Evaluation of an Algal Turf Scrubber™ (ATS) Approach for the Remediation of Perfluoroalkyl Substances (PFAS)

Abstract

Per- and polyfluoroalkyl substances are a large group of synthetic organic chemicals ubiquitous and persistent in the environment due to their fluorinated alkyl chains. Existing methods for remediation of mixtures of PFAS in water media are limited and many times not applicable for shorter-chain PFAS. Algal Turf ScrubberTM (ATS) systems have been widely used for biomass production and pollutant removal through periphytic algae, but have not been yet investigated for PFAS. This project evaluated the suitability of an ATS approach for the remediation of a mixture of PFAS (PFOS, PFOA, PDHA, and HFPO-DA), and quantified the mechanisms of remediation. A mixed community of periphytic algae obtained from Chewacla Creek (32.5480°, -85.4806°) was cultured during 14 harvests in four flow-lane microcosms under a 16:8 light:dark regime. The dominant species identified through light microscopy were primarily composed of filamentous forms from the genera Spirogyra, Oscillatoria, Stigeoclonium, Mougeotia, Ulotrix, and Oedogonium. The experimental design consisted of four treatment channels and four controls (two positive and two negative), in which algal cultures where exposed to the contaminant mixture at 2 μg L-1 for a period of 72h. Water and algal biomass were repeatedly sampled from each channel, from which 66 water and 4 biomass samples were analyzed using ultra-high performance liquid chromatography coupled to triple quadrupole mass spectrometry (UHPLC-QqQ-MS). The amount of contaminants found in the biomass was equal to 1.24 ± 0.40% for PFOA, 1.21 ± 0.41% for PFOS, 0.26 ± 0.16% for HFPO-DA, and 0.76 ± 0.27% for PDHA, based on their initial concentration. In contrast, it was observed that between 35-92% of the initial concentration of PFOS and PFOA remained unaccounted for after a mass balance was performed. Sorption into the materials used to build the ATS system was hypothesized to be responsible for this mass loss, according to results from preliminary experiments. Finally, results from this project indicate that ATS might not be an effective alternative for PFAS remediation, due to the low removal rates. Nonetheless, results from this analysis can contribute to the growing understanding on the bioaccumulation potential of these compounds. Periphytic algae are in the bottom of several food chains and can potentially biomagnify PFAS into upper levels. Furthermore, findings in this study are in agreement with reports that suggest shorter chain compounds are less bioaccumulative and present lower half-lives in organisms, when compared to legacy PFAS.