Evaluation of co-foaming agents for enhanced removal of per-and polyfluoroalkyl substances (PFAS) by foam fractionation.

Foam fractionation has emerged as a leading method to remove per- and polyfluoroalkyl substances (PFAS) from impacted aqueous matrices due to the low cost and rapid PFAS removal. Although foam fractionation has been shown to efficiently remove long-chain PFAS, cationic co-foaming agents are often necessary to improve the removal of short-chain PFAS. However, many of the best performing co-surfactants used for short-chain PFAS removal, such as cetyltrimethylammonium bromide (CTAB), are of concern due to their potential toxicity and low biodegradability. The objective of this study was to evaluate the performance of lower-toxicity co-foaming agents for enhanced removal of both long-chain and short-chain PFAS compounds. Six candidate co-foaming agents were tested in a laboratory-scale foam fractionation system that consisted of a 60-cm acrylic column equipped with a 0.5-μm air diffusor, injection and sampling ports, and a vacuum-assisted foam collection reservoir. Based on the results of experiments conducted using water containing long- and short-chain PFAS, a naturally derived zwitterionic surfactant derived from Shea butter was identified as the most promising alternative co-foaming agent. Subsequent experiments demonstrated that the shea butter derived surfactant (SBDS) performance was improved by lowering the pH to 3, and under these conditions, SBDS was able to remove greater than 99.5 % of the PFAS from groundwater collected from AFFF-impacted military installations. These findings demonstrate the efficacy of a low-toxicity, biodegradable co-foaming agent as a replacement for traditional cationic surfactants, which are known to be toxic and persistent in the environment.