Sonochemical degradation of perfluorinated chemicals in aqueous film-forming foams

Aqueous film-forming foams (AFFFs) are complex mixtures containing 1-5% w/w fluorocarbons (FCs). Here, we have investigated degradation of two commercial AFFF formulations, 3M and Ansul, using sound field at 500 kHz and 1 MHz, with varying initial concentrations ranging from 200 to 930× dilution. The foams were readily degraded by 1 MHz, with percentage of defluorination ranging from 11.1 ± 1.4% (200× dilution of 3M) to 47.1 ± 5.8% (500× dilution of Ansul). Removal of total organic carbon (TOC) ranged from 16.0 ± 1.4% (200× dilution Ansul) to 39.0 ± 7.2% (500× dilution Ansul). Degradation of AFFF was affected by sound frequency with rates of defluorination 10-fold greater when the frequency was 1 MHz than when it was 500 kHz. Mineralization of TOC was 1.5- to 3.0-fold greater under 1 MHz than 500 kHz. Rate of fluoride release was 60% greater for the greatest initial concentration of FC in Ansul compared to the least initial concentration. While the rate of mineralization of AFFF was directly proportional to the initial concentration of Ansul, that was not the case for 3M, where the rates of mineralization were approximately the same for all three initial concentrations. Results of the study demonstrate that sonolysis is a promising technology to effectively treat AFFFs.