Evaluating A Continuous Liquid-phase Plasma Discharge Process for Destroying PFAS in Water

Due to the lack of effective conventional treatment techniques for removing and destroying PFAS, non-thermal plasma technology has come to the center stage, but with limitations. In this study, a novel, continuous-flow, liquid-phase plasma discharge (CLPD) process was established and evaluated for its effectiveness and efficiency in removing PFOA in water. Experiments were carried out in two phases. In phase I, two carrier gases (argon and air) were studied and compared for their performance in removing PFOA by CLPD, and argon gas was found to be more effective than air (91.75% for argon vs. 79.55% for air). Then in Phase II, Argon was used as the carrier gas to evaluate other operating parameters including gas flow rate, water flow rate, water conductivity, and power applied using a two-level partial factorial design. The results showed that gas flow rate was the most significant factor among the four factors affecting the removal efficiency of PFOA by CLPD (p = 0.0029). The best combination of the four operating parameters was obtained (conductivity = 300 µs/cm, water flow rate = 150 mL/min, gas flow rate = 1.5 sL/min, and power = 100 W), under which the CFLPPD could achieve a PFOA removal rate of 93.4%. The breakdown pathway was estimated to be from PFOA to PFHPA, to PFHXA, to PFHeA, to PFBA, and then to H2O, CO2, F, and short-chain organics. Based on the results from this study, it may be concluded that the CLPD process evaluated in this project can be developed into an effective treatment to remove PFAS in contaminated water.