Shea-derived cationic surfactants are effective and low-toxicity alternative co-surfactants for foam fractionation of per- and polyfluoroalkyl substances (PFAS)

Foam fractionation is a cost-effective separation method that utilizes air bubbles and co-surfactants to remove and concentrate PFAS in small volumes of foam. Co-surfactants with a positive charge, such as cetyltrimethylammonium bromide (CTAB), have been shown to remove both long- and short-chain PFAS from water due to their ability to interact with negatively charged PFAS, however, there are concerns over the use of CTAB due to its toxicity. To address this issue, we evaluated the foam fractionation performance of several co-surfactants and identified a cationic surfactant, shea butteramidopropyltrimonium chloride (SBATC), that is derived from shea (Vitellaria paradoxa) as an alternative to CTAB. Surface tension data confirmed accumulation of cationic shea co-surfactant at the air-water interface. Subsequent laboratory-scale foam fractionation experiments demonstrated rapid removal of both long- and short-chain PFAS with SBATC, and greater PFAS foam enrichment compared to CTAB. Cytotoxicity studies performed with petroleum-based and shea-derived co-surfactants using human intestine and zebra fish cell lines demonstrated that shea-derived co-surfactants are lower toxicity alternatives for foam fractionation applications.