for e.g. PFOS) No proven techniques available for the biological or chemical breakdown Incineration, high temperatures (> 1000 C) are needed to cleave the stable C-F-bonds Immobilization with GAC or commercial products (soil mixing). Solidification (e.g. cement) is a yet unproven long-term option Site characterisation is complex and requires high resolution sampling to build a robust site conceptual model There is a need for new/alternative methods!
SCOPE OF THE WORK Develop a comprehensive yet cost effective analytical methods to assess the true content of the PFAS compounds ( Dark Matter ) in soil & groundwater prior to (any) lab scale experiments To evaluate the presence of Dark Matter on impacted soil and groundwater from a fire training site. Are the current standard methods missing out a large fraction of PFAS? Provide proof of process for the new ScisoR technology demonstrate mineralisation of PFOS Demonstrate to what extent the ScisoR technology is effective in PFAS destruction in bench scale experiments using site soil and groundwater Evaluate the need for improvements in the standard analytical procedures used
TOP ASSAY DIGEST PFAS PRECURSORS AND MEASURE THE HIDDEN MASS Microbes slowly biotransform simpler PFAA s (e.g. PFOS / PFOA) from PFAS (precursors) over 20+ years Need to determine precursor concentrations Too many PFAS compounds and precursors so very expensive analysis (if possible) This analytical method mimics years of microbial action using conventional oxidation over a few hours Then measure simpler PFAS s using analytical method Done in addition to LCMSMS to provide difference between precursor and free PFCA & PFSA concentrations Analytical tools fail to measure the hidden PFAS precursor mass, the TOP assay solves this
TOTAL OXIDISABLE PRECURSOR (TOP) Assay on Composite Samples Soil Composite Groundwater Composite 248% increase 195% increase Significant increase in perfluorinated carboxylic acids and sulphonic acids (PFAAs) following TOP assay representing the hidden mass of PFAS present which will produce additional PFAA s including PFOS as dead end daughter products; Sum PFAS increase of 248% in soils and 195% in groundwater using TOP assay; Demonstrates matrices impacted with AFFF contain a greater mass of PFAS than identified by conventional analysis with LCMSMS (EPA Method 537).
SCISOR REACTION MECHANISMS ScisoR chemistry remain commercially sensitive with further research into reaction mechanisms in progress A range of oxidising & reducing free radicals and reactive species likely involved including SO 4, O 2 -, solvated electrons Proposed mechanism for PFOA destruction via sulfate radical oxidation by Katsuna and Hori (2007) unzipping cycle continues along perfluorinated chain SO 4 more powerful direct e- transfer oxidant than OH Novel ScisoR activation may enable similar mechanisms for oxidative pathways for PFOS in addition to reductive pathways Loss of COF 2 as perfluorinated chain unzips Measured as fluoride (HF pka ~3.17)
PFOS DESTRUCTION & FLUORIDE MASS BALANCE DURING SCISOR 10 mg/l PFOS starting concentration 3 replicate data sets 83 to 90% PFOS destruction after 14 days 71% to 118% fluoride released from PFOS during SCISOR Overall fluoride mass balance (remaining fluoride in PFOS + fluoride released to solution) 86% to 126% of theoretical All treated samples were blind spiked with 10 mg/l fluoride 80% to 99% spike recovery Spike analyses demonstrate ion measured is fluoride, results are quantitative Longer reaction times and repeat applications of ScisoR will cause complete destruction of PFOS Replicate Data. Error bars are % Standard Error of Measurement (SEM)
PFOS DESTRUCTION WITH SCISOR USING SITE GROUNDWATER 350 300 250 [PFOS] Low ScisoR 250 200 [PFOS] Medium ScisoR 250 200 [PFOS] High ScisoR 200 150 150 150 100 50 100 50 100 50 0 3.5 days 7 days 14 days 0 3.5 days 7 days 14 days 0 3.5 days 7 days 14 days Destruction of PFOS up to 68% after 14 days - site specific reaction kinetics and residual ScisoR reagents indicate further destruction will occur with extended reaction period PFOS precursor breakdown will be producing additional PFOS throughout the reaction period Full destruction will likely occur over a longer time period and/or via repeat applications of ScisoR
TOTAL PFAS MASS AFTER SCISOR APPLICATION TO SOIL COMPOSITE Baseline 55% Reduction 67% Reduction 75% Reduction Destruction/reduction of multiple PFAAs after 21 days - site specific reaction kinetics and residual ScisoR reagents indicate further destruction will likely occur with extended reaction period Total PFAS mass reduced by between 55% and 75% in soil and groundwater Complete destruction of all compounds will likely occur over a longer time period and/or via repeat applications of ScisoR
CONCLUSION & OUTLOOK The analytical methods used show: Total PFAS concentrations have increased by up to 240% as a result of transformation of hidden PFAS precursors PFOS concentrations have increased by up to 200% as a result of transformation of hidden PFAS precursors the new analytical tools (TOP assay etc.) are essential to characterise impacts from PFAS The ScisoR technology has been proven to mineralise PFOS when present as a single compound (spiked) The ScisoR technology has been shown to reduce PFOS in the site soil and groundwater samples significantly and to reduce other common PFAS compounds More research by ARCADIS on the ScisoR process are underway ScisoR can potentially be applied for : - In Situ remediation of PFAS impacted source areas - Regeneration of PFAS saturated granular activated carbon (GAC) - Soil mixing to destroy PFAS either on-site or in-situ
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