Continuous fixed-bed column adsorption of perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) from canal water using zero-valent Iron-based filtration media

Per-and polyfluoroalkyl substances (PFAS) belong to a class of anthropogenic chemicals that were popularly used by industry for their hydrophobicity and stain resistance; yet the latest studies demonstrate that PFAS possess adverse ecological and human health effects. This study investigated the mechanisms and efficiencies of removal of perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) from C-23 canal water when using two filtration media including iron filings-based green environmental media (IFGEM) and sand-based filtration media, denoted as clay, tire crumb, and sand (CTS). The C-23 canal is connected to the St. Lucie River estuary in Florida, which is ecologically sensitive. A fixed-bed column study using IFGEM demonstrated removal rates above 95% for PFOA during the first 9 h of column operation, while removal rates above 97% for PFOS were observed throughout the duration of the column run based on spiked concentrations of 70 ng.L-1 each of PFOA and PFOS. IFGEM outperformed CTS in terms of PFOA removal, attributable to its larger rate constant, higher adsorption capacity, and larger surface area relative to CTS. When comparing selected dynamic adsorption models, the Thomas model was determined to be the most suitable model to describe the media adsorption behavior for PFOA removal. PFOS removal via CTS and IFGEM was highly likely for the greater affinity of alumina (Al2O3) for PFOS functional groups, and PFOA removal was governed by hydrophobic and electrostatic interactions with the media constituents. For the same mass of media, IFGEM sustained PFAS removal for approximately 36 h before breakthrough, much longer than that of CTS. The high performance of IFGEM can be attributed to the functionalities of the incorporated zero-valent iron.

Automated summary

This study investigated the mechanisms and efficiencies of removal of PFOS and PFOA from C-23 canal water, with IFGEM outperforming CTS in terms of PFOA removal due to its larger rate constant, higher adsorption capacity, and larger surface area.