Soil washing for removal of per- and polyfluoroalkyl substances from investigation-derived waste

The accumulation of significant amounts of investigation-derived waste (IDW) from investigations of per- and polyfluoroalkyl substances (PFAS) contamination at active and former military installations has generated the need for viable disposal methods, which are currently limited to incineration or landfilling. Soil washing has been proposed as a more environmentally friendly alternative method to remove PFAS sorbed to IDW media, potentially allowing more cost-effective disposal of the media as nonhazardous waste. This systematic investigation of IDW washing explored the effect of water-, methanol-, and salt-based solutions, which are typically used for ion exchange (IX) resin regeneration. These solutions were tested for PFAS removal using four different field IDW solids with different pHs, total organic carbon content, and anion exchange capacity. In long washes extending to a week, distilled water was found to be effective in the removal of short-chain PFASs (perfluorcarboxylic acids with fewer than seven fluorinated carbon atoms and perfluorosulfonic acids with fewer than six fluorinated carbon atoms) and some long-chain PFASs including perfluorooctanoic acid, but not perfluorooctane sulfonic acid (PFOS). PFOS was only removed using water:methanol solutions with salt. Optimized 30-min washes containing water:methanol and salt effectively removed precursors, and short- and long-chain PFAS. Kinetic, soil extraction, and leaching experiments revealed that PFAS can be removed within a matter of minutes, with greater than 70% PFAS removal on the first wash; however, longer-chain PFASs required up to three washes to be removed. Important IDW wash solution relationships influencing PFAS desorption are discussed and PFOS is proposed as an indicator species for IDW washing effectiveness. Results demonstrate that adapting components of IX regeneration solutions to IDW wash solutions facilitates an alternative means to separate PFAS contaminants from IDW, advancing PFAS remediation efforts.

Automated summary

This study investigated the effect of different solutions on PFAS removal and found that a solution containing water, methanol, and salt effectively removes PFAS. The washing time can be short, but longer-chain PFAS require multiple washes for complete removal. The results demonstrate that adapting components of ion exchange resin regeneration solutions to IDW wash solutions facilitates the progress of PFAS remediation efforts.