(402f) Engineering High Frequency Ultrasound for Degradation of per- and Poly-Fluoroalkyl Substances

Per- and poly-fluorinated substances (PFAS) are man-made chemicals, used for more than 50 years in plastics, waterproofing, non-stick pans, surfactants and aqueous firefighting foams. Due to their widespread use, and extreme persistence PFAS are now everywhere in the environment. However, PFAS are toxic, bioaccumulate in animals and plants and can lead to numerous ill-health effects. Many PFAS are now banned or heavily regulated and hence legacy and environmental PFAS require destruction.

Many processes have been adapted for PFAS removal, such as nano-filtration, ozofractionation and adsorption. However, these generate concentrated PFAS streams which require further treatment, usually incineration at 1,000^oC+ that emits HF and organofluorine compounds, which necessitate scrubbing [1]. PFAS contain a hydrophobic fluorinated carbon chain and hydrophilic head group(s) giving them desirable chemical properties which also makes them extremely recalcitrant to typical degradation methods. High frequency ultrasound mineralizes aqueous PFASs into less harmful and easily treatable species, such as CO₂ and F^- ions [2].

We will explore the challenges associated with sonolytic parameter selection using standard characterisation techniques. Presentation of sonoluminescence (SL) and sonochemiluminescence (SCL) to visualise and quantify the active bubble distribution will be presented alongside and iodide dosimetry to quantify the concentration of reactive oxidant species (ROS). A new image-processing-based quantitative method is introduced to overcome noise and glass reactor-reflected light interference in SL/SCL measurements. Typical ultrasonic behaviours will be discussed and results on use of machine learning to predict characterisation outcomes explored.

An overview of how sonolytic degradation of PFAS is expected to be useful toward total remediation of environmental contaminations will be presented. We focus on high frequency ultrasound (100 - 1,000 kHz) and examine parameters such as frequency, liquid height, power density and reactor configuration. Considerations of how high frequency ultrasound may be employed in an industrial setting will be discussed.

[1] I. Ross et al., “A review of emerging technologies for remediation of PFASs,” Remediation, vol. 28, no. 2, pp. 101–126, 2018.

[2] C. D. Vecitis, H. Park, J. Cheng, B. T. Mader, and M. R. Hoffmann, “Enhancement of perfluorooctanoate and perfluorooctanesulfonate activity at acoustic cavitation bubble interfaces,” J. Phys. Chem. C, vol. 112, no. 43, pp. 16850–16857, 2008.